Crop Evolution and Genetic Resources:: Agricultural and Horticultural Crops [1 ed.] 9781783323173, 9781783322671

Citation preview

Crop Evolution and Genetic Resources

Crop Evolution and Genetic Resources

Darbeshwar Roy

α Alpha Science International Ltd. Oxford, U.K.

Crop Evolution and Genetic Resources 616 pgs. | 61 figs. | 211 tbls.

Darbeshwar Roy GB Pant University of Agriculture and Technology Pantnagar Copyright © 2016 ALPHA SCIENCE INTERNATIONAL LTD. 7200 The Quorum, Oxford Business Park North Garsington Road, Oxford OX4 2JZ, U.K. www.alphasci.com ISBN 978-1-78332-267-1 E-ISBN 978-1-78332-317-3 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the publisher.

Preface In most crops yield has reached plateau and this yield barrier can be broken by gene introgression from the crop’s own gene pool and/or from its distant gene pool. To start with gene pool can be the primary gene pool (GP1)but if the desired gene is not available in GP1 and then one can go the other gene pools such as- GP2, GP3 or GP4. Initially cytogenetic studies were conducted which provided information regarding the crossability of the cultivated variety with crop’s other species with unique trait(s). For a plant breeder to know which particular species and which breeding method to be used for a desired gene transfer breeder would have to churn the literature but if the same information is provided in the form of gene pools of a crops species then gene transfer program can be executed immediately. For knowing a crop’s genetic resources one will have to study the evolution of a crop, its origin and distribution of its wild/weedy and other related species. This will throw light on the gene centres for gene for resistance to biotic and abiotic stresses from where the species with desirable gene can be obtained and used. These genes will provide yield stability in the present scenario of climate change which is the requirement of the day and in long term will break the yield plateau. Further, study of crop evolution will help in understanding the cultivated species’ constitution, its similarity and differences with other species from the same genus or different genera from the same family and will further make possible its resynthesis and gene transfer from distant relatives. Evolution can be studied at the phenotypic level and now at gene sequence level. It is an era of genomics and gene mining, the objective now a days is to search for different desirable genes in the crop’s own gene pool as well as crop’s other gene pools. There is a need to estimate the genetic distance between different cultivars within a crop species and to establish phylogenetic trees. With the patenting of crop variety and plant breeders’s right in operation and free exchange of materials rather difficult it is necessary to collect and conserve the plant genetic resources and it will serve as gold reserve for a country.

vi

Preface

This book is written keeping these objectives in mind. The author had taught fruit breeding courses at G.B.P.U.A.&T., Pantnagar for a number of years besides being associated with groundnut, sunflower, sesbania and crotalaria, tea, papaya, litchi and mango. Further, besides being Dean, Agriculture at Bihar Agriculture University, Sabour(Bihar), the author had the opportunity of heading the department of Vegetable and floriculture and heading the crop improvement group over there and got chance of interacting with various research workers associated with improvement of fruits, vegetables and ornamental crops and seeing closely various horticultural crops growing and thus the knowledge gained during this period inspired me to work on this type of book. I would like to thank Mr. N.K. Mehra, Publisher and Managing Director for quickly accepting the proposal for publishing this book. Finally I would like to thank my wife, Veena, daughter, Cynthia and son, Shishir for the encouragement. Dr. Darbeshwar Roy Professor, Genetics and Plant Breeding

Contents Preface

v

1. Evolution 1.1 Theories of Evolution 1.2 Speciation 1.3 Founder Induced Speciation 1.4 Reproductive Isolation 1.5 Geographical or Spatial Isolation 1.6 Adaptation 1.7 Cytological and Moleculer Basis of Evolotion 1.8 Crop Evolution 1.9 Domestication of Crop Species 1.10 Centres of Diversity and Centres of Domestication 1.11 Collection of Germplasm for Gene(s) for Resistance to Diseases and Pestsfrom Gene Centers

1.1 1.1 1.2 1.5 1.6 1.6 1.9 1.10 1.14 1.15 1.19 1.23

2. Forces in Evolution 2.1 The Hardy-Weinberg Equilibrium 2.2 Changes in Gene Frequency 2.3 Mutation 2.4 Selection 2.5 Competitive Selection 2.6 Migration 2.7 Drift 2.8 The Founder Principle

2.1 2.1 2.5 2.8 2.12 2.16 2.16 2.18 2.23



Contents

viii

2.9 2.10 2.11 2.12

Gametic Selection Meiotic Drive Genetic Load Natural Selection

2.24 2.25 2.25 2.28

3. Genetic Resources: Collection and Conservation 3.1 Collection of Germplasm 3.2 Sampling Strategy 3.3 Estimation of Number of Alleles Per Locus 3.4 Sampling Theory of Alleles 3.5 Sampling of Sites 3.6 Points to be Considered During Collection of Germplasm 3.7 Collection of Genes for Resistance to Diseases 3.8 Collection of Rare Alleles 3.9 Evaluation of Germplasm 3.10 Estimation of Genetic Diversity 3.11 Conservation of Genotype 3.12 phenotypic Diversity 3.13 Conservation of Germplasm 3.14 Effective Population Size 3.15 Storage of Seed 3.16 Gene Bank

3.1 3.2 3.2 3.3 3.4 3.4 3.5 3.5 3.6 3.6 3.6 3.10 3.12 3.12 3.14 3.15 3.16

4. Polymorphism and Phylogenetic Inference 4.1 Polymorphisms and their Applications 4.2 Phylogenetic Inference 4.3 Approaches to Deriving Phylogenetic Trees 4.4 Clustering Methods 4.5 Characters for Constructing Tree 4.6 Measuremnet of Genetic Distance at Nucleic Acid Levels Instead of Proteins 4.7 Evolutionary Distance 4.8 Phylogenetic Networks 4.9 Estimation of Diversity 4.10 Use of Protein/Isozyme Taxonomic and Evolutionary Studies

4.1 4.1 4.2 4.4 4.5 4.13 4.14 4.15 4.17 4.22 4.24

5. Origin and Genetic Resources of Cereals 5.1 Wheat 5.2 Buckwheat 5.3 Triticale 5.4 Rye 5.5 Rice

5.1 5.1 5.5 5.6 5.7 5.10

Contents

5.6 Oat 5.7 Maize 5.8 Sorghum 5.9 Barley 5.10 Millets

ix 5.14 5.17 5.22 5.26 5.28

6. Origin and Genetic Resources of Legumes 6.1 6.1 Chickpea 6.1 6.2 Common Bean 6.4 6.3 Cowpea 6.6 6.4 Faba Bean 6.8 6.5 Lathyrus 6.9 6.6 Horse Gram (Macrotyloma Uniflorum) 6.10 6.7 Lentil 6.11 6.8 Pea 6.11 6.9 Pigeonpea 6.13 6.10 Asiatic Gram 6.15 7. Origin and Genetic Resources of Oilseeds 7.1 Rapeseed and Mustard 7.2 Castor 7.3 Flax 7.4 Groundnut 7.5 Niger 7.6 Safflower 7.7 Sesame 7.8 Soybean 7.9 Sunflower

8. Origin and Genetic Resources of Fibre, Green Manuring, Starchy, Sugar and Fodder Crops 8.1 Cotton 8.2 Jute 8.3 Mentha 8.4 Lac 8.5 Sesbania and Crotalaria 8.6 Lucerne 8.7 Berseem 8.8 Guinea Grass 8.9 Azolla 8.10 Bacteria 8.11 Arbuscular Microrrhizal Fungi (AMF)

7.1 7.1 7.7 7.10 7.12 7.15 7.15 7.17 7.19 7.20 8.1 8.1 8.3 8.6 8.8 8.10 8.12 8.13 8.15 8.16 8.16 8.17

Contents

x

8.12 Potato 8.13 Sugarcane 8.14 Sugarbeet 8.15 Tobacco 8.16 Sweet Potato 8.17 Mishrikand 8.18 Yam 8.19 Taro-Arvi 8.20 Cassava

9. Origin and Genetic Resources of Fruit Crops 9.1 Characteristics of Fruit Crops 9.2 Apple 9.3 Apricot 9.4 Strawberry 9.5 Rubus Crops 9.6 Mangosteen 9.7 Currants and Goose Berries 9.8 Kiwi Fruit 9.9 Banana 9.10 Citrus Fruits 9.11 Mango 9.12 Litchi 9.13 Papaya 9.14 Peach 9.15 Pears 9.16 Plum 9.17 Almond 9.18 Walnut 9.19 Olive 9.20 Cherries 9.21 Grape 9.22 Guava 9.23 Sapota 9.24 Persimmon 9.25 Pineapple 9.26 Aonla 9.27 Coconut 9.28 Oil Palm 9.29 Palmyrah Palm

8.17 8.22 8.25 8.26 8.27 8.31 8.31 8.34 8.35 9.1 9.1 9.14 9.17 9.18 9.21 9.22 9.22 9.25 9.26 9.32 9.37 9.40 9.42 9.44 9.45 9.47 9.48 9.49 9.51 9.52 9.53 9.57 9.59 9.60 9.61 9.63 9.63 9.64 9.65

Contents

xi

9.30 Date Palm 9.31 Phalsa 9.32 Loquat 9.33 Pistachio 9.34 Avocados 9.35 Fig 9.36 Chestnut 9.37 Annona spp. 9.38 Pomegranate 9.39 Cashew Nut 9.40 Jack Fruit 9.41 Bael 9.42 Ber 9.43 Passion Fruit 9.44 Carambola 9.45 Mulberry 9.46 Tea 9.47 Coffee 9.48 Cacao 9.49 Eucalyptus 9.50 Poplar 9.51 Sheesham 9.52 Bamboo 9.53 Rubber 9.54 Pecans 9.55 Bluberry 9.56 Hazelnut 9.57 Improvement of Underutilized/Commercially Grown Fruit Crops 1. Introduction 2.  Breeding Methodologies 3.  Germplasm Conservation

9.65 9.66 9.67 9.67 9.68 9.69 9.69 9.70 9.72 9.73 9.76 9.77 9.78 9.81 9.83 9.84 9.85 9.87 9.88 9.90 9.92 9.94 9.95 9.98 9.99 9.100 9.102 9.103 9.104 9.105 9.125

10. Origin and Genetic Resources of Vegetable Crops 10.1 Introduction 10.2 Tomato 10.3 The Brassicas or Crucifer Vegetables 10.4 Onion 10.5 Garlic 10.6 Fennel 10.7 Coriander

10.1 10.1 10.6 10.10 10.16 10.21 10.22 10.22

Contents

xii

10.8 Fenugreek 10.9 Lettuce 10.10 Spinach 10.11 Chicory 10.12 Endive 10.13 Capsicum (Chilli Peppers) 10.14 Cucurbitaceous Vegetable 10.15 Pea 10.16 Brinjal 10.17 Beetroot 10.18 Amaranth 10.19 Kalaunji 10.20 Ajwain 10.21 Okra 10.22 Jimikand 10.23 Turmeric 10.24 Zinger 10.25 Black Pepper 10.26 Betel Leaves 10.27 Saffron 10.28 Cardamoms 10.29 Cinnamon 10.30 Nutmeg 10.31 Cloves 10.32 Vanilla 10.33 Drumstick 10.34 Makhana 10.35 Chow Chow 10.36 Carrot 10.37 Sweet Corn, Baby Corn 10.38 Water Chestnut 10.39 Mushroom 10.40 Imali 10.41 Seed and Pod Vegetable 10.42 Asparagus 10.43 Crop Improvement 10.44 ‘Diseases and Pests of Some Vegetable Crops’ 10.45 Description of Different Vegetables

10.23 10.24 10.26 10.28 10.29 10.30 10.35 10.48 10.53 10.57 10.59 10.60 10.61 10.61 10.65 10.66 10.68 10.69 10.72 10.73 10.73 10.75 10.76 10.77 10.77 10.78 10.78 10.79 10.79 10.81 10.82 10.84 10.87 10.87 10.90 10.93 10.109 10.112

Contents 11. Origin and Genetic Resources of Floricultural Crops 11.1 Introduction 11.2 Marigold 11.3 Gerbera 11.4 Tuberoses 11.5 Chrysanthemum 11.6 Dahlia 11.7 Orchid 11.8 Antirrhinum 11.9 Anthurium 11.10 Carnation 11.11 Rose 11.12 Gladiolus 11.13 Lily-water Lily 11.14 Lotus 11.15 Pansy 11.16 Zinnia 11.17 Bird of Paradise 11.18 Alstroemeria 11.19 Stock 11.20 China Aster 11.21 Statice 11.22 Zantedeschia 11.23 Hibiscus 11.24 Bugambilia 11.25 Juhi, Bela and Chameli 11.26 Petunia 11.27 Cactus 11.28 Foliage Plants 11.29 Hedge Plants 11.30 Lawn / Turf Grass 11.31 Genetics and Plant Breeding 11.32 Mutation Breeding in Vegetatively Propagated Crops 11.33 Methods of Developing Pericilnal/Solid Chimera 11.34 Genetics and Breeding of Variegation 11.35 Improvement of Flowering Trees Index

xiii 11.1 11.1 11.9 11.10 11.11 11.13 11.15 11.15 11.18 11.19 11.20 11.22 11.25 11.26 11.26 11.27 11.28 11.28 11.28 11.28 11.29 11.29 11.29 11.29 11.30 11.30 11.32 11.33 11.34 11.35 11.35 11.36 11.76 11.87 11.96 11.98 I.1

C H A P T E R

Evolution

1

1.1  THEORIES OF EVOLUTION Evolution can be defined as a change in the hereditary composition of population. It is a composite of many types of changes. These changes could be quantitative as well as qualitative. Considernig the characteristics of the population, the evolution can be defined as the changes in gene frequency and considering most evolutionary changes are quantitative rather than qualitative polygenes are important in evolution. Considering a single locus model, evolution can be regarded as a process of increasing the frequeney of other trait and eventually leading to the fixation of favourable phenotype and this shift is referred to as gene substitution. The rare variants which were once relatively ill-adapted may then become the chosen genotype. These changes may or not be associated with changes in chromosome number or ploidy level. The mechanism of a changing gene and genotype frequencies is the essence of Neo-Darwinian theory of evolution. It is a fusion of theory of Darwin’s selection and theory of heredity. The basic principles of the Darwinian theory of evolution are as follows: (i) The number of individuals in any population tends to increase geometrically when environments permit the survival of progeny. (ii) The potential for rapid increase is seldom realized. (iii) Darwin concluded from these facts that a struggle for existence occurs in which many individuals are eliminated. (iv) Variation in the form of individual differences exists in every species or population which led to the conclusion that some variations are environmental while others are hereditary and can be transmitted from parent to offspring. (v) From the observed differences between individuals as well as between varieties Darwin deduced that elimination process was selective and there is survival of the fittest. (vi) Evolution is a gradual change in the hereditary make up of the species.

1.2

Crop Evolution and Genetic Resources

Fisher argued that evolution is taking place through a process of succession of small steps (micro evolutionary steps) each of which is selectively advantageous leading eventually to large differences (macro-evolutionary process) by accumulation of many smaller steps. Thus evolutionary changes can be quantified into different orders of magnitude. (i) micro-evolution and (ii) macroevolution. The microchanges in evolutionary short time lead to larger changes in long time and the evolution involves a progressive change in gene frequencies. Evolution manifests itself in two ways, first it produces adaptive characters and secondly, it produces species. Here evolution can be defined as the development of new species of plants or animals with better environmental adaptation. Considering a population with large number of genetically variable individuals with a limited environmental opportunity there starts a struggle for existence amongst the different individuals and thus there is operation of natural selection. Using Herbert Spencer’s terminonology the ‘survival of the fittest’ only those individuals (or genotypes) survive who are most adaptive (or fittest) to the environment and process thus leads to evolution of a new genotype or form. Again with the change in environment, the phenomena of struggle for existence and survival of the fittest leads to the emergence of the emergence of yet more adapted genotype. This process of evolution thus goes on and on until an equilibrium is established. The adaptation is thus procured by successive gene substitution. The continuously changing environment causes the fitness of different alleles to change with it. A previously deleterious allele now becomes favourable and gets fixed through natural selection and thus the process of gene substitution continues. During the course of substitution there is loss of defective or unfit individuals through genetic death and thus population can be said to be under continuous genetic load. Once the population has reached an adaptive peak (a position of high fitness with a specific environment) further evolution will depend on origin of a new environment and the creation of a new adaptive peak. Thus plant populations are structured in time and space. Population is not a randomly arranged assemblage of genotype but its genetic structure results from action of mutation, migration, selection and drift which are described in chapter 2 and which in turn must operate within the historical and biological context of each plant species. Genome organization and meiotic process also affect allele and genotype or genetic frequencies. Ecological factors affecting reproduction and dispersal ability are likely to be particularly important in determining genetic structure. The spatial and genetic patterns result from environmental heterogeneity and differential natural selection. The forces which can create variation are hybridization, recombination, mutation and polyploidy. Thus what is required here is to know the forces that generate conserve, restrict or destroy the variation within a system. Any study of speciation, adaptation or genetic change must take into account genetic patterns and processes by which they are modified.

1.2  SPECIATION The origin of species thus involves splitting of a single population into two or more races which further differentiates and produces two or more species. Races or varieties

Evolution

1.3

comprise populations of the same species which differ markedly from each other. Races may differ in the relative frequency of a particular gene. The different races within a single species allow gene exchange amongst them but if the population evolved genetic differences which prevent them from exchanging genes with other population a species is formed. A species consist of groups of actually or potentially inter-breeding population which are reproductively isolated from other such groups. Speciation which can be defined as formation of a species is the evolution of reproductive isolation. There are two approaches to the speciation: (i) Fisherian approach (ii) Wrightian approach In Fisher’s approach, the deterministic force (natural selection pressure) will push up the population to a neighbouring peak and this alone is responsible for the evolutionary change. Fisher’s fundamental theory of natural selection contributed to the theoretical foundation of the Neo-Darwinian synthesis. Fisher (1930) showed that the rate of increase in fitness is equal to the genetic variance in fitness. Fisher defined fitness in terms of the logarithmic rate of increase in number calling it the Malthusian parameter of population increase (m) and showed that under certain idealized conditions. the rate of change in mean fitness of a population is d m ___ ​   ​ = VA(m) dt where VA(mt) is the additive genetic variance in fitness. Since a variance must be d m ___ positive, ​   ​ must be positive so that fitness defined in these terms will always tend to dt increase. However the mean fitness of the population cannot increase indefinitely. For most species the mean fitness over any long period of time must be close to 1.0. In constant environment with no mutation, natural selection will exhaust the additive genetic variance for fitness and there could be then no further evolutionary change but as the environment (both physical and biotic) does not remain constant, there will remain genetic variations for fitness in the population. Fisher further showed that the rate of evolution (r) is equal to product of selection pressure (s) and genetic variation (v) on which selection is acting. r = sv Thus the amount of genetic variation will influence only the rate of evolution i.e. the time needed to reach the optimum. Genetic factors which prevent the direct access to the optimum phenotype through natural selection are (i) genetic transmission, (ii) the genetic and population structure, (iii) mode of selection, (iv) breeding system, (v) relation between genotype and phenotype. The genetic correlation (linkage or pleiotropy), absence of genetic variation, non-randomness of spontaneous mutation, epistatic interaction and developmental organization, result in a non-linear relationship between genotype and phenotype. The fitness components may have a non-zero heritability i.e. there is genetic variation for those traits segregating in natural population.

1.4

Crop Evolution and Genetic Resources

Wright’s approach  Here the stochastic forces such as sampling, drift can knock the population form one peak to another peak. In Wright’s approach the evolutionary change involves a combination of chance and deterministic force. The change in selection pressure and genetic drift wilt result in the rapid shift of many genes to a new unadapted combination which is reproductively isolated from the ancestral population. Supposing two loci A and B, there will be 9 genotypes in the population. Let us assume that the fitness of A-B- > aabb > A-bb and aaB-. Evolution means the development of an ideal population of infinite size reaching a stable equilibrium. Now it the prevailing genotype (i.e. genotype at equilibrium) A-B-genotype, the better fit type will take place from the inferior genotype A-bb or aaB-which itself evolves from aabb. The evolution of A-bb or aaB represents an unstable equilibrium before a better fit polygenic case and considering dominance, interaction, likage and pleiotropy, fitness of individuals in the population can be represented by numerous peaks and valley. Peaks represent the individuals of higher fitness whereas the valley, the individual of lower fitness, the non-adaptive genotypes. But as the polygenes are having very small effects and show environmental effects, the fitness surface will be much more flatter and peaks will shift because of environmental changes and thus the adaptive landscape of attaining higher peaks i.e. individual with higher fitness of Wright is not static. The invididual with higher fitness has to pass though valley i.e. through the evolution of individuals of lower fitness (individuals with low fitness Æ individuals with high lower fitness (transitory) Æ individuals with high fitness). The alleles will be selected because of their average effects and the population will be improved by direct selection based on additive genetic variance. Wright’s (1931, 1932) shifting balance theory of evolution is concerned with the origin and spread of noval adaptations in geographically subdivided populations. The interaction of genetic and environmental factors produces an intermediate optimum phenotype for a set of characters of an organism, implies a large number of adaptive combinations because many different genotypes, can produce nearly the same optimum phenotype with only minor differences in the phenotype due to pleiotropic effects of the genes. There may also be more than one optimum phenotype or ecological niche available to a population. A population is represented as a point on a multidimensional surface with many peaks and valleys. The height of this adaptive land scape is the mean fitness of the population, the other dimensions are gene frequencies. Selection in a large population always moves the population uphill on the adaptive land scape, increasing the mean fitness provided that the selection forces on pairs of genetic are weaker than their recombination rates. So that genes at different loci are approximately recombined at random in the population (near linkage equilibrium). The essence of Wright’s shifting balance theory is that instead of marking a number of independent gene substitutions at individual loci there is a coordinated shift in allele frequencies at a number of polymorphic loci simultaneously and the balance that is shifting is the balance of allelic frequencies. In this theory drift is critical for the rapid increase of favourable genotype but it does not supplant natural selection. According to Fisher, the best population is a large random mating one in which statistical fluctuations are slight and each allele can be fairly tested in combination with many alleles. Fisher

Evolution

1.5

was for one to one relationship between gene and character whereas Wright argued that the gene interaction is the norm. In Wright’s approach a large population is split up into a number of sub-populations (demes) with migrations sufficiently restricted between the groups and the size sufficiently small to permit random drift to occur which changes the gene frequency. These demes thus move across non-adaptive valleys of the adaptive landscape which represents the multidimensional fitness surface with numerous peaks and valleys. Wright’s (1969) optimum model in which there are multiple fitness peaks results from pleiotropy. The antagonistic pleiotropy implies overdominance for fitness itself. Selection further changes the gene frequencies and thus some of the demes having higher average fitness will increase in size and through one-way migration i.e. migration from this population with high average fitness to low fitness, displaces all other populations until eventually the whole population has a new favourable gene combination.

1.3  FOUNDER INDUCED SPECIATION Species are often quite uniform across the central part of their ranges and are generally divergent in peripheral isolates. This observation led to the foundation of theory of funder effect. A new species may be formed allopatrically following a simple type of population sub-division, the establishment of new population from one or a few founder individuals. As Mayr’s founder are derived from peripheral population of ancestral species, the speciation mechanism can be called as peripetric speciation. The Fig. 1.1 shows the effect of founding event. The founders (B) have got a fraction of the genetic variation of the parental population (A) and further genes are lost during the ensuing genetic revolution (from B to C). The reduction in the level of genetic variation is the most important effect of founder event. But the variation is gradually recovered (D) if the population can find a suitable niche until a new level (E) is reached. There is thus loss and gradual recovery of genetic variation in a founder population. Mayr showed that new species are formed in rare catastrophes. Speciation usually results from genetic revolution triggered by founder effect. Both changes in selection pressure and genetic drift result in rapid shift of many genes to a new coadapted combination which is reproductively isolated from ancestral population. In other words, selective forces altered by increased homozygosity may affect all loci at once and thereby triggering the genetic revolution Fig. 1.1  Loss and recovery of genetic variation in a founder population according to Mayr (1954). A is the parental that breaks up the old coadapted gene population. The founders (B) have only a fraction of the genetic complexes and thus speciation takes place of the parental population. B to C shows the loss of genes as a consequence of the acquisition of the during the ensuing genetic revolution. D shows the gradual new coadapted gene complex. According recovery of variation and the population reaches a new level (E) in a suitable niche to Wallace, genes are said to be coadapted if high fitness depends on specific interaction (fitness epistasis) between them.

Crop Evolution and Genetic Resources

1.6

1.4  REPRODUCTIVE ISOLATION Speciation results in divergence and development of mechanism of reproductive isolation. Isolation is the division of a population into two or more isolated portions which no longer interbred. Isolation comes about as a product of evolutionary change. Reproductive isolation is the isolation by various genetically controlled mechanisms which prevent gene exchange between two populations and preserve the differences in the gene pools of populations previously achieved by natural selection and geographic isolation. The reproductive isolation is builtup gradually in a series of small steps. Reproductive isolation between species is usually accompanied by qualitative differences between species. Initially there is quantitative difference which further accumulates and results into qualitative differences. The reproductive isolating mechanism can work out at two levels. (i) prezygotic level and (ii) post-zygotic level. The various pre- and post-zygotic mechanisms along with mode of action are given in Table 1.1. The mechanisms include devices which range from not allowing two species to mate to prevent fertilization and zygote formation, to the production of weak, inviable or sterile hybrids. Table 1.1  Various reproductive isolating mechanisms A.

Prezygotic mechanisms preventing fertilization and thereby zygote formation.

(1)

Habitat

Populations in different habitats or niches within the same region.

(2)

Seasonal or temporal

Populations maturing at different time.

(3)

Ethological

Populations are isolated by different and incompatible behavior before mating and are found only in animals.

(4)

Mechanical

Cross fertilizing is restricted or prevented due to difference in structure of reproductive organs.

(5)

Gamete incompatibility

Gametes fail to fertilize in alien reproductive organ.

B.

Post zygotic mechanisms. Fertilization takes place and hybrid is formed but these are inviable, weak or sterile hybrids

(1)

Hybrid inviability or weakness.

(2)

Developmental hybrid sterility: Hybrids are sterile because reproduction organ develop abnormally or meiosis breaksdown before its completion.

(3)

Segregation hybrid sterility: Hybrids are sterile because of abnormal of gametes of whole chromosomes, chromosome segments or combination of genes.

(4)

F2 Breakdown: F1’s are normal and fertile but F2 contains many weak or sterile individuals.

Adapted from ‘Processes of Organic Evolution’ by G.L. Stebbins. between them is sterile, evolution of species have occurred. Allopatric Speciation is common.

1.5  GEOGRAPHICAL OR SPATIAL ISOLATION Depending upon whether or not geographical or spatial isolation is essential for speciation, speciation can be allopartric or sympatric.

Evolution

1.7

1.5.1  Allopatric Speciation In allopatric speciation, the geographical isolation of a population is essential. The population splits into two or more geographical zones and remains isolated from each other and there is no gene flow amongst them. The genetic differentiation among these geographic groups of populations occurs through the operation of random genetic drift and selection. The process of the differentiation is fast if the geographical zones have different environments but even if they have similar environment, differentiation will occur (as there are genetically different ways of responding to the same environmental challenge). If the differentiation has occurred to the extent that it prevents gene exchange between them i.e. the hybrid between them is sterile evolution of species has occurred. Allopatric speciation is common.

1.5.2  Sympatric Speciation Speciation occurs without geographical isolation. Sympatric speciation model differs from allopatric in the extent of physical separation. A particular geographical area can be divided into numerous microgeographical niches (a niche has multi-dimensions-temperature, humidity, nutrients, etc) which represent different habitats. Thus if a population breaks up into different ecological groups within a geographical zone, genetic differentiation occurs between groups which can lead to be the development of reproductive isolation mechanism and thus to development of species. Genetic differentiation within a species is strongly correlated with environmental heterogeneity. A significant amount of variability is associated with both geographical and micro-geographical difference in environmental factors. Polypoidy is one mechanism of sympatric speciation. If two diploid species get crossed and the hybrid is sterile, the hybrid can adapt asexual means of the reproduction or by the doubling of chromosome, there will be production of the amphidiploid which is a different from the parental species and thus gets isolated from the parental species and thus at one stroke a new species is evolved. This is called secondary speciation and has taken place in wheat and Brassica. A diploid upon chromosome doubling can become tetraploid which is immediately isolated from the parental species as it will not produce fertile hybrids. The advantages associated with polyploidy are I the effect of higher DNA content on cell size and developmental rate II dosage effects of genes and III increased heterozygioity. Thus the isolating mechanism can develop accidently and not through selection of isolating mechanism i.e. gradual development. When the hybrids of the two populations, races or species are viable and fertile and are better adapted than the parental population to a newly suddenly created environment, it gets isolated. The evolutionary significance of the hybridization is that it brings about recombinational changes involving not only individual loci but co-adapted gene complexes or super gene as well. Introgressive hybridization continuously leads to gene flow between species. Incorporation of one or more chromosomes or chromosome segments into a population from other population may occur through hybridization followed by backcrossing, a

Crop Evolution and Genetic Resources

1.8

process known as introgressive hybridization (Anderson, 1949). How important it is in the evolution, is still open to question. In case of Tripsacum and Maize (Zea mays) cross the hybrid is fertile but its subsequent generation population is not adaptive because of F2 breakdown. Backcrossing of F1 with either of the parent will allow transfer of few genes or gene complex to the established parent and thus successive backcrossing will result in addition of new genes or gene complex. This method of gene flow is sufficient to introduce novel genes / gene complex into widely separated population continuously. This interpopulation migration repeatedly generates new genetic combination (or genetic variation). The gene flow thus acts as a force linking natural plant populations and enhances frequency of potentially favourable alleles to arise. Table 1.2 shows the role of hybridization in the evolution of different crops. Disruptive selection also provides a model for sympatric selection could lead to the development of reproductive isolation provided that the optimal phenotypes are distinct and independent and if forms are mutually inter-dependent i.e. if the selection is frequency dependent, then the outcome will depend on the relative magnitude of this inter–dependence and of competition. Disruptive selection may in certain circumstances lead to the development of either stable polymorphism or reproductive isolation. Disruptive selection has played an important role in the development of different crops such as Kali, broccoli, cabbage, kohlrabi and Brussels sprouts. Diverse races of rice, chickpea and chilli peppers have also been developed as a result of disruptive selection. Table 1.2  Showing extent of role of hybridization in evolution of different of some crops. Crops

Origin

Extent of role of hybridization in evolution

Wheat

Allopolyploid, polyphyletic, multiple origins

Greater

Rice

Complex diploid hybrid, polyphyletic

Greater

Maize

Single ancestor, monophyletic

Little

Soybean

Single ancestor, monophyletic

Little

Barley

Single ancestor, monophyletic

Greater

Cotton

Allopolyploid, polyphyletic

Little

Sorghum

Single ancestor, monophyletic

Greater

Finger millet

Single ancestor, monophyletic

Moderate

Pearl millet

Single ancestor, monophyletic

Moderate

Dry beans

Single ancestor, monophyletic

Greater

Rape seed

Allopolyploid

Greater

Groundnut

Allopolyploid

Little

Sunflower

Single ancestor, monophyletic

Greater

Potato

Complex autopolyploid

Greater

Sugar cane

Complex autopolyploid

Greater

Evolution

1.9

A summary of different modes of speciation along with their causes, population sizes, extent and speed of differentiation are presented in the Table 1.3 given below. Table 1.3  Showing modes of speciation along with important characteristics Modes of speciation and causes

Separation

Population size

Differentiation before reproductive isolation

Speed / rate of speciation

Allopatric Geographic(Geographic separation, selection)

Wide

Large

Much

Slow

Peripatric(Founder-induced speciation or, random genetic drift and selection)

Wide

Small

Little

Quick

Parapatric(or Neighbouring sympatric, Ecological differentiation)

Touching or bordering(One population being on one side and another on other side of the boundary)

Large

Much

Slow

Sympatric(Due to mutation, disruptive selection)

None(one population surrounded by another population

One or a small group

Little

Quick

1.6  ADAPTATION Adaptation depends on the presence of sufficient genetic variation within the species. There is existence of genetic variants showing reduced adaptive values at each of the prevailing conditions. A genotype contributes to load if its removal would increase the population fitness but is a pre-requisite for the preservation of adaptability. Evolution success of a species depends on the environmental conditions in combination with components of its genetic system that serves the maintenace of genetic variation without implying excessive reduction in population fitness Adaptation can be viewed as a short term evolutionary process. Everchanging environments require the capacity to adapt to these conditions and it depends on the presence of sufficient genetic variation. Thus the capacity to adapt to variable environmental conditions is determined by genetic structure which reveals dynamic gene conservation as a measure of preservation of adaptability. The evolutional process which produces adaptive polymorphism and there-by allowing the species to occupy more and more habitats and niches rarely happens in a very short time. The degree of heterogeneity or the number of genotypes at the population level is most important for adaptiveness. Variation in traits such as dormancy, rate of development, fecundity, reproductive efforts and seed dispersal are of adaptive significance. According to Darwinism the evoluation of adaptation takes place as a result of natural selection. For Darwinian theory to work the requirement is that the genetic differences contribute significantly to phenotypic variations within a population.

1.10

Crop Evolution and Genetic Resources

Co-adapted gene complex or super gene as Mather and Dobzanski (1951) called is of fundamental importance in the adaptation of population to their environment. An extreme type of co-adaptation is called canalization (Waddington 1942 and Mather, 1943). It refer to organisms being resistant to genetic and environmental perturbations i.e. the developmental patterns are buffered against a broad amplitude of genetic and environmental conditions. There is greater role of inter-genotypic competition, linkage and gene interactions on the buildup of co-adapted gene complex. Adaptive changes involve physiological, morphological and/or biochemical changes. The coarse adaptation to environmental changes through changes in qualitative or quantitative traits can be by regulatory changes. Continued evolution in environments now changing requires genetic variation for adaptive changes and certain ecological conditions for reproduction and persistence.

1.7  CYTOLOGICAL AND MOLECULER BASIS OF EVOLOTION Evoloution of major chromosomal rearrangement has been through translocation, inversion and duplications.

1.7.1  Translocations and Inversion Translocations heterozygotes are strongly selected against as it produces unbalanced types of gametes but when homozygous, it produces viable gametes. Which ever type is most common, is selected for. The frequency of translocation heterozygotes can increase through population bottlenecks and random drift and its frequency can be maintained by selection in large population. Population bottlenecks and random processes have important influence in those species in which morphological changes have been fastest. The situation is similar with inversion in which the crossing over within the inverted regions leads to production of unbalanced gametes and so it is selected against but when its frequency increases through population bottlenecks and random drift and become more common, they are selected for. Translocation and inversion are common features of evolution especially in the evolution of mammals. Inversion restricts recombination within chromosomes while the translocation heterozygosity restricts recombination between chromosomes. Thus they lock groups of genes together and thus they carry along whatever hitch-hiking genes night be linked to it. Further establishment of translocation heterozygotes or inversion in population indicates their evolution from a very small population sometime in the past. Besides translocation and inversion, other chromosomal rearrangements are centric fusion and fission and like the former they are selected against when in minority but favoured when in the majority (Wright 1940, 1941). Exceptions to this rule are small inversions or centric fusion between telocentric chromosomes of nearly equal length and paracentric inversions in Diptera which constantly produce normal gametes (White, 1973). In most outcrossing species, these major chromosome rearrangements suffer a substantial heterozygote disadvantage due to production of aneuploid gametes. Translocations are found in a number of genera including Archis, Brassica, Campanula, Capsicum, Clarkia Crepis, Datura, Elymus, Galeopsis, Gilla, Gossypium, Hordeum, Layia,

Evolution

1.11

Madia, Nicotiana, Paeonia, Secale, Trillium and Triticum (Grant, 1975; Holsinger and Ellstrand, 1984; Konishi and Linde-Laursen, 1988; Stalker et al., 1991 and Livingstone et al., 1999). Translocation heterozygotes are common in Paeonia brownie (Grant, 1975), Chrysanthemum carinatum (Rana and Jain, 1965), Isotoma petraeea (James, 1950, Clarkia (Snow, 1960). The most extreme example of translocation heterozygosity is in Oenothera biennis in which all the nuclear chromosomes contain translocations and a complete ring of chromosomes is formed at meiosis in heterozygous individual. Inversion polymorphisms have been found in a number of plant genera and one of the best examples is Paeonia californica. Inversion of six chromosomes distinguish between H.annuus, H.petiolaris and their hybrid derivatives, H.anomalus (Reisenberg et al., 1995). Tomato and potato differ by five inversions (Tanksley et al., 1992) and pepper and tomato by twelve inversions (Livingstone et al., 1999).

1.7.2 Duplication Duplication is believed to be a major source of addition of new additional genes to the organism during the course of evolution. The mechanisms involved in duplication are (i) polyploidy-aneuploidy, (ii) exchanges (unequal crossing over between sister or nonsister chromatids results in the production of tendem duplications), (iii) error in DNA replication and (iv) transposable elements. Of which chromosomal duplication, insertion of transposable elements and polyploidy appear to be the most important mechanisms for increasing the number of genes and for producing duplicate loci. Transposable elements are stretches of DNA that have the capacity to move from place to place (within and between chromosomes) in the genome. Their length varies from a few kilobase to tens of kilobases. They usually include genes which code for enzymes required for transposition. Regulation of transposition rate is by mechanisms residing either in the element elsewhere in the genome. Transposable elements disrupt the function of a gene and show mutational effects if it moves to the functional gene but original function is restored if the elements leave the point or if transposable element is excised. In higher organism the transposable elements move to a chromosomal region with no function and become integrated in the chromosomes. It may there loose its capacity to move but then it makes the chromosome longer than before. The evolution of the major chromosomal rearrangements in a strongly subdivided population with local extinction and colonization provides a simple example of Wright’s shifting balance process since every spontaneous rearrangement with a heterozygous advantage creats a new adaptive peak for the population which can be attained by (i) random genetic drift across an adaptive valley and (ii) selection up the new peak and spread by migration and colonization. The third phase of Wright’s shifting balance process involves interdeme selection by selective diffusion in which deme containing individuals with relatively high mean fitness disperses more emigrants colonizers than other demes (Lande, 1985).

1.12

Crop Evolution and Genetic Resources

Duplications have been estimated to be 72% in maize genome (Ahe and Tanksley, 1993; Gant and Doebley, 1997) and 60% in Arabidposis thaliana (Blanc et al., 2000). Most ‘single copy’ genes belong to the larger gene families even in putatively diploid genomes. In many plant species mobile elements (particularly RNA transposons) make the majority of the nuclear genomes (Bennetzen, 2000a; SanMiguel and Bennetzen, 1998). Most of the transposons are inserted into non-coding regions but sometimes they are found in exons. For example, wrinkled seed trait in pea is due to insertion of transposon like elements into the gene encoding starch-branching enzyme (Bhattacharya et al., 1990). Further, most of the flower variations in flower colour observed in morning glory is due to the insertion and deletion of transposable elements (Clegg and Durbin, 2000; Durbin et al., 2001). Transposition results in amplification. Most polyploids are thought to have originated through the production of unreduced gametes (Harlan and deWet, 1975; Bretagnolle and Thompson, 1995) and only occasionally polyploids have arisen through somatic doubling and generation of polyploidy meristems, called ‘sports’. 2n gametes are produced in different crop species such as potato, cassava, blueberry, cotton, strawberry and cherry. Tetraploid inheritance have been observed in lucerne, potato, Haplopappus, Tolemiea, Hauchera and Vaccinium. In case of most aneuploids (Citrus, Rubus, Poa, Nicotiana, Gossypium, Allium, Lycopersicon) base numbers differ by a few chromosomes but extensive variations involving dozens of chromosomes occur in some groups (Abelmochus and Saccharum). For details on these see Cytogenetics, Roy (2009). Genome evolution  Wide variation has been observed in nucleotide sequence (point mutation), gene order on chromosomes as a result of translocations, inversions, and deficiencies, gene number as a consequence of deficiencies and duplications and genome number due to polyploidy. Genetic maps have been constructed and compared between different crops to study the rates of genome evolution. Various molecular studies have shown conservation of the organization of sets of orthologous genes within related genomes. Gene order has been found to be highly conserved among the Fabaceae lentil, and pea and Solanaceous potato and tomato (Tanskley et al., 1992). Similarly, gene order has been found highly conserved in the Poaceae species maize, rice and sorghum. The phenomenon of conservation of gene order is often referred to as synteny or colinearity. It refers to conservation of gene content, order and orientation between chromosomes of different species or between non-homologous chromosomes within a single species. The colinearity based on genetic mapping is termed ‘macrosynteny’ whereas that based on gene order ‘microsynteny’.

1.7.3  Molecular Evolution So far we considered the evolution in terms of change in gene frequency or gene substitution. As we know gene produces enzymes/proteins and thus evolution can be studied by examining the variation in gene product. We can go further and study the evolution by examining the variation at the DNA level i.e. the variation in the nucleotide sequence as it is the DNA which produces enzyme/protein. Changes in amino acid

Evolution

1.13

sequence in protein can be a result of genetic changes i.e. due to change in nucleotide sequence in DNA. At present there are more than 1000 proteins whose amino acid sequences are known. Two species can be said to be related if they have large number of amino acid sequences in common. Many of the species whether prokaryotes or eukaryotes (higher organism with true nucleus) have some kinds of protein in common. Further they all share similar enzymes involves in biochemical processes such as amino acid synthesis, protein synthesis and DNA replication. Study of amino acid sequence and nucleotide sequence will provide insight into the evolution if a new species and higher taxonomic categories such as new orders, genera. Systematic and stochastic processes like mutation, recombination, segregation, selection and genetic drift are sufficient mechanisms for intraspecies evolution. The reduancy of the triplet codon i.e. a single amino acid can be coded by several codons implies the possibility of allelic differeces not expressed at all in functional proteins. The first two nucleotides in the different codons are identical i.e. they have identical nucleotides at first and second position but they differ only in nucleotides at third position. Third position in many codons is the one which is most easily subject to translational error. The rate of amino acid substitution for each protein is roughly constant but differs greatly for different proteins. Further the rate is inversely related to the specificity of the individual amino acid. For each protein, the rate of evolution in terms of amino acid substitution is aproximately constant per year per site for various lines as long as the function and the tertiary structure of molecule remain essentially unaltered. Analyses of haemoglobin have shown that amino acid substitution which reflects the fixation of a codon occurs at approximately the rate of one substitution per codon per billion years. Although this rate of evolution can account for entirely by the fixation of neutral alleles, it does not imply that evolution occurs wholly by genetic drift and natural selection is not playing any important role. Homologous proteins from differnt species have shown that some regions of each molecule are more susceptible to evolutionary changes than others. The degree of ionization of a charged group depends not only on amino acid itself but on its steric and chain neighbours as well. Thus polypeptide is an integral molecule and not just a string of amino acid. Further functionally less important molecules evolve faster than more important ones. Conservative subsititutions occur more frequently in evolution than more disruptive ones. Advantageous mutant substitutions are a minority when compared with a relatively large number of non-Darwinian type mutant substitutions. Very highly deleterious mutations as well as selectively neutral mutations play an important role in molecular evolution. Rates of molecular mutations are much less variable than the rates of changes in morphology and physiology. Nucleotide substitutions, a form of gene mutation, are the most prevalent evolutionary charges at the molecular level. Nucleotide substitutions that cause no amino acid changes (called synonymous or silent substitution) occur at a much higher rate in evolution than those which lead to amino acid changes. Most of nucleotide changes at the third position of the codon are synonymous. Also nucleotide changes in the intervening sequences, introns (regions of genes that are not translated)

1.14

Crop Evolution and Genetic Resources

are more prevalent evolutionary changes than in the translational part, exons of the DNA at the molecular level. Further pseudogenes (genes that have arisen by duplication and have lost their function) evolve faster than functional genes. The smaller the effect that is caused be nucleotide change, the more rapid that changes in the evolutionary time (Crow, 1992). Those changes that produce a large effect are more likely to be harmful and are eliminated by natural selection. A majority of nucleotide substitution in the course of evolution must be the result of random fixation of selective neutral or nearly neutral mutant rather than positive Darwiniam selection and many of the enzyme polymorphisms are selectively neutral and maintained by balance between mutational input and random extinction. Selective elimination of definitely deleterious mutants and random fixation of selectively neutral alleles occur far more frequently than positive Darwinian selection of definitely advantageous mutants. Is most of the amino acid substitution that has occurred in evolution of a species, a consequence of natural selection or of random genetic drift? Any differences observed in polymorphism between introns and exons, between third position bases and other bases cannot be assigned to genetic drift or to changes of history or to differences in mutation rate but must be referred directly to selection differenting between functional classes of DNA. Regulatory changes are responsible for various major changes in evolution. Regulatory mutation can play a larger role in the morphological and functional differentiaton of species than do changes in structural genes. So differentiation leading to the origin of new species, new genera, new order or new family (called macro-evolutionary) can arise from regulatory changes. Large phenotypic effects can occur over a relatively short period of time due to regulatory mutation and which will result in quick speciation. Thus a population undergoing only small gradual changes (micro-evolutionary process) may persist that way for a long period until regulatory changes occur which allow one or more of its group to evolve into a distinct population of a higher taxonomic category. In the evolution of a species, evolution takes place at the level of genetic codons, then comes the evolution of genetic systems which includes the development of mitosis and meiosis mechanisms, development of modes of reproduction (asexual or sexual) and breeding system (autogamy, allogamy). Some populations in the process of gradual speciation through differential adaptation have diverged to the point of ecotypes (races) but have not speciated. There are cases in which there exists similarity between species. Although the different species evolves separately, they have same trait(s) because they have similar phenotypic adaptations i.e. they were inhabiting the same or similar environments and thus faced similar adaptive problems. Such type of evolution is a case of parallelism or convergence.

1.8  CROP EVOLUTION The mechanisms of crop evolution are the same as those of natural (Neo-Darwinian) evolution except that besides natural selection, artificial selection by man has also played an important role.

Evolution

1.15



The law of homologous series (Vavilov, 1949, 1951) suggests the following. 1. The variation in one plant of a species will be found in plants of other species or genera because of the occurrence of parallel forms. The more closely the related species, the greater will be the resemblance among the series of variation. 2. Definite cycles of variation occurs among all families of plants and common traits develop through all the genera and species making up the family. Different crops have similar phenotypic adaptations which have evolved separately. Different genes in different species (crops) or genera act to produce the same phenotypic result. Similar forms, structures, shapes and functions occur in a large number of species, related or unrelated as they have faced similar adaptive problems. Thus one can obtain in nature the corresponding forms through genetic manipulation, crossing, and selection and thus they have predictive value. Convergent phenotypic evolution refers to the appearance of the same trait in independent evolutionary lineage. It is manifest in the repeated evolution of classical domestication traits such as loss of seed shattering and loss of seed dormancy in most cereal crops. Parallel phenotypic evolution refers to the appearance of the same trait in closely related or potentially interbreeding lineages and both can occur in crop domestication. It occurs as the appearance of same domestication trait in multiple, independent origins of a single domesticated crop.

1.9  DOMESTICATION OF CROP SPECIES There are crops like capsicum, cotton, beans, tobacco, squash, etc. in which there are more than two or more cultivated species. This poses the problem of whether speciation preceded domestication which implies that the individual crop species were domesticated independently from distinct wild ancestor or whether speciation followed domestication (in which case each crop may have been domesticated once). In cotton, G. hirsutum and G. barbadense domesticated independently from distinct wild ancestor whereas in Solanum the case is different. In chillies peppers in some instances speciation preceded and in other instances speciation was accentuated by domestication. Domestications are continuously spread over-time. Some crops crops like rice, sorghum, soyabean and sugarcane are the oldest whereas sugarbeet was domesticated during 18th century and oil palm during 19th century. Forage grasses and clovers-have been recently domesticated. Settled agriculture enhanced the domestication of crops. Domestication of a crop depended on the realization of its utility by human beings. The diversity within a crop reflects the diversity of human need for product as well as the diversity of environment. Polyploidy preceded domestication in crops like wheat (tetraploid), groundnut, cotton and Arabica coffee whereas in crops like Brassica, oat, hexaploid wheat, strawberries and tobacco, it was concurrent or followed domestication (Simmonds, 1979). Domestication of a crop plant  Domestication refers to genetic modification of a wild species to create a new form of plants altered to meet the human requirements. In other words, wild plants when taken into cultivation become genetically altered in the

1.16

Crop Evolution and Genetic Resources

process of domestication. Domestication is a continuous process and the evolutionary changes which follow domestication is also a continuous process. Both processes occur wherever agriculture is practiced. Both natural and human selection are operating during domestication. There is regression of some traits and progression of some other traits required for domestication and human needs. Fitness traits in wild are different than in cultivated condition but one trait common will be the reproductive fitness. Both natural and human selection will lead to enhance reproductive fitness with improved adaptation. During domestication change in growth habit (from perennial to annual), breeding system (from predominantly outbreeding to inbreeding), loss in seed dormancy, pod dehiscence, etc have occurred. The study of domestication of a crop includes obtaining evidence for multiple, geographically, independent, distinct domestication events and the speed of domestication. The geographical origin of a crop relies on genome-wide neutral markers which are used to assess allele frequencies in crop compared with the populations of its wild relatives. During domestication there is occurrence of a strong genetic bottleneck (random genetic drift). Theoretically allele diversity in a crop is expected to be a subset of that found in wild population(s) from which it was derived. Geographical origin(s) of domestication is confirmed when populations of wild progenitors are extant in the geographical location(s) where domestication occurred. Genetic data suggest single domestication events for many but not for all crops. The duration of domestication events is inferred from the severity of the genome-wide bottleneck and by whether a selectively favored ‘domestication allele’ spread to fixation quickly or slowly as measured by the size of the ‘selective sweep’ (region of reduced variation) in the surrounding genomic regions. Characteristics of domesticated plant  The process of domestication brings about genetic and phenotypic changes in a number of traits such as non-shattering, synchronous flowering, loss of seed dormancy, reduced toxicity, reduced branching, determinate growth habit, etc. The traits, namely, increase in fruit or grain size in comparison to wild progenitor, more determinate growth and/or apical dominance, robust stature and loss of dispersal mechanisms are found in every variety of a domesticated species. The crop improvement following domestication involved selection of grain quality, fruit or grain color, shape, flowering time (synchronization) or loss of photoperiod sensitivity and plant height. At genome level the common feature of the domesticated genome is the reduction in genetic diversity in domesticated crops in relation to its wild progenitor(s). This reduction in genetic diversity is because of two reasons. First, domestication is thought to have involved small population size, constraining genome-wide genetic diversity by a familiar concept of a ‘genetic bottleneck or random genetic drift’. The second reason is that the domestication involved a ‘directional selection’ for local genomic regions which distinguish domesticated crops from their wild ancestors. After domestication artificial selection was practised for few, big, easily harvested heads, long and easily harvested fibers, non-prickly plants, palatable products and attractive

Evolution

1.17

colours and patterns. Selection was for succulence, sweetness, loss of fiber content in fruit crops, reduced seed content, for parthenocarpy in pineapple, figs, banana and bread fruit and stenospermocarpy in grapes. Further, plant size (small), growth habit (short cycle), breeding system, uniformity, improved partition towards product (increased harvest index), more adaptability, reduced competitive ability, etc. Adaptation is achieved by successive gene substitution in evolving population, leading to local differentiation and ultimately to speciation. Plant species are commonly geographically differentiated into subspecies, ecotypes, clines, etc. as a result of natural selection on genetic variability. The domesticated or cultivated crops have narrow genetic base because domestication was started with a small founder population (genetic drift or founder effect) and it further got narrowed down because of local adaptive pressures which led to produce both geographical differentiation and tolerance of a degree of inbreeding and the elite breeding bottlenecks. In other words, the erosion of genetic diversity is because of domestication and breeding. Crop wild relatives are sources of allelic diversity. Einkorn and emmer wheat, flax, peach vetch and lentils were the first ones to be domesticated in Near East during 6000-7000 BC. During the same period Phaseolus vulgaris and Cucurbita were domesticated in Peru and Mexico. Bluberry was domesticated during 20th century in U.S.A. There are two kinds of vegetatively propagated crops, those producing a vegetative product and those producing a fruit. None of the clonal crops grown for a vegetative product is reproductively normal, flowering is suppressed and fertility reduced. Polypl-oidy and hybridity contribute to sterility. Yams, aroids and sweet potato are the extreme example in which there is no suppression of flowering but there is problem of reproductive abnormalities and sterility. Polyploidy occurs in some apples, pears, Rubus spp., banana, strawberry and bread-fruit. In banana there is vegetative parthenogenesis and many clones are seed and pollen sterile. Pineapple is also parthenocarpic but there is self incompatibility. Clonal planting produces seedless fruits but if pollinated can produce seedy fruits. Many mangoes and citrus produce polymebryonic seedlings, identical to mothers. In Rubus raspberry changes from SI to SC at the diploid level and blackberry changes to a mixture of polyploidy, hybridity and subsexuality. Strawberry and grape change to hermaphrodite from dioecism. In annual herbs, particularly cereals there has been inhancement of inbreeding as inbreeding is regarded as an aid to close adaptation in small isolated groups. Further, self fertilization developed from SI ancestors. Multiple origins of barley, Phaseolus beans and Asian rice is confirmed and multiple origins is suggested for peppers (Capsicum spp.), squash (Cucurbita spp.) and African rice (O.glaberrima). Traits associated with domestication process are given below: 1. Increased reproductive effort. 2. Larger seeds and fruits.

1.18

Crop Evolution and Genetic Resources

3. More even and quick germination. 4. Non-dehiscent fruits and seeds. 5. Self pollination. 6. Trends to annuality. 7. Increased palatability. 8. Colour changes. 9. Loss of defensive characaters. 10. Increased local adaptation. Genetic basis of domestication traits  There are a number of approaches to work out the genetic architecture of domestication traits. 1. QTL mapping. 2. Map-base cloning (Positional cloning). 3. Association or Linkage disequilibrium mapping. 4. Genomic scam. 5. Resequencing of genome. Researches have shown limited number of QTLs to be associated with domestication traits which suggests that domestication occurred through changes at relatively few loci and individual domestication genes themselves could have major phenotypic effects. The best known examples include identification of a QTL for fruit weight in tomato, fw2.2 and two major genes, tb1 and tga1 in maize that control phenotypic differences between maize and teosinte. Further, two seed shattering genes, sh4 and Qsh1 were identified in rice. Both were present in wild and cultivated rice. sh4 domestication allele was fixed in all cultivated rice and this locus differentiated wild rice from cultivated one. Qsh1 domestication allele is fixed in only a subset of temperate japonica rice varieties and is supposedly important for improvement or modification within japonica variety. But then we know that the resolution of QTL mapping is low (and low allele richness) and each QTL peak can potentially span more than 100 genes. In the QTL mapping wild x domesticated cross is made and RILs (recombinant inbred lines) are obtained. QTL and Association mapping both statistically associate segregating allelic variation with a phenotype of interest. Linkage mapping depends on recent recombination whereas association mapping takes advantage of historic recombination and performed by scanning a genome for SNPs in linkage disequilibrium with a trait of interest and thus identifies recombination blocks. However, with association mapping associations are inferred using population samples of potentially unrelated individuals rather than the progeny of a selectively made cross. Association mapping identifies a restricted region or even the causal SNPs determining the trait of interest. Only drawback with association mapping is that in inbreeders there is build up of linkage disequilibrium because of long history of recombination in natural population. The advantages with NAM (Nested Association Mapping) are use of low marker density, high allele richness, high mapping resolution and high statistical power. It has been used successfully in maize.

Evolution

1.19

Genomic scan  It is also referred to as ‘hitchhiking mapping’. Through this technique diversity at molecular markers in wild and domesticated populations is compared to identify reductions in variation consistent with selection. It is unbiased about the type of locus(loci) that might be identified which are important in domestication. Genomic scans in sunflower and maize have revealed signature of selection at genes involved in amino acid synthesis in the domesticates. Genome scan predicts genes using protein homology information. The input proteins are suspected to be similar to regions of the desired DNA sequence. The correct protein is found by doing a BLASTX comparison of the DNA sequence to all known proteins or by running GENSCAN and then comparing the results to known proteins using BLASTP. The input protein is put in FastA format. The genome scan will thus identify markers which can then be used to identify gene(s) responsible for domestication. NAM (Nested Association Mapping)  NAM population is a group of RILs. Here one wild line is crossed to a number, say 25 of diverse cultivated lines and F1’s are generated. Inbreeding is practiced for 6-8 generations and thus at least 200 RILs are developed from one cross and so the total number of RILs comes to 5000 lines which constitutes the NAM population. Each RIL is genotyped with a similar number of molecular markers and the recombination blocks are identified. After each parental line is either (sequenced) or high-density genotyped. Result of sequencing / genotyping is overlaid on the recombination block identified for each RIL. Now all RILs are compared with each other and analysed together. HTP resequencing technique  Results from this high throughput resequencing technique will complement to the other approaches. In this technique resequencing of a candidate domestication gene or of a diversification or improvement gene in population level is done. This approach can be used for testing the presence of ‘selective sweep’ and when combined with a phenotypic assay, it enables pinpointing of a functional polymorphism. Further, base sequence data can be used for fine mapping. Alternatively, if domesticates experienced severe genetic bottleneck which makes the detection of ‘selective sweep’ difficult, these resequencing of genome can identify regions of high divergence between crops and wild species which are also candidate regions for changes associated with domestication. For details on these techniques see Biotechnology, Roy (2010).

1.10 CENTRES OF DIVERSITY AND CENTRES OF DOMESTICATION Vavilov (1951) observed that the centre of diversity is a guide to centre of domestication. He distinguished primary centre where diversity is a consequence of ancient cultivation from secondary centre where the diversity may be a consequence of hybridization. However, Harlan (1971) and others suggested that ecological diversity, farming practices, human migration pattern and / or breeding systems of crops could produce localized

1.20

Crop Evolution and Genetic Resources

centres of diversity in which diversity would however, be unrelated to the length of time for the crops had been cultivated. Some cultivated plants such as the bottlegourds have no centres of diversity but probably domesticated repeatedly throughout the range of their wild progenitors. Variability may be a misleading evidence on place of domestication as in case of maize, the centre of diversity is in Peru but it was domesticated in Mexico. In many crops domestication has not been accompanied by qualitative changes of a sort (Table 1.3) that could be detected archeologically. However, some domestication has been accompanied by morphological changes. There seems little connection between sources of wild ancestors, area of domestication and area of evolutionary diversity. De Candolle (1986) considered that agriculture had originated independently in three regions. China, Middle east and Egypt and Tropical America. Vavilov recognised 8 centres of origin of cultivated plants including 2 in New world Table 1.4. Recent researches have shown that agriculture may have developed essentially independently in four different parts of America (Meso-America). Multiple origins seem likely for new word agriculture in general as well as for most of the new world crops which include more than one species. Even a single species may have been domesticated repeatedly within the range of their wild progenitors. The gene centre refers to area of high diversity and it must represent the centre of origin. As the crop diffuses to new areas, it evolves new races and develops nodes of variability here and there as a result of difference in selection pressure and environment. Thus a crop originated in primary centre develops vast arrays of genetic variants in secondary centre. Primary centre is recognised by presence of wild forms and prevalence of dominant alleles. The centres of diversity are generated as much by people a by ecological or climatic diversity. Some times gene center exists and some times it does not exist. Each crop is a case of its own but a crop by crop analysis shows a certain consistency of evolutionary behavior. The features of evolution are: (i) geographical range, (ii) ecological amplitude and (iii) time. The first two reflects the capacity for genetic variability. There is a basic mode of interaction between space, time and genetic variability. The centres of human development coincide with the centres of crop evolution. The different crop species differ in phytogeography. The pattern of geographical deversity can best be examined on a crop by crop basis (Harlan, 1971). Harlan (1956) wrote “centers of diversity are a real phenomena and do exist but whether or not they represent centres of origin as in classical Vavilovian theory is certaintly debatable”. There exists several centers of diversity in different crops which could not be regarded as centers of their origin (Harlan, 1955, Kuckuck, 1963). Harlan (1975, 1976) classified domestication patterns of crops into five classes: Endemic crop:  The centre of origin and the centre of whatever diversity there may be must coincide. It is thus geographically restricted and thus never spread very far from centre of origin, e.g. Guinea millet.

Evolution

1.21

Table 1.4  Showing eight center of deversily Centre Crop plant 1. South Mexian and Includes southern sections of Mexico, Guatemala, Honduras and Costa Rica. central American centre • Grains and Legmes:maize, common bean, lima bean, tepary bean, jack bean, grain amaranth. • Melon Plants: Malabar Gourd, Winter pumpkin, chayote. • Fiber Plants: upland cotton, bourbon cotton, henequen (sisal) • Miscellaneous:sweetpotato, arrowroot, pepper, papaya, guava, cashew, wild black cherry cheerry tomato, cacao. 2. South American Centre

Three subcentres (2) Peruvian, Ecuadorean, Bolivian Centre: • Root Tubers: Andean potato, other endemic cultivated potato species. Fourteen or more species with chromosome varying from 24 to 60, edidle nasturtium. • Grains and Legumes: starchy maize, lima bean, common bean • Root Tubers: edible canna, potato • Vegetable Crops: pepino, tomato, ground cherry, pumpkin, pepper • Fiber Plants: Egyptian cotton • Fruit and Miscellaneous: cocoa, passion flower, guava, heilborn, quinine tree, tobacco, cherimoya (2A) Chilean Centre (Island near the coast of southern Chile) • Common potato (48 chromosomes), Chilean strawberry (2B) Brazilian-Paraguayan centre • Manioc, peanut, rubber tree, pineapple, brazil nut, cashew, erva-mate, purple grandilla.

3. Mediterranean centre Includes the borders of the Mediterranean sea. • Cereals and Legumes: durum wheat, emmer, polish wheat, spelt, Mediterranean oats, sand oats, canarygrass, grass pea, pea, lupine • Forage Plants: Egyptian clover, whiter clover, crimson clover, serradella • Oil and Fiber Plants: flax, rape, black mustard, olive. • Vegetables: garden beet, cabbage, turnip, lettuce, asparagus, celery, chicory, parsnip, rhubarb. • Ethereal oil and spice Plants: caraway, anise, thyme, peppermint, sage, hop 4. Middle East

Includes interior of Asia Minor, all of Transcaucasia, lran and the highlands of Turkmenistan. • Grains and Legumes: einkorn wheat, durum wheat, poulard wheat, common wheat, oriental wheat, Persian wheat, two-row barley, rye, Mediterranean oats, common oats, lentil, lupine. • Forage Plants: alfalfa, Persian clover, fenugreek, vetch, hairy vetch • Fruits: fig, pomegranate, apple pear, quince, cherry, hawthorn.

5. Ethiopia

Includes Abyssinia, Eritrea, and part of Somaliland, rich in wheat and barley. • Grains and Legumes: Abyssinian hard wheat, poulard wheat, emmer, polish wheat, barley, grain sorghum, pear millet, African millet, cowpea, flax, teff • Miscellaneous: sesame, castor, bean, garden cress, coffee, okra, myrrh, indigo

6. Central Asiatic Centre Includes Northwest India (Punjab, Northwest Frontier Provinces and Kashmir), Afghanistan, Tajakistan, Uzbekistan and western Tian-Shan. • Grains and Legumes: common wheat, club wheat, shot wheat, peas, lentil, horse bean, chickpea, mung bean, mustard, flax, sesame. • Fiber Plants: hemp, cotton • Vegetables: onion, garlic, spinach, carrot. • Fruits: pistachio, pear, almond, grape, apple. Contd...

1.22

Crop Evolution and Genetic Resources

Contd...

Centre 7. Indian Centre

Crop plant Two sub-centers (7) Indo-Burma: main centre (India): Includes Assam and Burma, but not northwest India, Punjab, nor Northwest Frontier Provinces, • Cereals and legumes: rice, chickpea, pigeon pea, urd bean, mung bean, rice bean, cowpea. • Vegetables and Tubers: eggplant, cucumber, radish, taro, yam • Fruits: mango, orange, tangerine, citron, tamarind • Sugar, oil and fiber plants: sugar cane, coconut palm, sesame, safflower, tree cotton, jute, crotalaria, kenaf • Spices, stimulants, dyes and miscellaneous: hemp, black pepper, gum Arabic, sandalwood, indigo, cinnamon tree, croton, bamboo. (7A) Siam-Malaya-Java: Java: Indo-Malayan Centre: includes indo-china and the malay archipelago, • Cereals and Legumes: job’s tears, velvet bean • Fruits: pummel, banana, breadfruit, mangosteen • Oil, sugar, spice and fiber plants: candlenut, coconut palm, sugarcane, clove, nutmeg, black pepper, manila hemp.

8. Chinese Centre

• Cereals and Legumes: e.g. broomcorn millet, ltalian millet, Japanese barnyard millet, Kaoliang, buckwheat, hull-less barley, soybean, adzuki bean, velvet bean • Roots, Tubers and Vegetable: e.g. Chinese yam, radish, Chinese cabbage, onion, cucumber. • Fruit and Nuts: e.g. pear, Chinese apple, peach, apricot, cherry, walnut, litchi • Sugar, Drug and Fiber Plants: e.g. sugar cane, opium poppy, ginseng, camphor, hemp.

Semiendemic crop:  It is a geographically restricted crop but has spread out from the centre of origin and developed some local nodes of high variability, e.g. African rice and teff. Monocentric:  Monocetric crops are relatively new (restricted in time) and have not developed complex variation patterns, e.g. the plantation crops such as tea, coffee, rubber, cocao and oil palm. The centre of origin and the centre of diversity coincide and are clearly discernible. Oligocentric:  These crops are ancient ones with widespread dispersal providing ample time and space for complexities to evolve and show nodes of high variability in several areas e.g. Triticum aestivum. For a widespread crop with centres, it would be logical to assume a temporal sequence from endemic to semiendemic to oligocentric. The crops here have definable centre of origin and have one or more secondary centres of diversity. Whole East is the centre of barley, Emmer wheat, flax, pea, lentil, oats, maize, lima bean and chickpea. All have secondary centres in India and / or China. Noncentric:  These crops have been derived from progenitors with wide dispersal and frequently involved multiple domestications, e.g. sorghum, common beam (Phaseolus vulgaris), radish, pearl millet, cole crops and bottle gourd.

Evolution

1.23

1.11 COLLECTION OF GERMPLASM FOR GENE(S) FOR RESISTANCE TO DISEASES AND PESTS FROM GENE CENTERS Where to search for the source germplasm for gene(s) for resistance to diseases, pests and nematodes? Gene centers of cultivated plants and their wild progenitors serve as the main source of gene(s) for resistance to diseases, insect pests and nematodes. Plant species from primary and secondary centers of diversity of particular crop plants may provide additional gene pools for developing resistant cultivars. Gene centers usually contain the highest number of physiological and pathogenic races (Leppik, 1970) and germplasm collected from these centers is thought to have gene for resistance to various diseases and pests. The following Tables 1.5 (a, b, c, d, e, f, g, h) show germplasm of some crops having genes for resistance to diseases and pests with their centers of diversity. Gene pool  A cultivated plant and its immediate wild progenitors form a common gene pool and can be considered from genetic point of view as members of the same species (Harlan and de Wet, 1971). Tables 1.5 (a-h) showing some crops and their gene centers for disease resistance (Adapted from Leppik, 1970) and CMS (Cytoplasmic Male Sterility). Table 1.5a  Wheat Crop Wheat

Species

Disease/pest

T. monococcum var. hornemannii (2n = 14)

Gene center Russia

T. timopheevii (2n = 28)

Disease and pest resistance, CMS

T. militinae (mutant from T. timopheevii)

Highly resistant to rusts, ergot, downy mildew and Helminthosporium

T. zhukovsky (2n = 24)-a spontaneous amphidiploids derived from T. timopheevii and T. monococcum var. hornemannii

CMS

T. persicum syn. T. carthlicum (2n = 28)

Highly resistant to rusts and Erysiphe graminis

T. timonovum (2n = 56)–an autooctoploid derived from T. timopheevii through chromosome doubling

Resistant to common wheat disease

T. fungicidum (2n = 56) derived from the cross, T. persicum × T. timopheevii

Resistant to rusts, ergot and downy mildew

Haynatricum derived from the cross, Haynaldia villosa (2n = 14) and T. dicoccum var. farrum (2n = 28)

Provides resistance to rusts, ergot and mildew through formation of waxy layer on the plant

Aegilops umbellulata

Resistance to rusts have been transferred to wheats

Russia (west Gruziya)

Turkey

Crop Evolution and Genetic Resources

1.24

Besides the different species of Aegilops presented in the Chapter 5 (Table 5.2), T. dicoccoides var. spontaneovillosum, T. dicoccoides var. nudiglumis, T. araraticum, T. boeticum and Secale cereale are also sources of CMS. In other words, their cytoplasms interact with T. aestivum to produce male sterility. The main donor of resistance to rust is T. timopheevii from Transcaucasian mountain region. This region contains the greatest number of physiological races of Puccinia graminis f.sp. tritici, P. recondita and P. triiformis. Table 1.5b  Potato Crop Potato

Species

Disease/pest resistance

Gene center

Solanum tuberosum (2n = 24, 36, 48, 72, 96)

Domesticated in Andes

S. demissum (2n = 36, 48, 60, 72)

Blight resistance

Central America (Late blight pathogen originated)

S. bulbocastanum (2n = 24, 36)

Highly resistant to other diseases

S. cardiophyllum (2n = 24, 36)

Highly resistant to other diseases

Table 1.5c  Tomato Crop Tomato

Species

Disease/pest resistance

Lycoperson esculentum (2n = 12, 24, 36, 48)

Gene center Peru and Chile

L. esculentum var cerasiforme

Galapagos island

L. pimpinellifolium (2n = 24, 48)

Resistance to diseases

L. hirsutum (2n = 24)

Resistance to diseases

L. peruvianum (2n = 24)

Resistance to diseases

L. peruvianum var. dentatum (2n = 24) (syn. L. chilense)

Resistance to diseases

Maize  It has multiple sites of origin. Mexico is one of the sites. Another center of variability is in the highlands of Peru, Bolivia and Ecuador. Several resistant maize lines have been obtained from Peru and Guatemala. Table 1.5d  Alfalfa Crop

Species

Lucerne or alfalfa Medicago (n = 7, 8)



Disease/pest resistance

Gene center

Wild/cultivated

Mediterranean, distributed to Eurasia

M. sativa (2n = 32, Tetraploid)

Mongolia

M. falcata (Tetraploid)

Mediterranean

M. sativa var. glutinosa (Tetraploid)

Caucasus

Cultivated species

Mountaneous central and eastern Asia could provide genes for resistance.

Evolution

1.25

Table 1.5e  Cucumber Crop Genus Cucumis

Species

Disease/pest resistance

C. heptaductylus C. leptodermis C. myriocarpus C. sativus (2n = 14, 24), C. hardwickii (2n = 14) C. anguria (half cultivated, half naturalized species), West Indian gherkin C. longipes Cucumis melo, muskmelon

Multiple resistance to diseases and insects Multiple resistance to diseases and insects Multiple resistance to diseases and insects Most genes for resistance

Gene center East Africa and adjacent Arabian peninsula as well as Mediterranean as primary center South Africa as secondary center South Africa as secondary cente South Africa as secondary center India, cultivated cucumber developed here West Indies

African wild species morphologically similar to C. anguria All genes for resistance to powdery Primary center is unknown but mildew have come from India India, Persia, Russia and China are considered secondary center

Table 1.5f  Sunflower and Bean Crop Sunflower

Species

Disease/pest resistance

Helianthus annuus (2n = 34), cultivated species H. argophyllus (2n = 34), H. petiolaris (2n = 34) and other wild species

Beans

Gene center North America-primary center and Russia, secondary center

Source of genes for resistance to rust, downy mildew, Verticillium wilt, broomrape and other diseases and pests

North America

Phaseolus (2n = 22)

Two centers of distribution-Asia and Central America

P. acutifolius (Tepary bean) and P. lunatus (Lima bean)

Central Ameica

Table 1.5g  Cabbage and Lettuce Crop Cabbage

Genus/Species

Disease/pest resistance

Gene center Mediterranean origin. Eurasia as center of origin of host and pathogen

Brassica

Possible wild progenitor

B. sylvestris Lettuce

Lactuca sativa and L. serriola

Role in evolution

Resistance to downy mildew and mosaic

Eastern Mediterranean basin

Crop Evolution and Genetic Resources

1.26 Table 1.5h  Apple and Grapes Crops Pomoideae

Grapes

Genus/Species

Disease/pest resistance

Eastern Asiatic origin

Malus, Pyrus, Prunus, Cydonia, Mespilus and Amygdalus Malus

Disease resistance is typical of East Asiatic species (Scab resistant species, M. hupehensis, M. pumila and M. micromalus from China and M. formosana from Taiwan) and Middle Asiatic, European, and American species are susceptible to diseases.

Five centers of speciation (East Asia (China and Japan), Middle Asia, Caucasus, Europe, and North America)

Malus baccata

Source of genes for frost resistance

East Siberia

M. orientalis, a wild species

Caucasian center

M. sylvestris and M. praecox

European center

Several wild species usually known as crab apples

North America

Pyrus and Prunus

China

Pyrus serotina, Pyrus bretschneideri and Pyrus calleryana

Source of resistance but species from Central Asia and Europe are susceptible to diseases

Genus-Vitis

American species are resistant to Plasmopara North America viticola and Phylloxera devastralix. European species are highly susceptible to these diseases Eurasian (Transcaucasia and Middle Asia

V. vinifera, V. sylvestris V. amurensis Gooseberries

Gene center

Frost resistant

Far East

American species have genes for resistance to mildew (Sphaerotheca mors-uvae) but European and Asiatic species are susceptible

North America (46 species), Asia (6) and Africa (6), Europe (one species-G. reclinata

Evolution of C4 plants  C4 photosynthetic pathway differs from C3 pathway by the addition of a CO2 concentrating mechanism at the site of carboxylation. This reduces photorespiration, enabling leaf to fix more carbon than C3 plants in warmer, open environment. C4 plants(maize, sorghum, sugarcane) are thought to have evolved in hot regions of the world in response to decreasing atmoshpheric CO2 concentrations through Tertiary. Such regions fall in between about 30°N and S of the equator, experiencing ~ 200 mm to ~ 3000 mm mean annual precipitation, warm enough and wet enough to support closed forest. There was appearance of C4 grassy ecosystems simultaneously in Asia, Africa and Americas. CO2 concentration will now exceed the threshold at which C4 plants have a photostnthetic advantage over C3 plants (Hoffman et al., 2008).

Evolution

1.27

GENE POOL Harlan and de Wet’s (1971) concept of gene pool: Gene pool (GP1) includes cultivated varieties (GP1A) and wild and weedy related species (GP1B) which hybridizes easily and hybrids are fertile. GP2 includes cross-compatible species producing (Weak to low fertility, partially sterile) fertile hybrids with cultivated species, chromosomes may pair poorly or not at all and recovery of desirable genotype(s) may be difficult in the subsequent generation. GP3 comprises cross-compatible species producing viable but sterile hybrids with the cultivated species, cross-compatible species producing inviable hybrids and incompatible related species. Thus GP3 species are more distantly related to GP1 species. Here one can employ embryo rescue technique, can induce polyploidy through chromosome doubling using colchicines and make bridge cross (with members of GP2). Pre- and post-zygotic barriers can be transferred only through genetic engineering techniques and the cultivars developed using this technique are called transgenics. Now a days genetic transformation techniques are being advocated for transferring traits from GP1 and GP2 species to cultivated species and the varieties developed are called intragenics and cisgenics. The standard backcrossing method takes longer time to transfer a trait from donor to recipient variety and further there is problem of linkage drag and this is where genetic engineering technique is used to hasten the process of developing variety and only the desired trait is transferred. This is particularly true in case of perennial fruit and forest trees. Cis gene is an identical copy of a gene from sexually compatible species (species from gene pool 1) including promoter, intron and terminator which is transferred. During transformation cis gene is inserted within Agrobacteriums derived T-DNA borders. Intragenesis allows in vitro recombination of elements from different genes within the sexually compatible gene pool and thus in this transformation protocol there is no need of introns and C-DNA or fragments of genes can be used. Thus these are two different transformation concepts (Rommens, 2004, Schouten et al, 2006). Total germplasm (or genetic resources) within a crop species have been grouped into three gene pools on the basis of characteristic F1 they produce (Table 1.6). GP1 species have been used in breeding program for improving rice, barley, sweet potato, sunflower, oil palm, sesame, tomato, carrot, bell pepper, grapes, apple, strawberry, sugarcane, sugarbeet, rubber and cotton. GP2 species have been used in maize, potato, cassava, tomato, peas, sugarcane, tobacco and cotton in their improvement. GP3 species have been used in wheat, tomato and cotton. Wild species have been used to create variability which has been reduced over the years. Wild gene pools are more diverse than the domesticated pools. In case of oil palm and rubber the attempt is to seek gene pool within the species which was best suited to domestication. They have also been the sources of resistance to diseases. Besides, use of other domesticated forms of a species have been used in the improvement program of crops such as sugarcane(S.chinense), potato(neo-tuberosum group of South America). Use of rarer gene has been transferred from wild species to cultivated species, e.g. presence of j2 gene for jointless pedicel in tomato allowing mechanical harvesting has been transferred from L.cheesmanii.

Crop Evolution and Genetic Resources

1.28

Table 1.6  Showing gene pool, type of species, and crossing reaction following Harlan and de Wet Gene pool

Constituents

Harlan and de Wet category

Experimental taxonomic category

st

a. Cultigen

GP1

same ecospecies (biological species)

nd

b. Weedy form (wild counterpart)

GP1

same ecospecies (biological species)

rd

3 order

Cross-compatible species producing± fertile hybrids

GP2

Same coenospecies (syngameon)

4th order

Cross-compatible species producing viable but sterile hybrids

GP3

Same coenospecies (syngameon)

5th order

Cross-compatible species producing inviable hybrids

GP3

Same comparium

6th order

Incompatible related species

1 order 2 order

References Allard, R.W. 1986 Principle of Plant Breeding, John Wiley & Sons. nderson, E. 1949 Introgressive Hybridization John Wiley, New York. A Barber, H.N. 1970. Hybridization and the evolution of plants. Taxon 19:154-160. Bennetzen, J.L. 200a. Transposable element contributions to plant gene and genome evolution. Plant Mol. Biol., 42:251-269. Bennetzen, J.L. 200b. Comparative sequence analysis of plant nuclear genomes: microcolinearity and its many exceptions. Plant Cell 12:1021-1029. Bingham, E.T. 1980. Maximizing heterozygosity in autopolyploids. In: Lewis, W.D.(ed.) Polyploidy: Biological Relevance, Plenum Press, NY, pp: 471-490. Breese, E.L. 1989. Regeneration and Multiplication of Germplasm Resources in Seed Genebanks: The Scientific Background. IBPGR, Rome. Briggs, D. and Walters, S.M. 1984. Plant variation and Evolution. Cambridge University Press, Cambridge. Burnham, C. 1962. Discussions in Cytogenetics. Burgress, Minneapolis. Carson, H.L. and Templeton, A.R. 1984. Genetic revolution in relation to speciation phenomena: the founding of new populations. Annual Review of Ecology and Systematics 15:97-131. Carson, H.L.1971. Speciation and the founder principle. University of Missouri Stadler Genetics Symposium 3:51-70. Charlesworth, B., Lande, R. and Slatkin, M. 1982. A. neo-Darwinian commentary on macroevolution. Evolution, 36: 474-498. Coyne, J.A. and Lande, R. 1985. The genetic basis of species differences in Plants. Am. Nat., 126: 141-145. Darlington, C.D. 1939. Evolution of Genetic Systems, Cambridge. University press, Cambridge.

Evolution

1.29

De Candolle, A. 1984. Origin of Cultivated Plants, Paul Kigan, translator. (Original published in French at Geneva, 1982). De Nettancourt, D. 2001. Incompatibility and incongruity in wild and cultivated plants. Springerverlag, Berlin. Fisher, R.A. 1930. The Genetical Theory of Natural selection. Clarendon, Oxford. Ford, E.B. 1975. Ecological Genetics: The Evolution of Super-genes. Chapman & Hall, London Genetics. 2nd ed. Sinauer Associates, Inc., Sunderland, M.A. Goodman, M.M. 1990. Genetic and germplasm stocks worth saving. Journal of Heredity 81:11-16. Gottleib, L.D. 1984. Ganetics and morphological evolution in plants. Am. Nat., 123: 681-709. Grant, V. 1981. Plant speciation, 2nd ed. Columbia Press, New York. Grant, V. 1981. Plant Speciation. 2ed edn. Columbia University Press, NY. Grant, V. 1985. The Evolutionary process: a critical Review of Evolutionary History. Columbia University Press, NY. Haraln, J.R. 1975. Geographic patterns of variation in some cultivated plants. J. Heredity, 66: 182191. Harlan, J.R. 1967. Agricultural origins: centers and non-centers. Science 174: 468-474. Harlan, J.R. 1971. Agricultural origins: Centres and Non-centres. Science, 174: 468-473. Harlan, J.R. 1992. a. Crops and Man. American Society of Agronomy Madison, Wisconsin Harlan, J.R. and deWet, J.M. J. 1972. A simplified classification of cultivated sorghum. Crop Science 12:172-176. Harlan, J.R. and deWet, J.M. J. 1971. Towards a rational classification of cultivated plants. Taxonomy 20:509-517. Harlan, J.R. and Zohary, D. 1966. Distribution of wild wheats and barley. Science 153: 1074-1080. Hillis, D.M. and Moritz, C. (eds.). 1990. Molecular Systematics. Sinauer Associates, Inc., Sunderland, M.A. Kimura, M. 1983. The Neutral Theory of Molecular Evolution. Cambridge, Cambridge University Press. Levine, D.A.2000. The Origin, Expansion and Demise of Plant Species. Oxford University Press, NY. Lewis, H. 1966. Speciation in flowering plants. Science 152: 167-172. Lewis, W.D. (ed.). 1980. Polyploidy: Biological Relevance. Plenum Press, NY, pp: 445-476. Moore, P. How far does pollen travel? Nature260:280-281. Nei, M. 1987. Molecular Evolutionary Genetics, Columbia University Press, New York. Nei, M. 1987. Molecular Evolutionary Genetics. Columbia University Press, NY. Ochno, S. 1970. Evolution by gene duplication. Springer-Verlag, NY. Otto, S.P. and Whitton, J. 2000. Polyploidy incidence and evolution. Annual Review of Genetics 34:401-437. Pendergast, H.D.V. 1995. Published Sources of Information on Wild Plant Species. CAB International, Wallingford, UK. Purseglove, J.W. 1972. Tropical Crops: Monocotyledons. Longman, London. Simmonds, N.W. 1979. Principles of Crop Improvement. Longman, Burnt Mill.

1.30

Crop Evolution and Genetic Resources

Smartt, J and Simmonds, N.W. (eds.) 1995. Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK. Snow, A.A. and Palma, P.1997. Commercialization of transgenic plants: potential ecological risks. BioScience 47:86-96. Soltis, P.S., Soltis, D.E. and Doyle, J.J. (eds.). 1992 b. Molecular Systematics in Plants, Chapman & Hall, New York. Stebbins, G.L. 1957. Variation and Evolution in Plants. Columbia Univ. Press., Stebbins, G.L. 1971. Chromosomal Evolution in Higher Plants. Edward Arnold, London. Templeton, A.R. 1989. Mechanisms of speciation- a population genetics approach. Annual Review of Ecology 12: 23-41. Templeton, A.R. 1989. The meaning of species and speciation: a genetic perspective. In: Otte, D. and Endler, J.A.(eds.) Speciation and its Consequences. Sinauer Associates, Sunderland, Massachusetts, pp: 3-27. The Origin and Domestication of Cultivated Crops, Elsevier Science Publishers, NY. Vavilov, N.I. 1926. Studies on the Origins of Cultivated Plants. Institute of Applied Botany and Plant Breeding, Leningrad. Vavilov, N.I. 1949-50. The Origin, Variation, Immunity and Breeding of Cultivated Crops. Chronica Botanica, Waltham, Massachusetts. Vavilov, N.I. 1951. The Origin, Variation, Immunity and Breeding of Cultivated Plants. Selected Writings of N.I. Vavilov, Translated from the Russian by starr Chester. Ronald Press, New York. Waddington, C.H. 1957. The Strategy of the Genes. Allen & Unwin, London. Wallace, B. 1970. Genetic Load. Prentice-Hall, Englewood Cliffs, New Jersey. White, M.J.D. 1973. Animal Cytology and Evolution 3nd ed. Cambridge Univ. Press, Cambridge. White, M.J.D. 1978. Modes of Speciation. Freeman, San Francisco. Wright S. 1969. Evolution and Genetics of Populations. Vol. 2. The theory of Gene Frequencies. The University of Chicago Press. Chicago and London. Wright, S. 1932. The role of mutation, inbreeding, Crossbreeding and selection in evolution. Proc. 6th Int. Congr. Genet., 1: 256-366. Wright, S. 1931. Evolution in Mendelian populations. Genetics 16: 97-159. Wright, S. 1940. Breeding structure of populations in relation to speciation. Amer. Nat., 74: 232-248. Wright, S. 1941. On the probability of fixation of reciprocal translocation. Amer. Nat., 75: 513-522. Wright, S. 1969. Evolution and the Genetics of Populations Vol. 2. The Theory of Gene Frequencies. University of Chicago Press. Chicago. Zohary, D. 1993 and Hopf, M. 1993. Domestication of Plants in the Old World: the Origin and Spread of Cultivated plants in West Asia, Europe and the Nile Valley, 2nd edn. Clarendon Press, oxford.

C H A P T E R

Forces in Evolution

2

Population refers to the community of sexually interbreeding or potentially interbreeding individuals. It is characterized by (i) gene pool and (ii) gene frequency. The gene pool refers to the sum total of all the genes in the reproductive gametes of a population and it is the gene frequency which determines the genetic structure of a population.

2.1  THE HARDY-WEINBERG EQUILIBRIUM Considering single locus with two alleles A and a there will be three genotypes in the population, AA, Aa and aa. Let the frequency of allele A, f (A) be u and the frequency of allele a, f (a) be v and f (A) + f (a) = 1. Further assuming that the individuals are mating at random, the genotypic frequencies of these three classes (Aa, Aa and aa) of individuals will be AA(u2), Aa(2u) and aa (v2) as shown in Table 2.1. Table 2.1  Genotypic Frequencies in Random Mating population A(u)

a(v)

A(u)

AA u2

Aa uv

a(v)

Aa uv

aa v2

+

Since the genotypic frequencies total equals unity, i.e. u2(AA) + 2uv(Aa) + v2(aa) = 1 (this equation can be regarded as the binominal expansion of (u + v)2) the gene frequencies can then be calculated from the genotypic frequencies as:

2.2

Crop Evolution and Genetic Resources

f (A) = (u2 + 1/2 2uv)/(u2 + 2uv + v2) . . . = u and f (a) = (v2 + 1/2 2uv)/(u2 + 2uv + v2) . . . = v Again, in the next generation assuming random mating the genotypic frequencies of the three classes of individuals will remain constant as u2, 2uv and v2 and the gene frequencies will also remain constant as u and v. The population can thus be said to be in the Hardy-Weinberg equilibrium. Hardy in England and Weinberg in Germany independently proposed this equilibrium in 1908. Genotypic and gene frequencies in the equilibrium population are called equilibrium genotypic and gene frequencies, respectively. The population will thus continue with this constitution generation after generation till the following assumptions hold: 1. There is random mating in the population. 2. No selection. 3. No mutation. 4. No migration. 5. No drift and the population size is infinite.

2.1.1  Testing Goodness of Fit Using the observed frequencies of three genotypes, the frequency of gene can be estimated and thus the expected equilibrium genotype frequencies can be found and the test of goodness of fit can be made using c2. If required, Yates correction can be used. The failure will result if all the assumptions are not fulfilled. On the other hand, a reasonably close fit does not prove panmixia and other assumptions as unusual patterns of evolutionary change can give a close fit. Also, under various degrees of inbreeding, genetic changes can occur which are significant in evolutionary time but too small to be detected in the chosen sample. The individuals belonging to each of the three genotypic classes can be identified using immunological/isozymatic study or simple tests. The inability to taste PTC (phenyl theo carbamide) is under control of single recessive gene. Having known the frequency of nontaster (homozygotes) the frequency of homozygotes and heterozygotes taster can be estimated in the population. In the distribution of M-N blood groups, the two antisra; anti-M and anti-N can distinguish MM, MN and NN individuals. Anti-M will react with MM red cells and anti-N will react with red cells of NN individual whereas red cells from MN individuals will react with both.

Forces in Evolution

2.3

There is a relationship between genotypic and gene frequencies. With u = v = 0.5, the frequency of heterozygotes Aa is maximum (i.e. 2uv is maximum) whereas the frequency of homozygotes AA or aa increases or decreases with the increases or decreases of gene frequency of A, f(A) or a, f(a), respectively. The total gene frequency (f(A) + f (a)) being 1.0. Further it can be shown that no matter what is the constitution of the starting population, i.e. be it made of only homozygotes, 1/2AA and 1/2aa or any deviation from the equilibrium genotypic frequencies of 1/4AA: 1/2Aa: 1/4aa such as 1/3: 1/3: 1/3 or 2/5: 1/3: 1/3 or 3/7: 1/7: 3/7, the Hardy-Weinberg equilibrium is achieved after a single generation of random mating.

2.1.2 Extension of H. W. Equilibrium to Case of Multiple Alleles, Sex-Linked Genes and Polygenic Inheritance Hardy-Weinberg equilibrium can also be applied to cases of multiple alleles, sex-linked genes and polygenic inheritance. With two alleles system as we have seen the zygotic frequencies u2(AA) + 2uv(Aa) + v2(aa) are obtained by expanding the binomial (u + v)2. With multiple alleles, say alleles having the gene frequencies u1, u2, ..., un and​ n

S  ​ ​​ u1

i = 1

= 1, the frequencies of the different genotypes in equilibrium can be described

by the multinomial expansion, (u1 + u2 + un)2. Thus for any two alleles of a multiple allelic series the equilibrium is attained after a generation of random mating. With three alleles A1, A2 and A3 with their respective frequencies u1, u2 and u3, the six genotypes at H.W. equilibrium will be in the proportion of u2A1A1: 2u1u2A1A2: u22A2A2: 2u1u3A1A3: 2u2u3A2A3 and u23A3A3. Thus when all the three alleles are of equal frequency 2/3 of the population is heterozygous. With four alleles this proportion will be 3/4 and with n alleles it will be (n – 1)/n. That is why in case of single locus multiple allelic sporophytic incompatibility system, the frequency of heterozygous is so high that virtually sib mating is compatible. For three alleles case, we have example of A, B and O blood group in human where the six genotypes AA, AB, AO, BB, BO and OO can be grouped into four phenotypes A, AB, B and O, as A is dominant over O, B is dominant over O whereas AB shows codominance. Assuming p, q and r being the frequencies of A, B and O allele, respectively the equilibrium genotypic frequencies of the six genotypes will be p2(AA): 2pr(AO): 2pq(AB): q2(BB): 2qr(BO): r2(OO). The gene frequencies can be obtained from the observed propotions of the different genotypes in human population as: __

______



r = ÷ ​ r  2 ​ = ÷ ​ f(OO) ​    



p = 1 – (q + r) = 1 – ÷ ​ (q   + r)2   ​

_______

___________

= 1 – ​÷q     2 + 2qr + r2 ​ _____________________

= 1 – ​÷f(BB)       + f(BO) + f(OO) ​

Crop Evolution and Genetic Resources

2.4

and

_______

q = 1 – (p + r) = 1 ​÷(p   + r)2   ​ ____________

= 1 – ​÷p     2 + 2pr + r2 ​ _____________________

= 1 – ​÷f(AA)       + f(AO) + f(OO) ​ where f (AA), f(BB), f(AO), f(BO) and f (OO) are the observed frequencies of AA, BB, AO, BO and OO individuals, respectively. Since it is assumed that p + q + r = 1.0, if the calculated frequencies do not sum to 1.0, the Bernstein formula can be used to correct the estimated gene frequencies as: Estimated gene frequency

Corrected gene frequency

pˆ

p(1 + 1/2d )

qˆ

q(1 + 1/2d )

rˆ

(r + 1/2d ) (1 + 1/2d )

Sum = pˆ + qˆ + rˆ

where d = 1.0 – ( pˆ + qˆ + rˆ ). Having calculated the correct gene frequency the expected equilibrium genotypic frequencies can be calculated and test of goodness of fit can be done using c2 and if required Yates’ correction can be applied.

2.1.3  Sex-Linked Loci In case of sex-linked gene, for example color blindness in man a recessive trait under control of one gene with 2 alleles, there will be five genotypic classes of individuals assuming the homogametic sex to be female and the heterogametic sex to be male. The genotypes along with their respective frequencies are given below: Female XA X A 2

u

Male XAXa uv

Xa Xa v

2

XAY

XaY

u

v

XAXA, XAXa and XaY individuals will be normal while XaXa and XaY individuals will be color blind. The frequency v = f(a) in female population will be (2R + Q)/2(P + Q + R) where P, Q and R are the observed numbers of individuals of XA XA, XAXa and Xaa genotypes, respectively. The frequency of v = f (a) in male population will be

Forces in Evolution

2.5

T / (S + T ) where S and T are the observed number of individuals of XAY and XaY genotypes, The overall frequency of v will be (2R + Q + T )/(2(P + Q + R) + (S + T )) When male and female populations are considered separately, the H.W. equilibrium is achieved after one generation of random mating. But assuming that the sexes are equally frequent, the equilibrium frequencies come to be 1/2u2: 1/2 (2uv): 1/2v2 for females and 1/2 u and 1/2v for males, respectively in order that the sum of the frequencies of five genotypes equals unity (Mather, 1973). The equilibrium is not attained after one generation of random mating as we saw in case of autosomal genes. However, the population will approach very close to H.W. equilibrium after 5 to 6 generations of random mating.

2.1.4  Polygenic Traits The H.W. equilibrium obtained in case of one locus with 2 alleles system and discussed above can be extended to cases of two or more loci (polygenes) determining a trait (Li, 1955). Assuming two loci A and B with two alleles at each locus, the two parents would be AABB and aabb which upon random mating will produce AABB, aabb and AaBb genotypes, respectively as shown below:   AB ab

AB

ab

AABB AaBb

AaBb aabb

In the next generation of random mating the gametes produced by these individuals would be AB, Ab, aB and ab. If C1, C2, C3 and C4 are the proportions of gametes, the population generated will be in equilibrium if C1 × C4 = C3 × C2. Initially C1C4 π C2C3 but the difference between the two C1C4 – C3C2 will gradually decrease in successive rounds of random mating but then how fast or slow it is will depend on the recombination frequency and the tightness of linkage (see Roy 2000, 2012). Thus H.W. equilibrium is not attained after one generation of random mating.

2.2  CHANGES IN GENE FREQUENCY Out of the five forces (random mating, selection, mutation, migration and drift) mating system does not impel changes in gene frequency but four other force can change gene frequency and thus these are the evolutionary forces which determine the genetic structure of a population. In population genetics any change in gene frequency which results in a change in the genetic structures of a population is defined as the evolution.

2.6

Crop Evolution and Genetic Resources

The mathematical treatment of these forces were developed mostly by R.A. Fisher, J.B.S. Haldane and S. Wright in the 1920s. The processes of selection, mutation and migration bring about changes in allelic frequency which are predictable in magnitude and direction, i.e. if the initial gene frequency and the selection differential, the mutation rate or the migration rate are known, the magnitude and direction of the change in allele frequency can be predicted. All these processes will eventually lead to the fixation or loss of an allele unless they are opposed and a stable equilibrium is reached which we shall see later in the section. These processes have been described by various workers as deterministic, directed or systematic in their mode of action.

2.2.1  Effects of Non-Random Mating Inbreeding and assortative mating are the deviations from random mating. While selffertilization is the most extreme form of inbreeding which occurse in hermaphrodite species, the other mild forms of inbreeding are mating of close relative such as full-sib mating, half-sib mating, parent-offspring mating, double first cousins, single first cousins, etc.

2.2.2 Self-Fertilization Considering one locus with 2 alleles, the three genotypes (AA, Aa and aa) in the F2 population will be in the proportion of 1/4: 1/2: 1/4. The frequency of heterozygote is 1/2. Now if selfing is started in this F2 population, then upon selfing the individuals AA will breed true whereas the heterozygote Aa will produce AA, Aa and aa individuals. Thus the frequency of heterozygote will reduce by half in every generation i.e. to 1/4 in F3, to 1/8 in F4 and so on. In terms of gene frequency u and v, the frequency of heterozygote in the nth generation of selfing will be equal to (1/2)n 2uv and the frequency of homozygotes AA and aa will be u-uv(1/2)n and v-uv(1/2)n, respectively. Thus after a large number of generations of selfing, the heterozygote will be lost and the population will compose of individuals of homozygotes AA and aa.

2.2.3  Sib Mating Unlike self-fertilization which is possible only in plants, sib-mating is possible in plants as well as animals. Like selfing, the regular mating of sib leads to homozygosis though distinctly more slowly. The frequency of heterozygote under full-sib/parent-offspring mating decreases according to the series 1/2, 1/2, 3/8, 5/16, 8/32 and thus the frequency of homozygotes increases in the series 1/2, 1/2, 5/8, 11/16, 24/32, etc. in the population starting as an F2. The homozygosis is slower than full-sib/parent-offspring mating in halfsib/double first cousins and is followed by single first cousins. These mating systems have been discussed in detail by Fisher (1949). Formulas for calculating inbreeding coefficient have been given by Wright (1921).

Forces in Evolution

2.7

2.2.4  Assortative Mating When like phenotypes preferentially mate, it is called positive assortative mating. The matings AA × AA, Aa × AA, Aa × Aa and aa × aa are positive assortative mating. Because of dominance of A over a, AA and Aa will be phenotypically similar. The two genotypes will look similar because of environmental effects. Now if the phenotypic assortative mating is between like genotypes then mating will lead to inbreeding and when it is carried out for long enough, the heterozygote will be eliminated and the population will comprise of two groups (AA and aa) of individuals and thus the variance increases. The original variance in an F2 population was 1/2D + 1/4H which is now only D. In this system of mating inbreeding affects only those loci which control the character and for which the mating is assortative. This is unlike inbreeding which leads to homozygosis for all the genes in the genotype. In case of no dominance AA, Aa and aa individuals are clearly distinct phenotypically and the consequence of assortative mating will be similar to that of complete dominance and it can be shown that two generations of phenotypic assortative mating will raise homozygosis to the level achieved by one generation of assortative mating where dominance is incomplete. The inbreeding thus has a greater effect than assortative mating on the homozygosity. If two or more than two genes having similar effects as in polygenic system, are determining the phenotypic assortative mating, the progress to homozygosity for these loci will be slower than for one locus as the same phenotype will be produced by different combinations of genes at the various loci. For example, considering two loci A and B, AABB, AABb and AaBb will be phenotypically similar. The efficacy of assortative mating is reduced further because of environmental effects. Thus in case of polygenic traits, the effect of assortative mating is not to increase the homozygosity but rather to increase population variability. The additive genetic variance is only or mainly increased. The dominance genetic variance hardly changes at all and epistatic component changes very little (Crow, 1952). Thus assortative mating coupled with selection can increase the rate of progress in the population. The effect of assortative mating depends on the degree of resemblance (can be measured by correlation coefficient). If the correlation is high, r = 1.0, the population can become homozygous. This is in contrast with most forms of inbreeding which eventually lead to complete homozygosity.

2.2.5  Negative Assortative Mating Negative assortative mating is the mating of unlike phenotypes. Phenotypic differences could be due to the difference in sex, incompatibility system, physiological or morphological. Unlike positive assortative mating, negative assortative mating tends to maintain the differences. The mating AA × aa and Aa × aa will be called negative assortative mating. Thus at equilibrium the genotypic frequencies come to 1/4 for A allele and 3/4 for a allele. Although with these gene frequencies, the frequency of heterozygote in H.W. equilibrium will be 3/8. Thus negative assortative mating is similar to random mating in effect in that

Crop Evolution and Genetic Resources

2.8

it also produces a half heterozygosis. We have example of sporophytic heteromorphic incompatibility wherein pin (ss) × thrum (Ss) combination is compatible. If the negative assortative mating is restricted to between two different homozygotes such as AA × aa, the maximum frequency of heterozygote that can be maintained by adjusting the mating system is 2/3 the attainment of which in case of polygenic system would require an unrealistic restriction on mating. In case of sex differnce where XX is female and XY is male and in a population of equal males and females the frequency of X, f(X) will be 3/4 whereas the frequency of Y, f (Y ) will be 1/4. But here it must be recognised that it is group of genes (linked) rather than the single gene which decides whether or not to mate whereas in the determination of sex mechanism, chromosome can be involved. The negative assortative phenotypes are maintained in the population at reasonable frequency which cannot be maintained by mutation. The different mating systems thus do not affect the gene frequencies but they do affect the distribution of genes between homozygotes and heterozygotes.

2.3  MUTATION Assuming one locus with two alleles A and a there are two possibilities: either A can mutate a (a forward mutation i.e. mutation from wild or normal type to mutant allele) or a can mutate back to A (a reverse mutation i.e. mutation from mutant type to wild or normal type). Asssuming m being the mutation rate per generation, mA is the rate with which A mutates to a and ma is the of reverse mutation. At equilibrium, rate of forward mutation will equal to the rate of back mutation. If u and v are the intial gene frequencies of A and a, respectively, the frequency of A allele, f(A) will be reduced by an amount umA but because of back mutation the frequency will be increased by vma after one generation of mutation. Likewise, the frequency of a allele, f(a)will be reduced by umA; but increased by umA and at equilibrium and

umA = vma

ma u ___ __ ​  v ​ = ​  m   ​ A This shows that when mA = ma , i.e. when mutation rates are equal, the gene frequencies u and v are identical and when the mutation rates differ, the equilibrium gene frequencies will also differ. Thus whether u or v is higher at equilibrium depends on whether dominant mutation is higher or lower to recessive mutation. Mutation thus unlike mating system affects gene frequencies rather than affecting the distribution between homozygotes and heterozygotes. As mutation rates are generally of the order of 10– 5 or 10– 6 or even lower, the attainment of equilibrium would be a slow process. Further, between the forward and the reverse mutation, the later would appear to be much rarer and thus at equilibrium u will then be lower than v. As a consequence of mutation then the population would come to be dominated by mutant phenotypes—a result which is not found in nature. The

Forces in Evolution

2.9

very low frequency of mutant phenotype that is observed indicates that the frequency of mutant allele is rare. This points to some other force such as selection which is opposing mutational force. As mutant genes are deleterious and in extreme case can be lethal, mutant phenotypes are less fit and do not survive.

2.3.1  Balance Between Mutation and Selection The best examples of balance between mutation and selection are that of achondroplasia, a form of dwarfing and dominant mutation and of phenlketonuria, a recessive mutation in man. The model of fitness in case of dominant and recessive mutation will take the following form: I

Dominant mutation Genotype

II

AA

Aa

aa

2

Frequency

u

2uv

v2

Fitness

1.0

(1 – s)

(1 – t)

AA

Aa

aa

Frequency

2

u

2uv

v2

Fitness

1.0

1.0

1–t

Recessive mutation Genotype

In case of dominant mutation the homozygous genotype aa is usually lethal. Heterozygous genotype carrying the dominant allele a is defective and is less fit in comparison to aa genotype while AA genotype is a normal phenotype. In case of recessive mutation both AA and Aa genotypes are normal whereas aa genotype has lower fitness. Assuming the net mutation to be in the direction of a from A the gene frequencies of allele A, f(A) and allele a, f(a) in the next generation will become

f (A) = (u2 + uv (1 – s) – vm)/1 – 2 uvs – v2t)

= (u – uvs – um)/(1 – 2 uvs – v2t) and

f (a) = (v2 (1 – t) + uv(1 – s) + um)/(1 – 2uvs u2t)

= (v – uvs – v2t + um)/(1 – 2 uvs – v2t) Since, it is a rare defective mutant v is small; v2 will be very small and the aa phenotype will be virtually non-existent in the population and thus we can safely ignore the term v2t in the denominator. u___________ – uvs – um Thus, f(A) = ​         ​ 1 – 2 uvs

Crop Evolution and Genetic Resources

2.10

and at equilibrium

u – uvs – um = ____________ ​          ​=u 1 – 2 uvs Since v is small, u will be approximately equal to 1.0 and the above equilibrium equation reduces to v = m/s The expected frequency of mutant phenotype (Aa) in the population will be 2v = 2 m/s The frequency of mutant phenotype can thus be increased by either increasing m, the mutation rate or decreasing s, the unfitness of heterozygote. m can be increased by exposing the individuals to radiation whereas s can be decreased by treating medically the affected individuals. In case of recessive mutant, the gene frequencies, f (A) and f(a) in the next generation will become

f (a) = (uv + v2) (1 – t)/(1 – tv2)

= v(1 – tv)/(1 – tv2) and

The change in gene frequency Da, due to selection will be



f (A) = (u2 + uv)/(1 – v2t) = u/(1 – v2)

2 v(1 – tv2) tv (1 – v) _________ v – ​ _________  ​     = ​   ​    2 1 – tv 1 – tv2

The change in gene frequency Da due to mutation will be um. Then at equilibrium



um = ​ 

2 tv (1– v) ________  ​    1 – tv2

Since v is small; v2 will be very small and so tv2 will also be very small and can be neglected and thus

um = tv2(1 – v)

Again, since v is small (1 – v) approaches 1.0 and then the above equation reduces to v2 = m/t and

___

v = ÷ ​ m/t     ​

Thus the frequency of mutant phenotype in case of recessive mutation can be increased by either increasing m; the mutation rate or decreasing t, the unfitness of homozygotes aa but unlike dominant mutation the increase in the frequency of mutant phenotype will be less rapid with the decrease in s. In general, the increase will be somewhat slower when it depends on the reduction is s than when it depends on increase in m.

Forces in Evolution

2.11

We also have a case of sickel cell anemia. It is caused by a single recessive mutant gene (h). Homozygous (hh) recessive individuals suffer from sickle cell anemia which causes abnormal development commonly leading to early death but shows resistance to malaria and have S-type hemoglobin. Homozygous dominant (HH) individuals for this gene have normal haemoglobin and do not suffer from anemia but are susceptible to malaria. Heterozygous individuals (Hh) have both types of haemoglobin—normal and S-type haemoglobin (the normal round shape of RBC changes to sickle shaped, S-type haemoglobin differs from normal haemoglobin in that the glutamic acid is replaced by valine at position 6 in it). The heterozygous individuals show heterozygous advantage in that they do not suffer from anemia and simultaneously show resistance against malaria. This is an example of polymorphism where both homozygotes are less fit than the heterozygote but only in the presence of malaria. Let us now see how the very delerious gene can be kept at higher frequency in the population. The model of fitness takes the following form: Genotype Frequency Fitness



AA

Aa

aa

2

2uv

v2

1.0

1 – sa

u

1 – sA

The frequency of allele A, f (A) and allele a, f(a) after one generation will become



u¢ = f (A) = u2(1 – sA) + uv



v¢ = f (a) = v2(1 – sa) + uv

Assuming mutation rate to be very small um can be safely ignored in the calculation. At equilibrium, u2(1 – sA) + uv u __ ​  ______________        ​ = ​ v ​  2 v (1 – sa) + uv which upon simplification becomes msA = vsa u¢ __ ​   ​  = v¢

u __ or ​  v ​  =

sa __ ​  s   ​  A

Form the above equation, the equilibrium gene frequencies can be calculated as:

sa u _____ ​       ​ = ​ ______     ​ = u( f(A)) u + v s A + sa sA v _____ ______ and ​       ​ = ​      ​ = v( f(a)) u + v sa + sA Further it can be shown that very deleterious gene can be kept in population at higher frequency. In case of balance between selection, mutation and heterozygous advantage

Crop Evolution and Genetic Resources

2.12

the selection maintains the status quo of population by removing recurrent mutants and segregants from favoured heterozygote. Rare variants that arise from artificial mutation or recombinations are thus maintained in the population by a balance between mutation, migration or recombination and selection.

2.4  SELECTION Selection is the most important force of evolution as bulk of the changes in gene frequency is caused by it. While discussing the H.W. equilibrium, it was assumed that an individual’s contribution to the next generation is independent of its genotype. In other words, the individuals of these three genotype AA, Aa and aa do not differ in viability and fertility or more precisely in fitness. Fitness refers to the ability to survive and reproduce. Fitness or selective value of an individual can be defined as the proportionate contribution of offspring to the next generation (Falconer, 1960). In other words it refers to the relative reproductive success of an individual. For example, if A genotype produces 100 offspring and a genotype produces 90 offspring then the selective value of A would be 1.0 whereas that of a will be 0.9 and thus the selection coefficient will be 0.0 for A and 10/100 = 0.1 for a. Now if these three genotypes differ in fitness this will bring about a change in the gene frequency which we will see here. Here, the selection practised is natural selection but in practice, we are doing similar thing when, in population, we are allowing only a particular phenotype (or genotype) and not others to make the next generation population. In other words, the genotype selected for, makes greater contribution to the next generation population whereas the genotype selected against makes a smaller contribution. The contribution of any individual to the next generation population will vary according to whether the population size is increasing or decreasing or stable and according to the contribution made by individuals of other genotypes. Let us now consider a population consisting of three genotypes AA, Aa and aa. Assuming complete dominance AA and Aa will be phenotypically identical and can be clearly distinquished from aa individuals. Further assuming that selection is against aa genotypes in the population and t being the selection coefficient the model takes the following form. t can take values from 0 to 1.0. When t is zero, all the three genotype in the population are contributing equally to the next generation population but when t = 1.0. the recessive homozygotes are selected against and thus not allowed to make any contribution to the next generation population. In artificial selection t is called the selection pressure. The gene frequency f(a) called the selection pressure. The gene frequency f(a) changes when the selection is against aa genotype and becomes Genotype

v¢ = f(a) = uv + v2(1 – t)/(1 – v2t) AA

Aa

aa

Frequency

u

2

2uv

v2

Fitness

1

1

1–t

Forces in Evolution

2.13

where 1 – v2t is the total gene frequency. The change in gene frequency (a), the Da becomes Da = v¢ – u 2 v____________ (1 – t) + uv = ​      ​   –v 1 – v2t 2 – tv (1 – v) __________ = ​      ​   1 – tv2

For small value of t, 1 – tv2 can be replaced by 1 and then Da closely approximates to

Da = – tv2(1 – v)

This can be rewritten as a differential equation by replacing Da with dv/dt

dv ___ ​   ​  = tv2(1 – v) dt dv ___ Setting this equation to zero and solving for v, the ​   ​ (or Da) is at a maximum when v dt is 2/3 (Li, 1955). This shows among other things that when a favourable gene appears in the population, it spreads very slowly at the beginning i.e. the rate of change is slow but becomes faster when the gene frequency is at intermediate level. The v decreases at a rate approximately equal to the product of selection coefficient and the term v2(1 – v) from which it can be said that with constant selection pressure t, the change in gene frequency is a function of gene frequency in the previous generation. Selection is most effective at intermediate gene frequency i.e. when u = v = 0.5. Finally, Dv becomes very small when v approaches 0 or 1.0. In other words, selection is least effective when either v is very large or small.

2.4.1  Complete Elimination of Recessive Homozygotes In this situation the selection coefficient t = 1.0 and the model of fitness takes the form as:



Genotype

AA

Aa

aa

Frequency

u02

2u0v0

v 20

Fitness

1

1

0.0

The frequency of allele a, f (a) after one generation of selection becomes



u0v0 v0 __________ ______ v1 = ​        ​ = ​      ​ 2 u 0 + 2u0v0 1 + v0

Crop Evolution and Genetic Resources

2.14

Starting with the v1, the frequency of a, v2 after the second generation of selection will become v1 ______ v2 = ​      ​ 1 + v1 Similarly, the frequency of allele a after third and fourth generation of selection will be v2 ______ v3 = ​      ​ 1 + v2 and

v4 = ​ 

v3 ______     ​ 1 + v3

respectively. Thus, in general, the frequency of allele a after nth generation of selection will become vn – 1 ________ vn = ​      ​, 1 + vn – 1 v2,v3, vn can be expressed in terms of starting gene frequency v0 as v0 _______ v2 = ​      ​, 1 + 2v0

v3 = ​ 

v0 _______     ​, 1 + 3v0

and

vn = ​ 

v0 _______     ​ 1 + nv0

v0 ______     ​into the recurrent series one 1 + v0 term at a time as we go to generation 2, then generation 3 and so on. Now, by rearranging v0 _______ the equation vn = ​      ​the number of generations required to achieve a given change 1 + nv0 in the frequency becomes

This is obtained by substituting equation v1 = ​ 



v______ 0 – vn 1 __ 1 __ n = ​  v v  ​     = ​ v   ​ – ​ v   ​  0 n n 0

The gene frequencies v0 or vn can be calculated as

÷ 

_______________________________



Number of aa individual observed _______________________________ v0 or vn = ​ ​                ​ ​ 2 × population size

The time required to change the allele frequency at different s is



2 __ t = ​  s ​  ln

v_________ t(1 – v0) ​     ​ v0(1 – vt )

Forces in Evolution

2.15

For small s (i.e. when selection is weak) the time required for a specified change in allele frequency is inversely proportional to the intensity of selection. With natural selection, in case of mast evolutionary changes, the value of s is 0.001 or less and so the rates of changes are constant but in long periods of time even this very small selection pressure can produce large changes in allelic frequencies. But in case of diseases and insects resistance, the evolutionary large changes in pathogen/pest have been rapid because of higher value of selection coefficient because of intensive use of fungicide/insecticide and resulted in rapid evolution of pasts having pesticide resistance. Resistance is acquired by natural selection.

2.4.2  Balance between Selection and Inbreeding When two forces are acting simultaneously the change in gene frequency of an allele in a population can be predicted as the sum of the changes due to the two forces separately. If the forces are antagonistic, v will approach an equilibrium value vˆ where Dv is zero. In case of inbreeders, the heterozygotes upon selfing produce homozygous pure breeding lines which are as vigorous as the heterozygous individuals but in case of outbreeders, the inbred individuals produced by inbreeding are commonly less fertile in comparison to the heterozygous (non-inbreds) individuals and in many cases one cannot continue with the process of inbreeding indefinitely as after a certain generation of selfing, depending upon the crop species (the genetic organization of species) the inbreds produced would be too weak continue further inbreeding. Thus it is worthwhile to examine the effect of fitness of homozygote on the process of inbreeding. Considering the heterozygous advantage that the heterozygotes have the model of fitness takes the following form: Genotype Frequency Fitness

AA

Aa

aa

2

2uv

v2

1–s

1

1–s

u

In the above model, the fitness of homozygous genotypes (AA, aa) is the same as 1 – s in comparison to 1 for heterozygous genotype Aa. The valve of s can range from o to 1.0. Now if s = 0 i.e. when homozygotes do not differ from heterozygote in fitness, selfing will ultimately lead to population of homozygotes (AA and aa). When s = 1.0 i.e. when the fitness of homozygote is zero, half the population will continue generation after generation and will consist of heterozygotes. Thus under condition of heterozygous advantage selection in favour of heterozygote can prevent full homozygosis being being attained. Under the condition s > 1/2 i.e. when the homozygotes are at least ‘half as fit as the heterozygotes, selfing will ultimately lead to the population consisting solely of homozygotes (AA and aa) although the rate of progress towards homozygosis will be slower then when s is zero. Thus when (1 – s) ranges from 0 to > 0.5, complete

2.16

Crop Evolution and Genetic Resources

homozygosis is attained sooner or later but when (1 – s) is less than 0.5 i.e. when s lies in between 0.5 to 1.0 which in turn means that homozygotes are less than half as fit as heterozygotes, full homozygosis will never be attained no matter how long the selfing continues. The proportion of homozygotes obtained falls from 1.0 at s = 0.5 to 0.5 when s = 1.0. Thus under selfing a value of s > 0.5 prevents loss of heterozygotes while in the other milder forms of inbreeding such as full-sib mating or parent offspring mating and half-sib mating s > 0.257 and s > 0.19 prevent loss of heterozygotes (Hayman and Mather, 1953).

2.5  COMPETITIVE SELECTION So far we have assumed fitness of an individual to be independent of other individuals in the population but then selection can come about as a result of competition among individuals of the population. Competition can be between individuals of the same genotype (intra-genotypic) i.e. between individuals of AA or Aa or aa genotype or between individuals of different genotypes i.e. between AA and aa, AA and Aa or aa and Aa (inter-genotypic competition). The impact of competition thus will vary with the genetic structure of the population. With limited resources, the intensity of competition increases with increase of population size and the competition is thus density dependent. Thus fitness of an individual which obviously depends on the intensity of competition in turn depends on the relative density of population and is thus density dependent. An equilibrium is established under competitive selection and the alleles will be maintained in the population (Mather, 1973). Competition will also depend on the frequency of these genotypes AA, Aa and aa in the population which in turn depends on the gene frequencies u = f (A) and v = f(a). The competitive selection is therefore frequency dependent as well. In frequency dependent selection, the fitness of the alleles is not constant but changes with their frequencies. For example, in case of S-locus with multiple allelic system of incompatibility in Oenothera organism an allele is at selective advantage (i.e. has higher fitness) when its frequency is high but an equilibrium is established which is stable. But not all frequency dependent selections lead to equilibrium for if the selection advantage of an allele increases with the increase of its frequency, it will inevitably lead to extinction of the other alleles. Thus the selection as we have seen cannot only lead to the fixation of one allele and elimination of another but can also maintain the two alleles at some intermediate equilibrium point between 0 and 1 by striking a balance with countervailing forces like mutation or migration. An equilibrium will also be established between competitive selection and inbreeding.

2.6  MIGRATION Moving out and moving in of individuals from one population to another is called is migration. When the two populations differ in gene frequencies migration brings about a change in gene frequency in the same way as mutation. Suppose there are two populations.

Forces in Evolution

2.17

One having gene frequencies f (A) = u and f (a) = v and another having gene frequencies __ __ f(A) = ​u​  and f(a) ​v​.  Thus for gene frequency of allele a, f(a) the difference between the __ two populations will be v – ​v​.  Let m be the proportion of individuals being exchanged per generation. The frequency of a allele f(a), after one generation of exchange will become __

(1 – m) v + m​v​ 

The change in gene frequency, Da will then become __

__

(1 – m) v + m​v​  – v = – m (v – v​ ​ ) 



Thus the change in gene frequency due to migration depends on the number of immigrants and the difference in gene frequency between the populations. The difference between the two populations in gene frequency after one generation would become __

(1 – m) (v – ​v​)  After many generations, the gene frequencies in the two populations would be the same and this would be fast if m is large.

2.6.1  Balance between Selection and Migration If there is selection operating on the boundary, a balance can strike between migration and selection, i.e.

__

– m (v – u​ ​ )  = tv2(1 – v)

__

where the chagen in the gene frequency, Da due to migration is – m(v – ​v​)  and the change __ in the gene frequency due to the selection is – tv2(1 – v). At equilibrium, – m(v – v​ ​ )  – tv2(1 – v) = 0. From the selection model we know that when the selection is against homozygous recessive, the change in gene frequency is maximum at v = 2/3. Using this value of __ v = 2/3 in the equation – m(v – v​ ​  ) = tv2 (1 – v), the value of Dv = 0.15 t which shows that migration is at least equally important a force in evolution and usually more so than selection pressure of equal magnitude.

2.6.2  Models for Studying the Population Structure Considering a population distributed over a large area, the whole population can be assumed to be made up of local subpopulations which could be formed as a result of presence of different ecological niches. These subpopulations thus constitute a case of isolation by distance. Isolation leads to differences in genetic structure between subpopulations and migration reduces such difference. There are two different models to study the populations structure. Wright’s island model assumes that all subpopulations exchange individuals/gene at the same rate regardless of the relative distances, i.e. the immigrants come randomly from the rest of the population. ‘Stepping stone” model of Kimura is based on the assumption that only neighbouring subpopulations exchange

2.18

Crop Evolution and Genetic Resources

individual or gene, i.e. immigrants are more likely to come from subpopulation close by. In this model sub populations are assumed to be spread in a rectangular grid and immigrants into a subpopulation come from one of the four adjacent subpopulations. These models thus represent long and short range gene flow. While the assumption behind island model is unrealistic, the finite stepping stone model does not lead to simple solution. The estimates of GST which measures the degree of population subdivision in these models, do not differ greatly. A small increase in migration rate in island model has as expected proportionally larger effect than changes in migration rate in ‘Stepping stone model’ in reducing genetic differentiation. A single migrant in an ‘island model’s about as effective as effective as 12 to 20 migrants in ‘stepping stone model’. The difference in the effectiveness of migration between these two models is thus not as great as expected (Crow, 1992). These two models represent the two extremes and most natural populations probably fall between these two extremes and some use can be made of GST. However, the applications of these models have been so far limited. Migration differs from mutation in that first, the rate of immigration can be high unlike mutation rate and thus it can maintain the immigrant allele even though it is aberrant at high frequencies and secondly, unlike mutation it can change the gene frequency at many loci simultaneously and whole genotype (individuals) rather than a particular gene as in mutation is involved in the process.

2.7  DRIFT While discussing the systematic processes we assumed an ideal population with no mutation, migration and selection and with no difference in the viability and fertility among individuals) of infinite size although in practice populations are not infinite and in small populations quite large changes on allelic frequency may occur by chance. The random changes in gene frequency through sampling error were called genetic drift by Wright and it arises because each generation of surviving offspring is produced from a sample of all possible gametes, the gene pool. Wright (1931, 40 and many other papers) showed the importance of random genetic drift (random fluctuation of gene frequencies) in determining the genetic structure of the population. Changes in gene frequencies are not linked to the starting gene frequencies. The magnitudes of the changes produced by drift are predictable but their direction is not. Such processes have been described as stochastic, non-directional or dispersive processes. We will first examine the effect of small population sampling using probability theory on the structure of the derived population. Considering a large random random mating population of a self-fretilizing species in H.W. equilibrium with genotypic frequencies as u2(AA), 2uv (Aa) and v2(aa) and with equal gene frequencies i.e. u = f(A) = v = f(a) = 0.5, the genotypic frequencies will be 1/4: 1/2: 1/4. Now if only one individual survives by chance or is randomly selected to breed there is a 50% change that the individual would be Aa which upon random mating of uniting gametes A and a, produced in equal number, will produce population with the same gene and genotypic frequency as in the parental population. There is also a 50%

Forces in Evolution

2.19

chance that the surviving or the selected individual will be either AA or aa and so the offspring produced would be either AA or aa and thus there is a loss of an allele either a or A. Table 2.2 shows the effect of sampling on allele and genotype frequencies. Table 2.2  Sampling effects on allele and genotype frequencies Probability

Genotype of parents

Effects on allele and genotype frequencies

1/4

Aa × Aa

No change

1/8

AA × aa

No change

1/8

AA × aa or aa × aa

One allele is lost completely

1/2

Aa × AA or Aa × aa

Allele and genotype frequencies change

It can be seen from Table 2.2 that in 1/8 cases, one allele either A or a is lost and in 3/8 case there will be will be no change in allele frequencies and in 5/8 cases there will be change in gene and genotype frequencies. Likewise, the probability of fixation or loss of an allele can be calculated for increasing number of survivors and it can be shown that in a single generation, the probability of an allele being eliminated decreases rapidly as the number of surviving or randomly selected parents increases and at N (the number of parents) = 50, the change of loosing an allele is very rare and the changes in gene frequency will be very little. The magnitude of the effect is thus proportional to the size of the population. Thus we see that in the variable sampling of gene pool, each generation will result in random genetic drift. The change in gene and genotype frequencies is due to sampling error and the genetic drift is thus caused by decrease in population size. Now we will study the statistical procedure through which the effect of genetic drift can be roughly estimated. Consider that a larger intermating population with equal gene frequencies (u = f(A) = v f(a) = 0.5) is separated into a number of sub-populations of size N with equal gene frequencies (u0 = v0 = 0.5). After one generation, the frequency of allele A in the sub-population is expected to follow the binomial distribution with________ a mean, u1 = u0 = 0.5 and a variance of v(u) = u0v0 / 2 and the standard deviation SD(u1) = ​÷u   0v0/2N ​  . Since our aim is to estimate the magnitude of change in the gene frequency of some allele a, Dv after one generation, due to chance alone, it is essential to see the distribution Dv in a number of sibs of size N and the dispersion of Dv among all the sub-populations is measured by the variance. If the distribution is random then the mean of Dv among sub-populations will be zero and the populations have the same Dv value. The expected variation in gene frequency due of sampling errors between sub-population is inversely proportional to N, the sub-population size. Assuming that the binomial distribution can be approximated by the normal curve, it can be found from the normal probability integral that 95% of the sub-populations have an allele frequency in the range of u1 ± 2SD (u1) and the rest have allelic frequencies falling outside this range. Figures 2.1 and 2.2 show distribution of allele frequencies in population of size 5 and 50, respectively. Now if the population remains small in size and the sampling error is effective in each generation, then the drift is continuous and it can be shown that the average or expected

Crop Evolution and Genetic Resources

2.20

gene frequency overall sub-populations and the variance in gene frequency among subpopulations after t generations are:

u1 = u0 v(ut) = u0v0(1 – (1 – 1/2N)t )

Fig. 2.1  Distribution of allele frequencies in population of size 5 after one generation of drift, with an initial allele frequency of 0.5 In 5% of populations, (f(A) = u < 0.19 or > 0.81)

Fig. 2.2  Distribution of allele frequencies in population of size 50 after one generation of drift, with an initial allele frequency of 0.5 in 5% of population, f(A) = u < 0.? or > 0.06

This shows that as t increases, the variance becomes larger with each successive generation. After many generations, the mean gene frequency over all sub-populations remains same as the starting gene frequency. The variance in allelic frequencies among sub-populations increases and tends to u0v0. This implies that eventually A will be fixed in a proportion u0 of population and that a will be fixed in the remaining v0 populations. This further leads to an important conclusion that if a selectively neutral allele arises by mutation, at least once in a population of size N, the probability that this allele is fixed is 1/2N. This probability is higher in smaller population but lower in larger population and lends to zero as the population size tends to infinity. Further, as the drift proceeds, the probability that both alleles coexist within a population is reduced. That is, the drift is accompanied by a reduction in the frequency of heterozygote in each population as the

Forces in Evolution

2.21

allelic frequencies become more extreme. The mean time required for the absorption of an allele (until an allele is either fixed or lost i.e. the frequency of heterozygote is reduced to zero) can be shown to be

_

t​ ​ = –  4Nu0 loge u0 + v0 loge v0 generations

when u0 = 0.5, the value of t is maximum, 2.8N generations. The mean absorption time is shorter when u0 is near 0.0 or 1.0. The mathematical treatment of drift thus shows the following there main effects of random genetic drift on the frequency of neutral allele in small populations assuming no mutation or migration: (i) The different population differ in gene frequencies. (ii) There is less genetic variation within a population than between populations. (iii) There is loss of heterozygotes.

2.7.1  Effective Population Size We have just seen above that if the population size is not infinite, there will be random genetic drift and its magnitude of effects is proportional to size of the population. The population size that is relevant when describing the drift is not the total number of individuals, the census population size but the number of mature, mating individuals who contribute the offspring to the next generation and which is called the effective population size. Wright (1973) showed that if the census population size changes with time, the effective population size can be calculated from the population size in each successive generation. 1 1 ___ 1 1 1 ___ __ ___ ___ ​    ​  = ​  t ​  ​ ​    ​ + ​    ​ + ... ​    ​  ​ Ne N1 N2 Nt

[ 

]

where N1, N2, ... Nt are the effective size at successive rounds of mating. Considering 10, 102, 103, 104, 105 and 106 being the population size in six successive generations, the value of effective population size comes to 54 individuals. Thus even though the population size increases from 10 to a million in six generation, the effective population size behaves as one with a constant size of 54 individuals. This shows that when a population size is small, it will have a disproportions effect. A bottleneck in population size for example, caused by harsh biotic or abiotic stress environment can cause the drift to occur. Under the condition when all individuals (males and females) contribute equal number of gametes to the next generation, Li (1955) pointed out that the effective population size (Ne) becomes

Ne = 2N

where N is the number of individuals. In case of controlled mating when the males and females are different individuals and contribute unequally to the next generation, the effective population size is calculated as:

Ne = 4Nf ◊ Nm/(Nf + Nm)

Crop Evolution and Genetic Resources

2.22

where Nf is the number of female parents and Nm is the number of male parents. The effective population size is proportional to the harmonic mean of Nm and Nf and the harmonic mean is more influenced by the smaller values. Therefore, if the number of females (Nf ) is not equal to the number of males (Nm) then which is smaller will determine the effective size of the population.  When the lines to be recombined are inbred lines such as S2 then the effective population size (Ne) is reduced. In case of the inbred parents, the effective population size takes the following form: 2N ______ Ne = ​      ​ 1 + Fp where Fp is the inbreeding coefficient of parents. When F = 1.0 i.e. when parents are completely homozygous lines, Ne = N. Falconer (1960) expressed the inbreeding coefficient as a function of Ne, the effective population size as: 1 1 ___ ___ Ft = ​    ​ + ​ 1 – ​    ​  ​ Ft – 1 = 1 – (1 – DF)t 2N 2N 1 __ where t corresponds to the cycle of selection and DF = ​   ​  N. In the absence if self 2 fertilization 1 _______ F = ​       ​ 2N + 1 is a preferable approximation. Further the difference in fitness of parents will reduce the effective population size.

( 

)

2.7.2  Random Genetic Drift in Natural Population Random genetic drift undoubtedly influences allele frequency in small populations. In large populations, chance events occur but changes in opposite directions tend to cancel out so that both alleles persist. However, even in relatively large populations there is a small but finite chance that fixation may occur. Random genetic drift is more important when an allele is rare and alleles which have frequencies near zero or 1:0 may become lost or fixed as a result of chance fluctuations even in the presence of strong opposing selection pressure but then mutation may soon regenerate the lost allele in large populations. Although random genetic drift is often advocated as an important evolutionary force, there are contradictory views on its role in evolution. The question is whether or not the drift can be maintained in the face of operation of other evolutionary forces, especially selection. The models of drift described above are based on the assumption that no other evolutionary forces are operating. This implies that alleles are selectively neutral with respect to each other i.e. alleles have neither positive or negative selective values. There are different views about the importance of neutral mutations and similarly, there are different views on the role of random genetic drift in evolution. If the mutations are effectively neural then the drift must be responsible for their frequencies and fixation in neutral populations. Some believe that neutral alleles are common whilst other doubt that truly neutral alleles can exist in nature.

Forces in Evolution

2.23

The model of genetic drift considered above gives the amount of change in gene frequency which is the upper limit in the absence of other evolutionary forces. As these evolutionary forces are operating in real population, they will diminish the effect of the genetic drift and the extent will depend on the magnitude and direction of selection, mutation and migration. This shows that even if the population size is small, drift will have less influence on gene frequency if the alleles are subjected to higher selective pressure and conversely drift will have a greater effect on relatively large population if the selection pressure is less. Further, an allele selected against can be fixed by drift so long as it is not disadvantageous as to lead to the extinction of its carriers. Conversely an allele selected for, may by lost by drift before it could show its full effect. However, over many populations the selected alleles will be fixed more often than the other. Thus in small population with intense selection, a population nearly always becomes the homozygous for the advantageous alleles. Considering mutation, migration and selection separately in a small population, a as a rule of thumb, the random genetic drift will predominate if 4Nm, 4Nm or 4Ns are less than 1.0 where N is the population size and s are the mutation rate, migration rate and the selection coefficient, respectively. If any of these expression is greater than 1.0, the population will behave as if it were large and random genetic drift will be swamped by the effects of mutation, migration and selection. A change in selection, a change in environment, an unusual favourable mutation rare hybridization, and an unusual swarnping by mass immigration can result in change of gene frequency in an unpredictable way.

Role of random genetic drift In theory the genetic drift might play an effective role in the evolution of small natural populations in three situations. When the populations remain small in size and sampling error is effective in each generation, continuous drift is said to be operating. In the two other situations there is reduction of population size. When the population is occasionally reduced to a size small enough to allow drift to occur and drift is of intermittent type. If mortality is at random at the time of reduction of population size, the sample of survivors can have a different genetic composition due to chance alone (the bottleneck effect). Further, if the population remains small for at least 2 generations i.e. if the drift continues in the two successive generations the process of continuous drift is then initiated.

2.8  THE FOUNDER PRINCIPLE Random drift is perhaps most typically exemplified by Mayr’s (1954) ‘founder principle’ which designates the establishment if a new population of a species or form by a small number of individuals, the founding immigrants who carry only a small fraction of the genetic variability of the parental population and hence the allelic frequency of the founding immigrants may deviate from it if chance events occur. Thus new populations started different founders will be genetically distinct from one another and also from the parental population. The consequences of founder effect are genetic divergence, reduced

Crop Evolution and Genetic Resources

2.24

genetic variation and increased homozygosity in a populations founded by a small number of individuals. The resulting genetic revolution will enable new forms or species to be formed. The founder principle is of potential importance in the origin of species. Founder effect in crop plant evolution indicates the value and the breeding potential of the genetic variability in its wild relatives. Founder effect has been shown to have operated in the evilution of allopolyploids cultivated crops. Allopolyploid crops plants derived from a limited number of interspecific hybridization followed by chromosome doublings show narrow genetic variability (consequence of founder effect) in the crop population compared to its wild progenitors. When alloploids evolve from a single diploid hybrid, its descendents will possess a very small fraction of the genetic variability of the diploid species. Founder effects can be suspected to be operating when the chromosomal variation in the wild progenitors is greater than the cultivated counterpart. Also, indication of isozyme polymorphism in the wild species as compared to cultivate points the founder affect. Lewontin (1965), however criticizes that only rare alleles will be lost during a founder effect and these contribute only marginally to the overall genetic variability. Further, remarks that although a genetic revolution is possible within an extremely small and isolated population, this type of population will probably go extinct soon after being established. These points have cast doubt on the real significance of founder effect in the origin of species (Barton and Charlesworth, 1984). However, the high incidence of the genetically determined disability, porphyria, in certain South African people can be explained by the founding principal. For futher information on founding principle see Plant Breeding (Roy, 2012).

2.9  GAMETIC SELECTION So far we have considered selection at the diploid or zygote level. There selection changes the gene and genotypic frequencies of diploid genotype but selection for or against a particular allele can occur in the gamete i.e. at haploid level. Suppose u be the frequency of allele A and v be the frequency of allele a in the gametic pool. Assuming 1 – s be the fitness of a allele relative to 1.0 of A allele the model of fitness takes the following form:



Gamete

Gamete

Genotype

A

a

Frequency

u

v

Fitness

1

1–s

The frequency of allele a after a generation of selection will become v(1 – s)/(u + v) (1 – s)

and the change in gene frequency Dv will be v(1 – s)/(u + v)(1 – s) – v

Forces in Evolution

2.25

which upon simplification becomes – vs(1 – v) _________  ​     1 – vs If s is small, vs will be smaller and thus the change in gene frequency, Dv becomes – vs(1 – s). This shows that the change in gene frequency depends on the selection coefficient and the starting gene frequency. ​ 

2.10  MEIOTIC DRIVE The unequal gene frequency can result because of inability of certain class of gametes to conjugate according to the usual pattern, the phenomenon termed meiotic drive. The phenomenon of meiotic drive is an example of gametic selection in which the heterozygote Aa instead of transmitting an equal number of two types of gene, A and a transmits an excess of one and it deviates from Mendel’s laws of heredity and thus it causes changes in gene frequencies. In Drosophila female, the shorter chromosomes, a homologous pair is preferentially included in the egg. In maize there is often nondisjunction of B-chromosomes during the final cell division in the pollen tube and nucleus with the extra B-chromosomes somehow regularly fertilizes with the eggs. The number of B-chromosomes increases until it starts affecting the viability and thus an equilibrium is achieved which can be described as mutation selection balance (Crow, 1992). Segregation Distorter allele (SD) in Drosophila melanogaster is a well studied example of meiotic drive. Although the SD allele in homozygous condition causes self destruction of sperm it is transmitted to 95% or more of the progeny. The SD acts through another locus, Rs, the sensitive responder on the homologous chromosomes and the chromosome having SD in cis-phase with Rs locus, acts as a killer chromosome. As SD chromosome occurs in less than 10% of population, it can be said that it is subject to some opposing selective forces and their low frequency in population further suggests the operation of some kind of equilibrium determined by selection. These phenomena can have the evolutionary significant. On one hand if a chromosome causing significant distortion has no harmful effects then it will sweep through the population to fixation and it will carry along the effect of the linked hitch hiking genes but on the other hand if the chromosome shows harmful effects then the whole population will be wiped out.

2.11  GENETIC LOAD We have seen that the genotypes AA, Aa and aa in a population differ in fitness considering the rare deleterious mutants or polymorphism. Some individuals show optimum fitness whereas some other have lower fitness and thus the average fitness of the individual in the population reduces and this reduction in fitness is the genetic load. The genetic load this refers to the reduction in population fitness resulting from the presence of genetic variation. The genetic load can be defined as the proportionate decrease in average fitness

Crop Evolution and Genetic Resources

2.26

relative to that of the fittest population. Mutation thus contributes to the genetic load. With 10,000 loci in an organism the total genetic load which will be equal to the sum of genetic load for each locus will be of the order of 10–1 or 10–2. Any organism keeping a greater number of alleles in the class 0.01 < P < 0.05 represents deleterious recessive and constitutes the mutational load. As the mutation rate is of the order of 10–5 or 10–6 the mutational load it produces is of the order of 10–5 or 10–6.

2.11.1  Segregational Load In case of the heterozygous advantage, the gene frequencies of recessive and dominant gene at equilibrium are sa sA ______ ______ u = ​      ​ and v = ​       ​ sA + sa sA + sa

The segregational load thus becomes u2sA + v2sa



Putting the values of u and v in the above equation the genetic load becomes sAsa ______ ​      ​ sA + sa

As the values of selection coefficients s1(sA) and s2(sa) are much greater than the mutation rate, it can be shown that the segregation load produced by a single polymorphism would be as great as that from a very large number of loci undergoing mutation. Further, considering 10,000 loci, the segregational load will be so high that population would have to go extinct many times over to achieve such a level of polymorphism. In the above case alleles at different loci are treated as isolated, independent units and selection is acting on individual locus. Considering the individual as unit of selection and not the locus and that environment acts upon the total finished phenotype rather than upon the loci separately and further assuming that the alleles at different loci are acting in a cumulative fashion or interacting, the cost of maintaining many loci in a polymorphic state could be lower. Study of biochemical traits like protein/isozymes in many populations has revealed that a typical species having about one third or more of all loci, in a single population, have two or more alleles in a polymorphic state and individuals in the population are heterozygous for about 10% of its loci. The finding is in contrast to the classical evolutionary theory that predicted that the most efficient from of an isozyme should over time become predominant in isolated population with an occasional rare allele produced through mutation. As stabilizing selection is required for maintaining a locus in polymorphic state how can enough selection occur to keep this percentage of loci polymorphic. How the population could carry as enormous load of unfitness? The cost of maintainig such a higher percentage of loci in the polymorphic state would be very high. Further, as with n loci (1/2)n of the individuals will be simultaneously heterozygous for all the loci and knowing that an organism contains a very large number of genes, the number of individuals heterozygous at all loci will be very small. With n = 40 only one in million will be heterozygous at all the loci, so the individuals having optimum fitness will have

Forces in Evolution

2.27

heterozygosity at less number of loci and the frequency of such individual will be high and so the load calculated will be misleadingly high. The high level of genetic load the impression that only a few loci could have substantial impact on fitness and that number of loci whose variation is maintained by selection must therefore be linked-to a few dozen loci. Consideration of genetic load and the number of loci that might be maintained by selection led some biologists to propose that the majority of the genetic variation was adaptively neutral. Though the genetic load is measured as deviation from the optimum genotype, the optimum genotype may itself vary in time and space or may even differ in the same place. A population with little or no genetic load may become extinct within a short period with a change of environment but a population with relatively large genetic load when subjected to new environment may survive because the deleterious genes are now at an advantage. In case of genetic load which lowers fitness of genotype and is calculated as

L = ​ 

W max – W _________  ​    Wmax

where Wmax is the fitness of the fittest genotype and W is the average fitness of the entire population, the individuals having lower fitness have reduced reproductive ability in comparison to the optimum genotype and thus contributing enormously to the genetic load of the population. In extreme case individual because of sterility or inability to find a mate may not be contributing at all to the population and these are thus lost. This condition refers to as the genetic death of individual. Although the genetic load can arise from a variety of reasons such as mutation, incompatibility of mother and foetus as in the casa of Rh factor, non-disjunction of chromosomes, hybridization of otherwise discrete population, polymorphism and so on. The two types of loads—mutational load arising from deleterious mutations and the segregational load due to segregation in polymorphic population when the different alleles are maintained by the heterozygous advantage are most important and are discussed as follows.

2.11.2  Mutational Load We saw in case of balance between rare deleterious mutation and selection that at equilibrium the frequency of recessive gene is m/s whereas the frequency of dominant gene is 2m/s. As the effect of mutation is to lower the fitness of an individual and if their reduction is by an amount s then the frequencies of affected individual of affected individual multiplied by their loss of fitness(s) provides the estimate of the genetic load. From this the load for recessive gene in the population can be calculated as m/s × s = m and for dominant gene as 2m/s × s = 2m. This shows that the genetic load is dependent on the mutation rate m, but is independent of the fitness s. It is no surprising as when such mutation occurs, it almost always confers a lower fitness at least in the homozygous condition. Homozygotes are therefore eliminated or held at low levels within the individuals resulting in death if the individual and thus contribute to genetic load of the population

2.28

Crop Evolution and Genetic Resources

but as the component of fitness includes longevity, time to age a first reproduction, fertility besides survivorship, the lower fitness of an individual can be due to production of a comparatively less number of offspring per generation. It will also contribute enormously to the genetic load or if an individual in comparatively more competitive in a new habitat or niche the less competitive genotype (s) will contribute to the genetic load. As selection involves complex interactions between an organism and its biological and physical environment while calculating the fitness in the estimation of load it is assumed that the selection is of Wallace’s hard selection type (hard selection results from interaction between individual and its environment) i.e. the relative fitnesses of different genotypes are constant but infact, it is not and this the estimate of load is biased. Further considering Wallace’s soft selection (which is the result of competitive interactions between individuals of the population and that the carrying capacity of a particular environment is fairly fixed for a species) the relative values of fitness depend on the number and the frequency of other genotypes. The genotypic fitnesses are likely to be frequency and density dependent. Frequency dependent selection does not produce any load as all the genotypes are equally fit when they are present in equilibrium proportion. Through soft selection unlimited number of polymorphic loci could be selectively maintained. If the change in environment makes the predominant genotype lethal or semi-lethal the population will not be able to maintain itself as the only rare genotype which can survive will not be able to fill the carrying capacity of the environment and thus the load i.e. reduction in population size is produced by hard selection. Thus the population will have to go extinct before evolving to the present day level. On the other hand, if the change in environment makes the predominant genotype comparatively less fit than the rare genotype, then the rare genotype will be able to maintain its number and thus soft selection will incur no load and the substitution of rare genotype could take place and thus the evolution takes place without incurring load. Extending the case of heterozygous advantage in sickel cell anemia to a polygenic case, the load will be extremely high i.e. the population size will be reduced greatly due to hard selection and thus the cost of maintaining polymorphism will be very high. From the above consideration it can be said that the term fitness is relative and conditional. It is relative in that the fitness of an individual depends on the genotype of the individual with which it is competing and it is conditional because it is density dependent. Further, fitness is a comparative quality relating the environment (physical or biotic) in which it is grown. the environment as we know is heterogeneous in space and tine and thus the selection coefficient is not constant as assumed throughout the discussion. Further information on these aspects can be found in Li (1967), Crow and Kumura (1970) and Cook (1971).

2.12  NATURAL SELECTION Considering one locus with 2 alleles (A, a) system we have AA, Aa and aa genotypes in a population. Further, assuming additive gene action these genotypes will represent three phenotypically different classes. Individuals from AA and aa classes represent the

Forces in Evolution

2.29

Fig. 2.3  Effects of different types of selection on the population frequency distribution of a phenotypic character. the arrow (Ø or ≠) show selection pressures in different parts of the population frequency distribution. In these figures the ordinates represent the frequencies of individuals in the population and abscissas, the phenotypic variation

extreme types whereas individuals belonging to Aa class is of intermediate type. When we are considering k loci together as in case of quantitative trait, we see that a quantitative trait follows a normal distribution as shown in Fig. 2.3. Although normal distributions are common but not universal among continuously varying characters. Loosely, we van classify the curve into 3 parts (or class), the two tails represent the two extremes expression of a trait and the third represents the expression of average population. Now depending upon which one or more than one classes of individuals is favoured by selection (natural or artificial) we can have three types of selection: (i) Stabilizing selection, (ii) Directional selection, (iii) Disruptive selection.

2.12.1  Stabilizing Selection In the stabilizing selection individuals with means equal to or very close to population mean are selected and thus become the parents of the next generation population as shown in Fig. 2.3. The next generation population will have the same mean as the prevgious one but with a narrow range (or reduced variance). Stabilizing selection is generally considered as the most prevalent type of natural selection. The evidence for this type of selection to have occurred is seen when the majority of the population closely approximates the optumim phenotype. Phenotypes close to the mean have highest fitness and decline in fitness increases with the departure of phenotypes from the mean. As a result of

2.30

Crop Evolution and Genetic Resources

selection, individuals which have low fitness are eliminated and loss of viability or fertility (which are fitness character) is due to: (i) ecological control of population size and (ii) to differential effects between genotypes (competitive ability) i.e. to selection. Those which survive have better fitness and better competitive ability. The selection affects the genetic components of variation. There is reduction in additive genetic variance. There is reduction is non-heritable variance but then it depends on the G × E interaction. The developmental component of variation is also reduced. The reduction in additive genetic varance is due to the development of repulsion phase linkage of favourable relevant genes. Thus stabilizing selection results in the decrease of phenotypic variation. Non-fitness characters are under stabilizing selection. Breese and Mather (1960) showed that stabilizing selection for character will tend to produce ambidirectional dominance and interaction if it is prevalent at all. Further, Mather (1974) showed then that [h], [i], [j] and [l]tend towards 0. Also as neither + allele nor-allele has under stabilizing selection any advantage over the other, the average value of u – v taken over all loci tends to 0 also. This will result in the reduction of DR and HR. Mather (1987) discussed the consequences of the stabilizing selection on genetic structure of the random mating population. Assuming random mating and absence of epistasis, the stabilizing selection acting on a pair of alleles (A, a) can have any the three possible outcomes depending upon the relative values of m and h which characterize the effects of the gene differences on the primary character viz. (i) a stable equilibrium in the population where in respect of the primary character, Aa is near to the optimum than both homozygotes (AA, aa), (ii) fixation of the fitter alleles where Aa is intermediate between the homozygotes in its departure from the optimum and (iii) a therortical unstable equilibrium leading to dixaton of the commoner allele where Aa departs further from the optium than both homozygotes but only the first outcome can lead to the conservation of variation in the population. We have seen in case of balanced polymorphism that Aa indviduals are favoured over the homozygotes AA and aa and this shows that stabilizing selection is operative. Every equantitative trait in any species having an intermediate optimum and natural selection keeps the population near this optimum. With intermediate optimum both alleles are maintained in the population and hence the population variability is increased. Mutation (and possibly overdominance, epistatic pleiotropic effects) maintain variability. The phenotypes contain a great deal of additive genetic variance which allows it to move quickly to a new optimum whenever the environment changes. Thus evolution is through the continual stabilizing selection toward a slowly changing optimum rather the result of directional selection.

2.12.2  Directional Selection In the directional selection, selection is for an extreme expression of a trait. However, as we can see in Fig. 2.3 the two tails represent the two extremes (one in positive and the other in the negative direction) exression of a trait shown in directional selection, selection can be either in the direction of higher mean or lower mean. For a trait like yield, directional selection is for higher yield but for trait like maturity, direction selection can

Forces in Evolution

2.31

be for either early maturity or late maturity. Thus in directional selection only individuals representing one extreme are selected over generations. The mean of the next generation population is shifted in the direction of selection pressure applied but the range may be somewhat contracted though the reduction in variance due to selection is very small. In the natural population, the traits such as the viability and fertility are under directional selection through the changes in environmental condition or heterogenous environments. Directional selection tends to produce unidirectional dominance and duplicate type of interaction and favour coupling type of linkage With duplicate interaction there is reduction in the apparent additive (DR) and dominace (HR) components and this assuming other things being equal, the genetical contribution, of the variance of character in population would be expected to be lower and consequently the heritability h2 to be lower. Thus the fitess characters should have lower heritabilities than non-fitness characters which experience a pre-dominance of stabilizing selection.

2.12.3  Disruptive Selection In this type of selection the next generation population is formed by individuals, selected from more than one class as shown in Figure 2.3. In case of natural population when selection favours more than one phenotypic optimum (and different genotypes) and discriminiates against intermediate, it is called disruptive selection. The consequences of disruptive selection (Mather, 1955) are (i) increase of genetic and/or developmental variabnility followed by an increase of phenotypic variability and the appearance of bimodal or multimodal distribution of the selected trait while the mean value of the selected character remains unchanged, (ii) breakage of linkage or maintenance of linkage disequilibrium (favouring coupling type of linkage), (iii) establishment of polymorphisms, some of which are very similar in genetic principle to sex dimorphism and mimicry polymorphism in possessing switching super genes and modifing (enhancing) genetic background, (iv) divergence and reproductive isolation. Disruptive selection can produce and maintain divergence between two populations between which there is a very high rate of gene flow and it can also split a population into two between which there is considerable reproductive isolation (v) correlated response to selection and (vi) breakdown of self incompatibility. In practical plant breeding programme, disruptive selection can be used for breaking of tight linkage, for correlated response to selection, for release of latent genetic variability and for transfer of polyploidy from wild type to cultivated plants. The development of wild, intermediate and cultivated populations with gene flow between them ensures the production and increase of the very large amount of variability needed for the development of a cultivated crop. Differents species adjust to the variation in environments in different ways: (i) Some become highly specialized, restricted in range to a uniform and stabilized area and (ii) some have incorporated genotypes with wide reaction norms—genotypic and phenotypic

2.32

Crop Evolution and Genetic Resources

flexibility. Individuals adjust developmentally and physiologically to changes in their environments that may occur at various times. When a random mating population is raised in constrasting environments because of the spatial variation among the individuals of the population the different individuals will be subjected to different selection pressures and thus a population may show two or more optima (i.e. genotypes having different optimal phenotypes in different environments). When two optima coexist their relative frequencies may be critical to the function of each. Genetics but some time environment can also play a role in few systems of this nature. In other case, we can have a function dependencies between the two optima. When the optima alternate in time, a common genotype may characterize a population over several generations but produce distinct phenotypes under different environmental conditions-a case of seasonal polymorphism (Mather, 1973). Disruptive selection can be of two types: (i) D+ selection (divergent direction selection) selection and (ii) D – selection. In D+ selection, individuals with either increasing alleles for a trait mate (High × High) or decreasing alleles mate (Low × Low), and there is no gene flow between these two groups of population. This can be due to distance (geographical isolation) or the barrier. This type of disruptive selection will lead to represent a model of allopatric speciation. Within these two groups of population there will be increase in additive genetic variance but decrease in environmental and G × E interaction. In case of D– selection, individuals having increasing and decreasing alleles mate which then leads to genetical polymorphism and this population will not show only increase in additive genetic but also in environmental and genotype × environmental interaction variance. When the population without geographical isolation are in two different habitat or niche, making different selection pressures, the genetical divergence will be produced provided that (i) the density dependent factor regulating the population size operates separately in the two niche and (ii) the selection differentials are large (at least 30%). This is a model of sympatric speciation. Geneticists differ in views on whether divergence among subpopulations can lead to reproductive isolation in the face of gene exchange among groups, and thus evolution of a new species. Only very strong distruptive selection forces can lead to such situation. Whether that intensity of selection occurs in nature in not known. Thoday and Co-workers, working with Drosophila, showed that (i) polymorphism could be established in a population under disruptive selection even with high gene flow between diverging groups, (ii) the divergent groups could be maintained distinct under high gene flow with negative assortative mating and (iii) the reproduction isolation occurred between the divergent groups in spite of full opportunity for random mating.

References Allard, R.W. 1988. Genetic change associated with the evolution of adaptedness in cultivatied plants and their wild progenies. J. Herd., 79: 225-238. Allard, R.W. and Habnsche, P.E 1965. Population and biometrical genetics on plant breeding. In Geneties.

Forces in Evolution

2.33

Today, Vol. 3, Proc, XI th Int. Congo Genetics, The Hague, The Netherland, 1963. Geets, S.I. (ed). Pergamon proess, Oxford, pp, 665. Barton, N.N. and Charlesworth, 8. 1984. Genetic revolution, Founder effects and speciation. Ann. Rev. Ecol. Syst. 15: 133-164. Bradshaw, A.D. 1984. The importance of evolution-any ideas in ecology, Sharrock B. (ed.), Blakckwell Sci., Publ., Oxford. Breese, E.L. 1960. the genetic assessment of breeding material. In: VIIIth Int. Grassland Cong., pp. 45-49. Breese, E.L. 1983. Exploitaton of genetic resources through plant breeding Lolium species. In: Proc. Symp. on Genetic Resources of Forage Plants. Bray, R.A. and Mclvor, J.G. (eds.). CISRO, Melobourne, pp.275-288. Crow, J.F. 1986. Basic concepts in population, quantitative and evolutionary genetics, W.H. Freeman and Company New York. Crow, J.F. and kimura, M.1970. An Introduction to Population Genetics Theory. Harper and Row, New York. Falconer, D.S. 1989. Introduction to Quantitative Genetics. Longman, Burnt Mill. Fisher, R.A. 1930. The Gentical Theory of Natural Selection, Clarendin Press, Oxford. Fisher, R.A. 1949. The Theoryof inbreeding. Oliver and Boyd, Edinburgh. Hardy, G.H. 1908. Mendelian proportions in mixed population. Science 28: 49-50 (Reprinted in the collections of Gabriel and Fogel and Peters). Hayward, M.D. 1985. Adaptation, Differentiation and population Structure in Lolium Perenne. In: Genetic Differentiation and Dispersal in Plants. NATO ASI Series, G. Vol. 5. Jacquard, P. and Geims, G. (eds.) Springer-Verlag, Berlin, pp. 83-93. Hayward, M.D. 1990. Genetic strategy and future prospects for breeding cross pollinated species. Norwegian Agricultural Research, Supplement. 9: 77-84. Hayward, M.D. and Breese, E.L. 19 68. Genetic organisation of natural population of Lolium perenne. III Productivity. Heredity, 23: 357-368. Hayward, M.D. and Breese, E.L. 1993. Population structure and variability. In: Plant Breeding. Hayward, M.D. Bosemark, N.O. and Romagosa, I (eds.). Chapman and Hall, London. pp. 16-29. Kimura, M. 1970. The length of time required for a selectively neutral mutant to reach fixation through random frequency drift in a finite population. Genet. Res., Cambridge, 15: 131133. Lewontin. R.C 1965. Discussion of paper by Dr. Howard. In: The Genetics of colonizing species. ed. H.G. Baker; G.L. Stebbins. of colonizing species. ed. H.G. Baker; G.L. stebbins. p. 481, New York Academic. Li, C.C. 1955. Population Genetics. University of Chicago Press. Chaps. 1-10. Mather, K. 1953. The genetical structure of populations. Symp. Soc. Exp. Bio., 1.7: 66-95. Mather, K. 1973. Genetical structure of Populations, Chapman and Hall, London. Mayr, E. 1954. Change of genetic environment and evolution. In: Evolution as a Proess. ed. J.S. Huxley, A.C. Hardy, E.B. ford. pp.156-180. Allen and Unwin, London. Wilson, E.O. and Bossert, W.H. 1971. A Primer of Population Biology. Sinauer Associates. Inc. Publishers, Sunderland, M.A. Wright, S. 1921. Systems of mating. Genetics, 6: 111-178.

2.34

Crop Evolution and Genetic Resources

right, S. 1931. Evolution in Mendelian Populations, Genetic, 16: 97-159. W Wright, S. 1940. Breeding structure of population in relation to speciation. Amer. Nat., 74: 232248. Weinberg, W. 1908. Uben Den Nachweis der Vererbung bein Memschen.

Genetic Resources:

C H A P T E R

Collection

and Conservation

3

The improvement and sustenance of a cultivated crop species requires variability. Within a crop species there may be millions of different genotypes. This can be visualized by looking at the changes in the nucleotides as a result of base substitution, rearrangements, permutation through addition and deletion, that is, the DNA undergoes mutation, recombination, selection and interaction with the environment. The structural changes consist of deletion and insertion of one or more nucleotides as well as transposition and inversion of larger DNA segment. Then there may be genomic changes i.e. changes in the level of ploidy. The gene recombination led to may genetically different plants adapted to specific area, soil type, climate. The genetic resources which will represent the total variability within a crop species include (i) land races or primitive cultivars which were in cultivation before the introduction of improved cultivars, (ii) weed races, (iii) related wild species, (iv) cultivars currently under commercial cultivation, (v) obsolete commercial cultivars and (vi) induced or natural mutants. Collection and maintenance of germplasm is essential as it will provide genetic diversity within a crop which is essential to reduce its genetic vulnerability. The genetic diversity is being destroyed by the destruction of natural habitat by man. Also, global warming which is due to increased concentration of CO2, water vapour, chlorofluorocarbons (CFC) from refrigeration unit and methane from rice field is predicted to be greatest at higher latitude. The concentration of CO2 which stores heat energy has increased which has resulted in holes in the ozone layer which stops UV rays from coming to earth and thus the earth surface has been warmed up and this effect is called the green house effect. Increased CO2 in atmosphere will benefit C3 plants but it will not be as beneficial to C4 plants. Some crops may even be wiped out. Thus, global warming will result in loss of biological diversity. The cropping pattern will change as a result of change in rainfall. Further changes in practices of raising crops have led to the replacement of many varieties by modern high yielding ones with restricted genetic diversity. Thus it is essential that the genetic resources of cultivated plants are

3.2

Crop Evolution and Genetic Resources

collected, evaluated, conserved and made available for use by plant breeders. The varietal improvement programme depends on variability and so long as we have desired variants with us we can use it immediately to our benefit.

3.1  COLLECTION OF GERMPLASM The genetic resources comprise population of genotypes collected from different places. In terms of alleles, the genetic resources for a crop species comprise all alleles at a locus at all loci. We should not collect and maintain all the genotypes as many of which may be just duplicate. Thus we will have to ensure that there is a minimum of repetitiveness of genotypes (or genes) in the collection and during conservation, we should mainly be interested in preserving at least one copy of each of the different alleles in the target area and thus the knowledge of average number of alleles per locus provides the measure of the genetic diversity for the purpose of exploration and conservation. Further our aim should be to preserve the maximum amount of useful genetic variability while keeping the total number of samples within an acceptable limit. Thus sampling comes into picture at the level of exploration and conservation. We can have a sample of genotypes or populations which can represent the total variability present in the whole of the germplasm. In other worlds, genetic diversity could be represented by a smaller number of carefully chosen lines. Thus we will have to adopt a sampling procedure which preserves maximum level of genetic diversity. For this we have to know how the genetic variation is distributed throughout a species. In other words, we should know the genetic structure of a species. As we have seen the genetic structure of a population can occur on two basic axes, (i) geographic and (ii) genomic. The geographic pattern (population differentiation) is affected by founder effect, migration, breeding system, diversifying selection and population size whereas the genomic association (linkage disequilibrium) is affected by linkage, mutation system, breeding system, epistatic selection and population size (Brown 1992).

3.2  SAMPLING STRATEGY When we are collecting sample of plants, we are infact, collecting sample of alleles. Alleles can be neutral, deleterious or favourable. The distribution of these three types of alleles will differ in the population. Alleles can be classified as common allele when its frequency is greater than 0.5 and rare when its frequency is less than 0.5. Further, common or rare allele can be classified as widespread or local depending upon its distributions as shown below: Frequency Distribution Common Widespread Local Rar Widespread Local

Genetic Resources: Collection and Conservation

3.3

Thus there are in all four categories of allele (Marshall and Broun, 1975), namely, common and widespread (CW), common and local (CL), rare and widespread (RW) and rare and local (RL). If allele belongs to CW class, it does not require any sample strategy. The CW class of allele represents adaptive variants and CL alleles are of great importance as regards sampling strategy. A collector is more interested in sampling these alleles which are occurring locally but have frequency greater than 0.5. They constitute a significant part of most species’ genetic variation. Thus the objective should be to collect and conserve at least one copy of allele occurring with a frequency greater than 0.5 in the target population. In case of rare but widespread alleles, sampling of alleles depends on the total number of plants taken from the target population. The sample size will depend on the frequency of alleles. A higher sample size will be required to sample rare deleterious recessive alleles. Also, in case of highly variable quantitative traits or highly polymorphic loci, a higher sample size will be required. However, a low sample size is required to sample alleles at intermediate gene frequency and for alleles determining qualitative traits. In small population most alleles will be either common or rare but as the population size increases, it will contain a greater portion of alleles at intermediate gene frequencies (0.5 to 0.3). If the population size is very large, it will have virtually infinite number of alleles occurring at very low frequency. If the distribution of alleles among and within population is assumed random then the amount of genetic variation captured by the sample depends wholly on the sample size (the number of plants collected). If there is little variation within a population and there is higher variation among populations then one should keep the sample size small for sampling within a population but sample all the populations. On the other hand, if there is higher within variation in a population then the sample size will increase. The general strategy would be to sample as many populations as possible rather than taking large sample from a population within the target area. The factors influencing the sampling are (i) population factors—the size of interbreeding units which is a function of number and density of plants, mating system and level of pollen and seed dispersal and (ii) the ecological factors such as degree of heterogeneity of soil types, slopes, moisture regime and the associated flora. Thus sampling size in predominantly self-fertilizing crops will be different than that of in cross-fertilizing or vegetatively propagated crops. Also, sampling size will depend on whether a species is cultivated or wild or weedy. Populations of most wild plants are patchily distributed through a habitat and occur as small populations.

3.3  ESTIMATION OF NUMBER OF ALLELES PER LOCUS Following Kimura and Crow (1970), the expected number of neutral alleles (ne) with allelic frequencies lying between p and q (0 < p < q < 1) at equilibrium in a population of effective population size Ne is estimated as:

Crop Evolution and Genetic Resources

3.4 q

q

p

p

Ne = Ú​  ​ ​ ​ f(x) dx = q ​Ú  ​ ​ ​ (1 – x)q – 1 dx where f(x) dx is the expected number of the neutral alleles with frequencies lying between x and x + dx (0 < x < 1) and q = 4 Ne m, where m is the mutation rate. Further, Ewen (1972) showed that the expected number of alleles per locus, E(k) in a random sample of n gametes is estimated as:

q _____ q q __ ________ E(k) = ​   ​ + ​       ​ + ... + ​       ​ q q+1 q+n–1

where q = 4 Ne m as before and the sampling variance of k, Var (k) becomes,

q2 ________ q2 q2 __ ___________ Var (k) = E(k) – ​  2 ​ + ​    2   ​+ ... + ​       ​ q (q + 1) (q + n – 1)2

3.4  SAMPLING THEORY OF ALLELES Considering two alleles A1 and A2 occurring with frequencies p1 and p2, respectively in a population, the probability that at least one copy of each allele occurs in sample of n gametes is

p (A1¢, A2¢ ) = 1 – (1 – p1)n – (1 – p2)n + (1 – p1 p2)n

From this it can be shown that with p = 0.95 and p2 = 0.05, a sample of 51 gametes will contain at least a copy of each allele with 95% certainty. This probability expression can be extended to cover more than 2 alleles but with the increase in the number of alleles the expression becomes cumbersome. Using this expression with different values of p1 and p2, the values of n containing at least a copy of each allele can be calculated with 95% certainty. It has been found that even in case of 20 alleles with frequency of 0.95, the sample size of gametes comes to about 120 from which it can be safely concluded that a random sample of 50–100 individuals (individual is the unit of selection and not the allele) would be adequate under most circumstances. For estimating optimum sample size, the estimates of the average number of alleles per locus or within and between family variances for 5 to 10 populations are required. A random sample of 50–100 plants would be more than adequate to sample common alleles. In case of wild species, sample size of 50 plants will be appropriate. In case of vegetatively propagated crops, 10 individuals per site constitute an adequate sample. A sample size of 15–25 individuals are adequate for rejuvenation of collected population (Brown and Marshall 1983 and Yonezawa, 1985).

3.5  SAMPLING OF SITES Sampling sites more or less distributed over the target area will capture the amount of variability associated with the broad geographical (macro-geographical), edaphic and climatic factors which include altitudes, latitudes, longitudes, direction and degree of

Genetic Resources: Collection and Conservation

3.5

slopes, temperature, rainfall, soil and vegetation. Further within a locality, the selected sites should be as diverse as possible in order to sample the variation arising out of the microgeographical variation (the local topography, soil, vegetation). Within a site sampling could be random or stratified. Clustered sampling (taking a number of sample form population at a site) in case of wild or weedy species has been suggested on the ground that distinct populations amongst which there is no gene flow can exist at a particular site. Such species show the genetic differentiation over distances as small as a few meters (Bradshaw, 1975).

3.6  POINTS TO BE CONSIDERED DURING COLLECTION OF GERMPLASM The following points are worth considering during the collection of germplasm: 1. One must collect germplasm from areas of species distribution. We must see where the significant gene pool of a species occurs. In other words, we must point out the target area of collection on the basis of centre of origin, centre of diversity and the area of distribution of the crop. We should concentrate collection in areas within the primary and secondary centers of diversity of the species in question. These centers are generally regarded as the most likely areas in which any particular trait may have arisen. A particular region can be given priority for collection on the basis of two criteria: (i) whether one is interested in collection of interspecies diversity, (ii) whether one is interested in collection of intraspecies diversity. Area of interspecies diversity will be different than area of intraspecies diversity. Collection should be made from diverse sites both geographically and ecologically. 2. One must put emphasis on the number of sites at the expenses of the number of individuals collected per site within the target area. As the collector’s aim would be collection of maximum amount of genetically useful variability in the target species, the following points should be considered in order to reduce the chance of variability not being represented in the sample: (i) Number of plants sampled per site. (ii) The total number of sites to sample. (iii) The distribution of sampling sites within each area.

3.7  COLLECTION OF GENES FOR RESISTANCE TO DISEASES As host-pathogen association has been naturally co-evolved, so collection for gene for resistance should be made in areas where a crop is being grown. Correlations between resistance pattern and gross climatic factors are usually weak because of the problems associated with sampling procedure. There is uneven distribution of resistance in host. Pattern of disease resistance within and between host populations is different. Parameters such as life span of individual (annual or perennial), the ecological niche

3.6

Crop Evolution and Genetic Resources

(colonizers vs. non-colonizers) and breeding system (inbreeding vs. outbreeding) determining the genetic structure of population will also determine the pattern of disease resistance. So a single approach to the sampling of wild species will not maximise the collection of gene for disease resistance for all host-pathogen associations. As relatively few pathogens have precisely the same environmental optima and so the collection strategies designed specifically around the optimum environmental conditions of one pathogen may/will fail to cover other potentially important pathogens. But then one should concentrate on collected efforts in areas where the environment is generally favourable for growth and development of the appropriate pathogens (Harlan, 1977), area which is considered as hot spot for that disease.

3.8  COLLECTION OF RARE ALLELES Collection of extremely rare and deleterious alleles may not be of breeder’s immediate interest but have to be collected and conserved as they might be of use in future as is happening in case of different cytoplasmic and genetic sources of male sterility alleles.

3.9  EVALUATION OF GERMPLASM The germplasm collected should be properly evaluated. The characters to be observed can be anatomical, morphological, chemical, biochemical or physiological characters. One should also study the sources of cytoplasm and other traits such as mitochondria, chloroplast and polypeptides, resistance to biotic streses (diseases and insects) and abiotic stresses (drought, flooding, heat alkalinity, salinity, toxic elements). One of the objectives would be to measure the amount of variability. The variation at the level of genotype i.e. the variation in nucleotide sequence is called genetic variation. The amount of variation at DNA level is very much greater than at the polyploid level. The variation at the level of phenotype is called phenotypic variation. We can then measure the diversity—genetic diversity and phenotypic diversity.

3.10  ESTIMATION OF GENETIC DIVERSITY The measures of genetic diversity are: 1. Percentage of polymorphic loci. 2. Average heterozygosity per locus. 3. Average number of alleles per locus. 4. Nei’s index of gene diversity. 5. Shannon-Weaver information index. 6. Wright’s fixation index. Of these, 1, 3, 4 and 5 provide the statistics which are indices of genetic diversity and 2 and 4 provide measure of the distribution of genotypic frequencies in the population. All these statistics can be estimated from the isozyme data.

Genetic Resources: Collection and Conservation

3.7

Allelic diversity or the allelic heterogeneity is measured using allele frequency. The larger the number of alleles and the closer they are to equal frequency, the greater is the allelic diversity. The observed frequency at each locus is used to calculate the expected frequency of heterozygotes using H.W. equilibrium. The problem of using such estimate as a measure of genetic diversity is that heterozyosity and polymorphism are quite inadequate descriptors of variation because they are heterogeneous. The observation of sequential gel electrophoresis, calibration experiments and of DNA sequency have revealed two types of heterozygosity. At amino acid level, there is a class of major polymorphism of two or more alleles in roughly equally high frequency and there exists a vast array of minor polymorphism producing a long list of rare alleles which together constitute a significant heterozygote. Besides these two classes there is presence of some loci which are totally monomorphic lacking both kinds of heterozygosity. Thus any calculation of heterozygosity which confounds the two quite different phenomena confounds the different causes of variation. The amount of heterozygosity per nucleotide is greater for DNA as a whole than for protein coding region. Intervening sequences, exons and pseudogenes have the largest amount of heterozygosity. The less significant a nucleotide difference is the more likely it is to be heterozygous. Thus, neither the average heterozygosity nor the polymorphic loci will by itself yield complete picture of the variation in population. The number of alleles in the total population is a direct measure of the genetic polymorphism whereas the amount of differentiation among sub-populations is measured by the variance of allele frequency at a diallelic locus. The genetic diversity measured by calculating the amount of actual or potential heterozygosity is as follows: Thus, total genetic diversity of the polymorphic loci (HT) can be written as: HT = HS + DST where HS is the mean genetic diversity within population at polymorphic loci. A locus is polymorphic if the frequency of the most frequent allele is less than 99%, sometimes > 95%. DST is the genetic diversity among populations. The proportion of total genetic diversity found among populations is estimated as DST  H S – HT ________ _____ GST = ​   ​ = ​        ​ HT HT The GST is thus a measure of the extent of the differentiation (Nei, 1975). Thus the total genetic diversity within a species can be partitioned into between races and within races. HS measures the mean percentage of loci heterozygous per individual. It is a function of the number and evenness of allele frequency within populations. It represents the polymorphic index or expected heterozygosity. The difference in HT primarily results from variation in the proportion of polymorphic loci. The actual or potential heterozygosity is calculated as: H = 1 – S​ p​i2​  ​

Crop Evolution and Genetic Resources

3.8

It measures the genetic diversity whether or not the population is random mating. Here H is the probability that the two randomly chosen alleles are different and thus is a measure of actual heterozygosity. It is a function of gene frequency and the number of alleles in the population. The HS and HT are now estimated as:

HS = (1 – ​S  ​ ​ ​  pi s2)/n

and

HT = 1 – ​S   ​ ​​​​  p​​ i2​  ​

i

_

i

_

where n is the number of sub-populations, p​ ​ i  is the average frequency of allele Ai in the entire population and pi is the frequency of allele Ai in the subpopulation.

3.10.1  Shannon-Weaver Information Index Diversity can be expressed in terms of not only the number of species but also the relative abundance of each. S.W. measure of diversity is thus a function of gene-frequencies (allelic eveness) and number of alleles in the population (allele richness). The diversity index is expressed as:

s

HS = S ​   ​ ​​ pi log 2 pi i = 1

where S is the number of species, HS is the amount of diversity in a group of S species, pi is the relative abundance of the ith species measured from 0 to 1.0 and log pi is the logarithm of pi, it can be to the base 2 or 10. The value of HS will be greatest if the species are all equally abundant. This measure of diversity bas no upper limit i.e. if more and more species are included in the study, HS will tend to increase. Also, if different independent classifications are used, the sum total of HS obtained using each classification provides a measure of the total amount of diversity. The diversity index can be estimated using the qualitative as well as the quantitative traits. The quantitative trait is analysed as qualitative trait and it is classified into 11 or more point scale. The diversity index then takes the form as:

n

H 1 = S ​   ​ ​ ​pi log 2 pi t =1

where n is the number of phenotypic classes for a trait and pi is the proportion of entries in the ith class. The variance of diversity index, VH 1, is calculated as: Spi log 22 pi – (Spi log 2 pi)2 n_____ –1 _________________________ VH 1 = ​           ​ + ​   ​  N 2N2 where N is the sample size. The test of significance is done using t test. Determining representative variation within and among collection of genotypes is key to the success of world gene bank. The Shannon-Weaver information index (H1) provides

Genetic Resources: Collection and Conservation

3.9

a measure of phenotypic diversity based on frequency data. It can be used to evaluate geographical patterns of diversity and to determine specifically the relative contributions of various countries to the germplasm source of an excising world collection. The estimate of diversity (H 1) ranges from 0 to 1.0. 0 indicates no variation whereas 1 shows maximum variation. Figure 3.1 shows the relationship between the genetic distance and the geographical distance.

Fig. 3.1  Association between geographical and genetic diversity

3.10.2 Estimates of the Degree of Similarity or Differences Between Two Populations Nei’s (1973) index provides the estimate of degree of similarity or difference between two populations. The index is expressed as:

JXY ______ IL = ​ _______   ​  ​÷J  xy ◊ JY   ​

where Jxy = Sxi yi , where xi is the frequency of ith allele in population X and yi is its frequency in population Y ◊ Jx = S​ x​i2​  ​which is the sum of squared allele frequency in population X and Jy = S ​y​i2​  ​is the sum of squared allele frequency in population Y. The genetic distance D based on the identity of genes between the two populations is expressed as: D = – In I where I is the normalized identity of genes between two populations. It measures the accumulated allele differences per locus. If the rate of gene substitution per year is constant, it is linearly related to the divergence time between populations under sexual isolation. It is related to the geographical distance or area in some migration models (Nei, 1972). Nei’s genetic distance (D) is said to measure a biological prosperity—the mean number of electrophoreti-cally detectable substitution per locus that have accumulated since the two populations diverged from the common ancestor. The coefficient can be corrected for error due to sampling size but it is non-metric. Considering 3 species A, B and C, the distance between A and C (A – C) must be A–C£A–B+B–C

Crop Evolution and Genetic Resources

3.10

However, it does not satisfy the triangular inequality. The branch length may be negative which is an undesirable and biologically unpredictable result for a coefficient used in restructuring phylogenes. Nei (1972) noted that ‘I ’ could also be computed as the arithmetic mean of Ij (I considering j th locus) over loci but the genetic interpretation of this statistic was less straight forward. Hillis (1984) has argued that the mean locus identity defined as

I* = S Ij|L

where L is the number of loci and its corresponding genetic distance D* = – log eI* may be more appropriate measures of diversity and distance than I and D, as is usually observed.

3.11  CONSERVATION OF GENOTYPE Where there are serious problems of diseases and insects in raising of the crops and where there is a need of keeping seed/or vegetative material in disease free condition in order to make it available to breeders world over or when it is required to get a rapid multiplication of the stored material in short time one can go for in vitro methods of germ plasm storage for long periods. In case of vegetatively propagated crops. in vitro methods could be extremely valuable since large number of clones can be stored in a relatively small space in a disease free condition with very high speed of multiplication and with minimum need of maintenance as annual vegetatively propagated crop plants and the perennial woody species take lot of space and are vulnerable to disease. The periods of storage can be made longer by routine subcultures. It is the cheapest and safest method which requires no expensive equipment and thus should facilitate conservation of valuable genotypes of crops plants. The minimal growth rate is required for increasing the longevity of cultures. To achieve this either specific growth inhibitors (e.g. abscissic acid) or physical conditions which have more general effect on the metabolic rates (e.g. temperature, osmotic condition, gaseous condition, nutrients availability) can be utilized (Henshaw, 1979). The problems associated with in vitro methods are problems of genetic instability and loss of morphogenetic potential. The problem here is of keeping the tissue alive for longer periods in a non-dividing state and thus we will have to ensure minimal growth conditions and suspending metabolic activity. The adventitious callus culture is not fit for long term storage because of the lack of genetic stability and frequency loss of regeneration capacity since callus cultures are generally initiated from non-meristematic tissue which are polysomatic and thus are not representative of the genetic constitution of the parental genotype. However, callus culture can be used for long term storage in those species in which long term genetic stability and the retention of morphogenetic potential has been satisfactorily demonstrated. Shoot tip (apical meristem) culture can be used for long term germplasm storage and it can be subcultured after 1 or 2 or 3 years. Shoot tip culture from different genotypes of a species could differ in medium

Genetic Resources: Collection and Conservation

3.11

(organic nutrients especially nitrogenous compounds, hormones requirements) and so it is important to work out a routine by which these variations can be readily identified.

Freeze preservation Liquid nitrogen freeze storage at – 196°C can be used for long term storage of germplasm. It can be used for long term storage of meristem type of culture in completely nondividing state but not applicable to callus or suspension culture in which there is possibility of genetic change in the cultures during the growth phases before and after storage (Bajaj and Reinert, 1977). Vegetative material can be stored for indefinitely in liquid nitrogen at – 196°C. In liquid nitrogen, all physical and chemical processes of the cell cease. While thinking of going for freeze preservation one should (i) choose the suitable cell for freezing, (ii) carefully control the cooling and thawing condition, (iii) use the cryoprotectant against freezing damage. One should choose specific cells having low water content. Percent survival is related to the cooling rate. One will have to maintain the thermodynamic equilibrium. Glycerol and dimethyl sulphoxide are used which have got colligative effect. The cell culture needs a show freezing process where as organized culture requires a very fast freezing procedure. In case of auxillary bud meristem, one will have to choose the right physiological stage for freezing (liquid nitrogen) preservation. The limiting factor with in vitro conservation is the damage that occurs as a result of ionizing radiation which might become significant after decades (Whiuingham et. al., 1977).

Genomic or gene libraries In case of species where there is not a convenient long term storage potential, we can go for DNA storage. The genome of all the plant species of the world can virtually be stored in a small room. When the genomic DNA is partially digested with restriction enzymes, it produces a population DNA fragments. These DNA segments can be either stored in-definetely as purified lyophilised DNA in a test tube or can be incorporated into plasmid or bactriophage molecule which is capable of multiplying in bacteria and can be stored in a test tube. We know that the eukaryotic genes in general, are interrupted i.e., the coding sequences, the exons, are interspersed with non-coding sequences, the introns. The introns although are transcribed in the initial primary transcript but are then spliced out during the production of functional mRNA. Thus from the whole genome intronless genes can be derived. The isolated mRNAs can be enzymatically copied into DNA sequence called cDNA which can be inserted into appropriate vectors and thus stored. The cDNA libraries can serve various functions. They can be employed to (i) identify genes which are abundantly expressed at the time of RNA isolation, (ii) develop gene specific probes for identification of restriction fragment length polymorphism (RFLPs), (iii) identify clones encoding gene products for which antisera are available and (iv) express gene-coding sequences giving heterologous transcription, promotion and termination signals. cDNA is an in vitro prepared DNA copy of polydenylated or mRNA.

3.12

Crop Evolution and Genetic Resources

Both cDNA and genome DNA libraries can be employed in screening of differentially expressed clones. However as cDNA clones have the advantages of encoding only a single gene while genomic clones may harbor many genes whose expression could be both up and down modulated or constitutive and such clones might be lost in a differential screen.

3.12  PHENOTYPIC DIVERSITY It measures the portion of genetic diversity which is expressed phenotypically. So it varies with the character under study and the genetic background and the environment in which it is measured. The measures of genetic diversity based on variance of quantitative traits may be unreliable indicators of diversity in a population at the level of individual gene. But diversity at the molecular level (isozymes, RFLPs) may be a reasonable estimate of phenotypic diversity. The degree of differentiation is related to several biological attributes such as breeding system, mode of population and seed dispersal, life history, geographical range, successionl stages, etc. The outbreeding populations are much less differentiated whereas the selfers or apomicts are strongly differentiated. Populations of outbreeders contain different alleles especially the rare alleles which contribute little to the diversity. Inbreeders should have greater interpopulations diversity and less intrapopulation diversity than the comparable outbreeders. Further, inbreeders are more prone to show an even distribution of their genetic diversity among populations and this makes their optimum sampling more difficult and any evidence of the geographic pattern of this diversity levels would greatly improve sampling efficiency but geographical and / or environmental factors rarely explain more than 50% variation.

3.13  CONSERVATION OF GERMPLASM Conservation of germplasm can be in situ or ex situ.

3.13.1  In Situ Conservation It is a method of preserving germplasm in their natural habitat. In situ conservation will allow natural evolution to take place. In situ conservation includes different types of plants ranging from wild species related to crop plants to forest and pasture species. Here we will have to study the problems of survival or extinction of population, adaptive evolution, maintenance of variation in population, and of species abundance within communities (competition). Genetic variation plays a role in population regulation. The genotypic fitness is likely to be frequency and density dependent. The population fitness evolving under selection may in turn relate to r, the intrinsic rate of increase and k, the carrying capacity of the environment. We know the role of genetic variation in evolutionary change and we also know that the variation is reduced by directional selection, stabilizing selection,

Genetic Resources: Collection and Conservation

3.13

inbreeding and genetic drift whereas it can be maintained by gene flow, disruptive selection, outbreeding, mutation, linkage and heterozygous advantage. Thus, our aim should be to know how much variation is required for avoiding extinction.

3.13.2 The r and k Selection As parameters r and k in particular environment are determined by genetic structure of the population they are subject to evolution. A species will succeed best in a short lived unpredictable habitat if it (i) has the ability to adapt quickly to this environment, (ii) it reproduces fast i.e. r is higher in comparison to other species and (iii) it has higher dispersability. In contrast, a species in a long lived stable environment as in case of forest trees will flourish if it has higher competitive ability in comparison to other species or population and so it is able to tap more solar energy, more nutrients and water form soil and thus best competitor will be taller and have well developed root system. The favoured species will thus maintain the densest population at equilibrium and will cover the space while the less competitive genotypes will get eliminated. If the different species or populations are at the saturation level k in a long lived stable environment, k selection starts operating. But when the highly competitive species come to equilibrium and the environment cannot sustain more number of individuals the r of the favoured genotype itself is reduced. Large k may result from lowered mortality and plastic response to density. In stable environment, there is no use to increase r but in unstable environment, increase in r is required for survival. The rate of colonization depends on the relative rates of birth b and death d, dispensability and the evolutionary changes in these parameters. The b/d ratio vs. (b – d)/d and the rate of carrying capacity determine the relative rates of extinction. In most cases, the population size is regulated through density dependent effects. The factors having such effects are inter- and intra-specific competition and the environmental factors such as nutrients, moisture, insects, pathogens, etc. and thus keep the population size toward k. In most cases these factors lower the birth rate and increase the death rate of the particular factor or combination of factors involved in the regulation of population size varies from species to species. The populations where growth is not under control of density dependent effects are destined for relatively early extinction. For a constant population size (i.e. when r = 0), the time of extinction T depends on b b __ __ carrying capacity of the environment k and ​   ​ ratio such that a small increase in ​   ​ ratio d d raises the value of T considerably. Hence for small populations to persist they require a high k with high positive r (b > d) or b/d = 0.1. The extinction of a species can be due to (i) failure to adopt to changing environment and (ii) over specialization with the result that r(= b – d) becomes negative. The adaptive failure can be due to (i) lack of genetic variation to cope with the changing environment, (ii) time response delay such as due to life historical factors and (iii) competition (replacement of one species by a newly evolved highly competitive species). The chances of extinction are high in species with fewer sub populations, lower dispersal rate, low Ne (effective population size) or higher variances in Ne, low genetic variation, long but simple life cycles and habitat specialization.

3.14

Crop Evolution and Genetic Resources

What is required for preserving germplasm in their natural habitat is the preservation of ecosystem, diversity of habitat and topography.

3.13.3  Ex Situ Conservation Raising germplasm in field year after year will continue to be the preferred method of conservation in case of crops (seed or vegetatively propagated crops) where there is cheap labour. The problems associated with this method of conservation of germplasm are: (i) Rare alleles are difficult to conserve than common alleles. (ii) Population under conservation may loose variability due to natural selection. The effect of natural selection can be minimized if plants are raised in optimum condition and the genetic contribution of different plants to the next generation is the same. (iii) Chance effect will lead to loss of variability. The effect of chance is minimized if the genetic contribution of different plants is made equal. (iv) In inbreeding species to make equal reproductive contribution one offspring from every parent plant is taken. Further, a minimum of 20 plants should be raised every generation. (v) In outbreeding species, the bi-parental mating with reciprocal crosses is made and two offspring from every seed parent is collected and bulked and at least 25 plants be raised every generation but if possible raise as many plants as possible and raise one offspring form every parent.

3.14  EFFECTIVE POPULATION SIZE The effective size of a population is an important aspect of germplasm preservation. As we are preserving a sample of the whole population, we would like to know the size of the samples required to preserve so that the genetic properties of the populations are not lost. The degree of maintenance of genetic properties of a population depends partly on the number, N, of seeds or individuals in the population but primarily on the number of individuals intercrossed in previous generation which reflects the effective population size, Ne. We have seen in Chapter 2 that 1 1 1 1 1 ___ ___ ___ ___ ​ ___  ​  = ​    ​ + ​    ​ + ​    ​ + ​    ​  Ne N1 N2 N3 N4 where N1, N2, N3, N4 are the effective population sizes in generation 1, 2, 3, 4, respectively. With N1 = 100, N2 = 100, N3 = 20 and N4 = 1000, the effective number of a corresponding population of constant size would be Ne = 56.3. What is worth considering here is to examine the effect of bottleneck in the third generation after growing a constant

Genetic Resources: Collection and Conservation

3.15

population size in the earlier two generations. If the population size in the 4th generation is increased to 10,000 the effective population size would come to 57.1 and thus the bottleneck cannot be overcome in just one generation by increasing the population size. This is a point worth keeping in mind when one is engaged in maintaining germplasm that one should keep the population size constant over generations during maintenance and if bottleneck occurs, this can only be overcome by growing larger sample size in one or more generation depending upon the extent or reduction in the population size in a generation. Assuming that out of t generations, a constant population size of N1 was raised over t – k – l generations and then followed a bottle neck for one generation with the population being reduced to N2 (N2 < N1) and hoping that original effective population size (N1) would be recovered in the next K generations by increasing the effective population size of N3 (N3 > N1), it can be shown that the recovery of loss in effective population size is possible only when (K + 1) N2 > N1 and that the required effective size in the last K generations must be (Hallauer and Miranda, 1980) N3 = (KN1N2)/[(K + 1)(N2 – N1)] If the objective is to recover the loss in just one generation after the bottleneck i.e. with k = 1, it is possible only when N2 > N1/2. This shows that one should be very careful about the size of the populations being maintained over generations as if the reduction in population size in a generation is very high, we will not be able to recover the population with the original genetic properties. In cross-fertilizing species, races and varieties are populations of individuals each with unique genotype and it requires about 200–250 individuals to maintain genetic characteristics and one can maintain this size by sib-pollination. But if a cross-fertilizing species can tolerate inbreeding, a sample size of 80 individuals can be adequate. The other ex situ conservation methods are seed storage, vegetative material storage through tissue culture, cryogenic preservation and DNA storage.

3.15  STORAGE OF SEED Seed can be stored in gene bank, the store house of germplasm. It is the safest and cheapest method of preserving germplasm. For many crop species, the genetic diversity can be conserved in the form of seeds which can be stored in a relatively small place for many years unlike conservation by field planting which requires lot of space, labour, time and where human error can lead to loss of genetic variability. At decreased moisture content and low temperature, true seed can be stored for over 100 years. At 20°C and 5% moisture, barley can be stored for over 70 years. Dry seed can be stored in liquid nitrogen for long term storage of germplasms. The problem here is of duplicate type which will increase the number of samples to be stored.

3.16

Crop Evolution and Genetic Resources

3.16  GENE BANK Collection of germ plasm at genetic resource centers can be divided into two groups: (i) Base collections, which are kept for long term storage and (ii) Active collections which are kept for mid term storage, regeneration, multiplication, distribution, evaluation and documentation. The core collection should be maintained by the centres in order to make readily available the useful variants to individual plant breeders. This core collection represents the genetic diversity. For all characters there are two extremes, low and high values. For example, for yield-high yielding and low yielding, maturity-early and late maturity, disease and pest resistance-resistance and susceptible, protein-low and high protein%, oil-low and high oil%, height-dwarf and tall, etc. The entries representing these extremes for different anatomical morphological, physiological, chemical and biochemical taints comprise a collection called ‘Core collection’.

References Bretting, P.K. and Widrlechner, M.P. 1995. Genetic markers and plant genetic resource management. In: Plant Breeding Reviews. Janick, J. (ed.), 13: 11–86. Brown, A.D.H. 1989. The case for core collections. In: The Use of plant Genetic Resources, Brown, A.D. H.; Marshall, D.R., Frankel, O.H. and Williams, J.T. (eds.). Cambridge University Press, Cambridge, pp. 136–156. Brown, W.L. 1983. Genetic diversity and genetic vulnerability-an appraisal. Eco. Bot., 37: 42–12. Burton, G.W. and Davies, W.E. 1984. Handling of germ plasm of cross pollinated forage. In: Holden, J.H.W. and Williams, J.T. (eds.). Crop genetic resources: Conservation and evaluation. Allen and Unwin, London, pp. 180–190. Frankel, O.H. and Brown, A.H.D. 1984. Current plant genetic Resources. A Critical Appraisal. In Genetics: New Frontiers, Proc. XV, International Congress of Genetics. Vol. IV. Chapra, V.L., Joshi, B.C., Sharma, R.P. and Bansal. H.C. (eds.). Frankel, O.H. and Hawkes, J.G. 1975. Crops Genetic Resources for Today and Tomorrow. Cambridge University Press, Cambridge. Hallauer, A.R. and Miranda. Fo, J.B. 1988. Quantitative Genetics in Maize Breeding. Iowa State Univ. Press, Ames, Iowa, USA. Harlan, J.R. 1976. Genetic resources in wild relatives of crops. Crop Sci., 16: 329–333. Harlan, J.R. 1977. Sources of genetic defense. Annals of the New York Academy of Sciences, 287: 347–356. Harlan, J.R. 1984. Evaluation of wild relatives of cropplants. In: Holden, J.H.W. and Williams, J.T. (eds.). Crop Genetic Resources: Conservation and evaluation. Allen and Unwin, London, pp. 212–222. Hawkes, J.G. 1980. Crop Genetic Resources. A field collection Manual. IBPGR, Rome. Hillis, D.M. 1984. Misuse and Modification of Nei’s genetic distance. Systematic Zoology, 33: 238–240.

Genetic Resources: Collection and Conservation

3.17

Hodgkin, T. 1991. The Core Collection Concept. In: Crop networks. Searching for new concepts for collaborative genetic resources management. EUCARPIA Symposium, Wageningen, 1990, IBPGR, Rome, pp. 43–48. Hoyt, E. 1988. Conservating the wild relatives, IBPGR/IUCN/WWF, Rome. Kimura, M. and Crow, J.F. 1964. The number of alleles that can be maintained in a finite population. Genetics, 49: 725–738. Marshall, D.R. and Brown, A.D.H. 1975. Optimum sampling strategies in genetic conservation. In Frankel, O.H. and J.G. Hawkes (eds.). Crop genetic resources for today and tomorrow. Pp. 53–80. Cambridge Univ. Press. Marshall, D.R. and Brown, A.D.H. 1983. Theory of forage plant collection. In: Genetic resources of Forage Plants. pp. l35–138. Mclver, J.G. and Bray, R.A. (eds.) CSIRO, Melbourne. Nei, M. 1972. Genetic distance between populations. Amer. Naturalist. 106: 283–292. Nei, M. 1973. Analysis of gene diversity in sub-divided population. Proc. Natl. Acad. Sci., USA. 70: 3321–3323. Nei, M. 1975. Molecular Population Genetics and Evalution. Amsterdam. North-Holland, American Elsevier. Plucknett, D.L., Smith, N.T.H., Williams, J.T. and Anishetty, N.M. 1983. Crop germplasm conservation and developing countries. Science, 220: 163–169. Sasson, A. and Costarini, V. (eds). 1989. Plant Biotechnologies for Developing countries. Technical centre for Agriculture and Rural Cooperation (CTA) and Food & Agriculture Organization of the United Nations (FAO), Wageningen. Withers, L.A. 1991a. In vitro collecting: concept and back ground, In: In vitro collection Techniques in the conservation of Plant Genetic Resources. IBPG–CATIE Training Manual, IBPGR, Rome, CATIE, Turrialba. Yonezawa, K. 1985. A definition of the optimal allocation of effort in conservation of plant genetic resources with application to sample size determination of field collection. Euphytica, 34: 345–354.

Polymorphism and Phylogenetic Inference

C H A P T E R

4

4.1  POLYMORPHISMS AND THEIR APPLICATIONS Measures of similarity and distances among nucleotides or amino acid sequences have been used to find related regions in long sequences, to test for homology, to assess phylogenetic and functional relationships and to estimate divergence in time between pairs of evolutionary related sequences (Sankoff et al., 1990). Different scoring systems have been introduced primarily for derivation of evolutionary trees. The evolutionary distance between proteins or nucleic acids can be inferred from differences between their sequences. Residues occupying equivalent positions are thought to share common ancestors / or to have equivalent biological roles. Alignment of sequences will provide the following types of information. Singleton polymorphism refers to any single base difference between otherwise completely monomorphic (i.e. identical) DNA sequences. A segregation site is one which is polymorphic. A sample of aligned sequences also contains sites which provide information about the genealogy or ancestral relationships among sequences. A polymorphic nucleotide site is said to be phylogenetically informative if at least one minority nucleotide is not a singleton. Such sites permit the sequences to be split into two groups, each containing two or more members in which members of each group are more similar to each other than they are to members of any other group. For example, site 2 in the Fig. 4.1 is phylogenetically informative because the (3, 2) configuration splits the sample into 3 with C and 2 with T at that site. This indicates that at an earlier time in evolutionary history the site may have been monomorphic for either C or T and a nucleotide substitution created a second lineage with the site occupied by the alternative nucleotide. This inference is justified as long as each type of nucleotide substitution at a site occurs only once and there is no reverse mutation which can restore the original nucleotide. Methods for constructing such trees are discussed on next page.

Crop Evolution and Genetic Resources

4.2 5

2

3

4

G C C

T

C G C

1

C

6

7

8

A G C C

C

C

T

A

C

T

G

T

9 10 11 . . . . . . . . . . T

C

T C C T C T C C C A T

Fig. 4.1  Showing phylogentically informative polymorphic site at 2 and phylogenetically noninformative sites at 4 and 8

4.2  PHYLOGENETIC INFERENCE Study of evolution can be made via phylogenetics. Phylogenetics is the science which deals with the evolutionary links between organisms. Phylogeny refers to the evolutionary history of a set of organisms. Sequence data can be used for drawing phylogenetic inferences. In other words, genome sequencing now makes it possible to monitor evolutionary changes on a time scale concomitant with the rate of such change (Drummond et al., 2003). Phylogeny refers to the description of biological relationships among objects and is usually expressed as a tree. Phylogeny of modern species refers to the origin of different species from a common ancestor (monophyletic). A mosssnophyletic group is one consisting of a common ancestor plus all (and only all) descendants of that common ancestor whereas polyphyletic group is one containing two or more common ancestors. A paraphyletic group comprises of a common ancestor but not all descendants of that common ancestor. Another possibility in the evolution of plants is reticulation the hybridization of two previously diverged taxa forming a new lineage. Our aim thus becomes to infer patterns of ancestry from the relationships among characters: the topology of the phylogenetic relationship (informally, the family tree). The molecular phylogeny infers evolutionary mechanisms and relationswhips of organisms by comparing sequences of the nucleic acids and proteins. It does with the genome what the traditional comparative biological approach has done with anatomical, morphological, biochemical and developmental features. The underlying principle is that the more divergent two sequences are from each other, the more distant in time it is since they shared a common ancestor. The monomeric subunit sequence and the three dimensional structures of individual nucleic acids and proteins can be used to analyze the evolutionary relationships. The molecular phylogeny based on gene sequences is consistent with that the classical phylogeny based on macroscopic structures (morphological traits). Although the organisms have diverged continuously at the level of gross anatomy but the molecular structures (the DNA sequences that encode proteins or the protein sequences) and mechanisms remained similar from the simplest to the most complex organisms. A number of methods have been developed for inferring ancestral relationship among a set of aligned sequences. They can be compared by the analysis of phylogenetic trees obtained either through computer simulations of the sequence evolution (Nei, 1996) or from real organisms when true phylogeny is known (Hills et al., 1994). In other words, phylogenetic relationships can be described as trees.

Polymorphism and Phylogenetic Inference

4.3

The correct evolutionary tree is a rooted tree which graphically shows the cladistic relationships existing among the operational taxonomic units (OTUs), i.e. contemporary sequences. Phylogeny is commonly represented in the form of a cladogram (or phylogenetic tree). A cladogram is simply a phylogenetic tree that describes the relatedness of objects being compared. In other words, cladogram (or phylogenetic tree is a branching diagram that conceptually represents the evolutionary pattern of descent. The lines of a cladogram are known as lineages or clades that denote the sequence of ancestraldescendant population through time. Any branching of the cladogram represents lineage divergence, the diversification of lineages from one common ancestor. The two lineages could diverge into what would be designated as separate species. Formation of two separate lineages from one common ancestor could lead to formation of two species from one—a phenomenon termed ‘speciation’. The point of divergence of one clade into two (where the most common ancestor of the two divergent clades is located) is called a node and the region between two nodes is termed an internode. In computer science, a tree is a particular kind of graph. A graph is a structure which consists of points (nodes) connected by lines (edges or branches between the points). The graph is thus connected which shows that one can get from any point to any other point by traversing one or more contiguous branches. The connected graph is a tree rather than a network as there is only one possible path between any two nodes. In other words, a connected graph is graph containing at least one path between any two nodes. A path from one node to another is a consecutive set of edges beginning at one node and ending at another. A directed graph is one in which each edge is one-way street (e.g. HMM and Neural Networks). A rooted tree starts from the root which is the node ancestral to all other nodes (Moore et al., 1973). In other words, the root generally represents the ancestor of all other portions of a tree and gives temporal directionality to the tree. Each ancestral node gives rise to two descendant nodes. Terminal or exterior nodes have no further descendants and these nodes correspond to operational taxonomic units, i.e. contemporary sequences (extant species). In other words, a node is exterior if only branch connects to it and interior otherwise. A particular node may be selected as a root but this is not necessary and abstract trees may be rooted or unrooted. Unrooted trees show the topology of relationships but not the pattern of descent. A rooted tree in which every node has two descendants is called a binary tree. All nonroot, nonexterior nodes are interior nodes and they correspond to ancestral sequence (extinct species) such as may be inferred from the contemporary sequences by maximum parsimony principle. The connecting line between two adjacent nodes is a link in the tree. The number of nonmatching sites between aligned sequences of the two adjacent nodes is the length of that link. The number of these sequence changes counted over all links constitute the length of the tree (Czelusniak et al., 1990). In other words. in most cases the lengths of the lines connecting the nodes are proportional to number of amino acid substitution separating one species from another. If we trace two extant species to a common internal node (representing the common ancestor of the two species) the length of the branch connecting each external node to the internal node represents the number of amino acid

4.4

Crop Evolution and Genetic Resources

substitutions separating one extant species from this ancestor. The tips of a tree represent the sequences analyzed. In an unrooted tree all interior nodes have at least three branches incident to them and if all interior nodes have exactly three incident branches the tree is said to be strictly bifurcating. The ancestral relation among interior nodes is unstated in an unrooted tree. A rooted tree is obtained by adding extra nodes with only two incident braches. An unrooted tree (sometimes called a network) is a method of representation of relative character state changes between taxa. An unrooted tree is branching diagram which minimizes the total number of character state changes between all taxa. Unrooted trees are constructed by grouping taxa from a matix in which polarity is not indicated (i.e. in which no hypothetical ancestor is designated) perhaps because of the polarity of one or more characteristics can not be ascertained. Knowledge of character polarity is essential for recognizing shared derived character states that define monophyletic taxa. Polarity is the designation of relative ancestry to the character states of a morphocline. No evolutionary hypotheses are implicit in an unrooted tree. Evolutionary trees can be constructed on a variety of different proteins. The evolutionary tree based on the sequences of one protein may differ from those of a tree based on the sequences of another protein. This is because of so many reasons. Some proteins evolve faster then others or change faster within one group of species than another. Further, a large protein with many variable amino acid residues may show a difference between two closely related species and a small protein may be identical in the same two species. The calculation of tree length can be simplified by removing the root from the tree, Such as unrooted tree or network still retains the interior nodes and the exterior nodes. A network of N exterior nodes has N-2 interior nodes and 2N-3 links. Thus a network of N OUTs can be converted into 2N-3 dendograms. The dendogram is created by putting the root on any one of network’s link. The maximum parsimony method can reconstruct ancestral sequence for each internal node of a tree but it can not determine which interior node or which pair of adjacent interior nodes is closet to the root. Assumptions underlying the construction of a tree  In the phylogenetic tree the different objects to be classified arise by a branching process. First, it is usually assumed that all branches are dichotomous i.e. a single ancestral lineage splits to give rise to two descendant lineages. If two such splits are followed closely one after another then in practice, it may be impossible to decide which occurred first but the assumption that all splits are dichotomous is unjustified. Secondly, lineages split but never rejoin. In other words, history is to be represented by a tree and not by net, It further means that it there has been recombination between lineages, then a tree representation is an inappropriate representation of evolutionary history.

4.3  APPROACHES TO DERIVING PHYLOGENETIC TREES Phylogeny states a topology of the relationships based on classification according to similarity of one or more sets of characters or on a model of evolutionary processes. Thus there are two approaches to driving phylogenetic trees.

Polymorphism and Phylogenetic Inference





4.5

1. Phenetic approach  This approach makes no reference to any historical model of the relationships. It proceeds by measuring a set of distances between species and generates the tree by a hierarchical clustering procedure. 2. Cladistic approach  This alternative approach considers possible pathways of evolution, infers the features of the ancestor at each node and chooses an optimal tree according to some model of evolutionary change. The difference between two approaches is that phenetics is based on similarity whereas cladistics is based on genealogy. Phylogenetic classification based on evolutionary history or patterns descent may or may not correspond to overall similarity (phenetic classification).

4.4  CLUSTERING METHODS Clustering is bringing together similar objects and distinguishing classes of object as that are more similar to one another than they are to other objects outside the classes. Clustering is more subjective in the sense that some workers prefer lager classes. tolerating wider variation while others prefer smaller tighter classes. Hierarchical clustering refers to the formation of clusters of clusters of objects. Hierarchical clustering is perfectly capable to produce a tree even in the absence of evolutionary relationships. For example, a departmental store has goods clustered into sections according to the type of the product, for example, clothing or furniture and sub clustered into more closely related subdepartments such men’s and women’s shoes. Men’s and women’s shoes have a common ancestor but there is no implication that shoes and furniture do. There are different methods of clustering (see A, B and C below). Clustering for a given set of species, determines for all pairs, a measure or similarity or difference between them. The traits used could be morphological traits or one could use the number of different bases in alignments of mitochondrial DNA. Short fragments of mitochondrial DNA have been the pre-dominant genetic markers applied to phylogenetic and population genetic studies. Cladisitc method  The objective here is to select the correct tree by utilizing an explicit model of evolutionary process. Cladistic methods deal explicitly with patterns of ancestry implied by the possible trees relating a set of taxa. Cladistic methods include maximum parsimony (MP) and maximum likelihood (ML) approaches described below. Neither MP nor ML could be applied to anatomical traits such as average height. The different methods differ in (i) their efficiency in the use of computer time and the number of sequences which can be analyzed, (ii) power in identifying the correct tree with increasing probability for a given amount of data, (iii) consistency in identifying the correct tree with increasing probability as the amount of data increases and (iv) robustness in identifying the correct tree even when some of the assumptions of the methods are fulfilled. As no method is superior by every criterion under all conditions a variety of methods coexist. A detailed discussion of the methods and their relative advantages and disadvantages are given in Hills and Moritiz (1990), Hillis et al,. (1994), Nei (1996) and Li (1997). The most commonly used methods are classified under the following three broad headings.

Crop Evolution and Genetic Resources

4.6



A. Distance methods. B. Parsimony methods. C. Maximum likelihoods. A. Distance method  These are based on the pair-wise differences between the sequences. Distance is defined as the number of positions on aligned sequences which are occupied by different symbols. This means the distance will jump to and fro from high-dimensional subspaces that on whole would differ. Further, even such a definition for a given subspace does not make any sense because of context dependent probabilities at individual positions. The true distance between any two points depends on historical details of the interplay of mutation and selections. Distance correlations are expressed as dendograms. Dendograms that refer to distances which do not reflect these uncertainties correctly even if the correlation between segment length and time is taken as having statistical nature. The various distance methods include unweighted pair group method with arithmetic mean, minimum evolution and neighbor joining. 1. Unweighted pair-group method with arithmetic mean (UPGMA)  This method (Sneath and Sokal, 1973) is based on the assumption of a constant rate of evolution in each branch and performs poorly when this assumption is not fulfilled (Li et al., 1987). The phylogenetic tree is constructed for a set of taxa from their pair-wise evolutionary distance. To achieve this, a distance matrix, D is calculated from all possible pair wise sequence comparison. The distance matrix, Dij is calculated as the edit distance (Hamming distance), i.e. the minimum number of nucleotide substitutions needed to transform sequence i into j. Sometimes the Hamming distance will underestimate the true number of substitutions as multiple changes at the same position can not be accounted for. UPGMA starts with grouping of those two taxa between which the evolutionary distance is minimal. The different steps involved in the construction of phylogenetic tree are described below. Also, a simple example of how clustering procedure works is given below. Suppose there are four species characterized by homologous sequences ATCC, ATGC, TTCG and TCGG, respectively. Now, a measure of dissimilarity based on the number of different bases in alignments is determined for all pairs. In other words, the following distance matrix is generated taking the number of differences as the measure of dissimilarity between each pair of species.

ATCC ATGC TTCG TCGG

ATCC

ATGC

TTCG

TCGG

0

1

2

3

0

3

3

0

2 0

Polymorphism and Phylogenetic Inference

4.7

As the matrix is symmetric one needs to fill on only the upper half. In the distance matrix the smallest distance is 1 between ATCC and ATGC and therefore, the first cluster is (ATCC, ATGC). In other words, the two most closely related species are selected first and a node is inserted to represent their common ancestor. So the tree will contain the fragment:

ATCC

ATGC

Now the two selected species are replaced by a set containing both and the distances from the pair to the others are replaced by the average of the distances of the two selected species to the others. The reduced distance matrix thus generated takes the following form.

(ATCC, ATGC)

(ATCC, ATCG)

TTCG

0

1/2(2 + 3) = 2.5

TCGG 1/2(4 + 3) = 3.5

0

TTCG

2 0

TCGG

The next cluster is (TTCG, TCGG) with a distance of 2. Finally, linking of the clusters (ATCC, ATGC) and (TTGC, TCGG) gives the following tree.

1.5

1.5

0.5 0.5 1 ATCC

ATGC

TTCG

1 TCGG

Branch lengths are assigned according to the rule: branch length of edge between nodes X and Y = 1/2 distance between and X and Y. Branch length can be estimated by the method of Fitch and Margoliash (967). Suppose that the number of substitutions distinguishing sequence i and j is dij. Now if the tree relating sequences of three species have branch lengths A, B and C (Fig. 4.2) which represent branch length s from the most recent common ancestor, then the branch lengths can be estimated from the following equations.

Crop Evolution and Genetic Resources

4.8



A = 1/2(d12 + d13 – d23)



B = 1/2(d12 + d23 – d13)



C = 1/2(d13 + d23 – d12)

Where d12 = A + B, d13 = A + C and d23 = B + C. A Species 1

B

C

Species 2

Species 3

Fig. 4.2

Figure 4.2 showing a simple phylogenic tree with branch lengths A, B and C from the most recent common ancestor 2. Minimum evolution  This method examines every possible tree and selects the one which minimize the total lengths (Edwards and Cavalli-sfroza, 1963; Zuckerkandl, 1964). This method is not suitable for a large number of sequences as it results in many possible trees, namely, (2n – 5)!/[2n – 3 (n – 3)!] 3. Neighbor joining  This method sequentially groups the most closely related pairs of sequences. This method is computationally very efficient and generates tree close to the minimum evolution tree. Li (1989) proposed a two-step approach. The first step is to infer the branching order. One can use the transformed distance method (Ferris, 1977; Klotz et al., 1979; Li, 1981), the neighbor-joining method (Saitou and Nei, 1987). or any other method which does not assume rate consistency and that has been found to be effective for obtaining correct tree. The second step is to estimate the branch lengths by least square method (Cavalli Sfroza and Edwards, 1967; Chakarborty, 1977). The neighbor-joining algorithm calculates a genetic distance between all pairs of strains. It then selects two nearest neighbors and replace them by a single genotype which is a suitable ancestor of the two neighbors. This process is repeated until only two genotypes remain and thus a tree is constructed. Cluster analysis  Cluster analysis does not have any kind of theoretical theme. These are non-probability based methods used for grouping objects into clusters of like objects. If we consider the early history, the taxonomy of plants, then one can classify plants into species based on characteristics. Thus it is natural to consider Hierarchial (evolutionary, genetic, family) tree method as shown on next page.

Polymorphism and Phylogenetic Inference

4.9 Progenitor

1

2

3

4

5

Assume that the distance function between objects r, s drs is defined. There are two main methods of tree construction: 1. Divisive method which starts with one big group, divide into smaller ones according to drs. This method involves very heavy computation and thus not used. 2. Agglomerative – In this method one stats with single object, merges into clusters according to some algorithm. This quickest algorithm is Nearest Neighbor or single link method. Suppose that at certain stage we have a number of groups. Now fuse or link the groups together which have the minimum distance between their nearest members. For example, given five objects the drs between pairs of objects are as given below. drs 1

1

2

3

4

5

0

2

6

10

7

0

5

9

3

0

4

8

0

5

2 3 4

Formation of cluster considering minimum distance between nearest members is shown below. Level 0

Clusters (3)

(4)

(5)

(3)

(4)

(5)

d12 = 2

2

(1, 2, 5) (3)

(5)

d(1, 2) 5 = 3

3

(1, 2, 5)

(3, 4)

d34 = 4

1

4

(1)

(2)

Minimum distance between nearest members

(1, 2)

(1, 2, 3, 4, 5)

Clustering will result in a tree diagram called DENDOGRAM as shown on next page.

Crop Evolution and Genetic Resources

4.10 5

4

3

2

1 1

2

3

4

5

This method of clustering is very quick but it suffers from ‘chaining’. The two quite unlike clusters may be joined by such one pair of elements close together. Furthest Neighbour (Complete link) In this method groups are fused according to minimum distance between most unlike members. Level 0 (1) 1

Clusters (2) (3) (1, 2)

2 3

(4)

Minimum distance between furthest members (5)

(3)

(4)

(5)

d12 = 2

(1, 2)

(3, 4)

(5)

d(3, 4) = d(3, 4) 5 = 8

(3, 4)

d(1, 2)5 = 7, d(1, 2)(3, 4) = 10

(1, 2, 5)

Although the tree has a similar structure here but it would not be usually. This method of clustering has quite opposite weakness of Nearest Neighbour. It is too relucant to join similar groups together. Group Average Method This method merges groups which have the minimum average distance between groups. Level 0 (1) 1 (1, 2) 2 3 4

(2) (1, 2)

Clusters (3) (3)

Minimum average distance between clusters (4) (5) (4) (5) d12 = 2 (3, 4) (5) d1, 2(3) = (6 + 5)/2 = 5.5 (1, 2, 5) (3, 4) but the minimum (1, 2, 5, 3, 4) is given by d34 = 4 and d12(5) = 5

Polymorphism and Phylogenetic Inference

4.11

This method of group average generates a more satisfactory tree structure and thus used in most applications but has computational problem in the sense that it is slower. Distance measures between groups in the above described methods satisfy a recurrence formula. For distance between object k and a group (i, j ) formed by merger of objects or clusters i and j,

dk(i, j) = a1 dki + a2 dkj + bdij + g |dki-dki|

where a1 a2, b and g are constants. In case of Nearest Neighour: a1 = a2 = 1/2, b = 0, and g = –1/2 Min (dki, dkj) Furthest neighbour: a1 = a2 = 1/2, b = 0, and g –1/2 Max (dki, dkj) and Group Average: a1 = ni/(ni + nj) where ni, nj are cluster size of i and j. a1 = nj/(ni + nj), b = g = 0 (dk(i, j)) = average distance between k and objects in (i, j). B. Parsimony methods  These methods search among possible trees and identify the one which involves minimum number of mutational steps (Farris, 1970; Fetch, 1971; Moore, 1973, 1976). A tree containing the minimum number of steps or changes, required to generate the observation is called a maximum parsimony tree. The maximum parsimony is also called maximum homology. A maximum parsimony tree accounts for the evolutionary descent or related sequences by the fewest possible genetic changes. Such a tree maximizes the genetic likeness associated with common ancestry while minimizing the incidence of convergent mutations. Such common ancestry rather than convergent mutations is the most possible reason for extensive interspecies matches or either nucleotide sequences or amino acid sequences. Thus search for evolutionary tree by maximum parsimony homology principle allows finding the best supported genealogical hypotheses. For example, given species characterized by homologous sequences ATCG, ATGG, ACCA and TTCA tree can be constructed as follows which contains four mutations. ATCA AÆG

AÆT

ATCG

TTCA CÆG

ATCG



An alternative tree is as follows.

ATGG

TÆC

TCCA

TICA

Crop Evolution and Genetic Resources

4.12 ATCG GÆA ATCA

AÆT TTCG

AÆG

A Æ T, T Æ C

ATCG

TCCA

TÆC TÆA CÆG ATGG TTCA

This tree hypothesizes seven mutations. In many cases several trees may postulate the same number of mutations fewer than any other tree. in such cases maximum parsimony does not give a unique answer. A character is a number position and a character state is the particular nuceotide in that position. For example, the third character of a coding sequence, say AUG is the third position and its state is G. Each character of a sequence is represented by four-bit nibble in which A = 1000, C = 0100, G = 0010 and T = U = 0001. This allows ambiguity to be easily represented. For example, purine = R = (A and/or G) = 1010, pyrimidine = Y = (C and/or U) = 0101, etc. This is especially useful as AND and or operations can be performed in decimal numbers themselves which range from 1 to 15 = N. The different parsimony methods include: 1. Unweighted parsimony which treats each type of change, for example, transition or transversion as equally informative. 2. Weighted parsimony which attaches more importance to certain type of changes, usually transversion in selecting the best tree. This method is superior to unweighted parsimony. Workers weigh those nucleotide substitutions that are transversions more heavily than those that are transitions as transversions may be much less common than transitions. C. Maximum likelihood  Maximum likelihood method assumes a model of nucleotide or amino acid substitution and identifies the tree which maximizes the probability of obtaining the observed sequences. In other words, it assigns quantitative probabilities to mutational events rather than merely counting them. Like maximum parsimony ML reconstructs ancestors at all nodes of each tree considered but it also assigns branch lengths based on the probabilities of the mutational events postulated. For each possible tree topology, the assumed substitution rates are varied to find the parameters that give the highest likelihood of producing the observed sequences. The optimal tree is the one with the highest likelihood of generating the observed data. This method is quite robust and performs well even when substitution rates differ moderately in different branches. Cavalli-Sfroza and Edwards (1967) applied the ML method to phylogenetic tree construction using gene frequency data. ML algorithm for construction of unrooted phylogenetic tree from nucleotide sequences was developed by Felsenstein (1981).

Polymorphism and Phylogenetic Inference

4.13

4.5  CHARACTERS FOR CONSTRUCTING TREE A phylogenetic tree can be constructed using either morphological data or molecular data. When using sequence data the two points which need to be emphasized are (i) the choice of molecule and (ii) the likelihood of parallel changes occurring in different lineages. The choice of molecule depends on the group being classified. For a group of closely related organisms, one required rapidly evolving molecule that varies sufficienly within the group, for example, mitochondrial DNA. But for a more distantly related group one needs a slowly evolving molecule such as DNA coding for ribosomal RNA so that resemblances between the more closely related members of the group are still recognizable. Although morphologist can reasonably assume that the pentadactyl limb evolved only once but in case of nucleic acid sequence data, the substitution, say of an A by a G at particular site in a gene could well occur independently in two different lineages and allowing such repeated events or homoplasies is a major difficulty in tree construction. Homology can be defined as similarity resulting from common ancestry. Similarity between taxa can arise not only by common ancestry but also by independent evolutionary origin. Similarity which is not the result of homology is termed homoplasy. Homoplasy can arise in two waysconvergence (parallelism) or reversal. Convergence refers to the independent evolution of a similar feature in two or more lineages. Reversal refers to the loss of a derived feature with the re-establishment of an ancestral feature (Simposon, 2006).

Mitochondria and Chloroplast DNA All plant organelle genomes are highly autopolyploids. There are 25-500 plastids per leaf cell and within each plastid are hundreds of identical plastid genome(plastomes) depending on the species, light levels and stage of development (Scott and Possingham, 1980; Boffey and Leech, 1982; Baumgartner et al., 1989). There are also high copy number of mitochondria per cell but there are few estmates of genome copy number per mitochondria(260 copies per leaf in mature pea leaves and 200-300 copies inetiolate hypocotyls of watermelon, courgette and musk melon, Lampa and Bendech, 1984). Thus in somatic cells they exist in multiple copies but in meristematic cells their numbers are generally low. Plastids and mitochondria replicate independently from the nucleus and their assortment into daughter cells is generally random. Any mutation in organelle genome can become fixed in cells during cell division due to random sorting and ultimately establish sexual tissues which produce gametes with unique cytoplasm. Finally, both organelles are also inherited maternally due to unequal contribution of the egg cells with only a few exceptions such as Medicago sativa (Lucerne)shows paternal inheritance. There are similarities between genomes and protein-synthesizing systems of chloroplasts, mitochondria and prokaryotes but there are differences too. 1. A striking feature of organelle genome is that like eukaryotes it contains intercistronic spacer regions. Split genes and RNA splicing mechanism appear to be present in mitochondria. Split genes are absent in prokaryotes such as bacteria and blue green algae.

4.14

Crop Evolution and Genetic Resources



2. Organelle genomes are highly redundant. Redundancy can be achieved either by having many organelles per cell with a few DNA molecules each or having a few organelles with many DNA molecules per organelle. 3. Inheritance is either uniparental (maternal or paternal) or biparental. 4. Shows maternal inheritance(shows reciprocal differences), the non-Mendelian inheritance. 5. Rapid conversion of heterozygotes into homozygotes often by somatic segregation 6. mtDNA and cpDNA universally code most, if not all, of unique tRNAs. 7. They make some of the components of mitochondria and chloroplast in which electron transport and ATP synthesis take place. mt genes respond to toxins produced by B. maydis. 8. There is interaction between nuclear and organelle genomes 9. rRNA and tRNAs of mitochondria are mitochondrially encoded (nuclear are distinct from cytoplasmic translation system). 10. Mammalian mitochondria possess a genetic code and decoding system different than other mitochondria. 11. Presence of overlapping genes in mtDNA. cp genome produces large subunit of fraction I protein, resistance to streptomycin, lincomycin, atrazine and tentoxin and various forms of albinism and CMS is mt based. Behaviour of plastids after fusion mixing is to either quickly showing random sorting out, unilateral transmission or rarely recombination. Construction of evolutionary trees  Evoutionary trees have been built up based on sequence homologies(Ritland and Clegg; Soltis, D and Soltis, 2000). A number of specific plant genes such as rbcl(large subunit of ribulose 1, 5-diphosphate carboxylase / oxygenase), rDNA gene besides chloroplast genes have been sequenced to study phylogeny. As these sequences are evolutionary conserved so they have proved to most useful for inferring higher relationships. The rDNA gene is composed of several genes including 5S, 5.8S, 18S, and 26S rDNA and ITS(internal transcribed spacer). The 18S and 26S sequences are highly conserved sequences and have been used to resolve higher order relationships whereas ITS regions show much more variability and thus have proved to be useful in distinguishing species. The nuclear genes Pgi, adh(adh1, adh2) and GapA are being studied now as they are rapidly evolving and provide variability at the species and even population level. Further, 16S rRNA which forms 30S subunit of prokaryotic ribosome is a highly conserved sequence and found in different species of bacteria and archaea. Mitochondrial and chloroplast rRNA are also amplified using 16SrRNA.

4.6 MEASUREMNET OF GENETIC DISTANCE AT NUCLEIC ACID LEVELS INSTEAD OF PROTEINS The problems associated with measurement of genetic distance at nucleic acid level are as follows:

Polymorphism and Phylogenetic Inference

4.15



1. There are wide fluctuations in nucleotide compositions among different organisms and to well established properties of the genetic code such as its triplet structure and degeneracy. 2. The rate of evolution in mRNA coding genes by far exceeds particularly for silent codon positions than that of the corresponding proteins. So, purely divergent model of molecular evolution becomes untenable when referred to nucleic acids. Deterministic models like the distance matrix and the maximum parsimony approach belong to this class based on divergent evolutionary changes only are destined to fail in any quantitative analyses of evolutionary processes at the molecular level.

4.7  EVOLUTIONARY DISTANCE Evolutionary distance refers to the distance by which the evolutionary relatedness is measured quantitatively. It can be at morphological and molecular levels. In case of evolutionary distance at molecular level the number of nucleotide and amino acid substitutions are the most popular measures. The number of nucleotide sequences is estimated by making pair-wise comparison of nucleotide sequences and correcting for multiple substitutions at the same site. The one-parameter method of Jukes and Cantor (1969) assumes rates of nucleotide substitutions between all possible pairs of different nucleotides being equal to each other and nucleotide substitution is calculated by Kn = – 3¢/4 ln (1 – 4/3p) where p represents the fraction of nucleotide differences. Kimura’s (1983) two-parameter method is based on the assumption that the rates of transition mutations and transversion mutations are different. Kimura’s empirical method gives value of substitution rate close to the above-mentioned method. The number of amino acid substitution is also used as a measure of evolutionary distance. Assuming substitution rates between any pairs of amino acid being equal (although it is well known that substitution rate between a pair of similar amino acid is much higher than between a pair of dissimilar amino acids), the number of amino acid substitutions is given by Ka = – ln (1 – p) where p denotes the amino acid differences. Dayhoff (1978) developed the algorithm to estimate the number of amino acid substitution taking into account the similarity matrix of amino acids but the formula given is very complicated. To minimize this Kimura invented an empirical formula by adding one term to the formulae given earlier. Ka = – ln (1 – p – 1/5p2). Substitution rate estimated by this formula is very close to Dayhoff’s estimate. There is a known dynamic programming algorithm (Sellers, 1974) for computing the evolutionary distance between two finite sequences. Its principle application is within context of genetic sequences where it provides a measure of homology. This distance is defined as the minimum total number or weight more generally) of mutations and deletions in the two sequences needed to make them equal. It was introduced as mathematical concept by Ulam (1972) and shown to be a metric. The algorithm detects similarities by computer between pairs of biology sequences such as proteins and nucleic acids (Sellers, 1979). Species tree  A species tree reflects the species evolutionary history correctly but it is generally unknown to investigator for a group of organisms. Reconstructing a phylogeny for

4.16

Crop Evolution and Genetic Resources

a given set of species will help in understanding the evolutionary history and relationships of the species. Gene tree is a phylogenetic hypothesis constructed from one gene. It may not represent the true evolutionary history of the species. Gene trees are not isomorphic with species trees. The incongruence occurs due to biological or analytical reasons in the phylogenetic reconstruction. The biological reasons include paralogy, lineage sorting and horizontal gene transfer whereas the analytical reasons include data sampling bias and use of models in the phylogenetic analysis. Most of the previous approaches are based on a subset of conserved regions extracted from the corresponding genomes for the inference. The distance between each pair fo species is usually derived from the similarity of the selected conserved regions. The accuracy of the generated phylogeny thus depends in the choice of these regions. There are limitation with this approach. There may be cases that these regions do not truly reflect the whole evolutionary history of the species. Further, different phylogenies may be obtained by selecting a different set of regions or if only a small portion of the genome is selected then there may be problem of mutation saturation, i.e. selected regions are not powerful enough to differentiate the phylogenetic relations of some genome. Genome-wide approach  Problems associated with the species and gene trees can be overcome using complete genome data as all information is included in the tee inference by comparing gene contents or gene orders. This approach suffers from primitive mathematical model and temporal data scarcity problem. Two approaches have been proposed recently to solve this problem. The first approach is the gene-order approach and the main algorithm for gene-order based phylogenetic reconstruction is break-point analysis. It is a method for minimizing the number of breakpoints between genomes where a NP-hard problem has to be solved in each iteration. Another approach is ‘gene concatenation’. Its main idea is to include more genes in gene tree construction by randomly combining a set of widely distributed orthologous genes selected from genomic data. It gives no consideration of gene functionality in the phylogeny. Uses of phylogenetic trees  Phyologenetic tree is used to determine (i) the role of recombination (ii) the mechanism of speciation and (iii) as a comparative method (Maynard Smith, 2006). If sequences for several genes for a set of related strains are available then a phylogenetic tree can be constructed for each gene separately and if, the trees are similar for different genes, then it can be suggested that the recombination between stains were not frequent. It is also possible to test for recombination (intragenic recombination) by examining the sequences of the same gene from a set of strains. Unequal branch lengths in a tree imply unequal rate of evolution which in turn sugests the role of directional selection. Phylogenetic trees can also be used for identifying the selective forces responsible for some characteristic by comparing species. Groups for which tree construction is justified  Construction of phylogenetic tree is justified in the following cases. 1 Member of asexual population 2. Member of different sexual species provided inter-species hybridization can be ruled out or of higher taxa 3. Mitochondrial genes, either between species or if inheritance is strictly maternal, within

Polymorphism and Phylogenetic Inference

4.17

species 4. Y-chromosomes 5. Chromosomal genes provide intragenic recombination has not occurred. Reliability of the tree  The reliability of a tree depends on the error associated with it. There are two types of error: systematic and random. Systematic error arises because of inappropriate assumptions. For example, any tree could be inappropriate in case where there has been recombination or horizontal gene transfer. A tree based on RNA molecule secondary structure will be not be appropriate as changes at one site in a hair pin loop will change the likelihood of a change at the complementary site. This means that the assumption of changes at different sites to be independent is not met. Further, a tree is not appropriate in case of excessive homoplasy. This is particularly important in case of maximum parsimony methods if branch lengths are very unequal. Random error arises because of insufficient data but then this can be corrected using boot strap method.

4.8  PHYLOGENETIC NETWORKS Unlike eukaryotes which evolve largely through vertical lineal descent, bacteria acquire genetic material through the transfer of DNA segment across species boundaries – a process called horizontal gene transfer (HGT). (HGT) refers to the non-sexual exchange of genes across hierarchical boundries. Together with transformation and phage mediated transduction, conjugation is a key mechanism for HGT in bacteria. HGT plays a major role in bacterial genome diversification and is significant mechanism by which bacteria develop resistance to antibiotics. Further, genes conferring metabolic functions and virulence determinants have also been transferred through HGT. Conjugal DNA transfer is driven by the F plasmid unidirectionally from a F + plasmid donor cell to an F – recipient cell. The F plasmid contains all the genes necessary for conjugation (e.g. mediating the contact between donor and recipient cells) and for regulation of DNA mobilization and its unidirectional transfer. At low frequencies, the F plasmid can integrate into the chromosome of the host cell, giving rise to an Hfr (high frequency of recombination) strain. Chromosomal genes of the Hfr bacterium can be mobilized and transferred to a recipient. In some case, F plasmid can excise from the chromosome of Hfr creating an F ¢ molecule which carries chromosomal genes as well as the conjugation genes. Both Hfr and F ¢ can serve as DNA vehicles in HGT between bacteria. In the presence of HGT, the evolutionary history of a set of organism is modeled by a phylogenetic network which is a directed acyclic graph obtained by positing a set of edges between pairs of the branches of an organismal tree to model the HGT of genetic material (Moret et al., 2004) (see Figs. 4.3(a-c)). The evolutionary history of groups of higher organisms such as plants and fish, may also be more appropriately modeled by phylogenetic networks due to the process such as hybrid speciation (Linder and Reiseberg, 2004). The transfer of DNA between diverse organisms is referred to as lateral gene transfer (LGT). LGT facilitates the acquisition of novel functions. LGT is involved in the evolution of antibiotic resistance, pathogenicity and metabolic pathways.

4.18

Crop Evolution and Genetic Resources

Fig. 4.3  (a) A phylogenetic network with a single HGT event from X to Y, (b) Showing the underlying organismal (species) tree and (c) The tree of a horizontally transferred gene

4.8.1  Phylogenetic Network Reconstruction and Evaluation Three categories of non-tree like models have been addressed (Jin et al., 2006). 1. Split networks – These are graphical models which capture incompatibilities in the data due to various factors, not necessarily HGT or hybrid speciation. 2. Recombination networks – These are used to model the evolution of haplotypes and genes at the population level. 3. HGT networks – These are extension of phylogenetic trees which enable the modeling of reticulation events such as the HGT and hybrid speciation. These networks are also called reticulate networks and so phylogenetic networks are referred to as reticulate networks.

4.8.2  Genetic Distance/Divergence We know that the magnitude of heterosis depends on the difference in the gene frequencies in the parents and thus is a measure of the genetic divergence of the parental stocks but then lack of heterosis can not be used to infer a lack of genetic divergence. This is because the magnitude of heterosis also depends on the dominance and if the dominance effects at some loci are positive and at others negative then the net dominance effect would be little or no and thus we would expect little or no heterosis even though there is a difference in gene frequency. Thus, the validity of evaluating the degree of genetic divergence based on the heterotic effects is subject to question. There are numerous examples of unexpectedly poor hybrid performance in spite of superior parental stocks and genetic diversity. The genetic phenomena linkage and epistasis have been proposed as the causes of this poor performance. Even in the absence of linkage and epistasis, Cress (1966) showed how the effect of multiple alleles can account for this variable performance. Moll et al., (1965) in their study on the relationship between the magnitude of heterosis and the degree of divergence concluded that although the amount of heterosis is a linear function of difference in allele frequency for loci having dominance or over-dominance effects, the linearity disappears when highly differentiated populations or inbred or pure breeding lines are crossed. Thus, there is an optimum degree of genetic divergence for a maximum expression of heterosis and this optimum occurs within a range of divergence that is narrow enough so that incompatibility barriers are not apparent. Within this range the

Polymorphism and Phylogenetic Inference

4.19

amount of heterosis is linear function of the difference in allele frequency, i.e the amount of heterosis increases with the increase of divergence. There are different indices of genetic distance. 1. Morphological quantitative genetic distance 2. Biochemical distance. The genetic distance based on morphological data is particularly useful for inter group classification below the species level. As natural selection affects morphological traits linked to adaptive characters, genetic distances allow inferences about adaptation and co-adaptation pattern of populations. The divergence of quantitative traits on the basis of heterosis can be related to differences in allele frequency between populations and finally the genetic distances are relevant to evaluation of germplasm resources and in the context of breeding programmes. Genetic distance can also be used to derive a grouping of populations with regard to their genetic similarities or dis-similarities which is achieved through dendograms or dendrites (minimum spanning trees). Biochemical and molecular traits (i.e. isozymatic variability) not affected by environmental variations are generally used to estimate genetic distance to establish phylogenetic pattern and to describe evolutionary process. Variation at enzyme level does not influence the quantitative traits to a major extent. That is why there is frequent discrepancies between morphological and biochemical distances which suggests that inferences concerning the rate of evolution and variation apply only to a particular kind of character. Pattern of morphological evolution may not be same as that inferred from biochemical traits (Giles, 1984, Price et al., 1983). At molecular level over-dominance has not clearly been demonstrated. With enzymatic system the enzymatic activity of heterozygote is about half-way between the activities of corresponding homozygotes (Gillespie and Lanley, 1974). Thus enzymatic system seems neutral for heterosis and no relation has been found between the amount of heterosis and the level of heterozygosity for different enzymatic systems (Lefort Buson and de Vienne, 1985). The mitochondrial complementation (the increased oxidative and phosphorylation efficiency of mixed mitochondria from certain inbreds) has been reported as correlated with seedling heterosis in corn, wheat and barley but there is no convincing evidence that either mitochondrial complementation or hybridization phenomenon alone is correlated with the yield potential. Serkissian and Srivastava (1967) observed complementation of purified cytochrome oxidase and cytochrome C reductase but suggested complementation as a result of conformational changes in mitochondria. It has been shown that mitochondrial complementation requires physical contact and occurs instantaneously upon mixing (Mc Daniel, R.G. 1969). Some workers (Ellis et al., 1973 and Zobl et al., 1972) were unable to detect significant mitochondrial complementation in wheat and barley cultivars. But then heterozygosity for regulatory system might be more significant for explanation of heterosis which can lead to greater homeostasis in changing environment.

4.8.3  Estimation of Genetic Distance Genetic distance can be estimated using qualitative traits or quantitative traits. Methods of measuring genetic distance based on qualitative traits are discussed in (See, Roy, 2012).

Crop Evolution and Genetic Resources

4.20

This type of genetic distance statistics in allozyme studies cannot be used in the vast majority of quantitative traits because one can rarely determine the number of loci controlling a particular trait, much less the allele frequency. Using quantitative traits the genetic distance among the populations is calculated using D2 statistics (Mahalanobis, 1936) on the basis of the multiple characters. The phenotypic mean is taken as the best available estimate of genetic effects.

DG2 = XT S –1 X

where X is a vector of phenotypic mean difference between sample i and j for n quantitative traits and S –1 is the inverse of the sample dispersion matrix. This method is based on the assumption that populations follows a multivariate normal distribution and that the dispersion matrices are relatively homogeneous. The statistical distance between cultivars/ populations i and j, D2ij is then simply the sum of squares of the differences for quantitative traits under consideration. When the characters studied are independent then the statistical distance is

D2 = d12 + d22 + d32 + d42 + ... dn2 = S d i2

Simple phenotypic data can lead to biased estimates of genetic distances as morphological traits are more or less correlated and widely influenced by the environments. The original or correlated character means can be transformed to un-correlated set of variables using the pivotal condensation method as described by Rao (1952). Canonical variate transformation permits an optical visualization of the differences between cultivars/ populations through a reduction of dimension that preserves most of the biological information.

4.8.4  Cluster Formation The clustering of varieties is done by a method suggested by Tocher (Rao, 1952). A pair of cultivars say i and j, with smallest D2 value is selected first and its D2 value is compared with an arbitrarily selected D2 value to be decided by the worker. Generally this selected D2 value is close to the maximum D2 value observed between a pair of cultivars. If this D2 value is less than the selected D2 value the two cultivars are clustered together. To this group of 2 another cultivar say k, is added which is next closest as far as the D2 value is 3×2 _____ concerned. Now with 3 cultivars there would be ​   ​   = 3 combinations of cultivars such 2 as i, j; i, k and j, k with distances between them as Dij2, Dik2 and Djk2 , respectively. After inclusion of the cultivar k, the average distance rises to (​D​ i, 2 k​​ + D ​ ​ j, 2 k​ ​)/2 and 2 if this value is less the selected D value i, j and k cultivars form one cluster. With the inclusion of cultivars l there would be (4 × 3)/2 = 6 combinations of cultivars with D2  2 values (​D  ​ i,2­­­ j​ ​, ​D​ i, 2 k​ ​, ​D 2​ i,  l​ ​, ​D2​ j, k   ​,​  ​D​   ​  and ​D 2​ k, l  ​ ​). The denominator for estimating the average  j, l distance would be 3 with average D2 value being (​D i,​ 2 l​ + ​D j,​ 2 l​ + ​D k, ​ 2  l​ ​ )/3. This process of 2 inclusion of a cultivar continues until the increase in average D value is less than the arbitrarily fixed D2 value.

Polymorphism and Phylogenetic Inference

4.21

Once a cluster is formed another pair of cultivars with least D2 value is picked up and its D2 value is compared with the same arbitrarily fixed D2 value and if less than this value then the selected pair forms another cluster. Again another cultivar is added to this group of 2 and following the above procedure another cluster is formed. The criterion used in clustering of cultivars is that any two cultivars beloging to the same cluster must at least on the average show a smaller intracluster distance than intercluster distance.

4.8.5  Intra-and Inter-Cluster Distances The intra-cluster distance for a cluster of say n, cultivars is calculated as the mean of all D2 values for all possible combinations of n cultivars. With n cultivars there will be n(n – 1)/2 such combinations. The intercluster distance between two clusters say cluster I having n1 cultivars (i, j, k, l ) and cluster II having n2 cultivars (m, n) is calculated as: 2 2 [D im + D 2jm + D 2km + D 2lm + D 2in + D 2jn + D kn + D 2ln ]/n1n2

Contribution of individual character to genetic divergence One of the aims in D2 analysis is to find a character which shows major contribution to overall genetic divergence or in other words to overall discrimination in the material under study and also a trait showing high correlation between genetic diversity and geographical diversity as the aim of D2 analysis is to have a quantitative measure of the presumed association between geographical and genetic diversity. A particular character’s contribution can be said to be highest to genetic divergence if for that character maximum number of cross combinations yield highest values of D2. For p characters each cross combination will have pD2 values and rank 1 is associated with the highest D 2 value and the lowest rank is attached with the lowest D2 value. The contribution of a character is calculated as the number of cross combinations yielding D2 values of rank 1 to the total number of cross combinations. Although experimental design can control most of the environmental variation and other non-genetic effects such as age or the developmental stage of a plant but the ontogenic factors, which bring about changes in variance and covariance and which is a general phenomenon in animal at least, can be difficult to control by means of experimental design. Thus individuals to be measured in the experiment should be at the same stage of development in order to avoid measuring differences (distances) arising from differential gene activity at different stages of development.

4.8.6  Use of Genetic Parameters in the Estimation if Genetic Distance As the morphological distances based on phenotypic data may lead to biased estimates of genetic distances, the interpretation of morphological distances in genetic terms is not easy so it would be better to measure genetic distance based on genetic parameters.

4.22

Crop Evolution and Genetic Resources

Cultivars may differ in genetic effects such as additive, dominance, etc. or heterotic effect and these genetic parameters can be estimated from a suitable breeding design. The multivariate technique then allows the measurement of genetic distance (also called Mahalanobis distance) as a linear function of the estimated parameters (Camussi et al., 1985). The appropriate genetic distance matrix can be defined in terms of the estimated parameters. The use of T 2 statistic defined in terms of vector of contrasts specifying the distance permits the testing of the significance among distances between any pair of populations or lines. The linear transformation of the original data into canonical variates can be done for better representation of the results. The matrix of genetic distance based on heterosis or genetic effects will be particularly useful as complementary information for a better estimation of genetic divergence between populations.

4.9  ESTIMATION OF DIVERSITY There are two approaches for studying the genetic diversity within and between populations or group of individuals. The first approach is based on determining allele frequencies over a number of polymorphic loci and it is used for partitioning the genetic variation into components of variation within and between units and is discussed above. This approach may be chosen when dominant markers such as RAPD, AFLPs, ISSR are employed to haploid individuals or co-dominant markers such as allozymes, RFLP and SSR are used with haploids or diploids assuming no linkage. The second approach is used with all types of markers and organisms and it is based on comparisons of individual genotypes within and between populations. This type of approach can be employed for clustering and analysis of diversity within and between populations and for studying the relationship between populations. A genetic dissimilarity matrix is constructed from all possible pair-wise combinations of individuals. This approach is used when there is linkage disequilibrium. Three methods are used for the calculation of similarity coefficients. 1. Simple matching coefficient (or squared Euclidean distance) 2. Jaccard’s similarity coefficient and 3. Dice’s similarity coefficient. In the formulae a, b, c and d are defined as follows considering two individuals (or genotypes), i and j. a = number of bands that are present in both individuals, i and j b = number of bands that are present in ith genotype and absent in jth genotype c = number of bands that are absent in ith individual and present in jth individual d = number of bands that are absent in both individuals (double absence) Negative value (or non-occurrence) is not important and counting the non-existence (non-occurrence) of a band in both individuals may have no meaningful contribution to either similarity of dissimilarity.

Polymorphism and Phylogenetic Inference

4.23

The formulae for calculation of different similarity coefficients are give in the table 4.1 below. Also given in the Table 4.1 below is the correlation between different similarity coefficients. Table 4.1  Showing different methods of estimation of similarity coefficient Methods of estimation of similarity coefficients

Formulae

Reference

Simple matching(SM)

(a + d)/(a + b + c + d)

Sokal and Michener, 1958

Jaccard’s coefficient(J)

a/(a + b + c)

Jaccard, 1901

Sorensen-Dice’s coefficient(SD)

2a/(2a + b + c)

Sorensen, 1948; Dice, 1945

Comparisons between different methods Jaccard and Dice are similar and they differ from SM. S-D coefficient of similarity is frequently referred to as the measure of genetic similarity of Nei and Li, (1979). Genetic similarity is defined was the ratio of two expections– the number of bands for a pair of randomly selected individuals(one from each population) and number of bands shown by a randomly sampled individual from the pooled population. For a given data the values of Jaccard’s coefficients are always smaller than those of S-D similarity and SM. However, S-D similarity coefficient can be greater or less than SM depending on the positions with shared bands, a is less or greater than the number of positions with shared absence of bands, d, respectively. Jaccard or S-D coefficient differs from SM in that they do not consider negative co-occurrences. Jaccard and S-D coefficients are equivalent except that double weight(2a) is given to positive occurrences (a) in the S-D coefficient whereas the SM coefficient includes negative co-occurrences (d). In other words, Dice is similar to Jaccard but gives twice the weight to agreement. There is no change in ranks using any of these coefficients (J or S-D) and they classify the similarity among strains exactly in the same order. The squared Euclidean distance for AMOVA and Dice for constructing neighbouring trees are two qualitatively different measures of similarity. Simple mismatch coefficient and normalized squared Euclidean distance are identical measures as M = e2/n. Euclidean distance (eij) between ith and jth individuals or its squared value e 2i, j = b + c. Estimates from SM and SED (Squared Euclidean distance) generally differ from those measured by J’s and D’s indices. There is no one universally accepted approach for assessing the dissimilarity between individuals with molecular markers. Result depends on the type of DNA marker (dominant, co-dominant) used in the study and the ploidy level of the organism. Different measures are relevant to dominant and co-dominant markers depending on the ploidy of the organism. Dice coefficient can be suitable for haploids with co-dominant markers and it can be applied directly to (0, 1)-vectors–binary pattern representing banding profiles of the individuals. 1 indicates the presence of a band and 0 indicates the absence of the band at some position. Size of (0, 1)-vector reflects the total number of polymorphic

Crop Evolution and Genetic Resources

4.24

loci(n) represented in the same. Measurement of the asymmetric information thus can be on binary (or non-binary) variables. Similarity values based on dominant markers should be regarded as tentative. None of the measures, Dice, Jaccard or SM (or the squared Euclidean distance) is appropriate for diploid with co-dominant markers. The simple mismatch coefficient is the most suitable measure of dissimilarity between banding patterns of closely related haploid forms. For distantly related haploids, Jaccard’s dissimilarity has been recommended. In general, there is no suitable method which can be proposed for estimating genetic dissimilarity between diploids with dominant DNA markers. Banding patterns of diploids with dominant markers and polyploids with co-dominant markers represent individual’s phenotypes rather than genotypes. In case of co-dominant(RFPLs, SSRs) marker data genetic distance are often estimated using formula of Nei and Li(1979) whereas in case of dominant marker data(RAPDs, AFLPs) Jaccard’s coefficient(1908) is generally used. Table 4.2  Showing correlation between the different similarity coefficients Similarity coefficients

J

SD

J

1.0

SD

1.0

1.0

SM

0.87

0.87

SM

1.0

Measurement of coefficient of diversity The coefficients of dissimilarity in case of above mentioned different methods can be calculated as follows.

SM- (b + c)/n = 1 – Mi, j



Jaccard- (b + c)/(a + b + c) = 1 – Ji, j



Dice- (b + c)/(2a + b + c) = 1 – di, j

4.10  USE OF PROTEIN/ISOZYME TAXONOMIC AND EVOLUTIONARY STUDIES Origin of cultivated plants particularly polyploidy crop species a can be ascertained through the use of seed storage protein profile obtained by electrophoresis (Ladizinsky and Hymowitz, 1979). This is based on the finding that changes such as chromosomal rearrangements or even chromosome doubling has no or little effects on the seed protein profile. Uniformity and uniqueness of seed protein profile are typical of many groups of plant species and additiveness is another feature of seed protein profile. When proteins of two electrophoretic variants are mixed the uncommon bands will persist in the gel while the common bands will merge but no new bands will be expressed. In other words, one can detect the parents of a hybrid by comparing its protein profile with a profile obtained

Polymorphism and Phylogenetic Inference

4.25

by a protein mixture of the suspected parents. Further, in case of amphidiploids species the seed protein profile of synthetic allopolyploids will show an exact summation of the number of bands of their diploid parents. While studying the seed protein profile one must see how to interprete the variation in the darkness and the thickness of the bands. This type of variation can arise due to differential extraction or solubility of proteins from different accessions or due to lack of separation of proteins because of similar migration rates. Difference in the position of a band in the profile can be due to the co-dominance nature of locus. When variation is in the number of bands and particularly in the positions of bands one must make sure that this is not due to experimental error. True variation in the number or the position of bands can be expressed by measuring Rf value (which refers to the relative mobility of a band and is proportional to the distance between the two reference standards (Hymowitz and Hadley, 1972), by estimation of correlation coefficient based on the optical density values of bands (Johnson and Thein, 1970) or by calculating the similarity index based on the banding patterns between two gels (Vaughan and Denford, 1968) which expressed as the ratio: Number of pairs of similar band = ​  ______________________________________________              ​× 100 No. of different band + No. of pairs of similar band Using seed protein profile the origin and evolution of cultivated polyploid crops such as wheat, cotton have been elucidated which corroborated the cytogenetic evidence regarding the origin. The hexaploid wheat has a genomic structure, AABBDD which was derived from T. dicoccum, a tetraploid (AABB) and Aegilops squarossa, a diploid wild species (donor of DD genome). Comparison of the seed protein profiles of tetraploid wheat with Aegilpos speltoides which was thought to be one of the diploid progenitors of hexaploid wheat, showed the albumin bands of Ae. speltoides were missing in the bands of tetraploid wheat and thus it could not be considered as one of the donors. Similarly, in case of tetraploid cotton, Gossypium hirsutum which is composed of genomes, AADD, protein mixtures of Gossypium arboretum (donor of the A genome) and G. raimondii, representative of the D are identical to that of the tetraploids, G. hirsutum, G. barbadense and G. tomentosum. Seed storage proteins have been useful in classifying relationships within GP1 for beans, lentils, chickpea, pigeonpea, watermelon and peanuts (Gepts, 1990) while isozymes studies have been used for banana, barley, foxtail millet, maize, quinoa, rice and tomato (Deobley, 1989).

Origin and Genetic Resources of Cereals

C H A P T E R

5

5.1  WHEAT Wheat (Triticum aestivum) the most important food crop and grown throughout the world belongs to the genus Triticum. There are four sets of chromosomes or four genomes designated as A, B, D and G. The genus contains diploids, tetraploids and hexaploid with 2n = 14, 28 and 42, respectively (Table 5.1). The three commercially grown species in the genus Triticum are T. aestivum, T. durum and T. compactum. Most of the wheat grown throughout the world is hexaploid T. aestivum or common bread wheat. T. durum (has high gluten content which makes it sticky when wet) is used for paste products such as noodles, spaghetti, macaroni, etc. T. compactum is called club wheat. The evolutionary relationship of Triticum species was presented by Briggle (1980) and wheat classification was proposed by Morrison and Sears (1967). Bowden (1959, 1966) first reported that two of the three genomes of hexaploid wheat were derived from Aegilops (Ae. speltoides(?) and Ae. squarrosa). T. monococcum with A genome got crossed with unknown species which contributed B genome and their F1, upon doubling of chromosome produced a tetraploid wheat called T. turgidum. This T. turgidum when crossed with T.tauschii (Aegilops squarrosa), the donor of D genome produced F1 which upon doubling of chromosome produced hexaploid common bread wheat, T. aestivum (Fig. 5.1). Figure 5.2 shows origin of wheat using the morphology of inflorescence of different species. Wheat is best suited to regions between 30° and 50° N latitude and 25° and 40°S latitude. It is C3 crop. It is a normally self-pollinated crop but small amount(1-4%) of cross pollination occurs. T. timopheevii is the source of CMS and genes for resistance to many diseases of cultivated wheat. The center of origin of wheat is South West Asia (Eastern Turkey, Lebnan, Syria, Iraq, Israel). Depending upon the growth habit there are two types of wheat varieties-winter wheat and spring wheat. The winter wheat (or winter cereals) have a high tillering ability but have vernalization requirements. Thus, the specific objectives of spring x winter crosses

Crop Evolution and Genetic Resources

5.2

Table 5.1  Showing various diploid, tetraploid and hexaploid wheat species and their place of origin (Adapted from Feldman and Sears, 1981) Species

Ploidy level

Genome

Common name

Domestication

Origin

Diploid (Rachis brittle)

2n – 2x

T. monococcum

14

AA

Einkorn (one seed per spike), winter and spring

Cultivated

Unknown (possibly extinct)

14

BB

_

_

T. tauschii (formerly A. squarrosa)

14

DD

_

Wild

T. dichasians (formerly A. caudata)

14

CC

_

Wild

Tetraploid

2n – 4x

T. turgidum (rachis not brittle) (formerly T. diococcum (Rachis brittle), T. durum (Rachis not brittle), T. polonicum (rachis not brittle)

28

AABB

Emmer/Durum (hard wheat) T. durum (mostly spring), T. turgidum (winter and spring), T. polonicum (rachis not brittle) (spring)

Cultivated

Near East

T. timopheevii (Rachis brittle)

28

AAGG

_

Cultivated

Soviet Georgia

Hexaploid

2n – 6x

T. aestivum (rachis not brittle) (formerly T. spelta (rachis brittle), T. compactum (rachis not brittle),

42

Cultivated

Trans- Caucasia (Nothern Turkey) and Caspian Sea

AABBDD Bread wheat (soft wheat), winter and spring, high in protein gluten

Iran, Iraq and Turkey

include transfer of the superior disease resistance, cold tolerance and possible drought tolerance from the winter wheat to spring wheat and spring wheat can contribute superior bread making quality and genes for leaf and stem rust resistance that differ from the genes carried by the winter wheat and thus winter x spring cross can be made in the hope of isolating wheat Fig. 5.1  Showing the origin of hexaploid cultivated wheat variety with wider adaptability. Hexaploid hard red winter bread wheat chromosome when put in the cytoplasm of

Origin and Genetic Resources of Cereals

5.3

T. timopheevii (2n = 4x = 28) leads to male sterility. The primary gene pool (GP1B) of Einkorn wheat is T. boeoticum, of Emmer is T. dicoccoides, of T. timopheevi is T. araraticum and there is none for hexaploid bread wheat. The secondary gene pool (GP2) includes all species of Aegilops, Secale and Haynaldia plus Agropyron elongatum, A. intermedium and A. tricophorum. The tertiaty gene pool includes many species of Agropyron, Elymus and Hordeum vulgare (Harlan, 1975). GP2 consists of many Triticum and Aegilops species with A, B or D genomes or combinations of these. GP3 consists of related species in the tribe

Diploids 14 chromosomes

Goat grasses

Einkorn wheat (AA)

(BB)

(DD)

x

x Tetraploids 28 chromosomes

Emmer, durum wheat, etc (AABB)

Bread wheats (AABBDD)

Fig. 5.2  Probable origin of domesticated wheats (adapted from P.C. Mangelsdorf, 1953).

Crop Evolution and Genetic Resources

5.4

Triticeae including Hordeun, Secale and Agropyron. Einkorn (T. monococcum, genomes Am Am) is a diploid species whereas durum (T. turgidum ssp. durum) and common wheat (T. aestivum) are polyploid that originated from interspecific hybridization of two and three different diploid species, respectively. The domesticated emmer is T. tugidum subspecies (ssp.) dicoccon genomes (BBAA) and wild emmer wheat is T. turgidum ssp dicoccoides (Dubcovsky and Dvorak, 2007) and Aegilops tauschii has genomes DD. South Eastern Turkey is the most likely site of domestication. Breeding objectives in wheat include breaking yield barrier through genetical and/or physiological manipulation, bridging the yield gap through crop management practices, reducing losses due to biotic stresses and improving adaptation under climatic change. Durum wheat  It is a variety of wheat, Triticum durum which contains high gluten content. It contains 1.5 to 2% more protein than bread wheat (T. estivum). Further, it contains higher beta-carotene (precursor of vitamin A) too. It is cultivated for making suji (semolina), pastas, spaghetti. The advantages associated with durum wheat are that it posses high level of resistance to drought and high temperature and it requires less number of irrigation (3-4 irrigations in comparison to 5-6 in case of T. aestivum variety). It also has higher level of resistance to yellow rust, leaf and stem rust. It has high yield potential. In India durum wheat is grown on about 10% of the area under wheat. Breeding objectives include developing early maturing variety (it takes normally 145 days to mature), resistance to diseases like leaf blight, and powdery mildew, high grain mottling under high humid conditions, resistance to lodging (so developing dwarf variety) and developing variety suitable for heavy soil. Durum wheat grows well on light soils. Agropyron  The 22 species of Aegilops with some characteristics are given in the Table 5.2 below. Aegilops is a monocot and known as goatgrass. It belongs to family Poaceae. The genus Aegilops consists of 23 annual species. Aegilops species have been closely involved in wheat (Triticum aestivum) evolution, have played a major role in wheat domestication and will play a critical role in future wheat improvement. Table 5.2  Showing the different species of Aegilops. Species

Ploidy level

Genome

Ae.aucherii

14

SS

Ae.biuncialis

28

CUMb

Ae.caudata

14

CC

Ae.columnaris

28

CUMC

Ae.comosa

14

MM

Ae.heldreichii

14

MM

Source of gene

Yellow rust

Ae.kotschyi A.elongissima Contd...

Origin and Genetic Resources of Cereals

5.5

Contd...

Species

Ploidy level

Genome

Source of gene

U b

Ae.machrochaeta

28

CM

Ae.mutica

14

Mt

Ae.ovata

14

CUMO

Ae.recta

42

CUMtM2

Ae.speltoides

14

SS

Ae.triaristata

42

CUMtM2

Ae.trincuialis

28

CCU

Ae.umbellulata

14

CUCU

Ae.recia

Ae.squarosa

Ae.variabilis Ae.tauschii

CS 14

DD

AA

u

Weed

Ae.cylindrica Ae. uniaristata

Brown rust

u v

M

5.2  BUCKWHEAT Bukwheat (or kuttu) is not a cereal and thus not a grass but used as wheat. It belongs to family polygonaceae rather than Poaceae. The genus contains about 15 species. Buckwheat flour is used for making puri on occasions such as navoratri, mahashivratri or jaamashthami. It contains 18% proteins and has higher concentration of lysine, threonine, tryptophan and sulfur containing amino acids but does not contain gluten and contains, Fe, Zn and selenium. Rice and wheat are deficient in lysine. Fagopyrum esculentum, common buckwheat is used as grain as well as cover crop and is an annual crop. The other commercially grown species are F. sagittatum (grown in U.S.A.), F. emarginatum and F. tartaricum. F. esculentum and F. tartaricum are mainly cultivated in temperate regions (Table 5.3). F. tartaricum is also cultivated in Himalayan. Wild ancestor of common buckwheat is F. esculentum ssp ancestral whereas wild ancestor of F. tartaricum is F. tataricum ssp potanini. The F1 from the cross F. homotropicum x F. esculentum is infertile. Wild forms are found in Yunan. Buckwheat shows considerable amount of rutin as well as several vitamins and dietary fibre and shows high protein quality. Buckwheat has a dimorphic plant type where short-styled (thrum) and long-styled (pin) flowers are borne on separate plants. Each plant in a population bears either thrum or pin flowers. Fertilization within a styler type is prevented due to heteromorphic sporophytic SI system (Morris, 1947). Seed production depends on insects and wind to mediate cross pollination although honey bee and other winged insects are major pollinators.

Crop Evolution and Genetic Resources

5.6

Table 5.3  Showing species, chromosome number, breeding system in Buckwheat Species

chromosome number

Annual/perennial

Breeding system

F. esculentum

2n = 16

Annual, cultivated

Dimorphic, self sterile, SI Cross pollination is the rule

F. tataricum

2n = 16

Annual, cultivated

Self fertile, produces flower of one kind

F. emarginatum

2n = 16

Annual, cultivated in India

F. cymosum

2n = 16

Perennial

Origin

It is the original parent of both F. esculentum and F. tataricum Heteromorphic SI

F. gigantium H. himalianum

This crop can be used as green manure, erosion control and feed. Russia is number one in production. This crop is cultivated as grain crop where short season is available. It grows quickly, comes to flowering in three weeks, produces seeds in about six weeks and ripens in 10-11 weeks. France, China, U.S.A. and Canada also produce buckwheat. Buckwheat can be used for nectar production. It has fragrant while flowers Nectar from buckwheat produces dark colored honey. This crop can be grown in low fertility soil or acidic soil but should be well drained. It is a day neutral crop, largely self-incompatible and cross-pollinated through insects (honeybees and other pollinators). Presence of pollinator greately enhances yield. This crop attracts insects which deter pests of other crops such as potato, broccoli, green beans and other vegetables and thus acts as biocontrol agent. Roots of buckwheat exudates oxalic acid which permits it to grow well in soil with high aluminium(Al). There is immobilization and detoxification of Al by phosphorus(P). Further, this crop takes P and transforms it into available form.

5.3  TRITICALE Triticale is the first man made crop. Triticale has been synthesized by combining genomes of wheat (T. aestivum) and rye (Secale cereale). The F1 of wheat x rye cross is normally completely sterile which upon doubling of chromosomes (spontaneous or induced) produces amphidiploid which is partially fertile. Wilson (1875) described the occurrence of the naturally occurring wheat-rye hybrid which, however, was sterile. It was described in 1890 (Zillinsky and Borlaug, 1971) that Rimpau found partially fertile triticale which resulted from the spontaneous doubling of chromosomes which could reproduce itself through seed. This primary triticale was shown by Muntzing (1939) to be octoploid (2n = 8x = 56) arising from hexaploid wheat (2n = 6x = 42) and rye (2n = 14). With the discovery of colchicines for chromosome doubling in 1937 (Eigsti, 1938) and development of embryo culture techniques in the 1940s the development of commercial triticale began.

Origin and Genetic Resources of Cereals

5.7

As the initial octopoloid triticale plants were partially sterile, had shrivelled grain and showed chromosomal irregularities such as aneuplody and meiotic disturbances this triticale plant had little commercial value although it had high degree of winter hardiness, ability to grow well on sandy and acidic soils and had large kennels. To overcome these problems hybridization and selection programme was initiated by Muntzing and now the best octoploid triticale is available which yields 90% of the bread wheat yield. To overcome the problem of meiotic instability hexaploid triticale (2n = 6x = 42) was synthesized which showed more vigor, higher tillering capacity and greater cytological stability but incomplete fertility remained a problem. This problem of incomplete fertility was solved by crossing octoploid with hexaploid triticale and then selection was practiced for higher fertility in the segregating generation population and this led to the development of a secondary hexaplod triticale as shown in Figure 5.3. A third class of triticale called secondary substitutional triticale (Muntzing, 1979) in which specific rye chromosomes are replaced by homoeologous chromosomes from the D genome of wheat. Continued research at the University of Manitoba resulted in the release of hexaploid triticale variety, Rosner, in Canada in 1969 and in 1968 CIMMYT, Mexico, developed a hexaploid triticale called Armadillo with improved fertility, test weight, better yield and good nutritional quality and one dwarfing gene and with the introduction of two gene dwarf (for increasing lodging resistance) secondary hexaploid triticale Cinnamon gave yield comparable with the best wheat yield during 1972-73. Further efforts directed towards broadening the genetic base of triticale, reducing seed shriveling and high fertility resulted in triticale lines showing yield as much as top wheat cultivars but then problems such as abnormal endosperm formation with an associated wrinkled coat, deep crease and a lackluster seed are still there and until these are solved the triticale may not be attractive to farmers.

5.4  RYE The cultivated rye (Secale cereale) with 2n = 2x = 14 is a diploid, cross-pollinated crop and is the most frost hardy of the cereals. It is grown for human food and as winter forage crop. It performs well on acidic soil and soil low in fertility and shows resistance to drought. It is more greatly adapted to a wide range of cool temperature conditions. Both winter and spring forms of rye exist. Although it is capable of producing a leavened flour product, rye bread is dark, heavy with distinctive nutty flavor and thus not preferred over wheat bread and its products. It lacks gluten, the protein which gives the dough of wheat elasticity. Its protein is of higher quality because it is rich in amino acid lysine. It contains pentosans which binds water during mixing to produce a dough suitable for backing. It can also be used for distillation of alcohols and adhesives. In northern Europe and Asia it is used as a bread grain. Rye seedlings can be distinguished from other cereal seedlings in that in case of former the sheath has a fine pubescence. Also the flag leaf is typically much smaller in case of rye and is less important as the photosynthetic source for grain sink development.

5.8

Crop Evolution and Genetic Resources

Fig. 5.3  showing development of man made crop, Triticale

The cultivated rye belongs to the genus, Secale L. which in turn consists of 4 to 12 species depending upon the criteria used for species definition. All species can be inter crossed and form at least partially fertile hybrids. Under natural conditions crossing between species occurs and hybrids can usually be found. The center of origin of rye is Anatolian plateau of Nothern Europe. The genus includes annuals, perennials, weedy species, inbreeders and outbreeders. S. cereale is normally cross pollinated crop but it responds quickly to selection for self-fertility. Annuals have fragile rachis and large seeds whereas the perennials have stiff rachis with small seeds. The growth habit, annual or perennial, is single gene controlled. Roshevitz (1947) recognized three major series of Secale. S. cereale and all weedy annual relatives constitute a series called Cerelia all

Origin and Genetic Resources of Cereals

5.9

members of which have three translocated chromosomes. All annual weedy types have the same chromosomal arrangement as S. cereale. S. montanum (outbreeder) and all perennial forms constitute a series called kuprijanovia, members of which are all identical with respect to translocated chromosomes. S. silvester (inbreeder) is having the same chromosomal arrangement as S.montanum (syn. S. strictum) and constitute the third series called S. silvestria. Stutz (1972) concluded from various studies (cytological, morphological, ecological) that the cultivated rye, Secale cereale, appeared to be originated from weedy products derived from introgression of S. montanum into S. vavilovii. S. vavilovii appears to have been derived from S. silvestre as a consequence of chromosomal translocations (Fig. 5.4) and S. silvestre was in turn derived from S. montanum or a common ancestor. S. cereale differs from S. montanum by two reciprocal translocations involving six of the 14 chromosomes (Riley, 1955). S. vavilovii is the only species having the cereal like chromosomal arrangement which is not associated with human agriculture. S. africanum, S. dalmaticum, S. ciliatoglume and S. kuprijanovii appeared to be only slightly modified populations of S. montanum. Further, populations of S. anatolicum are weedy forms of S. montanum and are genealogically and chromosomally distinct from the weedy annual forms of from which S. cereale arose. When the crosses, all species x S. cereale, produce F1s showing 7 IIs and the crosses, all species x S. montanum produce F1s showing a six chromosome translocation configuration it shows the species are all phylogenetically together but when the crosses, all species x S. cereale produce F1s showing translocation configuration and crosses, all species x S. montanum, producing F1s showing 7 IIs the species constitute a separate distinct phylogenetic group. Triticum, Secale and Aegilops constitute the secondary gene pool of rye (Secale cereale). Table 5.4  Showing species, ploidy level and distribution of rye Species

Distribution

Annual/Perennial

1. Annuals- Series- Cerelia Cultivated (CP)

a. S. cereale 1. S. afghanicum

Eastern Iran, Afghanistan

Weed

2. S. dighoricum

Nothern Ossena

Weed

3. S. segetale

Eastern Europe, Middle East

Weed

4. S. ancestrale

Southern Turkey

5. S. turkestanicum

Central Asia, Trans Caucacia

b. S. vavilovii

Lower slopes of Mt. Ararat and banks of Araxis river

Weed (often CP), drought resistant

c. S. silvestre (constitutes Series-S. sylvestria with S. montanum)

Central Hungary to Southern Russia

Weed SP

2. Perennials-Series-Kuprijanovia Contd...

Crop Evolution and Genetic Resources

5.10 Contd...



Species

Distribution

Annual/Perennial

a. S. montanum (constitutes Series S. sylvestria with S. sylvestre)

Morocco,Spain,Italy, Turkey, Iran, Iraq

1. S. dalmaticum

Jugoslavia

2. S. ciliatoglume

Turkey

Weedy

3. S. daralgesii

Armenia

Weedy

4. S. kuprijanivii

North Caucasus mountains

b. S. anatolicum

Turkey, Western Iran and Iraq

Weedy

c. S. africanum

South Africa

Self fertile

CP, large stature, frost resistance, larger seed

The GP1 for cultivated rye is its wild and weedy races.

5.5 RICE Rice (Oryza sativa) belongs to the family Gramineae. It is a diploid with 2n = 24 and is a self pollinated crop. The extent of out crossing ranges from none to 3% with an average of about 0.5%. It is a C3 crop and is a very important cereal in the tropical and subtropical regions of the world. It is grown in temperate areas as well. Rice flowers differ from other cereals in having six stamens instead of three. Rice can be classified as either nonglutinous (non-waxy) or glutinous (waxy). Starch of waxy rice contains little if any amylase. Low amylase content makes the grain cohesive or sticky when cooked. The genus Oryza contains two cultivated species–Oryza sativa, Asian cultivar and O. glaberrima, African cultivar and 21 wild species (Table 5.5). O. sativa is the most commonly and extensively cultivated species and further O. glaberrima is inferior to O. sativa in yielding ability and disease resistance and so the majority of the reseach is directed towards O. sativa. O. rufipogon the wild and weedy species constitutes the GP1B of Asian rice, O. sativa. O. barthii and O. stapfii constitute the GP1B of African rice, O. glaberrima. The genus Oryza contains annuals, perennials, diploids and tetraploids. Eight genomes, A, B, C, E, F, G, H and J have been identified. The GP1 includes O. rufipogon, O.nivara, O. glampatula, O. meridionalis, O. breviligulata, O. longistaminata and the two cultivated species. The species comprising O. officinalis complex constitute the GP2 and the species belonging to O. meyeriana, O. ridleyi and O. schlechteri complexes constitute the GP3. The two cultivated rice had common ancestor or progenitor and they followed the following path.

Wild perennial  Æ  Wild annual  Æ  Cultivated annual.

The genus Oryza originated in the Gondwana land continent (the super continent which fractured into Africa, South America, Asia, Australia and Antarctica), from the unknown common ancestor which may not now exist. The Asian common rice, O. sativa evolved from wild annual, O. nivara which in turn evolved from wild perennial, O. rufipogon. The center of origin of O. sativa is South China to East India. Similarly,

Origin and Genetic Resources of Cereals

5.11

Fig. 5.4  Showing evolution of rye

African rice, O. glaberrima evolved from wild annual O. breviligulata which in turn evolved from O. longistamoinata. The center of origin of O. glaberrima is West African savanna. The weed races of Asia and Africa are designated as spontanea and Stapfi forms of O. sativa and O. glaberrima, respectively (Fig. 5.4). O. rufipogon is found in swamp land and have prostrate and floating habit, have awns, largely asexually propogated, weakly rhizomatous and found in India, China, Indonesia and New Guinea. O. nivara is semi erect, seed propogated and without rhizomes. As O. sativa has wide distribution and wide adaptation Kato et al. (1928) classified it into two varietal groups (biotypes or ecogeographical races, ecospecies) namely indica and japonica (also sinica or keng) and Morianga (1954) added a third group which he called javanica to include bulu and gundil varieties of Indonesia. Indicas have tall plants, weak straw, photoperiod sensitivity, easy shattering, broad drooping leaves and grain dormancy and has world wide distribution. Japoincas have more leaves, and few tillers in comparison to indica, resistant to shattering, short broad grains with low amylase content. Javanicas are morphologically similar to japonicas except for wider and more pubescent leaves and a beard or hair like awn. The indica and japonica biotypes are of interest because of their contrasting

Crop Evolution and Genetic Resources

5.12

characters. Hill rices of South east Asia and South east India are the prime stock of all the three biotypes, i.e. indica, japonica and javanica (Fig. 5.5). Glaszmann (1987) observed javanica varieties falling within the japonica group and so are now classified as tropical japonica and the so-called typical japonica is referred to as temperate japonica. Indicas were probably domesticated in the foot hills of Himalayas and in eastern India and japonica in south China or northern Thailand. Both Indicas and japonica rices had polyphyletic origin. Aus, the short duration drought tolerant upland rice and japonica types were derived directly from O. nivara whereas aman type is a product of introgression. Figure 5.6 shows origin of ecotypes of Oryza sativa. A classification study based on isozyme analysis by Glaszmann (1987) showed formation of six distinct groups which corresponded with indica, japonica and javanica, Aus, Ashimas and Rayadas (deep water or floating rices of Bangladesh and India), aromatic rices of Indian subcontinent including basmati considering the morphological characteristics. The center of diversity of aromatic rices are the foot hills of Himalayas (the Indian states of U.P. and Bihar and Tarai region of Nepal). There is varied and complex cross fertility and chromosome pairing among the wild, weed and cultivated races and thus Harlan and De wet (1971) proposed classification of wild relatives of a crop species does not work. The principal barriers to gene flow between wild and cultivated species have been hybrid sterility, non-viability or weakness and some of these barriers are controlled by complementary or duplicate genes. Indica x O. spontaneum, wild annual cross is the source of cytoplasmic male sterility. CMS WA (wild abortive) in rice was introduced into Indica rice varieties from male sterile plant obtained from wild rice, O. rufipogan. Gondwana land Common ancestor Tropical africa

South and south east asia WP

Rufipogon AA

Weedy annuals

I I

Longistaminata A A

Spontanea WA

Sativa A

CA

g g

Nivara AA Stapfii

Barthii A A (formerly called O. breviligulata)

g g

Glaberrima A A

Indica Japonica Temperate Tropical

Introgressive hybridization

Fig. 5.5  Evolutionary pathway of two cultivated species of Rice (Chang, 1976c). WP = wild, perennial; WA = wild, annual

Origin and Genetic Resources of Cereals

5.13

CMS-BoroII was developed from a wide cross involving Chinsurah BoroII (O. sativa subsp. Indica) and nucleus of Taichung 65 (subsp japonica). Rice can be taken thrice a year. Although a kharif crop, summer rice (March transplanting) can be taken. Further, ratoon crop of rice can also be taken. This ratoon crop requires management of insect-pests. Table 5.5  Showing species, chromosome number, genome designation and distribution of rice Species

2n

Genome

Distribution

O. sativa

24

AA

Worldwide, cultivated

O. nivara

24

AA

Tropical and subtropical Asia, Source of gene for grassy stunt viries

O. rufipogon

24

AA

Tropical and subtropical Asia, Res. to BLB

O. breviligulata

24

AgAg

Africa

24

g g

West Africa, cultivated

g g

O. sativa complex (GP1)

O. glaberrima

AA

O. longistaminata

24

AA

Africa

O. meridionalis

24

AmAm

Tropical Australia, drought resistance

O. glumaipatula

24

O. officinalis complex

24

O. punctata

gp gp

A A

South and Central America, Deep water

24 48

BB BBCC

Africa

O. minuta

48

BBCC

Philippines and Papua New Guinea

O. officinalis

24

CC

Tropical and subtropical Asia, tropical Asia

O. rhizomatis

24

CC

Srilanka

O. eichingeri

24

CC

O. latifolia

48

CCDD

South and Central America

O. alta

48

CCDD

South and Central America

O. grandiglumis

48

CCDD

South and Central America

O. australensis

24

EE

Tropical Australia

O. brachyantha

24

FF

Africa, source of gene for res. to stem borer

O. granulata

24

GG

South and Southeast Asia

O. meyeriana

24

GG

South and Southeast Asia

O. longiglumis

48

HHJJ

Iran, Java, Indonesia and Papua New Guinea, Res. to blast

O. ridleyi

48

HHJJ

South Asia

South Asia and East Africa

O. meyerianacomplex

O. ridleyi complex

Unknown genome O. schlechteri

48

unknown

Papua New Guinea

O. barthii

24

AgAg

Africa

5.14

Crop Evolution and Genetic Resources

Fig. 5.6  Figure showing origin of ecotypes of O. sativa

5.6  OAT Oat (Avena sativa) is used as breakfast cereal and feed for animal especially horses. Rolled oats and oat meal are used as breakfast cereal. Seeds contain relatively high protein and fat contents. There is presence of husk with higher fiber content which reduces the feeding value of oats as compared with other cereals. Fodder is of higher quality because of high digestible crude fiber content. It is primarily a self pollinated crop and cross pollination seldom exceeds 0.5-1.0% and it is through wind (anemophily). The two cultivated forms of oat are: Avena sativa, the white common oat grown primarily in temperate regions of the world and A. byzantina, the common red oat grown in warmer climate as winter season oat and both are hexaploid (2n = 6x = 42). The genus Avena comprises 19 species which includes 10 diploids, 5 tetraploids and 4 hexaploids (Table 5.6) (Rajhathy and Thomas, 1974). There are four distinct genomes (A, B, C, D). The center of origin is Mediterranean and the wild species are found in Asia minor to the eastern Mediterranean. A. nuda is a hull less or naked oat called groat. The two wild oat species A. sterilis and A. fatua readily cross with cultivated oat species, produces fertile progeny and are mostly used in the improvement of the cultivated oat. A. fatua is the source of gene for shattering resistance, dormancy, earliness, cold hardiness, short plant height, resistance to barley yellow dwarf virus and powdery mildew. A. sterilis is the source of genes for disease and insect resistance and high protein content in groat (caryopsis). The tetraploid species, A. barbata is the source of gene for oat stem rust resistance. The diploid A. strigosa is the source of crown rust resistance and A. hirtula is the source for powdery mildew (Erysiphe graminis avenae). A. sativa originated from A. byzantina and all other oats originated from A. sterilis (Fig. 5.7). The genus Avena consists of diploid (2n = 14 chromosomes, A and C, genomes), disomic tetraploid (2n = 4x = 28 chromosomes, AB and AC genomes) and disomic hexaploid (2n = 6x = 42 chromosome, ACD genomes). Thus, B and D genomes are present only in tetraploid and hexaploid species. Primary gene pool consists of hexaploid

Origin and Genetic Resources of Cereals

5.15

species with ACD genomes. Secondary gene pool consists of tetraploid species with AC and AB genomes, respectively and tertiary gene pool consists of diploid species with A and C genome, respectively. Tetraploid species, A. barbata, A. vaviloviana and A. abyssinica are thought to have evolved from duplication of A. hirtula or A. wiestii (As genome). A. agardiriana is through to have evolved as a result of duplication and translocation from A. canariensis. Table 5.6  Showing species, ploidy level, genome and gene pool of oat Species Hexaploids A. sativa A. byzantina A. nuda A. sterilis A. fatua Tetraploids A. abysinica A. barbata A. murphyi A. magna A. vaviloviana A. insularis A. maroccana Diploids

Genome AACCDD -

Gene pool CULTIVATED Wild GP1B Wild, weed, GP1B

AABB AABB AACC AACC AABB AACC AACC

Cultivated Wild GP1B Wild C&W

A. pillosa A. ventricosa A. strigosa A. hirtula A.claride A. clauda

CC CvCv AsAs ApAp CC CpCp

W W C, GP1B W, GP1B W w

A. canariensis

ACAC

W

A. weistii A. longiglumis A. eriantha A. brevis A. lusitanica A. matritensis A. altantica

Ploidy level 2n – 6x – 42

Nothern Europe

2n – 4x – 28 Ethiopia

2n – 2x – 14

14, 28

AsAs

14 14

A1A1 CpCp As As As As

A. damascena

Ad

A. prostrata

Ap

A. ludoviciana

Distribution

Mediterranean

5.16

Crop Evolution and Genetic Resources

Fig. 5.7  Showing evolution of oat

Fig. 5.8  A comparison (left to right) of the inflorescences of rice, oats, barley, wheat and rye



Figure 5.8 shows inflorescens of wheat, rice, oat, barley and rye.

Origin and Genetic Resources of Cereals

5.17

5.7  MAIZE Maize or corn (Zea mays) is the most important cereal food in Mexico, central America and South America. It is a diploid with 2n = 20. It is a cross pollinated crop with 95% or more cross pollination (by a mechanism, called protandry). Pollination is effected by wind and thus resulting in both self-and cross-fertilization. It is monoecious and is a C4 plant. It exhibits xenia (the immediate observable effect of foreign pollen on the maternal endosperm tissue). There are five types of maize depending upon physical appearance (endosperm composition). Dent  It is characterized by a depression or dent in the crown of the seed, sides of seeds have a corneous starch while soft starch extends to the top of the seed. Rapid drying and shrinkage of the soft starch result in characteristic denting. Flint  Kernels are hard, smooth and contain little soft starch. The relative amounts of soft and corneous starch vary in different varieties. Sweet corn  Kernels are wrinkled when dry, translucent, brittle, horny appearance when immature. It differs from dent by only one recessive gene which prevents conversion of sugar to starch. The dominant starchy allele (Su) changes recessive sugary (su) locus. Field or dent or other types of corn are homozygous for this dominant starchy allele (SuSu). In the sweet corn there is homozygosity for the recessive allele (susu). The uniqueness with sweet corn is the accumulation of sugar and water soluble polysaccharides (glucose) in the endosperm. Total sugar per cent in starchy corn is 17.6% whereas in sweet corn it is 25% or more. Sucrose percent in sweet corn is 15.4% when it is only 8.2% in starchy corn. Glucose is not present in normal maize. Starch (amylase and amylopectin) is much lower in sweet corn. Flour maize  Kernels are composed largely of soft starch but have little or no dent. Pop corn  It is an extreme form of flint with endosperm containing only a small portion of soft starch. The ability to pop seems to be controlled by the relative proportion of horny endosperm where the starch grains are embedded in a tough elastic colloidal material which confines and resists the steam pressure generated within the granules upon heating until it explodes with force. Figure 5.9 shows different types of maize. Waxy corn  It contains waxy kernels, starch is gummy and used for adhesive, gums, paper sizing and puddings. Corn with increased amylase is used for various commercial products. Waxy starch is composed entirely of branched chain of amylopectin from which starch is made. Common maize consists of 78% amylopectin and 22% amylose (straight chain fatty acid). Pod corn  Here each kernel is enclosed in a pod or husk. Ear is also enclosed in husks. Pod corn is cultivated or grown commercially. Baby corn  Baby corn is a small ear which is harvested either before or just at the silk emergence stage (in just 50-60 days). The dehusked ear can be used as salad, chopsuay, soup, can be mixed with other vegetables, pickle, and can be canned. It has got better nutritional quality in comparison with some other vegetables.

5.18

Crop Evolution and Genetic Resources

Maize belongs to the tribe, Maydae (also called Tripsaceae) which includes eight genera. The three genera, Zea, Tripsacum and Teosinte are American or New world genera. Zea and Teosinte have now been merged and called Zea and thus there are only two New world genera. The genus Zea contains four species, corn (Zea mays), annual diploid teosinte, Zea mexicana, Zea perennis (perennial tetraploid), Zea diploperennis (perennial diploid) and Z. mays ssp. parviglumis(annual) (Table 5.7). Teosinte is the common name for a group of 4 annual and perennial species. Teosinte (wild, annual, diploid) is native to Mexico and Guatamala. Teosinte crosses readily with corn to produce fertile hybrids. It differs from corn in that pistillate spikes bear 6-12 kernels in hard, triangular shell like structures. The seeds break apart and shatter when mature-a means of natural seed dispersal. The genus Zea is characterized by male terminal inflorescences with paired staminate spikelets and lateral female inflorescences with single or paired pistillate spikelets. Modern maize is either of hybrid origin or that it is a derivative of Teosinte. The genus Tripsacum is a close relative of Zea. It has more diverse and wider habitat than teosinte. In Tripsacum each seed is enclosed by a horny covering but seeds are not covered by leaves or husks as for maize or Teosinte (Fig. 5.10). The genus Tripsacum is characterized by bisexual terminal and lateral inflorescences. There are five diploid (2n = 2x = 36) and four tetraploids (2n = 4x = 72) and all are perennial (Table 5.7). They are found growing in Mexico, Central America and SE. USA. Tripsacum has been suggested as a potential donor of genes for disease and insect resistance. The five genera belong to Oriental maydae or Asiatic maydae and are native to Asia. Oriental maydae have no immediate bearing on the origin of corn but there appears some involvement of Coix in the origin of corn. Hybridization between species  Annual Teosinte and maize have the same chromosome number, 2n = 20. Maize and Teosinte cross readily and produce fertile offspring. Z. mexicana (Teosinte) is the GP1B of the cultivated maize, Zea mays. Wild Teosinte and corn show reciprocal introgression. The basic genomes of maize and annual Teosinte are essentially homologous. Chromosomes of Teosinte resemble those of maize but tend to have more knob-like structures than those of maize and cytologically similar with essentially the same frequency of crossing over in the region tested except for the short arm of chromosome 9 (Beadle, 1932). Annual teosinte plant resembles maize but have several tillers/plant. Maize and its closest wild relative Teosinte differ strikingly in the morphology of their female inflorescence or ears (Fig. 5.11). Ears are smaller and have 5 o 6 seeds/ row and 2 rows per ear. The cross between maize and Tripsacum produces F1 which is male sterile. Tripsacum species and Z. perennes constitute the GP2 of the cultivated maize. Teosinte and Z. perennis are reproductively isolated from Tripsacum and hybrid between Teosinte and Tripsacum has not been obtained so far. Out of the five Asiatic genera Coix is the only genus that has been successfully crossed with maize. Maize has been crossed with sugarcane. Sugarcane crosses with a number of grasses. Origin of maize  There are two possible centres of origin of corn: I. The high land of Peru, Equador and Bolivia and II. The region of Southern Mexico and Central America.

Origin and Genetic Resources of Cereals

5.19

There are four hypotheses regarding origin of maize. 1. Maize, Teosinte, Tripsacum and perhaps some of the Andropogoneae originated from a common but now extinct ancestor native to Mexico or Guatamala (Weatherwax, 1955). 2. Maize originated from a cross between two species, probably Coix (2n = 10) and sorghum (2n = 10) (Anderson, 1945). It was proposed that maize (n = 10) is an ancient tetraploid which arose through the combination of genomes from two n = 5 ancestral species (Rhoades, 1951). 3. Tripartite hypothesis  Mangelsdorf and Reeve (1939) proposed that: (i) Cultivated maize originated from a wild form of pod corn indigenous to the low lands of S. America. Pure pod corn plant differs from ordinary maize by only one gene. (ii) Euchlaena (Teosinte) is a natural hybrid between Zea and Tripsacum that naturally occurred after cultivated maize had been introduced by man into Central America. This hypothesis was later rejected by Mangelsdorf (1974). (iii) The majority of the Central and north American varieties originated from the cross, maize and Tripsacum or Teosinte. Mangelsdorf (1950) suggested the role of four main evolutionary factors in the evolution of modern maize such as natural selection, mutation (from more or less extreme forms of pod corn occurred (wild or primitive type of maize), hybridization with Teosinte (gene introgression from Teosinte) and crossing of varieties and races. Weatherwax and Randolph (1955) stated that there is no support from cytogenetics or cytotaxonomy for the following hypotheses that maize is 1. a hybrid of teosinte and some unknown member of the Andropogoneae (Collins, 1912, Harshberger, 1893) 2. an amphidiploid hybrid of Asiatic species belonging to the Maydae and Andropogoneae 3. a trigenic hybrid of pod corn, Euchlaena and Tripsacum (Brieger, 1944) and 4. a product of the hybridizarion of a South American derivative of pod corn and Central American Tripsacum with Teosinte as a by-product (Mangelsdorf and Reeves, 1939). On the contrary the cytological evidences support the hypotheses that Zea, Euchlaena and Tripsacum originated separately from a common ancestral form (Montogomery, 1906, Weatherwax, 1918, 1935) and that Zea was derived from Euchlaena by mutation (Ascherson, 1880, Langham, 1940 and Longley, 1941b). 4. Teosinte hypothesis  Considering all the evidences Galinat (1977) concluded that two alternatives exist regarding the origin of maize. (i) Either the present day Teosinte is the wild ancestor of the maize (Beadle, 1939, 1972, 1978) or a primitive teosinte is the common wild ancestor of both maize and teosinte. (ii) A form of pod corn now extinct was the ancestor of maize with Teosinte being a mutant of this pod form. Some varieties of teosinte are cytologically indistinguishable from maize and capable of forming fully fertile hybrids with maize. Molecular analysis has identified one form of Teosinte (Z. mays ssp. parviglumis) as the direct progenitor of maize (Doebley, 2004).

Crop Evolution and Genetic Resources

5.20 Table 5.7  Showing species, ploidy level and distribution of maize Genus

Chromosome number

Annual(A) Perennial(P)

Gene pool

New world (Meso-american origin), North and South America

Genus-Zea

Zea mays (Indian corn or maize)

Distribution

20

A

Z. mexicana (or Euchlaena mexicana)

20

A

Z. diploperennis

20

P

Z. luxurians

20

A

Z. perennis

40

P

Z. mays ssp. Parviglumis (or Balas teosinte)

20

A

Genus-Teosinte GP1 (wild and weedy race)

GP2

Genus-Tripsacum (or gamma grass)

GP2

T. dactyloides

2n – 36,54,72

P, Rhizomatous (R)

T. floridanum

36

P,R

T. lanceolatum

72

P,R

T. pilosum

72

P,R

T. zopilotense

36

P,R

T. andersonii

64

P,R

T. bravum

36

P,R

T. maizar

36

P,R

T. laxum

36

P, R

T. australe

36

P, R

T. latifolium

72

P, R Asiatic origin India to Burma through the East Indies and into Australia

Oriental maydeae or Asiatic maydeae Genera-Chionanchne -Coix (Job’s tears)

2n – 20 10,20,40

-Polytoca

40

-Sclerachne

20

-Trilobachne

?

GP2

Origin and Genetic Resources of Cereals

5.21

Endosperm types

Soft starch Hard starch Sugary

Fig. 5.9  Major types of modern maize. Left to right: popcorn, sweet corn, flint maize, flour maize, and dent maize. Endosperm types are depicted below each ear. (Adapted from H.G, Baker, 1970)

Fig. 5.10  Grain-bearing inflorescences of maize and its relatives. Left to right: tripsacum dactyloides, Zes mexicana and zea mays.

Crop Evolution and Genetic Resources

5.22 MI PLB

PLI

SLI

PLI

SLI

Teosinte

Maize

Fig. 5.11  Differences in fruiting structure of maize and teosinte. Note that tassels and ears are on the same fruiting stalk of teosinte, while on maize they are segregated on different spikes. MI, main inflorescence; PLI, primary lateral inflorescence; SLI, secondary lateral inflorescence; PLB, primary lateral brach. (Used with permission from J. Doebley et al., 1990)

5.8  SORGHUM Sorghum (S. bicolor) is a diploid with 2n = 2x = 20. It is a self pollinated crop but the amount of cross pollination averages 6% in sorghum but it may be as high as 30% in Sudan grass. The grain does not contain any gluten and so it can not be used to prepare bread. The sorghums have been classified into four agronomic groups. 1. Grain sorghum is used for human food and feed. 2. Sweet sorghum or sorgo is grown as forage and for animal feed, has sweet juicy stalk which contains 16 to 17% sugar. It can be used for production of syrup or molasses. 3. Grass sorghum is grown for pasture or hay and silage. It includes S. sudanansis, the annual sudan grass and S. halepense, the perennial tetraploid Johnson grass. 4. Special purpose type sorghum which includes broomcorn for making brooms, pop sorghum and waxy sorghum. Thus sorghum can be grown for grains, fodder, syrup, alcohol and fuel. Seed of sorghum often contains no gluten and hence it is not suitable for bred making. It is a C4 plant with resistance to drought. The center of origin of sorghum is Africa Savanna zones of Sudan-Chad) and maximum diversity is found in Ethiopia and adjacent areas of East Africa. Snowden (1936) classified the cultivated sorghum into 31 species (Table 5.8) even though all species readily intercross. Within the grain sorghum Harlan and de wet (1972) recognized 15 races of S. bicolor, 5 primary races (bicolor (B), guinea (G), caudatum (C), kafir (K) and durra (D)) on the basis of spikelet morphlogy within the panicle types and 10 intermediate races namely G-B, C-B, K-B, D-B, G-C, G-K, G-D, K-C, D-C, K-D, originating from the 10 possible hybrid combinations among the primary races. The characteristic features of the five races are as follows.

Origin and Genetic Resources of Cereals

5.23

In caudatum the grain is flattened at the lower side. When the grain is flattened on both sides and twisted between the glumes it is guinea. Elongated seed with long glume is bicolor. If the seed is broadest above the middle and glumes very wide and thus texture of tip of the seed is different from the base, it is durra. The wild type has small grain, linear oblong, completely covered by glumes, symmetrical dorso-ventrally, racemes fragile and spikelts deciduous. Shattercane is similar to wild type but grains are larger and rounder occasionally slightly exposed at the tips. In case of kafir the seed is spherical. Each of the main races of sorghum appears to be associated with one or other of the wild species. The grain sorghums have been classified into seven groups. Milo  It is recognized by compact head borne on a curved peduncle, large yellow or white seed, stalks are slender, dry, pithy and tiller considerably. It is more tolerant to heat and drought in comparison to kafir and is the source of cytoplasmic male sterility. It is found in east-central Africa. Kafir  Grown in South Africa. It is having strong stout stalks, juicy and moderately sweet, heads cylindrical and borne erect, seeds are of medium size, white, pink or red. It is the source of fertility restorer gene. Hegari  Distributed in Sudan. It is abundantly leafedbut less tiller, more nearly oval heads, sweeter juice, seeds are more chalky white in appearance than kafir. Table 5.8  Showing species, races, distribution and gene pool in sorghum Species

Genome

Gene pool

Distribution

Chomosome number

Cultivated

Cultivated races S. bicolor ssp. bicolor Basic races- bicolor

B

-

Africa

Guinea

G

-

WAfrica, Malavi,Tanzania, India

Caudatum

C

-

Eastern Nigeria to eastern Sudan, Uganda

Kafir

K

-

East Africa, Southern Africa

durra

D

-

Ethiopia, zones of Africa, near Sahara, India

Spontaneous races S. bicolor ssp. arundinaceum arundinaceum

Wild and weedy races GP1B

Aethiopicum

-

Virgatum

-

Verticilliflorum

-

Propinquum

-

Tropical Africa

2n = 2x = 20

Asia, Indonesia, Philippines

2n = 2x = 20 Contd...

Crop Evolution and Genetic Resources

5.24 Contd...

Species Shattercane S. aterrimum

Genome

Gene pool

Distribution

Chomosome number

Shattercane

S. drummondii

-

S. nitens

-

S. margaritiferum

G

S. guineese

G

S. mellitum

G-B

S. conspicum

G

S. roxburghii

G-K

S. gambicum

G

S. exsertum

B

S. basutorum

K-B

S. nervosum

B,C-B,K-B

S. melaleucum

G-B

S. ankolib

D-B

S. splendidum

B

S. dochna

B

S. bicolor

B

S. miliforme

K-B

S. simulans

K-B

S. elegans

G-C,K-B

S. notabile

G-C,C-B

S. coriaceum

K

S. caffrorum

K

S.nigricans

K-C,C

S. caudatum

C,G-C,D-C

S. dulucicaule

G-C

S. rigidum

D-B

S. durra

D

S. cernum

D

S. subglabrescens

D-B

Cultivated

Contd...

Origin and Genetic Resources of Cereals

5.25

Contd...

Species

Genome

S. membranaceum

Various

Gene pool

Distribution

Chomosome number

GP2 S. halepense

2n = 2x = 40

S. alum S. propinquum GP3 Saccharum Zea Sorghastrum Miscanthus

Ferreta  Head is compact, have few leaves and borne erect, seeds are large, white and chalky and tend to shatter. It is found in Sudan. Durras  Have bearded, fuzzy heads, large flat seeds and dry stalks, found in North Africa, Southern Europe, The Near East and Middle East. Shallu  Shallu from India has tall, slender and dry stalk, loose open head, pearly white seeds. Kaoliang  Kaoliang from China, Japan, Korea has tall, dry, woody stalk and bitter brown seeds. Most of the sorghum hybrid programme are based on crosses involving milo and kafir and occasionally involve other groups. Sorghum belongs to tribe Andropogoneae and subtribe, Sorghastra and genus, Sorghum and section Eu-sorghum (Sorghum). The section sorghum is divided into two subsections. 1. Halepensia which includes perennial, rhizomatous wild grasses and 2. Arundinacea which includes annual or perennial wild grasses or cultivated sorghum, without rhizomes (Clayton, 1961). S. halepense (2n = 4x = 40) is a tetraploid rhizomatous species indigenous to western Asia and northern Africa. The diploid Eu-sorghum (2n = 20) spread along southern Africa to India and differentiated into S. arundinaceum, wild diploid (2n = 20) occur in Africa and S. propinquum (2n = 20), rhizomatous and a member of Halepensia, in South east Asia and possibly in India they hybridized and chromosome number doubled and this led to the development of tetraploid species, S. halepense (Johnson grass) with 2n = 4x = 40. This S. halepense was taken to America and there it got crossed with cultivated sorghum, S. bicolor and thus evolved S. almum, the columbus grass (Endrizzi, 1957). Cultivated sorghum (S. bicolor) probably originated from S. bicolor ssp. arundinaceum through human selection for non-shattering heads, large seeds and heads, threshability and suitable maturities (Doggett, 1976). Cultivated sorghum in cross with S. arudinaceum produces fully fertile F1. Also cultivated sorghum hybridizes with S. propinquum. Introgression of S. arundinaceum

5.26

Crop Evolution and Genetic Resources

with S. propinquum—a wild rhizomatous species with small hard seeds, present in S.E. Asia contributed to the development of kaoliang sorghums of China. The GP1 includes 28 cultivated species, 11 wild and 3 weedy species. GP2 includes S. halepense with its tetraploid races, the perennial wild grass and GP3 includes Saccharum, Zea, Sorghastrum and Miscanthus, et alia.

Speciality/Fodder Sorghum Sweet sorghum varieties are primarily used for foliage and syrup production from which ethanol can be made. These varieties are taller than grain sorghum plant and having Brix value of 16%. Makkhan grass is an annual, multicut, tetraploid sorghum. 13 to 15 mt can be obtained per cut per care at 30 days.

5.9  BARLEY Barley (Hordeum vulgare) is a diploid with 2n = 2x = 14 and belongs to the family, Poaceae. It is an annual cereal, resistant to salt and adapted to wide range of conditions in the cool temperate zone. Grain is used as human food, livestock feed and for malt production. Like wheat it is mostly a self-pollinated crop but cross pollination is normally around 0.5-1% (Allard, 1988). The genus Hordeum comprises about 30 species (Bothmer et al., 1981) and among the wild species are diploids, tetraploids , hexaploids, annuals, perennials, self pollinator and cross pollinator (Lundqvist, 1962). Annuals are mostly inbreeders whereas H.bulbosum and H. brevisublatum are perennial and are specialized outbreeders with two locus self incompatibility system (Lundqvist, 1962). In barley the inflorescense is a spike and at each node of rachis (the main axis of the spike) there are three spikelets, each containing one floret. If all are fertile there will be three rows of grain on each side of the rachis and this form of barley is called a six rowed barley. In the two rowed barley only the middle spikelet contains grain and thus there is one row of grain on each side of the rachis. Some barley are nacked or husk less and in this form of barley the caryopsis is enveloped by lemma and palea. The center of origin of barley is Middle east and the secondary center of origin is Ethopia. H. vulgare and H. bulbosum are considered to share common basic genome. The immediate progenitor of H. vulgare ssp.vulgare is the two rowed form H. vulgare ssp. spontaneum (also a source of cytoplasmic male sterility). Only a few recessive alleles separate the cultivated H. vulgare ssp. vulgare from wild H. vulgare ssp. spontaneum (Nilen, 1971). I. The wild forms have spikes that shatter easily at maturity while the cultivated carry a recessive allele (Bt1) that produces a much tougher spike II. The domesticated forms have six-rather than two-row glumes due to a single recessive mutation (vv) and III. the wild forms have tight glumes (difficult to thresh) whereas the cultivated forms have a recessive gene (n) that permit the husks to be easily removed. Relatively large chromosomes of barley allow detection of several kinds of chromosome aberration such as change in chromosome number and structure and numerous easily

Origin and Genetic Resources of Cereals

5.27

classified characters but it lacks distinct landmarks particularly heterochromatic segments. Haploids can be produced using the wild cross-pollinated barley species, H. bulbosum for producing haploids in common barley, H. vulgare (Kasha and Kao, 1970). H. spontaneum is the GP1B of the cultivated barley and is H. bulbosum the only one GP2 species. Table 5.9  Showing species, ploidy level, distribution and gene pool in barley Species

Ploidy level

Distribution

Annual/perennial

Gene pool

H. vulgare subsp. Vulgare

2x, 4x

Cultivated

A

GP1

Subsp. Spontaneum

2x

SW Asia, Israel

A

GP-1B

H. bulbosum

2x, 4x

Mediterranean

P

GP2

H. murinum subsp. murinum

4x

-

A

Subsp. glacum

2x

-

A

Subsp. leporinum

4x, 6x

-

A

H. marinum subsp. marinum

2x

-

A

Subsp. gussoneanum

2x, 4x

-

A

H.muticum

2x

South America

P

GP3

H. cordobense

2x

-

P

GP3

H. chilense

2x

-

P

GP3

H. stenostachys

2x

-

P

GP3

H. erectifolium

2x

-

P

GP3

H. flexuosum

2x

-

P

GP3

H. euclastom

2x

-

A

GP3

H. intercedens

2x

W USA

A

GP3

H. pusillum

2x

North America

A

GP3

H. jubatum

4x

NA-EAsia

P

GP3

H. comosum

2x

South America

P

GP3

H. pubiflorum

2x

-

P

GP3

H. lecheri

6x

-

P

GP3

H. procerum

6x

-

P

GP3

H. arizonicum

6x

SW USA

A/P

GP3

H. secalinum

4x

Europe-NAfrica

P

GP3 Contd...

Crop Evolution and Genetic Resources

5.28 Contd...

Species

Ploidy level

Distribution

Annual/perennial

Gene pool

H. bogdanii

2x

Central Asia

P

GP3

H. roseviitzii

2x

-

P

GP3

H. brevisubalatum

2x, 4x

EAsia

P

GP3

Subsp. Violaceum

2x, 4x

SW Asia

P

GP3

Subsp. Turkestanicum

6x

Central Asia

P

GP3

Subsp. Nevskianum

4x

-

P

H. iranicum

6x

WAsia

P

GP3

H. brachyantherum

4x, 6x

WNAmerica-EAsia

P

GP3

H. californicum

2x

W USA

P

GP3

H. depressum

4x

-

A

GP3

H. guatemalense

4x

Central America

P

GP3

H. capense

4x

South Africa

P

GP3

H. parodii

6x

South America

P

GP3

H. tetraploidum

4x

-

P

GP3

H. fuegianum

4x

-

P

GP3

H. patagonicum

2x

-

P

GP3

Subsp. Mustersii

2x

-

P

GP3

Subsp. Santacruscense

2x

-

P

GP3

Subsp. Setifolium

2x

-

P

GP3

Subsp. magellanicum

2x

-

P

GP3

5.10  MILLETS Pearl millet (Pennisetum americanum) is an excellent food and forage crop. This crop tolerates low fertility and low soil pH and is a C4 crop. It is a diploid with 2n = 14 and is a cross pollinated crop. The amount of cross-pollination is about 69-82% and is through wind (anemophily). One inflorescence can produce 1000 seeds or more and a plant can produce 25 or more inflorescence and the flower is prominently protogyous. The center of origin of pearl millet is Africa (Sahelian zone from western Sudan to Senegal) (Harlan, 1975). The cultivated pearl millet, P. americanum is synonymous with P. typhoides, P. spicatum, P. glaucum. Pennisetum is a genus with over 140 species (Brunken, 1977). Pennisetum genus is divided into five sections and Pennisetum americanum

Origin and Genetic Resources of Cereals

5.29

belongs to Penicillaria section (Stapf and Hubbard, 1934). Brunken (1977) merged all annual Penicillaris with pearl millet, P. typhoides and called P. americanum. The Pennisetum genus has species with x = 5, 7, 8 and 9 and thus it contains species ranging from 2n = 10 to 2n = 72. Both sexual and apomictic species as well as annual and perennial species are included in the genus Pennisetum. P. americanum subspecies americanum includes all the cultivated races of pearl millet, subspecies mondii contains wild, semiwild, grassy and weedy races of pearl millet and subspecies stenostachyum which is morphologically intermediate between subspecies americanum and mondii and includes all mimetic weeds associated with the cultivation of pearl millet (Table 5.10). Table 5.10  Showing species, ploidy level and gene pool in bajra Species

Ploidy level

Gene pool

P. americanum

14

Cultivated

Subsp. Mondii

14

GP1

Subsp. Stenostachyum

14

GP1

Schmeinfurthii

14

GP3

P. purpureum

28

GP2

P. ramosum

10

GP3

P. massaicum

16, 32

GP3

P. alopecuroides

18

-

P. atrichum

36

-

P. bambusiforme

36

-

P. basedowii

54

-

P. cattabasis

18

-

P. clandestinum

36

-

P. distachyum

36

-

P. divisum

36

-

P. flaccidum

18, 36

-

P. fruescens

63

-

P. hohenackeri

18

-

P. lanatum

18

-

P. latefolium

36

-

P. macrostacyum

54

-

P. macrourum

36

-

P. nervosum

36

-

P. nodiflorum

18

-

P. nitarisii

36,54

-

P. orientale

18,36,54

Contd...

Crop Evolution and Genetic Resources

5.30 Contd...

Species

Ploidy level

Gene pool

P. pedicellatum

36,54

-

P. ploystacyon

36,54

--

P. pseudotrilicoides

18

-

P. setaceum

27

-

P. schimpeii

18

-

P. setosum

54

-

P. squamulatum

54

-

P. subangustum

36,54

-

P. tempisquense

72

-

P. thunbergii

18

-

P. trisetum

36

-

P. villosum

18,36

GP3

54 P. violaceum

GP1

Pearl millet has AA genome and P. purpureum or napier grass has A¢A¢BB and thus has the A genome in common with pearl millet. Most of the forage characteristics such as vigorous growth, forage yield potential appear to be on B genome and B genome is dominant over A¢ genome. A genome determines inflorescence type, plant type, maturity and fertility restoration.The most closest related species to pearl millet is napier grass, Pennisetum americanum (2n = 2x = 14), rhizomatous, perennial and native to tropical Africa. The GP1 includes subspecies mondii and subspecies stenostachum and P. purpureum constitutes the GP2 and the rest of the species constitute GP3 which includes both sexual and apomictic species, both diploids and polyploids, annual, perennial, rhizomatous and non-rhizomatous and are the sources of apomixes gene, drought tolerance, cold tolerance, pest resistance and cytoplasmic diversity. The species belonging to subspecies mondii are the source for new cytoplasm, stable cytoplasmic sterility, insect and pest resistance, fertility restorer and hybrid vigor. The species, P. orientale and P. villosa are useful for studying the effects of polyploidy. The cytoplasmic male sterile and maintainer line used in the development of hybrids were Tift 23A and B U.S. origin and additional cytoplasmic male sterility sources were discovered in India. Napier grass From the interspecific cross of P.americanum x P. purpureum (Napier grass) a number of commercially cultivars have been isolated. The F1 is triploid (3n = 21) which is sterile but can be vegetatively propagated and used in pasture. The amphidiploid is hexaploid and fertile. Seed setting is excellent and there is high seedling vigor. Forage yield of hexaploid is comparable to triploid hybrid. P. purpureum is tall (243-486cm), perennial grass. It was introduced from Africa. It grows in clumps of

Origin and Genetic Resources of Cereals

5.31

20-200 stalks similar to sugancane. Leaf blade is 2-3cm wide. P. purpureum is adapted to hot, low land tropics. P. clandestinum grows best at higher and cooler elevation. Although vegetatively propagated but sexual reproduction is normal. Other millets  The other millets that are grown in India are: 1. Finger millet. 2. Foxtail millet. 3. Common millet. 4. Barnyard millet. 5. Kodo millet. 6. Little millet. Finger millet (ragi or Mandua), Eleusine coracana (2n = 36) is generally a selfpollinated crop but cross pollination does occur by wind and insects. Seed contains 15% protein in comparison to 11.0% protein of wheat. It is an excellent source of Ca, Fe, Mn and methionine. The center of origin is Africa. The immediate ancestor of E. coracana is E. indica. E. indica spp. indica is a diploid with 2n = 18 and E. coracana spp. Africana is a tetraploid, largely confined to eastern and southern Africa. The other species are E. brevifolia, E. lagopoides and E. verticillata, all having 2n = 36. It is grown in late spring or as Kharif crop. Besides being used as grain crop this crop is also used as hay or silage (fodder crop). There are two subspecies in the Eleusine coracana, E. coracana subsp. coracana, the cultivated diploid subspecies and subsp. Africana, the allotetraploid, wild and weedy subspecies. Further, the cultivated subspecies is divided into five races, namely Coracana, Vulgaris, Elongata, Plana and Compacta on the basis of inflorescence morphology (Wet et al. 1984). E. indica and E. floccifloia are the puatative donors of A and B genome, respectively, of E. indica subsp. Africana (Bist and Mukai, 2001). Four types of panicles depending upon shape are found in finger millet. 1. Top curved 2. In curved 3. Open 4. Fisty. In the top curved type the fingers are long and center is hollow whereas in in curved type the fingers are short and curved in and thus results in closing up the central hollow and thus the panicle is ovate in shape. In the open type the fingers are the longest and the panicle takes the characteristic funnel–shaped. The fisty has the in curved spikelets with higher intensity and thus results in a round, fist like shape. The average number of spikelets per finger ranges from 67 to 73 and the density of spikelets (number of spikelet/cm) ranges from 6.7 in open to 9.5 in top curved, 11.8 in in curved to 14.8 in the fisty. The culm of this plant has congested nodes at the base, i.e. 2-4 nodes are almost clubbed (have less internode length). Koni  The foxtail millet or Italian millet or Koni or Kakaun or Kangri, Setaria italica is a self-pollinated crop with 2n = 18. It contains 12.3% protein. The center of origin is China. The foxtail millet probably evolved from Setaria viridis, the wild relative grown in Eurasia. It is grown in mountains of India and Pakistan. It is sown in late spring and also used as hay or silage. It matures in 65-70 days. Foxtail millet can be classified into four races, namely maxima, moharia, indica and nana (Deka prelevich and Kasparian, 1928; Prasada rao et al., 1993). Gritzenko (1960)

Crop Evolution and Genetic Resources

5.32

divided the race maxima into Manchurian, Korean and Mongolian types. The origin is East Asia-China and Japan. China is the center of diversity and a possible center of origin. The characteristics (Li et al., 1995) of these races are given in the Table 5.11 below. Table 5.11  Showing different races of foxtail millet Races

Distribution

Characteristics

Maxima

Japan, Korea and China

Few tillers, tall plants, strong cums, many nodes, long and pendulous inflorescence, high yield, medium to late maturity

Moharia

European countries

Short culms, few tillers, early maturity, low yield,

Indica

india

Adaptation to tropical and subtropical environments, Tall stalks, some tillers, strong culms, late maturity

Nana

Lebnana, Afganistan

Resembles mild green foxtail, S.viridis, short, slender with many tillers, low yield, early maturity

Proso millet  The common millet or Proso millet or Russian millet (Panicum miliaceum) or Cheena is mainly a self-pollinated crop but a very small amount of out crossing takes place (>10%). It is a diploid with 2n = 36. Stems and leaves are covered with hairs. It has low transpiration ratio. It is a very short duration crop with low water requirement and is used as catch crop. It has got the highest protein content (Lysine 4.3%) in comparison to wheat’s 1.9% and paddy’s 3.7%. The center of origin is China and its progenitors are unknown. It matures in 60-90 days. It is used as human and animal feed. Barnyard millet  The Barnyard millet (Ehinochloa colonum) or Japanese millet or Sawa or Mandura or Jhingura is a diploid with 2n = 36. There are other species with 2n = 48 (E. crusgalli), 54(E. stagnina) and 72. Self-pollination is the general rule. E. colona var. frumentacea is closely related to E. colona the common weed. Figure 5.12 shows major types of millets. Kodo millet  Kodo millet or kodo (Paspalum scrobiculatum) with 2n = 40 is a self pollinated crop (mostly cleistogamous). The genus contains about 250 species. The chromosome number varies rom 2n = 20 to 2n = 60 It is resistant to drought and thus serves as an insurance against famine. It evolved from wild form P. scrobiculatum var. commmersonii. The other related species is P. longifolium. Different species in the genus Paspalum are given below in the Table 5.9. It is a C4 plant. Little millet  Little millet or kutki (Panicum miliare) is a diploid with 2n = 36 and is a self-pollinated crop. The cross pollination amounts to 0.05%. This crop can be grown at an altitude of 7000 ft. It is grown in mountains of India and Pakistan. It is closely related to the true wild form P. psilopodium. Besides these millets other millets include Digitaria exilis, the fonio millet, Echinochloa frumentaceae, the Japanese millet and Brachiaria ramosum, the brown top millet or Guinia millet.

Origin and Genetic Resources of Cereals

5.33

Fig. 5.12  Major types of millet: pearl, broom-corn foxtail and barnyard (Adapted from J.F. Hancock, 2004) Species

Chromosome number

Grain/fodder crop

Common name

Paspalum scrobiculatum Three races1. regularis 2. irregularis 3. variabilis

40

Cultivated as grain or fodder crop

P. notatum

20, 40

-do-

P. conjugatum

40

P. compactum

40, 50

P. delatatum

40

P. commensonii

40

P. distichum

40, 48, 60

Water couch grass

P. gigantium

120

Knot grass

P. lanceolatum

40

P. longifolium

40

Unique breeding system

Apomixis Sour grass

Cultivated as grain or fodder crop

Dallis grass

Apomixis

Contd...

Crop Evolution and Genetic Resources

5.34 Contd...

Species

Chromosome number

P. muchlenberzii

18, 20, 22

P. quandreferium

20, 30, 60

P. scrobi

40

P. setaceum

40

P. virgatum

40, 80

Grain/fodder crop

Common name

Unique breeding system

Origin and Genetic Resources of Legumes

C H A P T E R

6

6.1  CHICKPEA Chickpea (Cicer arietinum) is winter season pulse crop grown in semi-arid tropics. It is called Bengal gram in India. It is a diploid with 2n = 16 and is a self-pollinated crop. It contains up to 20% protein and can be used as such or as split pea or as flour. There are major morphological forms of chickpea in cultivation. 1. Desi-small, angular with rough brown to yellow testa, purple flower and grown in Indian sub-continent, Ethiopia, Mexico and Iran and 2. Kabuli-predominantly produced in Afganistan through W. Asia to N. America and Southern Europe and is relatively large, plump with smooth, cream colored testa, and white flower. The genus Cicer contains 34 cultivated species and 9 wild species (Table 6.1). Cultivated varieties differ from wild relatives by a more erect growth form and pods with reduced dehiscence. The center of origin is South Eastern Turkey (Anatolia in Turkey) (van der Maesen, 1984). C. reticulatum is the progenitor of chickpea. Chromosome structural change is a significant component of the isolating mechanism. Parental species differ by a major reciprocal translocation. C. reticulatum and C. arietinum belong to the same biological species. Within species accessions differ by a paracentric inversion and an interchange and this is not uncommon in situation within a pulse species. Ladizinsky and Adler (1976b) assigned different species of Cicer into three crossability groups. Group I included C. arietinum, C. reticulatum and C. echinospermum; Group II contained C. judaicum, C. pinnatifidum and C. bijugum whereas the third Group comprised of a single species, C. cunnetum. Within groups F1’s could be obtained but they varied in level of fertility. Hybridization was not successful between members of different groups. Their study showed that there are no barriers to gene flow between C. arietinum and C. reticulatum but as hybrids involving C. echinospermum as one of the parents were difficult to produce and were sterile and so the gene flow was restricted. Meiotic studies showed that the

Crop Evolution and Genetic Resources

6.2

parental species differ by a major reciprocal translocation besides there is cryptic structural hybridity. It is a predominantly self-pollinated crop and cross pollination is through insects (Purseglove, 1968). Thirty four wild relatives of chickpea are perennial species and nine including cultivated species are annuals. The primary genepool consists of C. arietinum, the cultivated species and other two wild annual species, C. echinospermum and C. reticulatum. Some authors associate wild perennial species, C. anatolicum with GP1 as well. C. reticulatum is the putative wild progenitor of C. arietinum. Secondary genepool consists of three annual species, C. judaicum, C. pinnatifidum and C. bijugum. The tertiary gene pool consists of three annual wild species, C. yamashitae, C. cuneatum, C. chorassanicum and thiry four wild perennial species.(Ahmad et al., 2005). Table 6.1  Showing species ploidy level and gene pool in genus Cicer Genus- Cicer

Ploidy level

Gene pool

Source of useful gene

Sub-genus-Pseudononis Section1-Monocicer Series-Arietina C. arietinum (C. reticulatum)

2n = 2x = 16 2n = 2x = 16

GP1A and GP1B

Res. to Fusarium wilt

C. bijugum

-

GP2

Res. to Ascochyta blight, grey mold, cyst nematode, Fusarium wilt, high protein

C. echinospermum

-

GP1

Res. to Fusarium wilt

C. judaicum

-

GP2

Res. to Ascochyta blight and Fusarium wilt, high protein

C. pinnatifidum

-

GP2

Res. to Ascochyta blight and Fusarium wilt

2n – 2x – 16

GP3

Multiple seeds, Res. to Fusarium wilt

Series-Cirrhifera C. cuneatum Series- Macro-aristae C. yamashitae

GP3

Section2 Chamaecicer Series- Annua C. chorassanicum

GP3

Res. to Fusarium wilt

Series-Perennia C. incisum Sub-genus Viciastrum Contd...

Origin and Genetic Resources of Legumes

6.3

Contd...

Genus- Cicer

Ploidy level

Gene pool

Source of useful gene

Section3 Polycicer Sub-section Nano-polycicer C. atlanticum Subsection Macro-polycicer Series-Persica C. kermanense C. oxyodon C. spiroceras C. subaphyllum Series Anatolo-Persica C. anatolicum C. balaericum Series- Europaeo-Anatolica C. floribundum C. graecum C. heterophyllum C. isauricum C. montbretii

Res. to Ascochyta blight, multiple seeds

Series Flexuosa C. baldshuanicum C. flexuosum C. grande C. incanum C. korshinsky C. mogoltavicum C. nuristanicum Series Songorica C. feldtschenkoi Contd...

Crop Evolution and Genetic Resources

6.4 Contd...

Genus- Cicer

Ploidy level

Gene pool

Source of useful gene

C. multijugum C. paucijugum C. songaricum Series Microphylla C. microphyllum Section 4 Acanthocicer Series Pungentia C. pungens C. rechingeri C. stapfianum Series Macracantha C. macracanthum C. acanthophyllum C. garanicum Series Tragacanthoidea C. tragacanthoides C. laetum C. rassouloviae

6.2  COMMON BEAN Common bean (Phaseolus vulgaris) is a diploid with 2n = 2x = 22. It is used as both pulses and green vegetables. Seed contains haemagglutinins which destroys RBC but the toxic factors are destroyed by heat as in soybeans. Seed is used in the canning and frozen food industries. Seeds are extremely variable in color (white, yellow, green, buff, pink, blotched or striped) with a distinctive colored eye formed around the hilum. Seeds also vary in shape and size and 100 seed weight ranges from 200 to 600 gms. The large domesticated beans have seed size of 1gm (one seed) and the smallest seed weighs 100mg. Cultivation of Phaseolus species ranges from cool temperature to humid tropics and Asiatic Vigna species covers a much narrow climatic and agro-ecological range comparatively. It is a self-pollinated crop but outcrossing does occur. The center of origin is Mexico. It is a non-centric crop. There are five cultigens in the genus Phaseolus and all have wild counterparts (Marechal, Mascherpa and Stainer, 1978) (Table 6.2). The three very closely related species are P. vulgaris, P. coccineus and P. polyanthus and they

Origin and Genetic Resources of Legumes

6.5

allow gene flow. P. coccineus has a higher rate of outcrossing than P. vulgaris. General appearance of karyotypes in different species is similar and the genetic differentiation between species involved a large measure of chromosomal structural change. Cryptic structural differentiation may occur between different geographical races of the same cultigen as well as major structural change such as interchanges which are occasionally observed (Smartt 1999). P. polystachyus, annual or perennial is the wild form of Phaseolus. Clear discontinuits have developed between nonspecific and cultivated Phaseolus and Vigna species whereas no morphological discontinuity is apparent between wild and cultivated Lathyrus. Primary gene pools have been recognized in all important cultivated crops which have evolved distinct wild and cultivated sub-gene pools. The development of secondary gene pool is most extensive in the Phaseolus vulgaris- P. coccineus- P. polyanthus- P. flavescens complex and apparent but less developed in V. radiata-mungo and V. angularis- V. umbellata. No GP2 has been identified for P. lunatus, P. acutifolius, V. unguiculata or V. subterranea. GP3 has been established for American Phaseolus species and the Asiatic Vigna species but not for V. unguiculata or V. subterranea (Smartt, 1981). Table 6.2  Showing species, gene pool and distribution of common beans Section-Phaseolus

Cultivated/wild

Gene pool

P. vulgaris L. Var. vulgaris Var. aborigineus

Cultivated (warm temperature), edible green pods

GP1, self-pollinated

P. coccineus

CULTIVATED (cool temperature), edible green pods

GP1, generally outcrossed

Ssp. coccineus

Distribution

Common name

Domesticated both in Middle and South America

GP1

Scarlet runner

Ssp. obvallatus Ssp. formosus Ssp. polyanthus

Cultivated (edible green pods)

GP1, self-pollinated

Cultivated (tough and fibrous green pods)

GP1, self-pollinated

Mexico to Columbia

P. glabellus P. augustii P. acutifolius Var. acutifolius (GP3) Var. latifolius P. filiformis

Gray tepary

GP3

P. angustissimus P. wrightii P. grayanus Contd...

Crop Evolution and Genetic Resources

6.6 Contd...

Section-Phaseolus

Cultivated/wild

Gene pool

Distribution

Common name

(Mexico and Peru)

Lima

P. polystachyus Var. polystachyus Var. sinuatus P. pedicellatus P. oaxacanus P. polymorphus P. microcarpus P. anisotrichus P. ritensis P. lunatus Var. lunatus Var. silvester

Cultivated (tough and fibrous green pods)

GP1

P. tuerckheimii P. brevicalyx P. pachyrrhizoides

GP2

P. sonorensis P. xanthotrichus P. micranthus Section-Alepidocalyx P. parvulus P. amblosepalus Section-Minkelersiay P. galactoides P. nelsonii P. pluriflorus P. vulcanicus P. chacoensis P. costaricensis

GP2

P. parvifolius

GP2

P. maculatus

GP2

P. salicifolius

GP3

P. jaliscanus

GP3

Origin and Genetic Resources of Legumes

6.7

6.3  COWPEA Cowpea (Vigna unguiculata) is a diploid with 2n = 2x = 22. It is predominantly a selfpollinated crop. It is an important food legumes grown for grain, vegetable and fodder. The genus includes the annual cowpeas and ten wild species (Table 6.3). Seed contains about 25% protein and it is largely free of flatus–producing sugars. It is largely grown in Asia, Africa, South and Central America. The seed appears to be relatively free of anti-metabolites and flatus producing sugars. The primary center of origin is central Africa and the secondary center of origin is India and China. It comprises five subspecies (Table 6.3). The three cultivated subspecies are unguiculata, cylindrica and sesquepedalis and the two wild forms are dekindtiana and mensensis (Verdcourt, 1970b). V. unguiculata ssp. Dekindtiana is the progenitor of modern cowpea. It is more closer morphologically to cultivated cowpea. Crossing between cultivated and wild form is possible but wild type must be used as male. Table 6.3  Showing subspecies, varieties, breeding system and distribution of cowpea Subspecies

Cultivar group

Cultivated/wild

Breeding system

Distribution

V. unguiculata ssp unguiculata (cowpea) var. unguiculata

Unguiculata

Cultivated (seed type), 20-30 cm

Inbreeder

Africa

Ssp. Cylindrica (Catjang bean)

Biflora

Cultivated (fodder type), 7.5-12.5 cm

Inbreeder

Asia

Ssp. Sesquipedalis (Yard long or asparagus bean)

Sesquipedalis

Cultivated (vegetable type), 30-100 cm

Inbreeder

Asia

Ssp. Dekindtiana

Wild (GP1B)

Inbreeder

Africa, Ethiopia

Ssp. Mensensis

Wild (GP1B)

Outbreeder

Ssp. alba

wild

Ssp. baoulenis

Wild

Ssp. burundiensis

Wild

Ssp. letouzeyi

Wild

Ssp. pawekiae

Wild

Ssp. pubescens

Wild

Ssp. stenophylla

Wild

Ssp. tenuis

Wild

Ssp.unguiculata var. spontanea

wild

Crop Evolution and Genetic Resources

6.8 Subspecies

Cultivar group

Cultivated/wild

V. unguiculata ssp. unguiculata var. unguiculata

Textilis

Used for peduncle fibres

V. unguiculata ssp. unguiculata var. unguiculata

Melanophthalamus

Seed crop

Breeding system

Distribution

6.4  FABA BEAN The faba bean or broad bean (Vicia faba) is used for human and livestock food. It is the protein source of animal feed stuffs. It contains very low level of lectin and protease inhibitor protein and so it does not require heat or microbial inactivation as in Phaseolus and soybeans. But there is problem of glucosides vicin, convicine and DOPA glucosides which incite haemolytic anemia in individual having deficiency of the enzyme glucose-6-phosphate dehydrogenase. Cultivation of faba bean is undertaken throughout the northern temperate zone and at higher altitudes in some tropical regions. China produces 60% of the world’s crop. Three distinct types of faba bean differing in size are in cultivation-small (for livestock), medium and large (for human with improved palatability, cooking quality and low tannin content). The V. faba belongs to a genus which contains more than 130 members. It is assigned to the sub-genus Vicia and section Faba of the sub-genus Vicia. The section Faba includes 6 species (Kupicha, 1976) as given in Table 6.4. V. faba is a diploid with 2n = 2x = 12 whereas the rest species are diploid with 2n = 2x = 14. Karyotype of V. faba is different than V. narbonensis, V. galilaea and V. hyaenescyamus which are closely related (Ladizinsky, 1975b) in terms of chromosome Table 6.4  Showing ploidy level, gene pool and distribution of faba bean Section- Faba

Ploidy level

Cultivated/wild

Gene pool

Distribution

V. Faba ssp. paucijuga ssp. Faba ssp. Faba var. minor ssp. Faba var. equina

2n = 2x = 12 2n = 2x = 12 12, 14 12 12

Cultivated

GP1A

V. narbonensis

2n = 2x = 14

Wild

GP3B

Europe, W. Asia, N. Africa

V. galilaea

2n = 2x = 14

Wild

GP3B

Israel, Turkey

V. V. hyaeniscyamus

 2n = 2x = 14

Wild

GP3B

Syria, Lebnan

V. johannis

2n = 2x = 14

Wild

GP3B

S. Europe, W. Asia, Libya

V. bithynica

 2n = 2x = 14

wild

GP3B

Europe, W. Asia, Algeria

Afganistan, Pakistan and India (N.W.)

Origin and Genetic Resources of Legumes

6.9

homology and further Giemsa banding pattern shows no homologies between chromosome arms in the three wild species. Within V. faba there occurs subspecies or botanical varieties such as paucijuga (< 300), minor (310-400mg), major (> 1700mg) and equina (600-1000mg) (Murantova, 1931; Hanelt, 1972b; Cubero, 1974). Var. major is synonymous with ssp faba var. faba (12, 14). There is no clearly identified wild progenitor of faba bean and V. faba var minor and ssp. paucijuga are probably the closest to the ancestral form. Faba bean is a cross pollinated crop. Pod sets may be affected adversely by low levels of bee pollinator activity. Various levels of inbreeding (self-pollination to cross pollination) have been observed in faba bean populations. ssp paucijuga is auto fertile. Auto sterile line requires abrasion of the stigmatic surface. GP1B the conspecific wild population is not known and also not known is the GP2. Mediterranean or Near East is the center of origin of faba bean. Chromosomal structural change is an important aspect of the overall divergence between species in Vicia faba. All the species in V. narbonensis group- V. narbonenesis, V. galilaea and V. hyaenis-cyamus are cross compatible but they are incompatible with V. faba (Ladizinsky, 1975b). And V. faba has not evolved from the V. narbonensis group of species. Cluster beans  Guar beans (Cyamopsis tetragonaloba) is an annual legume. It is grown in arid and semiarid regions of India. It is domesticated in India and evolved from African species, C. senegalesis. It is a diploid with 2n = 14. 80% of the world production comes from India. Endosperm makes up 34-40% of the dry weight of seed of which 80-90% being pure galactomannan. Galactomannan is a polysaccharide comprising mannose and galactose in the ratio of 2:1. Galactomannan works as gelling agent and thus guar gum is produced which has got industrial uses. It is used as viscosity enhancer for both food and non-food purposes. The plant reaches 2-3mt in height. Stems and leaves are hairy. Flowers are white to bluish in color and they are produced in clusters in the axil of leaf. Pod contains 5 to 12 small seed. This crop is drought tolerant and also salinity tolerant (can be grown at 7-8pH). It is raised as rainfed kharif crop, sown in June-July and susceptible to frost. This crop is also used as green manuring crop. Breeding objectives include development of high yielding variety with quality. Seed contains trypsin inhibitor. Toasting is done to destroy trypsin inhibitor.

6.5  LATHYRUS Lathyrus sativus, the grass pea, is a self–pollinated crop with 2n = 2x = 14 but crosspollination would occur if appropriate pollinators are available. It is used as grain crop (pulse) and fodder crop and is tolerant to drought and water logging conditions. It is found naturally in Eurasia, North America, temperate South America, Mediterranean base and the Near East and East Africa. The seeds contain ODAP (b-N-oxalyl-L-a, b diaminopropionic acid), the water soluble non-protein amino acid and is a cause of neuro-lathyrism and the BAPN (g-L-gltutamyl) aminoproprionitrile is the cause of osteo-lathyrism. It is used as pulse crop mainly in India. The center of origin is S-W and Central Asia.The genus Lathyrus is broken down into 13 sections containing about

Crop Evolution and Genetic Resources

6.10

150 species (Kupicha, 1983). The species belonging to the section-Lathyrus are given in the Table 6.5. Two forms of Lathyrus found are-Lathyrus sativus and L. sativus var. stenophyllum. Most species of the genus are diploid with 2n = 2x = 14. Polyploidy with 2n = 4x = 28 is found in North American species (Hitchcock, 1952) and karyotype on the whole is symmetrical with the chromosomes having median-sub-median chromosomes for the most part (Sen, 1938a, b and Davis, 1958). Hybridization is difficult between species of the genus. L. sativus is probably a derivative from genetically nearest wild species L. circera L. Reduction in the level of ODAP and BAPN results in loss of yield during selection programme. Table 6.5  Showing various species of genus Lathyrus L. mulkak

L. chrysanthus

L. cirrhosus

L. trachycarpus

L. grandiflorus

L. lycicus

L. rotundifolius

L. phaselitanus

L. tuberosus L.

L. sativus L.

L. undulatus

L. amphicarpos L.

L. heterophyllus L.

L. cicera L.

L. latifolius L.

L. stenophyllus

L. slyvestris L.

L. marmoratus

L. tingitanus L.

L. blepharicarpus

L. tremolsianus

L. ciliolatus

L. annus L.

L. hirticarpus

L. hierosolymitanus.

L. basalticus

L. cassius

L. lentiformis

L. odoratus L.

L. gorgoni

L. hirsutus L.

L. psedo-cicera

L. chloroanthus

6.6  HORSE GRAM (Macrotyloma uniflorum) Horse gram or kulthi is a diploid with 2n = 20. The genus Macrotyloma comprises some 25 species (Verdcourt, 1980). It is cultivated mostly in southern India. It is hardy, drought-tolerant and can be grown on a range of soils. Seeds are used as pulse but not very palatable. This crop is also used as fodder crop. It is a low-grade pulse in the sense that relative to other pulses tryptophan and sulfur amino acids are low in content. Seeds contain cyanogenic glycosides, protease inhibitors and lectins.

Origin and Genetic Resources of Legumes

6.11

Kulthi or gahat (Dolichos uniflorus) is another legume grown for food and fodder in topical and subtropical regions. It is suited to dry land agriculture. Seed contains higher amount of trypsin inhibitor and hemagglutin and natural phenols which can be destroyed by prolonged cooking. Seed is hard in texture. Dolichos unifolrus or D. biflorus is synonymous with Macrotyloma uniflorum. The member species M. uniflorum, includes M. uniflorum var. uniflorum and M. uniflorum var. stenocarpum. The perennial horse gram belongs to M. africanum, M. axillare and M. bieense.

6.7  LENTIL The lentil (Lens culinaris) is a diploid with 2n = 2x = 14. It is a self-pollinated crop. The nutritional value of this crop is high because of higher protein content (25%) and low levels of toxic and anti-metabolic materials. There are two types of lentil depending upon the seed size: macrospermous (bold seeded) and microspermous (small seeded). The macrospermus have bold sized seed (greater than 4 gm/100 seed), yellow cotyledon color, resistant to rust and grown in temperate Europe, north and south America. It takes longer times(2x times) for cooking in comparison to small, red seeded lentil. The micro spermus are small seeded with red cotyledon and cultivated in Asia and Africa. The genus Lens comprises six species (Table 6.6). L. montbretii is well separated from the other five species. L. ervoides, L. nigricans, L. orientale and L. culinaris constitute culinaris group. Williams et al., (1974) and Ladizinsky (1979a) suggested that L. orientale and L. culinaris are closer to each other than nigricans, and further suggested that nigricans and orientale are species morphologically closest to the L. culinaris. The cross, culinaris x orientale produces F1 with high fertility and the cross, culinaris x nigricans also produces F1 which is not completely sterile. L. orientale represented the wild ancestral type of L. culinaris (Barulina, 1930). The karyotypes of L. culinaris and L. orientale are very much similar whereas there are karyotypic differences between L. culinaris and L. nigricans. The center of origin is West Asian or Eastern Mediterranean (Barulina, 1930). Ladizinsky et al., (1984) re-examined the taxonomy of genus Lens included in the tribe Vicieae of the family Fabaceae. The genus Lens consists of two species and five subspecies. L. culinaris (ssp. culinaris, orientalis and odemensis) and L. nigricans (ssp. nigricans and ervoides). Table 6.6  Showing species, ploidy level and distribution in Lentil Species

Ploidy level

L. montbretii

2n = 2x = 14

Gene pool

Distribution

GP1A

Eastern Mediterranean (Tigris and Euphrates)

L. ervoides

GP1A wild

Ethiopia and Uganda

L. nigricans

GP2 (wild)

Israel to Spain, Algeria, Morocco and Cenary island

L. orientalis

GP1A (wild)

Turkey, Israel, Uzbekistan

L. culinaris

Cultivated

L. odomensis

GP3

Crop Evolution and Genetic Resources

6.12

6.8  PEA Pea (Pisum sativum) is a cleistogamous crop and fertilization takes place approximately 24 hours before opening of the flower. Seeds contain about 22% protein. Under subtropic to tropic conditions cross-fertilization occurs (Govorov, 1928; Harland, 1948). Pea contains trypsin inhibitor and lectin (Liener, 1982) and is wholesome in uncooked state. There are two major types of pea in cultivation: the garden pea, produced primarily for human consumption and the field pea, grown for feeding animal. There are three distinct types of garden pea. Starchy pea (or round peas of Mendel)-green immature or dried seed is eaten. Sweet or sugary pea (wrinkled pea of Mendel) contains high concentration of sugar, lower concentration of starch. Immature seed fresh or frozen is used. The genus Pisum comprises two species-I. P. sativum and II. P. fulvum (Davis, 1970; Polhill and van der Maesen, 1985). P. sativum is a complex aggregate of wild and cultivated species centered in Mediterranean basin and Near East. The garden pea generally has white flowers. Seed shape may be round, dimpled or wrinkled. Seed color may be green, cream or yellow. Field pea has pigmented vegetative parts, flowers and seeds. In case of garden Table 6.7  Showing species, ploidy level, gene pool and distribution of pea Species

Ploidy level

Gene pool

Distribution

Characteristics

P. sativum ssp. sativum

Cultivated (GP1A)

var. sativum

2n – 14

Cultivated

White flowered garden pea

var. arvense

–

Cultivated

Colored flower field pea

ssp. elatius

–

Wild (GP1B)

Var. elatius

–

Wild

var. pumilio (P. humile)

–

Wild

var. brevipedunculatum

–

Wild

P. fulvum

–

GP2, wild

P. abyssinicum

Eastern Mediterranean, Turkey and the fertile Crescent Eastern Mediterranean

Cultivated in Ethopia and Yemen

P. aucheri

Tuber forming

P. formosum.

Tuber forming

P. jormardi P. transcaucasicum

Origin and Genetic Resources of Legumes

6.13

pea pigmentation of testa is virtually eliminated and loss of anthocyanin pigments is associated with improvement in palatability. All wild forms of peas (Pisum sativum) such as P. elatius (tall, climbining type), P. humile (short type) previously classified as species have a diploid chromosome number of 14 and no sterility barrier exists (Blixt, 1978) and gene exchange is complete and so were merged with P. sativum. P. fermosanum(or P. aucheri) was assigned to the Genus Vavilovia. The related genera Vicia, Lathyrus with Vavilovia constitute the tertiary gene pool (GP3). P. fulvum and P.abyssinicum, the Ethiopian form have in common certain distinctive proteins of P. fulvum (Kloz, 1971). The fulvum seems to be characterized by a series of translocations, duplications. Inversion seems to be present in ecotype humile and some others. The bulk of material contains thus chromosome structural changes. The primary center of diversity is Mediterranean and the secondary center of diversity is Ethiopia and the Near East (Blixt, 1970). The basic gene pool of cultivated peas is presumed to have originated from the ancestors of the northern Israeli wild ‘pumilio’ population (Ben-ze’ev and Zohary (1973) which closely resembles the cultivated P. sativum. Further , translocation (involving short arms of chromosomes IV and VI) observed in P. sativum variety could have been introgressed from var. elatius and/southern var. pumilio or even from P. fulvum. The four main taxa in Pisum-P. sativum, P. elatus, P. humile and P. fulvum are cytogenetically closely related and can exchange genes on large scale (Ben-Ze’ev and Zohary, 1973). Spontaneous hybrids between P. humile and P. fulvum have been reported. P. elatus P. arvense P. humile

P. fulvum P. jormardi

P. sativum

P. abyssinicum

Fig. 6.1  Shows the crossability between different species of Pea

Æ Indicates viable F1 plants; Æ indicated no seed/viable plant obtained; direction of arrow Æ points to the female plant and ´ indicates reciprocal crosses can be made. GB3 consists of genera Vicia, Lathyrus and Vavilovia.

6.9  PIGEONPEA The pigeonpea (Cajanus cajan) is the only cultivated crop of Cajaninae subtribe of the tribe Phaseoleae which includes species such as Phaseolus, Vigna, Cajanus, Lablab,

Crop Evolution and Genetic Resources

6.14

Macrotyloma. The subtribe Cajaninae contains 11 genera including Rhynochosia (130 spp.), Eriosema (200 spp.), Dunbaria and Flamingia. The genus Cajanus includes six sections (Table 6.8) and contains 32 species (van der Maesen, 1985). The genus Cajanus includes the former genus Atylosia. The greatest number of wild species occur in the regions, Burma, Yunan (China) and Nothern Australia. There is hybridization between the two genera. There is strong resemblance between the chromosome complements of Cajanus and Atylosia (2n = 2x = 22) and Atylosia does not differ sufficiently from Cajanus to warrant a generic status. Atylosia differes from Cajanus in having the presence of a seed strophiole which is under control of two genes (Reddy et al., 1981). 18 species are found in Indian sub-continent and 13 are endemic to Australia and one to west Africa. Australia is another center of diversity. The pigeonpea originated in India and the secondary center of diversity is in eastern Africa. 85% of the total world production is done in India. Tur the early maturing short pigeon pea is cultivated in Indian peninsula (South India) and Arhar is the perennial, bushy, late maturing plant with purple or red markings on standard is grown in Nothern India. The maturity thus ranges from 90 to 3oo days. It is a dipoid with 2n = 2x = 22 and is self-pollinated crop but cross-pollination averages about 20% depending upon genotype, environment. C. cajanofolius is the closest wild relative (the available progenitor type) of the cultivated pigeon pea. Pulse provides alternative to red meat as protein source thus avoiding excessive intake of saturated fats and a source of dietary fiber. The vast majority of legumes are protected by a range of toxic and antimetabolites materials. These range from highly toxic alkaloids to non-protein amino acids, lectins, protease inhibitors and cyanogenic compounds. Table 6.8  Showing species, distribution, gene pool and characteristic of pigeon pea Section- Cajanus

Source of useful some sytoplan

C. cajan C. cajanifolius

CMS

Distribution

Gene pool

Growth habit

Pantropical

GP1

Erect

S. E. India

GP2

erect

Section- Atylia

Erect

C. cinereus

Australia

–

C. confertiflorus

–

–

C. lineatus

CMS

C. sericeus

GP2

Australia

C. lanuginosus C. reticulatus

S. India, Sri Lanka

Res. to pod borer Res. to pod borer, CMS

C. trinervius

– GP2

–

S. India

GP2

–

S. India, Sri Lanka

GP2

Erect

Section- Fruticosa C. acutifolius

–

Erect Res. to pod borer, bruchids

GP2

Erect Contd...

Origin and Genetic Resources of Legumes

6.15

Contd...

Section- Cajanus

Source of useful some sytoplan

Distribution

Gene pool

Growth habit –

C. aromaticus C. crassicaulis

Australia

–

C. kerstingii

W. Africa

GP3

–

C. lanceolatus

Australia

GP2

–

C. latisepalus

–

GP2

–

C. niveus

Burma, S. China

–

C. pubescens

Australia

–

C. viscidus

Australia

Erect

SectionCantharospermum C. albicans

Climbing species Res. to pod borer

GP2

–

C. elongatus

N. E. India, Vietnam

C. goensis

India, S. E. asia

GP3

–

C. rugosus

S.India, Sri Lanka

GP3

–

S. S. E. Asia, Pacific Coastal Africa

GP2

–

C. scarabeaoides

Res. to pod borer, bruchids, CMS

–

Section- Volubilis

Climbing species

C. crassus

–

C. grandiflorus

N. E. India, S. China

C. heynei

S.W.India, Sri Lanka

GP3

–

C. mollis

Himalaya foothills

GP3

–

C. villosus

N. E. India

C. volubilis

CMS

India, S. E. Asia

–

– GP3

SectionRhynchosoides C. platycarpus

C. mareebenis C. marmoratus

Trailing species

Res. to pod borer, bruchids, phytophthora blight, CMS

Indian sub-continent, Java Australia

GP3

–

– –

–

Crop Evolution and Genetic Resources

6.16

6.10  ASIATIC GRAM The Asiatic gram includes, green gram or mung bean (Vigna radiata), black gram or urd (Vigna mungo), adzuki bean (Vigna angularis), rice bean (V. umbellata), moth bean (V. acontifolia), and V. trilobata. The green gram is widely cultivated in the Old World and the New World. Black gram is widely cultivated in India. Addzuki bean is popular in Japan and Korea. The rice bean is cultivated in Indo-China and Thailand. Urd is less palatable in comparison to moong bean. The cotyledon is white in urd but dirty yellow in moong. They are all diploid with 2n = 2x = 22) and all are small seeded. All five species belonging to the genus Vigna along with their wild forms are given in Table 6.9. V. sublobata included two distinct wild forms which were not freely cross compatible but which could be crossed easily with cultigens, one with V. radiata and one with V. mungo. V. sublobata Type A or Race A (9-12 seeds/pod with moderate hairs on stem and pod) is similar to moong and resistant to yellow mosaic virus whereas Type B or Race B of V. sublobata with 6 seeds/pod and dense pubescence on stem and pod is susceptible to YMV. The former is crossable with V. radiata and the later is crossable with V. mungo. Chromosome structural rearrangements are a significant part of the genome differentiation between V. radiata and V. mungo. The two closest relatives V. radiata and V. mungo have some structural differentiation of their genomes. The two groups have separate gene pools and gene flow can be induced between them. Table 6.9  Showing species, gene pool and origin of Vigna Species

Cultigen

Wild forms (GP1A)

GP2

GP3

Origin

V. angularis

var. angularis

var. nipponensis

V. trilobata

V. radiate, V. mungo

Far Eastern

V. mungo

var. mungo

var. sylvestris

V. radiata

V. umbellate, V. angularis, V. glabrescens, V. trilobata

India

V. radiata

var. radiata

var. sublobata

V. mungo

V. umbellate, V. angularis, V. glabrescens, V. trilobata

India

V. umbellata

var. umbellata

var. gracilis

V. angularis

No distinction recognised

V. acontifolia

V. acontifolia

Indo-China and South-East Asia -

India

Origin and Genetic Resources of Oilseeds

C H A P T E R

7

7.1  RAPESEED AND MUSTARD Rape-seed and mustard of commercial importance belong to the genus, Brassica and the two most important commercial oilseed producers are B. campestris (or B. rapa) which has world wide distribution and is known as turnip rape, Polish rape, toria and sarson. Three distinct ecotypes of B. rapa or B. campestris, brown and yellow sarson and toria are grown in India. B. napus is one whose cultivation is restricted to Europe and north Africa. B. napus is the rape or rape seed of Europe and Canada and is known as Argentine rape, Swede rape and colza. In both B. campestris and B. napus winter and spring varieties are available. Another Brassica species, B. juncea, rai is also an important oilseed crop in India. Mustard includes Brassica species like B. juncea, B. nigra and B. carinata the Ethiopian mustard. The genomic relationship between Brassica species is given in the Fig. 7.1 (Morinaga, 1934 and U., 1935). B. nigra, B. oleracea and B. campestris are the three primary species and are diploid whereas B. carinata, B. napus and B. juncea are called secondary species and are allopolyploids. The primary species are cross-pollinated whereas the secondary species are self-pollinated. The center of origin of diploid B. oleracea is Mediterranean region. The Cruciferae species, Brassica oleracea has yielded a number of vegetables. The crops originated from wild cabbage, B. oleracea subspecies oleracea are cabbage, kale, Brussels sprouts, cauliflower, broccoli and kohlrabi. Cauliflower is most closely related to broccoli whereas cabbage is most closely related to the kales (Song, Osborn and Williams, 1990). B. cretica contributed most to the development of cauliflower. (Helm, 1963). Rape seed and mustard traditional variety contains 60% erucic acid and 80-120 m mol/gm glucosinolate. The single zero cultivar is the variety having low erucic acid (< 2%), a double zero variety is one with low erucic acid and low glucosinolate and a triple zero variety is one with low fiber content along with low glucosinolate and erucic

Crop Evolution and Genetic Resources

7.2

acid. A canola refers to seed having < 2% erucic acid, and < 30 m mol/gm glucosinolate. Yellow seed color is thought to be associated with lower tannin content and with thinner seed coat offering potential for more oil and protein and less fibre in the meal. Pungency in taste and smell is because of glucosinolate or mustard oil glucosides or thioglucosides which in the presence of enzyme, myrosinase produces isothiocyanates which is goitrogenic. Thus one can either breed variety free of glucosinolates or go for inactivation by enzyme or heat treatment. Several wild species constitute the GP1 in B. oleracea. B. rapa and B. nigra also exist as wild forms. In GP2, B. napus × B. rapa interspecific cross can be made. Further, B. oleracea × Raphanus, inter generic crosses are possible. Brassicoraphanus is an amphidiploid between B. japonica (= B. Campestris ssp. japonica) and Raphanus sativus and Raphanobrassica is an amphidiploid from the cross Raphanus sativus × B. oleracea. In GP3 many species from Brassicaea can be intercrossed using embryo rescue technique. Table 7.1  Showing species, plody level, breeding system and distribution of Brassicas Rape seed

Plody level

Breeding system

Characteristics

B. campestris or B. rapa (Indian rape seed)

Origin Europe (Central Asia, Afganistan or India may have been another center of origin (Vavilov, 1949)

B. campestris var. Toria

2n – 20

Highly C. P.

B. campestris var. yellow sarson

2n – 20

Highly S. P.

The most cold hardy cultivar of Brassica oilseeds

B. campestris var. brown sarson B. campestris. var. brown sarson Tora type

C. P.

B. campestris. var brown sarson Lotini type

S. P.

B. napus (Canadian rape seed) Gobhi sarson, Rape seed or rape of Canada and Europe, Swede, fodder or oil rape

2n – 38

S. P.

B. nigra (Black mustard) Banarasi rai

2n – 16

> 20% C. P.

B. juncea (rai, raya or Indian mustard

2n – 36

S. P. (C. P. up to 10%)

Southern Europe

Mustard

Matures early and adapted to drier conditions

Middle east (Central Asia and China suggested as sites of primary center with secondary centers in India, china and the Camacasus Contd...

Origin and Genetic Resources of Oilseeds

7.3

Contd...

Rape seed

Plody level

Breeding system

Characteristics

Origin

B. juncea (brown mustard) B. juncea (yellow mustard) B. carinata (Ethiopian mustard) Karan rai

2n – 34

S. P.

Seed large and North-East Africa predominantly black. Yellow seed forms are also available and thus are a source of large yellow seed, resistant drought, perform better under saline conditions, resistant to shattering and disease

B. nigra n=8 BB (diploid)

Ethiopian mustard

Cabbage, Cauliflower, Broccoli kale, Kohlrabi, Brussels sprouts

B. carinata n = 17 BBCC (amphidiploid)

B. oleracea n=9 CC Diploid

Black mustard

B. juncea n = 18 AABB (amphidiploid)

B. napus n = 19 AACC Amphidiploid

Leaf mustard

B. rapa n = 10 AA Diploid

B. campestris oilseed rape (canola) Turnips

oilseed rape Rutabaga, swede

Fig. 7.1  Showing the relationships among different Brassica species (U, 1935)

Brassica Different species of the genus Brassica are given in Table 7.2.

Crop Evolution and Genetic Resources

7.4 Table 7.2  Showing 38 different Brassica species Brassica species B. assyriaca B. aucheri B. balearica B. barrelieri B. brachyloma B. cadmea B. carinata B. cretica B. deflexa B. deserti B. desnottesii B. dimorpha B. elongata B. fruticulosa B. graveinae B. hilarionis B. incana B. insularis B. iranica B. juncea B. macrocarpa B. montana B. napus B. nigra B. nivalis B. oleracea B. oxyrrhina B. procumbens B. rapa B. repanda B. rupestris B. somalensis B. souliei B. spinascens B. taurica B. tournefortii B. tyrrhena B. villosa B. campestris

Chromosome number(n)

Genome constitution

Characteristic

11

17 9 7

BBCC Realtive of B. oleracea group.

11 8 11 Realtive of B. oleracea group. Realtive of B. oleracea group. 18

AABB Realtive of B. oleracea group. Realtive of B. oleracea group.

19 8

AACC BB

9 9

CC

10 11

AA Realtive of B. oleracea group.

10

TT

10

AA

Wild species Realtive of B. oleracea group.

Origin and Genetic Resources of Oilseeds

7.5

The two groups of genera– one group with non heteroarthocarpic fruit (in which fruit beaks keep its primitive seedless condition) such as Sinapidendron, Eruca (EE, n = 11, E. sativa (Taramira) cultivated and Taramira oil is produced), Euzomodebdron, Vella, Boleum, Carrichtera, Succowia, Moricandia, Rytidocarpus, Douepia, Conringia, Chalcanthus, pseudofortunia, Ammosperma, Pseuderucaria, Savignya, Henophyton, Quezeliantha, and subgenera Diplotaxis and Hesperidium of Diplotaxis and subgenus Brassicaria of Brassica and another group of genera with seeded beak (heteroarthocarpic fruits with varying degree of beak development) such as Erucastrum, Hirschfeldia, Brassica, Sinapis, Coincya, Ertucaria, Trachystoma, Rhaphanus, Enarthocarpus, Cakile, Ceratocnemum, Cordylocarpus, Crambe, Didesmus, Eremophyton, Fortuynia, Guiraoa, Hemicrammbe, Muricaria, Otocarpus, Physorrhynchus, Rapistrum, Fezia, etc. are associated with the evolution of Brassica. These two groups of genera are linked through the subgenus Rhynchocarpus of Diplotaxis. The species and genera related to Brassica crops have been grouped into 36 cytodemes which are capable of exchanging genetic materials (Harberd, 1976). These cytodemes are characterized by high interfertility within them but crossing between the cytodemes is possible using special techniques. Genera Diploitaxis

Species

Chromosome number

D. acris

7

D. erucoides

7

D. siettiana

8

D. assurgens

9

D. cathiolica

9

D. tennuisilliqua

9

D. virgata

9

D. berthautii

9

D. siifolia

10

D. viminea

10

D. harra

13

Eruca

Eruca spp. (E. sativa, E. vesicaria) Erucastrum (ES) ES. cardominoides

11, EE

Cultivated/wild

Characteristic

Some Diplotaxis species are cultivated.

Cultivated in India (Taramira oil is produced)

9

ES. virgatum

7

ES. varium

7

ES. abyssinicum

8

ES. nasturtiifolium

8

ES. strigosum

8 Contd...

Crop Evolution and Genetic Resources

7.6 Contd...

Genera

Species

Chromosome number

Hirschfeldia

Hirschfeldia spp.

7

Sinapidendron

Sinapidendron spp.

10

Sinapis

S. auchari

7

Sinapis alba

12, SS

S. flexuosa

12

S. arvensis

9

S. pubescens

9

Raphanus spp.

9

Raphanus Trachystoma

Cultivated/wild

Cultivated

Characteristic

High mucilage in comparison to B. juncea. Contains 4-hydroxybenzyl isothiocyanate (2-3%) in comparison to 07-1.0% 2-prpenyl(allyl) glucosinolate (sinigrin) of B. juncea.

Wild mustard

8

Sinapis alba (syn. B. hirta) with n = 12(SS), white or yellow mustard as called, is a more closely related Cruciferae species and has large seed. Wild species of Brassica species, B. tournefortii (TT, n = 10) has drought tolerance. M. arvensis a species from a related genus Moricandia represents an intermediate stage between C3 and C4 species and also shows much higher water use efficiency in comparison to B. napus and B. rapa. Sinapis arvensis (SS, n = 12) is closest species to B. nigra. Further, the species Eruca satuva (EE, n = 11) has also drought tolerance. These useful traits from these species / genera can be transferred to cultivated Brassica oilseed crops.

Classification of the Brassica 1. Kingdom-  Plantae Subkingdom-  Tracheobionata(Vascular plant) Super division- Spermatophyta(Seed plant) Division- Magnoliophyta(Flowering plant) Class- Magnoliopsida(Dicotyledon) Subclass- Capparales Family- Brassicaceae 2. Family Brassicaceae Tribe - Brassicaceae

Origin and Genetic Resources of Oilseeds

7.7

Subtribe- 1. Brassicinae 2. Raphaninae 3. Moricandinae Genera 1. Brassica(20) 1. Enarthocarpus(1) 1. Moricandia(1) 2. Coincya(1) 2. Raphanus(1) 2. Pseuderucaria(1) 3. Diplotaxis(13) 3. Rytidocarpus(1) 4. Eruca(1) 5. Erucastrum(11) 6. Hirschfeldia(1) 7. Sinapis(5) 8. Sinapidendron(1) 9. Trachystoma(1) Numbers within the brackets denote the number of cytodemes present in the genera. The cytodeme refers to as group of any number of species or genera which have the same chromosome number and within which there is interfertility. Herberd(1972) established 38 cytodemes but at present 63 cytodemes have been recognized(Hinata, 1983). The genus Brassica and its allied taxons are called Brassica coenospecies.

7.2  CASTOR Castor (Ricinus communis) is a member of Euphorbiaceae. The genus Ricinus is considered to be monotypic and R. communis in the only species including the many polymorphic forms. The center of origin is Ethiopia (Weiss, 1971). There are four large centers of variability (Irano-Afghanistan–USSR region, Palestine-S. W. Asia, Indo-China and Arabian Penninsula), each with its own specific plant characteristics to support a polyphyletic origin for this crop (Moshkin, 1977). Oil has industrial uses and plant fibers can be used for cellulose, cardboards and newsprint. Oil has laxative value, alleviating dry and rough skin conditions. It is a diploid with 2n = 20. There is cross-incompatibility between lines representing ecological extremes. The species has 6 subspecies and 25 varieties (Table 7.2) (Moshkin, 1986). Six types of inflorescence can be observed- I. stable female to stable male II. unstable female III. inclined towards female IV. Male and female interspersed V. common monoecious VI. Male. Lower portion of receme bears male flowers and the upper female. The ratio between male and female flowers depends on the climatic conditions, age of the plant and day length. Figure 7.2 shows a plant of castor. Table 7.3  Showing species, characteristic and distribution of castor Species

Characteristics

I. Subspecies communis

var. communis

Distribution South West Asia, Africa, Southern Europe and secobdarily in America, Australia

Common variety, under cultivation and weed,red stem Contd...

Crop Evolution and Genetic Resources

7.8 Contd...

Species

Characteristics

var. roseus

Pink variety, under cultivation and weed

var. Microspermus

Small seeded variety

var. viridis

Green variety

var. brevinodes

Short plants, short internode, indehiscent, red or violet

II. Subspecies persicus

Russia, NWAsia and central Asia, secondarily in Africa, America, Australia

var. persicus

Persian variety, dehiscent, stem dovecolored(green)

var. virens

Green stem variety

var. indehiscens

Indehiscent variety, small seed or medium sized seed

var. violaceocaulis

Violet stem, indehiscent

III. Subspecies sinensis

Russia, W. Asia, Africa, America, Australia

var. sinensis

Chinese variety, dwarf, dove colored green

var. caesius

Violet variety, dwarf

var. japonicus

Japanese variety, indehiscent, seed dark brown

IV. subsp. Indicus

India, Pakistan, SEAsia. Secondarly in Africa, America

var. indicus

Indian variety, plant violet, small capsules,reddish seed sometimes

var. griseofolius

Small seeded variety, grey leaves

var. leucocarpus

Dove colored, large capsule variety

var. inermis

Violet, large capsule variety, under cultivation

V. subspecies zazibarinus var. zazibarnus

Distribution

Africa secondarily America, SWAsia Zazibarian variety, Tall plants, large seeds Contd...

Origin and Genetic Resources of Oilseeds

7.9

Contd...

Species

Characteristics

var. glaucus

Dove colored, tall plants, indehiscent seeds

var. purpurascens

Purple variety, Tall plants with violet, red and pink stem, seeds mostly red, under cultivation

var. balifundensis

Large capsule variety, strong tall plants

var. nanum

Dwarf variety

VI. subspecies ruderalis

Distribution

Asia, Africa, Southern Europe, secondarily America, Australia

var. ruderalis

Weedy cultivated variety, small seeded

var. spontaneous

Uncultivated variety

var. aegyptiacus

Egyptian variety, small seeded , leaves small, medium height

var. mexicanus

Mexican variety, tall, small seeded

Fig. 7.2  Showing castor plant

7.10

Crop Evolution and Genetic Resources

7.3  FLAX Linseed (Linum usitatissimum) is grown for seed for oil and fiber. Seed is used for human consumption and linseed cake is used for livestock feed. It is a diploid with 2n = 30 but occasionally 32. It belongs to family Linaceae. Seed contains 35-44% oil and 20% protein. Reddish brown seeds are rich in estrogenlike compounds – lignans, a weapon against breast cancer. The oil contains 30-60% linolenic acid. Oil is used for industrial purposes such as paints,varnish and cosmetics. Fiber is used for spinning/weaving, paper and packaging components. Linen fabrics is made from linen flax. There is presence of cyanogenic compound in the oil. The auto oxidation causes substances with bad flavor to be formed. The genus comprises about 100 species with n = 8, 9, 10, 12, 14, 15 and 16. The most common numbers are n = 9 and 15. The center of origin is South-Western Asia and Mediterranean area of Europe. It is normally a self-pollinated crop with natural outcrossing ranges between 0.03 to 2%. It is a Rabi season crop. Flax and other pulse crops such as lathyrus and chickpea are grown in a special type of cropping system called ‘utera’. In this cropping system seeds of any of these crops are broadcasted before harvesting of the rice crop when there is sufficient moisture in the field. This system is particularly useful for clay soil or heavy soil in which the moisture after harvesting of rice reduces drastically which makes ploughing difficult and germination percentage gets reduced. This system helps in the utilization of moisture required for germination of seeds and further using early sowing and thus avoiding the end of the season moisture stress during hot summer. Seeds germinate and gown into a small plants when harvesting of rice is done. Thus separate types of varieties be developed for ‘utera’ condition and the other condition in which rice is harvested, land is prepared ensuring sufficient moisture and then seeds are either broadcasted or line sown. Table 7.4 shows different species, ploidy level and characteristics. Linseed cultivars have been classified into two types depending on the utilization. 1. Linseed type 2. Flax type. Linseed type plants are of short type and produce many short secondary branches in comparison to flax type. Flax type plants are taller and less branched. Other species of Linum includes L. bienne and L. rigidum. L. lewisii is a wild perennial. L. angustofolium is the most likely progenitor of L. usitatissimum. L. usitatissimum crosses successfully with other 9 Linum species with 2n = 30(Seetharaman, 1972). Linum bienne, the pale flax is the wild progenitor of the cultivated species L. usitatissimum. Disruptive selection has been practiced in Beta vulgaris, Linum usitatissimum and Brassica oleracea where more than one distinct crop has evolved within a single biological species. Each crop has developed its own distinctive gene pool. The GP1 species consists of seven species including L. angustifolium. The GP2 species consists of other species in the genus. Along with L. ustiatissimum, L. suffruticosum and L. grandiflorum are the species of horticultural importance.

Origin and Genetic Resources of Oilseeds

7.11

Table 7.4  Showing species and chromosome number of Flax Species

Ploidy level

L. alpinum

18

L. altaicum

18

L. anglicum

32

L. angustifolium

30

L. austriacum

18

L. bienne

30

L. campanulatum

28

L. cathaticum

16

L. crepitans

30

Characteristics

Uses

Gene pool

GP1 GP1

GP1

L. elegans L. extraaxillare

18

L.flavum

30

L. grandiflorum

16

L. hirsutum

18

L. hologynum

18

GP1

L. komarovii L. lewisii

18

L. mesostylum L. monogynum

30

GP1

L. narbonensis L. perenne

18

L. strictum L. strictum va. Strict L. suffruticosum L. tenuifolium

Lowest linolenic acid per cent 18

Ornamental

Lowest linolenic acid per cent

L. thracicum L. trigynum

20

L. usitatissimum

30

Ornamental

GP1

Linseed or flaxseed or alsi lowers cholesterol. It is a rich source of omega-3 fatty acid which protects heart. Further, it contains lots of dietary fibers which absorb bad cholesterol. Seed contains apoli poprotein A1 which converts bad cholesterol into HDL cholesterol, good cholesterol.

Crop Evolution and Genetic Resources

7.12

7.4  GROUNDNUT The groundnut (Arachis hypogaea) is grown in warm temperate and tropical regions from 40°N to 40°S. The seed contains 43 to 55% oil and 25 to 28% protein. It belongs to the family Papilionaceae. A. hypogaea is synonymous with A. rasteiro and A. nambyquarae. Peanut (Arachis hypogaea) is a self-pollinated crop. It is an allotetraploid with 2n = 2n = 40. There are three different cultivated forms of groundnut such as runner (Virginia), Spanish and Valencia. The latter two are erect forms of peanut (Krapovickas, 1968). The primary center of origin is South America and the secondary center of origin is Africa. The five centers of diversity are I. Guarani region II. Goias and Minas Gerais (Brazil) III. Rondonia and north-wast Mato Grosso (Brazil) IV. Easter Andean foot hills of Bolivia V. Peru and VI. North-east Brazil (Gregory, 1976). The nearest wild relative of Arachis hypogaea is A. monticola the wild tetraploid which has less strong pod and larger carpophores than A. hypogaea and which is regarded as conspecific. It has been suggested that A. hypogaea is an amphidiploid resulted from chromosome doubling of the F1 between A. cardenasii (A genome donor ?) and A. batizocoi (B genome donor), the two putative parents. Both putative parents occur in reasonable proximity in Bolivia (Smartt et al., 1978). Although morphological and phytogeographical evidences support the above hypothesis but chemotaxonomic evidence does not and A. duranensis has been suggested as an ‘A’ genome donor. The genomes in the two sections Rhizomatasae and Arachis could be designated as R1 (prorhizomatasae), R2 and R3 (Eurhizomatasae) and A1, A2 for section Arachis (Fig. 7.2). Similarly, section Erectoides comprises three sub genomes (E1, E2 and E3) corresponding to the series within the genus. The Series Annuae comprises one or the other sub genomes (A1 or A2), the Series Amphiploides species probably contain both (A1 + A2) while series perennes species possess the same sub genome (A1). ‘A’ genome is typical of the section Arachis and ‘B’ genome is typified by A. batizocoi. Groundnut is a Kharif season crop but now a days it is also grown as a spring season crop. The genus Arachis is comprised of 22 described species and some 40 or more annual or perennial species collected from South America are yet to be described. These species have been assigned to seven section with several of it being subdivided into series as show in the Table 7.5 shows different species, ploidy level and their distribution. Table 7.5  Showing cultivated forms, salient characteristics and distribution of groundnut Cultivated forms Arachis hypogaea

Distinguishing features

Distribution

Alternately branched forms

Ssp. Hypogaea Var. hypogaea (Virginia group)

Short main axis

Bolivia, Amazonian region

Var. hirsuta

Long main axis

Peru

Ssp. Fastigiata

Sequentially branched forms

Var. fastigiata (Valencia)

Simple inflorescences

Guarani region, Goias, Minas Gerais, north-east Brazil and Peru Contd...

Origin and Genetic Resources of Oilseeds

7.13

Contd...

Cultivated forms

Distinguishing features

Var. vulgaris(Spanish)

Section-Arachis

Distribution

Compound inflorescences

Wild/cultivated

Guarani region, Goias, Minas Gerais and north-east Brazil

Ploidy level

Gene pool

Genome constitution

Series-Amphidiploids A. hypogaea

Cultivated

A. monticola

Wild

Series-Annuae

2n = 4x = 40 2n = 2x = 20

GP1B(resistant to Puccinia) GP2

A. batizocoi

–

–

BB Genome

A. duranensis

–

–

BB Genome

A. spegazzinii

–

–

A. sternosperma

–

–

A. ipaensis

–

–

Series- perennes

–

–

A. helodes

–

–

A. villosa

–

–

A. digoi(var. correntina)

–

–

AA Genome

A. cardenasii

-

-(immune to C. personatum)

AA Genome

A. chacoense

2n = 2x = 20

-(resistant to C. arachidicola)

Section- Erectoides

2n = 2x = 20

GP3

Series- Trifolialatae

–

A. guaranitica

–

A. tuberose

–

Series-Tetrafolialatae

–

A. benthamii

–

A. paraguariensis

–

A. oteroi

–

BB Genome

Series-Procumbensae Contd...

Crop Evolution and Genetic Resources

7.14 Contd...

Section-Arachis

Wild/cultivated

Ploidy level

A. rigoni

–

A. lingosa

–

Section- Caulorrhizae

–

A. repens

–

A. pintoi

–

Section-Rhizomatasae

2n – 2x – 40

A. burkatii

2n = 2x = 20

A. glabrata

2n = 4x = 40

Resistant to Puccinia

–

A. hagenbeckii Section-Extranervosae

2n = 2x = 20

A. marginata

–

A. tutescens

–

A. villosulicarpa

–

A. macedoi

–

A. prostrata

–

Section- Ambinervosae

Gene pool

No species

Section-Triseminalae

2n = 2x = 20

A. pusilla

2n = 2x = 20

GP3

GP2

GP1A

Arachis (2x)

A. hypogaea (4x)

Rhizomatosae (2x, 4x) Triseminalae (2x)

1B A. monticola (4x)

Erectoides (2x) Ambineryosae (2x)

Caulorrhizae (2x)

Extranervosae (2x)

Fig. 7.3  Showing crossing involving different sections of Arachis

Genome constitution

Origin and Genetic Resources of Oilseeds

7.15

7.5  NIGER Niger (Guizotia abyssinica) or kalatil or ramtil, sorguza is more widely grown in India than in other country. It is a member of Compositae and tribe Heliantheae and family Asteraceae. It is a diploid with 2n = 2x = 20 (Simmonds, 1976). The genus contains three species native to tropical Africa. The center of origin is the Ethiopian high lands and the center of gene variation in Guizotia. It is basically a cross-pollinated crop with some self-pollination known to occur. It is strictly a self-incompatible crop species with a sporophytic self-incompatibility system, one locus (S) with multiple alleles (about 10 alleles have been reported). The seed contains 25 to 45% oil and selected lines can have oil up to 50-60%. Seed contains 12-25% protein. This crop can be grown on any soil including saline soil. There are varieties which can mature in 50-65 days. Further seed contains ~ 50% linoleic acid and in selected strains the percentage can be as high as 85%. Oil from niger can be a substitute for sesame oil. There are significant differences between Ethiopian and Indian types. The six species of Genus Guizotia are given in the table 7.6 below (Baagoe, 1974). It is a Kharif season crop. G. abyssinica crosses well and produces hybrids (F1 and RF1) with G. scabra ssp. schimperi, G. scabra ssp. scabra and G. villosa but seed set is more when G. abyssinica is used as male. The first three species are closely related and G. abyssinica is evolved from G. schimperi. Table 7.6  Showing species and distribution of Niger Species

Annual/perennial

Cultivated/wild

Annual

Cultivated species

G. abyssinica

Distribution

G. scabra, ssp schimperi, ssp scabra

ssp. scabra (Perennial)

G. schimperi

ssp. Schimperi (wild)

G. villosa

Annual herb

Ethopia

G. reptans

Perennial, postratie and mat forming herbs

Kenya

G. zavattari

Perennial

Ethopia

G. arborescens

Woody Perennial shrub

Ethopia

7.6  SAFFLOWER Safflower (Carthamus tinctorius) or kusum is a diploid with 2n = 2x = 24. It belongs to the family Asteraceae of Compositae. It is a dryland crop, resistant to drought and highly salt tolerant. It is grown for seed (contains 12 to 22% protein) and oil (26-37%). Seed contains 73% linoleic acid. Genotypes with as high as 80% linoleic acid or 80% oleic acid have been produced. It is a self-pollinated crop which allows 8.3 to 100% outcrossing. The pollinator is the insect (Honey bees). Cross-pollination is essential for optimum

Crop Evolution and Genetic Resources

7.16

fertilization and maximum yield. The main centers of diversity are Afganistan and India and a secondary center in Middle East. The genus Carthamus contains approximately 25 valid species of which only one C. tinctorius is cultivated (Table 7.7). The basic chromosome numbers are believed to be 10 and 12. Section I contains species with 2n = 24, section II with 2n = 20, section III with 2n = 44 and section IV with 2n = 64(Ashri and Knowles, 1960). Species from section III are presumed to have evolved from crossing of species from section I and section II and subsequent chromosome doubling of F1. Similarly, species from section IV are supposed to have evolved from crossing of species from section II and section III and subsequent doubling of F1. C. oxyacantha the wild safflower from India is the ancestor of the cultivated safflower. The two most agriculturally important species closely related to C. tinctorius are C. oxyacantha and C. palaestinus and they are most likely ancestors of the cultivated safflower. It is grown in Spring season in India. There are two types of varieties in safflower-Variety with spiny leaves and variety with spineless leaves. Safflower oil contains 90% unsaturated fatty acids (oleic and linoleic) and 10% saturated fatty acid (palmitic and stearic). A greater number of different types of oils can be developed through the combination of major genes controlling the levels of stearic, oleic and linoleic and changing environments (Knowles, 1989). Safflower is also cultivated for extraction of color (dye) from the flowers, food flavoring, and in medicine. Colors of flower include orange, yellow, red and rarely white which changes to other color at the wilting stage (Lin and Mundel, 1996). Two colouring materials that can be obtained from safflowers include carthamidin, the water soluble yellow and cartharmin the orange-red dye, insoluble in water but soluble in alkaline solution. The ornamental values of plants reside in flower color (orange, yellow) and few or no spines on the leaves and bracts. Dried flowers are plucked regularly which results in development of new flower buds and there is continuous picking of flowers from this crop. Nipping out central shoots before flowering in safflower induces increase in branching, number of seed heads/plant and total yield. The most important effect of temperature is the seedling tolerance of low temperature and susceptibility to high Fig. 7.4  Drawing of C. temperature at flowering. Figure 7.4 shows a plant of safflower. tinctorius from Dioscorides ‘De Materia Medica’.

Table 7.7  Showing pecies, ploidy level and gene pool of Safflower 2n = 2x = 24

Gene pool

C. tinctorius

Section-I

Cultivated, Annual

Cultivated/wild

–

GP1

Distribution

C. palaestinus

Wild, Annual

–

GP1B

Negev Desert

C. oxyacantha

Wild, Annual

–

GP1B

India Contd...

Origin and Genetic Resources of Oilseeds

7.17

Contd...

Section-I C. flavescens syn. C. persicus

Cultivated/wild Wild

Section II

2n = 2x = 24

Gene pool

2n = 20

GP2

C. glaucus

–

GP3

C. tenius

–

GP3

C. alexandrinus

–

C. leucocaulos

Distribution

–

–

Section III

2n = 44 –

C. lanatus Section-IV

2n = 64

C. baeticus

–

C. turkestanicus

–

C. caeruleus

Perennial

2n = 24

Blue flower

C. arborescens

Perennial

2n = 24

Yellow flower

7.7  SESAME Sesame (Sesame indicum) or til is the single readily available source of protein rich in sulfur containing amino acids. S. indicum is synonymous with S. orientale. It belongs to the family Pedaliaceae. The genus Sesame contains 36 described species (Nayar and Mehra, 1970) (Table 7.8). 18 species have African origin, 8 are of Indian origin, 5 belongs to Ceylone region and others from several regions. Ethiopian region is genrally accepted as the origin of cultivated sesame. Some authors including Mehra (1967) favour Afghan- Persian region to be the center of origin. West Asia to india is the secondary center of diversity. Besides, S. indicum, S. angustifolium, S. radiatum and Ceratotheca sesamoides (false sesame) with 2n = 32 are also cultivated to a limited extent in Africa. Sesame is self-pollinated with a small amount of natural outcrossing (average outcrossing around 5%) although 14 to 65% outcrossing can occur. The level of outcrossing depends on the environmental conditions and insect population. It is a Rabi season crop. It is also grown for extraction of color from the flowers. This crop has drought resistant qualities and gives excellent crop with a rainfall of 500-600mm. Table 7.8  Showing species, chromosome number and distribution of sesame Species

Chromosome number

Distribution

S. angolense

32

T Africa

S. angustifolium

NK

-Cultivated to a limited extent

S. antirrhinoides

–

– Contd...

Crop Evolution and Genetic Resources

7.18 Contd...

Species

Chromosome number

Distribution

S. auriculatum

–

Crete

S. biapiculatum

–

Congo

S. brasiliense

–

Brazil

S. caillei

–

Guinea

S. calycinum

–

At

S. capense

26

TA, India and Australia

S. ligitaloides

NK

TA

S. denterii

–

TA

S. hendelotii

–

TA

S. indicum

26

Cultivated species, India

S. indicum ssp. Malabaricum

26

India

S. laciniatum

32

India

S. latifolium

NK

E. Africa

S. lepidotum

–

TA

S. malabaricum

–

India

S. marlotii

–

Africa, East Indies, Australia

S. microcarpum

–

TA

S. mombazens

–

TA

S. pedaloides

NK

TA

S. prostratum

32

India

S. radiatum

64

TA, Ceylone, cultivated to a limted extent

S.repens

NK

TA

S. rigidum

–

TA

S. sabulosum

–

Sudan

S. schenckii

26

TA, India, East Indies

S. schinzianum

NK

Africa

S. somalense

–

,East Indies

S. talbotii

–

Somalia

S. thonneberii

–

Nigeria

S. trifoliatum

–

TA Contd...

Origin and Genetic Resources of Oilseeds

7.19

Contd...

Species

Chromosome number –

S. tryphyllum

Distribution India Africa, East Indies

NK = Not known; TA = Tropical Africa

7.8  SOYBEAN Soybean (Glycine max) belongs to the family Papilionaceae. Self-pollination is the rule and is a diploid with 2n = 2n = 40. Natural outcrossing amount is less than 1%. It contains 15-22% oil and 40-50% protein. There is negative correlation between oil and protein per cent. Oil is a varietal characteristic, influenced by climate and environment. Higher linolenic acid results in poor flavor or flavor instability in soybean oil. Seed weight varies from 5 to 40 gm. Pale yellow color oil is commercially acceptable. Only 25% flowers produce seeds. The growth habit can be determinate or indeterminate. The genus Glycine contains 9 species. It is highly photoperiodic. The two sub genera within the genus Glycine are Glycine (7 species) and Soja (2 species) (Table 7.9) (Hymowitz and Newell(1980). The two gene centers are I. Eastern Africa and ii. Australasian region and the secondary center is China. The evolutionary path of cultivated soybean (Hymowitz, 1970) is as follows. G. ussuriensis (wild) Æ G. gracilis (weedy) Æ G. max (cultivated). Cultivated soybean has been derived from accumulation of gene mutations without having undergone chromosomal arranagement. Leguminosae are less prone to generate polyploidy forms in comparison to Gramineae. G. ussuriensis is considered wild progenitor of cultivated soybean. G. soja is synonymous with G. formosana and is black seeded, low yielder and resistant to YMV. There is no GP2 in soybean. The subgenus Glycine contains seven perennial, wild species. All of which are indigenous to Australia. All perennial species are twining or scrambling herb with a thick tap root. They contain genes for resistance to drought, heat and cold, apparent day length insensitivity and to diseases. Thus they are the valuable source of germplasm. Table 7.9  Showing species, 2n number and distribution of soybean Genus-Glycine

Cultivated / Wild

2n

Genome

Gene pool

Australian distribution

GP3A

Australia

Subgenus-Glycine Glycine cladestina

Wild, perennial

40

A1A1

Var. cladestina

-

40

-

-

Var. sericea

-

40

-

-

G. falcata

-

40

FF

-

-

G. latifolia

-

40

B1B1

-

Contd...

Crop Evolution and Genetic Resources

7.20 Contd...

Genus-Glycine

Cultivated / Wild

2n

Genome

Gene pool

Australian distribution

G. latrobeana

-

40

A3A3

-

Taiwan, Pacific Island

G. canescens

Wild, perennial

40

AA

-

-

G. tabacina

-

80 (40)

B2B2

-

Taiwan, Philippines

G. tomentella

Wild, perennial

38, 40, 78, 80 (diploid,tetraploid and aneuploid)

EE,DD, COMPLEX, COMPLEX

GP3A

China, Coast, Australia

G. albicans

40

II

G. arenaria

40

HH

G.argyrea

40

A2A2

G. curvata

40

C1C1

G.cyrtoloba

40

CC

G. hirticaulis

80

H1H1

G. lactovirens

40

I1I1

G. microphyta

40

BB

G. pindanica

40

H2H2

Sub genus-Soja

Asiatic distribution

G. max Ssp. max

Cultivated, annual

40

GG

Ssp. soja

Wild annual, vine

40

GG

China GP1B

China, Korea, Japan

The evolution of the Glycine subgenus Glycine polyploid complex is shown in Fig. 7.5.

Fig. 7.5  The Glycine subgenus Glycine polyploid complex. Lines connect tetraploids with diploid progenitors. All taxa lacking names are classified as G. tomentella. Boxed taxa marked A are members of the A genome group, and H are members of the H genome species. (Adapted from J.J. Doyle et al., 2002)

7.9  SUNFLOWER Sunflower (Helianthus annuus) is cultivated in temperate to cool tropical climates with USSR being the largest producer. The seed contains as much as 50% oil which is largely

Origin and Genetic Resources of Oilseeds

7.21

polyunsaturated (73%). Roasted and baked seeds are eaten by human. It belongs to the family Compositae. It is a diploid with 2n = 34. It is an insect pollinated cross-pollinated crop. Open pollinated varieties differ in the degree of cross-pollination or self-pollination and there is some degree of self incompatibility. Sunflower is photoinsensitive or day neutral, has allelopathic effect and shows autotoxicity. Sunflower (H. annuus and H. tuberosus) is used as herbicide. It produces substances that inhibit the growth of other plants. These substances include a number of phenolic compound and fatty acids and it affects broad leaf weeds. Also, its residue in the field actually inhibit the growth of subsequent sunflower crop. Thus same crop should not be taken on the same field year after year. There are three subspecies, H. annuus subspecies annuus, H. annuus var. macrocarpous and H. annuus subspecies lenticularis which is probably the closest wild relative of oilseed sunflower. The commercial varieties grown for seed are H. annuus var. macrocarpous and H. annuus subspecies lenticularis. H. argophyllus, the silver leaf sunflower, is native to Texas and is most closely related to H. annuus. Most ornamental sunflowers are referred to H. annuus subspecies annuus, the weed sunflower. There are 150-odd species and subspecies of Helianthus and they are native to America. They include annuals with fibrous root and tap roots and perennials, diploids, tetraploids and hexaploids. Most of the Helianthus spp. have 2n = 34, 68 and 102 with exceptionally 2n = 14 and 28 or 2n = 32. Some produce tubers (H. tuberosus) and rhizomes (H. maximiliani). Next to H. annuus, H. tuberosus the hexaploid sunflower (or Jerusalem artichoke) is the most widely cultivated species, its tubers are very tasty and eaten. Sunflower was brought to Botanic garden is Spain (Madrid) in 1510 from America from where it spread to England, France, India, Italy, Egypt, China and Russia. Organized breeding work started in Russia by 1915. From Russia “Mammoth Russian Sunflower ” (10` or > 101 in height) was brought to Canada in 1870s and from Canada sunflower was brought to USA in 1880s. There are 13 annual species as given below in the table 7.10. All are diploid with 2n = 34. Except H. similis and H. paradoxua, all appear to a phylogenetic unit. Ornamental sunflower species include H.annuus, H. argophyllous and H. debilis (all annuals) and H. decapetalous, H. x laetiflorus, H. maximiliani, H. x multiflorus and H. salicifolius (all perennials). H. annuus x H.tuberosus (perennial) has beed made for improvement of sunflower. Also, H. annuus has Fig. 7.6  Wild Helianthus annuus next to a been crossed with H. giganteus and H. maximiliani. monocephalic cultivar. Figure 7.6 shows cultivated and wild sunflower plant.

Crop Evolution and Genetic Resources

7.22

Table 7.10  Showing some species, chromosome number and characteristics of sunflower Species

Chromosome number

Annual / perennial

Other uses

H.annuus

2n = 34

Cultivated for oil,annual

ornamental

GP1

H. argophyllus

2n = 34

Annual

ornamental

Source of gene for resistance to disease. GP1

H.neveus

2n = 34

Annual

H.petiolaris

2n = 34

Annual

H.neglectus

2n = 34

Annual

H. praecox

2n = 34

Annual

H. bolanderi

2n = 34

Annual

H. anomalous

2n = 34

Annual

H. deserticola

2n = 34

Annual

Not known

Annual

H. agrestis

2n = 34

Annual

H paradoxus

2n = 34

Annual

H. debilis

2n = 34

annual

Hsimilis

H. tuberosus



2n = 6x = 102

Genetic resource

Source of cytoplasmic male sterility. GP1

ornamental

Perennial, cultivated for food

Source of genes for disease resistance, GP2

A Table showing sources of cytoplasmic male sterility in sunflower, is given below. Types of male sterility

Source species / crosses

PET1

H. petiolaris

ANL1

From interpsecific cross of H. tenticularis and cultivated sunflower

PET2

H. petiolaris

GIGI

H. giganteus

MAX1

H. maximiliani

ARG1

H. argophyllous × cultivated sunflower

R1G1

H. rigidus

ANN2, ANN3

Wild H. annuus

Origin and Genetic Resources of Fibre, Green Manuring, Starchy, Sugar and Fodder Crops

C H A P T E R

8

8.1  COTTON Cotton (Gossypium hirsutum) is cultivated in tropical and subtropical climate. It belongs to family Malvaceae. It is an often cross-pollinated crop and bees do the cross-pollination. Amount of cross-pollination varies from 5 to 30%. Amounts in excess of 50% have also been reported. Amount of cross-pollination depends on the insects population in the cotton field. The genus Gossypium contains 39 species of which 33 are diploid with large chromosomes. Some representative species of Gossypium are given in the Table 8.1. Of the total world cotton production 90% are G. hirsutum and 8% G. barbadense. The diploid species are grouped into 7 genomes (A, B, C, D, E, F and G). A, B, E and F are found in Africa or Asia (old world species). C or G is found in Australia and D genomes are found in Americas (new world species), has Mexican distribution, also grown wild in Peru and Galapagis archipelago. G. herbaceum originated in Middle east is the progenitor of G. arboretum grown widely in India. In India tetraploid cotton, G. hirsutum is now being grown. Tetraploid cotton originated as a result of crossing of two diploid species (one from the new world with D genome and the other from the old world with A genome) and subsequently amphidiploidy. New world tetraploid cotton, N. tabacum and T. aestivum are classic examples of crop plant evolution through hybridization and natural amphidiploidy. G. raimondii is also considered as progenitor of tetraploid cotton and contributed D genome(D5). There are five races of G. herbaceum, namely, Africanum, Acerifolium, Persicum, Kuljianum and Wighitianum. Similarly, the five races of G. arboreum are Indicum, Burmanecum, Sinense, Sudanense and Cernum.

Crop Evolution and Genetic Resources

8.2 AA(Old world) 2n = 26 Big chromosomes

X

DD(New world) 2n = 26 Small chromosomes

F1 AD Amphidiploidization

AADD (Tetraploid New world cotton)

Fig. 8.1  Showing evolution of tetraploid, new world cotton.



Table 8.1  Showing species, chromosome number, genome designation and distribution of cotton Species

Chromosome number

Genome

Cultivated/wild

Distribution

G. herbaceum

26

A1 (Large)

C, GP2

Africa, often cross pollinated

G. arboretum

26

A2 (large)

C, GP2

India, often cross pollinated

G. anomalum

26

B1 (medium)

W, GP2

Africa

G. triphllum

26

B2

W, GP2

Africa

G. barbosanum

26

B3

W

Africa

G. Capis-viridis

*

G. sturtianum

26

C1 (large)

W, GP3

Australia

G. robinsonii

26

C2

W, GP3

Australia

G. australe

*

GP3

Australia

G. costalalum

*

-do-

populifolium

8

-do-

G. cunnighamii

*

-do-

GP2

G. pulchellum

*

G. stocksii

26

E1 (large)

W, GP3

Indo-Arab

G. somalense

26

E2

W, GP3

Africa

G. areysinanum

26

E3

W, GP3

Arabian peninsula

G. incanum

26

E4

W, GP3

-do-

G. longicalyx

26

F1 (large)

W, GP2

Africa

G. bickii

26

G1 (large)

W, GP3

Australia

G. thurberi

26

D1 (small)

W, GP2

America

G. armourianum

26

D2 (small)

W, GP2

America

G. harknessii

26

D2

W, GP2

America

G. klotzschianum

26

D3

W, GP2

America

G. aridum

26

D4

W, GP2

Mexico

-do-

Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.3

Contd...

Species

Chromosome number

Genome

Cultivated/wild

Distribution

G. raimondii

26

D5

W, GP2

Peru

G. gossypioides

26

D6

W, GP2

Mexico

G. lobatum

26

D7

W, GP2

Mexico

G. tribolum

26

D8

W, GP2

Mexico

G. laxum

26

D9

W, GP2

Mexico

G. hirsutum

52

(AD)1 26 large, 26 small

C, GP1

America, often cross pollinated

G. barbadense

52

(AD)2

C, GP1

America, often cross pollinated

G. tomentosum

52

(AD)3

W, GP1

America

G. caicoense

52

(AD)4 26 large, 26 small

W, GP1

Brazil

G. mustelinum

2n = 2x = 52

Tetraploids

GP1

G. darwinii

GP1

Diploid species G. anapoides

26

K

GP3

Australia

G. costulatum

26

K

Australia

G. cunnighamii

26

K

Australia

G. enthyle

26

K

Australia

G. exiguum

26

K

Australia

G. londonderriense

26

K

Australia

G. marchaantii

26

K

Australia

G. nobile

26

K

Australia

G. pilosum

26

K

Australia

G. populifolium

26

K

Australia

G. pulchellum

26

K

G. rotundifolium

26

K

GP3

G. turneri

D10

GP2

G. davidsonii

D3-d

GP2

G. schwendimanii

D11

GP2

Australia Australia

C = Cultivated; W = Wild

8.2  JUTE The genus Corchorus contains 40-100 species. Two cultivated species in India include Tossa jute (Corchorus olitorius) and white jute (C. capsularis). Both are diploid with

Crop Evolution and Genetic Resources

8.4

2n = 14. They belong to family Sparrmanniaceae. Leaves from young jute plant is eaten as green leafy vegetable. C. olitorius is softer, silkier and stronger and fit for medium to mid high land whereas C. capsularis is used for making ropes and twines and is suitable for low to medium low land. It is a 110-120 days crop. Planting is done in March-April and harvesting in July-September. Seed rate is about 7.5kg/ha. Jute fibres are finner and stronger than Mesta fibes and thus they are better in quality. The centre of origin is Africa. Edible species of Corchorus (C. olitorius) is rich in protein, vit A, C, E and rich in minerals such as Ca and Fe. Different wild and weedy species are given in Table 8.2. Jute has thus food, fibre and medicinal values. Morphological differences between C. capsularis and C. oliterius are given in the Table 8.2 below. Table 8.2  Showing distinguishing characteristics of two species. Morphological trait

C. capsularis

C.oliterius

Height

Shorter

Longer

Leaves

smaller

Larger

Taste of leaves

Bitter

Tasteless

Flower

smaller

larger

Shape of pod

Globular or pear shaped

Long and cylindrical

Seed color

Chocolate brown

Steel grey or black

Seed size

larger

Smaller

Fiber colour

whitish

Yellow to grey or reddish

Fiber

Coarse

Finer, softer, stronger, more lustrous

Root system

Tap root, shorter, more branched

Adaptibility

All types of land, low, high(wider adaptability)

High land, susceptible to water logging

Amount of cross-pollination

Relatively low

Relatively higher

Uses as vegetable

Young shoots edible like spinach

Different cultivated and wild species of the genus Corchorus are give in the table 8.3. Hexaploid (26x = 42) and aneuploid (2n = 2x – 2 = 26) are also reported (Kubitzki and Bayer, 2003). Table 8.3  Showing different species of Corchorus. Species

Cultivated / wild

Ploidy level

C. capsularis

Cultivated

2n

C. oliterius

Cultivated

2n

Distribution

Unique traits

Africa Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.5

Contd...

Species

Cultivated / wild

Ploidy level

Distribution

C. aestuans

Cultivated

2n

Africa

C.tridens

Cultivated

2n

Africa

C. trilocularis

2n

Africa

C. fascicularis

2n

Africa

C. depressus

2n

C. pseudo-capsularis

2n

Africa

C. baldacci

2n

Africa

C. gilletti

2n

C. sidioides

2n

C. neocaledonicus

2n

C. hrisutus

2n

C. walcottii

2n

C. elachocarpus

2n

C. asplenifolius

2n

C. junodii

Wild species

Natural tetraploid (4n)

C. pascuorum

Wild species

4n

C. cunnighamii

Wild species

4n

C. hirtus

Wild species

4n

C. argutus

Wild species

4n

C. siliquosus

Wild species

4n

C. orinocensis

Wild species

4n

Africa

Australia

America and Carribean

C. brevicornutus

Africa

C. pseudo-oliterius

Africa

C. shimperi

Africa

C. urticifolius

Africa

C. schimeri

Africa

C. antichorus

Africa

C. africannus

Africa

Unique traits Fibre (good fiber but of lower quality) and vegetable, highest Fe content

8.6

Crop Evolution and Genetic Resources

Mesta (Kenaf, Roselle)  Jute, kenaf and mesta are bast (phloem) fibre plants next to cotton. There are two species. H. sabdariffa with 2n = 72 (Roselle) and H. cannabinnus (Kanaf) with 2n = 36. They belong to family Malvaceae. Roselle shows slow growth in the initial stage but picks up at later stage in the development. Kenaf shows faster growth in the start but rate of growth slows down in the later stage. Roselle has light yellow flower with scarlet to magenta throat and depending on the extent of pigmentation on stem four groups have been identified, namely, full green, green pigmented, green light red and red. Calyx of roselle is used for coloring food. H. machowiii and H. asper are the immediate wild progenitors of H. sabdariffa. H. sabdariffa var. Altissima obtained from Thailand was tall type grown for fibre purpose. Calyx of wild type is fleshy and used for making jam and jelly. India is the largest producer of kanaf fibre. These two crops are suitable for warm and humid climate. They are late maturing and take about 150 days to mature. They are used for sacking and hessian cloth. Hessian cloth is used as packing material for cement and fertilizer. Fine hessian is also used as carpet backing. Retting is an important step in the production of good quality fibre. In this practice jute bundles are immersed in clean, slow water for 2-3 weeks. Harvesting of this crop is done when 50% of the plants have produced pods. Harvesting at this stage gives good yield and fibre quality. Assessment of quality of fibre is on the basis of root content, color, luster, strength, defects, etc. Flowers are hermaphrodite and generally self pollinated but a small amount of cross pollination occurs.

8.3  MENTHA Mentha crop is grown for extraction of menthol. It contains 57-73% menthol. There are four species in this genus Mentha (Tucker and Naczi, 2007). All species are hybrid and they are all polyploids. Menthol is the primary constituent of essential oil of peppermint. The center of origin is Europe. There are two species producing menthol: 1. Mitcham or Mentha x piperata and derived cultivars and 2. Chinese cornmint or Japanese peppermint, Mentha canadensis L. Carvone is the primary constituent of essential oil of 3. Scotch peppermint, Mentha x gracilis and 4. Native or American spearmint, Mentha x villosonervata/ M. spicata. These four hybrid species have been derived from the following crosses. 1. M. x piperata (2n = 72) is the F1 from the cross of M. aquatica (2n = 96), watermint and M. spicata(2n = 48), spearmint. It is sterile. It is also known as M. balsamea 2. Chinese corn mint, M. canadensis is the F1 derived from the cross, M. arvensis (2n = 72) x M. longifolia (2n = 24). The M. canadensis is having 2n = 96. It is fertile and gynodioecious. 3. Scotch peppermint, M. x gracilis is derived from the cross, M. arvensis and M. spicata. It has 2n = 84 and it is almost completely sterile. 4. Native or American spearmint has been derived from the cross, M. spicata and M. longifolia or as a self of M. spicata. It has 2n = 36 and it is also completely sterile. Honey bees forage on the flowers of mint plants which produce nectar. Propagation is through vegetative means as F1 is sterile and does not produce seed.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.7

Cytomixis  The different chromosome number of the F1s of the above mentioned crosses can be explained by a phenomenon called ‘‘Cytomixis” (Gates, 1911). It was first observed in cells of saffron (Crocus sativus) (Kornicke, 1902). It is referred to an extrusion of chromatin from the nucleus of one mother cell to another adjacent mother cell through cytoplasmic connections. This definition now includes the cellular transfer of organelles or other cytoplasmic constituents. Maheswari (1950) reported that in some plants individual chromosomes or group of chromosomes or even the spindles are said to be carried from one cell to another. Because of occurrence of this phenomenon F1 hybrids with 2n = 48, 60, 72, 84 and 96 were obtained from the cross, M. arvensis (2n = 72) x M. spicata (2n = 48). Thus cytomixis can lead to aneuploid and polyploid gamete production. It occurs in pollen mother cells. Cytomixis has been observed in both mitotic and meiotic cells. Cytomixis can be caused by 1. genes, especially male sterile genes, altered by environmental factors such as pollution, fungal infection, etc. 2. abnormal formation of cell wall during premeiotic division and/or micro environment of the anther. 3. chemical/physical mutagens-Colchicine, EMS, MMS, rotenone, sodium azide, triflralin and/or g-irradiation can cause cytomixis. Thompson (1962) coined the term ‘Complement fractionation’ for this phenomenon, cytomixis. Chromosome complement is subdivided into independently operating groups within the cell which results in cell division products with variable chromosome numbers. In case of Mentha, chromosomes migrated in multiples of monoploid number, x = 12 which explains the results of cytomixis in Mentha. Cytomixis has been reported in a number of crops belonging to different families such as Agavaceae, Alliaceae, Brassicaceae, Chenopodiaceae, Fabaceae, Lamiaceae, Liliaceae, solanaceae, Orchidiceae, Rutaceae, Rosaceae, etc. (Tucker, 2012). Breeding objectives include development of disease and pest resistant, high and better oil content cultivars. Most successful breeding methods have been mutation breeding particularly using gamma irradiation and controlled hybridization. In M. canadensis two varieties, Himalaya and Kosi have been developed through controlled hybridization involving varieties, Kalka and Gomti. F1s were evaluated for yield and disease resistance(Kumar et al., 1999). Silviculture  There are four varieties of silk. Pat silk is produced by silk worm, Bombyx mori which is reared indoor on Mulberry plant. Eri (Endi or Errandi) silk is produced by insects, Philosamia ricini which feeds mainly on castor leaves. Muga silk, the golden yellow silk is produced by Antheraea assamensis which feeds on aromatic leaves of i. Som (Machilus bambycina or Persea bombycina) and ii. Sualu (soalu) (Litsaea polyantha). Muga silkworm is multivoltine with 5-6 broods per year. Oak tasar silk produced by A. proyeli feeds on oak. In China oak tasar is produced by A. pernyi. And tsar is produced by A. myelitta which thrives on Asan (Terminalia tomentosa) and Arjun (Terminalia arjuna) and shal (Shorea robusta) trees. Races of A. mylitta include Daba BV, Daba TV, Laria, Modal, Modia, Raily, Sukinda and Sarihan. Mulberry  Bombyx mori chiefly feeds on M. alba, M. latifolia and M. bombysis. Many varieties of these species are diploids with 2n = 2x = 28. Also there are several excellent triploid (2n = 3x = 42) varieties. Autotetraploids often as cytochimeras (2-4-4, 4-2-2 and 2-4-2)

8.8

Crop Evolution and Genetic Resources

have been produced using colchicines and irradiation (Kukimura et al., 1976). These indicate that most mutants must be periclinal chimeras (Katagiri, 1967a). Grafted plants when irradiated followed by cutting shoots back three times in succession results in isolation of ‘wholly’ mutated plants (so called pericilnal chimeras). Mulberry is highly heterozygous. The main objectives in mulberry breeding include higher leaf yield, better leaf quality, resistance to disease or climatic hazards, ability to adapt to different climatic conditions, rooting ability of cuttings, time of sprouting, dry matter per unit area, etc. The silk worm can also be genetically modified to produce super silk through genetic engineering technique. Thus plants and insects both should be improved.

8.4  LAC Besides silk worms and bees, lac insects are the other economically important insects. Lac is produced by insect, Kerria lacca. It belongs to family Coccidae. There are nine genera of lac insects. Out of which only five secrete lac and only one is most widely occurring species in India. It is a small sized insect. Female insects secrete exudates from the body which forms protected covering for the insect to complete life cycle. Lac insects suck plant sap and grow and secrete resins from their bodies. Secretary glands are found in mouth, mesothoracic spiracle and anus. It colonizes branches of different tree species such as palas or dhak (Butea monosperma), kusum (Schleichera oleosa), ber (Ziziphus mauritiana), Semialata (Fleminga semialata), a leguminous bush perennial tree, khair, babul (Acacia auriculiformis), pepal, etc. There it secretes resinous pigment. The coated branches of the trees are cut and harvested as stick lac. Lac is separated from the stick and crushed and sieved to remove impurities. Seived lac is washed in order to remove insect parts and other soluble materials and the resulting product is called seed lac. Thus resins are harvested in the form of amber flakes. Purified resin is the shellac of commerce. Lower grade shellac is used as wax and for varnish whereas the higher grade shellac is used for lacquer work. There are two strains of lac insects species Kerria lacca. Rangeeni strain and Kusum strain. On kusum tree using kusum strain two crops-winter crop (from June-July to February) and summer crop (from Jan-February to June-July) can be taken. In other words, young shoots are inoculated with broodlac in June-July in winter crop and in January-February in winter crop. Pruning is done for obtaining young shoots on the tree. From 1kg seed lac 7-8 kg seed lac in six months can be produced. Normally 4-6kg seed lac is required per tree and from which 35-45 kg seed lac can be obtained. Table 8.4 shows strains of lac insects, host trees and the types of lac crop. Table 8.5 shows suitable trees and lac strains for lac production. Using rangeeni lac strain two crops of lac on dhak are taken. 1. Summer crop (October to April-May) and 2. Rainy season crop (from June-July to October-November) and thus crops can be harvested in 8 and 4 months, respectively. 90% production comes from Aghani and Baisakhi. Kusumi strain can be grown on kusum, ber and flemingia sp. Rangeeni strain can be grown on palas, ber, ficus, etc. Kusumi lac is superior because of lighter colour of resin which fetches higher price in the market.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.9

On ber tree both strains, kusumi and rangeeni of lac insect can be raised where as kusum strain can be raised on only kusum tree and rangeeni strain can be raised only on palas. Table 8.4  Showing strain of lac insect, host tree and types of lac crop Strain Kusumi Rangeeni

Host tree Kusum

Crop

Start

Maturity

Jethwi

June/July

January/February

Aghani

January/February

June/July

Katki

June/July

October/November

Baisakhi

October/November

June/July

Ber

Baisakhi

October/November

June/July

Flemingia sp

Aghani

June/July

January/February

Katki

January/February

June/July

Palas

Table 8.5  Showing various trees suitable for lac production along with various lac strains Common name

Suitable strain

Butea monosperma

Botanical name

Host crop

Palash

R (Rangeeni)

Major crop

Schleichera oleosa

Kusum

K (Kusumi)

Major crop

Zizyphus mauritiana

Ber

K

Major crop

Flemingia semialata

Vanchhola

K

More suitable and economical

F.macrophylla

Bhalia

More suitable and economical Host plants of minor importance

Acacia auriculiformis

Akashmani

K

Acacia catechu

Khair

K

Albizia lucida

Gulwang

K

Cajanus cajan

Pigeon pea

R

Ficus benghalensis

Bargad

R

Ficus religiosa

Peepal

R

Grewia letiaefolia

Dhaman

K K

G. disperma G. serrulata

Pansaura

K

Shorea letura

Sal

R

Samanea saman

Rain tree

K

Zizyphus xylopyrus

Khatber

R

8.10

Crop Evolution and Genetic Resources

8.5  SESBANIA AND CROTALARIA Sesbania aculeata and S. rostrata and Crotalaria juncea are the green manuring crops. They belong to family Leguminosae (Papolionaceae). Besides these, other species such as S. sesban, S. china type, S. speciosa and S cannabina are also cultivated as source of green manure or fodder. In India besides S. aculeata and S. rostrata, S. cannabina is grown for green manuring. In S. rostrata N2 fixation is by root nodules and stem nodules. S. bispinosa is used for reclamation of soil. S. aculeata is most fit for rice-wheat crop rotation system. It is a tetraploid with 4n = 48. There are about 50 species in the genus. Majority of them are annuals, distributed in tropics and subtropics. It is used as fodder, fuelwood and green manuring. S. seban var. nubica, S. goetzi and S. keniensis are perennial and diploids with 2n = 12. S. speciosa and S. brachycarpa are also diploids with 2n = 12 and S. aculeata and S. benthamiana are tetraploids (Herring and Hanson, 1993). All three perennial species are self pollinated and cross compatible. Outcrossing is through bees species Xylocarpa, Apis mellifera, Megachile bituberculata and Chalicodoma sp. Outcrossing is the common method of reproduction under natural condition. There are about 350 species in the genus Crotalaria (sunn hemp). Most of the species in this genus are diploid with 2n = 16. Some species like C. paulina and C. stipularia are tetraploid with 2n = 4x = 32. C. incana is diploid with 2n = 2x = 14. Other species include C. anagyroides, C. retusa and C. scassellatii. The three species, namely, C. spectabilis, C. retusa and C. pallid were introduced in U.S.A. as green manuring crop. It is used for manure, fodder and bast (phloem) fibre. C. juncea is generally a cross pollinated crop but self pollination does occur. These crops fix atmospheric nitrogen. Now a days sesbania is also being grown for fire for cooking food in the villages. For green manuring 30 or 45 days crop is ploughed in the soil and left for decomposition for at least 15 days and after that a crop should be sown or planted. There are other crops from Leguminosae family which fix atmospheric nitrogen and are discussed elsewhere. Sesbania  Green biomass yield of Pant Ses-1, a variety of Sesbania developed by the author, at 45 days was about 16t/ha and at 60 days 30t/ha and dry biomass yield at 45 days was about 4.5t/ha and at 60 days 7.5t/ha and seed yield of more than 20 qtls/ha. The breeding objectives in the green manuring crops include quick early growth, succulent and fast decomposition and efficient in nitrogen fixation. Nitrogen fixation in legumes  Plants obtain nitrogen from two sources: 1. From soil through chemical fertilizers, manures and/or mineralization of organic matter and 2. From atmospheric nitrogen through symbiotic N2 fixation. Soil nitrogen in the form of NO3 first get reduced to NO2 and finally into NH4 as shown below (Figure 8.2). This reaction is catalyzed by nitrate reductase and nitrite reductase, respectively. Between the two nitrate reductase is key and rate limiting plant enzyme, involved in regulation of NO3 and atmospheric nitrogen is reduced by microbial enzyme, nitrogenase. Nitrogenase is synthesized under anaerobic and nitrogen limiting conditions. The NH4 from these two sources are finally assimilated into amino acids, aspartate and asparagines and finally protein. This reaction is catalyzed by aspartate amino transferase and asparagines synthase with phosphoenolpyruvate carboxylase providing a portion of the carbon chain of the amino acids.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.11

Fig. 8.2  Showing steps involved in atmospheric nitrogen fixation.

Symbiotic N2 fixation is through the Rhizobium-legume symbiosis but there are examples of occurrence of symbiotic N2 fixation in non-legumes such as between Eleagnaceae and actinomyceste Frankia and between Azolla (water fern) and cyanobacteria. Symbiotic N2 fixation in Rhizobium-legume symbiosis occurs in root nodules. Nodules have been classified into two major groups on the basis of shape, , meristematic acitivity and fixed nitrogen product 1. Nodules that are cylindrical with indeterminate apical meristematic which transport N as amides (alfalfa, pea and clover) and 2. Nodules which are spherical with determinate internal meristematic activity which transport N as ureides (soybean and common bean). Rhizobium symbiotic genes  There are three types of symbiotic genes. 1 Genes which affect nodulation (nod). 2. Genes determining nitrogenase (nif ) and 3. Those affecting nitrogen fixation (fix). nif anf fix genes are essential for nitrogen fixation. These genes are highly conserved in all rhizobia. They are clustered on plasmids in case of R. meliloti and R. leguminosarum but are found scattered on chromosomes in Bradyrhizobium. Eight genes comprise the nod gene cluster. nod, A, B and C are common nod genes and conserved in most rhizobia. nod D is involved in nodulation. It is a regulatory gene, acts as a positive regulator for other nod genes. Mutation in nod D gene results in no-nodulation or delayed nodulation. nod E, F, G and H are involved in host specificity. All these nod genes are in specify in R. meliloti but only node and F are determine specificity in R. leguminosarum. Nodulation in rhizobial species is very host-specific. For example, R. meliloti nodulates in alfalfa but not in clover or soybean. Further, host-specific genes occur within strains of some Rhizobium species. nif genes are located on plasmids in R. meliloti, R. trifolii and R. leguminosarum. They are found in all Rhizobium and Bradyrhizobium. These genes have similar function in rhizobia and Klebsiella. nifA gene product is a transcriptional activator for other nif operons. fixA, fixB, fixC and fix occur as a single operon. Host plant genes are also involved in symbiosis. Some 25 plant genes or plant gene products have been found to be either induced or enhanced during root nodule development and function (Verma et al., 1986; Govers et al., 1987).

8.12

Crop Evolution and Genetic Resources

nod gene activation is by secondary plant products from root exudates (flavones, flavonones and isoflavones). There is interaction between root exudates and nod gene product. Isoflavonoides also play a role in disease resistance in legumes. Nitrogenase comprises two separate proteins: 1. Fe protein (homodimer) and 2. MOFe protein (tetramer). Fe protein is under control of nif H gene and it donates electrons to MoFe protein. MOFe protein consists of two subunits-a subunit under control of nif D and b subunit under control of nif K. MOFe protein transfers electron to nitrogen and H +. In Klebseilla pneumonia some 17 nif genes are transcribed in eight adjacent operons. nif H, D, and K are structural proteins for nitrogenase. nif B, V, N, E and Q determine proteins involved in the synthesisof MOFe cofactor. nif F and J are flavodoxin electron transport proteins. Function of nif  U, X and Y are not known and nif A and nif L are regulatory proteins affecting other nif genes. Pant Ses-1 developed at G.B.P.U.A. & T., Pantnagar by the author gave green biomas yield of 20-25 qtl/ha at 45 days and 40-45qtl/ha at 60 days, respectively. Further, N-accumulation by this variety was 180kg/ha.

Fodder Crops-Lucerne and Berseem

8.6  LUCERNE Besides pulses, there are fodder crops such as Lucerne or Alfalfa (Medicago sativa) and berseem or Egyptian clover (Trifolium alexandrinum) which fix nitrogen. Lucerne belongs to Papilionaceae family, is a tetraploid. It is a perennial flowering plant and has deep root system (root can go up to 15mts) has 5 to 25 or more stems and commonly attains a height of 2-3 feet. Economic yield can be obtained for 4 to 8 years. It is recommended to take crop for atleast 2 years prior to seeding. This crop is resistant to drought. Lucerne belongs to family Fabaceae. It can be propagated either through seeds or vegetative means. Seeds have hard seed coat and thus it is sacrified in order to enhance germination. There is self sterility in this forage crop. There are four types of varieties in alfalfa. 1. Non-hardy Peruvian type 2. Common 3. Turkistan and 4. Variegated. The first three types of varieties have blue flowers whereas the in the variegated types different types of flowers such yellow, white, blue and green are within the same variety. Synthetic varieties can be developed in M. sativa. The species, M. falcata is a Siberian type Lucerne and has yellow flowers. The genus contains 60 annual, diploid (2n = 2x = 16) and 30 tetraploid (2n = 4x = 32), perennial species. It is a cross pollinated species. Cross pollination is through honey bees and bumble bees. The Medicago sativa complex includes tetraploid cultivated alfalfa and several other diploid and tetraploid taxa. The two principal diploid taxa are subspp. caerulea with purple flower and coiled pods and subspp. falcata with yellow flower and falcate pods. Both subspecies sativa and falcata are cultivated as forage crops. Subspecies varia is hybrid between subspp. sativa and subspp. falcata Evolution has taken different paths in the development of these two subspecific taxa, subspp. sativa and subspp. falcata. The autopolyploid M. sativa subspp. sativa arose

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.13

from diploid subspp. caerulea and M. sativa sub spp. falcata arose through introgression from M. prostrata(Havananda et al., 2010, 2011). mtDNA in M. sativa is maternally inherited and cpDNA is biparentally inherited with strong paternal bias. The species M. marina, M. arborea, M. citrine and M. strasseri from dry Mediterranean are the sources of genes for drought resistance. Tripping is required for seed production. In lucerne, pollen is dispersed by an explosive action, called, ‘tripping’. Flowers are usually tripped by bees although automatic tripping may occur occasionally through wind, rain or heat. Fertility of lines ranges from high self fertility to high sterility or incompatibility. In forage crops vegetative propagation can be by stolen-runner or creeping stem above ground, rhizome- underground stem which develops root or stem cutting. Forage legumes such as Lucerne or berseem are readily propagated through stem cuttings.

8.7  BERSEEM Egyptian clover, Trifolium alexandrinum is an annual summer or winter legume. It is a winter hardy crop. It fixes nitrogen @100-200lbs/acre. Both diploid and tetraploid exist. There are two types of varieties (Zohary and Heller, 1984). T. alexandrinum var. alexandrinum, is a single cut, unbranched with apical branching variety belonging to ‘Fahli’ group. T. alexandrinum var. serotinum belongs to ‘Mescavi’ group with basal branching, multicut (4-6 cut). Saidi group of varieties produce both basal and apical branch with 2-3 cuts per crop. In India berseem is predominantly cross pollinated but requires tripping for higher seed set. T. berytheum and T. salmoneum are the primary ancestors of T. alexandrnum. There is presence of B-chromosome in berseem. Table 8.6 shows some N-fixing crops along with their N-fixing capacity. There are some 90 species in the genus, Trifolium. Genetic resources of berseem are given in the table 8.7 (Ravagnani et al., 2012). Table 8.6  Showing N-fixing crops and their N-fixing capacity Species

Name

N Kg/ha

T. pratense

Red clover

17-154

T. repens

White clover

128-268

T. hybridum

Alsike clover

21

T. incarnatum

Crimson clover

110-184

T. alexandrinum

Egyptian clover

62-235

T. fragiferum

Strawberry clover

T. subterraneum

Sunterranean clover

T. resupinatum

Persian clover

T. semipilosum

Kenya white clover

Melilotus alba

Sweet clover

M. officinalis

-do-

Flower color

More palatable than any other grass or legumes

More palatable than any other grass or legumes

21-205

9-140

Distinct feature

White flower Yellow flower

Crop Evolution and Genetic Resources

8.14

Sweet clovers are inferior to lucerne and red clover because of lower palatability and there is presence of toxic substance (dicoumarine) in the leaves and stems. Table 8.7  Showing different species of Trifolium Species

Cultivated/ wild

Perennial/Annual

Ploidy level

T. repens(white clover)

Cultivated, most important legume of gazed pasture in temperate areas

Perennial, outbreeding with gametophytic SI

Allotetraploid (2n = 4x = 32), vegetative propagation by stolens or horizontal stems

T. pratens(red clover)

Cultivated, widely used as cut forage and consumed as winter feed (for silage production) in temperate areas, high protein content

T. subterraneum

Common forage crop, Annual, common gown in Mediterranea n, forage crop Australia, Middle east, India

Diploid (2n = 14). It is the only species with n = 7.

T. truncatula T. ambiguum

Sequencing is complete Diploid(2n = 16)

Pasture legume

Gene pool

Perennial

Model legume, sequenced

Diploid(2n = 16)

T. occidentale

Diploid(2n = 16)

Likely progenitor of T. repens, paternal genome donor of T. repens, drought tolerant

T. nigrescens

Diploid(2n = 16)

High inflorescence and seed set

T. pallescens

Diploid(2n = 16)

Cold tolerant, likely progenitor of T.repens, maternal genome donor

T. diffusum

Annual

2n = 16, diploid

T. pallidum

Diploid with 2n = 16 closely related

T. medium

2n = 72

T. sarosience

2n = 48

T. alpestre

2n = 16

T. alexandrinum

Common forage crop, grown Annual species in Mediterranean, Australia, Middle east, India

2n = 16

T. eriosphaerum

2n = 14

GP1 of T. subterraneum

T. pilulare

2n = 14

GP1 of T. subterraneum Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.15

Contd...

Species

Cultivated/ wild

Perennial/Annual

Ploidy level

Gene pool

T. berytheum

2n = 16

GP1 of T. alexandrinum

T. salmoneum

2n = 16

GP1 of T. alexandrinum

T. resupinatum

2n = 16

GP1 of T. alexandrinum

T. apertum

2n = 16

GP3 of T. alexandrinum

T. constantinopolitanum

2n = 16

GP3 of T. alexandrinum

8.8  GUINEA GRASS Panicum maximum is an erect, 1-2.5m tall, perennial grass. It tillers profusely and clumps move up to 30cm or more in width. It is mostly used for pasture but can be used for green chop. It is vegetatively propagated through stem cuttings. Mature seed produced is less. Seed viability is less and thus germination per cent is less. Lack of good seeds limits its growth and development. Culivated species exists as diploid (2n = 16), tetraploids (2n = 4x = 32) and hexaploids (2n = 6x = 48). It is a cross pollinated crop with pseudogamous apospory. In pseudogamous apospory diploid embryosac is formed from somatic cells by mitotic division but pollination is required to stimulate development of cells. Interspecific hybridization of P. maximum with P. infestum and P. trichocladum has been obtained. Cynodon dactylon  Both diploid (2n = 18) and tetraploid (2n = 4x = 36) forms exist. There is production of 2n gametes in this species. All types of hybrids, namely, 2n × 2n, 2n × 4n, 3n hybrids have been obtained (Chedda, 1971). It is cross pollinated . It is highly self sterile. Anthesis and seed setting occurs. It is vegetatively propagated athough sexual reproduction is normal. The different species of the genus Cynodon are given in the table 8.8 below. C. arcuatus, C. barberi and C. plectostachus are the only three valid species. It is a native of India. Table 8.8  Showing species, chromosome number and distribution of Cynodon

Species

Chromosome number

Distribution

C. arcuatus

36

India, S.E. Asia, Malagasy

C. barberi

18

India

C. dactylon

18, 36

Ubiquitous

Var. dactylon Var. afganicus

18, 36

Var. aridus

18

South Africa, India, Malagasy

C. coursii

36

Malagasy

C. elegans

36

South Africa Contd...

Crop Evolution and Genetic Resources

8.16 Contd...

Species

Chromosome number

Distribution

C. aethiopicus

18, 36

Ethopia and East Africa

C. incompletes

18

South Africa

Var. incompletes

18

Var. hirsutus

18

South Africa

C. nlefuensis

18, 36

East Africa

C. plectostchyus

1188

East Africa South Africa

C. transvaalensis

8.9  AZOLLA Azolla is also being advocated for raising for fixing atmospheric nitrogen in soil and also as animal feed. It is associated with cynobacterium (symbiotic association) which fixes nitrogen from air and water. It is a water fern. There are seven species of Azolla: A. pinnata, A. filiculoides, A. mexicana, A. caroliniana, A nilotica, A. microphilla and Azolla rubra. It all fixes atmospheric nitrogen at the rate of about 30-40kg nitrogen/ha in single does application and makes available in three weeks time in the soil.

8.10  BACTERIA Rhizobium, Azotobacter and phosphate solublizing bacteria such as Pseudomonas and Bacillus spp. are being used for fixing atmospheric nitrogen and making available the unavailable phosphorus present in the soil. Further, Fungi, Trichoderma viride and T. harzianum are being used for controlling fungal plant pathogens such as Rhizoctonia solani, Pythium and Sclerotia rolfsii and bacteria, Pseudomonas fluorescence against fungal and bacterial pathogens such as Pythium, Phytophthora, Fusarium, Botrytis, Sclerotium, Sclerotinia, Rhizoctonia solani, Ustilao, etc. Application of rhizobium culture at the rate of 20-30gm per kg of seed results in 10-12% increase in yield of various pulse crops. Table 8.9 shows different Rhizobium strains and the crop associated with. Table 8.9  Showing Rhizobium strains and their association with different crops Genus Rhizobium

Brady rhizobium

species

Crop

R. leguminosarum vicia

Vicia

R. leguminosarum trifolia

Trifolium

R. leguminosarum faseoli

Faseolium

R. meliloti

Meliloti

R. japonicum

soybean

Rhizobium species

Chickpea, pigeon pea, moong, urd, etcetc

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.17

PSB  Phosphate solublizing bacteria increase the availability of phosphorus in the soil. Insoluble phosphorus is changed to soluble phosphorus which is readily absorbed by the roots of the plants such as wheat, chickpea and potato. PSB include Pseudomonas sp., Bacillus sp. Rate of application is 600-1000gm/ha Azotobacter  It can be applied in rice, wheat, rye, maize, jowar, Solaneous vegetable, cotton, sugarcane, etc. It fixes atmospheric nitrogen and makes available 20-25kg nitrogen/ ha to plants. Besides it provides plant hormones and plant growth regulating substances to plants. The different species of Azotobacter include A. raspeli, A. virilendi, etc. Rate of application is 600-1000gm/ha. Azospirilum  It is an atmospheric nitrogen fixing bacteria which make available 20-25 kg N/ha to plants. Rate of application is 600-1000gm/ha. In case of azotobacter, azospirilum and PSB, 2kg culture is mixed with 25kg compost plus 25kg soil and then is applied.

8.11  ARBUSCULAR MICRORRHIZAL FUNGI(AMF) These are fungi which increase the root area for adsorption of nutrients, particularly phosphorus and water from soil. There are two types of micorrhizal fungi. Endotrophic micorrhiza is made up of zygomycetous fungus and roots of herbaceous plant. Hyphae penetrate the cells of the roots and form swollen (vesicles) or branched haustoria (arbuscules) like structure. Ectorophic mycorrhiza is made up of basidiomycetous fungus and the roots of forest trees (pines, eucalyptus, oalc). They are intercellular. The various subgenera of arbuscular mycorrhizal fungi include Glomaceae (Glomus, Scherocystis), Aculosporaceae and Gigasporaceae (Gigaspora). Glomus and Gigaspora are easily maintained in open pot individually and in vitro. Rate of application is 100gm of innoculum/sq meter in nursery, 5-6kg/acre for soil application and in case of fruit trees 200gm/tree.

Crops for Raising Honey Bees Various crop plants such as mustard, safflower, niger (kharguja), drumstick (sahjan) and karanj (Pomgania pinnata) can be raised. Karanj  It is a drought resistant legume of Indian origin. It can withstand waterlogging, slight frost, highly tolerant to salinity and it fixes atmospheric nitrogen. It flowers during April-May. Seed contains 27-39% non-edible oil. Seeds contain two flavonoids- pongamol and karanjin. Pongamol oil is a source of biodiesel.

8.12  POTATO Potato (Solanum tuberosum) is a vegetatively propagated crop. About 70% of the production is in Europe. Potato contains 70-80% water and rest starch. It is also a good source of vitamin C and protein (1 to 6%). It was first considered an autotetraploid with 2n = 4x = 48 but is more probably a segmental alloploid, derived from the cross of S. stenotomum (cultivated diploid, 2n = 2x = 24) x S. sparsipilum (wild diploid, 2n = 2x = 24) (Fig. 8.3). Figure 8.4

8.18

Crop Evolution and Genetic Resources

shows origin of S. tuberosum subsp. tuberosum from S. tuberosum subsp. andigena which itself evolved from S. stenotomum complex. Small size of chromosomes, absence of distinct genome differentiation and meiotic irregularities in vegetatively propagated clones make it difficult to establish genomic relationship. Species differ from each other by very small chromosome segments which do not affect pairing in hybrids but which results in sterile F1 plants, or weak and unthrifty F2 progenies. Potato originated at high altitudes in the Andes mountain close to Chile, Peru and Bolivia. From there it was carried to throughout South and Central America. It was introduced into Europe (Spain) in 1570 and into England in 1590. British missionaries took potato to India, China, New Zealand and japan in the 17th century. These potatoes were the Andean form of tetraploid potato, S. tuberosum subsp. Andigena adapted to short (12 hour) day. Potato cultivation on field scale was possible only in the late 18th and nearly 19th centuries adapted to 16-18hrs of day of Europe. The ploidy level in cultivated potato ranges from diploids (2n = 2x = 24) to pentaploids (2n = 5x = 60) with all intermediates. The cultivated tetraploid is most widely grown in the Andes region. Potato species seem to have evolved through geographical and ecological isolation rather than by genetic incompatibility. Tetraploid and hexaploid species seem all to be self-compatible (self-incompatibility is lost in autotetraploid). The cultivated potato belongs to the series Tuberosa (Table 8.7). The genus includes 2 subsections and 29 series. Most diploid species are self-incompatible, due mainly to S-allele while polyploids are self-compatible and generally self-pollinated. Some 228 wild species are now recognized and have the same basic number X = 12 and ranges from diploid to hexaploid (Table 8.10). Nearly all the related wild species are in the same gene pool. Two series of genomes have been identified. An A series (A1, A2, A3, A4) of South American origin and a B series (B1, B2, B3, B4) of Mexican origin. The poor seed set in potato is due to male sterility or incompatibility and the inherent male sterility is dominant over fertility.

Fig. 8.3  Showing evolution of cultivated tetraploid potato, S. tuberosum

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.19

Table 8.10  Showing classification, species, ploidy levels and distribution of potato (Adapted from Hawkes, 1999) Subsection and series Subsection-Estolonifera (Absence of stolens or tubers) Series-1. Etuberosa (D genome)

2. Juglandifolia Subsection-Potatoe (Presence of tubers) Superseries, Stellata (primitive) Series-I. Morelliformia II. Bulbocastana (B genome)

Species

Ploidy level

Source of gene for resistance

Distribution (Hawkes and Jackson, 1992) South America

S. brevidens S. etuberosum S. lycopersicoides

S. morelliforme S. bulbocastanum S. clarum S. brachistotrichum III. Pinnatisecta (B genome) S. cardiophullum S. jamesii S. pinnatisectum S. trifidum S. polyadenium IV. Poyadenia (B genome) S. lesteri V. Commersoniana (AA genome) S. commersonii S. capsicibaccatum VI. Circaeifolia (A genome) S. circaeifolium S. lignicaule VII. Lignicaula S. olmosense VIII. Olmosiana S. chacoense IX. Yungasensa (Stellata advanced) S. tarijense S. yungasense X. Megistacroloba (Super Series, S. boliviense Rotata (primitive) S. megistacrolobum S. santae-rosae S. toralapanum S. infundibuliforme XI. Cuneoalata S. chomatophilum XII. Conicibaccata (A, AA genome) S. santolallae

Southwestern USA, Mexico, Central America

2x, 3x

LB, PCN

2x, 3x 2x, 3x

PCN

GP3

LB LB 2x, 3x PCN LB

W

VIRUS X, RKN

South America -

LB,VIRUS X PCN

South to central regions of South America -

Contd...

Crop Evolution and Genetic Resources

8.20 Contd...

Subsection and series

XIII. Piurana (A genome) Super Series, Rotata (advanced) XIV. Ingifolia XV. Maglia

XVI. Tuberosa (wild)

Species S. violaceimarmoratum S. agrimonifolium S. colombianum S. longiconicum S. oxycarpum S. moscopanum S. piurae S. tuquerrense S. ingifolium S. maglia

S.alandiae S. berthaultii S. brevicaule S. bukasovii S. canasense S. gandarillasii S. gourlayi S. hondelmannii S. kurtzianum S. leptophyes S. marinasense S. microdontum S. multidissectum S. neocardenasii S. oplocense S. Sparsipilum

XVI. Tuberosa (A, AA genome) (cultivated)

Ploidy level

Source of gene for resistance

4x 4x 4x 4x 6x

4x

Distribution (Hawkes and Jackson, 1992) Central to northern regions of South America -

2x, 3x (A type cytoplasm)

LB, C C 2x, 4x, W

PCN

W W 2x, 3x, W C

LB, RKN

2x, 3x, 4x, 6x, W W

PCN

s. Spegazzinii S. vernei S. verrucosum S. sucrense S. x ajanhuiri

W W

S. phureja

S

4x, W

WART, VIRUS X, PCN, RKN WART, PCN LB, PCN LB VIRUS X. PCN

North-West Argentina, C

LB, VIRUS X, RKN, gens for earliness

Northern Andes Valleys, C

Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.21

Contd...

Subsection and series

XVII. Aculia

XVIII. Longipedicellata (AB genome)

XIX. Demissa (AAB or ABB Genome)

Species

Ploidy level

S. stenotomum S. x chaucha

S 3x, S

S. x juzepczukii S. tuberosum subsp. tuberosum S. tuberosum subsp. andigena

3xC 4x (T type cytoplasm) 4x (A type cytoplasm)

S. x curtilobum S. albicans S. acule

5x, S 6x 4x, C

S. x vallis-mexici

3x

S. fendleri S. hjertingii S. papita S. polytrichon S. stoloniferum S. x semidemissum

4x 4x 4x 4x 4x 5x

S. x edinense S. brachycarpum S. demissum

5x 6x 6x, W

S. guerreroense S. hougasii S. iopetalum S. schenckii

6x 6x 6x 6x

Source of gene for resistance

LB, WART,

Distribution (Hawkes and Jackson, 1992) Nothern high Andes, C Andes valleys from Ecuador to Bolivia, C Central high Andes, C World wide, C

LB (immune), WART, VIRUS X, RKN, genes for adaptability to short days

Southern South America, C

VIRUS X,RKN

Central high Andes, C -

WART, VIRUS X, PCN, genes for adaptability to short days Southwestern USA, Mexico, Central America

LB -

LB (R1, R2, R3,etc.), genes for adaptability to short days

C = Cultivatid



• Triploids and Pentaploids with ‘x’ placed before species name indicated these to be naturally occurring hybrids.

8.22

Crop Evolution and Genetic Resources

There are about 200 species in potato. GP1 consists of S. tuberosum whereas GP2 includes important species such as S. acule, S. spegzinii, S. stoloniferum, S. vernei and S. demissum which are sources of resistance to different disease and pests. GP1 includes all land races and cultivars. The GP2 include about 180 tuber bearing species. GP1 and GP2 of potato encompass all species classified as super series Rotata plus species housed in the series Yungasensa of super series, Stellata (Hawkes, 1990). GP3 encompasses all species of super series, Stellata with exception of those in the series, Yungasensa. GP3 consists of 18-20 diploid species including two diploid non-tuber producing species of series, Eutuberosa and Juglandifolia. Wild potato evolved from Stellata (primitive) with star shaped flower and with EBN of 1 to Stellata (advanced) and then to Primitive Rotata with pentagonal corolla and broad triangular lobes and EBN of 2. On determinant of successs of interspecific hybridization is endosperm balance number (EBN) (Johnston et al., 1980). EBN acts as a screen for either 1 or 2n gametes depending on the EBN and chromosome numbers of the parental species. EBN defines crossability between species such that successful hybridization requires 2:1 ratio of maternal: paternal genetic contribution to the developing endosperm. Species with matching EBN values, regardless of ploidy level, will hybridize as long as other barriers (pre- or post zygotic) are absent. Ploidy and EBN values of wild relatives of potato include 6x(4EBN), 4x(4EBN), 4x(2EBN), 2x(2EBN) and 2x(1EBN). All species barring 2x(1EBN) which belongs to GP2, constitute GP1B. Cultivated potatois tetraploid with EBN of 4. Most GP2 are diploid with 2n = 2x = 24 although it includes triploid, tetraploid, pentaploid and hexaploid with EBN of 2. GP3 comprises diploids with EBN = 1. EBN like system has been suggested in a number of crops such as Impatiens, Lycopersicon, Avena, Trifolium. Sexual polyploidization results in greater variability, fitness and heterozygosity.

8.13  SUGARCANE Sugarcane (Saccharum officinarum) is an octoploid with 2n = 80. The basic genomes being X = 8,10 and 12. It is a cross-pollinated crop (anemophily) used for production of sugar. Cultivated plants are generally prevented from flowering because non-flowering plants have higher sucrose production. The fibrous residue left after sugar extraction is called bagasse which is used for production of paper or can be used as fuel. Molasses, the thick brown uncrystallized bitter syrup obtained from sugar during refining contain 50% sugar. Fermentation of molasses results in fermentation of alcohol and this may be distilled to yield rum. It is a vegetatively propagated crop and vegetative propagation is through short stem cuttings (usually setts are 20-25 cm in length) consisting of several nodes and internodes. Sugarcane belongs to the family Gramineae of Genus-Saccharum, Tribe-Andropogoneae and subtribe –Saccharastrae. The subtribe Saccharastrae contains 10 genera of which 6 genera such as Erianthus sect. Ripidium, Miscanthus sect. Diandra, Sclerostachya, Narenga and Saccharum constitute “ The Saccharum Complex” (Mukherjee 1954, 1957; Daniels et al., 1975c). The genus Saccharum contains six species given in Table 8.11 (Daniels and Roach, 1987). Ratoon crops can be taken in sugarcane. Amount of sucrose is inversely proportional to the amount of fiber. Timing of flowering

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.23

in sugarcane is a reflection of the day length of the latitude at which the plants are growing. Flower emergence begins near the equator before or during the autumn equinox (~ Sep. 22) and gradually progresses northward to reach 10°N by October, 20°N during November and 30°N in December (Brett, 1951; Mangelsdorf, 1956). The seasonal flowering pattern in the southern hemisphere is the mirror image of that in the northern hemisphere. Flowering progression in the southern hemisphere takes place from March through June. Further, clones evolved at higher latitudes tend to flower earlier than clones originating at lower latitudes. Clones grown south of their origin flowered earlier while those grown north of their origin flowered late. Sugarcane has relatively short flowering season (2 to 3 weeks) and the entire Saccharum complex has long flowering season (5 to 6 months). Flowering in late flowering clones can be advanced by imposing inductive day lengths in a photoperiod house before these day lengths occur naturally. Similarly, delaying flowering in early flowering clones can be achieved by increasing day lengths using lamps. The degree of male fertility ranges from 0 to 100%. Some varieties seem to be incompatible when crossed and some varieties are male sterile. Crossing of S. officinarum with related species, S. spontaneum followed by one or more back crossing to S. officinarum is termed Nobilization. The evolution of sugar cane probably involves combinations between elements of S. spontaneum, Erianthus sect. Ripidium and Miscanthus sect. Diandra (and possibly Sclerostachya). S. officinarum evolved from S. robustum by introgression with other genera and it evolved most probably in the east Indonesia/New Guinea area, east of the Wallace line from core taxa S. spontaneum, Miscanthus sinensis and Erianthus arundinaceus. S. robustum represents some very genetically diverse populations evolved from introgression of S. spontaneum with other genera (Erianthus arundinaceus, Miscanthus, etc.) in Wallacea/New Guinea. S. barberi was derived from the cross, S. officinarum x Erianthus sect Rapidium and has played an important role in the evolution of all groups of S. barberi. The Saretha group of S. barberi originated independently in northwest India (Barber, 1915; Vernkatraman,1938; Grassl, 1977 and Rao, 1980). S. sinensis contains two groups of clones. One group having mop like panicle (clone Tekcha) evoled by introgression from Miscanthus sacchaflorus to S. officinarum and clone China evolved from S. barberi clones. Intergeneric hybrids between sugarcane and related genera such as Sclerostachya, Narenga, Erianthus, Miscanthus and sorghum can be made easily and large number of F1’s can be produced. Chromosomal segmental exchange takes place in the successive backcrosses in the sugarcane x sorghum hybrid backcross-self complexes. In the Sugarcane x Bambusa cross fertilization took place but there was no further development of embryo and endosperm (Rao et al., 1967, 1969). The Saccharum (2n = 80) x Zea (2n = 20 + 2B) cross produced sterile seedlings with 2n = 52 to 58 (Janaki Ammal, 1938). The cross Saccharum x Imperata cylindrical (2n = 20) produced four types of seedlings, 1. vegetative seedling with 2n = 106 2. self or diploid parthenogenic seedling with 2n = 108-112 3. triploid self with 2n = 156 and 4. true hybrids with 2n = 120-134. The F1’s were similar to sugarcane (Janaki Ammal, 1941). Erianthus- Section – Ripidium (typically) 2n = 20, 30, 40 and 60 euploid clones), Miscanthus (typically 2n = 38, 40 and 76, euplodis) and Narenga (typically 2n = 30) are genera within the Saccharinae, closely allied with Saccharum. Different

Crop Evolution and Genetic Resources

8.24

Erianthus species of section Rapidium are E. arundinaceus, E. bengalense, E. elephantinus, E. longisetosus, E. procerus, E. rufipilus and E. trinii (Burner, 1991). Miscanthus sinensis and Narenga polyphyrocoma are the species of the genera, Miscanthus and Narenga, respectively. Table 8.11  Showing species, their characteristics, ploidy levels and gene pool in sugarcane Genus-Saccharum

Characteristics

Ploidy level 2n = 80

Groups of representative clones

S. officinarum (noble cane)

Cultivated, thick stalk sugarcanes, more sugar, more fibre, susceptible to stress environments and diseases

S. barberi

Cultivated in northern India. 80-124 with At present not in cultivation, considerable amount medium sugar content of aneuploidy (82,90,91,92)

Mungo, nargori, Saretha, Sunnabile

S. sinensis (thin cane)

Cutivated in China

Open panicle, mop like panicle

S. spontaneum

Wild cane from New Guinea 40-128 to the Mediterranean and Africa, low or little sugar, resistant to drought, water logging and saline conditions

Subspecies-indicum, aegyptiacum, luzonicum

S. robustum

Wild cane from Indonesia/ New Guinea, more sugar, more fiber

2n = 60, 80

Forma sanguineum, Teboe Salah, GP1 Wau/Bulolo, Port Moresby, Goroka and gian fencing clones

S. edule

Cultivated, Edible inflorescence sugarcane from New Guinea and Melanesia

60, 70 and 80 with aneuploid forms

NG28-201, NG57-28

106-120

Noble, no forth glume, fourth glume present, fourth glume awned, purplr hair color, pink to red flesh and brown flesh

Gene pool GP1

GP1

SubtribeSaccharastrae Imperata

GP2

Eriochrysis

GP2

Eccoilopus

GP2

Spodiopogon

GP2

Miscanthidium

GP2

Erianthus sectRipidium

GP1

Miscanthus sect- Diandra

GP1

Sclerostachya

GP1

Narenga

GP2 Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.25

Contd...

Genus-Saccharum

Characteristics

Ploidy level

Groups of representative clones

Gene pool

Saccharun Sorghum

GP3

Zea

GP3

Bambusa

GP3

8.14  SUGARBEET Sugarbeet (Beta vulgaris) crop is grown for producing sugar like sugarcane. The improved varieties contain as much as 20% sucrose. About 50% of the world’s total sugar comes from sugarbeet. It belongs to the goosefoot family, Chenopodiaceae. It is a diploid with 2n = 2x = 18. It is a temperate crop but can be grown in subtropical condition having cold winter and largely grown in Europe, USSR and North America. Seeds can be monogerm or multigerm. The former produces single seedling whereas the later produces cluster of seedlings and thus thining is required in the field. It is normally a cross-pollinated crop and cross-pollination is mainly through wind (anemophilous) and insect plays a minor role. Fertility ranges from 100% self fertile (self compatible) to self sterile (self incompatible). B. vulgaris originated from B. maritima. B. vulgaris in cross with species from sectionvulgaris produces fertile F1s but when crossed with species from other sections produces F1s which are usually sterile. Triploid varieties are a success in Europe but tetraploid varieties have not been successful. Cytoplasmic male sterility has been used to produce commercial hybrids. Table 8.12 shows different specis, chromosome number and genepool. Sugarbeet plant consists of a root system, a hypocotyl and an epicotyls with leaves. Crown is above the soil surface part of the beet. The beet yield is constituted by the epicotyls and part of the hypocotyls. Crown height is defined as the distance from the soil surface to the top of the epicotyls(top of the crown). This distance varies from plant to plant. Heterogeneity in crown height is an important source of losses in yield during harvest. Table 8.12  Showing species, chromosome number, gene pool and distribution of sugar beet Section- vulgaris

Chromosome number

Gene pool

B. vulgaris

18

B. maritima

18

GP1

B. macrocarpa

18

GP2

B. patula

18

GP2

B. atriplicifolia

18

GP2

Breeding system

Distribution

Mostly outcrossed & anemophilous Source of gene for res. & Cercospora leaf spot

Temperate parts of Europe and Asia

Section- Corollinae Contd...

Crop Evolution and Genetic Resources

8.26 Contd...

Section- vulgaris

Chromosome number

Gene pool

B. macrorhiza

18

GP3

B. trigyna

36, 45, 54

GP3

B. foliosa

18

GP3

B. lomatogona

18, 36

GP3

Breeding system

Distribution

Section-Nanae B. nana

18

Section-Patellares B. patellaris

36

B. procumbens

18

B. webbiana

18

8.15  TOBACCO There are two cultivated species of tobacco-Nicotiana rustica (2n = 48) and N. tabaccum (2n = 48). Tobacco is normally a self pollinated crop but outcrossing ranges from 4 to 10% and cross pollination is through insects. The genus Nicotiana comprises 3 subgenera, 14 sections and 65 species (Smith, 1968). The haploid number ranges from 9 to 24. N. tabaccum was evolved from the crossing of species, N. sylvestris (2n = 24, S genome) x N. tomentosiformis (2n = 24, T genome) and subsequent doubling of chromosome of F1 and thus it is an amphidiploid with 2n = 48. The genomic constitution of N. tabaccum is SSTT. Similarly, N. rustica arose from the cross, N. paniculata (n = 12) x N. undulata (n = 12) and subsequent doubling of chromosomes of F1. Cultivated species include, N. repanda, the finest tobacco grown in Cuba for cigar, N. rustica grown in Syria and Turkey, and N. Persia (Fina Shiraz). Flowering (ornamental) species include N. alata, N. sylvestris, N. langsdorffii and N. mutabilis.Various interspecific crosses have been made. Table 8.13 shows different species alongwith their ploidy level. Table 8.13  Showing species of Nicotiana and its chromosome number Species

Chromosome number

N. rustica

48

N. tabacum

48

N. alata

18

N. langsdorffii

18

N. sylvvestris

24

N. repanda

48

N. glauca

24

N. suaveolens

32 Contd...

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.27

Contd...

Species

Chromosome number

N. glutinosa

24

N. plumbaginefolia

20

N. tomentosiformis

24

N. otophora

24

N. longiflora

20

N. debneyi

48

Tobacco is an important source of phytochemicals such as solanesol, nicotine, proteins, oil (seed contains 35% oil and linoleic is the major constituent (66-76%, higher than safflower and sunflower oil) and organic acid such as malic and citric acid. Refined tobacco oil is used as edible oil in countries such as Turkey, Tunisia, Greece and Bulgaria. Solanesol is used as source of Vitamin K analogues and Co-enzyme Q10. Ten different types of tobacco based on usage are grown. These include cigarette (flue cured Virginia, burley, orientale) and non-cigarette types such as bidi, chewing,hookah, natu, cheroot, cigar and HDBRD (traditional burley cigarette type air cured). Breeding objectives include developing variety with high solanesol, high flavor, low nicotine, etc. Quality parameters in tobacco include color, body, texture, maturity/ripeness, graininess, hygrosopicity, shatterability, blemish, elasticity, fluffiness, aroma, leaf size and vein color. Manufacturing quality includes filling value, equilibrium moisture content, pore volume, shatterability, combustibility, lamina/mid rib ratio, number of leaves per kg and lamina weight per unit area. Chemical quality traits include nicotine content, total nitrogen and chlorides content and the quality ratios include sugar/nicotine, sugars/nitrogen and total nitrogen/nicotine. Quality of tobacco can be improved through adoption of package of practices which includes topping and sucker control, curing, bulking, grading and bailing. Topping refers to removal of auxillary buds at bud emergence stage. Topping improves leaf size, thickness, body, yield and overall quality. Alkaloid and sugar contents go up along with yield. Curing methods include flue curing (heat curing with exposing to smoke), fire curing, air curing and sun curing.

8.16  SWEET POTATO Sweet potato Ipomea batatas (L.) (6x = 90) is an important starchy crop. It is a perennial plant producing edible storage roots. It has high nutrient content (vitA, vitC, B2, B6 and E), low in fat and cholesterol and anticarcinogenic and cardiovascular properties (Hill et al., 1992). It is a good food for diabetics as it helps to stabilize blood sugar levels and to lower insulin resistance. Its root contains 25 to 28% carbohydrate and 1 to 2% protein. It is eaten by human either baked or fried, as animal feed and source of industrial starch. There are two types of crops- a starchy form with less sugar (apichu, kamote and aje) and a sweet type

8.28

Crop Evolution and Genetic Resources

with 3 to 6% sugar (batatas). It is propagated through stem cuttings. The genus contains more than 500 species. It belongs to the family Convolvulaceae with diploid (2n = 30), tetraploid (2n = 60) and hexaploid (2n = 90) (Austin, 1987). It is a cross-pollinated crop. The origin of sweet potato is Peru or Middle America. There are contrasting views on the evolution of the hexaploid I. batatas. According to some I. batatas is an auto hexaploid of a diploid, I. trifida whereas others think that I. batatas and I. trifida to have evolved separately from a non-existent, common ancestor (Kobayashi, 1984) (Fig. 8.5). I. trifida complex comprises a group of wild plants ranging from diploid to hexaploid. These are ancestral plants of sweet potato. Diploid and polyploid can be crossed with hexaploid sweet potato (2n = 6x = 90) and polyploid forms of I. trifida and hexaploid sweet potato have been produced by duplication of the genome in the diploid form of I. trifida. Thus I. trifida exists in diploid (2n = 2x = 30), tetraploid (2n = 4x = 60) and hexaploid (2n = 6x = 90). This is based on the finding that polyploid forms of I. trifida and hexaploid sweet potato can be produced by duplication of genome in the diploid form of I. trifida and so tetraploid and hexaploid of I. trifida and sweet potato must be autopolyploid. Another view is that sweet potato is an allopolyploid, showing tetrasomic inheritance (Zhang et al., 2001). Data suggest that I. batatas consists of two related and a third more distant genome (Magoon etal., 1970). Wild species are diploid and the cultivated species is hexaploid. Austin et al., (1991) recognised 12 sections in the genus lpomoea, namely Pharbitis, Mina, Calonyction, Batatas, orthiopomoea, Exogonium, Eriospermum, Erpiopomoea, Dasychaetia, Acmostemon, Xerophyla and Poliothamnus. Section Batatas includes wild species which are phylogenetically considered to be closely related to the only cultivated species(1988a). 13 different species of lpomoea along with different ploidy levels are l. batatas (hexaploid, tetraploid), l. gracilis, l. littoralis, l. tiliacea (tetraploid) and l. cynanachifolia, l. grandiflora, l. lacunosa, l. leucantha. l. ramosissima, l. tenuissima, l. trichcarpa, l. trifida, l. triloba (diploid). The three cytogenetic groups in the section Batatas are as follows (Nishiyama, 1982). 1. Group A genome-Self compatible (l. lacunosa, l. triloba, l. trichocarpa) 2. Group B genome-Self incompatible (l. batatas (6x), l. x leucantha, l. littorarils (4x) and l. trifida (6x)) 3. Group X-Self incompatible (l. tiliacea (4x), l. gracilis (4x)) Taramura (1979) defined two groups on the basis of crossability at the same ploidy levels. 1. At diploid level-l. lacunosa, l. triloba 2. At tetraploid level-l. gracilis, l. tiliacea 3. At hexaploid level-l. trifida, l. batatas Self compatibility was found in the diploid species and self incompatibility was found in diploid l. trifida, tetraplod, l. tiliaceae and both tetra and hexaploid l. batatas (Diaz et al. 1996). l. trifida x l. x leucantha may act as a ‘bridge species’ from gene flow wild Ipomoea species to the gene pool of sweet potato.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.29

Sweet potato arose through allopolyploidization. l. triloba and l. trifida are sweet potato’s closed extant relatives and its possible progenitors. The two species belong to two different genomes groups and are cross incompatible (Austin, 1988). It is a dicot and cross pollinated crop. Self pollination rarely occurs. There is high degree of self-incompatibility. Cross-incompatibility also occurs between certain parents. Height of stamen varies in different clones. Where stamens are shorter than pistil, it is easy to pollinate stigma but where stamens are of the same height as that of stigma or taller than pistil, it is difficult to find stigma and pollinate. Inflorescence is axillary which consists of 1-22 buds. They open in group of 2 or more after day break and fade by noon. Filaments vary in length from 5 to 21mm. Height of stamen varies in different clones. Where stamens are shorter than pistil, it is easy to pollinate stigma but where stamens are of the same height as that of stigma or taller than pistil, it is difficult to find stigma and pollinate. Flower color varies from white to lavender through degrees of lavender. Seeds are hard and remain viable for 20 or more years. Seed scarification is used with concentrated H2SO4. Sweet potato is propagated through root tubers and vines.

Ipomea trifida complex

Ipomoea trichocarpa

2x 2n = 30

3x

4x 2n = 60

5x

6x 2n = 90

Ipomoea batatas 2n = 90

Fig. 8.4  Showing relationship between different species of sweet potato (Kobayashi, 1984).

Fig. 8.5  Proposed evolution of cultivated potaoes (Adapted Grun, 1990)

Crop Evolution and Genetic Resources

8.30

There are many uses of sweet potato. Tubers are boiled, baked, used as fodder, source of starch, flour and glucose syrup and alcohols can be produced. Polyploidy (hexaploid), self incompatibility and sterility are barriers in crop improvement in sweet potato. The breeding objectives include developing variety for higher vit. A content, dry matter content, starch content, sugar content, skin colour, darker leaves, higher yields, frost resistance, flooding resistance. High yield, early maturity, well shaped, shallow rooting type with good storage and cooking quality, palatability, attractive skin colour and high vit. content, flesh colour and resistance to diseases and pests. The breeding problems with sweet potato, potato, several fruit trees, small fruits, grapes, cassava, banana, etc are the high heterozygosity, polyploidy, crossing barriers (SI or MS), juvenile phase extended to several years particularly in case of fruits, sterile triploid varieties, and obligate apomixis. Polycross and mass selection are most efficient methods of improvement in sweet potato and honey bees and bumble bees are the most important pollinators. Sweet potato is a root and the root system consists of absorbing roots and fleshy or storage roots. As this crop is auto hexaploid, the segregation pattern will be very different than in either diploids or autotetraploids. Haldane (1948) gave formula for calculation of total number of possible genotypes, N, as follows. N = [(g + m – 1)!/m!(g – 1)!]n



Where g is the number of alleles per locus, n is the number of loci and m is the level of autopolyploidy. Total number of possible genotypes with a given number of genes in diploid, autotetraploid and autohexaploid is given in the table 8.14 below. Table 8.14  Showing number of genotypes produced considering different types of inheritance No. of alleles per locus

Diploid No. of loci

Autotetraploid No. of loci

Autohexaploid No. of loci

1

2

3

1

2

3

1

2

3

2

3

9

27

5

25

125

7

49

343

4

10

100

1000

35

1225

42875

84

7056

592704

6

21

441

9261

126

15, 876

2 x 106

462

213, 444

98 x 106

For example, in case of 4 alleles at two loci, the number of genotypes is 100 in diploid, 1225 autotetraploid and 7056 in autohexaploid. This shows that larger segregation generation population needs to be developed to make sure that all the genotypes would occur in that population.

Mehtod of Transfer of Gene for Resistance in Sweet Potato There are two routes of resynthesizing hexaploids. In the first approach, seedling of triploid hybrid is treated with colchicines and thus hexaploids are produced which are then crossed to generate hexaploid with 0 to 6 genes of resistance. Another route is to

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.31

exploit the 2n gamete production potential. Here the two tetraploids are crossed and there is generation of hexaploid with 2 to 4 genes of resistance (Figure 8.6). Sweet potato  The GP1 consists of I. batatas, wild and cultivated taxa. The GP2 consists of other species of the genus. Repeated cycles of hybridization and polyploidy have played an important role in the development of sweet potato, sugarcane and potato. Breeding objectives include developing high yielding, early, well shaped, shallow rooting types with good storage and cooking qualities, palatability and resistance to viruses and pests. Attractive skin colour, high vitamin contents, frost and flooding resistance are also the objectives.

Shukurkund-Sweet Potato (Convolutus batatas)

8.17  MISHRIKAND Pachyrrhizus erosus-called Kasaur is a diploid with 2n = 22. It is a self pollinated crop. Some cross pollination (up to 8%) occurs through bumble bees. It belongs to family fabaceae, also called Mexican yam bean. It is a subtropical crop and requires frost free condition. There are two types of varieties- Mexican types are large tubers (500-700gm) and less sweet whereas local types are small (200-300gm), more sweet and less fibres. The crop takes about 110-145 days and yields 40-55 tonnes/ha. It is usually propagated through seed. Seed pods are 7-15cm in length and contain about 8-10 brownish yellow to red seeds. Mature pods contain toxic substance called rotenone which is harmful for cattle. Propagation can also be through sprouted roots of previous crop. Planting is done on ridges (30 × 30cm) in June-July with the onset of monsoon but it can be extended up to September. This crop is harvested on the occasion of Saraswati puja. Seed crop is harvested after 240 days during March-April. Mishrikand can be stored for an year. Intercropping with maize can be done. The other two cultivated species are P. ahipa (Andean yam bean) and P. tuberosus (Amazonian yam bean). The genus contains five species. P. panamensis and P. ferrugineus are wild type. The former is supposed to be the progenitor of P. ahipa and P. tuberosus whereas the later is supposed to be the progenitor of P. erosus. All species except P. ferrugineus produce fertile interspecific hybrids. All yam beans are diploid (Sorensen, 1996; Gruneberg, 2006) and there is only one primary gene pool.

8.18  YAM It is a staple food in W. Africa and Nigeria. Yam belongs to family Dioscoreaceae.The genus Dioscorea contains about 600-800 species. It has also medicinal value. Wild species of Dioscorea contains sapogenic precursors of cortisone and steroidal hormones. The three widely cultivated species in India are D. alata, D. esculenta, D. rotundata. Different species of yam are cultivated in different parts of the world. It contains 25 to 30% starch and 1.5 to 3% protein. Some contains toxic alkaloids which can kill or harm people

Crop Evolution and Genetic Resources

8.32

Method of resynthesis of hexaploids with resistant genes from diploids (Adapted from Shiotani, 1989)

r r

r r

Hexaploid vaiety A x diploid A (donor)

Hexaploid variety B x diploid B (donor)

r r

r r

r

r

Tetraploid hybrid x diploid C (donor)

Tetraploid hybrid x diploid D (donor)

r r

r r

Triploid hybrid

Triploid hybrid

x

Colchicine treatment

Colchicine treatment

r r r r Hexaploid

r r r r Hexaploid Unreduced gamete

x

r r r r r r

r r r r

Hexaploid resynthesized with 6 r-genes

Hexaploid resynthesized with 4 r-genes

Fig. 8.6  Showing resynthesis of hexaploid sweet potato using genes for resistance from four diploid donors.

but these compounds can be rendered harmless by peeling and boiling. It is propagated vegetatively through small tubers. D. rotundata is the most important species worldwide and polyploidy (aneuploidy) is common with 2n = 140. Old world variety is based on x = 10 whereas the new world types are based on x = 9 (Ayensu and Coursey, 1972). Different species evolved in different regions of the world (Table 8.15). The GP1 species consist of wild relatives of similar geographical origin and GP2 consist of other species of the genus, Dioscorea.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.33

Fig. 8.7  Strachy root crops: potato, sweet potato, taro and yam.

It is a herbaceous climbing plant (Fig. 8.7) grown for edible tubers. It has medicinal value. It contains steroids such as diosgenin, a precursor of cortisone from which progesterone, (a steroidal hormone) can be prepared. It is normally propagated from tubers or tuber pieces. It can also be multiplied from vine cuttings and detached leaves. Seeds are also obtained. Table 8.15  Showing species, its distribution and ploidy levels in Yam Region

Species

Ploidy level

Breeding system method of propagation

South East Asia

D. alata (Water yam)

20, 30, 40, 50, 60, 70, 80

South East Asia

D. esculenta (Chinease yam)

30, 40, 60, 90, 100

D. bulbifera (Aerial yam)

30, 40, 50, 60, 70, 80, 100

D. hispida

40, 60

D. opposite

40

D. japonica

40

Tropical Africa

D. cayenensis (Yellow yam)

36, 54, 60,63, 66, 80, 120, 140

Outbreeding, clonal

Tropical Africa

D. rotundata

40, 80

Outbreeding, clonal

D. dumetorum (Trifoliate yam)

36, 40, 45, 54

D. trifida (Cush-cush yam)

54, 72, 81

Japan

South America

Outbreeding, clonal „

Outbreeding, clonal

Crop Evolution and Genetic Resources

8.34

D. floribunda has yellow fleshed tubers, D. speculiflora has white fleshed tuber and D. composite is very closely related to D. floribunda. D. trifida is grown in Carribean and West Africa. D. pentaphylla, D. nummularia and D. transversa are grown in Oceania. Suthni  Dioscorea is an important staple food in tropics and subtropics, for its starchy tubers and medicine. Cultivated yams are vegetatively propagated whereas wild yams are sexually propagated. Dioscorea esculenta is cultivated in subcontinent of India. Its edible roots are similar in size to that of potato or sweet potato. It is a lesser yam and is one of the tastiest yam. D. bulbifera is cultivated in U.S.A. D. alata, D. rotunda and D. cayenensis are the main species of West Africa. D. batatas is the Chinese yam.

8.19  TARO-ARVI Colocasia esculenta is herbaceous, monocot and belongs to family Araceae or Aroid. Taro root is edible corms. It is a shade loving crop and thus can be intercropped with trees and other crops, thrives well under wet and flooded condition. Taro is adapted to salinity and VAM. It is the primary source of starch for people in Pacific and Carribbean Islands and W. Africa. Wild species of C. esculenta are found throughout SC Asia and exists in the two ploidy levels, 2n = 2x = 28 (diploid) and 2n = 3x = 42 (Triploid) (Kuruvilla and Singh, 1981). It is cultivated in flooded or swampy land for its underground corms (contains 30% starch, ~ 3% sugar and some protein (1%)) (Heiser, 1990a). Major species of edible Aroid are given in Table 8.16 below. Table 8.16  Showing species, its distribution and ploidylevels in Taro Region Asia

South America

Species A. indica

Ploidy level 2n = 28

A. macrorrhiza

26, 28

C. esculenta

28, 42

Xanthosoma atrovirens

26

X. sagittifolium

26

X. violacum

26

Cyrtosperma chamissonis

?

Thus there exits two gene pools- one comprising species from South East Asia and the other comprising species from South West Pacific. There are two botanical varieties of C. esculenta (Purseglove, 1972). 1. C. esculenta var esculenta (Dasheen type) has large cylindrical central corm with very few cormels 2. C. esculenta var antiquorum (eddoe type) has small globular central corm with several relatively large cormels. It is synonymous with C. esculenta var. globulifera. Eddoe type developed and selected from cultivated taro. Selection is for color of the corm flesh, maturity and taste. There are hundreds of varieties differing in corm, cormel or shoot

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.35

characteristics, agronomic or culinary attributes. It is closely related to Xanthosoma. In north the frequency of triploid accession is more and diploid is less and in the south the diploid accession is more and triploid is less. C. esculenta is taro. C. fallax is used as vegetable and C. affinis var. Jenningsii is an ornamental crop. GP1 species consists of cultivated and wild taxa. The GP2 consists of Colocasia specis. Surface of each corm is marked with rings. Apex of the corm represents the growing point and petiole is attached to the middle of lamina. Three main veins radiate from the point of attachment of the petiole. Taro is a herbaceous plant, 1-2m in height. It produces corm after three months of planting and harvesting is done by six months. It is a vegetatively propagated crop. Base of the main stem (head set) and suckers are used as propagules. It also produces seeds and there is sexual reproduction in many varieties of Melanesia. Flowering and seed setting are irratic. Each plant produces more than one inflorescence. The spadix (spike) -the short peduncle has female flowers (sessile) at the base and male flowers at the tip and in between there a zone of sterile flowers. The extreme tip called sterile appendage (no flowers at all). In eddoe type the sterile appendage is longer than male section of the spadix whereas in dasheen type the appendage is shorter than the male section. It is a cross pollinated crop. Number of seeds produced per spadix is about 1000. Most plants complete field life without producing flower at all and some varieties have never been known to flower. Corms is promoted under short day condition whereas flowering is initiated under long day condition. The important characters to be observed include alkaloids, anthocyanin, calcium oxalate, chlorophyll, nitrogen content and protein content. Greatest variability is found for Colocasia in India. Colocasia is known to content calcium oxalate which causes itching or has irritant quality. Calcium oxalate content varies 3 to 4 times in corms whereas it varies 10 times or more in leaf. The other related species are: 1. Cyrtosperma chamissionis or C. merkusii-giant swamp taro 2. Alocasia macrorrhiza-giant taro 3. Xanthosoma sagittifolium-cocoyam, tannia species with 2n = 2x = 26 Alocasia has South India orgin. It is a tuber producing crop, outbreeder, clonal propagated and it is diploid. Xanthosoma has Tropical America Orgin, a tuber is used as vegetable, outbreeder, clonal propagated and is diploid.

8.20  CASSAVA It is a perennial shrub with edible roots. It is commonly known as Tapioca (Manihot esculenta) in India and is a popular root crop. It is crop used as food, feed for livestock and has pharmaceutical value (for starch extraction). Wafers, chips, pappads, rava, noodles and dried chips for animal feed are the various products that can be made from this crop. In other words, roots can be roasted, baked, boiled, fried, and granules, paste and flour can be made. Further, roots can be stored in the ground while still intact on the growing plants for up to 24 months. The starchy roots contains cyanogenic glucosides which

8.36

Crop Evolution and Genetic Resources

produces HCN but processing eliminated most of the cyanides. Its origin is Latin America. It was introduced in India in 17th century. It is largely cultivated in Tamil Nadu, Kerala and Andhra pradesh. Although a kharif crop, it can be grown round the year under irrigated condition. It takes 10 months for harvesting of tubers. It is a diploid with 2n = 2x = 36. It is cross pollinatid crop (Fig. 8.8) and is clonal propagated. The genus contains 98 species (Rogers and Appan, 1973) and only cassava is cultivated. All the species of this genus are wild plants confined to American tropics. No native species are found in the old world (Rogers, 1965). Propagation is through stem cuttings obtained from 8-12 Fig. 8.8  The manioc or cassava plant. Its total height can months old and matured plant. Stakes are reach over 5 meters derived from the lower part of the stem. Vertical of the stakes results in uniform bulking of roots around the base. In case of close pruning (30cm from the ground) at 8 months after planting establishes fresh canopy and thus harvesting after 16 months, the yield is doubled as is seen in case of haldi and elephant foot yam. Seed multiplication rate is 10 times as we see in case of elephant foot yam. The various wild species are given below in the table 8.17. The breeding objectives in cassava include high yields, better nutritional quality, low hydrogen cyanide content, storability and resistance to diseases and pests. It is one of the most efficient producer of carbohydrate, having drought resistance and adaptability to poor soil condition. Beadlike starch is obtained from cassava root which is used in cooking as a thickening agent. Sago (sabudana) is prepared from the milk of roots of Tapioca root. Pulp is prepared from tapioca root from which milk extract is obtained which upon settling forms globules which is followed by roasting. Sago swells when cooked. Sweet varieties are called M. ultissima with lower level of cyanogenic glycosides whereas M. palmata, M. aipr are bitter varieties having higher level of cyanogenic glycosides. These varieties fall within M. esculenta. Tapioca root contains 30-35% starch. Interspecific hybridization followed by polyploidization and apomixis (which is through formation of aposporic embryos) has played a role in the evolution and adaptability of this crop to different environments. Apomicts have been found in different genera such as Taraxicum, Aster, Erigeron, Rudbackia, Poa, Crepis, Musa, Manihot, Malus, Rubus, Potentilla, Citrus, Allium and Tulipa (Grant, 1981). Frequent hybridization has been observed between M. reptans and M. alutacea. The genus comprises trees and subshrubs which are more dioecious than monoecoius. Tapioca also shows production of 2n gametes. The GP1 consists of local races and related wild species, wild M. tristis saxicola. The

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.37

GP2 consists of M. glaziovii. Breeding objectives include developing variety with high yield, better nutritional quality, low HCN content, resistance to viruses and insects and storability. Table 8.17  Showing various species of Cassava. Species

Comparison with cultivated species

M. stipularis

Shows most primitive traits

M. pusilla

-do-

M. longipetiolata

-do-

M. stricta

-do

M. purpureo-costata

-do-

M. salicifolia

-do-

Characteristics

Gene pool

dioecious

Nonlobed, sessile leaves

M. aesculifolia M. pilosa

High similarity with M. esculenta

M. corymbiflora

High similarity with M. esculenta

M. dichotoma M. pohlii M. neusana M. anomala M. reptans M. alutacea M. fruticolosa M. pentaphyla M. glaziovii

Tree like species

M. pseudoglazovii

Tree like species

GP2

M. caerulescens M. tristis

GP1

M. peruviana M. flabellifolia M. dulcis

Sweet cassava

The breeding objectives in this crop include developing early maturing variety, free from cyanogenic glucosides. Besides this another objective would be to synthesize newer levels of polyploids such as triploids and tetraploids. Developing hybrids using interspecific hybridization is another objective to accomplish. Mass multiplication through tissue culture and development of somatic embryos and synthetic seeds would be another objectives in the root crop.

8.38

Crop Evolution and Genetic Resources

References Alexander, J. and Coursey, D.G. 1969. The origins of yam cultivation. In: Ucko, P.J. and Dimbleby, G.W.(eds.). The Domestication and Exploitation of Plants and Animals. Longman, London, pp. 405-425. Ambrose, M.J. 1996. Pisum Genetic Stocks Catalogue, John Innes Centre, Norwich. Ambrose, M.J. 2004. A novel allele at the afila(Af) locus and new alleles at the tendril-less(Tl) locus. Pisum Gen. 36: 1-2. Ambrose, M.J. and Green, F.N.1991. A review of Pisum genetic resources and germplasm utilization. Asp.appl. Biol. 27: 243-251. Asins, M.J. and Carbonell, E.A. 1986. A comparative study on variability and phylogeny of Triticum species. 2. Interspecific relationships. Theor. Appl. Gent. 72: 559-568. Austin, D.F. 1978. The Ipomoeae complex-1. Taxonomy. Bulletin of the Torrey Botanical Club.105: 114-129. Ayala, F.G. 1982. Population and Evolutionary Genetics: a primer. Benjamin/Cummings Publishing Company, Menlo Park, California. Ayensu, E.S. and Coursey, D.G. 1972. Guinea yams. Economic Botany. 26: 301-318. Badami, P.S.; Mallikarijuna, N. and Moss, J. 1997. Interspecific hybridization between Cicer arietinum and C. pinnatifidium. Plant Breeding 116: 393-395. Bai, K.V. 1992. Cytogenetics of Manihot species and interspecific hybrids. In: Roca, W. and Thro, A.M. (eds.) Proceedings of the first International Scientific Meeting of the Cassava Biotechnology Network. Centro Internacional de Agricultura Tropical, Cali, Columbia, pp: 51-55. Baker, H.G. 1970. Plants and Civilization. Wadsworth Publishing Company, Belmont, California. Barber, H.N. 1970. Hybridization and the evolution of plants. Taxon 19: 154-160. Baum, B.R. 1977. Oats: Wild and Cultivated. A Monogram of the genus Avena L. (Poaceae). Biosystematics Research Institute, Canada Deptt. of Agriculture, Ottawa. Baum, B.R. 1985a. Avena atlantica: a new diploid specie of the oat genus from Morocco. Canadian Journal of Botany, 63 pp: 1057-1060. Baum, B.R. 1985b. A new tetraploid species of oat. Canadian Journal of Botany 63: 1379-1385 Bist, M.S. and Mukai, Y. 2001. Genomic in situ hybridization identifies genome donor of finger millet(Eleusine coracana). Theor. Appl. Genet. 102: 825-83. Bradshaw, J.E. and Mackay, G.R.(eds.). 1994. Potato Genetics.CAB International. Burke, J.M., Tang, S., Knapp,S.J. and Rieseberg, L.H. 2002. Genetic analysis of sunflower domestication. Genetics 161: 1257-1267. Busbice, T.H. and Wilsie, C.P. 1966. Inbreeding depression and heterosis in autotetraploids with application to Medicago sativa L. Euphytica 15: 53-67. Busbice, T.H. 1968. Effects of inbreeding on fertility in Medicago sativa L. Crop Science 8: 231-234. Carena, M.J. (ed.). 2009. Cereals. Springer. Carter, J.F. (ed.). 1978. Sunflower Science and Technology. American Society of Agronomy, Inc. Publishers.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.39

Chang, T.T. 1995. Rice, Oryza sativa and Oryza glaberrima(Gramineae-Oryzeae) In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harloe, UK. Choi, I.Y.; Lee, J.K.; Goo, H.J.; Park, J.H. et al., 2002. Genetic diversity and relationships among Dioscorea alata L. and related Dioscorea species revealed by AFLP analysis. Korean Journal of Genetics 24: 305-312. Coates, D.J., Yen, D.E. and Gaffey, P.M. 1988. Chromosome variation in taro, Colocasis esculenta: implications for origin in the Pacific. Cytologia 53: 551-560. Cock, J.H. 1982. Cassava, a basic energy source in the tropics. Science 218: 755-762. Coons, G.S. 1975. Interspecific hybrids between Beta vulgaris and the wild species of Beta. Journal of American Society of Sugar Beet Technology 18: 381-386. Coulibaly, S.; Pasquet, R.S.; Papa, R. and Gepts, P. 2002. AFLP analysis of the phonetic organization and genetic diversity of Vigna unguiculata L. Walp. Reveals extensive gene flow between wild and domesticated types. Theoretical and Applied Genetics 104: 358-366. Cubero, J.I. 1974. On the origin of Vicia faba. Theoretical and Applied Genetics 45: 45-47. Daniels, J. and Roach, B.T. 1987. Taxonomy and evolution. In: Heinz, D.J.(ed.) Sugarcane improvement through Breeding. Elsevier Press, Amsterdam. Daniels, J.; Roach, B.T.; Daniels, C. and Paton, N.H. 1991. The taxonomic status of Saccharum barberi Jeswiet and S. sinense Roxb. Sugarcane 3: 11-16. Dark, S.O.S. 1971. Experiments in the cross pollination of sugar beet in the field. National Institute of Agricultural Biology 12: 242-266. Davies, D.R. 1995. Peas: Pisum sativum(Leguminosae-Papilionoideae) In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK. Debouck, D.G. 2000. Biodiversity, ecology and genetic resources of Phaseolus beans-seven answered and unanswered questions. In: proc. Of the 7th MAFE Inter. Workshop on Genetic Resources, Part I. Wild legumes, AFFRC and NIAR, Japan, pp. 95-123. Debouck, D.G. 1991. Systematics and morphology: In: van Schoonhoven, A and Voysest, O.(eds.) Common beans: research for crop improvement. CABI, pp: 55-118. Debouck, D.G. and Smartt, J. 1995. Beans, Phaseolus spp.(Leguminosae-Papilionoideae) In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK. deWet, J.M. J. 1978. Systematics and evolution of Sorghum section Sorghum(Gramineae). American Journal of Botany 65: 477-484. deWet, J.M. J. 1995. Minor cereals: various genera(Gramineae) In: Smartt, J. and Simmonds, N.W.(eds.). 1995. Evolution of Crop Plants. 2nd ed., Longman, London, pp: 202-207. deWet, J.M. J. and Huckabay, J.P.1967. The origin of Sorghum bicolor. II. Distribution and domestication. Evolution 21: 787-802. deWet, J.M. J; Rao, K.E.P.; Brink, D.E. and Mengesha, M.H. 1984b. Systematics and Evolution of Eleusine coracana(Gramineae). American Journal of Botany 71: 550-557. Diaz, J.; Schmiediche, P. and Austin, D.F. 1996. Polygon of crossibility between eleven species of Ipomoea: section Batatas(Convolvulaceae). Euphytica 88:189-200. Doebley, J., Stec, A., Wendel, J. and Edwards, M. 1990. Genetic and morphological analysis of a maize-terosinte F2 population: implications for the origin of maize. Proceedings of the National Academy of Scieneces USA, 87: 9888-9892.

8.40

Crop Evolution and Genetic Resources

Doebley, J.; Stec, A.; Wendel. J. and Edwards, M. 1990. Genetic and morphological analysis of a maize-teosinte F2 population: implications for the origin of maize. Proceedings of the National Academy of Sciences, USA 87: 9888-9892. Doebley, J. 1990b. Molecular evidence and the evolution of maize. Economic Botany 44: 6-27. Doggett, H. 1988. Sorghum, Longman, London. Doggett, H. and Rao, K.E.P. 1995. Sorghum, Sorghum bicolor(Gramineae-Androponeae) In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 173-180. Doyle, J.J., Doyle, J.L., Brown, A.D.H. and Palmer, R.G. 2002.Genomes, mul;tiple origins and linkage recombination in the Glycine tomentella(Leguminosae) polyploidy complex: histone H3-D sequences. Evolution, 56: 1388-1402. Dvorak, J.; Luo, M-C.; Yang, Z-L. and Zhang, H-B. 1998. The structure of the Aegilops tauschi genepool and the evolution of hexaploid wheat. Theoretical and Applied Genetics 97: 657-670. Endrizzi, J.E.; Turcotte, E.L. and Kohl, R.J. 1985. Genetics, cytology and evolution of Gossypium. Advances in Genetics 23: 271-375. Eshbaugh, W.H. 1975. Genetic and biochemical systematic of chili peppers (Capsicum-Solanaceae). Bulletin of Torrey Botanical Club, 102: 396-403. Evans, G.M. 1995. Rye, Secale cereal (Gramineae-Tricinae) In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 166-170. Feldman, M.; Galili, G. and Levy, A.A. 1986. Genetic and evolutionary aspects of allopolyploidy in wheat. In: Barigozzi, C.(ed.) The Origin and Domestication of Cultivated Crops. Elsevier, Amsterdam, PP: 83-101. Fominaya, A., Vega, C. and Ferrer, E. 1988. Giemsa C-banded karyotypes of Avena species. Genome 30: 627-632. Ford-Lloyd, B.V. and Williams, J.T. 1975. A revision of Beta section Vulgaris (Chenopodiaceae) with new light on the origin of cultivated beets. Botanical Journal of the Linnean Society 71: 89-102. Fryxell, P.A.; Craven, L.A. and Stewert, J.M. 1992. A revision of Gossypium section Grandicalyx (Malvaceae) including the description of six new species. Systematic Botany 17: 91-114 Gepts, P. 1998. Origin and evolution of common bean: past events and recent trends. Hort Science 33: 1124-1130. Gepts, P. and Debouck, D.G. 1991. Origin, domestication and evolution of the common bean, Phaseolus vulgaris L. In: Common Beans: Research for Crop Improvement, A. Van Schoonhoven and O. Voysest(eds.). CAB International. Gepts. P.1990. Biochemical evidence bearing on the domestication of Phaseolus (Fabaceae) beans. Economic Botany 44: 28-38. Gray Stacey(ed.).2008. Genetics and Genomics of Soybean. Vol. 2. Springer. Gregory, W.C. ; Krapovickas, A. and Gregory, M.P. 1980. Structure, variation and evolution and classification in Arachis In: Summerfield, R.J. and Bunting, A.H.(eds.). Advances in Legume Science. Royal Botanical Gardens, Kew, pp: 469-481.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.41

Grun, P. 1990. The evolution of cultivated potato. Economic Botany 44: 39-55. Grun, P. 1990. The evolution of cultivated potato. Economic Botany, 44: 39-55. Hahn, S.; Bai, K.V. and Asidu, R.A. 1990. Tetraploids, triploids and 2n pollen from diploid interspecies crosses with cassava. Theoretical and Applied Genetics 79: 433-439. Hallauer, A.R. and Miranda, FO, J.B. 1981. Quantitative Genetics in Maize Breeding. Iowa State University Press, Ames. Hamon, P. and Bakary, T. 1990. The classification of cultivated yams (Dioscorea cayenensisrotundata) of West Africa. Euphytica 47: 179-187. Hancock, J.F. 2004. Plant Evolution and the Origin of Crop Species. 2nd ed. CAB International. Hanson, C.H. (ed.). 1972. Alfalfa Science and Technology. American Society of Agronomy, Inc. Publisher. Madison, U.S.A. Hartl, D.L. and Clark, A.G.P. 1997. Principles of Population Genetics. 3rd ed. Sinauer Associates. Hawkes, J.G. 1967. History of the potato. In : Haris, P.M.(ed) The Potato Crop. Chapman and Hall, London. Hawkes, J.G. 1979. Evolution and polyploidy in potato species. In: Hawkes, J.G.; Lester, R.N. and Skelding, D.(eds) The Biology and Taxonomy of the Solanaceae. Seminar Series No. 7, Linnean Society , London, pp: 637-646. Hawkes, J.G. 1990. The Potato: Evolution, Biodiversity and Genetic Resources. Belhaven Press, Washington, DC. Hedley, C.L. and Ambrose, M.J. 1981. Designing ‘leafless’ plants for improving the dried pea crop. Adv. Agron. 34: 225-277. Heiser, C.B. 1976. The Sunflower. University of Oklahoma Press, Norman. Heiser, C. B. 1995b. Sunflowers: Helianthus (Compositae). In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 449-451 Hemingway, J.S. 1995. Mustards: Brassica ssp. and Sinus alpa. In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 82-86. Hillman, G. 1978. On the origin of domesticated rye-Secale cereal: the finds from a ceramic Can Hasan III in Turkey. Anatolian Studies 28: 157-174. Hilu, K.W. and Johnson, J.L. 1992. Ribosomal DNA variation in finger millet and wild species of Eleusine(Poaceae). Theoretical and Applied Genetics 83: 895-902. Holden, J.H.W. 1976. Oats: In: Simmonds, N.W.(ed.) Evolution of Crop Species. Longman, London. Husted, L. 1936. Cytological studies of the peanut Arachis II. Chromosome number, morphology and behavior and their application to the origin of the cultivated forms. Cytologia 7: 396-423. Hymowitz, T. and Singh, R.J. 1987. Taxonomy and speciation. In: Wilcox, J.R.(ed.) Soybeans: Improvement, Production and Uses. American Society of Agronomy, Madison, Wisconsin, pp: 23-48. Hymowitz, T. 1995. Soybean: Glycine max(Leguminosae-Papilionoidae). In: Smartt, J and Simmonds, N.W. (eds.). Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp:261-266. IRRI.1986. Rice Genetics. Proc. 0f the Intl. Rice Genetics Symposium. 1985. IRRI, Philippines.

8.42

Crop Evolution and Genetic Resources

Iwanaga, M. and Peloquin, S.J. 1982. Origin and evolution of cultivated tetraploid potatoes via 2n gametes. Theoretical and Applied Genetics 61: 161-169. Jasska, V. 1983. Secale and Triticale. In: Tanksley, S.D. and Orton, T.J. (eds.) Ioszymes in Plant breeding and Evolution. Elsevier, Amsterdam, pp: 79-101. Jenings, D.A. L.1995. Cassava: Manihot esculenta (Euphorbiaceae). In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 129-132. Jugenheimer, R.W. 1976. Corn Improvement, Seed Production and Uses. John Wiley and Sons. Khus, G.S. and Stebbins, G.L. 1961. Cytogenetics and evolutionary studies in Secale. I. Some new data on the ancestory of S.cereale. American Journal of Botany 48: 721-730. Khus, G.S. 1962. Cytogenetics and evolutionary studies in Secale. II. Interrelationships of the wild species. Evolution 16: 484-496. Khvostova, V. V. (ed.). 1983. Genetics and Breeding of Peas. Oxonian Press Pvt. Ltd., New Delhi. Kihara, H.; Yamashita, H. and Tanaka, M. 1959. Genomes of 6 species of Aegilops. Wheat Information Service 8: 3-5. Kimber, D. and McGregor, D.I.(eds.). 1995. Brassica Oilseeds-production and Utilization. CAB International. King, R.C. (ed.). 1974. Handbook of Genetics. Vol. 2. Plants, Plant viruses and Protists. Plenum Press, New York. Kislev, M.E. 1985. Early Neolithic horsebean from Yiftah’el Israel. Science 228: 319-230. Kobabe, G. 1983. Heterosis and hybrid seed production in fodder grass. In: Heterosis-Reapraissal of theory and practice. (Ed.) Frankel, R. Springer-Verlag, Berlin. Kobayashi, K. 1984. Proposed polyploidy complex of Ipomoea trifida. In: Proceedings of the Sixth Symposium of the International Society for Tropical Fruit Crops. International Potato Center, Lima, Peru, pp: 561-568. Kochert, G.; Stalker, H.T. ; Gimenes, M. et al. 1996. RFLP and cytogenetic evidence on the origin and evolution of allopolyploid domesticated peanut, Arachis hypogaea(Leguminoseae). American Journal of Botany 83: 1282-1291. Koinange, E.M. K.; Singh, S.P. and Gepts, P. 1996. Genetic control of domestication syndrome in common bean. Crop Science 36: 1037-1045. Kuruvilla, K. and Singh, A. 1981. Karyotype and elctrophoretic studies on taro and its origin. Euphytica 30: 405-413. Langer, R.H.M. and Hill, C.D. 1982. Agricultural Plants, Cambridge University Press, new York. Lewis, B.G. and Matthews, P. 1984. The world germplasm of Pisum sativum: Could it be used more effectively to produce healthy crops? In: The pea crop: A basis for improvement., Hebblethwaite, P.D. et al.(eds.). Butterworths, London, pp. 215-221. Loebenstein, G. and Thottappilly, G.(eds.). 2009. The Sweet potato. Springer. Loebenstein, G. and Thottappilly, G.(eds.). 2009. The Sweetpotato. Springer. Lupton, F.G.H.(ed.).1987. Wheat Breeding. Its scientific basis. Chapman and Hall, London. Lush, W.M. and Evans, L.T. 1981. The domestication and improvement of cowpeas(Vigna unguiculata(L.) Walp.). Euphytica 30: 579-587. Mangelsdorf, P. C. 1953. Wheat. Scientific American, New York.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.43

Marshall, G.(ed.). 1989. Flax: Breeding and Utilization. Kluwer Academic Publishers. Maxted, N., Ford-Lloyd, B. V., Kell, S.P., Iriondo, J.M., Dulloo, M.E. and Turok, J. (eds.). 2008. Crop Wild Relative, Conservation and Use. CAB International. Nayar, N.W. 1973. Origin and cytogenetics of rice. Advances in Genetics 17: 153-292. Nene, Y.L., Susan, D. Hall and Sheilla, V.K.(eds.). 1990. The Pegionpea. CAB International. Newell, C.J. and Hymowitz, T. 1978. A reappraisal of the subgenus Glycine. American Journal of Botany 65: 168-179. Ng, N.Q. 1995. Cowpea, Vigna unguiculata (Leguminoseae-Papilionoidaea) In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants. Longman Scientific and Technical, Harlow, UK, pp: 326-333. Ng, N.Q. and Marechal, R. 1985. Cowpea taxonomy, origin and germplasm.In: Singh, S and Rachie, K.(eds.) Cowpea Research, production and Utilization. Wiley, Chichester, UK. Nilen, R.A. 1971. Barley Genetics II. Pullman, Washington, DC. Nishiyama, I.; Miyasaki, T. and Sakamoto, S. 1975. Evolutionary autopolyploidy of the sweet potato(Ipomoea batatas(L.)Lam and its progenitors. Euphytica 24: 197-208. Ochoa, C.M. 1990. The Potaoes of South America: Bolivia. Cambridge University Press, NY. Oka, H.I. 1988. Origin of Cultivated Rice. Japan Societies Press, Tokyo. Olsen, K.M. and Schaal, B.A. 1999. Evidence on the origin of cassava: phylogeography of Manihot esculenta. Proceedings of the National Academy of Sciences USA 96: 5586-5591. Orjeda, G.; Freyre, R. and Iwanaga, M. 1990. Production of 2n pollen in diploid Ipomoea trifida a putative ancestor of sweet potato. Journal of Heredity 81: 462-467. Phillips, L.L. 1979. Cotton. In: Simmonds, N.W.(ed.) Evolution of Crop Species. Longman, London. Plucknett, D.L. ; Pena, R.S. and Obero, F. 1970. Taro(Colocasia esculenta). Field Crop Abstract 23: 413-426. Plucknett, D.L. 1979. Edible aroids. In: Simmonds, N.W.(ed.) Evolution of Crop Species. Longman, London, pp: 10-12. Poehlman, J.M. and Sleper, D.A. 1995. Breeding Field Crops, 4th ed., Iowa State University Press/ Ames. Pratt, R.C. and Nabham, G.P. 1988. Evolution and diversity of Phaseolus acutifolius genetic resources. In: Gepts(ed.) Genetic Resources of Phaseolus Beans, Kluwer, Dordrecht, The Netherland, pp: 409-440. Ramage, R.T. 1983. Heterosos and hybrid seed production in barley. Hybrid wheat. In: HeterosisReapraissal of theory and practice. (Ed.) Frankel, R. Springer-Verlag, Berlin. Reddy, P.S.(ed.).1988. Groundnut. I.C.A.R., New Delhi. Riesenberg, L.H. and Seiler, G.J. 1990. Molecular evidence and the origin and development of the domesticated sunflower, Helianthus annuus(Asterceae). Economic Botany 44: 79-91. Sanjur, O.I.; Piperno, D.; Andres, T.C. and Wessel-Beabver, L. 2002. Phylogenetic relationships among domesticated and wild species of Cucurbita(Cucurbitaceae) inferred from a mitochondrial gene: implications for crop plant evolution and areas of origin. Proceedings of the National Academy of Science USA 99: 535-540.

8.44

Crop Evolution and Genetic Resources

Sauer, J.D. 1967. The grain Amaranths and their relatives- a revised taxonomic and geographic survey. Annals of the Missouri Botanical Garden 54: 103-137. Saxena, M.C. and Singh, K.B.(eds.). 1987. The Chickpea. CAB International. Shewry, P.R. (ed.). 1992. Barley: Genetics, Biochemistry, Molecular Biology and Biotechnology. CAB International. Simmonds, N.W. and Smartt, J. 1999. 2nd ed. Principles of Crop Improvement. Blackwell Science. Singh, S.P., Gepts, P. and Debouck, D.G. 1991a. Races of common bean(Phaseolus vulgaris, Fabaceae), Econ. Bot. 45, 379-396. Smartt, J. 1990. Grain Legumes, Evolution and Genetic Resources. Cambridge University Press, Cambridge. Smartt, J. and Simmonds, N.W.(eds.). 1995. Evolution of Crop Plants. 2nd ed., Longman, London. Smartt, J.; Gregory, W.C. and Gregory, M.P. 1978. The genome of Arachis hypogaea I. Cytogenetic studies of putative genome donors. Euphytica 27: 665-675. Smartte, J. 1999. Grain Legumes- Evolution and Genetic Resoirces. Cambridge University Press. Smith, J.M. 2006. Evolutionary Genetics. Indian edition. Oxford University Press. Spencer, H.A. and Hawkes, J.G. 1980. On the origin of cultivated rye. Biological Journal of the Linnean Society 13: 299-313. Sprague, G.F. (ed.). 1977. Corn and Corn Improvement. American Society of Agronomy, Madison. Stalker, H.T.; Desi, D.S.,; Parry, D.C. and Hahn, J.H. 1991. Cytological and interfertility relationships of Arachis section Arachis. American Journal of Botany 78: 238-246 Stevension, G.C. 1965. Genetics and Breeding of Sugarcane. Longman, London. Stutz, H.C. 1972. The origin of cultivated rye. American Journal of Botany 59: 59-70 U., N. 1935. Genome analysis of Brassica with special reference to experimental formation of B.napus. Genome 31: 143-154. Van der Maesen, L.J.G. 1987. Origin, history and taxonomy of chickpea, In: Saxena, M.C. and Singh, K.B. (eds.) The Chickpea. CAB International, Wallingford, UK. Van Slageren, M.W. 1994. Wild wheats: a Monograph of Aegilops L. and Amblyopyrum (Jaub. & Spach) Eig(Poaceae). Papers 1994., Wageningen Agricultural University, Wageningen. Vaughan, D.A. 1994. The Wild Relatives of Rice. The International Rice Research institute, Manila, Philippines. Vorsa, N. and Bingham, E.T. 1979. Cytology of 2n pollen production in diploid alfalfa, Medicago sativa. Canadian Journal of Genetic and Cytology 21: 525-530. Weiss, E.A. 1971. Castor, Sesame and Safflower. Leonard Hill, London. Weiss, E.A. 1983. Oilseed Crops. Longman, London. Wendel, J.F. 1989. New world tetraploid cottons contain old world cytoplasm. Proceedings of of the National Academy of Sciences USA 86: 7213-7218. Wilson, R.E. and Rice, L.L. 1968. Allelopathy as expressed by Helianthus annuus and its role in old field succession. Bulletin of the Torrey Botanical Club. 95: 432-448.

Origin and Genetic Resources of Fibre, Green manuring, Starchy, Sugar...

8.45

Yang, Q., Hanson, L., Bennett, M.D. and Leitch, I.J. 1999. Genome structure and evolution in the alloheaxaploid weed Avena fatua L.(Poaceae). Genome 42: 512-518. Yen, D.E. 1982. Sweet potato in historical perspective. In: Villareal, R. and Griggs, T.(eds.) Sweet Potato-proceedings of 1st International Symposium. AVRDC, Tainana, Taiwan. Zohary, D. 1972. The wild progenitor and the place of origin of the cultivated lentil: Lens culinaris. Merik. Economic Botany 26: 326-332. Zohary, D. 1973. The origin of cultivated cereals and pulses in the Near East. In: Wahram, J. and Lewis, K.R.(eds.) Chromosomes Today Vol. 4 . John Wiley & Sons, NY. Zohary, D. 1995. Lentil: lens culinaris (Leguminosae-Papilionoideae). In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants. Longman Scientific &Technical, Harlow, UK, PP: 271-274. Zohary, D. and Hopf, M.1973. Domestication of pulses in the old world. Science, 182: 887-894.

C H A P T E R

Origin and Genetic Resources of Fruit Crops

9

9.1  CHARACTERISTICS OF FRUIT CROPS Temperate fruits include apple, pear, peaches, plum, cherry, apricot, kiwi fruit, currats and goose berry, raspberry, black berry, blue berry and crane berry. Tropical fruits include papaya, sapota, avocado, jack fruit, tamarind, fig, banana and custard apple. The subtropical fruits include mango, citrus, guava, litchi, ber, pomegranate, loquat, jamun, aonl, karonda, bael, grapes, date palm, phalsa, pine apple, persimmon and carambola. Stone fruits include plums, peaches, cherry and nectarine. Various fruit crops, their botanical names, ploidy levels, breeding systems and origins are given in the Table 9.1. Table 9.1  Showing various fruit crops along with ploidy level, orgin and breeding system. Name

Botanical name

Family

Basic chromosome no.

Ploidy level

Origin

Breeding system Pollinator

Mango

Mangifera indica

Assnacardiaceae

n = 16

2n = 40 Burma, (amphidiploids) Russian

Crosspollination House (Entomophilous) Fly

Citrus

Citrus spp.

Rutaceae

n=9

Diploid

Kagzi limeindia, sweet orange -China, PummelaSouth East Asia

Crosspollination (Entomophilous

Banana

Musa spp.

Musaceae

n = 11

2x, 3x, 4x

South East Asia

Crosspollination Wind (ornithephilous) Anemophilous Contd...

Crop Evolution and Genetic Resources

9.2 Contd...

Name

Botanical name

Family

Basic chromosome no.

Ploidy level

Origin

Breeding system Pollinator

Pineapple

Ananas comosus

Bromeliaceae n = 25

2x, 3x, 4x

Brazil

Crosspollination Insect (ornithephilous) (Entomophilous)

Papaya

Carica papaya

Caricaceae

n=9

2x, 3x, 4x

Tropical America

Crosspollination Honey (Entomophilous) bee

Litchi

Litchi sinensis

Sapindaceae

n = 14, 15, 16

2x

China

Crosspollination Insect (Entomophilous)

Avocado

Persea americana

Lauraceae

n = 12

2x

Mexico & west indies

Crosspollination Honey (Entomophilous) bee

Aonla

Emplica officinalis

n=7

4x

Tropical Asia Anemophilous (Indo-China)

Beal

Aegle marmelos

Rutaceae

n=9

4x

India

Crosspollination Insects (Entomophilous) Honey Bee

Cashew (seed)

Anacardium occidentale

(Anacardiaceae)

n = 21

2x

Tropical America (Brazil)

Anemophilous Insects (Entomophilous) Honey Bee

Coconut (Seed)

Cocos nucifera

Aracaceae

n = 16

2x

Malaysia, Indonesia

Crosspollination Ant, (Entomophilous) Honey Bee

Custard Apple

Annona reticulata

Annonaceae

n=7

2x

Tropical America

Entomophilous

Insect

Date palm

Phoenix dactylifera

Aracaceae

n = 18

2x

West Asia & Arabia

Anemophilous

Wind

Fig

Ficus carica

Moraceae

n = 13

2x

West Asia

Entomophilous

Insect

Moraceae

n = 14

2x

India

Anemophilous

Wind

Jack Fruit

Wind

Karonda (Seed)

Carrisa Carividies

Apocynelene

n = 11

2x

India, Java

Entomophilous

Insect

Jamun

Sylygium cumuni

Myrtaceae

n = 20

2x

East IndiaMalaya

Entomophilous

Insect

Moraceae

n = 154

2x

China

Entomophilous

Insect

Mulberry Fruit (Seed) Passion Fruit (Seed)

Passiflora edulis

Passifloraceae

n=9

2x

Brazil

Entomophilous

Insect

Phalsa (Seed)

Grewa subiniequals

Tiliaceae

n=9

4x

India

Entomophilous

insect

Punicaceae

n = 89

2x

East Europe to Asia

Anemophilous

Wind

Pomegranate Punica granatum

Contd...

Origin and Genetic Resources of Fruit Crops

9.3

Contd...

Name

Botanical name

Family

Sapota

Manikara zapota

Sapotaceae

Tamarind (Seed)

Tamarcudaus Leguminosae indica

Grape

Vitis spp.

Guava

Basic chromosome no.

Ploidy level

Origin

Breeding system Pollinator

n = 13

2x

Mexico, Tropical America

Anemophilous

Wind

n = 12

2x

Tropical Africa, India

Entomophilous

insect

Vitaceae

n = 20

2x

Block sea to Caspian sea

Self pollinated

Psidium guazava

Myrtaceae

n = 11

2x, 3x

West indies to Peru

Flower orientation favours self pollination but to some extent cross pollination also occur.

Loquat (Seed)

Eriobotrya japonica

Rosaceae

n=7

2x

China

Entomophilous

insect

Rambutan

Nephelium lappeceum

Sapindaceae

n = 14, 15

2x

Malay

Entomophilous

insect

Apple

Malus x domestica

Rosaceae

n = 17

2x, 3x

Asia Miner to western Himalaya

Crosspollination Insect diploid = self pollinate Triploid = cross pollinated

Japanese plum

P. salicina

Rosaceae

n=8

6x

Europe west Asia

Cross pollinated Insect

Peach

Prunus persica

Rosaceae

n=8

2x

China

Cross pollinated Insect

Pecan nut

Carya spp.

Juglandaceae n = 18

2x

Southern USA

Cross pollinated Insect

Persimmon

Diopyros spp. Ebenaceae

n = 15

6x

China

Cross pollinated Insect

Quince

Chaenomeles Rosaceae japonica

n = 17

2x

South Asia

Cross pollinated Insect

Sour cherry

Prunus cerasus

Rosaceae

n = 16

2x, 3x, 4x

Europe west Asia

Cross pollinated Insect

Pears

Pyrus spp.

Rosaceae

n = 17

2x

Europe

Cross pollinated Insect

Fruit crops can be perennial trees, shrubs (Pineapple, guava, citrus, lemon, loquat, pomegranate), vines, climbers (Grape vine, kiwifruit, passion fruit) or annual. Further, fruit crops can be diploid, triploid (apple, banana, citrus, water melon, tetraploid (apple, kinnow), hexaploid (kiwifruit), octaploid (strawberry). The there are fruit crops such as kinnow, apple in which a variety of ploidies (diploid, triploid or tetraploid) exist.

Crop Evolution and Genetic Resources

9.4

Classification of fruits with examples are given in the table 9.2 below. The edible parts of various fruits are given in Table 9.3. Tables 9.4 and 9.5 show breeding systems and mechanisms involved in cross pollination, respectively. Table 9.2  Showing classification of fruits with examples Groups of fruits Simple fruits

Dry or fleshy Dry, Dehiscent

Dry, Indehiscent fruits

Splitting or schizocarpic fruits

Fleshy fruits

Aggregate fruits

Kinds of fruits

Example

Legume or pod

Pea, bean, gram, lenitl, pulses

Follicle

Calotropis, Asclepias, Hoya, Rauwolfia, etc

Siliqua

Mustard, Radish, Candytuft

Capsule

Cotton, Lady’s finger, Datura, Cock’s comb, poppy, etc

Achene

Mirabilis, Fagopyrum, rose, Clematis

Caryopsis

Rice, maize, wheat, bamboo, grass, etc

Cypsela

Sunflower, marigold, Cosmos, etc

Nut

Cashewnut, chestnut, walnut, hazelnut etc.

Lomentum

Acacia, Mimosa, Cassia fistula, Arachis, etc

Cremocarp

Coriander, anise or fennel, cumin, carrot, etc

Samara

Yam

Regma

Castor, Geranium, Jatropha, etc

Drupe

Mango, plum, coconut-palm, palmyra-palm, almond, peach

Berry

Tomato, gooseberry, grapes, banana, guava, papaya, date-palm

Pepo

Gourd, cucumber, melon, watermelon, squash, etc

Pome

Apple and Pear

Hesperidium

Orange, Pummelo-shaddock, lemon, etc.

An etaerio of follicles

Michelia, Vinca (periwinkle), Delphinium, etc

An etaerio of achenes

Rose, lotus, Strawberry, etc

An etaerio of drupes

Raspberry

An etaerio of berries

Annona (Custard apple), polyathia, Artabotrys, etc Contd...

Origin and Genetic Resources of Fruit Crops

9.5

Contd...

Groups of fruits

Dry or fleshy

Multiple or composite fruits

Kinds of fruits

Example

Sorosis

Pineapple, jackfruit, Mulberry

Syconus

Ficus (Fig), banyan, peepal

Table 9.3  Showing some fruits and their edible parts. Fruits

Edible parts

Apple

Fleshy thalamus

Banana

Mesocarp and endocarp

Cashes-nut (nut)

Peduncle and cotyledons

Coconut palm) fibrous drupe)

Endosperm

Cucumber (pepo)

Mesocarp, endocarp and placenta

Custard apple (Etaerio of berries)

Fleshy pericarp of individual berries

Date palm (one seeded berry)

Pericarp

Fig (Syconus)

Fleshy receptacle

Grape(berry)

Pericarp and placentae

Guava

Thalamus and pericarp

Jack fruit

Bracts, perianth and seeds

Litchi

Fleshy aril

Mango

Mesocarp

Melon (pepo)

Mesocarp

Orange

Juicy placental hairs

Palmyra-palm

Mesocarp

Papaya

Mesocarp

Pea

Cotyledons

Pear

Fleshy thalamus

Pineapple

Outer portions of receptacle, bracts, and perianth

Pomegranate

Juicy outer coat of seed

Pummelo or shaddock

Juicy placental hairs

Strawberry

Succulent thalamus

Tomato

Pericarp and placenta

Wood-apple

Mesocarp, endocarp and placenta

Crop Evolution and Genetic Resources

9.6 Table 9.4  Showing breeding systems in various fruits

Classification based on type of pollination Cleistogamy

Grape (Vitis), Papaya and Sapota

Homogamy

Apricot (Prunus armeniaca), Citrus, Dwarf coconut & peach (Prunus persica)

Self incompatibility - Mango & Cocoa Dichogamy

Walnut, Pecan nut, Annona & Avocado

Heterostyly

Litchi, Sapota, Almond, Pomegranate Functional Unisexuality- eg.

Reflexed stamen in grape

Hur, Bangui Abyad , Angoor Kalan

Self sterility

Peaches-(JH Hale, June Elberta, Halberta) Pears-Magness

Types of self Incompatibility Heteromorphic

No fruit crop

Homomorphic

Sporophytic–Mango, Aonla, Cocoa Gametophytic-Almond, Pineapple, Ber, Apple, Apricot, Cherry, Loquat & Pear.

Different types of Dichogamy Protandrous

Walnut, coconut, Annona muricats, sapota & Passion fruit.

Protogynous

Annona sp. excep. A. muricats, Fig, Banana, Plum & pomegranate.

Heterodichogamy

Pistachio nut

Protogynous diurnally synchronous dichogamy (PDSD)

Avocado

Dho-dichogamy

Chestnut

Heterostyly Pin type

Sapota, Pomegranate

Thrum type

Almond, Carambola

Table 9.5  Showing two mechanisms favouring cross pollination in various fruits Mechanism favoring crops pollination - Unisexuality/dicliny Monoecious

Banana, Jackfruit, Pecan, Tall coconut, hazelnut & walnut.

Dioecious

Chinese gooseberry, Date, Grape (Muscadine), pistachio and Papaya

Origin and Genetic Resources of Fruit Crops

9.7

Apomixis occurs in citrus and mango naturally. Banana, apple, grapes, guava, pineaaple, pear, papaw are parthenocarpic. Apple and pears are disomic polyploid. NAA induces parthenocarpy. In climacteric fruits there is production of ethylene which is synthesized autocatalytically in the early stage of fruit ripening. Non-climacteric fruits do not synthesize or respond to ethylene in this fashion. Climacteric or non-climacteric is based on the pattern of respiration and ethylene production during ripening. (Biale, 1960). In the nonclimacteric fruit respiratory activity is low and when ripening is initiated it progressively decreases as ripening progresses. In case of climacteric fruits, there is an increase in respiration during ripening which is accompanied by increase in ethylene production. Depending on the fruits ethylene cmiacteric precedes (banana), coincides with (pear, avocado) or follows (plums) the rise in respiration (Biale and Young, 1981) Ethylene is involved in a wide range of developmental process from seed germination to senescence. It is also important for regulating the ripening of climacteric fruit. Ethylene turns on the different genes involved in producing enzymes such as kinase, amylase, hydroxylase, pectinase which change the acid, starch, chlorophyll, pectin and large organics of unripe fruits to neutral state, sugar, anthocyanin, no pectin (soft) and aromatics. Fruits were defined as climacteric or non-climacteric depending on the presence or absence of a respiratory rise during ripening. But as there are examples of climacteric fruits (apple, kiwi, papaya or pear) with low respiration rate and non-climacteric fruits (black berry, rasp berry and strawberry) with high respiration rate hence presence or absence of climacteric is determined by the occurrence of autocatylytic ethylene production rather than the respiration rate per se. Non-climacteric fruits do not ripen after removal from the plant and so these fruits are harvested at the stage of commercial ripeness. But climacteric fruits can be harvested at a stage when they are physiologically mature, stored and subsequently ripened. Apple, apricot, avocado, banana, kiwi, mango, melon, papaya, peach, plum, persimmon, tomato, fig, pea and guava are examples of climacteric fruits. Non-climacteric fruits include strawberry, cherry, citrus (grapefruit, lemon, lime), orange, mandarine, cucumber, grape, litchi, olive, pineapple, banana, pomegranate and watermelon, pepper. Fruit is a composite tree with a rootstock and a scion and thus consists of two genotypes. The improvement in fruit crops then can be done either by improving the rootstock or scion or both. Occasionally, a genetically distinct trunk or inter stem is used. Specific adaptation to soil conditions and pests as well as root traits affects the performance of scion. Further, most fruit crops perennial in nature, highly herterozygous and are vegetatively propagated. They are mostly cross-pollinated which is facilitated by presence of self-incompatibility and male sterility. They require different breeding approaches than which is employed in improvement of annual food crops. Changes during ripening/maturation of fruits  During ripening process production of ethylene goes up and changes in sugar content and organic acid metabolism occur. Seed develops inside ovary and it increases in size with the process of fruit maturation. In the initial stage of seed development hormone cytokinin is involved whereas in the second

Crop Evolution and Genetic Resources

9.8

stage gibberellic acid is involved and in the final stage of seed development abscisic acid (ABA) is involved which causes embryo to become dormant. Trees raised from seeds have a high canopy and long gestation period (7-12 years). Eating quality includes flavour and texture of the fruits. Appearance, flavour and texture together constitute the sensory property of fruits. Taste plus aroma constitute flavour. Taste could be sweet (because of sucrose, fructose and glucose), sour (because of organic acid such as citric acid, malic acid, tartaric acid), bitter (due to alkaloids, terpenoids, phenylpropanoids), umami (because of amino acids such glutamate, aspartate) and saltry due to Na and Ca ions. Flavor is thus evaluated in terms of component traits such as sugar, organic acids, mineral salts and aromatic compounds. Many of the aromatic compounds are esters such as amylacetate (pear), methyl butyrate (pine apple), isoamyl isovalerate (apples). Substances giving specific odor to plants include essential oils and resins. Essential oils include terpenes, alcohols derived from terpenes, phenols and sulfuretted oils. Tannins give astringent and bitter flavour to food. A natural aroma , smell or ordor is made up of a number of different volatile compounds. Majority of the fruits have terpenes in their aroma profile. In climacteric fruits ethylene plays an important role in triggering aroma formation during fruit ripening. Aroma formation in non-climacteric fruits is not dependent on ethylene. Metabolic pathways involved in the production of aroma are discused in Chapter 11. Non-reducing sugars include sucrose. Reducing sugars include disaccharides such as glucose, fructose, lactose, maltose. Aromatic compound, acids and sugars in different fruit crops are given in tables 9.6 and 9.7, respectively. Post-harvest disorder, specific marketing periods, time of harvest, storage, shelf life and uniform ripening after storage, susceptibility to post-harvest physiological disorder such core breakdown, and bitter pit, associated with low Ca ion content of flesh, superficial scald associated with high level of alpha-farnesene become the breeding objectives in various fruit crops. Table 9.6  Showing aromatic compounds present in various fruits Fruit crop

Aromatic Compound

Apple

Ethyl-2-methyl butyrate (ripe) and hexanal (green)

Banana

Hexanal (green) and eugenol (ripe)

Lemon

Citral

Grape fruit

Velencene

Orange

Nootakatone

Table 9.7  Showing various sugars and acids present in various fruits Fruit

Acids

Sugars

Apple

Malic acid

Fructose, glucose, sucrose

Avocado

Malic acid and citric acid

Glucose, fructose Contd...

Origin and Genetic Resources of Fruit Crops

9.9

Contd...

Fruit

Acids

Sugars

Banana

Malic acid

Sucrose, fructose,glucose, maltose

Berries

Citric acid

Low content of sugar

Cherries

Malic acid

Glucose, fructose, sucrose

Citrus

Citric acid

Durian

Ascorbic acid

Sugar 33%, TSS 36%

Figs

Pectic acid

Glucose, fructose, sucrose

Guava

Citric acid, ascorbic acid

Fructose (3.4%), D-glucose (2.8%), sucrose (0.3%)

Dates

Citric, malic, phosphoric acid

Sucrose (35-40%)

Ltchi

80% non-volatile acids, 20% citric acid, succinic acid, levulinic acid, phosphoric acid, glutamic acid, melonic acid, lactic acid

Sucrose (18.3%), reducing sugars, TSS (17-618.4%)

Loquat

Malic acid

Fructose, sucrose

Lemon

Citric acid

Mango

Oxalic, citric, malic, malonic, succinic, pyrovik, adipic, galacturonic

Glucose, fructose, sucrose, xylose and arabinose

Papaya

Ketogluctaric, citric, malic, ascorbic acid

Sucrose (48.3%)

Passion fruit

Citric, malic

Fructose (29.4%), glucose (38.1), sucrose (32.4%)

Pineapple

Citric, malic, ascorbic, oxalic

Glucose (1-3.2%), fructose (0.6-2. 3%), sucrose (5.9-12. 0%)

Persimmon

Ascorbic

Fructose, glucose

Pear

Citric

Fructose, glucose, sorbitol, sucrose

Plum

Malic

Melon

Malic

Tamarind

Tartaric

31.01% total sugar, reducing sugar (23.05%)

Neutraceutical Traits in Fruits Fruits contain various neutraceutical (nutrition + pharmaceutical) compounds carbohydrates, protein, fats, minerals besides vitamins, fibers, phenolics, minerals, fatty acids. Anthocyanin is powerful antioxidant. And it removes reactive oxygen species (ROS) such as O–, H2O2, O2– or OH–. (Asada, 1991). Pectins are a structurally diverse group of heteropolysaccharides. It is a principal component of cell wall and middle lamella (the area of cell-to-cell contact). Pectin contributes to texture of the fruit. Texture depends on the strength of the cell wall and the wall to wall adhesion between cells. Fleshy fruits such as plums, grapes, berries, dupes contain 90% water plus sugar (glucose, fructose) and vitamins. Dry fruits and nuts contain carbohydrates, fats, proteins and mineral salt. Citrus and berries contain a relatively higher amount of micronutrients. Table 9.8 shows neutraceutical compounds present in various fruit crops.

Crop Evolution and Genetic Resources

9.10

Table 9.8  Showing various neutracentical compounds and the fruits containg it. Neutraceutical compounds Vitamins

Types Vit. A

Precursor/product a-carotene, b-carotene, g-carotene, xanthophylls, bcryptoxanthi cryptoxanthin are the precursors

Fruit crop (s) containing large amount. Cucumis melo var. cantalupensis, Apricot, Papaya, Mango

Vit. B complex

Avocado, Chili pepper, Okra, Banana

Vit. C

Black currant, Pepper, Kiwi, Citrus

Vit. E

Tocopherols and tocotrienols

Vit. K

Blue berry, black berry and grapes

Fiber

Cellulose, hemicelluloses, pectin, lignin, resistant starch and non-digestible oligosaccharides.

Fibers are mainly found in vegetables. Fibers account for only about 1-3% of the fresh weight in fruits in the form of cellulose (30 -35%), hemicelluloses (25-35%) and pectin (20-35%).

Phenolics

Phenolic acids

Products of benzoic acid and cinnamic acid

Flavonoids

Flavones and flavonols, isoflavones, Flavones (e.g., rutin, luteolin), Flavonols (quercetin, kaempferol), anthocyanins

Found only in peels or flesh of fruits. Citrus and blueberries. Berries have highest content of polyphenols

Other substances including lignans, stilbenes (resveratol), tannins (gallic acid esters of glucose and other sugars), coumarins Organic acids

Citric acid

Orange, lemons and

Citric and malic acids

Apple, pears, peaches

Tartaric and malic acids

Grapes

Quinic acid and benzoic acid

Banana and craneberries

Origin and Genetic Resources of Fruit Crops

9.11

Contd...

Neutraceutical compounds

Types

Precursor/product

Protein

Fruit crop (s) containing large amount. Climacteric fruits, apple avocado (Protein increases during early stage of ripening)

Lipids

Monounsaturated fatty acids decrease the low-density lipoprotein (LDL) cholesterol, the so called bad cholesterol

Minerals

N

Proteins, amino acids

Present in all fresh fruits

P

Nucleic acids

Avocado, kiwi, raspberry, strawberry, apricot

Carbohybdrates (3-20%)

C

Orange, fig, kiwi, lemon and black berry

Mg

Raspberry, avocado, banana, black berry

Fe

Avocado, berries, lemon, cherry, fig, grapes

Cu

Avocado, berries, lemon, cherry, fig, grapes

Zn

Avocado, blackberry, raspberry, fig

S and Na

Melon (cantaloupe), avocado

Polysaccharides, oligosaccharides and monosaccharides

Cucumber (3-5%), watermelon (10-14%). Inapple, pear, grapes and strawberry concentrations of glucose and fructose are higher than sucrose. In pineapple, banana, peach and melon sucrose is the main constituent of sweetness.

Sensory/Organoleptic Characters in Fruits As breeding objective in the past had been to improve yield, stability, shelf-life there has been continuous loss of flavor in the varieties developed. Flavor, taste and aroma are polygenic traits. Aroma is a result of interaction between volatiles and non-volatiles. Taste and aroma determines consumer’s choice. Sensory/organoleptic characters include those traits of fruits that stimulate sense organs such as vision, gustation, olfaction, touch and audition. Vision includes appearance of fruits which includes color, shape, size,

9.12

Crop Evolution and Genetic Resources

translucency, surface characters, etc. Gustation relates to heaviness, hardness, sweet, salty, sour, bitter, umami and kokuni attributed to mouth feel and also sensation such as hot, burning, tingling, cooling, astringent and texture perception refers to firmness, graininess, oiliness. Olfaction includes volatile molecules include aroma. Audition includes crispiness and crunchiness of the fruit (Ulrich and Olbricht, 2011). Increase in shelf life of fruits  Like in case of food crops the objective in fruits and vegetables is to make it available year round. Thus the breeding objective would be to improve post-harvest shelf-life. Ripening is associated with production of aromatic compounds, color changes, flesh softening and fruits become palatable and over softening leads to susceptibility to pathogens and development of undesirable flavor, skin color and thereby reducing fruit quality. Rate of fruit softening determines post-harvest shelf life. There are two groups of fruits- one group comprising peach, apricot, plum, kiwi, tomato which soften greatly as they ripe and thus have shorter shelf-life. And other group consisting of apple, quince, pears, watermelon, craneberry which soften moderately as they ripe and thus have longer shelf-life. Fruit softening is associated with cell wall composition and structure. Firmness of a fleshy fruit is a complex trait and includes cell shape, size, cell wall thickness and strength and cell turgor and extension and strength of adhesion areas between adjacent cells and presence of non-parenchymatous cells, most of which contain thickened walls (i.e., epidermal cells, vascular elements, fibers and sclereids) (Mercado et al., 2011). During ripening fruit softening and sweetening occurs. Starch breaks down to sugars which is further hydrolysed to glucose and fructose. Mango, kiwi, banana and melon accumulate sucrose during ripening. Also, there is hydrolytic break down of cell wall polymers (e.g., cellulose, hemicelluloses, pectins). There is a decrease in fatty acid concentration during ripening. Concentration of linoleic decreases whereas concentration of linolenic acid increases. Green pumpkin (Cucurbita pepo) has linolenic acid and myristic acid which are absent in ripe fruit. Textural changes in ripening fruits are associated with the dissolution of the middle lamella and the modification of composition and structure of polymers present in the primary cell wall (Goulao and Oliveira, 2008). During ripening the parenchyma cells are modified and cell adhesion reduced, combined with reduction in turgor pressure. Pectin metabolism plays a critical role in fruit softening and although all three mechanismspectin solubilization, pectin depolymerization and xyloglucan depolymerization involved in fruit softening are found in avocado, tomato, melon, kiwifruit, Japanese plum but pectin solubilization is a general characteristic of fruit softening. XTH and N-glycan modifying enzymes have great effect on fruit firmness and thus on post-harvest shelf life. Firmer genotypes have shown less transpirational water loss. Cuticle structure and compaction might be associated with the fruit shelf-life. Suppression of cell wall degrading enzymes such as polygalacturonidase, pectin methylesterase and b-galactosidase are not sufficient to significantly impact fruit texture (Giovannoni, 2001). But N-glycan is important in enhancing fruit firmness (Melie et al., 2010).

Origin and Genetic Resources of Fruit Crops

9.13

Softening of the fruits can be reduced by way genetic engineering technique of silencing of genes encoding cell wall disassembly of proteins but allowing normal development of other ripening events such as accumulation of sugars, volatiles or pigments (Brummell and Harpster, 2001). Allergenic traits in fruits  Allergy can be either by eating of various fruits or by pollen from different trees and grasses. The different fruit crops such as apple, pear, peach, mango, plum, sweet cherry, apricot almond, pineapple cause allergenic reactions. Besides these fruits crops litchi, loquat, melon, cucumber, watermelon, date, fig, mulberry, pomegranate, chestnut, mandarin orange, strawberry and raspberry are also reported to cause allergy (Gao and Gilissen, 2011). Pollen allergy can be from birch pollen of apple, kiwifruit, peach, jackfruit, mango and persimmon and from mugwort pollen of peach and kiwifruit. Important protein families causing allergy have been reported as PR10 (Pathogenesis related familiy 10 protein from apple (Mal d1), peach), nsLTP (Lipid transfer protein, PRP-14, e.g. Lyc e3 from tomato), profilins, e.g. Birch pollen protein, Lyc e1 from tomato), TLP (Thaumatin like protein) found in apple and kiwifruit, chitinase found in chestnut, banana, avocado, Indian date and cysteine proteases found in papaya, pineapple and kiwifruit. From the above it can be said that all those secondary metabolites which are involved in defens mechanism of plants seem to be involved in causing allergy. Thus while releasing variety measurement of these traits be done. Wide crosses have been important in orchards and arbor crops-apples, plum, cherries, grapes and various kinds of berries. Inter-specific hybridization has played an important role in their improvement. Hybridization is more important in vegetatively propagated species than in that which produce seeds. Antioxidants  Fruits and vegetables are grown for vitamins, mineral and antioxidants. Antioxidants function as singlet and triplet oxygen quenchers, free radical scavengers, peroxide decomposer, enzyme inhibitors and synergists (Larson, 1988). Antioxidants prevent diseases. Antioxidants are also found in spices, herbs and essential oils. It includes polyphenols (Flavones, Flavonols), hormones (Vit.A, Vit.C and Vit.E), carotenoiids (a-carotene, b-carotene, lutein, lycopene, zeazanthin), anthocyanins, salicylic acid, non-flavonoides (Curcumin, xanthones), organic antioxidants (capsaicin, citric acid, oxalic acid). For biosynthesis of these secondary metabolites see chapter 11 on flower crops. Pectin  It is a naturally occurring complex polysaccharide, found in cell walls and core of fruits and vegetable. During ripening pectin breaks down by enzymes, pectinase and pectinesterase and so fruits become softer as the middle lamella breaks down and cells get separated. The amount, structure and chemical composition of pectin differs among plants, within a plant over time and in various parts of the plant. It is made up of sugar residue- D-galacturonic acid and the dominant polysaccharides include homogalacturonan, rhamnogalacturonan I and II and xylogalacturonan. It combines with sugar and acid and forms a gel. Tannin  Tannic acid imparts bitter and astringent taste. Tannins are a type of polyphenol. Tannin quantity decreases on ripening. As tannins condense they produce other polyphenols such as flavonoids and catechins which are antioxidants

9.14

Crop Evolution and Genetic Resources

9.2  APPLE The apple (Malus genus) belongs to family Rosaceae. There are about 25 species and most can be crossed. M. domestica is the cultivated apple. M. pumila is the paradise apple and M. sylvestris is the wild crab apple. Apple is hermaphrodite. Apple cultivars are largely self-incompatible and thus are pre-dominantly cross-pollinated and many are apomictic. It is highly heterozygous and heterozygosity is reinforced by self incompatibility and inbreeding depression. Cultivars which are partly self-fertile, requires pollenizer. Fruits develop parthenocarpically without fertilization and without seeds. Parthenocarpic fruits can be either small and often misshapen or normal in size and appearance. They tend to ripe earlier and do not keep as well in storage as in seeded fruit. Because of high degree of self-incompatibility selfing is difficult to pursue and a great many flowers have to be selfed in order to get a few fruits with only a few seeds. Majority of Malus species are diploid (2n = 2x = 34) but there exists triploid, tetraploids and pentaploids (Table 9.9). The centre of origin is Asia minor. Several cultivated apple varieties are triploids. Triploid varieties have evolved as a result of fertilization of unreduced gametes as shown below. Triploids are often vigorous and produce larger fruits. Parents 2n × 2n Gametes 2n n 3n (Triploid) Triploid (2n = 51) apple requires pollenizer as pollen is not viable. Tetraploids (2n = 68) varieties have been evolved through isolation of tetraploid chimeras. If one diploid layer mutates then there is formation of tetraploid layer but if two diploid layers mutate than it behaves like diploid. Flowering starts in March and fruit is harvested in August-September. Apple browning is due to polyplenol oxidase. In peach, plum, apricot flowering starts in February and kiwi flowers in April. Quality traits in Apple  The quality traits in apple include appearance (size, color (pink, red preferable), appearance of blemishes, russet, crispiness, juiciness and sweetness. Acid content decreases during storage and thus making the taste of the fruit insipid. Perceived sweetness and sourness (sensory evaluation) are better predictors of liking than the fruit’s Brix value and titrable acid. The traits such as appearance, texture, flavor and juiciness be measured on a 9-point scale. Fruit color is controlled by both ground color of the skin (carotenoids and chlorophyll) and anthocyanin pigmentation. Color of the flesh could be red(novel quality), yellow or white. Eating quality components include texture, flavor and juiciness. The main sugars in apple are fructose, sucrose and glucose and acid in matured fruit is mainly malic acid. Flavor is determined by acids, sugars

Origin and Genetic Resources of Fruit Crops

9.15 .

and aromatic substances (alcohols, aldehydes and esters being the major constituents). The physiological disorders include russet, cracking and bitter pit (calcium defect). The functional substances in apple include many polyphenols and vit. C, having antioxidant properties. Fruits are usually harvested before they are fully matured for long term storage. Browning in apple is due to the oxidation of phenolics into quinines. Browning negatively affects the appearance of fresh-cut fruits or vegetables. Apple slices are treated with commercial ascorbic acid to prevent browning. Resistant cultivars have low levels of polyphenol oxidase and polyphenols. NAA @0.1-0.4% in talc is applied before rooting hard wood samples. Ethephon is applied @0.05 0.2% as spray for defoliating the nursery stock and TIBA @50mg/l is applied as spray after appearance of early spring foliage on 1-2 year old non-bearing trees for widening crotch angles and also for increasing flower induction (25mg/l, 4-5 weeks after full bloom and before new fruit bud formation). Daminozide @2.0 to 4.0 mg/l is applied at 14 days after full bloom to substantially reduce vegetative growth. Ethephon @0.04% is used for enhancing fruit maturity in apples, 7 to 14 days before expected harvest date. The cultivated apple is thought to be an allopolyploid (allotetraploid) but it behaves like functional diploid. It is a complex interspecific hybrid. Apple has probably been derived from hybridization involving M. sylvestris, M. dasyphylla, M. pumila and some Asiatic species particularly M. baccata. European apple is thought to have evolved as a result of hybridization between M. pumila and M. sylvestris whereas asian apple is believed to be evolved from the cross between M. pumila and M baccata. Mahal (Pyrus pashia) is used as rootstock in apple and pear. Apple’s ancestor, Malus sieversii is found in Kazakhstan. It is an important species considering the evolution of cultivated apple. It might have got hybridized with M. prunifolia, M. baccata and M. seiboldii while spreading to the East. Evolution is through duplication of almost all of the genome. The closest relatives of apple are strawberry and raspberry. Phosphoglucoisomerase 3(PGM3) isozyme is characteristic of M. xdomestica. Rootstock controls scion vigor and cropping and influences the scion’s response to abiotic and biotic stresses. Ideal rootstock should control tree size (dwarfing), tolerance of cold (hardiness), tolerance to pathogens(scab and fire blight) and pests, tolerance to wet or dry soil besides having long term graft compatibility and good health- freedom from virus and bacterial diseases. Rootstocks that are being used are M(Malling) and MM(Malling-Merton) series rootstock, EMLA (East Malling), CG(Cornell-Geneva) and crab apple (for colder area) rootstocks. Tree architecture–Branches are arranged symmetrically to form a regular pyramid shaped structure. Tree should be small productive suitable for high planting density, compact tree habit with high spur density, annual bearing, adaptation to extreme climates, resistance to fresh browning after cutting. Genetic transformation using antisense polyphenol oxidase (PPO) gene has been used to develop transgenic having lower browning.

Crop Evolution and Genetic Resources

9.16

Quantification of quality attributes  It is required especially in case of flavour and textural components of firmness, crispiness and juiceness. Breeding for development of low allergenic cultivars has been the objective in apple. Dessert apples have largest market and are sold considering the size, color, shape, free from blemishes and quality (taste and mouthful). Apples are produced in three months depending upon the maturity. High tannins cultivars are used to make juice for industry. Quality depends not only on genetic factors but also influenced by production practices, orchard management and climate. Asean markets prefer mild to sweet low acid apple whereas European and U.S. markets consider appearance and tartness. Apples below 57mm in diamer are called crab apple and they are used for juice extraction. Planting methods include square, contour or hexagonal. Spacing is 2 × 2.5m for dwarf, 3 × 4m for semi-dwarf, 4 × 5m for vigorous and 6 × 8m for very vigorous cultivars. Planting time is December-January. Flowering time is March-April and harvesting is during July-October. First bearing starts 4 years after planting. Nursery men would like to see the following traits in apple plants being produced. Easy propagation, good nursery performance, dwarfing, consistent cropping, precocity, resistance/tolerance to biotic and abiotic stresses, freedom from suckers and burr knots. are the characteristics to be considered. Table 9.9  Showing some species of apple, their ploidy level and country of origin (Adapted from Way et al., 1991) Species

Ploidy level

Origin

M. pumila

34

Europe, Asia minor

M. sylvestris

34

Europe

M. x domestica

34, 51, 68

Cultivated world wide

M. prunifolia

34

Korea, North China

M. asiatica

34

Korea, North and NE China

M. micromalus

34

Korea, South east China

M. baccata

34, 68

Japan, Korea, North China

M. prattii

34

South west China

M. fusca

34

Western North America

M. spectabilis

34, 68

China

M. floribunda

34

Japan

M. halliana

34

Japan

M. hupehensis

51

Central China

M. mandshurica

34

Manchuria

M. orientalis

?

Caucasia

M. dasyphylla

Contd...

Origin and Genetic Resources of Fruit Crops

9.17

Contd...

Species

Ploidy level

Origin

M. sieversii

?

North west China

M. sikkimensis

51

Himalayas

M. seiboldii M. coronaria

North America

M. angustifolia

North America

M. ioenesis

North America

9.3  APRICOT Apricots,  Armeniaca species are given in the table 9.10 below. Apricots have limited environmental range than other fruit trees and thus there is a need of broadening adaptation for specific growing regions. It is a diploid with 2n = 16. Breeding objective includes developing plum pox virus resistance. Fruit sugars, acids, pigments and volatile aromatic compounds have been quantified. Several stylar ribonucleases associated with self-unfruitfulness have been characterized. There is scarcity of documented monogenic traits in apricots which demands of applying marker-assisted selection. Presence of male sterility and self-incompatibility limits apricot improvement. Early detection is important. Gametophytic SI is under control of single locus multiple allelic system. In style the product of S alleles are S-ribonucleases. Self incompatibility can be identified by i. Self pollination ii. Fluorescence microscope and iii. Polymerase Chain Reaction (PCR). In case of apricot, self incompatible varieties can be manipulated by the relative number and distribution of pollinator trees. Pollination is carried out by wind and bees. Rootstocks used are wild apricot and peach. Planting method followed is square. Spacing is 6 × 6m. Planting time is DecemberJanuary. Flowering time is March and harvesting takes place in May. First bearing starts 4-5 years after planting. All cultivars have melting flesh. Sucrose is the principal sugar. Glucose, fructose, maltose and sorbitol and raffinose are in lower concentration. This fruit is rich in carotenoids (b carotene, b cryptoxanthin, c-carotene, lycopene and tutein). Flavor is due to lactones and there should be a balance between glucose and fructose. Low glucose to fructose ratio is of interest. Firmer, attractiveness and taste are the three attributes affecting quality in apricot. The physical quality traits include weight (or size), skin and flesh color, blush coverage, flesh firmness and dry matter. Chemical traits include soluble solid content and titrable acidity. Sensory traits include attractiveness, taste, aroma and texture. The breeding objectives in apricot includes development of cultivar with increased climatic tolerance and hardiness and resistance to diseases and improved characteristics such as size, appearance and shape depending on the use of the fruits (fresh, canned or dried) and the requirement of the region.

Crop Evolution and Genetic Resources

9.18 Table 9.10  Showing various species of Apricot Species

Common name

A. vulgaris var. ansu

Ansu apricot

Armeniaca, common apricot

Common apricot

A. brigantiaca

Alpine apricot

A. dasycarpa

Black apricot

A. fremontii

Desert apricot

A. holosericea

Tibetan apricot

A. hongpingensis A. hypotrichodes A. limeixing A. mandshurica

Manchurian apricot

A. mume

Japanese apricot

A. siberica

Siberian apricot

A. zhengheensis

9.4  STRAWBERRY It is a herbaceous perennial, spreading with runners that has a central stem or crown from which leaves, roots, stolen (runner) and inflorescence emerge. Edible fruits are large receptacle on which seeds are embedded. There is axillary bud at the top of leaf along crown which can produce runners, branch crowns or remain dormant depending on the environmental conditions. Strawberry is a soft fruit which is rich in vitamins and minerals. It can be grown in temperate as well as tropical/subtropical condition and is propagated vegetatively through runner rather than seed. The centre of origin is Europe. The cultivated strawberry (F. x anansa) is highly heterozygous. It belongs to family Rosaceae. The wild species F. vesca (2n = 2x = 14) and F. moschata are also cultivated albeit on a much smaller scale. The inflorescence is a cyme which terminates with a primary blossom which is followed by two secondaries, four tertiaries and eight quarternaries. A typical flower has ten sepals, five petals and 20-30 stamens and pistil number from 60-600. The highest number of pistils are found in the primary flowers and this number decreases successively. Cross pollination is common. Cross pollination is through insects, bees. All those breeding methods that are employed in case of cross-fertilizing species can be used for improvement in strawberry. This crop tolerates less inbreeding. Inbreeding results in loss of vigor and yield. There are diploid (2n = 14), tetraploid (2n = 28), hexaploid (2n = 56) and octoploid (2n = 84) strawberry species as shown in the Table 9.11. Octoploid species contains three types of flower-pistillate (devoid of anther), staminate (non-functional) and hermaphrodite. Modern varieties are hermaphrodite. Emasculation is done one to three days before anthesis to prevent self pollination. Fruits are ripe in 25-30 days after pollination. Reciprocal recurrent selection

Origin and Genetic Resources of Fruit Crops

9.19

has been used in the improvement program. Marker–free genetic transformation system has been successfully tested in strawberry. Breeding problems include developing day neutral cultivars. Gene determining cyclic flowering in F. x ananassa has been transferred from F. virginiana ssp. glauca. Yield components include fruit number (high fruit number) and size of the fruit, plant vigor. Crown number per row area is positively correlated with yield. Crown number increases with either increasing the levels of stolen production or branch crown production. Stolons of most species consist of two nodes. A daughter plant is formed at the second node whereas first node remains dormant or develops another stolon. F. xananassa usually produces 10-15 stolons/plant/year whereas F. virgianiana produces 2-3 times more than this number per year. Further, stolons of species F. xananassa and F. virgianina survive for one year whereas stolons of F. chiloense can last for several years. The breeding objective in strawberry is to develop variety suitable for mechanical harvesting, has extended harvesting season. The other traits include developing day neutral, short-day variety, time of ripening and concentration of ripening, fruit shape, symmetry, skin toughness, flesh firmness, skin color, skin glossiness, flesh color and flavor. Shipping quality includes firmness, appearance, size, color and flavor coupled with yield, adaptation, harvest efficiency and disease resistance and storage quality. Strawberry is consumed either fresh or used for processing. Processing market quality includes intense internal and external red color, low drip loss, exceptional flavor and high soluble solid content. Fruit weight can vary from 14.7gm to 23.5gm. The main classes of compounds involved in aroma include esters, alcohols/aldehydes, terpenoids and lactones. The proportion and total amount of soluble solid content and titrable acidy affect flavor. Thus while breeding variety antioxidant acitivity, flavonoids, vit. C and other chemical compounds present in the fruits must be measured. Sexes in strawberry  Sex in strawberry is regulated like a single gene determined trait (one locus with three alleles) with differing levels of dominance (Ahmadi and Bringhurst, 1991). Female(F) or pistillate is dominant over hermaphrodite(H) which in turn is dominant over male(M) or staminate (female > hermaphrodite > male). Thus females can be heterogametic (F / H or F / M) while hermaphrodite can be homo or heterogametic (H / H or H / M) and males are homogametic (M / M). Hermaphrodite is not complete in the sense that one can find self sterile (self infertile) as well as complete fertile plants (Stahler et al., 1995). Tetrasomic inheritance was also reported for sex(Staudt, 1967). Male suppressor, SuM(F) was dominant to male inducer, Su+(H) and to the female suppressor, SuF(M). SuF was dominant to Su+. Strawberry’s closest relatives are Duchesnea and Potentilla. Planting methods include ground spreading or bund. Spacing is 30-45cm x 15-20cm. Planting time is September-October (in plains) and July-August (in hill). Flowering time is January-February and harvesting time is March-June. Propagation is through runner but tissue culture technique has been found suitable for generation of planting materials. Table 9.11 shows species of strawberry, breeding systems & distribution.

Crop Evolution and Genetic Resources

9.20

Table 9.11  Showing species of strawberry along with ploidy level and breeding systems Ploidy level

Species

Characteristics

Distribution

F. vesca

SI, small fruited, wild species, grown commercially on small sacle.

North America, northern Asia and Europe

F. daltoniana

SC

Himalayas

F. gracilosa

SI

China

F. iinumae

SC

Japan

F. mandshurica

SI

Manchuria

F. nilgerrensis

SC

South-eastern Asia

F. nipponica

SI

Japan

F. nubicola

SI

Himalayas

F. pentaphylla

SI

China

F. viridis

SI

Europe and Asia

F. yesoensis

SC

Japan

F. corymbosa

Dioecious

North China

F. moupinensis

dioecious

Southern China

F. orientalis

trioecious

Northern Asia

F. x bringhurstii (35, 42)

dioecious

U.S.A.

Hexaploid (2n = 42)

F. moschata

Trioecious, grown commercially on small scale.

Northern and central Europe

Octoploid (2n = 56)

F. virginiana

low temperature hardiness, trioecious

Central and eastern North America

F. ovalis

winter hardiness

F. chiloensis

virus tolerance

F. x ananassa

trioecious

Worldwide

F. iturupensis

trioecious

Japan

Diploid (2n = 14)

Tetraploid (2n = 28)

The cultivated strawberry Fragaria x ananssa is an octoploid and developed as a result of hybridization between the two American species as shown below.

F. chiloensis × F. virginiana (2n = 8x = 56) (2n = 8x = 56)

F. x ananasa

Origin and Genetic Resources of Fruit Crops

9.21

Cross pollination is the common method of breeding. Backcrossing using molecular marker can also be applied. Further, marker assisted selection can be applied. Use of varietal cross, development of hybrids using inbred lines and use of backcrossing can be employed for improvement of strawberry. Micropropagation in strawberry  It is one of the first crops which is routenly multiplied through micropropagation. The explants include anther, callus, flower bud, leaf disc, protoplast, petioles, stem, stipules, roots and runners. Agrobacterium mediated genetic transformation has also been used to develop transgenic strawberry.

9.5  RUBUS CROPS It includes R.idaeus (red), R. occidentalis (black) and purple-a hybrid between red and black, raspberries, black berries, cloud berries. Raspberries can be differentiated from blackberries by how they are picked from the plants. In raspberries, receptacle separates from the fruit but remains on the plant (free receptacle) whereas the receptacle of blackberry fruit separates from the plant but sticks to the fruit. There is polyploidy, apomixes, pollen incompatibility and poor seed germination in Rubus. There is biennial flowering structure and canes live for two years. New canes come from either the crown or root (root suckers. Hardening is for one year, requires vernalization and become reproductive, called “floricanes” which produce flowers and fruit. Rubus spp.  It includes raspberry, black berry, arctic berry, etc. Rasp berry is one of the most important temperate fruit crops. It is used for making juice, yogurt, jam, flavoring, topping and for dessert. Red rasp berry is more important and more widely cultivated than black, purple or arctic rasp berries. They are mostly perennial shrubs, erect to trailing, mostly deciduous and a few evergreen, usually biennial and a few are perennial or annual canes. Breeding system ranges from apomixis to fully fertile. The chromosome number varies from 2n = 14(diploid) to 2n = 98. Most raspberries are diploid except a few are natural triploid and tetraploids. Black berries have chromosome number varying from 2n = 14 to 2n = 84. Rasp berry belongs to subgenus Idaeobatus which contains more than 200 species. R. idaeus, in general, is called red raspberry. It is a diploid with 2n = 2x = 14. There are two subspecies of raspberry. R. idaeus subsp. vulgatus- European red raspberry and R. idaeus subsp. strigosus, the North American red raspberry. Old varieties of raspberries were developed from the cross, R. idaeus subsp. vulgatus × R. idaeus subsp. strigosus. Recently developed cultivars have genes transferred from six species, R. occidentalis, R. cockburnianus, R. biflorus, R. kuntzeanus, R. parvifolius, R. pungens oldhanii from subgenera Idaeobatus, two species, R. arcticus and R. stellatus from Cylactis and one Anoplobatus species, R. odoratus. Other species of Idaeobatus which are likely to be used in future breeding program include R. crataegifolius, R. coreanus, R. spectabilis and R. phoenicolasuis. The donor of flavor will be R. idaeus, R. rcticus, R. pileatus, R. hirsutus, R. lambertianus and R.chingi. The fruit colour donor would be R. crataegifolius, R. spectabilis and R. strigusus. R. chamaemorus from subgenus Chamaemorus(Cloudberry), the North American origin is an octoploid with

9.22

Crop Evolution and Genetic Resources

2n = 56 has also potential for use in future breeding program. The desired fruit color for fresh market (Table purpose) includes brighter, glossier and less dark colour. Black berries come from several Rubus subgenera such as Eubatus, Caesii, Suberecti and Corylefolii. All produce edible fruits of commercial importance. Species range from evergreen subtropical types to deciduous Arctic types. Cultivated blackberries have been derived from a wide group of basic Rubus species and are complex allopolyploids. Black berry differs from raspberry in that the fruit of the former adhers completely or partially to the receptacle. Black raspberry is from R. occidentalis, native to Easter North America. Black and purple cultivars have been derived from the cross, black × red raspberry. Arctic raspeberry cultivars arose from cross, R. arcticus × R. stellatus or R. idaeus × R. arcticus. A number of varieties with 2n = 42 have been developed from the cross, Octoploid balck bery (2n = 56) × Tetraploid rasp berry (2n = 28). Most blackberries cultivars are tetraploids. The chromosome number ranges from diploid to 2n = 14x = 98 or possibly 2n = 18x = 126. There is facultative apomixis in blackberry. Breeding objectives include broadening the climatic zone of black berry and reducing its chilling requirement. Blackberries are more resistant then raspberries.

9.6  MANGOSTEEN It(Garcinia mangostana) is a deciduous, evergreen, tropical tree, takes 6-25m in height, up to 25-35cm in diameter, having symmetrically arranged branching and forms a pyramidical crown (Yaacob and Tindal, 1995) and found in Thailand and Myanmar. This species is dioecious but only female trees are found. Fruits are formed parthenocarpically. Fruit is berry and the edible pulp or aril consists of 4 to 8 ivory colored segments, some of which contain developed or underdeveloped apomictic seeds. Mangosteen is a polyploidy and possible allotetraplid having been derived from G. malaccensis (n = 42?) and G. hombroniana (2n = 48?). The other species of Garcinia are also from apomictic seeds and thus they are thought of consisting of single genotype.

9.7  CURRANTS AND GOOSE BERRIES These are temperate crops. Black currant is used for production of jam, jellies, coloring of yoghurts and other dairy products. Fruits contain high level of vit. C(ascorbic acid) and anthocyanins. It is a fruit crop used for flavouring food products.The genus Ribes contains about 150 species which are spiny and non-spiny shrubs, native to Nothern Europe. The genus Ribes contain 8 subgenera. The subgenus Ribesia contains red currants and subgenus Eucoresonia contains Black currants. The subgenus Grossularioides contains gooseberry-stemmed currants. The crossability between gooseberry species and Currants members of genus Ribes supports the theory of presence of single genus. Basic chromosome number, x = 8 and all species and cultivars of genus, Ribes are diploid. Black currant  Most important black currant species is R. nigrum. Other important species are given in the table 9.12 below.

Origin and Genetic Resources of Fruit Crops

9.23

Table 9.12  Showing different species of black currant, their common names, distribution and salient features. Species

Common name

Distribution

Characteristics

R. nigrum

European black currant

Nothern Europe, Central and Nothern Asia

Most important species

R. ussuriense

Similar to R. nigrum

Nothern Korea

Produces root suckers

R. pauciflorum

Small flowered black currant

Siberia and Manchuria

R. bracteosum

California to Alaska

R. petiolar

Nother-western U.S.A.

R. hudsonianum

Canada

R. americanum

North America

R. dikuscha

USSR

Winter hardiness

Red currant  It belongs to subgenus Ribesia from Nothern Eruope. White currants are a color form of red currant. Different species of red currant are given in the table 9.13 below. Table 9.13  Showing different species of red currant, their distribution and characteristics Species

Distributin

Characteristics

Main species for development of commercial cultivar R. sativum syn. R. vulgare

North-western areas

Presence of several ecotypes

R. petraeum

Montane species

Presence of several ecotypes

R. rubrum

Scandinavia

Other species of importance Norway

R. spicatum R. multiflorum

Gooseberry  It belongs to subgenus Grossularia. It has spines at the nodes. Different species of gooseberry are given in the table 9.14 below. Table 9.14  Showing different species of gooseberry, their common names, distribution and characteristics. Species

Common name

Distribution

Characteristics

Main important species R. grossularia syn. R. uva-crispa

European gooseberry

R. hirtellum

American gooseberry

United kingdom Extensively used in hybridization with R. glossularia

Other important species R. divaricatum

North America Contd...

Crop Evolution and Genetic Resources

9.24 Contd...

Species

Common name

Distribution

R. acicular

USSR

R. oxycanthoides

USSR

R. alpestre

China

R. grossularioides

Japan

Characteristics Spineless

Ornamental species R. aureum R. odoratum R. sanguineum

Highly popular flowering plant, used as donor of spinelessness trait.

R. glutinosum R. leptanthum

Used in breeding for resistance to diseases as donor parent

R. watsonianum

Used in breeding for resistance to diseases as donor parent

Craneberry  It is a long lived woody, trailing (creeping vines, stolons or runners), broad leaved evergreen of wet land areas. Fruits contain Vit.C. The two major commercially cultivated species in the genus, Vaccinium are given in the table 9.15 below with salient characteristics. It is a considered a model plant for study. Seed to seed takes about three years, thus has short breeding cycle which can be shortened to as short as one year through biotechnological manipulation (Serres et al., 1994). Cultivars are self fertile. There is presence of protandry and obligatory insect pollination (entomophilous) and thus it is a cross pollinated crop. Vegetative propagation is through cuttings and the cultivars are maintained as clones. There has been development and release of hybrids as commercial varieties. Table 9.15  Showing two different species of craneberry, ploidy level, characteristics and distribution. Species

Common name

Chromosome number

Characteristics

Distribution

V. macrocarpum

American craneberry

Diploid with 2n = 24

Large fruited

Eastern U.S.A.

V. oxycoccus

Mossberry

Occurs as population of mixoploids (diploid, tetraploid or hexaploid)

Small fruited

Russia and eastern Europe

Origin and Genetic Resources of Fruit Crops

9.25

9.8  KIWI FRUIT A. chinensis and A. delicosa are the most recently domesticated of all fruit crops and are closely related species of commercial importance. It has originated in China. It has high Vit. C (greater than 30mg/100g fresh weight). It is rich in minerals (Ca, K, Fe, Mg) and amino acids and dietary fibers. It belongs to family Actinidia. It is a temperate fruit. Some Actinidia species (Kiwifruit) are shown in the Table 9.16 below. Current commer-cial cultivars are large-fruited selections from the two closely related species, namely, A, deliciosa and A. chinensis, a tetraploid might be precursor of A. deliciosa, a hexaploid. It is dioecoius (there are male and female plants), perennial and climbing plant and has long generation time. Diploids, tetraploids, hexaploids and octoploids occur in diminishing frequencies. Breeding objectives include fruit quality, flavour, size, time of harvest, flesh color, length of storage life, environmental adaptation and vine productivity. There is excessive vegetative growth and thus there is a need to control growth to ensure fruiting. Different species of Actinidia are given as Table 9.16. Table 9.16  Showing species of kiwi fruit alongwith ploidy level (Adapted form Ferguson and Huang, 2007) Taxon

Ploidy level

Characteristics

Actinidia deliciosa

6x (x = 29)

Main Commercial cultivar Fruit-size (120 gm), good flavour

A. chinensis

2x, 4x

Main commercial cultivar, high vit. C., Large fruit size (100 gm)

A. arguta Planch.ex Miq

4x, 6x

Also grown in New Zealand, Cold tolerant, Smallfruit

A. arguta var. purpurea

4x, 8x

Late maturing

A. eriantha

2x

Very high vit. C. medium sized fruit, fig. like flavour, Also grown in New Zealand

A. henanensis

–

Small fruit

A. kolomikta

2x, 4x

Compact growth habit, short growing season, very cold hardy, very small fruit, high vit C. Also grown in New Zealand

A. latifolia

2x

Late maturing, very small fruit, very high vit C.

A. macrosperma

4x

Small fruit, large seed

A. melanandra

2x, 4x

Small fruit

A. polygama

2x, 4x

Small fruit, cold tolerent

A. rufa

2x

Small fruits, very productive

A. setosa

2x

Early maturing, medium sized fruit (30-40 gm)

A. tetramera

2x

Small fruit (30m height and >2m trunk diameter with long leaves (20-30cm) and is annual bearer. It is native to temperate Asia, North America and Europe. Great diversity is found in south east Asia and eastern U.S.A. It probably originated in Asia minor and China. Most important species include C. crenata, C. dentate, C. mollisima and C. sativa. Other species such as C. henryi, C. pumila, C. seguini produce potential edible nuts. It requires slightly acidic soil. It is diploid with 2n = 2x = 24. It is monoecious with male and female flowers grouped in either unisexual or bisexual inflorescences. Infloresecenses are borne on current season shoots. Female inflorescens

Crop Evolution and Genetic Resources

9.70

Fig. 9.3  showing relationship among different species of Persea

is in group of three female flowers. Life expectancy is around 300-1000 years Fungal diseases are number one problem world-wide. Different species of chestnut are given in Table 9.35. Table 9.35  Showing species, common name and characteristics of chestnut Species

Common name

Characteristics

Castanea sativa

European chesnut

C. crenata

Japanese chesnut or Asiatic chestnut

Resistant to ink disease and chesnut blight

Sweet chestnut

C. mollisoma

Chinese chestnut

Resistant to ink disease and chesnut blight

C. henryi C. davidii C. seguini C. dentata

American chestnut species.

C. pumila C. alnifolia C. ashei C. floridana C. paupispina

9.37  ANNONA SPP. These species are known for distinct flavour and aroma and they are highly nutritious. The most important Annona species are A. cherimola (cherimoya), A. muricata (soursop), A. squamosa (sugar apple). They belong to family Annonaceae. Atemoya is a hybrid between A. chrimola X A. squamosa with 2n = 2x = 14. It is similar to sugar apple in sweetness but taste like pine apple. Atemoya has been crossed with custard apple to develop custard apple variety. The other species are A. diversifolia (ilama), A. reticulata (custard apple, sarifa or sita fal), A glabra (pond apple) and A. scleroderma (cawesh).

Origin and Genetic Resources of Fruit Crops

9.71

A. lutescens is synonymous with A. reticulata. The origin is central and south America. Different species of the genus are given in Table 9.36. Three most widely consumed species are diploid with 2n = 2x = 14 or 16. A. diversifolia, A. montana and A. muricata are morphologically quite similar. Pollination and fruit set are a problem. Pollination is through beetles and flower is protogynous. Table 9.36  Showing various species of the genus Annona and its origin and characteristics. Species

Chromosome number

Characteristics

Common name

Origin

A. aurantica

Brazil

A. cacans

Brazil

A. cherimola

Diploid (2n = 2x = 14 or 16) Subtropical

Most widely consumed as pulp Ecuador, Peru, Chile

A. coriacea

Brazil

A. crassifolia

Brazil

A. diversifolia

Ilama or annona blanc

Brazil

A. furfuracea A. glabra

Mexico

Tetraploid

Rootstock for A. cherimola and A. muricata

Mountain soup, pond apple

Central America

A. longifolia

Mexico

A. longipes

Mexico Rootstock for A. muricata

A. montana A. muricata

Diploid

Tropical

West Indies Most widely consumed as pulp Antilles

A. mutans

Southern Brazil

A. paludosa

Guyana

A. purpurea A. reticulata

Diploid

Rootstock for A. muricata

Soncoya

Southern Mexico

Grafting on stock of same species

Custard apple

Antilles Brazil

A. salzamannii A. scleroderma

Cawesh

Southern Mexico

A. senegalensis

Wild soursop

East Africa

A. spinescens

Brazil

A. sparguei

Panama

A. squamosa

Diploid

Subtropical, Rootstock Most widely consumed as pulp Antilles for A. cherimola

A. testudina

Guatemala

A. xespertonium

Brazil

9.72

Crop Evolution and Genetic Resources

In A. reticulata male and female structures mature at different times. There is cross pollination and it is through insects and wind and this is the reason the yield potential of this fruit crop is not realised. So hand pollination is required for high fruit setting. Pollination should be carried out in the morning from 6.30 to 9.30 AM. Hybrids produce a large number of bisexual flowers which ensure fruit setting and thus high yield. Soursop fruit has flavour of strawberry and pineapple. It can be grown in relatively warm climate. Pond apple is grown in swamp land and salt water. Cherimoya needs hand pollination for better fruit set. A. cherimola is closely related to A. senagalensis, the wild custard apple and is a source of pollenizer in cherimoya. It is insect and wind pollinated. Strong wind affects fruit setting and thus this fruit. Breeding objectives in custard apple includes small seed, sweetness greater than 32° Brix (Total sugar-22.8%) and slow ripening. A. chrysophylla is a wild custard apple. Its fruit is very rich in tannins, dried leaves contain 8.2% protein. Seeds, leaves and young fruits have insecticidal properties and thus has medicinal values. In A. reticulata there is problem of fruit bats and chalcid fly. A. reticulata is seed propagated but it can be vegetatively propagated through inarching, grafting onto its own seedling, onto soursop or pond apple. Custard apple is being used as rootstock for multiplication of sugar apple, soursop and atemoya. A. montana is a wild soursop. Planting method followed in custard apple is square with spacing of 4-6m. Planting time is rainy season. Flowering occurs during March-July and harvesting time is during September-November. First bearing starts after 5 years of planting.

9.38  POMEGRANATE This fruit contains lots of antioxidants and thus considered best for health, fertility and eternal life. It contains sugar, vit. C, proteins, P, Ca, Mg and K. Punica granatum originated in Central Asia (Persia). It can be grown in tropics, subtropics and subtemperate regions. The genus contains two species P. granatum and P. protopunica. P. protopunica is a precursor of P. granatum. It has small fruit, less sweet and flower is pink rather than red of P. granatum. Two subspecies are recognized on the basis of ovary coloy: 1. SubspeciesChlorocarpa (red or reddish-purple) and 2. Subspecies- Prophyrocarpa (usually greenish). In India Maharashtra is the largest producer of this fruit. It is a diploid with 2n = 2x = 16). There is report of existence of ploidy level and B-chromosome. There is also occurrence of sexual polyploidization which is through production of unreduced gametes. This fruit can be stored in freeze for 2-3 months. Seeds have arils which is pulpy, juicy, sweet and variable in acidity. Calyx is at the fruit end. Wild forms of P. granatum constitute the GP2 whereas wild relative (P. protopunica) constitute the GP3. Sour variety contains highest amount of myristic and linolenic acid. There is positive correlation between sweetness of juice and fatty acid composition. Seedlessness is a desirable trait in pomegranate. Male flowers are sterile and ‘bell shaped’ whereas hermaphrodite flowers are ‘vase shaped’. Male flowers are more than 60-70% and it depends on the variety and season. Flowering an fruiting occurs in 3-4 waves (El Sese, 1988). Further, flowering continues for 10-12 weeks or more depending on the variety and geographical condition. P. nano is the ornamental dwarf pomegranate.

Origin and Genetic Resources of Fruit Crops

9.73

It is a deciduous fruit crop. This crop is best grown as bushes and so light pruning is required. Lopping, pruning and coppicing are the recommended management practices. The tree has large spines along its branches. Keep 3-5 suckers or trunks. Fruits are produced on short spurs formed on 2-3 year old stem. This crop is multiplied vegetatively through cuttings (hard wood cutting of 6-14 inch long). Sexual propagation is through seeds which show less germination (30-70%). Seeds lose viability after a month. As this crop is heterozygous direct seeding results in generation of lots of variability. Flowering takes place during mid April to mid May and fruits take 6-7 months to mature. Plants bear 1-2 fruits in the first year. After 2-3 years plants start bearing good number of fruit and continue up to 15 years. After that vigor starts declining. Plants bear single or double flower. Double flowering cultivars produce only few fruits. This fruit crop can tolerate drought, soil compaction, seasonal water logging but it is susceptible to frost. Dried seeed is called anardana which is used as spice. Fresh seeds contain proteolytic enzyme which has tenderizing effect on meat and thus it is like papaya fruit. Breeding objectives include improving fruit size, color, hardness of seed, juice content, acidity and astringency, time of ripening, disease resistance, plant size (dwarf), etc.. Flowers are monoecious-male and bisexual female flowers are borne terminally or laterally. Self pollination can occur. Also cross pollination occurs in which pollen can come from another flower of the same tree or another flower from different tree. Cross pollination (through bees) improves fruit setting and thus two or more plants should be planted at one place. Fruit cracking can occur because of severe drought and boron deficiency. In fruit crops like avocado, sugar apple, custard apple, flowers have both male and female reproductive organs but flowers change between male and female at different times of the day. In avocado flowers opens as female but next day it becomes male. In sugar apple flowers are female, remain closed but next morning flowers open as males. In atemoya flowers are slightly opened as females in the afternoon and next day afternoon it opens widely as male. Planting method followed is either square or hexagonal. Planting time is JanuaryFebruary and spacing is 5-6m. Flowering time is March-April. Harvesting time is JulyAugust. First bearing starts after 3-4 years.

9.39  CASHEW NUT Anacardium occidentale (Cashew nut, 2n = 2x = 42) is the only domesticated species and it is highly heterozygous. Chromosome number varies from 2n = 24, 30, 40 to 42. It belongs to family Anacardiaceae to which mango and pistachio belong and contains about 75 genera and 700 species. Various species of cashewnut are given in Table 9.37. It is a plantation tree crop, perennial, evergreen small tree (about 40¢ tall) with dense foliage (leaves 4-8˝ long and 2-3˝ wide, oval or elliptical in shape). Branches in this plant spread wide in an umbrella shape. Width of the plant is similar to height of the plant or it can exceed the height. Branches sometimes touch the ground and from there starts secondary roots. Grown well in tropical and subtropical climate with an optimum rainfall of 1500-

9.74

Crop Evolution and Genetic Resources

2000 mm but it can be raised in region with as low rainfall as 1000 mm. This crop does best in warm, humid climate. Temperature should fall below 10C. It can be grown in all types of soil from sandy to laterite. This crop prefers sandy or loamy soil with a pH of 4.5-6.5 and light coastal sand. It can be grown in waste land of low fertility. This crop has deep root system and thus is adapted to drought or long dry season. This crop is sensitive to low temperature and frost. There should not be rain during the period from onset of flowering to harvesting. Flowering time is December-January. It is dioecious (separate male and female flowers) and monoecious flowers may also be found on the same panicle and thus there is different number of male and hermaphrodite flowers. Both self and cross-pollination occur. Because of monoecious flower there is self pollination. Cross pollination is through bats and insect because of sticky nature of pollengrains. Flowering starts after the end of wet season. Flowers are produced at the end of the new shoot and thus are borne on the outer extremity of the canopy. Flowers occur as cluster of recemes with 6-10˝ long panicle. After pollination it takes 6-8˝ weeks to develop into mature fruit. The fruit is drupe. The pedicel enlarges shortly before the fruit matures (two weeks before ripening of fruit) and takes the shape of pear which is juicy sweet with yellow pulp. Cashew apple is eaten fresh and also juice, wine, marmalade or vinegar can be prepared from cashew apple. Cashew apple is a pseudocarp, thickened stem of the fruit to which the actual fruit, the cashew nut is attached. Oil found in shells is caustic and causes burn. Seeds can germinate within four days of falling from the tree and thus shows no dormancy. Apple and drupe must be separated and fruits be dried for 1-3 days. Two to four seeds are planted on permanent location. Raising of seedling in pot and then transplanting of strong seeding in field has not worked well. It takes one month to germinate. It would be better to sow three seeds in a triangular fashion (10cm triangle) per hole and after two years weaker seedlings are removed. The spacing is 10 × 12 mts (100 trees per ha). For three years plant should be protected. Tree begins to flower and fruit in the third year and reaches maximum productivity after 10 years and continues producing for another 20 years. 200-3000 fruits are produced per year per tree. Major insects are tea mosquito, stem and root bore and thrips. There are genotypes in Brazil which is 7-10mt in height and giving good yield under 400-800mm rainfall and thus show drought resistance. Processing starts from collection of seeds to roasting at 100°C for 10 mins to shelling followed by drying, cooling, peeling and finally grading. Drupe has 35-40% seed and 55-65% shell. Propagation is through sexual means, i.e. by seeds but trees propagated through seeds show lots of variability. Thus seedling raised from open pollinated seeds be used as rootstock for grafting (side, wedge, soft wood grafting or budding (chip budding) or top working (rejuvenation). It can also be propagated through air and ground layering and cutting 3-4 months seedlings are used as rootstock. Prunning is done to train tree. After two years lower branches must be pruned. Rain causes anthracnose (Colletotricum gloeosporioides) to develop which results in flower drop. This crop can withstand high temperature. Monthly average temperature of 27°C is considered optimum. It originated in north-eastern Brazil. The primary centre of diversity

Origin and Genetic Resources of Fruit Crops

9.75

is Amazon whereas the secondary centre of diversity is Planalto, Brazil., Although there are 8-11 Anacardium species, only A. occidentale is the economically important species. Some close relative species of cashew including A. fructosum, A. giganteum, A. microsepalum and A. spruceanum have edible fruits. The generation period in only 3-5 years. There is lot of variability in flowering which can range from October to March (Oct.-Nov., early, Dec.-Jan., mid season and late(Feb.-March), duration of flowering which ranges from 40 to 100 days, Number of flowers/panicle(100-1200), number of bisexual flower / panicle(0-120), number of fruits / panicle(0-10), yield / tree(1-25kg) and nut size(3-12cm). Top working is done on trees of 5 to 15 years old during June to October. Breeding objectives include increasing yield per canopy ground cover area, precocity, short duration of nut picking, finding appropriate method of vegetative propagation (grafting, budding, cutting, stooling), appropriate training and pruning method and rootstock identification. Cashew shows maternal effect which must be considered while developing variety. The objective is to develop hybrids with resistance to diseases (powder mildew, anthracnose) and pests (cashew bug, Helopeltis anacardii, thrips, etc) with weight of nut should be 5gm or more than 5gm and shelling percentage should be more than 85%. Table 9.37  Showing various species of cashewnut A. amapaense

Domesticated / wild

A. amilcarianum A. brasiliense A. caracolii a. corymbosum A. curatellifolium A. excelsum A. fruticosum A. giganteum A. humile A. kuhlmannianum A. microsepalum A. nanum A. negrense A. orthonianum A. parvifolium A. rondonianumm A. spruceanum A. tenuifolium Contd...

Crop Evolution and Genetic Resources

9.76 Contd...

A. amapaense

Domesticated / wild

A. macrocarpa A. micrpcarpum A. pumilum A. rhinocarpus A. occidentale

domesticated

Breeding objectives in cashew nut include development of inbred lines and thereby development of hybrids, development of dwarf genotype. The fruit weight should be 8-9 gm (kernel and shell) with a specific gravity of 1.0 or greater than 1.0. Selection for higher specific gravity ensures high rate of germination, genotype with higher percentage of monoecious flower, large fruit size and resistance to diseases and pests.

9.40  JACK FRUIT Artocarpus heterophyllus and A. altitis are grown mainly for edible fruits. Other species including A. chaplasha, A. hirsutus and A. lakoocha are important timber trees. It belongs to family, Moraceae and is Indian origin. Inflorescence is solitary. Flowers are monoecious. Flowers are a mixture of sterile and fertile ones. Female heads have a distinct annulus at the top end of the stout stalk and fertile female flowers are cylindrical or oblong (tubular perianth) whereas male flowers are tubular and bilobed. Male –barrel shaped flower heads are born in the axil of leaf. Female heads are born singly or in pairs, distal to the position of male heads. Flowering takes place during mid November to February (mostly December-January) and fruit is available from March (April-May) till August. It takes 7-8 to 10 years for tree to bear fruits. Spacing is 12 × 12m. Method of planting is either square or hexagonal. The flesh can be soft, juicy, sweet to sweet acid pulp or it can be firm, sweet, firm, and crispy pulp. It has 2n = 4x = 56 chromosome number and thus is tetraploid (x = 14). This fruit is used for table purpose. Jack fruit is also used cooked as vegetable. Unripe fruits can be used in the preparation of pickles. Seeds can be roasted or boiled and eaten. This fruit contains Vit. C and antioxidants. Variability is found in traits such as juicyness of pulp, quantity of fibre, flakes structure, color, aroma, fruit weight, size, shape, sweetness, flavour, taste. Fruit can be soft, almost dissolving or can have hard inner flesh. Variability is also observed in fruiting season, fruit shape, number of fruits/tree, size, shape and density of spines on rind, tree habit, growth rate, canopy, leaf shape, leaf size, leaf petiole and maturity. This fruit is grown as intercrop with betel nut, pepper, coffee and cardamom plantation in south India. The genus contains about 50 species. 11 species are known to produce edible fruits, some of which are given in the Table 9.38. A. heterophyllus hybridizes freely with A. integer (Champedak), A. lanceaefolius and A. rigidus and they are considered close to A. heterophyllus. Some species are graft compatible. Seedless bread fruit is graft compatible with seeded fruit and with A. comansi and A. sercicarpus (Pedalai).

Origin and Genetic Resources of Fruit Crops

9.77

There are seeded and non-seeded forms of A. altilis. Fruits weigh in the range of 0.5 to 3kg. Mature and unripe fruits are cooked and eaten much in the same way as tubers and roots. Thus it is a starchy staple food. Roasted seeds of jack fruits are very tasty and eaten. Table 9.38  Showing various species of Jack fruit Species A. altilis

Common name

Origin

Bread fruit weighs 0.5 to 3 kg and there are S.E Asia-W. Pacific seeded as well as non-seeded forms. Mature and unripe fruits are cooked and eaten much in the same way as tubers and roots

Breedy system Outbreeding Clonal

Ploidy level Diploid, Triploid

A. blancoi A. camansi

Kamansi

A. odoratissima Marang A. lancaefolia A. rigidus

Monkey jackfruit

Good flavour, smallest sized fruit

Barhal  Fruits of A. lakoocha have medicinal value. Ripe fruits can be used for jellis. Unripe fruits can be used for pickles. Fruits have high carotenoids which have got antioxidant properties. Flowering occurs in March. Fruits round, often irregular.

9.41  BAEL Aegle marmelos is a perennial, deciduous, slow growing, highly heterozygous fruit crop. It belongs to family Rutaceae. There are genotypes which are diploid (2n = 18), tetraploid (2n = 4x = 36). Every part of the tree such as, leaf, fruit, roots and bark has medicinal value. Fruit is rich source of Vit. B2. Fruit can help in smooth bowl movement and thus in constipation and gastrointestinal problems. It is a climacteric fruit. It also contains marmelosin and secondary metabolites such as skimmianine, aegelin, etc which have medicinal properties. Flowering time is May-June. Flowers are bisexual and born in clusters. Cross pollination is through honey bees (Apis dorsata) and wind. Fruit development takes 11 months. Fruits when ripened turn yellowish green. Propagation is through seeds, budding such as patch or shield budding done in June-July on seedling rootstock. Air layering has also been found successful in high humidity region. It can also be vegetatively propagated through coppices and root suckers. Breeding problems include long gestation period for flowering and fruiting with seedling plant or vegetative propagules. There is variability with respect fruit size, shape, rind thickness, pulp color, fibre content, mucilage content, acidity of pulp. TSS can vary from 22 to 44%. Fruit can attain the size of grapefruit or pumelo or even larger. The breeding objectives should be to develop variety with higher content of orange colored pulp, flavour, few seeds per fruit, less fibre and less mucilage which encapsulates seed and thin hard shell.

9.78

Crop Evolution and Genetic Resources

Planitng method used is square and spacing is 8 × 10m. Planting time is June-July. Flowering time is May (North India). Harvesting time is April-May, December-January (North India). First bearing starts after 4-5 years of planting.

9.42  BER There are two important domesticated species of the genus Ziziphus. 1. Ziziphus mauritiana and 2. Z. jujube. The former is called Indian ber and the later is called Chinese date. These two species are cultivated for their flavour, sweet, yellowish–red fruit. Another species Ziziphus spina-christi is grown for medicine, food and energy in Sudan and Ethopia and is tolerant to drought. Chinese date is deciduous, winter hardy and can tolerate temperature upto-20°C. Z. mauritiana is evergreen, tropical, shrub or small tree and can withstand temperature up to 45°C. Indian jujubes show a range of polyploidy of such as diploid, triploid, tetraploid, pentaploid, octoploid with n = 12, 20, 24, 30, 36 or 48. Fruits are attractive, golden yellow color and have good keeping quality. Indian jujube also works as lac tree. Chinese jujubes also represent a polyploidy series with 2n = 45, 60, 90. The genus Ziziphus contains about 100 species. Wild species include Z. rotundifolia, Z. lotus (diploid), Z. nmmularia (tetraploid), Z. Oenoplia (polyploidy series), Z. sativa, Z. mistol, Z. vulgaria. Z. mauritina has three types of growth habits-spreading, semi-spreading and erect. Further, there is variation with respect to leaf area and fruit characters such as apex type, stalk and stylar flesh cavities and shape. Tree begins to bear fruits 6-8 years after planting and yield increase is seen up to 15-20 years of planting. In the Ziziphus flowers are hermaphrodite and there is synchronous protandrous dichogamy, i.e., pollen availability precedes stigma receptivity and thus ensures cross pollination. In Z. mauritiana and Z. spina Christi there are two types of flowers. A type and B type. In A type genotypes anther dehisces in the morning whereas stigma becomes receptive in the afternoon and continues up to next morning. In the B type anther dehisces in the afternoon but the female becomes receptive in the evening and continues till afternoon on the following day. Besides there is self incompatibility and some cross incompatibility. Cross pollination is facilitated through honey bees (Apis spp.), yellow wasp (Polister herbraeus) and housefly (Musca domestica). In south Indian condition it blooms twice a year, September-January and again during March-June. In north Indian condition flowering occurs during July-October and fruits are mature between February-March. Ber fruits are rich in Vit. C, A and B. Ziziphus mauritiana is native to India. It belongs to family Rhamnaceae. This crop can be raised in all kinds of soil, sandy, clayey, saline and alkali soils. It is a crop of dry climate with no humidity. Multiplication is through vegetative means, through I or T budding. Seeds are sown in April and seedlings are ready for in situ budding in July and after 1-2 months of budding the plants are transferred to the main field sometime in August-September. Priming is done with sulphuric acid in order to enhance germination as is done in sesbania.

Origin and Genetic Resources of Fruit Crops

9.79

Classification studies in ber were conducted by many workers (Don, 1831; Hooker, 1857; Brandis, 1906, Suseenguth, 1953 and Lui and Cheng, 1995. The later based classification considering morphological traits, growth habits and geographical distribution. Brandis (1906) classified 14 Indian Ziziphus species into two groups. The first group’s characteristic features are axillary cyme, sessile or short pedunculate (Z. jujuba, Z. nummularia, Z. oenoplia, Z. napeca, Z. incurva, Z. trinervia, Z. glabra, Z. vulgaris, Z. oxyphylla, Z. xylopyrus, Z. horrida and Z. apetala and the second group is having cymes pedunculate, arranged in terminal or lateral prduncles and includes Z. rugosa and Z. funiculosa Table 9.39. Table 9.39  Showing classificaton along with characteristics of different species of Ziziphus. Number of sections Section-1

Section-2

Genus

Series

Ziziphus

Perdurans

Cymosiflorae

Species

Characteristics

Z. jujuba (Glabrous, deciduous)

Plants glabrous with deciduous fruiting. Distributed mainly in temperate regions.

Z. acidojujuba

-do-

Z. mauritiana (T)

Axillary cymes, glabrous ovary and fruit, thick and hard endocarp. Mainly distributed in tropical and subtropical regions.

Z. oenoplia (Semiscandent shrub) Z. cambodiana Z. spina-christii (T), var. microphylla (S) Z. nummularia (S) Z. horrida Z. incura Z. lenticellaria Z. lotus (S) Z. apetala Z. glabrata (S) Z. abyssinica (T) Z. mucronata Z. truncata (S) Z. guatemalensis Z. xiangchengensis Contd...

Crop Evolution and Genetic Resources

9.80 Contd...

Number of sections

Genus

Series

Species

Characteristics

Z. mairei Z. montana Z. publinervis Z. laui Thyrsiflorae

Z. rugosa (climbing shrub) Z. calophylla (C) Z. attopensis Z. hoaensis Z. kunstleri (CS) Z. borneensis Z. javanensis Z. fungii Z. joazerio (T) Z. mistol (T) Z. trinervia (T) Z. hammer (S) Z. parryi (S) Z. napeca (S) Z. mauri var. deserticola (S), var. orthacantha (S) Z. xylopyra (SSS) Z. elegans (CS) Z. affinis (C) Z. horsfieldu (C) Z. pernethyoides (C) Z. oxyphylla (SSS)

T = tree, S = shrub, SSS = Semi-scandent shrub), CS = Climbing shrub, and C = Climber

Terminal or axillary thyrse, pilose young fruit and/or ovary, thin and fragile endocarp.

Origin and Genetic Resources of Fruit Crops

9.81

Rootstocks in ber  Either seeds from same species (Z. mauritiana) or Z. nummularia syn. Z. rotundifolia or Z. abyssinica can be used for Indian jujubes. For grafting wedge grafting is used in ber whereas whip or tongue grafting is used in Chinese jujubes. Method of planting is square and spacing is 10-12m. Planting time is FebruaryMarch. Flowering time is September-November and harvesting time is February-March. First bearing starts after 2-3 years of planting.

9.43  PASSION FRUIT It is grown in tropics and subtropics. Passion fruit is normally self incompatible and cross pollination is through insects. Self incompatibility is due to two loci, S gene and a gametophytic gene which acts in association with a sporophytic gene. In yellow passion fruit self incompatibility is due to 2 loci, homomorphic, sporophytic system. It is a climber with 90 days juvenile period. Flowers are perfect. There are three types of flowers according to the curvature of the style. 1. Totally curved 2. Partly curved and 3. Standing style. Totally curved flowers are the most common type. Passiflora edulis f. flavicarpa (larger fruit), and its hybrids are preferred in tropical low lands and are exclusively seed propagated and P. edulis with purple fruit. The crop is best at high altitude of 1200-2000m. This fruit can be grown in warm tropical and cool subtropical regions. It can be propagated by seeds, cuttings and grafting onto seedling rootstock. Species-P. incarnate and P. caerulea can tolerate chilling. Most frequent ploidy levels are 2n = 2x = 18 and 2n = 2x = 12. Aneuploidy and polyploidy (2n = 14, 20, 22, 24, 36 and 84) have played an important role in Passiflora evolution. Different species of the genus passiflora are given in Table 9.40. Fruits can be used for use as fresh fruit or juice industry. The three important characters for juice production are yield, acidity and total soluble solids. Fruit quality characters include uniform size, yield of the pulp, juice, sugar: acid rario, aroma, color of the pulp, pericarp color and turgescence. Table 9.40  Showing species of Passiflora and its uses Species

Cultivated / wild

P. alata

Cultivated

P. cumbalensis

Wild and cultivated

P. edulis

Cultivars

P. filamentosa

Cultivated

P. incarnata

Cultivated

P. laurifloia

Cultivated

P. legularis

Cultivated

P. maliformis

Cultivated

Uses

Contd...

Crop Evolution and Genetic Resources

9.82 Contd...

Species

Cultivated / wild

P. nitida

Cultivated

P. pinnatistipula

Cultivated

P. popenovii

Cultivated

P. quadrangularis

Cultivated

P. tarminiana

Cultivated

P. tripartita

Cultivated

Uses

Medicinal

P. caerulia

Rootstock, ornamental

P. cicinnata

Rootstock, ornamental Rootstock, ornamental

P. coccinea P. cuneata

Wild

P. fieldiana

Wild

P. gabrielliana

Wild

P. glandulosa

Wild

P. mandoni

Wild

P. membranacea

Wild

P. mooreana

Wild

p. organensis

Wild

P. peduncularis

Wild

P. cyanea

Collected

P. foetida

Collected

P. manicata

Genetic resource

P. mixta

Collected

P. ingradenia

Genetic resource

P. pergrandis

Collected

P. platyloba

Genetic resource

P. riparia

collected

Medicinal

P. seemanni P. retipetala

Wild

P. rubra

Wild

P. serratifolia

Wild

P. seratodigetata

Wild

P. spectabilis

Wild Contd...

Origin and Genetic Resources of Fruit Crops

9.83

Contd...

Species

Cultivated / wild

P. subpeltata

Wild

P. trilob P. umbilicataa

Wild

P. villosa

Wild

P. warmingii

Wild

P. tiliaefolia

Collected

P. tolimana

Genetic resource

P. vespertilio

Collected

P. vitifolia

Collected

Uses

9.44  CARAMBOLA Averrhoa carambola. It is an understorey tree of rain forest. It attains a maximum height of 15m. Origin is South East Asia. This fruit (Kamrakh) is strongly acidic because of higher level of calcium oxalate. Taste ranges from sweet to slightly acidic to sour. Chromosome number ranges from 2n = 2x = 22, 24. It is a non-climacteric fruit, grown in tropics and subtropics. The juvenile period is 5-6 years. It is a vegetatively propagated tree and can flower in 2-3 years. Breeding objectives include control of ripening of fruit, controlling the fruit rib morphology in order to minimum damage, control of post-harvest loss by pathogens, reduction in concentration of oxalic acid. Flowers are heterodistylous. Flowers with long styles are self fertile whereas flowers with short styles require pollination, pollen from long styled flower. There is partial self incompatibility. Flowering is twice a year. Reduction in oxalic acid and selection for self compatibility are objectives in breeding program. Planting method followed is square system and spacing is 7-9m. Planting time is July-August. Two types of trees are planted for best yield. Flowering time is April-May, July-August and September-October. Harvesting time is July-September, NovemberDecember and January-February. First bearing starts 2-3 years after planting. Fruits are oblong with 3 to 6 longitudinal ribs, resulting in a star shaped cross section when cut (Popenoe, 1920). The fruits generally have 5 ribs and so called five corners or star fruits. Fruits have sweet, watery pulp and gives flavor of both apricot and passion fruit. Fruits vary in size (80-250mm) width (50-100mm) and colour can vary from orange to yellow-white and flesh texture from smooth to fibrous (Watson et al., 1988). Jamun (Syzygium cumini)  Syzygium cumini syn. Eugenia jambolana belongs to Myrtaceae family. It is a multipuropose tree. This genus comprises about 1100 species. This fruit is native to Indian subcontinent (India, Bangladesh, Pakistan, Indonesia). Other important species include S. javanicum (water apple), S. jambos (rose apple) and S. uniflora (Surinam cherry). Highest level of diversity is found in regions from Malaysia to northeastern Australia. Thai cultivated species include S. samarangensis as well as S. jambos.

9.84

Crop Evolution and Genetic Resources

S. megacarpum and S. formosum are wild species. This fruit crop has adaptability to high alkaline soil (pH10.5). The others of the genus includes S. aqueum (water apple), S. bracteatum, S. cerasoideum, S. malaccense (Mountain apple or Malay apple) and S. zeylanicum Fruit is rich in Ca, Fe, Vit. A and Vit. C, antioxidants and phytochemicals. It contains chemicals “jamboline” and glycosides which prevent the conversion of starch into sugars and thus good for diabetic patients. Fruit contains glucose and fructose and not even trace amount of sucrose. It contains anthocyanins responsible for colouring (of fruit) and of mouth and tongue when eaten (purple). It is sub-acidic and gives astringent taste due to the presence of gallic acid which may be the source of sourness and tannins present in the fruit. Leaves are used as fodder for livestock and food for tassar silkworms. This fruit crop shows lots of variation in fruit length (3-6cm), fruit girth (5-9cm), fruit weight (3-17gm), pulp content (54-85%), TSS (5-26%) and acidity (0.15-5.5%) and thus there is scope for improvement. Fruits contain malic acid, the major organic acid with a small quantity of oxalic acid. There are seeded as well as non-seeded varieties. There is report of asexual reproduction through budding (patch budding, T-budding) and grafting (cleft, soft wood, veneer grafting). Flowering occurs during February (end of February), March-April and fruiting during May- June. There are 5-13 panicles per shoot. Flowers are bisexual, self compatible and self pollination is common and geitonogamy is the mode of pollination for isolated tree but there could be apomixis. Insects and wind mediated cross pollination (xenogamy) also occurs. Thus it is a highly cross pollinated crop and it will not breed true. The problem with this fruit crop is that the branches are week and so difficult to pluck the fruits individually by hand. Giving jerks to twigs/branches and collecting the fruit in the net is the general practice. The breeding objective should be to develop immediately dwarf genotype so the fruits without any damage can be harvested. One can not relish damaged fruits and one can not store it.

Other Horticultural Crops

9.45  MULBERRY Most of the species of the genus Morus are diploid with 2n = 2x = 28. However, triploids are also cultivated for their adaptibilty, vigorous growth and quality of leaves. M. alba, M. indica (occupies 90% area under tropical condition) M. serrata and M. laevigata are found naturally in India. M. multicaulis, M. nigra, M. sinensis and M. philippinensis have been introduced to India. Morus alba and M. Indica have edible fruits. Leaves of M. Alba have antioxidant activity. Inflorescence is a catkin, containing a pendent or drooping peduncle bearing unisexual flowers. Male catkins are longer than female catkins. It is a cross pollinated crop (wind pollinated). Leaf quality is a major objective in mulberry breeding. The antioxidant activity of leaves of M. alba is due to the presence of b-carotene and a-tocopherol. Besides these compounds leaves also contain citral, linalyl acetate, linalool, terpinyl acetate which act as attractant, biting factor and swallowing factor for Bombax

Origin and Genetic Resources of Fruit Crops

9.85

moori. Hexane b-sitoterol and sterols in combination with water soluble substances act as stimulant for biting. Silk proteins which include fibroin and sericin comes from the leaves. Morus genus include 68 species. Paper mulberry (Broussonetia papyrifera) which resembles mulberry morphologically is cultivated for the manufacturing paper.

9.46  TEA This is a crop of acid soil. Camellia spp is an important beverage. Tea (C. sinensis) is a highly heterozygous and outbreeding crop. Tea plant is broadly classified as Assam type (C. assamica), China type (C. sinensis) and Cambodian race, C. assamica ssp. lasiocalyx. The typical China race is a shrub, with more or less virgate stems arising near the ground, 1-3 meter in height, and has relatively small (3-6cm long), hard, dark green leaves with a dull (matt) surface. It is suited to high latitudes where winters are cold and high altitudes in tropics. The typical Assam race is a small, 10-15 meter in height, many branched tree with large (15-20cm) light green leaves having glossy surface (Vesser). C. assamica ssp. lasicalyx is closely related to C. assamica. Assam tea is suited to subtropical condition, requires a rainfall of at least 1500mm, high humidity, a minimum temperature not below 15C and a maximum not over 29C. Cambodian type tea is a small tree, shiny and hard, erect leaves, evergreen and unprunned can attain 10-20 m. China tea can seldom reach 10 m. A tea shoot consists of two leaves and a terminal shoot. But then one can pluck one bud (one terminal shoot) plus one leaf or one bud plus two leaves or one bud with three leaves or even one leaf with four leaves and these will differ in the quality of the tea that will be produced. It contains 74 to 77% moisture, 23 to 26% solid matter of half is insoluble. Plucking interval is about 7 to 12 days. Economic life span of commercial tea ranges from 50 to 65 years. The gestation period is 3-5 years before one can start harvesting bud for preparing tea. The primary centre of dispersal is probably Central Asia (Kingdom Ward, 1950). The genetic resources include many species as given in the table 9.41 below. Table 9.41  Showing various species of Camellia Camellia spp./var.

Cultivated/wild

Distribution

Ploidy level

C. sinensis var. assamica

Assam tea, cultivated

India

2n = 2x = 30, 45

C. sinensis var. chinensis

China tea, cultivated

China

2n = 2x = 30

C. sinensis var. lasiocalyx

Cambodian tea, cultivated

Assam, Burma, Vietnam

2n = 2x = 30

C. kissi (drupiera)

Wild

Assam, Burma, Bhutan, Vietnam, Sikkim

2n = 2x = 30

C. caudate

Wild

Assam, Burma, Butan

2n = 2x = 30

Unique trait

E. japonica Contd...

Crop Evolution and Genetic Resources

9.86 Contd...

Camellia spp./var.

Cultivated/wild

Distribution

Ploidy level

Unique trait

E. acuminate C. japonica

China, Korea, Japan

30, 45

C. sasanqua

Japan

90

Burma

2n = 30

C. rosiflora

Sri Lanka

45

Camellia spp.

Dooars

C. irrawdiensis

Wild

No caffeine

Tea is diploid with 2n = 30. In some cases of China and Japanese varieties the chromosome number is 3n = 45. There are also reports of tetraploids, pentaploids and aneuploids (2n = 30 ± 1 – 29) in this crop. Crosses between tetraploid x diploid have succeeded but the reciprocal crosses have failed. Tea was used to be propagated by seeds but because of certain degree of genetic heterogeneity (highly heterozygous plant) and the subsequent variability of tea plants, tea cultivars are now propagated asexually. Methods of vegetative propagation include layering, budding, grafting on rootstock and single node cutting. Semi soft wood cutting with one leaf and one inter node is taken (cut is made half inch above and half inch below a node). Cuttings are planted in either April-June or during August-October. High humidity is maintained and further protection from direct sunlight is needed and that is why planted materials are covered by polythene. Cuttings are inserted in soil up to the axil of the leaf and in a slanting position which places leaf flat on the surface of soil. Node should just touch the soil surface. Root initiation takes place after 3 months and 4-6 months old seedlings are kept outside for hardening. Thus planting material is ready for transferring to field in 10-15 months (sometimes 20-24 months) during May-June or September-October. Because of low multiplication rate, poor survivability of some genotypes and requirement of copious planting material there is a need for developing micropropagation technique so that planting material could be developed rapidly and also the problems of root induction, long gestation period between hardening and field transfer and cost factor could be minimized. Tea leaf contains minerals, vitamins and caffeine. Tea quality is determined by polyphenol oxidase, caffeine and protein nitrogen contents. Tea polyphenols are antioxidants. Tea polyphenol are is made up of flavones, flavonols and glyconsides. Among them catechin the most important flavonols constitutes 80% of the polyphenols. Different types of tea such as green tea, oolong tea, black tea and CTC (cut, tear, curl) tea are prepared in the following manner. 1. Steaming----Rolling--------Drying---------Green tea 2. Withering---Turn over----Mass rolling----Drying-----Oolong tea (Solar and indoor) Fresh leaves

Origin and Genetic Resources of Fruit Crops

9.87

3. Withering-----Fermentation------Drying-------------Black tea (Indoor) 4. Withering-----Pre-conditioning-----Oxidation-----Drying---CTC tea Tea flowers are self sterile. Only pollen from another plant of the same or different species is effective and so crosspollination is the only method to produce seed. The breeding objectives in tea include improvement of high yielding cultivar with resistance to diseases, drought and for long cycle. Shade improves chlorophyll content and quality of tea. Flavor improves. Soft and dark green leaves are produced under shaded condition. Silver Oak (Grevillia robusta) is used as shade tree in tea plantation. Tea and silver oak do not compete for natural resources as later absorbs nutrients from lower strata of soil because of deep root system. The time pollarding is adjusted otherwise there is problem of blister blight, Exobasidium vexans and it must be completed by June in Western Ghats and pruning must be completed before August in North Eastern region.

9.47  COFFEE Coffee is a dicot, evergreen, perennial and belongs to family Rubiaceae and grown in tropical climate. Coffee originated in Ethopia. The genus coffee comprises about 100 species of which two species, namely, C. arabica (Ethopian origin) and C. robusta are commercially cultivated and the species C. arabica is the largest cultivated species (65% of total global production comes from C. arabica). The other species, not commercially cultivated but important from breeding point of view are C. liberica (native to Liberia), C. stenophylla, C. excels, C. canephora (syn. C.robusta) (native to Uganda), etc. There are four sections of the genus Coffee. 1. Eucoffea 2. Agrocoffea 3. Mascarocoffea 4. Paracoffea.The former three sections are exclusively native to Africa whereas section 4 is native to South-east Asia (e.g. C. bengalensis). Mascarocoffea is found in wild in Madagascar and contains almost zero caffeine. Majority of the species are diploid (2n = 2x = 22) and self incompatible but C. arabica is a tetraploid with 2n = 2x = 44 and self fertile (autogmous) and all kinds of polyploids such as triploid, tetraploid, pentaploid, hexaploid and octoploid have been found in C.arabica. C. robusta is cross pollinated. Cross pollination is through insects and wind. C.canephora and C.liberica are self sterile and mainly wind pollinated. The putative parental species of C. arabica include C. canephora and C. eugenioides. The secondary gene pool comprises C. recemosa, C. sessiliflora, C. kimbozensis, C. eugenioides, C. zanguebariae, C. fadenii, C. charrieriana and C. anthonyl. The breeding approaches include clonal selection and intra and interspecific hybridization. Traits from C. liberica have been transferred to C. arabica. Also traits from C. cogenesis has been transferred to C. canephora (robusta) to improve robusta coffee. Interspecific cross, C. cogenesis x C. canephora has produced Congusta hybrid. Through cross, C. cogenesis x C. canephora, improved robusta has been obtained. C. arabica arose from the cross, C. eugenioides (female parent) x C. canephora (robusta) or C. congensis or C. liberica (male parents), i.e., C. eugenioides is the putative female progenitor and C. arabica contains cytoplasm of this species.

9.88

Crop Evolution and Genetic Resources

Plant type of C. arabica differs from C. canephora (Robusta). C. arabica is tree type, has a straight trunk with branches paired off outward and lower branches tend to drop down towards ground and thus there are two types of stem growth-part grow vertically and part grow horizontally and fruits are produced on the horizontally growing branches. Whereas C. robusta is a shrub or small tree growing up to 10m height and has several trunks and thus gives bushy appearance. C. arabica takes 7-9 months to mature whereas fruits takes longer time (9-11 months) to mature in C. robusta and C. liberica. There is found variation with respect to leaf margin, leaf length, leaf width, shape, leaf base, leaf tip and color of leaf. C. arabica has better beverage quality, aromatic characteristics, low caffeine content (1-1.5%) in comparison with C. robusta (2-2.5%). C. robusta has stronger bitterness and higher caffeine content. Robusta is suited for hotter and humid climate but Arabica is not suitable for higher temperature condition. Although coffee remains in production for 60 years but economical production period is for 20 years. The plant starts production after 3-5 years of planting. Propagation can be through seeds and cuttings. Commercial Arabica is grown from seeds, raised in nursery and top working of the inferior plant is done. Robusta is more often multiplied by cuttings from selected clones. Like litchi, citrus, maize, roots of coffee are also colonized by AM fingi. Arbuscular Mycorrhizal fungi associated with roots of coffee include Glomus and Sclerocystis. Extraradical hyphal length of fungi determines the area of contact between AM fungi and soil where nutrient uptake occurs. The fruit is drupe and comes in cluster of berries. At maturity berry is bright red and this is when picking is done. Berry turns brown to reddish brown when ripe. Coffee can be cultivated without shade or under shade. In India where temperature is high, light intensity is high (there is higher incidence of death of young tertiary branches called dieback), and under drought , heavy rainfall and hail storm there is need of support trees. Arabica coffee requires 50-60% of filtered shade. There is two tiers shade canopy being practised. Dadap-Erythrina lithosperma for lower shade canopy at closer spacing and Silver oak are raised. The problem with silver oak is that fall of leaves on coffee plant leads to black rot and so Ficus spp., Albizzia spp., Terminalia spp., Artocarpus integrifolia (jack fruit) can be grown. Robusta coffee also requires shade for unirrigated condition as it is susceptible to drought although it shows tolerance to high light intensity and temperature to some extent.

9.48  CACAO It is a small understorey tree of the low land rain forests. The genus Theobroma is divided into six section as shown in the table given below. Theobroma cacao is the only cultivated species. Fat rich seeds are source of cocoa solids and cocoa butter. They are raw materials for the production of chocolate, confectionery and cosmetics. Seed fat includes fatty acids, sterols, tocopherol and tocotrienol. It is a diploid with 2n = 2x = 20. It has monophyletic origin. Purine alkaloids such as caffeine and theobromine are found only in T. cacao while other species of Theobroma except T. obovatum have tetra methyl urate (theacrine) (Hammerstone et al., 1994).

Origin and Genetic Resources of Fruit Crops

9.89

There are three forms (morphogeographic) of the species cacao. 1. Criollo 2. Forestero and 3. Trinitarios (Intermediate). T. cacao ssp. cacao constitutes Criollo group whereas T. cacao ssp. sphaerocarpum constitutes Foreastero group (Cuatrecasas, 1964). Characteristic features of these groups are given in the table 9.42 next page. Table 9.42  Showing characteristics of different varieties of Cacao Character Pods

Criollo

Forastero

Red or yellow when ripe, deeply furrowed, warty with a pointed end and thin husk, whilte or pale cotyledon, superior flavour

Non-pigmented, thick and hard husk with flat and dark purple seeds.There are two groups of trees. One group of wild or semiwild tree from upper Amazonian (self-incompatible). Second group of trees with uniform pod type called Amelonado from Lower Amazonian region (green pod with smooth, shallow furrows, melon shaped with a blunt end- the most prevalent cultivated type)

Trinitarios Hybrid between Criollo and Forastero population and so it might not be distinct from parental population

Highly heterogeneous population Highly heterogeneous population

Section Theobroma

Species

Andropetalum

T. mammosum

Glossopetalum

T. angustifolium T. canumense T. chacoense T. cirmolinae T. grandiflorum

Cultivated

T. hylaeum T. nemorale T. obovatum T. simiarum T. sinuosum T. stipulatum T. subincanum Oreanthes

T. bernouillii T. glaucum T. speciosum T. sylvestre T. velutinum Contd...

Crop Evolution and Genetic Resources

9.90 Contd...

Section

Species

Rhytidocarpus

T. bicolor

Telmatocarpus

T. gileri T. microcaroum T. cacao

Theobroma

Cultivated

Total amount of dry fermented cacao is a function of total number of pods/tree, average pod weight determined by the number of seeds/pod and seed weight. Yield/ha depends on planting density which is associated with tree vigor and agronomic practices followed including soil fertility. As is with any fruit crop the problems coming in the way of improving this tree is long juvenile period, high cost associated with maintenance and evaluation of large progenies for extended period and the highly heterozygous nature of the tree.

9.49  EUCALYPTUS It is gown for fuel wood, pulp and essential oils. Eucalyptus belongs to family Myrtaceae. Majority of the species in the genus Eucalyptus is diploid with 2n = 2x = 22. However, there are species with 2n = 20, 24 and 28. Chromosomes are small in size and their staining and their scattering are difficult, similar to that we find in fruit trees. There is lot of interspecific variability as a result of occurrence of interspecific hybridization. There is allogamic reproduction (cross pollination) in this genus (Pryor, 1978 and Boden, 1964). It is predominantly a cross pollinated crop. Flowering occurs twice, during March-April and September/October (sparse flowering). Eucalyptus are self compatible and so self pollination results in loss of vigor resulting in slow growing weak plant due to inbreeding depression. Cross pollination is through insects, birds and animals. E. hybrid (Mysore gum), the interspecific hybrid and E. tereticornis are the most important species widely planted in India. They are best suited to low altitude areas. The other species being grown in India are given in the table 9.43 below. Temperate plantation species include E. globulus and E. nitens. Coppice shoot cuttings (cuttings from 2-3 old saplings are the best juvenile materials for mass propagation. Propagation is also through seed. Besides this, epicormic (epicormic buds are found on stem and branches of he tree) shoots, lignotubers and semi-hard wood cuttings can be used for multiplication. Like Populus, Salix, Eucalyptus is associated with VAM. A 8-10 year crop rotation is suitable. Table 9.43  Showing species of Eucalyptus and its characteristics Species

Common name

Characteristics

Adaptability

E. camaldulensis E. citriodora

Oils (65-80% citronellal) Contd...

Origin and Genetic Resources of Fruit Crops

9.91

Contd...

Species

Common name

Characteristics

Adaptability

E. creba Oils (62% cineole)

E. globulus E. grandis

Rose gum

High altitude High altitude area High altitude area

E. robusta E. saligna E. tereticornis E. torelliana

Pulp wood

E. deglupta

Pulp wood

E. viminalis

Pulp wood

There is a need to develop breeding objectives for different products, to develop non-destructive sampling methods for assessment of wood properties as the traditional methods of assessment are destructive and expensive. There is a need to determine the suitability of species and provenances for particular environment considering the genotype x environmental interaction. The other characters to be considered during breeding program are the tree growth, survival, stem straightness and branch quality and other fitness traits required for survive abiotic and biotic stresses Different eucalyptus products such as pulp and paper, timber and composites require different wood properties to be recorded in the breeding program as shown in the table 9.44 below. From eucalyptus tree paper (photocopy paper and fine writing paper, newsprint), furniture, flooring and fibre board are made. Table 9.44  Showing parameters for assessing various qualities of products Pulp and paper

Timber

Composites

Basic density

Basic density and gradient

Basic density

Pulp yield/cellulose content

Microfibril angle

Lignin content

Fibre length

Strength and stiffness

Extractive content

Dimensional stability

Cellulose content

Shrinkage and collapse Tension wood Knot size Incidence of decay, spiral grain and end splits

Methods for assessing different wood properties are given in the table 9.44a below (Adapted from Raymond, 2002).

Crop Evolution and Genetic Resources

9.92 Table 9.44a  Showing methods of assessment of various parameters Character

Method of assessment

Basic density

Gravimetric assessment, Pilodyn (for indirect assessment)

Density variation, density gradient

X-ray densitometry

Microfibril angle

X-ray diffraction, confocal microscopy

Pulp yield

Digestion of chips to given residual lignin level

Cellulose content

Chemical analysis of ground wood

Lignin content

Near infrared reflectance analysis

Extractives

Raman spectroscopy

Fibre length

Optical measurement of separated fibres

Growth stresses

Displacement of markers after release of stress

Modulus of elasticity

Mechanical testing of boards, Acoustic/stress wave

Shrinkage

Measurement of green and dry boards

Tension of wood

Histological assessment

Incidence of decay and extent of decay

Felling of tree, cutting into pieces and physical examination, use of sress transmission or a Resistgraph in case of nondestructive method

Knot size

Measurement of branch size and incidence

9.50  POPLAR It is a very fast growing agroforestry tree, increases up to 5¢ to 8¢ per year, can attain 15 to 50 mt height and trunk diameter up to 2.5 mt. It produces a medium density (0.441g/ cc) hardwood. Roots can stretch up to 40 mts. It is native to North America. The genus contains 35 species. It belongs to the family Salicaceae. Three types of poplar include cotton wood, aspens and balsam poplar. Cotton woods and balsam poplars (grown in North America, Asia and cooler climate) have stick buds and bark, darker and deeply furrowed. Aspens have grey to green bark and non-sticky buds. It can thrive well on wet soil. Wood is soft and used for card board boxes crates, paper, veneer, ply wood, pallets and chopsticks. It also works as wind break, provides shade and leaves used for mulching. It is dioecious, separate male and female plants. Flowering takes place during deciduous phase. Catkins are pendulous. It is a cross pollinated crop and cross pollination is through wind. Seed dispersal is through wind. Hybrid poplar is developed from the cross-Populus deltoids x P.nigra. There are two important species of Eurasia which are black and white poplar (P. alba). Grey poplar-P. canascens is a close relative of white poplar, have deltoid leaves. Black poplar-P. nigra have oval and teethed leaves and have long trunk (about 35mt). Poplar is also used as avenues trees. eucalyptus and poplar trees are used for making sun mica and ply.

Origin and Genetic Resources of Fruit Crops

9.93

Indigenous and some exotic species grown in India are given below in Table 9.45. P. ciliate is the most widely spread indigenous poplar in India. Like wise, P. deltoids is the most widely planted exotic poplar in India. Two species are triploid (P. alba and P. canescens) and others are diploid with 2n = 38. In poplar there is tendency to produce unreduced gametes (pollengrains) which explains the occurrence of triploid. The natural hybrids poplar are, P. alba x P. grandidentata and P. alba x tremuloides. Except P. gamblei all poplars are multiplied through seed and stem cuttings. For timber production the spacing is 5 × 3m whereas for fuel production the spacing is 2 × 2m or 3 × 2m. For nursery raising the spacing followed is 80 × 60cm. This tree like eucalyptus shows allelopathic effects. It has allelochemical present in all parts of the plant. There is considerable reduction in yield up to 4m distance from the tree. 6-7 years old tree is used for paper pulp, 10-15 years old tree for match and packaging and 15-30 years old tree for furniture. Thus harvesting in done after 6-8 years as 7th year onward the yield of companion crop starts getting adversely affected. Table 9.45  Showing species of Poplar, its ploidy level and uses Species

Ploidy level

P. ciliata

2n = 38

P. gamblei

2n = 38

P. jacquemontii var. Glauca

2n = 38

P. rotundifolia

2n = 38

P. euphratica

2n = 38

P. alba

2n = 3x = 57

Flower

Sequencing

Uses Medicinal use and fodder for goat

Bisexual flower Medicinal use and fodder

Exotic species P. deltoids

2n = 38

P. nigra

2n = 38

P. trichocarpa

2n = 38

P. grandidentata

2n = 38

P. tremuloides

2n = 38

P. eugenei

2n = 38

P. canescens

2n = 3x = 57

P. laurifolia P. robusta P. balsamifera

Medicinal use and fodder for goat Genome sequencing completed

Good fodder

Crop Evolution and Genetic Resources

9.94

9.51  SHEESHAM It is the most important timber tree after teak and Bihar is the largest producer of sissoo. It is used for fuel, shade and shelter and all kinds of furnitures are made from it. It is also used as windbreak in mango orchards and tea and coffee plantation. It is a perennial and deciduous tree. Hard wood is golden to dark brown which is extremely durable and resistant to termites whereas sap wood is white to pale brownish white and susceptible to fungi and borer. It belongs to family Fabaceae. It is native to Indian subcontinent and adapted to tropical and subtropical climate (Temperature of 4-6C to 39-49C with 700-4500mm rainfall). It is a dicot and belongs to Papilionaceae and it fixes atmospheric nitrogen. The genus contains about 250 species. It is a diploid with 2n = 20. The various cultivated species of this genus are given in the table 9.46. Dalbergia latifolia produces hard durable wood with long straight bore. In case of D. sissoo regular pruning is a must to control its haphazard growth. Leaves are pinnate and have panicuate flowers. D. sissoo’s leaves have pointed leaves whereas D. latifolia’s leaves are rounded. Flowering occurs in April and pods are mature in November-December and thus pod takes 6-7 months to mature. Inflorescence is found as axillary panicle which is made of spikes with small sessile to sub sessile flowers. Flowers are numerous and white. Flowers are bisexual and self pollinated but cross pollination can occur through insects. Seed dispersal is through wind. Life span is about 60 years and tree reaches maturity in over 20 years. It is vegetatively propagated through cuttings (Hard wood cutting, Soft wood cutting) and suckers. Coppice shoots and root suckers are good source of juvenile cuttings which can be easily rooted. It can be sexually propagated through seeds. Each pod contains about 1-4 seeds. Problems associated with sheesham cultivation are the Fusarium, Ganoderma licidium and Phellinus gilvus which attach root and vescular system. Shisham  Another very important timber tree is Acacia lenticularis (Chah) with thorns on trunk and branches. Wood is used in the construction of houses and branches as fire wood. Another widely grown species is Albizzia ssp., Shirish grown for fuel. Table 9.46  Showing species of shisham and wood characteristics Species

Common name

characteristics

Dalbergia sissoo

Indian rosewood

Dark brown timber, leaves used as fodder

D. latifolia

East Indian rosewood, Indian black wood

Dark purple wood

D. aearensis

Brazilean wood

D. nigra

Brazilean wood,

D. retusa

Tropical South America

heavy dark colored wood streaked with black

Origin and Genetic Resources of Fruit Crops

9.95

9.52  BAMBOO It is a perennial grass, belongs to Gramineae-family Poaceae and subfamily bambusoideae subfamily. It can grow up to 20 mt in height. And growth rate is about 10cm per day. There are 116 genera and contains about 1439 species (Clark, 2012). India has about 18 genera and 128 species. Manipur has 53 species, Arunachal Pradesh has 50 species and NE India has 63 species. In Mizoram 40% of the area is under bamboo. There are three tribes. 1. Arundinarieae (temperate woody bamboo) which contains 533 species. 2. Bambuseae (tropical woody bamboo) which contains 784 species. 3. Olyreae (herbaceous bamboo) which contains about 122 species. Thus there are two types of bamboo- woody bamboo and herbaceous bamboo. Woody bamboos are gregarious, monocarpy with bizarre flowering cycles. Characteristic features of herbaceous bamboo include lack of differentiated culms/leaves and outer legules and restricted vegetative branching (Judziewicz and Clark, 2007). Members of Bambuseae/woody bamboo have x = 12 (Soderstrom, 1981) and there is occurrence of polyploidy. In herbaceous bamboo x with 7, 9, 10, 11, 12 are known, of which x = 11 is the most frequently reported number. Woody bamboos can be tetraploid or hexaploid whereas herbaceous can be diploid or tetraploid. Most tropical bamboos are hexaploid (2n = 6x = 72) while most herbaceous bamboos are tetraploid (2n = 4x = 48). Giant bamboo, Dendrocalamus giganteus is hexaploid with 2n = 6x = 72, about 30cm in diameter and 30mt height. Nodes are not swollen, internode length is bigger. But then one can seen bamboo with nodes swollen and varying internode length in different species. It can be small or big. Bambusa cacherensis is used for making furnitures, mats, etc. Atroviolacea, the black bamboo has more girth in comparison to Phyllostachys and Bambusa vulgaris has the least girth, golden yellow culm and is ornamental. Sasa is a genus of small, cold hardy bamboo with broad leaves. It is a runner and a slow growing bamboo. It has curved, cylindrical culms. Other runner type species include Pleioblastus (100 feet to 18 inch), leaf length, leaf width, solid/hollow culms, leaf color, etc. Some genera including (Arundinaria, Melocanna, Phyllostachys) are monopodial whereas some like Dendrocalamus and Bambusa are sympodial in nature. Some species are more useful as building materials while others are not so useful. The mechanical properties of bamboo depend on moisture content, diameter, wall thickness, height, age and species. Maturity takes 5-7 years. Color of the culm is in first year, changes to yellow in 2nd year, to indigo in third and to black in fourth year of growth. Table 9.47  Showing species of bamboo and its ploidy level and uses Genus/species

Chromosome number

A. deblis

36

A. recemosa

48

A. rolloama

48

Bambusa arundinaceae

72

B. balcooa

70

B. binghami

60

B. burmanica

70

B. kingiana

72

B. nana

70

B. nutans

70

Chimonobambusa callosa

Uses

Unique trait

Used for construction, crafts and shoots

Nearly solid culms

Paper making

36

C. griffithiana

48

C. hookeriana

48

C. khasiana

48 Contd...

Origin and Genetic Resources of Fruit Crops

9.97

Contd...

Genus/species Cepholostacyum capitatum CC. pegracile

Chromosome number

Uses

Unique trait

60 71, 72, 48, 54, 60

D. brandisii

72

D. flagellifer

64,70, 72

D. giganteus

72

Construction, pulp

D. hamiltonii

70

Roof, basket, mat, pickles

D. longifimbriatus

56

D. longispathus

48

D. membranaceus

46, 72

D. seiceus

60, 72

D. strictus

56, 72

Dinochloa maclellandii

72

Indocalamus wightianus

48

Melocalamus indicus

48

Melocanna bambusoides

72

M, humilis

72

Pseudostachyum polymorphum

48

Thamnocalamus aristatus

48

T. falconeri

48

Teinostachyum dulloa

56

T. wightii

72

Thyrsostacys oleveri

36

The largest bamboo of the world. Use in construction

Pulp making

Phyllostachys pubescens

One of the largest bamboo used as building materials

P. mannii

Easy to split, culms tough and durable

P. nidularia

Culms solid on nearly solid

P. edulis

Paper, food, timber, ply wood and flooring in China

P. edulis ‘Haterocycla’

Nodes slanted alternatively in opposite direction Contd...

Crop Evolution and Genetic Resources

9.98 Contd...

Genus/species

Chromosome number

Uses

P. heteroclada

Zig-zag culms

Indocalamus

Solid culms

Guada amplixifolia

Shorter internodes

G. angustifolia

Furniture and house construction

B. multiplex

Solid culms

Phyllostachys robustiramea

About 10’ tall, 1’’ thick

C. cornigera

Culms zig-zag

Melocanna baccifera

Thin walled, shoots and fruits edible.

Ochlandra stridula

Used for pulp, basket and craft work in Sri Lanka

B. blumeana

Thorny bamboo used for building material in India 38

India

54, 108

India

B. tulda

70

India

B. vulgaris

70

India

B. polymorpha B. schizostachyoides

Phyllostachys viridis

High quality wood

B. bamboos

Paper

B. pallida

Construction, pulp

Unique trait

Multipurpose type

Multipurpose type

Phyllostachys heterocycla var. Pubescens is a diploid with 2n = 48 (Moso bamboo) and its draft genome has been prepared (Peng et al., 2013). Moso bamboo is the largest temperate bamboo. It is ready for processing in five years. Muli bamboo (Meloccanna baccifera) is a clumped type bamboo, culm green when young but colored at maturity. It has a 48 year life cycle and seed setting occurs and there is viviparous germination. Further, like Saccharum × Sorghum cross, S. saccharum officinarum × Bambusa arundanacea cross has been made and F1 shows formation of both reduced and unreduced gametes (Raghavan, 1952).

9.53  RUBBER This crop was introduced in Asia in the late 19th century. It is an industrial crop from which natural rubber is produced. It is a perennial, deciduous tree. It is an outbreeding crop,

Origin and Genetic Resources of Fruit Crops

9.99

showing inbreeding depression. It is propagated through seed as well as by grafting (bud wood grafting). Thus once a promising line is isolated, it can be multiplied vegetatively. Hevea brasiliensis belongs to family Euphorbiaceae. There are eleven species in the genus Hevea such as H. benthamiana, H. guianensis, H. pauciflora, H. spruceana, H. microphylla, H. rigidifolia, H. netida, H. camporum, H. camargoana, H. paludosa. All the species are diploid with 2n = 26 except one clone of H. guianensis which is triploid (3n = 54) (Ramaer, 1935: Ong, 1975; Wycherley 1976) and one genotype of H. pauciflora which is diploid with 2n = 18 (Baldwin, 1947; Mazumdar, 1974). Generally there seems no biological barrier between species and some species are intercrossible by hand pollination. H. brasiliensis behaves like an amphidiploids. The source–bush garden is cut back every year to maintain the conservation of the germplasm and also to generate bud wood (bud wood grafting) for multiplication of genotype. The seedlings obtained from seeds are multiplied by grafting. Breeding objectives in rubber aim at improving yield of latex, better resistance to wind damage, resistance to diseases, growth vigour and suitability for vegetative propagation. Its origin is Amazon basin (Brazil, Bolivia, Peru, Ecuador, Venezuela, Surinam, French Guiana). Breeding methods are characterized by alternating use of generative and vegetative methods (Ferwerda, 1969).

9.54  PECANS Pecan  Carya illinoinensis is natïve to U.S.A. Nut (kernels) enclosed in the shell) is the main economically important product. Edible oil is extracted from pecan which is used for manufacturing of drugs and essential oils. Wood is used in the flooring, furniture, veneer, besides it is an ornamental tree. Flowers are monoecious. Male flowers are borne at the base of shoot and female flowers are borne on the terminal spike of new shoot growth. There is dichogamy and pollination is through wind. Pecans are heterodichogamous with protandrous or protogynous habit and thus promotes cross pollination. Dichogamy is affected by locational and seasonal variation. Propagation is through budding or grafting on to open pollinated seedling rootstocks. Species belonging to sections Apocarya and Carya and salient characteristics are given in the table 9.48. All species in the section Apocarya are diploid with 2n = 32 whereas species from the section Carya include both diploid and tetraploid (2n = 4x = 64). Pecans and hickories belong to family Juglandaceae. Section Apocarya contains pecans and hickories and section Carya contains true hickories. Natural hybrids between pecan and other hickories are called ‘hicans’ (McKay, 1961). All species in the section Apocarya have 4 to 6 valvate bud scales whereas species from the section Carya have 6 to 12 overlapping terminal bud scales. Hickory wood is used for smoking meat and cheese in order to impart characteristic flavor. The breeding problems include long period of juvenility (>10 years), low yield (22-45kg / tree) and that too once in three years (not a regular bearer) and large tree size of hickory.

Crop Evolution and Genetic Resources

9.100 Table 9.48  Shows different species of the genus Carya. Species

Common name

Cultivated/wild

Ploidy level

Section-Apocarya C. aquatica

Water hickory

2n = 32

C. cathayensis

Chinese hickory

C. cordiformis

Bitternut hickory

C. hunanensis

Hunan hickory

Cultivated

2n = 32

C. illinoinensis

Pecan

Cultivated, commands international market

2n = 32

C. kweichowensis

Guizhou hickory

2n = 32

C. myristiciformis

Nutmeg hickory

2n = 32

C. palmeri

Mexican hickory

2n = 32

C. poilanei

Poilane hickory

2n = 32

C. tonkinensis

Vietnam hickory

Cultivated

Shellbark hickory

Cultivated

Shagbark hickory

Cultivated

Cultivated

2n = 32 2n = 32

2n = 32

Section-Carya C. acrolinae-septentrionalis C. floridana C. glabra C. laciniosa C. ovalis C. ovata C. pallida C. texana

Black hickory

C. tomentosa

Mockernut hickory

9.55  BLUBERRY This fruit crop (Vacinium spp.) was domesticated in 20th century in U.S.A. This crop grows well on acidic, imperfectly drained sandy soil. Blueberry is one of the richest sources of antioxidants of all fruits and vegetables (Prior et al., 1998). Further, fruits contain Fe, Ca, vit.A, vit.C besides proteins, fats and carbohybrates. Bluberry belongs to family Ericaceae and cultivated blueberry belongs to section Cyanococcus, true or cluster-fruited blueberries. Different species described as shown in the table 9.49 next page. Species can be diploid, tetraploid or hexaploid. Further, different species can be grouped in to low bush (Rhizomatous and maintained between 0.3 to 0.6m), High bush (Crown forming and maintained between 1.8 to 2.5m) and rabbiteye types (Crown forming and maintained between 2-4m and suckering to varying degree) (Hancock and Draper, 1989).

Origin and Genetic Resources of Fruit Crops

9.101

Table 9.49  Showing different species of blueberry, ploidy level and characteristics. Species

Ploidy level

Low bush/high bush/ Rabbiteye types

V. boreale

Diploid

HB

V. corymbosum

Diploid

HB

V. darrowi

Diploid

V. elliottii

Diploid

V. myrtilloides

Diploid

V. pallidum

Diploid, Tetraploid

V. tenellum

Diploid

V. angustifolium

Tetraploid

V. V. corymbosum

Tetraploid, Diploid

V. hirsutum

Tetraploid

V. myrsinites

Tetraploid

V. simulatum

Tetraploid

V. ashei

Hexaploid

V. constablaei

Hexaploid

V. boreale

Characteristics

Low chilling species. Wild V. corymbosum is the source of gene for resistance to stem canker Source of gene for low chilling and heat tolerance

LB

LB

Rabbiteye types

Wild population

Wild species are found only in North America. Commercially grown varieties are divided into the following five major groups of three ploidy levels (Galletta and Ballington, 1996: Hokanson, 2001). 1. Low brush- Diploid and tetraploid varieties include wild populations of V. angustifolium, V. myrtilloides and V. boreale and improved cultivars. 2. High brush- Tetraploid varieties, V. corymbosum wild selection and hybrid cultivars with small percentage of V. angustifolium 3. Southern HB types- Tetraplid varieties include HB V. corymbosum and also low chilling species V. darrowi as well as varieties involving V. angustifolium, V. ashei and V. tenellum as one of the parents. 4. Half HB- This tetraploid varieties include species hybrids or backcross derivatives of LB × HB cross involving V. angustifolium × V. corymbosum. 5. Rabbiteye types includes hexaploid varieties including wild selections and hybrid varieties of V. ashei.

Crop Evolution and Genetic Resources

9.102

Interspecific hybridization has played an important role in the development of improved cultivars as there is lack of sterility barrier between species of the similar ploidy level. Interspecific hybridization involving species from different ploidy levels are being utilized for crop improvement. The interspecifici hybrid, V. darrowi × V. ashei is also the source of gene for resistance to low chilling and heat tolerance.

9.56  HAZELNUT Hazelnut (Filbert)  The term, hazelnut, is used for all nuts of all species of Corylus. Filbert is used for long husked types of C. avellana in order to distinguish it from short husk type. It belongs to family Betulaceae. The nine most widely recognized species include five shrubby species and four trees as given in the table 9.50. Most of the varieties are dichogamous being either protogynous or protandrous. There is usually overlapping of staminate and pistillate anthesis. Staminate flowers are borne on catkins which develop from lateral buds on the previous season’s growth whereas the pistillate flowers are borne terminally on the current season’s growth. Corylus avellana has a sporophytic system of incompatibility and it is under control of one locus with multiple allelic system (S-alleles). Table 9.50  Showing species of Corylus Species

Common name

Growth habit

Ploidy level

C. avellana

European hazelnut

Shrubby

2n = 2x = 22

C. americana

American hazelnut

Shrubby

-do-

C. cornuta

Beaked hazelnut

Shrubby

-do-

C. heterophylla

Siberian hazelnut

Shrubby

-do-

C.sieboldiana

Asian hazelnut

Shrubby

-do-

Tree

-do-

Tree

-do-

C. chinensis

Tree

-do-

C. ferox

Tree

-do-

C. colurna, var.glandulifera, var.colurna C. jacquemontii

Himalayan or Indian hazelnut

Physiological disorder in fruits and vegetables  Table 9.51 given below shows commonly observed physiological disorders in various fruits and vegetables. Reasons for physiological disorder could be genetic or environmental. Gene or genetic background of a variety plays a role in physiological disorder. It can also be due to deficiency of micronutrient. Tip burn in lettuce is due to Ca deficiency. Physiological disorder, fruit cracking in litchi or mango can be corrected through regular watering. Selection of line (s), free from defects be practised under condition conducive to the problem.

Origin and Genetic Resources of Fruit Crops

9.103

Table 9.51  Showing various crops and their physiological disorders Crop

Symptom

References

Cause

Apple and watermelon

Bitter pit, watercore and internal breakdown

Atkinson et al., 1980; Ciralli and Cicearese, 1981

Tomato and pepper

Blossom end rot

Winsor and Adams, 1987

Aocado

Mesocarp discoloration and pulp spot

Banana

Yellow pulp (Melin and Aubert, 1973)

Mango

Internal fruit breakdown-tip pulp, soft nose Sauco (2009) (waterlogging of the flesh near the distal end), jelly seed (over ripe flesh around the seed surrounded by firm flesh), stem end breakdown (an open cavity in the pulp at the stem end), spongy tissue (areas of flesh appearing spongy and have a grayish black discoloration, soft center and soft flesh). Lumpy tissue, ricy tissue, fruit cracking, black tip disorder and lenticel spot

Litchi

Fruit cracking

Lettuce

Tip burn, Rib blight

Genetic background is related to this disorder

Watermelon

Hollow heart, rind necrosis, blossom end rot and cross stitch

Genetic component

Summer squash

Leaf silvering

This disorder is due to the feeding of immature white flies (Bemissia spp.) and is exacerbated by drought stress.

Melin and Aubert, 1973

Section B

9.57  IMPROVEMENT OF UNDERUTILIZED/ COMMERCIALLY GROWN FRUIT CROPS Breeding methods discussed here under improvement of underutilized fruit crops will be equally applicable to the improvement of commercially grown fruit crops described in this chapter. At a time when people are becoming more health conscious and food crop plant breeders are trying to fortify the main sources of carbohydrates and protein with vitamins and minerals and oils with more polyunsaturated fatty acids, it would be more proper to use and improve the so-called underutilized fruit crops to supplement our diet with

9.104

Crop Evolution and Genetic Resources

supply of vitamins, minerals, sugars and oils. Use of nutrients from diverse plant sources will help in maintaining plant diversity as well as creating an ecological balance. Further, utilizing the under utilized fruit crops grown in adverse soil and climatic condition for commercial exploitation is the best way to make use of all kinds of edaphic and climatic niche existing in our country and thereby making best possible use of land resources. Now what is required is to genetically improve these fruit species and workout the production, evaluation and multiplication strategy in order to make raising of these fruit crops a more profitable venture. There are a number of underutilized fruit crop species (see Table 9.52). Before starting genetic improvement program it is essential to collect and evaluate different species and genotypes and conduct basic botany, genetics and cytogenetics studies in order to have information regarding breeding systems including extent of inbreeding and outbreeding, pseudo-reproduction, self-incompatibility, male sterility, ploidy level, genetic architecture of different qualitative and quantitative traits. The different breeding methods that can be employed for improvement of these fruit crops include conventional breeding methods such as clonal selection, hybrid breeding using haploids/dihaploids, synthesizing fresh auto/allo polyploids, mutation breeding and molecular breeding methods such as marker-assisted selection aiming at finding marker traits in juvenile plants correlating well with high yield and other desirable traits (fruit quality, resistance to biotic and abiotic stresses) of adults, transgenics-production of genetically modified fruit crops using genetic engineering techniques and application of tissue culture techniques aiming at increasing the multiplication rate, development of useful mutants, producing virus-free plants and preservation of species and thereby preventing from their extinction. The existence of mechanism of 2n gametes in fruit crop can be used for production of hybrids and higher level of ploidy. The underutilized fruit crops of today can be the source of genes for resistance to different biotic and abiotic stress and rootstocks for the present day commercially cultivated fruit crops. Combining traditional approaches with biotechnological approaches will speed up the rate of genetic improvement. Thus what is required is to adopt a co-ordinated approach involving breeders, biotechnologists, horticulturist, pathologist, entomologists and statisticians for making the cultivation of these so-called underutilized fruit crops more scientific and more profitable and thereby contributing more to improving the health of the people in a sustainable manner and finally, removing the tag-underutilized from them. This paper thus describes all available methods of genetic improvement which are currently employed in commercially grown fruit crops and which can be used in the genetic improvement of the underutilized fruit crops.

1.  INTRODUCTION The underutilized fruit crop can be said to be uncared, unattended and genetically uninvestigated or little investigated crops whose importance has been now realized. The underutilized fruit crops have now caught the attention for their improvement as they can help diversitfy the supply of nutrient sources in our diet, have medicinal values besides being the source of oil, dyes, pectin, tannins fodder, fire, fuel and other value added

Origin and Genetic Resources of Fruit Crops

9.105

products, for example, kiwi, aonla, bhava, karonda are rich source of vitamin C whereas jamun (useful in diabetes), kiwi, avocado are rich source of Ca, Fe. Nut fruits such as pecan, pistachio, chestnut are rich source of protein, fat and carbohydrate and walnut is a rich source of polyunsaturated fatty acid (90%) of which 25% is the omega 3-fatty acid a-linolenic acid, good for coronary heart disease. Fruits are potential sources of the antioxidants such as flavonoids, carotenoids, anthocyanins, ascorbic acid, glutathione which act as scavenger of the reactive oxygen both in plants and humans and protect against diseases. Some fruit crops (e.g. Assam apple and wild pear) have served as the rootstock with desirable properties. The different underutilized fruit crops of hilly regions of Kumaon, Garhwal and North-East are presented in the table 1 along with their breeding systems and ploidy level. Further, some other underutilized fruit crops are also found in hilly regions of southern parts of India. Besides underutilized fruit crops of hilly regions, there are underutilized tropical fruit crops which include bail, chironji, jamun, karond, ker, khirni, lasor and mahua. Few things are very clear from the table 1. I. The ploidy level ranges from diploid to polyploid. The growth habits include herbs, shrubs and trees. They also vary in their adaptation (tropical, subtropical and temperate). What is common to most fruit crop species is that they are all heterozygous and heterogeneous and cross-pollinated and multiply through vegetative means such as root cutting (e.g. apple, orange, raspberry and blackberry), stem cuttings (many timber trees and shrubs), runner (strawberry), sucker (banana), stolen (wild strawberry) layering, budding, grafting and through seeds. Sex found in these fruit crops ranges from monoecious to dioecious (separate male and female plants like Carica papaya, Pistachio vera, Phoenix dactylifera). Oil palm shows alternate male and female flowering cycles throughout the life of plant. Mangosteen is apomicti and plants are homogeneous and are of one genotype. Life span ranges from annual to biennial to perennial. They have different juvenile periods. They also differ in their productive life span Most underutilized fruit crops are grown in adverse soil and climatic conditions. Some fruits are climacteric and some others are non-climacteric. The genetic control of sex in trees varies from under control of gene control (e.g. one locus and three alleles in case of papaya, Storey, 1941) to chromosomal differences XX and XY system as in case of Actinidia-kiwi fruit. These underutilized fruit crops if genetically improved can be a valuable source of foreign exchanger earner. As the genetic structure of these underutilized fruit crop species is similar to the commercially grown fruit crop species, the conventional breeding methods that have been employed and the molecular methods that are being used to improve these fruit crops can be used for the genetic improvement of the these underutilized fruit crop species.

2.  BREEDING METHODOLOGIES 2.1  Breeding Objectives A look at different underutilized Commercially grown fruit crops show that yield and quality traits should be improved immediately. Fruit size in most cases is small and fruit is inferior in quality.

9.106

Crop Evolution and Genetic Resources

The breeding objectives common to all fruit crops will be as follows. 1. To increase fruit yield per tree/year. It is over here that objective would be to develop regular bearer cultivar in place of alternate bearer. 2. To develop self-compatible cultivar where self-incompatibility is found (e.g. in sweet cherries, almond, apricot, apple, pear, pineapple). The gametophytic self-incompatibility is under control of S-locus and 28 alleles have been identified in diploid and triploid apple. In sweet cherry there also exists single locus multifactorial system and over 20S-RNase have been identified and further self-compatible allele, S4¢ has been identified. Fully self-compatible cultivars can be grown as a monocultural system but self-incompatible cultivars must be grown with pollenizer. 3. To improve the adaptation of the crop Shifting the adaptation of the crops  Productivity can be increased by either improving the fruit yield/tree or by bringing in more area under cultivation or by both. One way of increasing the area would be to change the adaptation of the crop, i.e., by making temperate fruit a tropical/subtropical one or vice-versa or a high chilling required cultivar to low chilling required cultivar. In other words, develop cultivar which can be grown across a vast environmental zone. Thus environmental factors limiting the productivity in fruit crops include heat and drought, salinity, winter cold, frost and insufficient chilling hours. Cold hardiness is important in the more temperate crop and in the warmer regions more emphasis is on drought and heat tolerance. 1. Breeding for adaptation to low chill region is also an important goal in case of peaches, pears, plum. 2. To develop cultivars with low flower abscission and immature fruit drop. These problems are more in grafted cultivars than in seedling propagated cultivars. 3. Extending harvest season– Developing varieties which produce a continuous supply of quality fruit throughout the season or breeding location specific varieties and making quality fruits available round the year. 4. To improve fruit quality– Depending upon the type of usage (table purpose type or industrial uses) the quality parameters will change. One can control the fruit morphology in order to minimize damage during transportation/shipping. 5. To develop seedless (e.g. grapes, guava) or small seeded fruit (e.g. litchi, mango) cultivars. 6. To control post-harvest losses, to increase shelf-life. 7. To improve resistance against biotic and abiotic stress. 8. Improvement of specific trait in specific fruit crop. For example, in carambola the special objective would be to reduce the concentration of oxalic acid (calcium oxalate) which makes fruit strongly acidic. Adaptation to too high pH is an objective in quince breeding program. In fig one objective would be to eliminate caprification. In case of mulberry and tea breeding , the major emphasis will be on

Origin and Genetic Resources of Fruit Crops

9.107

the leaf quality. In litchi, cherry and mangosteen, one objective would be to breed for resistance to fruit cracking. 9. In case of nut fruit, the objectives are to improve protein and lipid traits. 10. Breeding for post-harvest disorders such as core breakdown and bitter pit and superficial scald in fruit, e.g. pear. 11. Some fruits such as peaches, cherries contain lipid transfer proteins (LTPs) called allergens which need to be looked during the improvement program. Similar LTPs have also been found in apricot and almond. 12. Multiplication of quality planting materials– Use of micropropagation, in vitro tissue culture can be used for rapid multiplication of mericlones. These objectives in fruit crops can be met by improving either the scion cultivars or rootstocks or both.

2.2  Conventional Breeding Methods Fruit cultivars have originated from three sources. 1. Chance seedlings 2. Selection from either seedling orchards or dooryard seedling and 3. Breeding program. Amongst these the second source has been the major source of commercially important cultivars. Breeding objectives  In summary, the objectives are to improve yield and quality of fruits and nuts. These objectives can be accomplished through genetic manipulation or environmental manipulation or through both. Horticulturists are engaged in developing package of practices and developing techniques of pruning, training for improving yield and quality and further developing post-harvest management practices for storing and increasing shelf life of fruits. Breeders are engaged in genetic manipulation aiming at improving yield and quality and overcoming post-harvest physiological disorders. The characters to be improved include tree characteristics, fruit characteristics, nut characteristics, resistance to diseases and pests, resistance to abiotic stresses, resistance to frost / winter injury, etc. The fruit tree characteristics include growth habit (dwarf type), timing of flower bud break, fruiting habit, dichogamy, self-incompatibility, leaf size, orientation, colour and retention, tree structure, size, shape, alternate bearing, precocity, prolific bearing, cluster size, length and density of fruiting shoots and fruit retention. Fruit characteristics include time of maturity (harvest) specific marketing period, fruit size, shape, colour, seed size and seed number (small, only a few seeds or seedlessness) and flavor (sugars, acids) and specific marketing requirements and different usage (table purpose, processing and product). Nut characteristics include shelling marking, shunk characteristics (pecan), nut size and shape, kernel colour, grooves, plumpiness and adaptability to mechanical harvest, ease of mechanical cracking and shelling and storage ability. Besides identification of seedling lines having superior rootstock characteristics, i.e., lack of variability, vigor and improved yield of scion becomes the breeding objective. The different breeding methodologies employed in case of annual food crops can be applied with modifications because of the differences that these fruit crops show. Fruit

9.108

Crop Evolution and Genetic Resources

crops are mostly perennial, highly heterozygous and outbreeders in nature. It can be multiplied through both seeds and asexually. Perennial fruit crops have the advantage that once a promising line is selected, it can be asexually propagated (i.e., the genotype can be fixed). Further, a fruit crop variety consists of two genotypes-scion genotype and rootstock genotype and thus the improvement in fruit crops can be achieved through improvement of either scion genotype or rootstock genotype or both. The commercially cultivated cultivars (scions) and rootstocks that we are seeing today are the result of clonal selection and originated as chance seedling or bud sport mutants in case of some scion cultivars. The standard methods of handling segregating generation population such as pedigree, bulk, single seed descent or dihaploidy can not be directly employed. As plants are heterozygous so F1s, the crosses between the two cultivars unlike in annual self pollinated crops, show lots of variation. Thus selection can be practised right in the F1 generation itself unlike waiting until F2 generation in self pollinated crops and once a promising tree is found, it can be fixed and multiplied and maintained through clonal propagation. If the juvenile period is short then one can raise F1 trees from the seeds and evaluate it and select the best one. Then the selected best tree can be multiplied through clonal propagation. If the juvenile period is long then raise seedlings from the seeds and graft it and then evaluate and select the most promising genotype. Again, once the best genotype is identified, it can be propagated vegetatively. Thus in the F1 generation derived from the two parents (highly heterozygous in case of fruit, ornamental and some many vegetables), individual plant selection is practiced as it is a segregating generation population. Now in a crop like potato or sugarcane or crops propagated through bulbs or corms (e.g., gladiolus, tulip, daffodils), cuttings (pelargonium, carnation) or division(hardy herbaceous perennial) the selected individuals are evaluated in the F2 generation in replicated trial. With the increase of planting material (tubers in case of potato and sets in case of sugarcane) the number of replication is increased in the subsequent generations and multilocational testing is carried out. In case of crops which are vegetatively propagated through either budding or grafting, the selected plants are used as source of scions or buds and grafted/budded on selected rootstock (s) and as mentioned above, replicated trial is conducted in the following generations with continuous increase in the number of replications and sites of testing with the increase in planting materials. Here one can use micropropagation technique to multiply the selected plant (s) in order to conduct multilocational replicated trial right in the F2/F3 generation (early generations). In case of seed propagated fruits (e.g., papaya) and vegetables and ornamentals (annual flowers) the standard method of handling F2 population such as bulk, pedigree, single seed descent or dihaploidy is applied.

2.3  Hybrid Breeding Mango breeders have crossed two different cultivars and selected tree from this cross and labelled them as hybrids. But then we know that the fruit crops are highly heterozygous

Origin and Genetic Resources of Fruit Crops

9.109

and so the cross between cultivars here can not be said to be like F1 derived from two pure breeding lines/inbreds. Further, the F1 in case of fruit crops is a population of genotypes. As two fruit crop cultivars differ in morphological, floral and fruit characteristics which are supposed to be under control of one or a few or many genes and further they do not breed true if seed propagated then the two cultivars can be supposed to differ in heterozygosity at these different loci. When we say that fruit crops are highly heterozygous, it does not rule out the possibility that at few loci there could be homozygosity. Thus different fruit cultivars within a fruit crop species will differ in the level of heterozygosity/ homozygosity and further some will have unique gene (s). Thus considering two loci with two alleles there will be four different genotypes such as Aabb, AaBB, AABb and aaBb. The four two parent crosses will as follows. i. Aabb x AABb------ AABb, AAbb, AaBb, Aabb ii. Aabb x aaBb------- AaBb, Aabb, aaBb, aabb iii. AaBB x AABb-------- AABB, AABb, AaBB, AaBb iv. AaBB x aaBb------ AaBB, AaBb, aaBB, aabb All crosses produce mixture of genotypes in the progeny with a quarter of genotypes being heterozygous at both loci. The two parental trees can not be either Aa (one locus two alleles system) or AaBb (two locus two alleles) as the different cultivars are different genotypes. We can consider this situation only in case of selfing or inbreeding a variety. In that condition the inbreeding/ selfing generation will consist of AA, Aa and aa genotypes or AABB, A-B-, aaB-, A-bb and aabb, respectively. The fruit breeder does not know whether the genotype of the selected plant is AA(homozygote) or Aa(heterozygote) or AABB or A-B-, or AaBb.

Suggested Method of Developing Hybrids Instead of just selecting two varieties, crossing them and releasing the selected tree from the progeny as hybrid, it would be much better if we do the selfing/inbreeding for one generation and thus obtain partial inbreds. Practice selection in this generation by way of raising seedlings from the harvested seeds and grafting or budding them on root stock. Selected partial inbred lines are then crossed to produce the hybrids. The heterozygosity is thus restored and is at a higher than the original level of heterozygosity. Besides, the selected plant will now contain less decreasing alleles and the probability of getting a novel hybrid increases The proposed method can be shown by a figure as given below. Figure 9.4 shows that the possibility of obtaining heterozygosity at all loci is high than in the usually employed method adopted by fruit breeders. Thus rather than directly making crosses between two varieties of fruits, one generation of selfing followed by crossing between partial inbreds will produce more heterozygotic plant with supposedly more hybrid vigor. This proposed method will although take more years to develop a hybrid but then the probability to produce highly heterozygotic tree is high.

Crop Evolution and Genetic Resources

9.110 AaBbCCDD

Selfing

AABBCcDd

Selfing

AABBCCBB, A-B-CCDD, aabbCCDD AABBC-D-, AABBccdd, AABBCCDD

AaBbCcDd

Fig. 9.4  Showing selfing and crossing program for hybrid development

Advantages of the proposed method over varietal crossing are as follows. 1. Probability of getting heterozygosity at most of the loci is higher in comparison to varietal cross hybrids. 2. Heterozygosity is restored to the original level as found in the parental cultivars which may or may not be the case in case of varietal hybrids. 3. There is generation of heterozygosity and homozygosity at new loci thereby increasing the chance of obtaining a hybrid with exploitation of newly developed interactions between genes and thereby increasing the probability of generating a novel hybrid. The only disadvantage with this proposed method is that it will take longer time to develop hybrids but in the long term it is not a limitation. As self-incompatibilty (gametophytic self-incompatibity) is found in a number of fruit crops, so this mechanism of facilitating cross pollination can be used to develop hybrids.

2.4  Molecular Breeding When we talk improving/developing a cultivar, we are talking of improving the mean performance of one particular trait or a group of traits of a cultivar. Before starting practical breeding program to develop a cultivar we must have some genetic information regarding the trait (s) to be improved. Whether a trait is qualitative or quantitative as selection of a breeding method depends on the nature of the trait. In other words, we must work out the genetic architecture of a trait, i.e., number of genes controlling a trait, the types of gene actions and interactions (epistasis), linkage between genes or pleiotropy, maternal effect/sex linkage, the extent of effect of environment on the trait development (genotype x environment interaction). Information on all these is there in case of annual crops but is lacking in perennial fruit crops and there is virtually no genetic information available in the underutilized fruit crops. The simple reason is that classical genetical and biometrical experiments can not be conducted so easily in these crops because of reasons mentioned earlier and so conventional plant breeding methods can be applied to improve

Origin and Genetic Resources of Fruit Crops

9.111

the underutilized fruit crops but with difficulties and one will have to work for atleast 20 years to develop a variety. Now with the advent of molecular marker technology, structural and functional genomics technologies and computational tools, it would be better to apply these technologies to generate information regarding genes, their positions in the genome, their effects, their sequencing and isolation and finally doing the cloning of the genes. Thus molecular techniques developed so far and used in commercially grown fruit species can be employed in the so-called underutilized fruit crops and their genetic improvement can be brought about. Fruit crops differs from annual food crops in that the former bear fruits for over 5 to 15 years (in case of peach) to over 50-100 years (in case of apple). Further, juvenile periods range from 2-3 years (in case of peach) to 3 to 10 (in case of apple). This points to two things. First, if an orchard with plants of wrong genotype is established it will bring heavy loss to the orchardists and this is where the molecular marker will help in confirming the identity of the cultivar. Secondly, if a marker is found in the sapling which correlates well with the yield and other economically important traits of tree then it will help in selecting a desired genotype right with high confidence in the beginning of the breeding program and discarding most of the nonpromising genotypes. This will help breeder in attempting large number of crosses and evaluating them. This is where the molecular marker technology will have its role. The molecular markers are the landmarks which are not affected by environment.

2.4.1  Types of Markers There are different types of markers. 1. Morphological marker 2. Isozyme marker 3. Cytological marker 4. DNA marker Isozyme/protein markers  Isozymes have been used to differentiate among fruit cultivars, to determine parentage of existing cultivars, to characterize seedling population following controlled pollination and to construct linkage map. The various enzyme systems that have been used to characterize cultivars/ accessions in the germplasm bank include acid phosphatase, alcohol dehydrogenase, diaphorase, glutamate oxalacetate transaminase, isocitrate dehydrogenase, malate dehydrogenase, malic enzyme, phosphoglucose mutase, 6-phosphogluconate dehydrogenase, shikimate dehydrogenase, superoxide dismutase, triose phosphate isomerase, peroxidase, endopeptidase, diapharase, leucine amino peptidase. DNA markers  Characterization of genetic diversity in germplasm at the DNA sequence level has now replaced the strategies of isozyme or polyphenol markers involved in the study of genetic diversity characterization. The various DNA markers that have been used in fruit crops include AFLP, EST-PCR, ISSR (inter-simple sequence repeat), ISTR (inverse sequence-tagged repeat), microsatellite, minisatellites, RAPD, RFLP, SCAR (sequenced-characterized amplified regions), SSR (simple sequence repeat). Co-dominant

9.112

Crop Evolution and Genetic Resources

markers (RFLP, AMP-FLP, SSR, CAPS) can be used to distinguish homozygotes from heterozygotes. Advantages of RFLP include high degree of reproducibility and robustness against experimental artifacts and thedisadvantages include requirement of large quanity of DNA, involvement of several experimental steps and labelled probes (radioisotope/ fluorescent). The disadvantages with RAPD include low reproducibility and dominance nature of the marker. Like RAPD, AFLP does not require knowledge of target genome, reproducibility is similar to RFLP but number of fragments amplified for each pair of primers (50-100 fragments) is higher than in any other technique. The disadvantages include requirement of large number of experimental steps in comparison to RAPD and further it is a dominant marker and thus can not distinguish between homozygous dominant and heterozygous dominant genotype. Microstellite markers require lots of time and labour for its development but the advantages include detection of high average degreeof polymorphism, high reproducibility and requirement of small amount of DNA. SSCP marker (In case of a DNA fragment of 3. The probability of a pollen grain landing on a compatible style is 1 – 2pi(1 – pi) / (1 – pi2) = (n – 2) / n. Thus a pollen grain containing a newly arising S-allele will always land on a compatible style and so its probability of fertilization relative to that of pre-existing allele equals 1 / (n – 2) / n = n / (n – 2). This is the relative fitness of a new mutation. For n = 3, 4, 5, 10, 50 and 100 it equals 3, 2, 1.67, 1.25, 1.04 and 1.02, respectively. Hybrids  CMS line can be developed from interspecifc cross as has been done in Brassicas (B. nigra × B. oleracea) and intergeneric cross as has been obtained in Brassica (B.oleracea × Raphanus sativus). B. oleracea genome has been put in the cytoplasm of R. sativus. This type of male sterility arise because of disturbance of the normal interaction between the cytoplasm and nuclear genes when both parents are not closely related. Hybrids effects are more pronounced in interspecific / intergeneric cross in comparsion to intervarietal (within species) crosses. Cauliflower  B. olercea var. borytis is a very important flower vegetable. It belongs to family Cuciferal head consists of tightly packed florets which begin to form but stopped at bud stage. It is packed up with Vit. C and Vit. B-complex and antioxidants and minerals. It contains low fat and no cholesterol. It contains phytochemicals such indole3-carbinol and sulforaphane which are anti-cancerous. Further, it contains di-indolylmethane (DIM) which is immune modulator. Cauliflower has similar nutritional and phytochemical profile as that of cabbage and broccoli. Broccoli is very susceptible to high temperature damage and so its cultivation is recommended for cool and moist climate. Cauliflower is also susceptible to heat but not to the same extent as broccoli. At high temperature curd in cauliflower may develop bracts (green bracts corresponding to auxillary leaves are actually present in the curd). Pusa katki has high heat tolerance, is early but has poor curd quality. Early cauliflower-Snowball types are self compatible but late maturing ones are self-incompatible. Indian cauliflowers are mostly early and are self-incompatible. In brassicas, self-incompatibility is sporophytic and under control of single locus (S-gene) and multiple allelic (S1, S2, ........., S50) system. Italy is the center of origin of cauliflower. Heat tolerant variety is required as cauliflower is heat susceptible although not to the same extent as broccoli. Under high temperature curd may develop bracts (green leaves) and curd colour may turn brown or purple or yellow. Solidity (compactness) of curd is essential as soft curded (or loose curded) plant will bolt readily. White or cream color curd is desirable. Colours such as green, orange, purple and yellow or golden are also available. Orange colour is due to the presence of beta-carotene. Italy is regarded as center of origin of cauliflower.

Origin and Genetic Resources of Vegetable Crops

10.13

Several varieties exist which have green, orange, yellow, purple and romanesco head in comparison to the most common snow-white variety. Romanesco is a multiheaded cauliflower. Orange color is due to the presence of beta-carotene. Bright green color is due to two recessive genes. Green curds are more frost tolerant than white curds (Gray, 1989). Creamy white head can be obtained by protecting it from the sun light by tying close the leaves together over the head when the head is of the size of a quarter. The breeding objective thus would be to develop genotype (s) with longer leaves which can can protect the curd from sun. Persistent whiteness of curd is under control of several recessive genes. Thus one can obtain white curd even at high temperature. Curd color changes to purple or brownish yellow if exposed to sun. Over maturity results in loose head and grainy surfaced head and it looses the flavour and tenderness. Green coloration can also be due to overexposure to sun light. Selection should be for snowy/creamy white and compact head. Solid curd character tends to be recessive. Most Brassicas have vernalization requirement which induces flowering and thereby production of seed. In practice, all Brassicas require vernalization but the temperature at which this occurs can be quite high, >25C for most broccoli and some summer cauliflower. And thus under most conditions these will flower without any artificial vernalization. However, biennial crops such as some cauliflower types, cabbage, kale, kohlrabi, collards and Brussels sprouts all require 2-3 months of vernalization below 10°C. In most cases 5°C is the most ideal temperature for vernalization. Where it is not possible the best way is to dug plants with the curd in the prime market stage and store the plants at 5°C for a month for acceleration of flowering. B. campestris has A genome, B. nigra has B genome and B. oleracea has C genome (see chapter 7). Pigmentation of curd in cauliflower is due to the presence of chlorophyll, anthocyanin and carotenoid. Green color is solely due to chlorophyll, violet is due to anthocyanin plus chlorophyll and/or carotenoids and yellowish-orange is due to carotenoids only. Cauliflower/broccoli can be vegetatively propagated through either grafting pieces of the selected curd/head on the selected cauliflower/broccoli rootstocks (Watts and Geotge, 1963) using stumps of the selected plants or by cuttings which are inserted in a rooting substrate. In seed production program rouging is done at two stages. At vegetative stage rouging of precocious or button curds which develop too early is done and uniformity in terms of leaf number, leaf shape and crinkle is checked. At harvesting stage observation is made on curd color, bractness, firmness, shape of the curd and leaf protection. In hybrid seed production program the male:female ratio is 1:2 but this ratio can vary in relation to the flowering ability of each parent. Transfer of male sterility from Raphanus sativus to B. oleracea is done to develop F1 hybrids using CMS system in Brassica. Genetic resources  The origin of cauliflower and broccoli crops from Mediterranean basin is linked to other likely relatives which includes B. cretica, B. montana, B. bourgeaui, B. incana, B. insularis, B. microcarpa, B. rupestris and B. villosa (Gomez-Campo and Gustafsson, 1991). B. villosa is the source of gene for glucosinate. Cauliflower is most closely related to broccoli and cabbage is most closely related to the kales.

10.14

Crop Evolution and Genetic Resources

Micropropagation  Small pieces of curd which 1-2mm in diameter are used as explants. They are removed from the curd and put in nutrient solution (MS medium). Roots and shoots develop and produce new plants. Grafting of curd portions on to the young stock plants has been found fairly successful.

Cabbage Cabbage (Brassica oleracea L. var. capitata) belongs to family Cruciferae. White headed cabbage is B. oleracea var. capitata f. alba, red cabbage is B. oleracea var. capitata f. rubra and savoy-headed cabbage is B. olearacea var. sabauda. Broccoli (green cauliflower), cauliflower, Brussels sprout, collards, Kale and Kohlrabi are the members of this species (Table 10.7) which are readily intercrossed. Boccoli differs from cauliflower in that the leaves are more divided and petiolate and further, the main head consists of cluster of fully differentiated green or purple flower buds which are less densly arranged with longer peduncles. Kales are ancient cole crops, closely related to the wild forms of B. oleracea. The center of origin is eastern Mediterranian and Asia minor. Genomic relationship between different Brassica species is given in chapter 7. Broccoli, Brussel sprouts, cabbage, carrot, cauliflower are predominantly cross-pollinated crops. Radish is a cross-pollinated crop. Red cabbage is pigmented and in chinese cabbage (B. campestris ssp. pekinensis) leaves are crispe (Table 10.8). Brassicas are sulphur rich vegetables. Collards are loose-leafed varieties of Acephala group of Brassica oleracea. It does not have the core (a head) like cabbage. Kale with green or purple leaves is closer to wild cabbage. It is a hardy member of cabbage family. It contains fortyfive different flavonoids. It makes isothionates from glucisinolates and thus lowers the risk of cancer. Isolation distance in cabbage is 500 to 1000m. In Brussels sprouts there were open pollinated varieties but now F1s are available. The traits to be included in breeding program are head shape (pointed, flat, round to extremely round), head leave, size of head, core width, core length, core solidity, frame size, head splitting, plant height, axillary heading, leaf toughness within the head, leaf or rib size, dry matter, storability and red coloration. Dry matter can range from 9-10%(high) to 6%(low). Savoy leaf texture cabbages are better flavored and less gas producing than the smooth–leaved variety. Yellow savoy varieties are high yielding and have the highest solid or dry matter. In comparison to all other common Brassicas cabbage produces the tallest plant at flowering stage. Non-heading type in cabbage has several wrapper leaves surrounding the terminal bud. Broccoli  The breeding objectives in broccoli are heat tolerant variety with nonbranching type. Broccoli is highly susceptible to high temperature damage in comparison to cauliflower. Branching is also influenced by high temperature which increases by increase in temperature. Non-branching type broccoli is similar to cauliflower plant in that lateral buds do not develop in the leaf axil and if head is removed no lateral bud develops. The third trait to be improved is the storability or shelf life besides yield and uniformity. Broccoli’s head should be dome shaped and heavy at maturity and a solid stem is desired.

Origin and Genetic Resources of Vegetable Crops

10.15

Swede/Rutabaga  The swollen root is pale orange fleshed with upper half being off-white or slightly yellow and the lower half brown. The desirable traits include uniformity, interior colour, smooth round exterior shape, smaller leaf attachment and good storability. Brussels sprouts  The breeding objective in Brussels sprouts includes good flavor, sweetness, medium sized bud (the preferred size) and dark green sprouts preferred over pale green.

Breeding Objective in Brassica Vegetables Breeding objective in cabbage include development of semi-solid, well rounded, fairly heavy in relation to size and leaves be more tender, juicy, thick and pliable. Light colored, very solid heads mean all core and less taste. Oblong or cracked heads, thin and wilted leaves are undesirable traits. Late, slow growing cultivars are best suited for storing. Dry matter of better storage type is higher. Smooth leaved cultivars are undesirable as they produce lots of gas. Green leaved cultivars are good for fresh market whereas white leaved cutivars are good for cool slaw. In cauliflower the traits for improvement include curd color, curd diameter, size, compactness, plant spread, stem length, dry matter percent, curd weight per plant, ascorbic acid, protein and minerals. In case of Chinese cabbage the characters to be recorded include soluble sugar, crude fibre, soluble protein, oganic acids, soluble pectin, soluble protopectin (hemicelluloses), chlorophyll content, Vit. C, dry matter and sugar > fibre > protein. In Romanesco, pyramidal shaped curd is desirable and the objective would be to reduce bractiness, riciness (i.e., early development of flower bud) and looseness which spoils curd surface. Other characters to be scored include pH, titrable acidity, cry matter, ascorbic acid and chlorophyll content. Thus color attributes, sensory attributes and texture index be observed while breeding variety. Flower initiation in cole crops depends on a low temperature stimulus. Vernalization requirement varies between different types and between varieties within individual type. Brassica crops are predominantly cross pollinating and bees and Diptera are the pollinating agents. The isolation distance is 1000-1500m in cole crops. The two types of varieties are open pollinated variety and hybrids. Some varieties of cabbage, kale and kohlrabi are used as fodder and animal feed. Functional food  It refers to those fruits and vegetables which have not only nutritional value but also prevent disease. Besides anthocyanins and carotenoids which are antioxidants, other antioxidants include ascorbic acid and glucosinolates in Brassicaceae. Glucosinolates have potential for preventing cancer. Principal glucosinolates identified in cabbage and kale include sinigrin, glucoiberin, glucobrassicin, progritrin, gluconapin, glucoraphanin (Rosa, 1999). Glucosinlates have allelopathic roles in plants. It provides resistance against fungi, nematodes, herbivores and weeds (Rosa et al., 1970). Improvement of aromatic profile could affect taste in Brassica vegetables and it is strictly related to glucosinolatesisothiocynates system of Brassicaceae. Glucoraphanin whichleads to production of sulfurafane is present in broccoli. Main breeding objective in development of new cultivar

Crop Evolution and Genetic Resources

10.16

in broccoli is the isothiocynate (glucosinolate precursor) enrichment of broccoli. To achieve this introgression of B. villosa genome into standard broccoli breeding is practiced. Table 10.7  Showing different vegetable crops of the Brassica oleracea B. oleracea (Cole crops)

Groups

Crops

Organ used

Acephala group

Kale and collards green

Leaves (Non head)

Alboglabra group

Chinese broccoli

Botrytis group

Cauliflower, Romanesco, broccoli and broccco flower

Inflorecences

Capitata group

Cabbage (white, red, savoy).

Leaves surrounding terminal bud (Head)

Gemmifera group

Brussels sprouts

Enlarged axially bud

Gongylodes group/var

Kohlrabi

Swollen stems

Italica group/var

Broccoli

Inflorecences

Var. sabouda

Savoy cabbage

Here Botrytis group of vegetable crops and other varieties of B. oleracea constitute the GP1 and other species, B. carinata, B. juncea, B. napus, B. nigra and B. rapa constitute the GP2. The GP3 includes related genera of Brassica crops such as Diplotaxis, Enarthocarpus, Eruca, Erucastrum, Hirsehfeldia, Rhynchosinapus, Sinapis, Sinapodendron and Trachystoma. Table 10.8  Showing Different Vegetable Crops of the Brassica campestris Crop Brassica campestris

Ssp or var.

Common name

chinensis

Pak choi

nipposinica

Genome AA AA

oleifera

Turnip rape

AA

parachinensis

Choy sum

AA

perkinensis

Chinese cabbage

AA

rapifera

Turnip

AA

tricularis

sarson

AA

10.4  ONION Onion (Allium cepa) is a bulb or common onion, a bulbing vegetable. It belongs to family Liliaceae Bulb is formed by thickening of leaf-base at a short distance above the stem. In other words, bulbs have a reduced disc-like rhizome at the base. Outer leaf bases are thin, fibrous and dry. The center of origin is Pakistan, Iran. Onion bulb is formed by swollen bases of leafsheaths whereas garlic bulbs consist of cloves which are buds from the axil of leaves. A. fistulosum (Chinese origin) is Welsh or Japanese bunching onion,

Origin and Genetic Resources of Vegetable Crops

10.17

A. x proliferum is Egyptian onion and A. canadense is Canadian onion (Jones and Mann, 1963). A. fistulosum does not produce real bulb and is perennial, propagated through seed or vegetative propagation. The closest relative of A. fistulosum is A.altaicum (supposedly progenitor), which contributed as primary gene pool and can be grown in subtropical region. Some varieties of A. cepa called shallot and potato onion which produce multiple bulbs. Shallots have finer flavour. Shallots (or scallions) grow in cluster at the leaf base. Like garlic most varieties are smaller than onion. Potato onion produces larger bulb but is similar to shallots. Onion and shallots are different developmental stage of the same species, A. cepa. A. cepa var aggregatum includes shallots and potato onion. A. cepa var. aggregatum with 2n = 16 has origin in tropical central and west Asia. Tropical and subtropical shallots have tolerance to hot and humid climate, better tolerance to diseases and pests and longer storage life than common onion. It is one of the major vegetables used as condiments and is adapted to rain-fed (short growing season). Onion is cross pollinating species. Flower is perfect and there is presence of genetic and cytoplasmic (S-cytoplasm) male sterility. Umbel contains more than 2000 tiny flowers. Umbel consists of the spathe and the flower. Flower stalk is called scape or seed stem. It is one node extension of the stem. Bulb formation in onions stats only after a certain day length is reached. The related species of A. cepa are given in the table 10.8 below. Onion, garlic, shallots and leek are sulphur rich. Garlic contains isothiocyanates and cyanides. Different edible species of the genus Allium are given in the table 10.8 below with distinguishing characteristics. Pungency in onion is due to sulphur-rich volatile oil. Milder cultivars are used for raw consumption in salads. Flavonols particularly quercetin provide color, texture and taste in onion. Amount of quercetin tends to be highest in red and yellow onion and lowest in white onion. Globe shaped onions are white, yellow, redwith strong flavour. Bremuda onions are large flat, white or yellow and mild in taste. Spanish onions are large, sweet and juicy, yellow to red in color with mild flavour whereas Italian onions are flat and often red and mild in flavour. Pearls onions are used for making pickles. Thus the traits for improvement in onion include bulbe weight, shape, firmness, soluble soild content, pungency and sugars (glucose, fructose, sucrose). Dormancy is considered while practising selection for storage quality. Produce from summer harvest goes to fresh market. The fresh market traits include yield, single centred bulbs, higher bulb diameter and low pungency. Storage onion comes from harvest during short days. Skin retention and storability are the main traits. Cooking onion should be medium sized, globe shaped and mostly yellow-brown color, more compact and firm bulbs. Storability depends on bulb firmness and sprout dormancy. Internal bulb quality traits include pyruvate and carbohydrate contents. CMS is used for development of hybrid onion. There are two types of cytoplasm, CMS-S (alloplasmic is most widely used and it is thermostable. CMS-T (autoplasmic) (Berninger, 1965) male sterility is restored by a dominant allele A or dominant allele at two complementary functioning loci, B and C. There is one restorer gene with two alleles (M, m). CMS-galathum is the new source of CMS in which cytoplasm from A. galathum is put into the nuclear background of onion. In onion the isolation distance

10.18

Crop Evolution and Genetic Resources

to be maintained in hybrid seed production program is 4km and the male to female ratio varies from 1:2 to 1:4. Bolting resistance is required to prevent yield loss in onion. Bulb color ranges from dark purple to pink, dark yellow to very pale yellow and to even brightness in the white. Bright yellow and very deep red onion lines are available. The economically important traits include long storage and high percent dry matter, bulb weight and diameter, bulb shape (extremely flat to oblong). Single center onions are preferred for producing round shaped onion and onion ring processing over multiple centers. Breeding objective in recent times have changed and there is demand of poor storage quality and lower soluble solids. Onions vary in pungency and one can have onion with lack of pungency. Pungency is important in cooking onions. Sulphur compounds give characteristics flavors and odours to Allium species. Qualitative and quantitative differences in the four ACSOs (S-alk(en)yl cysteine sulphoxides) that impart each Allium species its characteristic flavor are as follows. The ACSOs upon hybrolysis give flavor and pungency. 1. (+)-S-methyl-L-cysteine sulphoxide (MCSO). 2. (+)-S-propyl-L-cysteine sulphoxide (PCSO). 3. Trans-(+)-S-(1-propenyl)-L-cysteine sulphoxide (1-PECSO). 4. (+)-S-(2propenyl)-L-cystenine sulphoxide (2-PECSO). The flavor and lachrymatory effects in Allium cepa is due to high proportion of 1-PECSO content whereas it is due to 2-PECSO in Allium sativum. Salad onions should be mild in pungency, sweet and red for good flavor. Sweet and mild onion are used for fresh market. Firm and long storage type onions are required for processing and export and onions with a high percentage of dry matter and white color are required for dehydration. Dry matter should be greater than 20%, i.e. bulbs with high solids are required. These traits such as pungency, lack of pungency and sweetness are difficult to measure and show lots of G X E interaction. In India onions are grown in Kharif (short day) as well as Rabi season (long day) with some internal doubling. Rabi crop is the main crop for storage and export. Produce from Kharif is for the fresh market. Also, multiplier onions with several bulblets are grown in South India. South Indian onions are smaller than north Indian onions. Onions from Maharashtra, Punjab, Gujrat are big in size (40-65mm in diameter and flat to globe in shape) whereas onions from Karnataka are 25-35mm in diameter. Polyploidy is very rare in Allium cepa. Although triploid has been synthesized but two viviparous strains of A. cepa var viviparum (syn. A. x proliferum) have been reported with 2n = 2x  = 16 (diploid) and 2n = 3x = 24(triploid), respectively. There is one example of spontaneous polyploidy. One natural triploid onion cultivar ‘Pran’ is under cultivation in Kashmir from historical times. This viviparous onion is A. x cornatum. Ornamental Allium species include A. tuberosum, A. moly, A. tricoccum, A. cyaneum, A. giganteum (bulb circumference of 20-22 cm), A. neopolitanum, A. sphaerocephalum, A.caeruleum, A.unifolium, A. aflatunense (bulb circumference of 3 to 5 cm)., A. cristophii, A.karataviense (bulb circumference of 12 to 14 cm), etc. Seedlings of ornamental species with small bulbs flower in the second year of planting whereas seedlings of large sized

Origin and Genetic Resources of Vegetable Crops

10.19

bulb require 3-5 years to reach to flowering stage. Different species of Allium are given in Table 10.9 along with distinguishing characteristics. Table 10.9  Showing species, common name, characteristics and distribution of Allium Species

Allium cepa

Common name

Distinguishing characteristics

Onion, most impotant cultivated crop, 2n = 2x = 16

Predominantly cross pollinated seed propagated

Cepa var. aggregatum

Potato or multiplier onion and Produces fairly large bulbs Shallots (true shallots-not which produce multiple tops spring onion) and bulbs in the second year Cepa var. Top, tree or Egyptian onion Produces bulbils in proliferum flowerhead which may grow and bear similar bulbils themselves while still on the growing plant. A. sativum Garlic, most impotant cultivated crop, 2n = 2x = 16, diploid, 4x A. scordoprasum Serpent garlic Has a coiled, snake like flower stem A. ampeloprasum Great headed garlic, Giant or Leek like plant which Russian garlic, most impotant produces large garlic like cultivated crop cloves wild milder flavour than garlic Hexaploid seed sterile Leek (Sometimes called A. porrum), Europe and Japan, tetraploid (2n = 4x = 32), 6x

Kurrat

A schoenoprasum Chives (cultivated in temperate regions) Europe and Asia, 2x – 4x A. tuberosum Rottler exSprengel or A. odorum

Chinese chives (China, Japan, Taiwan)

Bulb characteristics and mode of propagation Well developed bulbs, seed propagated -do-

Region/gene pool GP1, Central Asia Commercially grown in Carribean and West Africa

-do-

Bulbs made of cloves, Outbreeder, clonal propagation Large bulb made up of big cloves Bulb made up of large fleshy inner cloves and small, hard outer cloves

Cloves few or not present, seed propagated, Outbreeder, clonal propagation Similar to leek but smaller in -dostature with narrower leaves. Leaves consumed in salads or used as condiment Forms dense clumps and Poorly developed green leaves are used bulbs, Out breeder seed and clonal propagation Leaves are long and grass Poorly developed like, flattened but not bulbs but forms hollow. Blanched shoots and rhizomes which green leaves are consumed are not edible, vegetative propagation through bulbils formed as a result of apomixes, Seed propagated

Central Asia

Mediterranean and Near East

Elongated bases are used, generally blanched, Predominantly cross pollinated

Europe

Grows both in wild and cultivated states in China. (East Asia) Contd...

Crop Evolution and Genetic Resources

10.20 Contd...

Species

Common name

Distinguishing characteristics

A. fistulosum

Welsh or Japanese Bunching onion, most impotant cultivated crop, East-Asia, 2n = 2x = 16, diploid

Hollow leaves which are round in comparison to onion and chives. Leaves and false blanched stems are Predominantly cross pollinated used,

A. chinense G. Don

Rakkyo (SEAsia and Japan) Cultivated strains include diploid, triploid and tetraploid

Forms clump like chives but results in clusters of small bulbs. Can be used raw but mainly as pickles

A. ascalonicum

Shallots

A. vavilovi A. galanthum A. roylei A. altaicum A. pskenema A. oschaninii

Bulb characteristics and mode of propagation Poorly developed bulbs , seed or vegetative division, Cross pollinated

Small, well developed bulbs, bulb propagated, Outbreeder, clonal propagation Vegetative and seed propagated

Region/gene pool GP2, East Asia.

Native of eastern China, East Asia

GP1 GP1 GP1 GP2 GP3 GP3

Besides two above mentioned species in GP3 there are another 20 species from the subgenera Cepa, Reticulatabulbosa, Polyprason and Anguinum. There are 30 species in the subgenus Cepa. The two most closely related wild species of onion are A. vavilovi and A. asarense from Iran. The other onion species of importance from breeding point of view include A. ampeloprasum, A. bouddhae, A. obliquum, A. nutans and A. odorum as they can be sources of genes for pest resistance. The other species such as A. roylei, A. fistulosum and A. attaicum are also sources of useful genes. Breeding objectives in onion include increasing shelf life and productivity. Low moisture and high sulphur content increase shelf life of bulb in onion. There two routes of seed production. 1. Bulb to seed 2. Seed to seed. Bulb to seed route is suitable although it takes longer time. Flower is protandry. Pollination is through bees and flies and other insects. Isolation distance is 1000m. In the hybrid seed production the ratio of male and female is 1:4 or 1:8. Roguing of male fertile plants from MS female parent is done. Duration of anthesis is about 4 weeks. When 5% of the capsules on individual heads are shedding then go for harvesting. Seeds are black when ripe. In leek both seed to seed and root to seed systems are used for seed production. It is a biennial crop and flowering occurs in the second year after vernalization. Kurrat is harvested as green bunched. It is a green leafy vegetable spices. It is propagated from the cloves which are less pungent than garlic.

Origin and Genetic Resources of Vegetable Crops

10.21

Distinguishing features of various Alliums sp. A. cepa plant differs from A. fistulosum plant in that in case of former, there is a swelling in its scape mid way in its length whereas later has a straight, uniform scape. A. sativum does not produce bulblets around the main bulb whereas A. ampeloprasum has a single large bulb with smaller bulbs or cloves attached. In Chives and A. fistulosum flowers open first at the top of the umbel and then successively towards the base which is different than all species of Allium. Rakkyo is similar to chives except that it bulb, divides and looks similar to small dividing onions. Garlic commonly produces bulbils. In Leek no bulb like structure is formed and so elongated foliage base is eaten. In other words, leek is a non-bulb forming type. Karrat is a leaf like from of small stature, propagated by seeds, raised for edible tops.

10.5  GARLIC Garlic is used for flavouring food and for medicinal purpose. It is used in making pickles, can be preserved in oil or vinegar and can be processed. Allium sativum is a monocot and belongs to family Allianceae. The primary centre of diversity is central Asia. Allium sativum is supposed to be a complex species comprising three main groups, namely, Sativum, Longicuspis and Ophioscorodon and two subgroups-subtropical and perkinense (Fritsch and Friesen, 2002). A. sativum ssp sativum (soft neck garlic) has mild flavour, cloves are smaller and high shelf life. A. sativum ssp. ophioscorodon (hard neck garlic) is closer to wild garlic with complex flavour, cloves are larger with shorter shelf life, skin slips off smoothly. They are topped with bulbils and tolerant to cold weather. The commercially grown types of garlic can be divided into four groups depending on photoperiod and cold requirement-I. Violet or Asian (cultivated in subtropical regions) II. Pink (requires long photoperiod and low requirement for cold) III. white requiring long photoperiod and moderate to high requirement of cold and IV. purple requiring long photoperiod and long period of cold. Further, it can also be divided into two groupshard-neck and soft neck garlic. Majority of the cultivated garlic is of soft-neck type which is easier to cultivate and has long shelf life. In hard neck garlic flowers abort and end into production of topsets whereas the soft neck garlic does not produce a scape. Wild ancestor of A. sativum is A. longicuspis which is endemic to Central Asia. Garlic is propagated through bulb. Species related to garlic and chives are given below in the Table 10.10. Table 10.10  Showing species, common name, method of multiplication and origin of garlic Species

Common name

Method of reproduction

origin

ursinum

Wild garlic

Produces seeds rather than bulbils (aerial bulblets) Native to Europe and Asia

vineale

Crow garlic

Produces aerial bulblets

oleraceum

Field garlic

Produces aerial bulblets

10.22

Crop Evolution and Genetic Resources

There are hybrids and open pollinated improved varieties in onion. It has been found that there is no difference in the yields and other traits between these two types of varieties which clearly demonstrates that improved open pollinated variety can give as much yield as hybrid variety can and this can be explained through genetics. Considering one locus with two alleles system (A, a) one can be able to select either AA or Aa which can give as much yield as Aa, the hybrid. It further demonstrates that inbred line (s) can give yield similar to hybrids variety.

10.6  FENNEL Saunf, Foeniculum vulgare is a spice crop. It is the sole species in the genus. It is a diploid with 2n = 2x  =  22. It belongs to family Umbelliferae. Origin is Mediterranean. It is cultivated as annual or perennial herb. It is a self pollinated crop but cross pollination can go up to 60%. Different distinct varieties within this species are F. vulgar var azoricum (Florence fennel) used as vegetable, F. vulgare var dulce (grown in France) sweet fennel, used as vegetable and F. vulgar var vulgare, bitter fennel, common fennel (grown in India, Russia, Romania, Hungary) used as spice. Both sweet and better fennel are varieties of the ssp. capillaceum from which oil is commercially extracted. F. vulgare var purpureum is being used as decorative garden plant. Seed is used as a digestive aid and breath freshner. F.vulgare ssp. capilaceum is a bitter fennel. Oil is extracted from both types of fennel. There is another ssp. F. vulgar ssp.piperitum.

10.7  CORIANDER Dhania, Coriandrum sativum is annual, herb cultivated as summer or winter crop although this crop can be raised round the year. It belongs to family Apiaceae (Umbelliferae). It is native to Sothern Europe, North America and South Western Asia. It is a diploid with 2n = 2x = 22. Both leaves and seeds are consumed. Seed is used as spice and leaves as herb. Seed contains antioxidants, terpene, linalool and pinene. Leaf is a rich source of vit A and C and Ca, Fe, Mn and Mg and carotene. Leaves have citrus flavor. 2-3 cuttings can be taken easily. Ripe fruits contain monoterpene alcohol, linalool and unripe fruits and vegetative parts contain aliphatic aldehydes and fetid like aroma. Volatile oils are extracted from coriander from which essential oil is produced. Harvesting at leaf stage improves seed yield. This is also seen in case of chickpea. There are two types of varieties in this species. C. sativum var vulgare the bold seeded (large seed size) variety, 3-5 mm in diameter, 1000-seed weight >10gm and oil per cent of 0.1 to 0.35. It is commonly grown in tropical and subtropical regions. The other is small seeded variety, C. sativum var microcarpa, 1.5-3 mm in diameter and 1000-seed weight 200gm/fruit. There are two types of growth habit in Capsicum-indeterminate and determinate. Breeders are breeding for new ideotype in these

Crop Evolution and Genetic Resources

10.32

two categories. Indeterminate chili plant of 18-24" tall, erect and compact and determinate ideotype of single unbranched stem with one or two fruit/node with branched, compact terminal cluster. Flavor traits include sweetness, sourness, bitterness, saltiness and aroma. Sweetness is primarily due to glucose and fructose and the two together constitute 5-10%. At maturity sugar is converted to glucose and fructose in similar molar ratio through acid invertase. Acidity in capsicum is mainly due to citric acid, malic acid and ascorbic acid. Aroma traits include sugars, organic acids and volatiles. Mature fruit color of capsicum is due to carotenoids of which capsanthin is the major constituent. The other components include capsorubin, zeaxanthin and b carotene. Anthocyanin and chlorophyll determine immature fruit color. The nutritional components include flavonoids, vitamins, pigments and pungency. The post harvest traits include water loss and firmness. Table 10.15  Showing different species of Capsicum, their center of origin and ploidy level and growing habits Species

Ploidy level

Center of origin

Characteristics

Annual/perennial

C. annuum

2n = 24 Cultivated

Mexico-primary Sweet and hot pepper, white corolla, centre; Guatamala- single fruited node, calyx teeth present, secondary centre rotate, corolla throat spot none, anther colour blue-purple

Annual, flower/fruit born singly, Sweet pepper

C. frutescens

-doCultivated

Amazonia

Spices, calyx teeth-none, tan seed, up to 5 fruits per node, white to greenish white corolla color, rotate corolla throat spot none, anther colour blue

A shrubby perennial with several flowers on each inflorescence, Chilli pepper

C. chinensis

-doCultivated

-do-

Spices, tan seed color, 1 to 3 fruits per node, calyx teeth present, rotate corolla throat spot none, anther colour blue

C. pendulum

Peru and Bolivia

White corolla, pendent fruit pedicels and leaf petiole, calyx teeth, rotate present seed colour black, anther colour yellow

C. pubescens

-do- Cultivated

Spices, black seed, purple corolla, calyx teeth present, rotate corolla throat spot none, flower/node-1, pale anther colour

C. galapogense

Galapogos

Calyx teeth–none, tan seed color, rotate corolla throat spot-none, flower/node-1

C. chacoense

Tan seed corolla throat spot-none, flower/ node-1, yellow anther color

C. schottianum

Black seed, calyx teeth-none, rotate corolla throat spot-yellow, flower/node5-7, yellow anther colour Contd...

Origin and Genetic Resources of Vegetable Crops

10.33

Contd...

Species

Ploidy level

Center of origin

Characteristics

C. praetermissum

Tan seed, white to lavender corolla, calyx, teeth present, rotate corolla throat spotgreen-yellow, flower/node-1, yellow anther colour

C. eximium

Tan seed color, white to lavender corolla, calyx teeth present, rotate corolla throat spot-yellow, yellow anther colour, flower/ node, 2-3

C. cardenasii

Tan seed color,blue corolla, companulate, shape corolla, calys teeth present corolla throat spot-greenish-yellow, flower/node1-2, pale blue anther colour

Annual/perennial

C. microcarpum C. baccatum

Cultivated

Spices, tan seed color, flower/node-1-2, yellow anther colour

C. tovari

The three species, namely, C. frutescens, C. pendulum and C. microcarpum have similar karyotypes, each with three similar, easily distinguishable chromosomes (one large satellited, one smaller satellited and one having subterminal constriction and a heterochromatic distal region) (Ohta, 1962). Like Zea mays developed from its fully infertile wild ancestral species, teosinte, a wide range of fruit shapes and sizes (from the small fiery Tabasco to the sweet bell type) in Capsicum have evolved as a result of selection in wild species by Indian farmers. There are two types of male sterility present in Capsicum. 1. Genetic male sterility and 2. Cytoplasmic male sterility. Genetic male sterility is conditioned by two different recessive genes (Shifriss and Frankel, 1997). Genetic male sterility has been used to develop commercial hybrids in bell and hot pepper types. CMS is not unstable in Capsicum. Fertility is restored in cooler temperature. Also genetic background of CMS line and maintainer are influencing the expression of the sterility trait. C. annuum has been given more importance in breeding program as there is lot of diversity for fruit and plant types within this species. Further, more varietal types are found within C. annuum, C. chinense and C. baccatum. Breeding objectives nowadays include developing pepper as nutrionally potential source of antioxidants and phytochemicals, higher level of ascorbic acid, flavonoids and carotenoids. The sweet pepper varieties, the “bell” types and long, “tapered prolific frying” types are characterized primarily by absence of the capsaicin-secreting glands on the plancenta. Varieties of peppers must show uniformity of shape, often a four-lobed thick walled fruit weighing more than 150gm each, uniform, dark green or a bright red color with a high gloss. The pungent small fruited, thin walled, prolific types are used as either to make ‘hot sauce’

Crop Evolution and Genetic Resources

10.34

or dried chili powder but paprika is made from mild pungent forms. There is lot of variability 1 in the genus C. annuum. Fruits can vary from __ ​   ​ " to 10" and from very slender to more 4 than 4" wide. Further, one can find large, sweet, thick walled and heart shaped fruits. Table 10.16  Showing different types of cultivar groups in Capsicum annuum, one exotic cultivar group of C. chinense and one cultivar group of C. frutescens. Species

Group

Fruit Characteristics(fruit size, shape, colour, wall thickness, pungent / nonpungent, etc.)

C. annuum

Bell group

C. annuum

Pimiento group

3-5” × 2-4”, smooth, thick walled, 3-4 lobed, square to rectangular, mostly non-pungent, usually green, tapering or longitudinal section 1 Large, heart shaped, 2 ​ __ ​  -5” × 2-3”, thick walled, green turning red 2

C. chinense

Squash or Chinese group

Small to large wider than deep, non-pungent, mildly pungent,

C. annuum

Ancho group

C. annuum

Anaheim group

Mexican chili, large heart shaped, 4-6” × 2-3”, smooth walled, mildly pungent, stem indented to top forming cup 3 Long green chili, 5-8” × __ ​   ​  -1”, tapering to a point, smooth flesh, medium thick to dark 4 green, moderately pungent to sweet

C. annuum

Cayenne group

1 Long, slender, 5-10” × __ ​   ​ -1”, thin walled, medium green, turning red, wrinkled, irregular 2 shape, highly pungent

C. annuum

Cuban group

1 3-6” × __ ​   ​  -2”, yellowish green, turning red, mild pungent, thin walled, irregular, blunt 2

C. annuum

Jalapeno

C. annuum

Small hot

Elongated, 2-3” × 1-2”, rounded, cylindrical shape, smooth and thick walled 1 1 1 ​ __ ​  -3” x ​ __ ​  -1”, medium to thin walled, green turning red, highly pungent 2 4

C. annuum

Cherry group

Small. Spherical, 1-2”, flattened, thick flesh, green turning red

C. annuum

Short wax

C. annuum

Long wax

2-3” × 1-2”, yellow, turning to orange-red, smooth, medium to thick walled 3 1 3-5” × __ ​   ​  -1 ​ __ ​ ”, yellow turning red, pointed or blunt 4 2

C. frutescens

Tabasco

Slender, 1-2” × 1/4”, yellow to yellow green, highly pungent

Pepper  Neutraceuticals and phytochemicals such as carotenoids, flavonoids, ascorbic acid, phenolic compounds and the pungent capsaicinoids are powerful antioxidants (Crossby, 2005c). Unique flavoids are found in the processed hot pepper such as chipotle and habanero and these are used by fast food industry. Fruit quality traits in hot red pepper such as cayenne or Asian types include high pungency, high ASTA, pleasant aroma, thicker flesh and good dry matter content. These also apply to green chilies and paprika types except pungency. Hot pepper for fresh market should have thick firm flesh, and moderate pungency levels. High yield and earliness and large fruits are important traits. Nutritive values related to presence of antioxidant compounds and phytochemicals, high levels of ascorbic acid, flavor and caroteoids.

Origin and Genetic Resources of Vegetable Crops

10.35

Development of haploids in pepper  Haploids are developed using parthenogenesis from haploid female or male nuclei in the embryosac. Further, haploids can be produced using a number of methods such as interspecific hybridization, by irradiation of bud and pollen, by chemical treatment of pollen, use of N2O gas treatment of the embryosac and through in vitro pollen culture (Chase, 1974). In nature haploids in pepper occur through process of polyembryony. Polyembryonic seeds produce 2-2n twin seedlings (Pochard et al., 1979). The frequency of occurrence ranges from 1 per 1,000 to 1 per 10, 000 plants which is quite high. Polyembryony is affected by environmental conditions. In comparison to green house environment polyembryony is found more in open field grown pepper. n-2n twin seedlings are produced from synergid and a fertilized egg. nucleus, respectively and n-n twin seedlings are developed from synergid and unfertilized egg nucleus or from a division of synergid nucleus. Vines  Foods and spices from tropical vines include sweet potato(accountable for 1/5th of the global root crop), yams, passionfruits, cucumber, gourds, squashes, pumpkins, watermelons, numerous beans, vanilla and black and white peppers. Ther are three types of growth habits. 1. Twiners 2. Tendril climbers 3. Root climbers. Twiners need thick support whereas tendril climbers require thin slender support. Root climbers are armed with extensive adhesive root lets. Vines show leaf heteroblasty (polymorphisms), i.e., producing leaf of different forms and also produce different shoot morphologies. Vines have fluted or lobbed xylem, interrupted by extensive rings or plates of soft celled rays and parenchyma. This structure allows the slender stem to act like cables. The movement of carbohydrates from base to upper portion of plant can be due to different characteristics. Many vines have massive below ground organ or they can generate root pressure to refill the emptied xylem or create osmoticum to resist drought. Twiners or tendril climbers have grasping organs. Twiners move through rotation of shoot apices and irritable tendrils. Vines usually show high prevalence of monoecy, i.e., they produce separate male and female flower on the same plant. Twining is the most primitive vine growth form and tendril climbing is the most advanced form (Putz and Mooney, 1992).

10.14  CUCURBITACEOUS VEGETABLE Cucurbitaceal contains most important cucurbit crops such as Cucumis, Cucurbita and Luffa.

Cucumis The genus Cucumis comprises of about 40 species but economically important species are cucumber (C. sativus), muskmelon (C. melo) and the West Indian gherkin (C. anguria). It belongs to family Cucurbitaceal Classification study of species has revealed four groups: 1. C. anguria. This group includes seven other species. 2. C. metuliferus 3. C. sativus 4. C. melo, C. humifructus and C. sagittatus (Table 10.17). It is a long trailing, annual and perennial herb with angular or lobed leaves, simple tendrils and branched and hirsute stems. Flowers are yellow and are fascicled or solitary and are usually trimerous, rarely pentamerous and

10.36

Crop Evolution and Genetic Resources

often borne at every node. Fruits contain many seeds which are either tan or white. Two major genes plus modifiers determine whether the plants are monoecious (male and female flower on the same plant), gynoecious (only female flowers), gynomonoecious (mainly female flowers but a few male flowers), andromonoecious (bisexual plus male flowers) or hermaphrodite (only perfect or bisexual flowers). Parthenocarpy is determined by one gene and this trait is required under insufficient pollinators conditions. Cucumber and musk melon are predominantly cross-pollinated whereas water melon and squash are cross-pollinated. Watermelon is a rich source of potassium. High K can reduce the risk of high blood pressure. Family-Cucurbitaceae Subfamily-Zanonioideae Subfamily-Cucurbitoideae Tribe-Melothrieae Genus-Cucumis Subgenus-Cucumis Species-C. sativus var. sativus var. hardwickii C. hystix Subgenus-Melo Species-C. melo subspe. agrestis subsp. melo Cucumber  The genus Cucumus is divided into two subgenera. Cucumus (2n = 2x = 14) and Melo (2n = 2x = 24). The subgenus contains 5 cross fertile species groups (Jeffery, 1980). The subgenus Cucumus comprises 3-4 Sino Himayalan species including C. sativus (2n = 2x = 14), C. hystrix (2n = 2x = 24). C. sativus has several botanical varieties including C. sativus var. sativus the cultivated cucumber and var. hardwickii, a wild free-living species, a wild relative of C.sativus var. sativus (see tables). In the subgenus Melo, C. melo species contains subspecies-agrestis and subspecies- melo. The GP1 include C. sativus var sativus, var. hardwickii and C. hystrix. C. hystrix crosses with C. sativus var. sativus and the F1 upon chromosome doubling produces amphidiploid called C. hystivus. The GP2 includes wild African Cucumus species of varying ploidy levels which are cross-incompatible with C. sativus (den Nijs and Custers, 1990). C. sativus is sexually incompatible with nearly all other Cucumis species because n = 7 in C. sativus and n = 12 in C. melo and most wild Cucumis species. Source  Sink relationships provide the practical constraints on fruit development. The breeding objectives include development of high quality fruit (i.e., brine quality), high carotenes and resistance to diseases.

Origin and Genetic Resources of Vegetable Crops

10.37

Sex in cucumber  Sex expression in cucumber is regulated by a balance between auxins, abscissic acid and gibberellins (Galun, 1959). The genetics of sex is explained by a 3-gene model, F, M and A, i.e three major genes determine sex types. The F-locus influences the degree of femaleness (FF > Ff > ff) whereas M locus determines whether flowers are unisexual (M-) or bisexual (mm). A conditions increased male tendency when a plant is homozygous recessive (aa) and ff. Interaction between these loci yield the basic types of sex found in Cucumber. Sex has effect on yield. Total yield over multiple harvests is not affected but early yield is affected. F1 from Gynoecious × Gynoecious and Gynoecious × Monoecoius crosses produces significantly higher yield in the first harvest than monoecoius × monoecious hybrids. Besides hybrid development, improved inbred line extraction is the objective which is achieved through carrying out population improvement program. Sex determination in cucumber  Sex expression in cucumber is determined by three loci, m, F and a, respectively. M locus controls the specificity of the stimulus to develop primordial staminate and pistillate flowers whereas m +/– genotypes are strictly declinous. F locus determines the degree of female tendency. The F allele is partially dominant over F+ and intensifies femaleness. This locus is strongly influenced by environmental factors such as photoperiod, temperature, etc. and background effect. The aa at a locus intensifies male tendency. Male intensification is also dependent on genotype at F locus. Combinations of genotypes at these loci yield different basic sex types as shown in the Table 10.16(a) below. Table 10.6(a)  Showing genotype and the corresponding phenotype of different types of sexes in cucumber Phenotype

Genotype Locus m

F

a

Andromonoecious

–/–

F+/F+

a/a

Monoecious

m+/m+

F+/F+

–/–

Hermaphrodite

m/m

F/F

–/–

Gynoecious

m+/m+

F/F

–/–

Sex expression in cucumber is also influenced by environmental factors. Low light intensity and low temperature lead to a higher proportion of females and high light intensity and high temperature favor development of male flowers. Yield in cucumber will not only depend on the number of female flowers (and thus the number of fruits) a genotype produces but also on the vegetative growth which supports high yield. There are two types of cucumber considering the uses-pickling type (smaller length/ diameter ratio than slicer type, light colored skin with more pronounced warts (tubercles)) and slicing type (white spined and dark green exterior color, thicker skinned and fruit length/diameter (fruit conformation) equal or greater than 4.0. The main breeding

Crop Evolution and Genetic Resources

10.38

objectives had been to reduce seed cavity size, seed maturation rate and placental hollowness. These days objective are to overcome brining defects (soft center) and fruit bloating. Fruit morphological characters include skin color, spine color, present or absent of warts and spines. C. sativus var. hardwickii is the source of the sequential fruiting trait. Cucurbitacin which imparts bitterness is a tetracyclic triterpene, often present in the species of Cucurbitaceae. It attracts cucumber beetles and thus resistance is associated with low cucurbitacin. C. moschata and C. mixta have hard woody stems with comparatively little parenchyma. C. maxima has softer stem and more widely scattered vascular bundles. C. moschata is used as bridging species in order to transfer gene for disease resistance from C. martinezii to C. pep. Here C. martinezii is first crossed with C. moschata and the F1 from this cross is further crossed to C. pepo. Table 10.17  Showing different species of genus Cucumis, their ploidy level and origin Species C. sativus

Common name Cucumber

C. hardwickii

C. melo

Muskmelon

Ploidy level

Origin

Characteristic

2n = 2x = 14

Asia (India)

Monoecious, GP1

2n = 2x = 14

Asia

A close relative of C. sativus, GP1, multiple fruiting and branching habit

2n = 2x = 24

Africa, India

Young fruits have hairs but not operculate spines, GP2

C. humifructus

2n = 2x = 24

-do-

C. sagittatus

2n = 2x = 24

-do-

2n = 2x = 24

Spiny fruited species, GP2

C. anguria

West Indian gherkin

C. haptadactylus

2n = 4x = 48

C. ficifolius

2n = 4x = 48

C. metuliferus

African horned cucumber

2n = 2x = 24

Citrullus lanatus

Water melon

2n = 2x = 22

C. hystrix

.

C. zeyhri

GP2 South Africa

2n = 24

A close relative of C. sativus

2n = 48

GP2

followed by a pistillate flower. Cucumis melo var. flexuosus, a variety of musk melon is Armenian cucumber or kakri. C. melo is closely related to cucumber. C. sativus. Current practice of growing cucumber involves mixing of seed of monoecoius pollinator with seed of a gynoecious to develop gynoecious hybrid variety. This type of variety has been replaced by breeding parthenocarpic gene into gynoecious variety in which fruit development takes place without pollination. A gynoecious line is perpetuated by treating the plants with a growth regulator to induce it to produce male flower or by crossing it with an isogenic

Origin and Genetic Resources of Vegetable Crops

10.39

line having perfect flower. Parthenocarpic cultivars are suited for protected cropping (green house cultivation) where insects are scarce and there are inefficient pollinators. The current practice is to develop gynoecious varieties that need to be grown with monoecious line for pollination. Gynoecious line is preferable as female plant because it can not self pollinate and all the seeds that it produces is hybrid. All Cucurbita species are susceptible to frost. Cucumber produces male and female flowers in equal proportions but it has the tendency to produce male flowers in the beginning . Under long day and high light intensities it produces more male flowers whereas under short day and low light intensities it produces more female flowers. Isolation distance is 1500m in cucumber. For obtaining parthenocarpic fruit (seedless fruit) growth regulator is used. Watermelon  Citrullus lanatus syn. vulgaris belongs to family Cucurbitaceae. It is a very rich source of K which is good for people having high blood pressure. This crop is native to South Africa and the secondary center of origin is China. There are four species of water melon as given in the Table 10.18. C. ecirrhosus is more closely related to C. vulgaris. Seedless water melon is triploid. Polyploids can be identified by counting the number of chloroplast in stomatal cells (stomatal guard cells). Stomatal chloroplast number in tetraploid plants is twice that of the diploid. Flow cytometry is also used for the detection of polyploids, mixoploids. In this technique analysis of nuclear DNA content is based on the analysis of the relative fluorescence intensity of the nuclei stained with a DNA fluorochrome. In most plants DNA content of the nuclei is isolated from the young leaf tissue. This analysis yields a histogram showing a dominant peak corresponding to the nuclei at the G1 phase of cell cycle (Dolezel, 1991). Ploidy level is determined by comparing the peak position of the G1 nuclei of a plant with the known ploidy with that of unknown sample. This method has advantages over chromosome counting in that it is convenient i.e. sample preparation is easy. It is rapid and several hundreds samples can be analysed daily. It does not require dividing cells and it is a non-destructive, i.e. one sample can be prepared from a few milligrams of the leaf tissue. Cultivars are mostly monoecious but some cultivars are andromonoecious. Pollination is through honeybees. Female or hermaphrodite flowers occur in every 7th leaf axil and intervening axils bear male flowers. Tetraploid x diploid cross will lead to production of triploid, seedless water melon. There are two types of plants-Andromonoecious and monoecious. These types of plants promote cross pollination. Isolation distance in production is 1000-1500m. Sex is under control of one locus (A) with two alleles system. Andromonoecious condition is under control of recessive gene, aa whereas monoecious condition is under control of dominant gene, AA. Sex is influenced by environmental factors such as temperature, humidity, light and nutrition. This crop shows lack of inbreeding depression. Cross-pollination is through honeybees (Apis mellifera) and bumble bees (Bombus impatiens). 85% of cross pollination is due to honeybees. The rate of outcrossing is affected by spacing, genotype and the climatic condition besides insects. At spacing of more than 10mt the rate of outcrossing is zero. In a typical water melon cultivar number of pistillate flowers (either

Crop Evolution and Genetic Resources

10.40

female or hermaphrodite) is low with a phenological interval of 4-15 male flowers. Bitter and wild race of C. vulgaris is the ancestor of cultivated watermelon. There is also non-bitter and wild race of C. vulgais (Shimotosuma, 1963). The leaves of watermelon differs from other Cucurbits in the that its leaves are pinnatified (lobed, 3-4 pairs of lobes) whereas leaves are non-lobed in all other Cucurbits. Further, edible part is placenta (endocarp) in watermelon whereas in all other Cucurbits it is mesocarp. This trailing vine grows up to 30feet and flowering starts 4-8 weeks after planting. Male flower appears first, followed by hermaphrodite or female flowers. The ratio of male to female or hermaphrodite flower is 7:1 but it can range from 4:1 to 15:1. Tetraploid watermelons have thicker leaves, slow stem growth and shorter stems than diploids. Number of chloroplast in each stomatal guard cells is 5-6 (10-12 total) in diploids in comparison to 10-14 (20-28 total) in tetraploids. Further, diploid watermelon can be distinguished from tetraploid by counting the chromosome number. Tetraploid is produced by treating shoot apex with colchicine at the seedling stage. Fruit production in tetraploid cultivars is limited by the availability of viable pollen which is required to induce fruit set. That is why up to 2/3 field is planted with triploid variety and up to 1/3 is planted with diploid variety acting as pollenizer in order to set fruits. Parthenocarpic fruit set which can be induced through either genetically or through application of hormone would allow the entire field to be planted with triploid cultivar. Bitterness trait in melon has come from C. colocynthis. Bitter flavor is dominant over non-bitter flavor. Table 10.18  Showing different species of genus Citrullus, their ploidy level and origin Species

Ploidy level

origin

Catullus lanatus syn. C. vulgaris

2n = 2x = 22, annual, cultivated African origin

C. ecirrhosus

Perennial

South west Africa, More closely related to C. vulgaris

C. colocynthis

Perennial

Morocco

C. rehmii Praecitrullus fistulosus

India, Pakistan

Acanthosicyos nandinianus

South Africa

C. naudinianus

Perennial 2n = 22

South West Africa

C. fistulosus

Annual, 2n = 24

India

Cucurbita The genus Cucurbita contains about 25-27 species and all are native to the Americas. Plants are annual or perennial, long running and climbing or short and bushy. Stems are normally angled or furrowed and often rooting at the nodes. Tendrils are often large and branched. Leaves are simple and deeply lobed. Flowers are monoecoius with creamy white to deep yellow corolla. Seeds are flat, ovate to oblong and with thickened margin.

Origin and Genetic Resources of Vegetable Crops

10.41

Seed color varies from white to buff and brown. Fruits from Cucurbitaceae family are used as salad (cucumber), cooking or vegetable preparation (all gourds) or picking (West Indian Gherkin) or dessert fruit (musk melon, water melon) or candied or preserved (ash gourd). Although vegetables are the sources of vitamins and minerals but cucurbits are not rich in these. Only pointed gourd and chow-chow are rich in vitamin C (531mg/100gm and 140mg/100gm, respectively) but seeds of Cucurbitaceae are rich in oil and protein, particularly in amino acid, methionine. Most cucurbits are annual, only chow-chow and pointed gourd have perennial habit. Further, most cucurbits are seed propagated when pointed gourd and chow-chow are vegetatively propagated. Majority of cucurbits are many seeded, only parwal and chow-chow have one or few seeds per fruit. Barring ridge gourd and snake gourd, all cucurbits contain cucurbitacin, a tricyclic triterpins. Cucurbits have branched stem, usually 3-8 branched, prostrate/climbing stems and can spread up to 9-10mt in cucumber and Lagenaria. They have long taproot system (175-180cm) and laterals are confined to top 60cm of soil. Finally, bottle gourd, ash gourd and pointed gourd are largely cultivated in river bed. In most Cucurbitaceae the breeding objective is to increase the female: male or hermaphrodite : male ratio or reducing the number of males prior to the appearance of first female flower on the vine. In all cucurbits except bottle gourd, flowers are bright yellow. Four species of Cucurbita, C. maxima, C. pepo, C. moschata and C. mixta produce squash and pumpkins. They are annual, herbaceous vines and numerous runner. C.lundelliana can be crossed with each of the four species. Interspecific hybrids involving cultivated species are highly sterile but amphidiploids have been obtained with some success.

Pumpkin vs Sqush Pumpkins are cultivars with round fruit and mature fruits are used whereas summer squashes refers to edible immature fruits. Mature fruits that are not usually round and that store well are called winter squash (Decker-Walters and Walters, 2000). C. pepo subspecies pepo is pumpkin and C. pepo subspecies texana is called ‘Acorn’ (Lorenz, 1949). They are winter squashes. They are grown for their mature fruits. Subspecies pepo have larger plant parts and fruits grow more quickly in comparison to subspecies taxana. Their major use is as winter squashes. Fruit is botanically called ‘pepo’. Among other species, C. argyrosperma and C. ficifolia are of less economic importance. C. argyrosperma is a putative ancestor of C. moschata. C. maxima and C. moschata are mainly winter squashes but some are also grown for their edible immature fruits (as summer squash). Summer squashes are the edible immature fruits of C. pepo which is easy to grow. It is a short season crop and fruits are harvested 2-5 days after anthesis (normally at 3 days). Fruit shape is most important component of summer squash quality. Fruit gloss is another quality trait. It is a sign of freshness and palatability. Flavor, nutritive value and texture are important as well in C. pepo. C. lundelliana, C. foetidissima and C. pedatifolia partially cross with C. ficifolia. C. argyrosperma subspecies argyrosperma includes three varieties

Crop Evolution and Genetic Resources

10.42

such as var. argyrosperma, var. callicarpa and var. stenosperma. There are two growth habits in Cucurbita-vines and bush. Wild Cucurbita species have generally vine plants. In C. pepo bush habit is due to the Bu allele (Bush habit). It is dominant to vine habit in young plant stage but recessive at maturity., i.e., uniform bush type appearance early in the season and then a more trailing phenotype in mid season. Bush type plants are early flowering, having higher ratio of female to male flowers and early maturing. Pumpkin and squash are to be improved for fruit color and morphology, increased productivity and for disease and pest resistance. In winter squash fruit size, shape and color are important. Eating quality is most often related to flesh color, consistency, flavor and sweetness. These traits are not that important in summer squash. Flesh quality includes dry matter of mesocarp. The main component of squash mesocarp is starch which is gradually converted into sugar. Dry matter (DM) varies according to balance between starch and sugar. Cultivars with DM too low in the beginning (or reduces during storage), if cooked are moist and fibrous which is unacceptable. Cultivars with DM too high initially will lead to dry flesh and low sweetness which is again unacceptable. Cultivars with DM of 20-30% and soluble solids of 11 to 13% are of the highest quality. Winter squashes are sources of antioxidants especially carotenoids (provit. A), also tocopherol (Vit. E) and ascorbic acid (Vit. C). Breeding is also for developing cultivars with high seed quality in pumpkin(increased fatty acids as well as tocopherol. Pumpkin seeds are rich source of phytosterol which reduces bad cholesterol level. Winter squashes and pumpkins are used as rootstocks for melon, watermelon and cucumber (Eldestein et al., 2004). There are five domesticated species of Cucurbita (see table 10.19) and 10 wild species in the genus ranges from mesophytic to zerophytic and from annual to perennial. Vigorous root system of Cucurbita species increases water and nutrient absorption. It provides resistance against biotic stress (mainly soil borne pathogens) and a source of endogenous hormones. C. moschata, C. maxima, C. argyrosperma and C. ficifolia are used as rootstocks. Wild mesophytic species C. lundelliana and C. okeechobeensis are cross compatible and the later can be crossed with C. ecuadorensis. C. lundelliana crosses with C. moschata, C. maxima, C. ficifolia are F1s are partially fertile. C. lundelliana can cross with C. pepo, C. argyrosperma and use of embryo culture can be made to generate F1 plant. Wild zerophytic species are weakly compatible with cultivated species, Cucurbita species. The eight cultivar groups of C. pepo are given in Table 10.20. Table 10.19  Showing different species of genus Cucurbita, their origin and ploidy level Species

Common name

Origin

Ploidy level

Characteristics

C. pepo

Summer squash, pumpkin

Mexico

2n = 40

Cultivated, annual, bush type, short internode

C. mixta

Winter squash

Mexico, Central America

2n = 40

Cultivated, annual

Adaptation

Contd...

Origin and Genetic Resources of Vegetable Crops

10.43

Contd...

Species

Common name

Origin

C. moschata

Winter squash, field pumpkin

Mexico, Central America

2n = 40

Cultivated, annual

C. maxima

Winter squash, large pumpkin

Nothern South America, Central America

2n = 40

Cultivated, annual, bush type, short internode

C. ficifolia

Fig-leaf gourd, Malabar gourd

Mexico, central America, northern South America

2n = 40

Perennial, cultivated

Lagenaria siceraria

White flowered gourd(bottle gourd)

Africa, the Americas 2n = 2x = 22

C. foetidissima C. martinezii

Characteristics

Adaptation

polymorphic Annual

Mesophytic Mesophytic

C. okeechobeensis C. lundelliana

Ploidy level

Perennial

Mesophytic, key species within mesophytic group

c. ecudorensis c. andreana C. sororia

All second sub group of species centre around C. sororia. It is probably closely related to C. pepo in the cultivated group

C. texana C. palmata

Xerophytic, closely related to C. moschata

C. digitata

-do-

C. cordata

-do-

C. cylindrica

-do-

Crop Evolution and Genetic Resources

10.44

Table 10.20  Showing eight edible cultivar groups of C. pepo (Adapted from Paris, 1986) Cultivar groups

Subspecies of C. pepo

Zucchini group

ssp. pepo

Cocozelle group

ssp. pepo

Vegetable marrow group

ssp. pepo

Pumpkin group

ssp. pepo

Scallop group

ssp. texana

Acorn group

ssp. texana

Straightneck group

ssp. texana

Crookneck group

ssp. texana

Pumpkin and squash  Pumpkin and squashes started with small fruits and bitter flesh(bitter taste) and domestication led to development of these fruits to be suitable for food with suitable seed and flesh. Melon  All species of Cucumis except C. sativus have 2n = 2x = 24. Melon is harvested immature. The sugar present in the fruit is sucrose. The recognized three species are C. melo, C. flexuosus and C. dudain. Many other species such as C. callosus, C. chate, C. conomon or C. momordica are now considered synonym of C. melo. Sex in melon  The table 10.121 shown below shows the genetics of sex and the influence of chemicals on the expression of sex. AgNO3 is the inhibitor of ethylene and ethrel is the precursor of ethylene. (Tables 10.21 & 10.22 showing effect of gene and chemicals on the expression of sex in melon.) Table 10.21  Showing the effect of gene and chemicals

Sex Determination in Muskmelon  Sex pattern in muskmelon is similar to cucumber but determined differently (Rowe, 1969).

Origin and Genetic Resources of Vegetable Crops

10.45

Table 10.22  Showing genotype, type of sex and its characteristics. Genotype

Sex

Characteristics

AAgg

Gynomonoecious

All female flowers with a few perfect

Aagg

Hermaphrodite

All perfect flowers

aaGG

Andromonoecious

Perfect and male flowers

AAGG

Monoecious

Female and male flowers

Sex expression can also be modified by hormone or chemical which can be beneficial in hybrid cultivar development program. Femaleness can be increased by application of ethephon or alar as in squash or the production of gynoecious stock can be maintained by the stimulation of male flower through the use of AgNO3 as is the practice in cucumber. Use of AgNO3 at the rate of 100-200ppm causes production of perfect flowers on the first 20 nodes of the gynoecious line (Owens, 1980) and thus this line can be maintained through sibbing or selfing. Although sex expression in both cucumber and muskmelon are controlled by ethylene, its pathway for control are different in the sense that GA is ineffective in melon (Rudich, 1980). High ethylene levels promote pistilate flower formation in cucumber, melon and squash but stimulate male flower formation in watermelon. Auxins control the evolution of ethylene. GA, in general, promotes maleness and is antagonistic to the action of ethylene (see chapter for more detail on the biosynthesis of hormones and interactions among hormones). Sex Determination in Cucurbita pepo  Ethylene regulates sex expression in cucurbits (Beyer et al., 1972). Two applications of ethylene at the two and four-leaf stage at the rate of 600ppm suppresses male flower formation completely during fruit setting stage (Shannon and Robinson, 1979). Ethephon application is effective in C. moschata like C. pepo but not precise in C. maxima. Fruit quality in melon includes traits such as sugar content, volatile compounds and flesh colour, fruit shape, skin color, netting and sutures. Developing neutraceutical foods such as fruits and vegetables rich in beneficial phytochemicals such as vitamins, antioxidants and minerals is requirement of the day. It is not necessary that the concentration of one particular molecule is always correlated with its final availability for human health. Melon seeds like seeds of squash, watermelon are rich in lipids and proteins (high energy source) and thus have good nutritional value. There are two types of fruits produced in melon- climacteric and non-climacteric. Climacteric fruits are associated with burst of respirational and autocatylytic ethylene production at maturity. Ethylene production independent traits include sugar, carotenoids production whereas ethylene dependent traits include volatile compounds, abscission, change of color and flesh softening. Decreasing the intensity of climacteric crisis enables to increase ‘shelf-life’ of the fruit. Recent classification on the basis of ovary hairyness of Cucumis melo considers the existence of two subspecies, namely, ssp. melo with long hairs and ssp. agrestis with

Crop Evolution and Genetic Resources

10.46

short hairs (Jeffery, 1985, 2000). Further, classification based on sex type and fruit traits shows six cultivar groups which was later revised to fifteen cultivar groups (Pitrat, 2008) as shown in the tables 10.23 and 10.24 below (Robinson and Decker-Walters, 1997). Primary and secondary centers spread from Eastern Asia to Mediterranean sea. Table 10.23  Showing different arlhran groups of Cucumis melo. Subspecies melo

Group Cantalupensis

Variety

Unique trait (s)

Cantalupensis (muskmelon)

Sweet, consumed mature

Reticulates

Sweet

Adana

Sweet

Chandalak

sweet

ameri

sweet

inodorous

Inodorous (winter melon)

Sweet, consumed mature

Andromonoecious

flexuosus

Flexuosus (snake melon)

Nonsweet, immature fruits used in salad, pickles or cooked

Usually monoecious, High acidity

chate

nonsweet

dudaim

Dudaim (mango melon)

nonsweet

momordica

Momordica (snap melon) Nonsweet Acidulous

agrestis

Taste

Canomon (pickling melon) Chinensis

Andromonoecious, monoecious

Andromonoecious Monoecious

nonsweet, immature fruits used in salad, pickles or cooked

High acidity

Sweet, immature fruits used in salad, pickles or cooked

Andromonoecious, Source of disease resistance for cantalupensis and inodorous cultivars

makuwa

Wild melon

tibish

Nonsweet

agrestis

nonsweet

There are two types of melon-climacteric (found in cantalupensis) cultivars and non-climacteric cultivars. In climacteric cultivars increase in respiration rate is accompanied by ethylene production and it has short shelf-life. In non-climacteric cultivars increase in respiration rate is not observed and has long shelf-life. In climacteric melon the aroma

Origin and Genetic Resources of Vegetable Crops

10.47

is due to acetate and nonacetate esters and alcohols whereas in non-climacteric it is due to aldehydes, organic acids and terpenes. Aroma is as a result of fatty acid, amino acid, phenols and terpenoid metabolism. Total soluble solid is an index of maturity and it depends on sugars (sucrose), organic acids and soluble pectin. Main organic acid is citric acid followed by malic acid, ascorbic acid, succinic acid, oxalacetic acid, etc. The nutritional content includes minerals, K, Ca, Fe, Mn, P and Zn, Vit. C and carotenoids (b carotene, lutein and zeaxanthin, pantothenic acid, folic acid). Sensory traits include color, texture (i.e., juiciness, fibrouness, firmness), aroma (volatile compounds) and taste (sweet, sour, salty bitter and umami sensation) besides morphological traits such as size, color and shape. Table 10.24  Showing different botanical varieties of muskmelon, C. melo(Adapted from Peirce, 1987) Botanical variety of C. melo

Characteristics

C. melo var. cantaloupensis

Medium sized fruit with tough unnetted warty rind (True cantaloupe)

C. melo var. reticulatus

Netted melons include aromatic melons and Persian melons, flesh color can vary from orange to green

C. melo var. inodorous

Lacks aromatic flavor

a. Casabas

Bright yellow, corrugated rind and white flesh

b. Crenshaws

Green, dull yellow to pale orange flesh at ripening

c. Honeydews

Creamy white rind at ripening and a light green flesh, very smooth skin

C. melo var flexuosus

Snake melon, slender, long shape and consumed immature, similar to cucumber

C. melo var. conomon

Small fruit with mottled skin, pickling melon

C. melo var. chito

Includes mango melon and garden lemon. Smaller fruits with acidic flavor, used for pickling

C. melo var. dudaim

Includes pomegranate melon. Small round fruit become very pubescent and have musky odor

C. melo var. momordica

Kakri

C. melo var. agrestis

Wild variety

C. melo var. callosus

Kachari

C. martinezii and C. lundelliana are closely related to cultivated species. C. moschata is the axis through which cultivated species are related to each other. The chromosome number is 2n = 40. Chromosomes are small and give dot like appearance and thus difficult to carry out cytogenetical study. There is no inbreeding depression reported in Cucurbita but F1’s have shown considerable heterosis or hybrid vigor. There are two subspecies in bottle gourd. L. siceraria siceraria (calabash) and L. siceraria Asiatic, the Asiatic gourd. L. sphaerica, wild melon is a close relative of calabash. There are four species of winter squash with pumpkin varieties in all of them.

10.48

Crop Evolution and Genetic Resources

Winter squash have hard, thick skin and must be peeled off before cooking. They are rich in vit. A, C, Fe and riboflavin. Summer squash have thin, edible skin and soft seed and requires little cooking. They are rich in Vit. A, C and niacin. Summer squash includes crookneck, zucchini (green and yellow), straight neck and scallop (pattypan).

10.15  PEA Pea (Pisum sativum) is discussed in the chapter 6. There are four types of peas. 1. Vining pea or garden pea, the immature seeds are used for freezing, canning. Pickling peas is also used as fresh vegetable. Some pods are consumed completely with immature seeds. Dry seeds of combing peas are processed or canned. It is also used as fodder crop. Forage peas are used for grazing, silage and hay making. Isolation distance for seed production is 20m. Peas are rich in vitamins and sugar. Vegetable pea is harvested as immature embryos while liquid endosperm is still present. There is requirement of more uniformity of the developmentl stage of seeds or pods, peas retaining a darker color and not becoming bleached. During maturation phase starch and proteins are accumulated and the level of sugar decreases. The different strategies of improving yield would revolve round maximizing the proportion of developing embryos of desired size at the right stage of development. The different approaches are as follows. 1. Selection for high number of flowers per node (Hardwick et al., 1979). 2. Development of a more determinate plant habit with a restricted number of flowering nodes. 3. Selection for simultaneous flowering at multiple nodes (Marx, 1977), more ovules/ node providing more embryos at the required stage. Multi pods where 3-4 pods are sucessfully held on a receme. In order to overcome the problem of fungal disease introduction of afila (af ) gene was made which converted leaflets into tendrils which led to the development of semi-leaflets pea (Snoad, 1974; Davis, 1977; Headly and Ambrose, 1981). Further, a more rigid canopy allows more light and air circulation deeper into the canopy and thus disease problem gets reduced. The resurfacing of an induced afila alleles expressed an intermediate form bearing a pair of leaflets in addition to the tendrils which offers further possibility for breeders to exploit. In peas there is problem of standing ability and thus plant architecture must be changed. Introduction of semi-leaflets form solved this particular problem to some extent but still there is problem of lodging even in the short strawed type. Thus what is required is to develop peas with stiffer stem. The proposed idelotype aims at broadening the upper section of stem, synchronizing flowering and clustering the pods at the top of the canopy rather than being spread throughout. Grafting in vegetable crops  Like grafting of woody plants herbaceous grafting has alo been practiced and found successful. Grafting is being used in melons-the cucurbits and members of Solanaceae family such as egg plant and tomato. Through grafting higher yield with high quality fruits with resistance to diseases (soil born pathogens), nematodes,

Origin and Genetic Resources of Vegetable Crops

10.49

insects and various abiotic stresses such as flooding, drought, salinity can be obtained. Three methods of grafting such as 1. Approach grafting, cleft grafting and tube or Japanese top-grafting have been used of which tube grafting is most common. It is used when plants are very small. Rootstock and scion plants are held together with a silicon tube-shaped clip. The rootstock for tomato is the interspecific hybrid-S. lycopersicum x L. jabrochaites. Rootstock for egg plant include egg plant (S. melongena) and other species such as S. torvum and S. aethiopicum. Egg plant can be grafted on tomato or tomato interspecific hybrid, L. esculentum x L. hirsutum. Further, S. integrifolium or interspecific cross involving S. integrifolium and S. melongena is used as rootstock. Cucurbits (watermelon, muskmelon and cucumber) can be grafted on interspecific hybrids of squash, C. maxima x C. moschata (producing more vigorous scion), bottle gourd (Lagenaria siceraria for chilling tolerance, figleaf gourd (Cucurbita ficifolia) or other melon (Cucumis melo or wild type). Muskmelon is best grafted on squash rootstock. Sponge Gourd and Ridge gourd  There are 5-7 species in the genus Luffa as shown in the table 10.25 given below (Chakravarty, 1959; Jeffrey, 1980). The centre of origin is Indo-Berma. Sponge gourd is very rich in Vit. C. It is a four month crop. Seed contains about 37-46% oil which has linoleic acid (about 65%) and stearic acid (about 19%). Four species are from the old world tropics and three from South America. Within L. cylindrica cultivated and wild forms exist. L. cylindrical var. aegyptica is a large fruited, smooth and cylindrical, less bitter cultivated form and produces best quality vegetable or sponge. L. cylindrica var. leiocarpa is a wild form occurring in Asia. L. acutangula is a ridged gourd, more thinner, bent or curved and more elongated than L. aegyptica. Only two species, L. cylindrica and L. acutangula are domesticated. L. operculata is a native of South America, is a cultivated form, has spiky skin and grown for strongly fibrous sponge, used for scrubbing house hold. The hybrid between L. aegyptica x L. acutangula shows reduced fertility. Interspecific hybrids are sterile or nearly so. Intraspecific hybrids within L. acutangula and L. cylindrica are fertile but within L. operculata hybrids are sterile. Biochemical studies have shown that L. acutangula, L. aegyptica and L. echinata form one group and they all contain flavones whereas L. graveolens and L. operculata are grouped together and they contain flavonols (Schilling and Heiser, Italics 1981). L. graveolens is more distantly related to L. acutangula than to L. echinata. There are three varieties of L. acutangula. L. acutangula var. acutangula(dome shcated), var. amara (wild, India) and var. forskalii (wild). All species of Luffa are diploid with 2n = 26. It belongs to family Cucurbitaceae and L. cylindrica is synonymous with L. aegyptiaca: The two other south American species are L. astorii and L. quiquefider besides L. operculata (Heiser and Schilling, 1988). Sponge gourd  Female flowers can be identified by having immature fruit at the base. Male flowers are held above the vine whereas female flowers are down directly on the vine itself. L. cylindrical crosses well with other species of the genus. Hybrids involving L. cylindrical x L. acutangula are found in cultivation.

Crop Evolution and Genetic Resources

10.50

Ridge gourd  The female flowers have small gourd shape below the flower whereas male flowers grow without the ball shape structure below the flower. Pollination is done by bees and beetles. While doing hybridization, pollination is done just before dark and by tapping the male flower on to the female flower. Table 10.25  Showing different species of genus luffa Species Luffa acutangula

Common name

Cutivated/wild

Ploidy level

Distribution

Ridge gourd

Domesticated

2n = 26

Asia

wild

L. graveolens L. cylindrica

Sponge gourd

(Monoecious) 2n = 26

Cultivated

2n = 26

L. aegyptiaca

Domesticated

2n = 26

L. echinata

wild

L. operculata

Medicinal vate

Asia

(Dioecism) 2n = 26 2n = 26

South America

Depending upon the different types of flowers plants are classified as given in Table 10.26 Table 10.26  Showing different types of flower Types of flower

Characteristics

Androecious

Only male

Monoecious

Male and female on the same plant

Andromonoecious

Male and hermaphrodite on the same plant

Gynomonoecious

Female and bisexual on the same plant

Gynoecious

Only female

Hermaphrodite

Bisexual

Snake gourd  Indian Archipelago is thought to be the place of orign. Wild forms occur in India, SE Asia and tropical Australia. This vegetable is good for people with heart problem. It is low in calorie and high in fibre content and has Ca, P, Fe, thiamine, riboflavin and niacin. Trichosanthes cucumerina var. anguina is a cultivated variant whereas T. cucumerina var. cucumeria is a wild variant. Both, interbreed freely. It has mucilaginous flesh like Luffa and the calabash. The length of the fruit can go up to 150cm. It has lace like flowers similar to pointed gourd. The flowers open only after dark. It is grown throughout the year. It is a good source of minerals, fibres and other nutrients Different species of the genus Trichosanthes are given in the table 10.27. Only three species have been recognized, namely, T. cucumerina, T. lobata and T. anguina and the former two species occur as wild. All are diploid with 2n = 22. Relationships among these three species are shown. T. anguina is supposed to have evolved from T. lobata which in turn could have evolved from T. cucumerina or T. anguina could have developed directly

Origin and Genetic Resources of Vegetable Crops

10.51

from T. cucumerina and T. lobata is a hybrid between T. cucumerina and T. anguina (Fig. 10.3). T. cucumerina

T. lobata

T. anguina

or

T. anguina

T. cucumerina

F1(T. lobata)

Fig. 10.3  Showing paths of evolution of T. anguina

Ash gourd  In ash gourd male flowers are found on long peduncles and the pistillate flowers on small stalk or are sessile. Benincasa hispida is a monoecious annual vine. However some cultivars bear hermaphrodite flowers. It is a diploid with 2n = 24. Benincasa is a monotypic genus with a single species. It is native to Asian tropics and thought to have originated in Java and Japan. It is widely cultivated in India and tropical countries. Mature fruit is eaten as vegetable. In India petha(sweet) is made particularly in U.P. This fruit is rich in proteins, fibers, sugar, P, K, Ca, Mg, Fe and Zn. It belongs to Cucurbitaceae. Tendrils are atypical of Cucurbitaceae. The yellow flowers develop 6 to 9 weeks after germination and fruit matures 2 to 3 months later. Ovary and young fruits are covered with hairs which are lost as fruit matures. Male flowers precede female flowers. The ratio of male: female flowers is 34:1. Flowers are large, 3.5cm length and 6.14cm diameter. Anthesis takes place in the morning from 4.30 to 7.30am and anther dehisces around 3-5pm. Stigma becomes receptive 8 hrs before anthesis until 18 hrs thereafter. Fruits vary in sizes, shapes and colours. Seeds also vary in sizes and shapes. Fruits of some modern varieties are up to 2m long and 45kg weight. Pointed gourd  T. dioica belongs to family Cucurbitaceae. It is a diploid with 2n = 2x = 22. The center of origin is India or Indo-Malayan region. Bengal-Assam area is the primary center of origin of this crop. It is a dioecious, perennial and vegetatively propagated vine crop. Pointed gourd differs from other Cucurbitaceous species in that it is dioecious and vegetatively propagated. Roots are tuberous with long tap root system. There are about 44 species in the genus Trichosanthes and out of which 22 species are found in India. Only two species, namely, T. dioica (pointed gourd) and T. anguina(snake gourd) are cultivated. The various species of Trichosanthes are given in the table 10.27. All species except T. cucumerina and T. anguina are dioecious climbers. T. dioica, T. anguina and T. palmata all have similar chromosome morphology. Fruits are rich in protein, vitamins A and C, tannins, saponins, alkaloids, mixture of novel peptides, tetra and penta cyclic

Crop Evolution and Genetic Resources

10.52

triterpens and Mg, Na, K, Cu and S. It lowers blood cholesterol and blood sugar. Juice extracted from leaves of T. dioica has medicinal value. It is available for eight months(from February to November). Vegetative propagation is through vine cuttings and root suckers. Seed germination is low. Vine can go up to 5-6 m and roots are tuberous and there is a long tap root. Flowering takes place from February to November and fruiting takes place 5 months after transplanting. Flowers are tubular white. For obtaining good yield female and male ratio be 9:1 as is there in case of papaya. Plants established from seeds may contain male and female plants in 1:1 ratio. Like other vegetables it is very susceptible to water logging. One can not determine the sex of the plant before flowering. Table 10.27  Showing different species of the genus Trichosanthes. Species of Trichosanthes

Ploidy level

Cultivated/wild

Breeding system

T. dioica

2n = 22

Cultivated

Dioecious

T. anguina

2n = 22

Cultivated

Monoecious

T. bracteata syn. T. palmata

2n = 44

T. cucumerina

2n = 22

Wild

Monoecious

T. lobata

2n = 22

Wild

Dioecious

T. nervifoli

2n = 22

Dioecious

T. wallichiana syn. T. multiloba

2n = 22

Dioecious

T. cordata

2n = 22

Dioecious

T. japonica

2n = 22

Dioecious

T. shikokiana

2n = 22

Dioecious

Use

Dioecious

T. cuspida

Medicinal value

T. incisa

Medicinal value

T. laciniosa

Medicinal value

T. kirilowii

Medicinal value

It can be taken round the year. It is dioecious crop rich in vitamins and Mg, Na, K, Cu and S. Propagation is through vine cuttings-pre-rooted (fleshy root) and fresh vine cuttings with 8-10 nodes and root suckers. Vine cutting is made in the fall of previous year and rooted during winter and planted in spring. The female and male ratio should be 9:1 in the field for proper fruiting. Vine can be left to grow on either ground or aerial support. There are two methods of vegetative propagation. First, cuttings of about 9” containing at least three nodes are taken and then in the first method either circular rings of the cuttings are made or cuttings are wrapped up in form of a cylindrical shape and put in the pit at a depth of 4”, covered with soil. In the second method, cuttings are planted in polythene bags containing soil. Here two of the three nodes are put inside soil. Irrigation is provided and be left for about a month. During that period rooting

Origin and Genetic Resources of Vegetable Crops

10.53

takes place. Plantings of this rooted cuttings are done during October-November. Female flower differs from male in that the lower portions near the vines are swollen. Spacing can be 5' × 5', 4' × 4' or 5' × 2'.

10.16  BRINJAL Aubergine or egg plant is Solanum melongena. The two other cultivated species are S. macrocarpum, Gboma aubergine grown in west Africa and S. aethiopicum, scarlet aubergine grown in central Africa. More than 16 species are there in the genus. Brinjal is native to India. The secondary centre of origin is China. Other species include S. xanthocarpum which has got medicinal uses and S. torvum which is a perennial, bushy plant, can be used as root stock and thus grafting on S.torvum will result in obtaining variety having resistance to root diseases that generally affect the crop when taken for second year. Heterostyly is found in brinjal. There are four types of flower. 1. Long style with large size ovary 2. Medium style with medium size ovary 3. Short style with rudimentary ovary 4. Psedo short style with rudimentary ovary. Flowers with long and medium styles produce fruits. Ideal varieties are i. With purple and oblong fruit and ii. Green and long fruit. Plant usually develop some spines and the degree of spineness depends on the cultivars. Color of the fruits varies from white, green, yellow, through degrees of purple pigmentation to black. Anthocyanins and phenolic acids are present in the flesh of brinjal and they have antioxidant properties. Further, anthocyanins and chlorophylls A and B are responsible for the great variation in color diversity. Male sterility, UGA1 has been used to develop hybrids in brinjal. There is failure of anther dehiscence in this type of male sterility. It is under control of single recessive gene. Cytoplasmic male sterility has been found in the backcross generations of interspecific cross, S. violaceum (female) x S.melongena (male). CMS is due to interaction between cytoplasm of female S. violaceum and nucleus of S. melongena (alloplasmic). It has also been obtained from back cross generation of the interspecific cross, S. gilo (S. aethiopicum) x S. melongena. One line with petaloid anthers and another line with vestigial, pollenless anthers were obtained from this cross. CMS is due to no dehiscence of anther and due to low pollen fertility. S. melongena plus E, F, G and H groups od species constitute the GP1 and all are interfertile. In brinjal boundary between primary, secondary and tertiary gene pool species are blurred and does not match exactly the limits as defined by Harlan and De wet (1971). GP2 species are crossable with S. melongena and GP3 species are difficult or impossible to cross with S. melongena. Fruit color in brinjal is due to anthocyanins-delphinidol and chlorophyll A and B. Combinations of these two with various combinations of their distribution patterns are responsible for fruit color variation. Bitterness in brinjal is due to two kinds of saponosides-glycol-alkaloids (solasonine and melongosides. The phenolic compounds include anthocyanins (phenols group of flavonoids) plus phenolic acids. Prickliness and hairiness in brinjal is linked to good organoleptic quality. Use of chimeric gene, DefH9-iaaM is used for genetic engineering parthenocarpy in brinjal. iaaM encodes for a tryptophane monoxigenase which is converted to indole-3-acetic acid. DefH9 is a

10.54

Crop Evolution and Genetic Resources

placental and ovule specific promoter, isolated from Antirrhinum majus and iaaM has been isolated from Pseudomonas syringae. Use of spray of chemicals such as auxin, tomatone, procarpil on flowers at anthesis results in development of parthenocarpic fruit. Mass of consumable flesh is larger sud-less fruit ratser than in seeded fruit. Hand pollination is relatively easy in this crop and thus hybrids can be produced economically. The flower is large with a stamina cone that releases pollen through pores at the tips of the five anthers. Anthers are removed a day before anthesis. Stigma is receptive at that time. Yield components in brinjal include size of the plant, number of primary branches, number of fruits / plant, number of days to flower and average fruit weight. Grafting  In Europe egg plant has been grafted on tomato, interspecific hybrid of tomato (L. esculentum × L. hirsutum) and wild species of tomato, S. torvum. In other words, cultivated variety of tomato, interspecific hybrid and wild species can act as rootstocks. S. torvum provied resistance to soil borne diseases, resistance to verticilium wilt. In Asia (Japan), S. melongena and its hybrids have been used as rootstocks for controlling Phomopsis blight. S. integrifolium i.e., S. aethiopicum or its hybrid (S. integrifoilium × S. melongena) as rootstock provides resistance to Fusarium and bacterial wilt. Egg plants and its relatives are also used as rootstocks for tomato. In Japanese graft decapitated rootstock under or above cotyledons is used, to which a scion is affixed and linked by a silicon tube. The problem with this type of graft is if the stem length of rootstock is adversely affected then the chances of passing of verticilium to scion increases. Wide hybridization  Wide hybridization can be achieved through ‘double pollination’ which has been found successful in Capsicum. In this method C. annuum is first crossed with pollen from C. baccatum and after 3-4 days second pollination is done with pollen from C. annuum. In the second method, the female gametophyte of C. annuum is given the nitrous oxide (N2O) treatment followed by pollination with pollen from C. baccatum. Further, it is a general rule that wide crosses are more successful when the smaller fruited wild type is used as female plant. Parthenocarpy  Parthenocarpy allows formation of fruits without the need of fecundation and seed set. In parthenocarpic fruit mass of consumable flesh is larger than in seeded fruits. Parthenocarpy is facultative in egg plant. It is environment (temperature) induced. Low temperature (7-10°C) induces parthenocarpy. It is oligogenically and dominantly inherited (Daunay et al., 2001b: Kuno and Yabe, 2005). Strong parthenocarpic tendency results in normal sized fruits with no seed whereas weak parthenocarpic tendency results in under sized fruit with few or no seeds. Elimination or cutting of stigma of flowers bud is a way of obtaining the expression of parthenocarpy (Fuzhong et al., 2005). Indian putative, S. incanum is a wild and weedy form (group E) of S.melongena which upon differentiation gave rise to S.cumingii, a closely related species of south east Asia (group F) and wild form of S.melongena which upon domestication gave rise to S. ovigerum, a small round or oblong fruit, white, green, violet and constituted group G which finally evolved into the advanced cultivars with large sized fruit and constituted group H (Deb, 1989). S. incanum reverted to strong prickliness, low straggling growth habit. E, F, G, H groups of S. melongena show narrow variability in comparison to

Origin and Genetic Resources of Vegetable Crops

10.55

A, B, C, D groups of S. incanum which includes S. campylacanthum (group A), S.delagoense (group B), S. incanum sensu strict (group C) and S. lichtensteinii (group D) which show large diversity. (Lester and Hasan, 1991). This shows the occurrence of genetic bottleneck during the evolution and domestications of the egg plant. Related wild and weedy species are given in the table 10.28 below. Table 10.28  Showing different species of brinjal, their ploidy level and characteristics Species

Ploidy level

characteristics

S. coagulans (S. incanum)

2n

Prickly

S. xanthocarpum syn S. virginianum

2n

prickly

S. indicum/S. violaceum

2n

prickly

S. maccani

2n

prickly

usage Medicinal use

Section- Leptostemonum S. integrifolium S. gilo S. zuccagnum S. sisymbrifolium

Source of resistance to bacterial wilt, vercilium wilt and nematode

S. torvum

Source of resistance to bacterial wilt, vercilium wilt and nematode. Used as rootstock

S. viarum syn S. khasinum

Other species of 2n = 2x = 24 Acanthophora includes S. casicoides, S. mammosum

S. aviculare

2n = 2x = 14, 24?

S. mammosum

22

Source of gene for resistance to shoot and fruit borer

S. marginatum S. pubescens S. campannulatum S. heinianum S. dennekense S. stramonifolium S. aculeastrum

Parthenocarpic Contd...

Crop Evolution and Genetic Resources

10.56 Contd...

Species S. beaugleholei

Ploidy level

characteristics

usage parthenocarpic

S. cerasiferum S. chippendalei S. cinereum S. clarkiae S. dioicum

Parthenocarpic

S. diversiflorum

Parthenocarpic

S. linnaeanum S. macrocarpum S. melanospermum S. phlomoides S. sessilistellatum S. tudununggae

Parthenocarpic

S. coaagulans S. lidii S. vespertilo S. aethiopicum S. anguivi S. burchellii S. capense S. catombelense S. coccineum S. cyaneopurpureum S. dinteri S. forskalii S. hastefolium S. kurzii S. lamprocarpum S. myoxotrichum

Parthenocarpic

S. pyracanthos S. rigescens S. rubertorum Contd...

Origin and Genetic Resources of Vegetable Crops

10.57

Contd...

Species

Ploidy level

characteristics

usage

S. supinum S. toliaraea

Parthenocarpic

S. tomentosum S. trilobatum S. grandiflorum S. giganteum S. goetzii S. hispidium syn S. warscewiczii S. schimperianum

Parthenocarpic

S. dasyphyllum S. cyaneopurpureum

S. torvum is perennial, bushy, erect plant being used as rootstock for egg plant. It shows resistance to root diseases. The grafted plant using S. torvum as rootstock is very vigorous and permits crop to continue for the second year. Fruits from S.xanthocarpum have medicinal uses. Bathua  Chenopodium album is the cheapest leafy vegetable and it is grown as weeds. It is a rich source of Ca, Fe, P, K, protein, Vit. A. It is wild relative of spinach. It belongs to family Chenopodiaceae. Center of origin is north temperate region. There are over 250 species including C. quinoa, C. pallindicaule. C. berlandieri. There exists diploid (2n =  2x  =  28) or hexaploid (6x = 56) varieties. It is cross pollinated crop and pollination is through wind. It is found in winter in the field.

10.17  BEETROOT It belongs to family Chenopodiaceae. It is a biennial crop with Europe as center of origin. There are four sections in the genus Beta (see chapter 8). There are six sub specis within B. vulgaris, vulgaris, ciela, maritima(wild sea beet), adenensis, trojana and macrocarpa. Cultivated beet root (B. vulgaris ssp maritime and ssp. vulgaris have swollen root. Fruit is multigerm containg 2 to 5 seeds. B. vulgaris ssp esculenta is beet root or red beet. B. vulgaris ssp cycla is spinach beet, leaf beet, chard or sweet chard. Beet root is cross compatible with other subspecies of B. vulgaris ssp. vulgaris (sugarbeet, mangolds, spinach beet and sweet chard). It is a diploid with 2n = 18. It is a cross pollinated crop. There is presence of protandry condition.There are two methods of seeed production, seed to seed and root to seed. Isolation distance between same type is 500m whereas between different types is 1000m. Cross pollination is through wind. Figure 10.4 show evolution of Beta crop.

10.58



Crop Evolution and Genetic Resources

Fig. 10.4  Showing evolution of Beta crop (Adapted from Ford-Lloyd, 1995)

B. vulgaris subsp. vulgaris is divided into four cultivar groups. 1. Leaf beets which do not have swollen hypocotyl and which are used as leafy vegetable. 2. Garden beets whose swollen hypocotyls is used as salad vegetable 3. Mangels whose swollen hypocotyls is mainly used as fodder crop 4. Sugar beet whose root is an important source of sugar. 5. Fodder beets which are hybrids between mangels and sugar beets and are used as animal feed. Mangel, wurzel, Beta vulgare and sugar beet are to have been developed from chard. B. vulgais subspecies vulgaris contains all cultivated forms (Fig. 10.5).

Fig. 10.5  Various forms of beets: (A) fodder beet, (B) sugar beet and (C) beetroot. Note differences in soil level. (Adaptd from R.H.M Langer and C.D. Hill, 1982)

Origin and Genetic Resources of Vegetable Crops

10.59

All species of the section Beta constitute the GP1 and other species of the genus constitute the GP2. Each chloroplast in Beta vulgaris contains 4-18 nucleoids and each nucleoid is estimated to have 4-8 ctDNA molecules(Hermann et al., 1974). Table beet  Beet roots are used as salads. It can be pickled, roasted, boiled or used for making soup. Pigments are extracted and are used as a source of natural food dyes. Beta procumbens and Beta webbiana are wild beet and the former is the source of gene of root nematode resistance. It is a cross pollinated crop. There is presence of SI under control of four loci (Lundqvist et al., 1973). SF, dominant gene overrides this system and allows for self pollination. CMS was studies by Owen, 1945. The loci x and z in association with sterile cytoplasm condition male sterility. Dominant alleles at either loci or both loci results in male fertility, for example, SXxzz or SxxZz is fertile. Maintainer lines first used were W32, W162, W163 and W187. Nxxzz is the maintainer line. In breeding program stock seed roots are graded for shape, prominence of tap root, absence of disease and trueness-to-type. Internal colour is judged by detecting the presence of ‘zoning’ which is the differential colouring between cambial rings. Pigments in table beet are the betalainsalkaloid pigments found in Caryophyllales and some fungi. Betalains are composed of red violet betacyanins and yellow betaxanthins. Breeding program aims at increased betalain concentration in red beet. Betalain production in beet is under control of two linked loci, R and Y (Keller, 1936). Earthy flavor of table beet- Trans-1, 10-dimethyl-trans-(9)-decalol is the compound responsible for the earthy flavor. It is due to the modification of geosmin compounds in the roots and leaves. Breeding objective in 60s and 70s were to develop hybrids using CMS , disease resistance, round to globe shaped root, improved colours and sweetness, multigerm and monogerm seed. From the sugarbeet, characters such as self fertility, annual growth habit, CMS and monogerm were transferred to tablebeet. Wild beta posses multigerm seed wherein each aggregate fruit may contain one to five seeds compressed into a single ‘seed ball’. Seed ball is a lignified flower carcass with a corky appearance. Thus multigerm seed give rises to a number of successful plants from each seed ball. Monogerm trait is conditioned by a recessive allele at m locus which was identified in sugarbeet (Savitsky, 1950). Monogerm trait is possessed by many sugarbeet cultivars.

10.18  AMARANTH Amaranth or chou lai (saag) or rajgira or ramdana is grown in tropics and subtropics. It is used as vegetable, cereal, ornamental and forage. Seed contains about 30% more protein than cereal like rice, sorghum, rye and it is rich in lysine. Seed protein ranges from 17 to 19% of dry weight. Leaves contain beta carotene, Ca, Fe, K, Zn, Cu, Mn and Vit. A, C, foliate, niacin and riboflavin. Different species of Amaranthus are given in the table. There are about 60 species in this genus and 15 species are found in Indian subcontinent. Origin is south east Asia (India). It belongs to family Amaranthaceae. Chromosome number varies from x = 16 to x = 17 and sometimes both types are found in the same species. There is also presence of B-chromosomes. There are monoecious (2n = 32) and dioecious species. Cross pollination is through insects. It is grown in summer or winter. It is a universal crop in the sense that flour, starch, bran and oil can be

Crop Evolution and Genetic Resources

10.60

produced from the seed. It is a drought resistant crop like majority of the C4 plants such as maize, sugarcane, etc. Amaranthus as vegetable crop, is primarily used for preparing salad rich in carotene, Vit. C, Fe, Ca and micronutrients. Leafy species, A. hybridus is a wild ancestor of grain species, A. paniculatus. A. lividus and A. graecizans are also leafy species. A. powellis and A. deflexus are wild species. Amaranthus species are monoecious and self compatible with outcrossing rates varying widely from plant to plant and show a high degree of heterzygosty. Different species Amaranth are given in Table 10.29. Table 10.29  Showing different species of Amaranth Species A. caudatus

Ploidy level 2n = 32

A. cruentus

Characteristic

Origin

Grain, ornamental

Indian

Grain, vegetable

Africa

Cultivated/wild

A. hypochondricus

2n = 32

Grain, ornamental

A. blitum

2n = 28

Leafy vegetable

A. dubius

2n = 64, tetraploid

Leafy vegetable

Caribbean

A. tricolor

2n = 34

Leafy vegetable

Asia

cultivated

Grain

America

Wild species

A. hybridus A. quitensis

Wild species

A. powellii

Wild species

A. spinosus

Leafy vegetable

A. viridis

2n = 34

A. tenuifolius

2n = 2x = 28

Wild species Green amaranth, cooked and served, Wild species

A. mantegazzianus 2n = 32 A. retroflexus

Grain

A. magnostanus

Leafy vegetable

A. viridis

Leafy vegetable

A. graecizens syn a.blitoides, A. angustifolius

Grain

A. albus

Grain

Wild

Amaranthus is a self pollinated crop but cross pollination occurs. Isolation distance of 1/2 mile to 2 miles is required in case of seed production. It has catkin-like cymes of densely packed flowers.

10.19  KALAUNJI Kalaunji or mangrela  Black cumin, Nigella sativa belong to family Ranunculaceae. It is an annual flowering plant. Seed is used as aromatic spice, for flavouring and has medicinal value. Seed contains thymoquinine- an antimalarial compound. Seed contains 20%

Origin and Genetic Resources of Vegetable Crops

10.61

protein, 38% fat and mineral such as K, P, Ca and Fe. It is a diploid with 2n = 2x = 12. It is native to South East Asia. It is a self pollinated crops but cross pollination occurs by honey bees. Flower is hermaphrodite. Plant is 20-30cm tall, branched stem with determinate flowering pattern (Cymose). Pollen matures a few days before stigma become receptive and thus cross pollination occurs. Capsule bears numerous seeds. The genus contains about 14 species as given in the table 10.30. N. damascene and N. hispanica are used as ornamental plants. The latter species produces larger flowers. Table 10.30  Showing different species of Nigella Species

Uses

N. arvensis N. cilians N. damascene N. hispanica

Ornamental -do-

N. integrifolia N. nigellastrum N. orientalis N. papillosa

10.20  AJWAIN Panch phoran or Carum copticum syn Trachyspermum ammi or Trachyspermum copticum can be grown in arid or semiarid areas. It grows well in heavily salt affected soil. It is an aromatic spice. Seeds act as digestive stimulant and prevent flatulence. Seeds also contain thymol-a major chemical compound which has got medicinal properties. This crop is a native of Egypt. It is a diploid with 2n = 18. Plants are tall, profusely branched and striated, annual herb, 60-90cm tall. It belongs to family Apiaceae or umbelliferae. Inflorescence is umbel. One umbel comprises 16 umbellets and each umbellet contains up to 16 flowers. It is andromonoecious in the sense that both male and bisexual flowers are found. Flowering can occur in either November or March. It is a cross pollinated crop.

10.21  OKRA Fruit (pod is) rich in calcium, thiamine, riboflavin and niacin, Vit. C and has high carotene content. Carbohydrates are present in the form of mucilage. When it is cooked in iron, copper or brass pan, it turns black. Fruits should never be washed before storing as they develop slime. One can get fruits within two months of planting. Seeds contain 20% protein and 14% oil. Harvesting is done prior to differentiation of fibers and before seeds are fully developed. Fruit pods can be canned, frozen or dehydrated. It is an annual plant with a deep tap root, zig-zaggy stem, hairy rough. It is a high water user vegetable crop. Leaves are 3 to 5 lobed, prominently veined and coarsely toothed. This crop can not tolerate low temperature for long. It is grown for immature edible fruits or pods. It is high in antioxidants. High mucilage cultivars are preferred in Sudan. It belongs to family Malvaceae. Although

Crop Evolution and Genetic Resources

10.62

it is a cross pollinated crop but self pollination occurs. Cross pollination is through insects, bumble bees. The chromosome number ranges from A. tuberculatus (2n = 38) to 2n = 198 in A. caillei, the African cultivated species. It has Ethopian origin. Cultivated species A. esculentus is thought to evolved as a result of amphidiploidization between A. tuberculatus and A. ficulneus and A. caillei from the cross A. esculentus x A. manihot. This genus is a complex of polyploidy species. There are three ploidy levels in okra, 2n = 56-72, 2n = 108-144 and 2n = 185-199. The cytogenetical relationship among different species of the genus Abelmoschus are given in the table 10.31. A. manihot (60-68), A. moschatus (72), A. ficulneus (72), A. angulosus (56). A. tuberculatus (58). A. manihot tetraphyllus (130-138). Three species, namely, A. esculentus, A. manihot and A. moschatus have cultivated as well as wild forms. A. crinitus, A. angulosus and A. ficulneus occur only in wild forms. A. esculentus differs from A. caillei in flower color, marking of seed and fruit size as shown in the table 10.32. It is often cross pollinated crop. Isolation distance is 500m. Flower buds start to appear in the axil of each leaf on the stem above 6-8 leaf stage and only one flower opens at a time. Flower blooms only for a day. Young, immature pod can be plucked with a slight jerk. Mature pod turns fibrous and difficult to pluck. Fruits with 7-8 inches long are harvested. Seed pod carries five distinct ridges showing five fused ovules. Pods can be angular, dark green round pods, spineless okra, okra with 10-13" pod or purple okra. According to van Borssum Waalkes (1966) there are only six species in the genus Abelmoschus as given below alongwith their distribution without considering A. callei. 1. A. moschatus a. A. moschatus ssp. Moschatus var. moschatus cultivated b. A. moschatus ssp. Moschatus var. betulifolius wild c. A. moschatus ssp. biakensis wild d. A. moschtus ssp. tuberculatus- Hilly area of U.P.(Saharanpur), wild North India 2. A. manihot a. A. manihot ssp. manihot Indonesia, New Papua Guinea cultivated b. A. manihot ssp. tetraphyllus var. tetraphyllus-Low altitude wild (0-400m) c. A. manihot ssp. tetraphyllus var. pungens-High altutude wild 400-600m), Indonesia, Philippines 3. A. esculentus-Africa, India, U.S.A. cultivated 4. A. ficulneus-Africa to Asia, Australia wild 5. A. crinitus-Low altitude, dry season, fire resistant, Asian origin wild 6. A. angulosus-High altitude (750-2000m), India, Asian origin wild Table 10.31  Showing relationship among different species of Abelmoschus Level I 2n = 58-72

Level II 2n = 120-140

Level III 2n = 185-200

A. moschatus (n = 36) Contd...

Origin and Genetic Resources of Vegetable Crops

10.63

Contd...

Level I

Level II

A. ficulneus (n = 36), F genome

Level III

A. esculentus (TF), n = 62-65

Nori-Asa, A.sp.“Guinean”(TFA)

A. tuberculatus (n = 29), T genome A. esculentus (n = 36) A. manihot (n(30-34), A genome A. pungens (n = 69) A. tetraphyllus (n = 69) Table 10.32  Showing difference between A. esculentus and A. callei A. esculentus

A. caillei

Flower-pale

Darkish Long and curved pedicel, large epicalyx segment

Marking of seed-dense

Wide

Fruit size greater than 20-40cm

10.35cm

Bitter gourd  Male flowers are found at the end of a thin, long stem and anther is octre yellow. Whereas female flowers have a miniature fruit at the base of the flower stem (have fat section between flower stem and vine) and stigma is pale greenish yellow. Female flowers are slightly smaller than male flowers. Pollination is done by honeybees. Pollination is carried oust during day time while attempting crosses. Isolation distance is 500mt. Bitter gourd (Momordica charantia) and Kakrol (M. dioica) belong to family Cucurbitaceal. Both crops are distributed all our India except north-east. The genus Momordica contains some 40 species. Kakrol  Memordica dioica, a summer cucurbitaceous, bitter less, vegetable.It is native to India and Bangladesh. It inhibits fats absorption. Bitter gourd, M. charantia is related to M. dioica. The different Indian species of genus Memordica are given in the table 10.33 below. M. chochinchinensis called Gac fruit has got medicinal value. It is vegetatively propagated through tuberous root. M. cochinchinensis has lycopene up to 70 times more than tomato. Lycopene is an important intermediate in the biosynthetic pathway of important carotenoids such as beta carotene and xanthopylls. Table 10.33  Showing different species of Memordica (Chakravarty, 1980; Joseph 2005) Species

Breeding system

Ploidy level and distribution

M. balsamina

Monoecious

2n = 2x = 22, Rajasthan & Gujarat

M. charantia

-do-

2n = 2x = 22, Throughout India

M. cochinchinenesis

Dioecious, wild relative of M. dioica. Large fruit

2n = 2x = 28, Andamans

M. dioica (s[piny gours, teasle gourd) -do-, small fruit

2n = 2x = 28, Throughout India Contd...

Crop Evolution and Genetic Resources

10.64 Contd...

Species

Breeding system

Ploidy level and distribution

M. sahyadrica

-do-

2n = 2x = 28, Western Ghats

M. cymbalaria (Syn. Luffa cymbalaria)

-do-

2n = 2x = 18, AP, MP, Karnataka, Maharashtra Tetraploid (2n = 4x = 56), North East

M. subangulata ssp. renigera

Kundru  Coccinia grandis is known as ivy gourd or baby water melon or gherkin. It belongs to Cucurbitaceae. It is also synonymous with Coccinia indica, C. cordifolia or Cephalandra indica. Chromosomes are diverged into autosomes and Y chromosome. Y chromosome is twice the size of autosomes. Entire Y chromosome is heterochromatic. 5S and 45S rDNA are found on autosomes but not on Y chromosome. C. grandis has phylogenic proximity to Cucumis sativus. XY type sex chromosome system could be present in spinach where Y chromosome lacks 45 SRNA. Bottle gourd  It has got different uses. Besides being used as vegetable it is used for making container, bowl, decoration, musical instruments or fishing boat. It has medicinal value as well. It contains highest level of choline. It is known to lower blood cholesterol. It belongs to family Cucurbitaceae. It is a diploid with 2n = 22. The genus contains five wild taxa and one cultivated species and given in the table 10.34 (Jeffrey, 1967; Morimoto et al., 2005). All wide taxa are found in Africa. The center of origin is Africa or it could have independently domesticated in Africa and Asia. It’s wild progenitors have not been identified. In case of vine crops, characters like vine length, vine thickness, vine strength, tendrils (branched to non-branched) be recorded and its association with fruit size be studied. Tendril is either a modified stemor a modification of an axillary bud or terminal bud as in vine (Vitis) or a modified leaf as in case of pea or wild Lathyrus. Table 10.34  Showing species of Luffa and their distribution. Species

Subspecies

Cultivated/wild

Ploidy level

Distribution

L. guineensis

Wild

Africa

L. rufa

Wild

Africa

L. sphaerica

Wild

Africa

L. breviflora

Wild

Africa

L. abyssinica

Wild

Africa

L. siceraria

Cultivated

2n = 22

Subspecies siceraria

African and American/New world

Subspecies asiatica

Asian gourd

Flowering occurs two months (50-60days) after sowing. Flowers open in the afternoon and remain open during night. Anther dehisces late in the afternoon and continues

Origin and Genetic Resources of Vegetable Crops

10.65

during night and thus requires insects at night to carry out pollination. Thus pollination must be carried out late in the afternoon before the sun set. Male flowers have long peduncles whereas female flowers have short peduncles. Female flowers are identified by have long fat section between flower and vine stem. The ovary takes the shape of the fruit. Anthers are grouped at the centre of flower. The stigma is short, thickened and branched. For planting seeds are soaked in water for 24 hrs and soaked seeds are wrapped in cloth bag and whole thing is kept in a pit covered with soil near a source of fire. Rise in temperature fastens germination which would take otherwise many days due to cold or low temperature during winter. Isolation distance is 500m in case of certified seed production but 1600m in case of foundation seed production. Germination takes 3-5 days after seeding. Flowering occurs at 30-35 days after sowing. Fruit is ready for harvesting 2-3 weeks after flowering. Thus harvesting can done around 55-75 days after sowing. Ideal variety-each node bearing fruit, 140-150 day crop, i.e., extending the harvesting period, prolific bearer (small fruit of 25-30 cm length and weighing around 300-350 gms), 45-60 days for first picking (early fruiting in 45-60 days). Because of competition for metabolites by early developing fruits over the later fruits or to the production of hormones by developing seeds, the yield of the lines being used for seed production goes down. Calabash  It is a bottle gourd (L. siceraria). Round varieties are called calabash. Young fruits are used as vegetable but matured can be used as utensils such as water container, bottle, pipe, etc. Lotus stem (Kamal kakdi)  Lotus (Nelumbo nucifera) is a perennial aquatic, edible species. It contains lots of minerals, carbohydrate, proteins, vitamins and folic acid. It is high in phenolics. It has got crispy rhizome which is edible. Seeds remain viable for many years under favourable conditions. Jute/Roselle  Hibiscus sabdariffa (Roselle)’s leaves and seed are used as vegetable. Further, Long fruited jute, Corchorus olitorius’s leaves and young shoots are used as vegetable. More on these can be found in chapter 8. Patwa or lal Ambari (Hibiscus sabdariffa) is also used as vegetable.

10.22  JIMIKAND Elephant foot yam has dark brown corm. It is the third most important source of carbohydrate after rice and maize. It is a 10-11 month crop, sown in April and harvested in February. Ideal seed material can be of 500-700 gm which can be produced by cutting the fruit of 2 or more than 1.5 kg in weight in four equal parts or the whole fruit of less than 1.5kg can be planted as such. Increase in seed weight is around 10 times the initial weight at planting. Weight of the harvested produce can range from 5 to 15kg. Pit of 1' × 1' is dug and chemical as well as FYM is applied. Variety with no fingers (Gajendra) is used for planting. If planting material is less than 500gm than it will be better to do the harvesting after 2 years. Fingers can be used as planting material but in this case crop is harvested only after two years but seed multiplication can be through use of fingers. The variety santaragachhi has fruit with fingers. Plant is 120cm in length, has single leaf with numerous leaf lets and may be 2m wide. Drying or yellowing of the leaves is indication

Crop Evolution and Genetic Resources

10.66

of maturity of the corm (dark brown) or tuber. Tubers and leaves contain calcium oxalate which puncture mouth and tongue causing irritation. Tubers of wild plant are highly acrid because of calcium oxalate. Seed is recalcitrant and dry seed is dead seed. So seed be left in the fruit itself. This is the way one can store seed or else seed can be wrapped up in sphagnum moss. Seed rate is 80-100qtls/ha. It is propagated through corm, corm pieces and cormels. Amorphophallus campanulatus is synonymous with, A. paeoniifolius is exlusively cultivated for edible tubers. It has china, India and Asia origin. It belongs to family Araceae. There are 303 species in the genus Amorphophallus. Some species are A. bulbifer, A. prainii, A. preussii. A. aberrans, A. abyssinicus and A. albispathus. It is a cross-pollinated crop and pollination is through carrion flies and beetles. Stigma is receptive only for one day. It has single inflorescence followed by a solitary leaf on a trunk (like petiole). There is no corolla in Amorphophallus. The spadix (spike) has three flower zones, female flowers at the bottom and middle zone contains male flower and the tip of the spike is tuberous called appendix. There is a bract surrounding the spadix (spathe)

10.23  TURMERIC Turmeric (Haldi)  Its underground rhizome is used as condiment, dye, drug and cosmetic. It contains antioxidant and anti-inflammatory compound. Turmeric contains yellow pigment called curcumin which ranges from 4 to 8% in dry rhizome. It is used for dyeing (hard, bright coloured rhizome) and it is the best spice(more aromatic, soft, light coloured rhizome). It is naive to India, South East Asia. Turmeric, Curcuma longa belongs to family Zingerberaceae. It is typically hexaploid (2n = 6x = 42). The genus contains about 70 species. About 30 species are present in India. It is tropical crop, can be grown in areas receiving 1500 mm rainfall. It can be raised under rainfed and irrigated conditions. Different species of economic and commercial importance are C. amada, C. caesia, C. aromatica and C. angustifolia. C. oligantha is substituted for turmeric. C. vamana is a wild relative of turmeric and C. zanthorrhiza is Javanese ginger which has medicinal value. Origin is India and about 40 species are found here. There is prevalence of 6x, 7x, 11x, 12x, and 15x species. Other species of Curcuma which are used and some of which are cultivated are given in the tables (10.35 and 10.36). Table 10.35  Showing different species of turmeric and their distribution Species C. aeruginosa C. amada C. angustifolia C. aromatica C. caesia C. mangga C. Purpurascens

Distribution Malaysia Mango ginger, India India Bengal Bengal Java, Malaysia Java

Cultivated/wild, Use Cultivated, medicinal use Cultivated, wild Wild Wild, also cultivated Cultivated to some extent, medicinal use Cultivated, Cultivated, wild

C. xanthorrhiza C. zedoaria

Java,Malaysia, North eastern India

Cultivated, wild Cultivated

Origin and Genetic Resources of Vegetable Crops

10.67

Planting is done during May 15-31. Spacing is 80 × 20cm. It is a 8-10 month crop. Propagation is through rhizome (8-10cm). The variety Rajendra Sonia is having 8.5% cucurmin. In the fertile soil one can harvest this crop after 10 months or so but in the low fertility soil it is better to harvest after two year. One finger can give rise to four fingers in high fertility soil. Seed rate is 20qtl/ha and production is 100-125 qtls/ha. In one 250gm of rhizome one can have as many as 20buds. Turmeric gives high yield under light shade condition and it can be raised successfully in intercropping with pigeonpea. Harvested produce if to be used as seed is not cured and stored as such in shade and can be sown again in May but it has to used as seed in the next year then it is to stored under low temperature (4°C) in cold storage. Curing is done for obtaining dry turmeric. Curing is done by boiling of rhizomes and drying in sun. Phtoestrogen producing curcuma includes C. comosa (2n = 42, 63) and C. elata (2n = 63), thus seems to the triploid. C. zedoaria (2n = 63, 66) is a medicinal and horticultural species used as spice, for tonic and perfume. Some species can be used as cut flowers and potted plants. As it is vegetatively propagated crop, clonal selection is practised for improvement. Because even though turmeric, C. longa is triploid, pollen fertility is about 60%. Seed set has been observed under open pollinated and controlled crossing condition and there is also germination of seed. This shows that conventional hybridization and selection program can be started for improvement of haldi. Breeding objective include development of short duration variety, resistant to soft rot, high yield, high curing % and high curcumin content. Table 10.36  Showing related species of Curcuma, their common name and characteristic. Species C. zedoaria

Common name

Characteristics

Arrow root production

C. aeruginosa C. malabarica

Arrow root production

C. comosa C. caesia C. amada C. sylvatica C. aromatica C. harita C. soloensis C. brog C. monatana

Arrow root production

C. latifolia

Sessile tuberising species

C. raktakanta

Sessile tuberising species Contd...

Crop Evolution and Genetic Resources

10.68 Contd...

Species

Common name

Characteristics

C. vamana

Stoloniferous type

C. aurantiaea

Non-sessile tuberising

C. pseudomonatana Arrow root production C. angustifolia

Arrow root production

C. caulina

Arrow root production

C. xanthorrhiza

Arrow root production

Non-sessile tuberising

10.24  ZINGER Zingiber officinale (2n = 30) is an aromatic spice. India is the largest producer of zinger. It is a monocot and belongs to family Zingerberaceae which include cardamom and turmeric. It contains 91% antioxidant. Zinger contains 1.5 to 2.5% volatile oil called gingerol which imparts taste and flavour. Under ground rhizome which is branched is used as spice and rhizome and leaves are used as medicine. It has spicy lemon scent. It is grown in hot, humid, shady condition. It requires large quantity of nutrients and calcium nitrate. Shoots are pseudostems and have 8-12 distinct leaves. There are three types of varieties. 1. Giant zinger, Z. Officinale var officinale (2n = 2x = 30) 2. Red zinger, Z. officinale var rubra (2n = 2x = 22) and 3. Small zinger, Z. officinale var amanum (2n = 2x = 30). Giant zinger is closely related to red zinger. Zinger originated in South East Asia, probably India. Other species of zinger include Z. montanum, Z. rubens, Z. kawagoii, Z. oligophyllum Propagation is through division and by intermodal cutting. Flowering is not a regular phenomenon in zinger. It is hermaphrodite. Non-fibrous rhizomes have high content of biomolecules and it can be used for candy preparation. Z. cassumunar and Z. zerumbet have medicinal values. Different clones vary in size, fiber, moisture content of the rhizome and yield. The breeding objectives are high yield and high percentage of dry ginger. In India local varieties plus varieties from China and Brazil are being cultivated. Kerala produces the largest quantity of ginger. There are two types of Jamaican ginger–yellow ginger or turmeric ginger and blue or flint ginger. Canton ginger is used for preserving as it produces more succulent thicker rhizome. The three races of Malaysian ginger are, haliya betal or true giner with pale-coloured rhizome, haliya bara or haliya padi and haliya udang. Both have externally red rhizomes, very pungent and being used as medicine. Time of planting is May. It is 8-10 month crop and harvested in February. Harvested zinger is stored on dry sand and can be kept in such condition for 3-4 months without losing viability. If stored under in normal environment rhizome rot will develop. The problems with this crop is that it has long vegetative phase, highly heterozygous, frequently polyploids, besides problems of self incompatibility, apomixes, sterility and thus breeding method to be employed for improvement of this crop is mutation breeding and use of somaclonal variation. Further, in order to provide farmers the clean planting

Origin and Genetic Resources of Vegetable Crops

10.69

material one should use micropropagation using tissue culture technique to produce clean, disease free materials. There is problem of bacterial wilt and soft rot caused by Pythium. There are also varieties of ornamental zinger belonging to Z. officinale.

10.25  BLACK PEPPER Piper nigrum is a perennial, glabrous, vine and can go up to 10, or more in height. It belongs to family Piperaceae. Seed is used as spice and for seasoning. Seed contain piperine (4-10%). Dried seed is called peppercorn. This family contains two more economically important species such as P. betle (Betel leaves) and P. longum. It is tropical crop, native to India (Western Ghats of India). It contains essential oil in leaves and seed. Vine has three markers in stem-main stem is upright involved in vegetative growth, there are knots on the stem from where leaf emerges. It also support the roots of the branch and fruiting branches have horizontal growth. And then there are fruiting branches which show horizontal growth. When the trailing stem touches the ground, rooting starts from that point. Leaves are simple, petiolate, large, 8-12" long and 12" wide. Upper surface of leaf is dark green and the lower surface is white green. From the mid rib of leaf there emerges 2-3 pairs of veins. Inflorescence is spike which comes out from the main stem. At leaf node flowers are borne on pendulous spike which is about 4-15cm long. Single stem produces around 20-30 spikes. Plants bear fruits from 4th to 5th year of planting and continue to bear for 7 years. Spike is closely packed up with tiny flowers. It contains about 70-100 tiny greenish yellow flower. Inflorescence is recemose and flowers open first at the bottom of spike and later at the top over a period of a week. Wild pepper is dioecious but cultivated peppers are bisexual and thus more productive. Pepper is protogynous and stigma receptive for 5-8 days. Stigma is exserted 3-8 days ahead of anthesis. It takes almost a week for all flowers to open. Since basal flowers develop before apical flower, pollination is accomplished by pollen from the flowers of the same spike by means of gravity. It is predominantly a self pollinated crop. Fruits appear after 9 months of flowering. It is initially green but turns yellow to red and finally black on maturity. Fruit is oval in shape. Each fruit contains one seed which is cream in color. Besides black pepper, green and white peppers are also produced. White peppercorn tastes hotter but lacks flavour. When outer layer is removed before and after drying leaving only the inner seed results in white pepper. Green pepper is unripe dried pepper, white pepper is unripe fruit seed and black pepper is unripe, cooked and dried seed. Green, unripe drups are picked up and cooked in hot water and the cleaned seeds are then dried under sun for several days or oven which results in development of wrinkled black layer. Piper is the largest genus in Piperaceae family. It is native to South Western India. The genus basic chromosome number is x = 13 but x = 12 and 16 have been reported. P. nigrum is a tetraploid (2n = 4x = 52) and there are species with 2n = 46, 52, 78, 104 and 2n = 128 have been reported. Most of the new world species have been found to be diploid and the old world species to be polyploid (Samuel, 1986). It is vegetatively propagated through marcotts, approach grafting or bud grafted. Breeding objectives include improving fruit set and pungency. Propagation is through cuttings of 40-50cm vine. There are species of

Crop Evolution and Genetic Resources

10.70

pepper which are ornamental and false peppers. Economically important species of pepper are given in the table 10.37 below and other species of pepper are given in Table 10.38 along with their chromosome numbers. Grafting of P. nigrum or P. colubrinum (2n = 226) which is a wild woody relative of P. nigrum, has been tried in order to develop resistance against soil borne pathogens but it showed late graft incompatibility. Other species being used as rootstocks include P. cubeba, P. hispidum and P. scabrum. Most of the cultivated types are bisexual and flowers are protogynous and most of them are multiplied by cuttings. Pepper vine in the wild state are dioecious. Selection in the breeding program is for development of hermaphrodite line. Table 10.37  Showing different species of black pepper, their distribution and breeding system Species

Ploidy level

P. nigrun

Cultivated 2n = 4x = 52

P. longum

Wild

Common name

Breeding system

Distribution

Tree pepper Dioecious

used as spice or as substitute

P. chaba P. melhysticum

Roots are used for production of beverage of Polynesians

P. clussi

Used as substitute, Tropical America

P. guineense

Used as substitute, Tropical America

P. kadzura P. betle P. cubeba

Wild, Cubeb or tailed pepper

dioecious

Medicinal use. Climber, used as spice or as substitute, Indonesia

P. retrofractum syn. P. officinarum P. saigonense

Used as substitute, Vietnam

P. longifolium

Tropical America

This crop requires support trees which are called standards on which the vines trail. The various trees include Erythrina indica, E. lithosperma, Garuga pinnata, Gliricidia sepium and Leucaena leucocephala. Raising this crop on support improves yield. At lower altitudes Alianthus malabarica is grown as support tree whereas at higher altitude Grevillia robusta (Silver oak) is grown as standard. In homestead gardens mango, jackfruit, coconut, areca nut are used as standards. When this crop is raised as intercrop with coffee, pepper is trailed on shade trees such as silver oak. 95% of the pepper production comes from homestead gardens where pepper is planted with perennials.

Origin and Genetic Resources of Vegetable Crops

10.71

Table 10.38  Showing species of black pepper and their ploidy levels Species

Chromosome number

P. anisotis

–

P. argophyllum

36, 39, 52

P. attenuatum

26, 36, 39, 52, 104

P. auranatiacum

–

P. barberi

52

P. betle

26, 32, 42, 52, 58, 64, 78, 195

P. boehmeriaefolium

52

P. canium

–

P. chaba

24, 104

P. galeatum

40, 52

P. griffithi

–

P. khasianum

–

P. hamiltonii

–

P. hapnium

52

P. hookeri

60, 104

P. hymenophyllum

104

P. longum

24, 48, 52, 60, 96

P. mullesua

132

P. muricanum

–

P. napalense

–

P. nigrum

36, 48, 52, 60, 65, 78, 104

P. P. nigrun var. hertellosum

–

P. peepuloides

156

P. petiolatum

–

P. pseudonigrum

–

P. rhytidocarpum

–

P. schmidtii

96

P. silentvalleyensis

–

P. sugandhi

52

P. sugandhi var. brevipilis

–

P. sumatranum

–

P. sylvaticum

–

P. syslvestre

–

P. thomsoni

–

P. trichostachyon

52

P. wightii

48, 52

P. colubrinum

26 Contd...

Crop Evolution and Genetic Resources

10.72 Contd...

Species



Chromosome number

P. cubeba

24

P. magnificum

24

P. ornatum

80, 120

P. brachystachym

–

First thirty six species are found in India.

10.26  BETEL LEAVES Betel pepper, P. betle leaves are chewed as a masticatory together with betel nut from the palm, Areca catechu. It is an evergreen, perennial, creeper/climber, shade loving, branching vine. It is grown as under strorey ground cover crop. Betel leaves are called Paan. Paan hides bad breath, soothes boils and abscesse. It acts as stimulant and has medicinal values. Betel leaves contain 0.8 to 2.0% essential oil, the chief component of which is eugenol. Indian cultivars contain higher percentage of oil and more pungentin taste. Paan masala, talc, perfumes and food additives can be prepared from leaves. It requires regular feeding and watering. It is native to tropical regions to subtropics. Flowering is not observed in subtropics due to lack of required photoperiod. Flowering is observed in Nothern and Western Ghats. Vegetative propagation is through cuttings. It can be through single node cutting (practised in North India) with a single mother leaf taken from the middle of the vine of 3-5 year old. 6-8 node cuttings are used in peninsular India and there 2-3 nodes are buried in soil. Planting is done in May-June on ridges (raised bed), 2’ apart. Saplings are twined around sticks of split bamboo and reeds. There are two systems of cultivation. One is under open system of cultivation using support plant and another, closed system of cultivation under artificial rectangular structures called Barejas. This structure can be covered with coconut leaves or paddy straw. Shade and support can be provided by raising Sesbania grandiflora, Sesbania sesban, Erythrina variegate and Moringa oliefera. Leaves are ready for plucking after one year of planting and production can last for several years. Shelf life is over four months. Betel leaf vine is dioecious. There is difference in leaf shape, amount of chlorophyll, essential oil composition, phenol and thiocyanate content between male and female plant. Usually male and female plants are cultivated. It is difficult to distinguish between male and female plant. Generally, leaf length, leaf width and leaf shape are used to identify male and female. Male plants have narrow, ovate leaf whereas female plants have cordate leaves. Female flowers are short and green whereas male lowers are bigger and white in color. Basic chromosome number, x = 13 and 2n = 26, 32, 64 and 2n = 78 have been found. Considering leaf shape, size, brittleness and taste of leaf blade, there are two types of varieties in betel leaf-pungent or non-pungent. Processing or curing  Leaves are processed which fetch higher price in the market. Processing is done through successive heat treatments at 60-70C for 6-8 hrs.

Origin and Genetic Resources of Vegetable Crops

10.73

Betel vine is a dioecious, perennial climber with stem branches fairly with terete nodes swollen, glabrous. Leaves alternate, stipulate, petiole length varies from 0.75 to 1.50cm, lemma variously shaped, ovate, oblong or ovate-cordinate, 5 to 7 ribbed, smooth with an entire margin and acute tip. Inflorescence consists of is pendulous spikes (catkins) dioecious. Male catkins are generally very narrow (4 to 9cm) whereas female catkins are smaller (4 to 7cm) with prominent peduncle. Most of the plants are male in India. It is possible that male plants have been selected in India and also because only male plants have been vegetatively propagated. Fruiting or pistillate inflorescence is rarely seen in India. There is preponderance of female plants producing fruits in Malaysia. Another species P. canium, found in Malay and Peninsula and Java, is also used for chewing purpose (Sundararaj and Thulasidas, 1976).

10.27  SAFFRON Saffron consists of the dried stigmas of Crocus sativus. Safflower florets are also used as a cheaper substitute and an adulterant for saffron. It is a small bulbous plant of Iris family. This crop is known for aroma, flavour and yellow dyes and thus has uses in pharmaceutical, food and textile industry. It is an annual flowering geophytes with corms (rhizomes or bulbs), dormant during summer and sprouting in autumn and growth in winter. It belongs to family Iridaceae. It produces 1-4 flowers in a cataphyll with linear leaves. Flower has 9-10cm style with a three red trumpet like stigma which is 2-5cm long. The dried flowers (dried stigmas) form the commercial spice, Saffron. Flower picking and separation of stigma is a laborious job. Saffron or kesar spice is produced by Crocus sativus and it is native to Greece or south west Asia. Iran is the largest producer of saffron. It is a monomorphic clone. Vegetative propagation is through manual divide and set of the starter clone. C. sativus is triploid, self-incompatible and male sterile. It is a triploid with 2n = 3x = 24 and thus vegetatively propagated. There is infertility and absence of fruits and seeds. C. sativus was generally thought to be autotriploid but now available data support the allopolyploidy nature of C. sativus. The putative parents are C. cartwrightianus and C. hadriaticus. Both are diploid with 2n = 16 and presently found in Greece and thus thought to have evolved by interspecific hybridization. Other possible parents include C. thomasi from Italy and Croatia, C. mathewii from Turkey and C. pallasii ssp. haussknechtii from Iran-Iraq, Jordon. Species of horticultural importance (colourful flower) include C.vernus, C. versicolor and C.aureus. Breeding objectives in saffron include variety with more number of flowers per plant, higher number of stigmas, stigma size and stigma with increased amount of dye and aroma (Fernandez, 2004).

10.28  CARDAMOMS Cardamoms (Elettaria cardamomum) are dried fruits of a perennial rhizomatous herb. Spices are obtained by drying of the fruit capsules of various Amomum and Aframomum species and wild Elettaria varieties. It is a small genus with 3-4 species. Its natural habitat is the evergreen rain forests of Western Ghats of South india. It is used for flavouring.

Crop Evolution and Genetic Resources

10.74

It belongs to family Zinzerberaceae. It is indigenous to Southern India and Sri Lanka (Purseglove et al., 1981). There are two botanical varieties in this species. E.cardamomum var. major is a wild cardamom of Sri Lanka and is occasionally cultivated. Another variety is E.cardamomum var. cardamomum syn. var. minor, syn. var. minuscule. It is a true cardamom This includes most of the cultivated species. Besides there are several races which include Malabar cardamom (Prostrate panicle), bleached cardamom, has pleasant and mellow aroma and flavour. It is grown in Karnataka. Mysore cardamom (Erect panicle) has harsher aroma and flavour, longer than Malabar cardamom. Mysore type is green cardamom. It is a tetraploid with 2n = 4x = 48. The third is Vazhukka with semierect panicle. Sweet flavour of the oil is due to the presence of three compounds, terpenyl acetate, linalyl acetate and linalool. Cardamom is a tall (2.5 to 5m) tall, perennial with branched subterranean rhizomes which give rise to several erect leafy shoots and erect or decumbent panicles. Inflorescences are 60-120cm long and born on the rootstock at the base of the leafy shoots. Flowers are self sterile. There is self incompatibility and thus requires pollenizer. In plantation there is mixture of clones. Cross pollination is through bees. Flowering occurs throughout the year on the panicles of current season growth as well as previous year growth. Bud initiation to maturity takes 140 days. Flowers open in the morning and about 65% anthesis takes place between 6-8 a.m. Vegetative propagation is through division of rhizomes (suckers) and sexual from seedlings coming from seeds. Two years old seedlings from nursery are transferred to field. Eletteria cardamomum belongs to genera Aframomum and Amomum. There are species belonging to these genera which are grown as substitute for cardamoms. Aframomum melegueta syn. Amomum melegueta is melegueta pepper called grains of paradise or Guinea grains. It is a perennial herb and serves as a spice and a stimulating carminative. Aframomum granum-paradise, a distinct species from west Africa is called true grains of paradise. Substitutes for the cardamoms are given in the table 10.39 below. Cardamom mosaic virus is the major problem. Table 10.39  Showing different species of cardamom substitutes belonging to genus, Aframomum and their distribution Species

Common name

Distribuion

Characteristics

Aframomum deniellii

Camerouns cardamom

West Africa

Aframomum korarima

Korarima cardamom

Ethopia

Aframomum angustifolium

Madagascar cardamom

Madagascar

Amomum subulatum

Great Indian or Nepal cardamom

Cultivated in Darjeeling. Perennial, highly Large cardamom crosspollinated, propagated through rhizomes. Emergence of flowering takes place during June/July and harvesting starts from September and continues up to January.Plantation thrives well over 25 years. Flowering starts after 6-10 years.

Aframomum mala

East Africa

Origin and Genetic Resources of Vegetable Crops

10.75

Cardamom substitutes belonging to the genus Amomum are given in the table 10.40 below. Table 10.40  Showing different species of genus Amomum grown as substitutes for true cardamom Genus -Amomum

Common name

A. aromaticum

Bengal cardamom

A. kepulaga

Round cardamom of Java

A. dealbatum

Java

A. maximum

Java

A. krervanh

Cambodian cardamom

A. globosum

Large round Chinese cardamom

A. xanthioides

Thailand bastard cardamom

10.29  CINNAMON It is a dried bark of C. verum (syn. C. zaylanicum). It is indigenous to Sri Lanka. It is a true cinnamon. Bark and leaves are strongly aromatic and oil is extracted from both. It is used for flavouring and is a source of eugenol. Cassia is inferior to true Cinnamon. Cinnamon belongs to genus Cinnamomum and family Lauraceae. It is an evergreen tree of tropics and subtropics. Cinnamon oil is used in flavouring and perfumery. It is a diploid with 2n = 24. C. verum and three species of Cassia, namely, C. cassia, C. burmannii and C. loureirii are important in international trade (Table 10.41). Flowers are born in lax axillary and terminal panicles on the ends of the twigs. It is a cross pollinated plant and pollination is through insects. As seeds are eaten by birds so netting of the tree is done. It is propagated through seeds as well as by vegetative means. Quality of the bark (aroma) is influenced by the edaphic factors (soil type) and climatic condition in which the plants are grown. The same thing is happening with aromatic rice. Water logging and marshy condition lead to bitter product with much less aromatic. Table 10.41  Showing various species of cinnamon, their distribution Species

Common name

Distribution

C. cassia

Chinese cassia

C. burmannii

Indonesian cassia

C. loureirii

Saigon cassia

Vietnam

C. tamala (Tejpat)

Indian cassia

Northern India

C. camphora

China, Japan

Use

Source of Camphor and camphor oil (rich in safrole), Camphor oil is extracted from woods and leaves Contd...

Crop Evolution and Genetic Resources

10.76 Contd...

Species

Common name

Distribution

C. culilawan

Moluccas

C. iners

Western India

C. javanicum

Malaysia, Indonesia

C. parthenoxylon

Malesia

C. sintoc

Java

Use

C. riparium C. perrotteiti C. wightii C. glaucense C. malabaricum

10.30  NUTMEG Jayaphala (Myristica fragrance) is an spreading evergreen fruit tree which produces two distinct spices, seed spice, the kernel of the seed, called jayaphala and mace (aril of the seed, that surrounds single seed within the fruit, called javitri. It belongs to family Myristicaceae. It is native to Indonesia. The chemical imparting flavour is myristicin and elemicin. It is diploid with 2n = 38 (Dhamayanthi and Krishnamoorthy, 1999), and is heterozygous. It is a mostly dioecious tree but female trees with a few male flowers and male trees with a few female flowers and trees with bisexual flowers are also found. Flowers secrete nectar and is thus insect pollinated (cross pollinated) Reproduction is through sexual or asexual means. Male trees are headed back and grafted with scion from female trees.Seeds produces 50% male tress. Sex can be known only after 6 to 8 years after planting when it comes to flowering first. In other words, fruit is harvested only after 7-9 years after planting and full production is achieved after 20 years. Vegetative propagation is through epicotyls grafting, approach grafting and patch budding and air layering. M. Malabarica is found in Kerala and is odourless and tasteless. M. argentia is Papuan nutmeg, has peculiar odour a rank flavor. Rootstock species include M. dactyloides and M. Malabarica. M. argentia and M. succedanea have also been used as rootstock. Semi-hardwood or hardwood cuttings are also used for vegetative propagation. Related species of Myristica are given in the table 10.42 below. Table 10.42  Showing related species of genus Myristica and their uses. Species

Uses

M. amygdalina M. andamanica Contd...

Origin and Genetic Resources of Vegetable Crops

10.77

Contd...

Species M. attenuata

Uses Rootstock

M. daachyloides M. gibbosa M. glaucescens M. irya M. kingii M. longifolia M. magnifica

Rootstock

M. malabarica

Rootstock

M. canarica

Rootstock

M. fragrans

Rootstock

M. laurifolia

Rootstock

M. contorta

Rootstock

M. beddomei

Rootstock

10.31  CLOVES Clove (Syzygium aromaticum (syn. Eugenia caryophyllus) is a dried unopened flower bud of an evergreen tree. It contains eugenol which imparts flavour and which can be converted into vanillin. It is a native of Indonesia. It belongs to family Myrtaceae. The genus contains about 500 species. Guava, Psidium guajava, another very important fruit, belongs to this family. Flowers are hermaphrodite with a fleshy hypanthium (1-1.5cm long). It is not clear whether self pollination or crosspollination occurs. Harvesting of inflorescenses is done when the buds have reached their full size but before they open so that the petals together with stamens forms the head of the dried cloves. There are two seasons of flowering. Bumper crop occurs only about once in every 4 years. Other species with insipid fruits include S. cumini (Jambolan), S. jambos (Rose apple) and S. malaccensis (Pomerac). Vegetative propagation is through softwood cuttings. Cloves are usually propagated by seeds.

10.32  VANILLA It is a herbaceous, perennial vine. It belongs to family Orchidaceae. It climbs by means of adventitious roots and can go up to 10-15m and thus requires support. It is a flavouring material and spice. Fully grown fruit of orchid, Vanilla fragrans is harvested before it is fully ripe and fermented and cured. The fruits are called vanilla beans. Vanilla extract is obtained from this bean. It is a diploid with 2n = 32. The origin is Mexico, central America.

10.78

Crop Evolution and Genetic Resources

The duration between flowering and harvesting is 6-9 months. Flowering takes place once a year. Hand pollination is a must to obtain fruits. Self pollination is impossible. There is separation of the stamens from the stigma by the rostellum. The other species include V. pompona,V. tahitensis and V. phaeantha which are resistant to fusarium root rot. Vegetative propagation is through stem cuttings. V. planifolia is the main source of commercial vanilla from central Mexico. This crop is endangered by Cymbidium mosaic virus. Some species of Vanilla that are native to India are V. andamanica, V. pilifera, V. walkeriae and V. wightiana. The highest quality vanilla refers to vanilla with creamy, sweet, smooth and mellow flavor. Maximum flower production is obtained after 7-8 years of age although flowering starts from the third year. Flowers are borne in axils of leaves on stem of previous year’s growth. Fruit is a capsule containing minute globose seeds.

10.33  DRUMSTICK Moringa oleifera or M. pterygosperma. It is also called horseradish tree. It has Indian origin, belongs to family Moringaceae. It has a deep root system and is tolerant/resistant to drought. Fruit is rich in protein, Fe and Ca, Vitamin B and C. It has nutrional and neuraceutical value. It is highly heterozygous and cross-pollinated crop. Crosspollination is through honeybees and bumble bees. The tree is in flowering for 9 to 10 months (February to November) if there is sufficient rain or irrigated. Flowering takes place after 6-8 months of planting. From second year onward there is regular bearing. The flowering time is March-April. Some varieties flower during September-October. Flowering to maturity takes 3 months. Vegetative propagation is through cuttings (Limb cuttings) in which 1-2m long limb is cut and planted during June to August. This tree has short life span (about 20 years). Sahjan honey is also obtained when honey bees feed on drumstick.

10.34  MAKHANA Makhana or Euryale forex is an aquatic herb. This crop requires hot summer and cold winter. It is a monotypic (only one) species belonging to the ‘water lily’ family Nymphaeaceae but now it has been give a separate family called Eurylaceae. It is native to Asia and found in India to Korea, Japan, Russia. In India 65% production comes from Bihar. It can be used in snacks or desserts or as vegetables. It can be roasted. It contains 9.7% protein, 76% carbohydrate, 0.1% fat and 0.5% minerals. It is low in saturated fatty acid, sodium and cholesterol. It is superior to dry fruits such as almond, walnut, coconut and cashew in terms of sugar, protein, ascorbic acid and protein. It is packed up with macro and micro nutrients. Protein is of higher quality because of presence of essential amino acids such as arginine, alanine, etc. It has got medicinal value. It is a diploid with 2n = 58. It is a 7-8 month crop. December-January-sowing of seed, April-transplanting and harvesting in August. Seeds are collected in late summer and autumn. Fruit is developed inside water. One month (about 35 days) for germination and transplanting about 55 days after germination. It has got thick rhizome (it does not have stem). Rootstalks are short, thick and fibrous, 3to 5 clusters, each consisting of about 15 rootlets and with leaves of about 25-120cm. Fruit is persistent with calyx. Leaves have prickles on both sides, upper surface green and

Origin and Genetic Resources of Vegetable Crops

10.79

the lower surface purple. Sepals are four and prickly outside. Petals, numerous, purple inside but green outside. Flowers are cleistogamous (60-70% flowers) but chasmogamous flowers are also produced(remains open for 2-3 days on water surface. Self pollination is more common than cross pollination which is through insects. Stamens are numerous. Fruit is densely prickly with size of an orange, dehisces and seeds get spread. Seeds vary in size, range from pea size to cherry. Seeds have black seed coat and mucilaginous aril. Pulpy aril keeps the seed floating for a few days but finally settle down to the bottom of the pond. There is lot of variation in qualitative as well as quantitative traits, number of leaves/plant (31-46), length of petiole (123-176cm), leaf length (101-175cm), leaf width (100-174cm), color of flowers(dark purple to light purple), number of flowers/ plant (10-19), number of fruits/plant (10-19), fruit length (26-38mm), diameter of fruit (19-28mm), weight of fruit (175-256g), number of seeds/fruit (120-168),weight of seeds/ fruit (74-165g), diameter of seed (10-14mm). Yield/ha varies from 19-32qtls. It is transplanted in first week of April and harvested in August. Seeds harvested during August-September are placed in gunny bag and stored in water and thus seeds are recalcitrant. Seeding is done in December-January, takes 4-5 weeks to germinate and seedlings are transplanted in March-April in well puddled soil. 1kg of seed gives about 400 gm of makhana. It can be grown in pond or field with water level ranging from 1-2 to 6ft.

10.35  CHOW CHOW Chow chow (Sechium edule)  It beongs to Cucurbitaceae. It is chayote squash. It is grown for immature or almost mature fruits. It is viviparous. It flowers throughout the year. It is ahoney-producing plant. It is a perennial, climber. It gives fruit with a single seed. Seed is rich in amino acids. Fruit is rich in Vit. C, Ca, P, Fe, thiamine, viboflowinand ABA. It has got industrial use (antimutagenic substance) as well as table purpose (vegetable). Fruit, stem, young leaves and tuberized portion of the root are eaten as vegetable. It can be grown in backyards. This crop should be replaced after every three years. It is grown on trellis. There are ten species in the genus Sechium. Only two species, namely S. edule and S. tabcaco are cultivated. The latter is cultivated in Cost Rica. It is indigenous to Southern Mexico and central America. The close relatives of S. edule include S. compositum and S. hintonii. The other species of the genus are S. chinantlense, S. jamaicense, S. panamense, S. pittieri, S. pittieri, S. talamacense, S. venosum (or S. villosum). Chromosome number is 26, 28. There are two types of varieties-white and green fruited. It is grown on acidic soil (PH 5.5-6.5). Flower is monoecious, cross pollinated. Cross pollination is through insects. It is commercially propagated through microcuttings. There are two types of varieties-pale green, medium sized and pear shaped and the other is small, white and globular fruit.

10.36  CARROT It belongs to the family Umbelliferae. Daucus carota var. sativum is diploid with 2n = 2x = 18. In Carota group there are four subspecies, namely maritimus, major, aroricus and parviflorus. The Gingidium group contains seven subspecies. Wild species of D. carota is D. capillifolius. Interspecific hbrids involving the two species have been

10.80

Crop Evolution and Genetic Resources

obtained. Interspecific cross involving D. capillifolius has been made to transfer resistance to carrot fly. Also, intersubspecific crosses with D. carota ssp. gadecaei, ssp. azoricus, ssp. dentalus and ssp. hispanicus have been made. The genus Daucus contains more than 80 species. The centre of origin is north and south of Mediterranean sea, north Africa, south east Asia and Ethopia. Afganistan is the primary center of diversity. It is a model plant for the study of plant morphogenesis. Single root cells show clear totipotency. Asiatic carrots are annual (purple to purple black, yellow, reddish-purple) whereas western carrots (orange red to white root) are biennial. Anthocyanin carrots were developed in Asia whereas carotene carrots developed in Europe. White and orange color (carotene) evolved as a result of mutation from yellow form. Orange color is primarily due to alpha and beta carotene. Yellow color is due to carotenoids lutein and red color is because of carotenoids lycopene and purple pigment is due to anthocyanins (Umiel and Gableman, 1972). Carotene is an antioxidant. There are different types of carotene, namely, alpha, beta, gamma, epsilon and zeta. Alpha, beta and gamma carotenes are precursor of Vit. A. Then there are temperate and subtropical carrots. Protandry and outcrossing is through insects. Primary umbel has over thousand flowers whereas secondary and tertiary umbels bear less number of flowers. Thus there are several flower stalks from a single plant. Flower is mainly bisexual but male flowers can occur frequently at the edge and center of an umbellate. Pollen from flowers at the centre is larger and frequently more fertile than that from peripheral male flowers. Seed contains less developed embryo and so takes longer time to germinate. Natural polyploidy species are D. Glochidiatus (tetraploid) and D. montanus (hexaploid). Two types of male sterility systems are found in carrots (Munger, 1953). CMS has been developed from the cytoplasm of three subspecies, namely D. carrota ssp. gummifera, ssp maritimus and ssp gadecaei (Nothnagel, 1992). CMS is similar to onion (Banga et al., 1964) and Brassica. This is also called brown anther form in which pollen does not develop beyond the microspore stage. In case of petaloid and carpeloid the stamens are modified to petals (petal like to filamentous, Eisa and Wallace, 1969). Most hybrids are produced from petaloid CMS. The female: male ratio ranges from 2:1 to 4:1 (Takahashi, 1987). While producing hybrids one must make sure that male produces adequate pollen, female produces adequate amount of seed with high germination percent. Further, female should not be very tall otherwise it will lodge. Finally, both lines should flower simultaneously and they should show similar level of insect pollinator attractiveness. The genetic male sterility is under control of two genes (Hansche and Gabelman, 1963). Petaloid and brown anther mitochondrial genomes gave been characterized. Breeding objectives include non-bolting type, carotenoids, fibre, texture, sugar, flavour, mineral and toxicants. Dark orange carrots have higher percentage of alpha carotene. Cool temperature (1500mm. This tree is tolerant to drought but susceptible to frost. The origin is Madagascar (Tropical Africa). Fruits are pods which can vary from 7.5 to 20cm in length and 2.0 to 2.5cm in width and about 1cm thick. Pods are more or less constricted between the seeds and are slightly curved, brownish ash coloured and scurfy. Pods contain about 3-12 seeds/pod. Flowering occurs during April-July and pods mature during February-April. The product of this tree is the pulp of the fruit which is soft, juicy, appetizing, tasty, delicious because of its brown, sticky, sour-sweet pulp which is used in curry, chutney, pickles, etc. Fruits contain high level of protein, carbohydrate and minerals (K, P, Ca and Fe). Fruit is acidic in taste and it contains tartaric acid and pectin. Reducing sugars include glucose (70%) and fructose (30%) and trace of non-reducing sugar, sucrose. Pod consists of 55% pulp, 34% seed and 11% shell and fiber. It is a predominantly cross pollinated crop. This crop exists as population (a population of genotypes) at a place. Cross pollination is through insects, red ants (Oecophylla smaragdna. There is high degree of self incompatibility and fruit set is only 1-2%. Propagation is through seeds and it will not breed true. The tree takes 10 years to come to regular bearing.

10.41  SEED AND POD VEGETABLE Beans are leguminous vegetables and are important sources of proteins. Leguminous vegetables are given in the table 10.44 below. In relation to Phaseolus, the common bean different gene pool species are shown in the table 10.44. Bean seed contains 20 to 25% protein. They are deficient in sulphur containing amino acid, methionine. Green pods of snap beans are superior source of calcium, iron and Vit. C. Table 10.44  Showing different types of beans and their origin Species

Common name

Vigna angularis

Adzuki bean

Vicia faba

Broad bean

Cyamposis tetragonoloba

Cluster bean

Phaseolus vulgaris

French bean, common bean, snap bean, kidney bean

Lablab urpureus

Hyacinth bean

Phaseolus lunatus

Lima bean

Vigna acunifolia

Moth bean

Vigna radiata

Mung bean

Gene pool

Origin

Meso and south America

GP4

Mexico, Peru

Contd...

Crop Evolution and Genetic Resources

10.88 Contd...

Species

Common name

Vigna umbellata

Rice bean

Phaseolus coccineus

Scarlet or Runner bean

Canavalia gladiate

Sword bean

Phaseolus acutifolius

Tepary bean

Mucuna pruriens

Velvet bean

Psophocarpus tetragonolobus

Winged bean

Gene pool

Origin

GP2

Mexico

GP3

Mexico

P. polyanthus

GP2

P. costaricens

GP2

P. parvifolius

GP3

P. filiformis

GP4

P. angustissimus

GP4

The different beans are cultivated in different areas depending on the taste and preference of the people. Seed vegetable includes rajmah (Phaseolus vulgaris) whereas pod vegetables include, bakla, Vicia faba, Dolichos purpureus, Yard long bean or bora (Vigna unguiculata subsp sesquepedalis and French bean (Phasolus vulgaris). Shim/sem-Dolichos lablab  Dolichos lablab or Lablab purpureus or Hyacinth bean is now called D. purpureus. It belongs to family Fabaceae. It is an Indian broad bean. It is an perennial. It is a good source of vitamins and minerals besides antioxidants. It is one of the major winter vegetables in India. It is diploid 2n with varying number of chromosomes (2n = 20, 22, 24). According to Verdcourt (1970) there are three subspecies. 1. Unicinatus 2. Purpureus and 3. Bengalensis. The subspecies unicinatuts is distributed in West Africa and domesticated only in Ethopia. It is characterised by small pods (40mm × 15mm) and is a wild ancestral form. The ssp purpureus has large pods (100mm × 400mm) and is commercially cultivated vegetables. The ssp. Bengalensis has linear oblong shaped pods (140mm × 10-25mm). Both ssp. Purpureus and ssp. Bengalensis are genetically very similar and thus most of the domesticated materials either belong to ssp. Purpureus or ssp. Bengalensis. It has Indian origin. Two types of lablab are cultivated in India. D. lablab var typicys (lablab bean) and D. lablab var. Lignosus (field bean) (Purseglove, 1968). In case of former, majority are pole types and some are bush type. The pod’s wall is parchmentless and hence whole pod is used for cooking. In case of later pod’s wall contains large amount of fibre and hence whole pod is unsuitable for consumption. The former is a perennial twining herbs (called shim or sem) cultivated as annual in tropical and temperate regions of Asia, Africa and America. D. labalab var lignosus plants are semierect, bushy, perennial and cultivated as

Origin and Genetic Resources of Vegetable Crops

10.89

annual. It attains a height of one feet. Leaflets are smaller than those of var. typicus. Pods are oblong, flat or broad, firmed wall and fibrous. Fruiting starts 60-65 days after sowing and continues up to 90-120 days. Mature seeds are harvested after 150-210 (about 300 days) after sowing. The breeding objective would be to develop stringless variety. Bora  Vigna uniguiculatus subsp. Sesquipedalis is a long podded (one and a half feet) cowpea or asparagus bean. It is a climbing , annual vine, grown in tropical and subtropical climate and eaten as greed pods. Pollinators are yellow jackets and ants. There are stringless varieties with pod length greater than 50cm. This crop is discussed in chapter 6 on Legumes. French bean  Kidney bean/snap bean (Phaselolus vulgaris). It is a common bean grown world wide. It’s green pods are used as vegetable which is delicious and nutritive. It is rich in protein, Ca, Fe, dietary fibre and vitamins. It is discussed in Chapter 6 on Legumes. It is a day neutral vegetable crop and can be grown throughout the year. Phosphorus is the most critical nutrient in the production of legumes. This species has got many types of cultivars grown for either immatured green pods (canned or frozen), green seed or ripe or dry seeds (canned or baked). The dry seed is called ‘Rajmah’. Isolation distance is 50-150m. It can be bush type or pole or climbing type. French bean / Snap bean  Phaseolus vulgaris can be used for table purpose (flat or oval podded) and processing (rund podded, canned, frozen, freeze-dried). Stringless character and round podded have been developed which were absent in the wild species. Cultivated species differ from wild in gigantism, i.e. larger stems, leaves, pods and seeds. Snap bean  Fibreless immature pods are used. Green shell or fresh grain beans (fresh, full sized seeds) are also consumed. Trehalose plays a role in drought resistance. Cultivars with lower amount of trehalose are poorly drought tolerant whereas those that accumulate high amount of trehalose are more drought resistant. P. acutifolius is a source of gene for drought resistance. Breeding objective in snap bean is the high yield. In snap bean from daily picking of immature pod is of extra fine and fine quality. Stage of development at harvest affects both yield and quality of green shelled beans. Picking of immature pods can stimulate compensatory increase in pod production. If the first set pods are retained then the majority of the remaining flowers abort. Single to two picks increases yield by 74%. One can develop dual purpose type variety, varieties with indeterminate growth habit for green bean plus seed beans (for seed). Breeding objective in tropical condition can be the multiple picking variety. One can go for developing climbing variety which is being indeterminate tend to flower over an extended period and which respond to regular picking by developing new pods. Climbing varieties of snap bean are popular in home gardens which produces pods over a longer period than bushy varieties. The breeding objectives besides yield include maturity and horticultural traits. The quality traits include suture and pod wall fiber development which can be related to seed development, flavor, texture, carpel separation, skin coating, interlocular cavitation, internal tissue breakdown and colour. Start of first dry pod is considered useful indicator for starting harvesting of green shelled beans as at least 85% of the estimated maximum yield has accumulated by

10.90

Crop Evolution and Genetic Resources

then. The major yield component in snap bean is pod number. Another objective in snap bean is to develop lines tolerant to density. It is essential for obtaining higher and stable yield per unit area. Selection for higher yield/plant has resulted in incorporation of genes for a wide spectrum of optimum plant density. Bakla  Vicia faba belongs to family Fabaceae. It is used as vegetable, cooked fresh immature seed or processed. Dried mature seed is also used. It is also used as animal feed (immature seed, hay or silage). It is grown during Rabi season. Flowers are white-purple. It is discussed in Chapter 6 on Legumes. Asparagus bean  Goa bean or winged bean (Psophocarpus tetragonobolus) is a climbing perennial but usually treated as annual. Immature pods are used as green vegetable. Leaves are also used as leafy vegetable. Further, tuberous roots are eaten. Mature seeds are soaked and cooked.

10.42  ASPARAGUS Inbred lines can be developed in Aspargus through selfing, full-sib mating and polyembryony. Polyembryony is a quick method of generating inbred lines. Polyembryonic seed contain haploids. Polyembryonic seeds produce multiple (2-3) seedling. The frequency of multiple seedlings is about 0.95% and that of haploid plants is 0.016%. In other words, the greatest proportion of multiple seedling is of diploids and number of haploids is 1.5 in every 10,000 seeds evaluated. To solve the problem of identification of haploids, the anthyocyanin marker-red stalk colour is used. Females recessive for a red-stalk colour are crossed with dominant green stem colour plants as male. In the progeny all seedlings possessing the red stalk marker are haploids. As all haploids are female, these are evaluated by vegetative means (Thevenin and Dore, 1976). Seed propagated inbred lines with normal sex ratio, nearhomozygous and near isogenic between sexes (male and female) are obtained by incorporation of male locus to homozygous female plants and through 5 to 6 backcrossing. Besides developing hybrids using inbreds, double cross hybrids using clones(heterozygous clones) have been developed which have shown higher yields over standard cultivars (Corriols-Thevenin, 1979). Also, single cross hybrids, three way hybrids have been developed. Haploids in asparagus can be obtained using anther culture (microspore culture) through two routes-calli (mixoploids) and embryoids. They develop adventitious roots and stems of one ploidy. Here one can synthesize homozygous super males (YY) or females (XY) using colchicines. Using these dihaploid lines a single cross hybrid with all male hybrids (XX × YY) or three way hybrids with all males can be produced (XY × YY). In the breeding program emphasis is placed on spear diameter, tightly closed heads and anthocyanin pigmentation. Tightly closed heads, smooth buds, compressed scales covering lateral buds are important for green asparagus variety (Ellison, 1986). It is a crop in which harvesting starts only after 2-3 years after seed germination. Yield from first two season harvest is an indicator of the potential yield of longer period (Bussell et al., 1987). Further, open pollinated cultivars have been found to be more stable over environments

Origin and Genetic Resources of Vegetable Crops

10.91

than hybrids. White asparagus is, in general, preferred without a purple spear tip. Purple spear tip can be due to exposure to light at the time of harvest. Spear quality includes size of spears (large spears fetching more price than small or medium sized). Good conformation of spears is preferred over narrow neck below the tip. The tip should be composed of tightly closed, smooth bud and lateral buds be smooth and covered by tightly formed bracts. A round section of spears is preferred over oval cross section. Flat cross section spears are undesirable. Further, fiber free spears are desirable. With aging the plants start producing small size spears than in their prime. However, there are genotypes which can maintain large spears in their old age and this type of genotype be selected for advancing. High branching spears are desirable. It is a monocot, herbaceous, perennial, and a diploid with 2n = 2x = 20. It is grown for succulent fleshy shoots (spears). The genus Asparagus contains about 150 species but Asparagus officinale is the only species which is cultivated as vegetable. There is another spiny species, A. acutifolius whose young spears are eaten. Its origin is eastern Mediterranean and Asia minor. Wild species, A. maritimus is similar in appearance to A. officinale. Ornamental asparagus species include A. plumosus, A. densiflorus and A. virgatus. Medicinal species include A. recemosus, A. verticillatus and A. adscendens. Asparagus is dioecious and male and female plants differ significantly in characteristics. Male plants give rise to more spears and thus are high yielding than female plants. Female plants produce heavier spears but few in number than in male plant. Normal ratio of male: female is 1:1. Thus the objective is to breed super male which will produce high and more stable yield. Further, the objective would be to develop hermaphrodite genotype in future. It is insect pollinated. Male bud is blunt at the top and more cylindrical whereas female bud is somewhat pointed at the top, pyramidal or wedge shaped. Fruit is one to nine seeded berry. Nine large black seed develop and seed longevity ranges from 3 to 6 years. Female flowers have vestigial stamens whereas male flowers have rudimentary pistils, a few of which are capable of setting fruits with one or more seeds. Some varieties are andromonoecious. Sneep (1953) proposed a method of developing uniform male hybrids. Male plants yield more than female plants. Further, male plants live longer than females. Advantage of male hybrid is that they produce no seedling weed, a problem in dioecious asparagus fields. Model of inheritance of sex (phenotype, sex and genotype) is given in the table 10.45 below (Franken, 1970). YY is supermale and XY is andromonoecoius. Tissue culture, especially mersitem culture is used to generate high yielding staminate plants. Table 10.45  Showing genotypes of different types of sexes of Asparagus Pistillate

Staminate

Andromonoecious

XX AA

XYAA

XYAa weak

XX Aa

YYAA

XYaa strong

XX aa

YYAa

YYaa

10.92

Crop Evolution and Genetic Resources

Female sex genotype is homozygous recessive (mm), male sex genotype is heterozygous (Mm) and dominant homozygote (MM) is super male. Homogametic super male (MM) can be distinguished from heterozygotic male through a sex genotype progeny test. Figure 10.6 shows the development of super male hybrid.

Fig. 10.6  Showing development of super male hybrid in Asparagus

Breeding objectives in asparagus include yield, adaptability to specific environment and spear quality and resistance to diseases. Large spears have more market value than small or medium sized spears. Asparagus requires at least two years to become established and comes into production from fourth year onward and it continues to produce spears and seeds for 10 to 20 years. Pollination is primarily by honey bees. Micropropagation  In asparagus microproagation can be used to multiply the planting material. Aseptic culture from spears produce plantlets. The shoots of plantlets are divided into one-bud sections which are grown to provide supple of stock plants. Shoots from these stock plants are again divided into sections bearing one lateral bud each. These sections are planted horizontally 1-2mm deep in soil. Protocol should be worked out to multiply pointed gourd as well. Globe artichoke  Edible parts of globe artichoke, Cynara cardunculus var. scotymus are the immature composite inflorescence (heads or buds referred to as capilula). This is used as fresh or canned. Each plant produces small, medium, large capitula. Largest capitulum is formed on the apex of central stem (primary head), the smaller capitula (secondary heads) develop on the lateral branches. The purple flower is surrounded by leafy green bracts. Both spiny and non-spiny types are cultivated. Cultivated cardoon is C. cardunculus var. altilis. This genus comprises seven species (Rottenberg and Zohary, 2005) as shown in the table given below. C. cardunculus crop complex comprises of three varieties (var.

Origin and Genetic Resources of Vegetable Crops

10.93

scotymus, var. altilis and var. sylvestris) and they are cross compatible (Table 10.46). C. syriaca is the closest member to the cultivated complex. Table 10.46  Showing different speeis of Cynara Genus Cynara

Species C. cardunculus

Variety

Cultivated/wild

var. scotymus

Globe artichoke

var. altilis

Cultivated cardoon

var. sylvestris

Wild cardoon

Gene pool

C. syriaca

Wild species

GP2

C. cornigera syn. C. sibthorpiana

-do-

GP2

C. algarbiensis

-do-

GP2

C. baetica

-do-

GP2

C. humilis

-do-

GP2

C. cyrenaica

Runner bean  It is a perennial with a tuberous root. It has central American origin. It is a twining form and grown on support. Partly developed green pods are used as vegetable. Although a self pollinated crop but cross pollination can go up to 40%. Cross pollination is through Apis mellifera and Bombus spp. (B. lucorum, B. terrestris). These insects rupture the stigmatic surface slightly which helps in penetration of pollen. Isolation distance for seed production is 100m. Dioscorea  Besides Taro root, there are starchy edible tubers which are used as vegetables which include Xanthosoma violaceum, X. atrovirens, Alocasia macrorrhiza and Typhonicum trilobaum (Aroid). Taro is propagated through cormel.

Section B

10.43  CROP IMPROVEMENT Breeding methods in vegetable and spice improvement  There are two groups of vegetable considering the methods of reproduction. Majority of vegetables are sexually propagated by seeds. A small number of vegetables are asexually propagated such as potato, sweet potato, Tapioca, Diascorea and Colocasia. Further, vegetable crops are mainly annuals. Perennial vegetables include asparagus, Jerusalem artichoke, horseradish, rhubarb, etc. Vegetatively propagated crops can be improved through clonal selection and through mutation breeding (Adventitious bud technique) (see Roy, 2000, 2012). Seed propagated vegetables  Among sexually propagated crops majority is cross fertilizing species. Self fertilizing vegetable species with less than 10 per cent cross pollination includes potato, tomato, brinjal, chilli, sweet pepper, pea, cowpea, hyacinth bean, French bean, cluster bean, runner bean, fenugreek, lettuce, etc. Further, there are self fertilizing vegetables which are labelled as often cross pollinated crops as they

10.94

Crop Evolution and Genetic Resources

allow more than 25% outcrossing. In other words, broadly speaking there are three groups of vegetables; 1. cross fertilizing vegetables 2. self fertilizing vegetables which allow < 10% out crossing and 3. Self fertilizing species which allow > 25% out crossing. The economically important traits are fruit, inflorescence, leaves, immature green pods, immature green seed, tubers, seeds, etc. Vegetable crops differ from food crops in that the former produces more seeds per plant and per fruit. Now for improvement of traits in self pollinated vegetable crops such as tomato, cowpea, peas and beans all conventional methods of breeding can be employed and cross pollinated vegetable crops can be improved through application of methods used for improving self as well as cross pollinated crops. But as one fruit produces lots of seed so it will be better to produce hybrids just through hand emasculation and pollination. Trellises and pandal system of cultivation  It improves yield performance of a cultivar by way of facilitating pollination by insects. Thus higher yield can be realized using environmental manipulation through changing cultural practices. Parthenocarpy  Parthenocarpy refers to the ability of plants to produce fruits without fertilization and no seed is produced. Parhenocarpic fruits are required in zucchini summer squash, cucumber, tomatoes and sweet peppers. When an often cross pollinated or normally cross pollinated vegetable species is grown in glass house under protected condition, insect is scarce and thus pollination is not complete which results in loss of yield and this is where there is a need to develop parthenocarpic cultivars. There are a number of methods of obtaining parthenocarpic fruit. i. Use of synthetic growth factors. ii. Use of mutation. iii. Inducing change in ploidy level. iv. Transfer of gene controlling parthenocarpy. Gibberellin and auxin are used for induction of parthenocarpy. In cucumber GA is used to induce parthenocarpy. There are three ways to induce parthenocarpy. 1. Three applications of GA3 at 1000ppm at 15days interval starting from when the plants are in 2-leaf stage. 2. Application of GA4 at 50ppm in the manner stated above. 3. A single application of silver nitrate at the rate of 600 mgl–1 before the first flower opens. Transgenic parthenocarpic fruit has been produced. Coding region of iaaM gene from Pseudomonas syringgae pv. Savastanoi placed under control of placental-ovule specific defh9 gene regulator sequences from Antirrhinum majus. Parthenocarpy is different than parthenogenesis or apomixes. Stenosparmocarpy  Ovule or embryo aborts without producing mature seeds, i.e. seeds die and thus fruit appears seedless. In this phenomenon normal pollination and fertilization occurs and thus differs from parthenocarpy where pollination may or may not occur. Seedless watermelon is produced when triploid is planted with diploid which act

Origin and Genetic Resources of Vegetable Crops

10.95

as source of pollen, i.e., pollination is required. In water melon multiplication is through tissue culture. Sprouting tip of a seedless water melon plant is placed in a petridish filled with growth regulator and nutrients. One tip will sprout to about 15 clone plants. In seedless cucumber and banana fruiting occurs without pollination. Seedless grape is an example of stenospermocarpy. Seedless citrus requires stimulation from pollin atom to produce fruits.

Sex Determination Homeotic mutant Sex ratio-Majority of the cucurbits are monoecious. The male: female ratio (sex ratio) varies from 25-30:1 to 15:1. High nitrogen, long days, high temperature induce maleness. Besides these environmental factors endogenous level of auxin, gibberellins, ethylene and absicisic acid also determine sex ratio and the sequence of flowering on the vines. A primordium can develop into either male or female and can be manipulated by application or no application of auxin. Plant growth regulator can change sex when applied at 2-4 leaf stage. Ethylene induces maleness, thereby increasing the number of male flowers in musk melon, summer squash and pumpkin. In cucumber, maleic hydrazide (50-100ppm), GA3(5-10ppm), ethrel (150-200ppm), TIBA (25-50ppm), boron (3ppm) induce femaleness. In cucumber, gynoecious lines are maintained by inducing male flowers through the application of GA3 (1500-2000ppm). Silver nitrate (300-400ppm) also induces maleness. Sex is genetically controlled but modified by environmental factors. No of nodes to the first male flower and total female flower are both reliable indices of sex. High nitrogen, short days, low light intensity and low night temperature favours female and the reverse favors maleness. Auxin, ethylene or ethrel and MH induce femaleness whereas GA induces maleness In bottle gourd, long days, high temp and spring-summer favour more female flower than autumn-winter and short days. Cucumber is bisexual in early development but later on develops into either male or female. Male flower at lower node is followed by female flower at higher node. In majority of cucurbits flowering starts 30-45 days after sowing and flowers follow a definite sequence. The first 4-6 flowering nodes bear male flowers and starts female flower. An alternate sequence of male and female flowers follows up to fruit set. Development of fruits in a vine determines the development of further female flowers further down in the vine. But this type of pattern (inhibition mechanism) is not found in crops where immature fruits are harvested at tender stage. In melon, pumpkin, ash gourd, even if perfect or female flowers are developed in the vine, fruits do not set or develop fully or if develop then shed in immature condition. This is the reason that the number of fruits/vine in a seed crop is less (4-5) than in vegetable crops (12-15 fruits/vine) in bottle gourd, ash gourd and cucumber.

10.96

Crop Evolution and Genetic Resources

Pollination takes place early in the morning between 6-8AM in cucmber, pumpkin, muskmelon and water melon. Pollination occurs during day when the temperature is high in case of bottle gourd and ridge gourd. In snake gourd and pointed gourd anthesis takes place during night and pollination occurs early in the morning. In cucurbits level of outcrossing is around 68-80% (highly crosspollinated crops) and it is being carried out by honeybees, bumblebees, beetles and moths. Bolting  The untimely initiation of flowering (sudden emergence of seed stalk) in plants is referred to as bolting. Bolting causes a great loss in quality vegetable production. This is an undesirable trait. It reduces the quality of curd in cauliflower and quality of leaves in leafy vegetables. It further reduces the quantity of vegetables. Bolting is a problem in many vegetables such as cauliflower, lettuce, spinach, radish, beet root, onion, leeks, carrot, turnips, etc. In onion bolting or premature flowers occurs before a bulb is formed. In onion bolting in plants will not produce marketable bulbs. Bolting in cauliflower will loosen the curd which will spoil the quality and thus fetches less price in the market. Bolting in carrot and onion is induced by cold. GA promotes bolting. GA is produced during the cold period. In lettuce bolting is a problem in tropically adapted cultivars. In lettuce bolting can occur because of high temperature (>20C), long photoperiod or long day length, higher incidence of disease, nitrogen levels and water stress. Dry soil encourages bolting. In onion bolting is determined by two factors, namely size of the plant and cold temperature. Critical size of bolting is reached when onion is in five-leaf stage of development. Cold temperature is also important. Early transplanting results in bolting. Further, some varieties are susceptible to bolting during cold temperature. All these findings suggest that bolting can be due to genetic and/or environmental reasons. In other words, bolting can be checked by either developing bolting resistant genotype or by adopting suitable cultural practices. Bolting resistant cultivars have been developed in beetroot, onions, carrots and turnips. Red onions are more prone to bolting. It can also be prevented by sowing and transplanting at the correct. In onion, late bolting is controlled by a single dominant locus. For overwintered onion bolting can be suppressed by spraying of nitrogen rich fertilizers. Genetics of flowering  Genetics of flowering time in Arabidopsis has shown involvement of four genetic pathways, namely, photoperiod, autonomous, vernalization and gibberellins pathway (Koornneeef et al, 1998). Mutants for the genes involved in photoperiod pathway show a late flowering phenotype under long day condition which is not responsive to vernalization treatments. These genes include genes encoding photoreceptors such as PHYTOCHROME (PHY) components of circadian clock, clock associated genes such as GIGANTEA (GI) and transcriptional regulator CONSTANS (CO), FLOWERING LOCUS T(FT) and SUPPRESSOR OF OVEREXPRESSION OF CO (SOCI. The autonomous pathway includes genes (FCA, FY, FVE, FLOWERING LOCUS D, FPA, FLOWERING LOCUS K and LUMINIDEPENDENCS) whose mutants show a late flowering independently of day length which can be rescued by vernalization. They regulate FLOWERING LOCUS C (FLC), a floral repressor which works through

Origin and Genetic Resources of Vegetable Crops

10.97

different mechanisms such as histone modification and RNA binding. Some of the genes of this pathway are also involved in ambient temperature signalling. The vernalization pathway includes genes (VERNALIZATION, INSENSITIVE 3, VERNALIZATION 1 and VERNALIZATION 3) whose mutants inhibit the promotion of flowering by vernalization. The GA pathway (discussed in chapter 11) includes genes (FLOWERING PROMOTIVE FACTOR 1 and genes involved in signal transduction) whose mutants show late flowering under short day condition. GAs have shown to positively regulate the expression of floral integrator genes such as SCOI and LEAFY.

How to Practice Selection in Radish, Carrot and Cauliflower? Cauliflower  In case of cauliflower desirable plants are selected on the basis of curd characteristics such as compactness of curd (loose or compact curd), curd size, curd color (white, butter white) and uprooted and planted in a separate field and left for flowering and fruiting. In case of more tight curd scooping in done in order to ensure uniform and simultaneous flowering. In case of very tight curd, ununiform flowering is there. Flowers come first only on the periphery. The central portion bear less flower and flowering is delayed and thus results in variation in maturity. Cauliflower  Heat tolerant variety is required as cauliflower is heat susceptible although not to the same extent as broccoli. Under high temperature curd may develop bracts (green leaves) and curd colour may turn brown or purple or yellow. Solidity (compactness) of curd is essential as soft curded (or loose curded) plant will bolt readily. White or creame color curd is desirable. Colours such as green, orange, purple and yellow or golden are also available. Orange colour is due to the presence of beta-carotene Italy is regarded as center of origin of cauliflower. Radish and Carrot  Radish crop is ready for harvesting after about 50 days of sowing whereas carrot is ready for harvesting for after three months of sowing. Radish seed germinates quickly and in three days, a small plant is observed and there are varieties which can be harvested in just 25 days. While employing selection plants are uprooted and one-third of the root from the lower side is removed and the whole plants are again planted in a new block for flowering and fruiting and thereby seed production. Radish  The cultivated radish is Raphanus sativus and is of Asiatic origin. The wild radish is R. raphanistrum. The species related to radish are mustard and turnip. R. caudatus is treated as variety of R. sativus by some workers. The plant produces indehiscent fruit. Intergeneric hybrids (diploid and polyploid) have been produced involving cabbage (Brassica) and radish (Raphanus). R. sativus x brassica rapa-produced allotetraploid is a fodder crop. B. tournefortii × R. caudatus produces diploid hybrid. Genome of R. sativus is designated as R.

Hybridization Processes Practiced in Vegetables The table 10.47 shows methods of hybridization for developing hybrids in vegetable crops.

Crop Evolution and Genetic Resources

10.98

Table 10.47  Showing various vegetable crops and the method of hybridization adopted Crops

Methods of hybridization

Tomato, Brinjal, Capsicum, Muskmelon

Both emasculation and pollination required

Cucurbits-Cucumber, watermelon, muskmelon, pumpkin and squash

Artificial pollination alone is required

Sweet corn, Baby corn

Detasseling and wind pollination

Spinach

Pulling out male plants (dioecious)

Cucumber, watermelon, pumpkin, squash and bottle gourd

Emasculation or removal of male flower and use of insect to carry out pollination

Cabbage, radish, turnip, Brussels sprouts, broccoli and cauliflower

Insect pollination, use of SI mechanism

Onion, carrot, parsnip and radish

Use of male sterility and wind pollination

The different breeding systems for developing hybrid vegetables are given in the table 10.48 below. Table 10.48  Showing different breeding systems found in vegetables Breeding system SI CMS

Crop Brussels sprouts Carrot, onion, parsnip

Gynoecious line (female line) x male line

Cucumber

Dioecy system, male x female

Spinach oleracea

Monoecious

Sweet corn

Manual (Hand emasculation and pollination)

Tomato, aubergine

Chemical suppressants

Chemical hybridizing agents-chemical gametocides such as gibberellins GA3 and GA4/7 have been used in field experiments in onion to induce male sterility. At higher concentration MS is complete but yield is reduced and at lower concentration gametocidal effect is strong with less reduction in yield. Croisor 100, a plant growth regulator is being used as chemical hybridizing agent for commercial hybrid wheat production in Europe.

Hybrids development in vegetable crops  F1 hybrid was first commercially used in Japan before 1925 (Kakizaki, 1930). Use of SI to produce hybrid in cabbage was proposed in 1932 and using CMS in onion in 1943 (Jones and Clarke, 1943). After that methods to use sex systems to produce hybrids were developed in spinach (monoecious), cucumber (genetically determined), squash(response to chemical) and carrots (CMS) (Pearson, 1983).

Origin and Genetic Resources of Vegetable Crops

10.99

Heterosis increases yield, uniformity and vigor. Hybrid varieties have been developed in spinach, onion, broccoli, maize, sorghum, rice. Systematic production of hybrids requires construction of heterotic groups. The different theories of hybrid vigor includes dominance vs overdominance, epistasic and epigenetic theory of overdominance. There is a role of miRNA. F1 shows higher level of miRNA than P1 or F1 showing lower value than P2. There could be non-additive expression of miRNA, i.e., in other words, there is nonadditive regulation of miRNA. Further, there could be non-additive acetylation and deamethylation of histone-H3. In other words, the acetylation and demethylation of specific amino acid in H3 can either activate or repress associated genes. Heterotic groups can be constructed using diallel and top cross to testers, hybrid index, diversity by Mahalanobis distance, genetic diversity by Euclidean distance and genetic diversity by SSR (simple sequence repeat) marker. Biplot analysis of diallel data can be used for quick overview of GCA and SCA effects of lines and their performance in crosses and grouping of similar inbreds through graphical representation. Genetic diversity base on SSR marker is the best method for constructing heterotic groups. Genealogy of the lines and use of molecular markers uses maximum likelihood (MLH) to estimate the proportion of alleles that are inherited from one of the two parents involved in crossing. Inbreeding depression  There are vegetable crops such as muskmelon (C. melo), summer squash (C. pepo) which do not show inbreeding depression whereas carrot shows high inbreeding depression. Use of male sterility/self-incompatibility  Hybrids can be developed using either using self-incompatibility or male sterility. Fluorescent microscopy can be used to provide direct measure of SI. It shows those pollen tubes which have penetrated the style and this process is completed within 12-15hrs. Aniline blue stain accumulates in the pollen tube which fluoresces when irradiated with U.V. light and pollen tube becomes visible. Penetration by few pollen tubes shows incompatibility reaction whereas penetration by many tubes indicates compatibility. There are 12 S-alleles in cabbage. Most of these alleles occur in kale or Brussels sprouts. S2 is by far the commonest allele as it is in B. oleracea as a whole. The highly recessive alleles, S5 and S15 are not particularly common in cabbage and this is the reason that sib problem is apparently less in F1 hybrids of cabbage than in Brussels sprouts. Characteristics of self-incompatibility in Brassica species are: 1. Co-dominance relationships are more frequent than dominance/recessive ones in both stigma and pollen. 2. Dominance occurs more frequently in the pollen than in the stigma 3. Allels which are dominant to others in he stigma are not necessarily dominant to the same alleles in the pollen. 4. Dominance is non-linear, i.e considering three incompatibility alleles, Sa, Sb and Sc, Sa > Sb, Sb > Sc but Sa > Sb > Sc (i.e., Sa > Sc). S2 and S5 are the commonest alleles in Brussels sprouts. The commonest alleles are recessive and the rare alleles are dominant. Dominant S-alleles confer higher degree of SI than recessive S-alleles. The recessive S-alleles when present at high frequency allow some inbreeding while dominant alleles even when present at low frequency promote out crossing. Because dominant S-alleles confer higher degree of SI, it is desirable to incorporate them into inbred lines used for production of hybrids.

10.100

Crop Evolution and Genetic Resources

Self incompatibility  41 S-alleles have been reported to occur in B. oleracea of which 13 alleles are common to both kale and Brussels sprouts. In cabbage number of S-alleles in a variety ranges from 4 to 13 and on an average there are 7 to 10 S-alleles per variety. Five S-alleles were exclusively found in only cabbage. The most recessive alleles in B. oleracea are S5 and S15 these are often associated with poor self-incompatibility both in kale (Thompson and Taylor, 1971) and Brussels sprouts (Smith, Blyton, Conway and Mee, 1982) but not particularly common in cabbage. S2 is the most commonest S-allele in B. oleracea including cabbage. Commonest alleles are recessive and rare alleles are dominant. This is the reason that sib problem in F1 hybrid production is less in cabbage than in Brussels sprouts. A cultivar with only 4 S-alleles, 3 of which are recessive, will certainly be subjected to more inbreeding than a cultivar having 11 S-alleles, four of which are recessive. Further, intense selection for uniformity could lead to loss of S-alleles, and accumulation of high frequencies of recessive S-alleles (Thompson and Taylor, 1966b). Most of the S-alleles in cabbage also occur in other cole crops which shows their common ancestry but distribution of S-alleles in cabbage differs from that of other cole crops. As these crops are fully interfertile, they must be kept separate if they are to retain their distinctive features. The splitting up of the cole crops gene pool has led to the differences in S-allele distributions which are maintained despite the fact that S-alleles can be transferred from one cole crop to another. The advantage of breeding inbred lines with dominant S-alleles is that they will be highly Sl and further they will be cross compatible with the majority of the inbreds. While synthesizing synthetic variety one must make sure that least 4 different S-alleles be present and it is probably best if most of the recessive S-alleles are excluded. Nuclear male sterility is determined by either dominant or recessive genes, its sterility can be restored easily but maintenance of sterility is difficult. Cytoplasmic male sterility is easy to maintain but difficult to be recovered. Ogu (Ogura) (Ogura, 1968) cytoplasm, first found in Japanese radish (Raphanus sativus) has been transferred to B. Oleracea from B. napus through protoplast culture (through interspecific cross). Rf0 the restorer gene from radish restores the fertility in B. napus. nap and pol (Polima) CMS have been transferred to B. oleracea from B. napus (oilseed rape). The restorers are Rfn and Rfp genes for the cytoplasm, nap and pol, respectively. They are different alleles or haplotypes of a single locus. This is in contrast to CMS in other species. The different forms of Brassica CMS are restored by the alleles of a single locus. There are other CMS such as mori (from Moricanda arvensis cytoplasm, 2n = 28), oxy (B. oxyrrhina cytoplasm causes male sterility in B. campestris), lyr (Enarthocarpus lyratus based CMS) and refined ogu. CMSs derived from somatic hybridiaztion have been found superior over those developed from sexual hybridization. Substituting the nuclear genome of B. rapa into the cytoplasmic background of E. lyratus using backcrossing method results in development of CMS. For CMS ogu INRA the restorer gene is Rf. CMS thus can arise spontaneously in wide crosses, through interspecific exchange of nuclear and cytoplasmic genomes or though mutagenesis. Ogura cytoplasm has been transferred to different Brassica crop species through interspecific hybridization. CMS is associated with chimeric mitochondrial

Origin and Genetic Resources of Vegetable Crops

10.101

ORFs and fertility restorer is associated with genes encoding pentatricopeptide proteins (Chase and Babay-Laughnana, 2004; Hanson and Bentolila, 2004). Male sterile pollen will be shrivelled and unstained when prepared with 2% acetocarmine stain and observed through 10x hand lens or under microscope using a haemocytometre. The fertile pollen will be round and red. Reactions of restorer genes against different types of male sterile cytoplasm are given in Table 10.49 below. Table 10.49  Showing cytoplasm and its interaction with restorer gene Cytoplasm

Restorer genes rfn, rfp

Rfn, rfp

Rfn, Rfp

cam

F

F

F

nap

S

F

S

pol

S

S

F

In bulb onion both CMS and genetic MS are found. In onion flowers are perfect and protandry. Large scale emasculation and pollination is practical. CMS is commercially used to produce hybrids in bulb onion, Japanese bunching onion (A. fistulosum) and chives (A. schoenoprasum). There are two kinds of cytoplasm-S-cytoplasm and T-cytoplasm. In case of S-cytoplasm nopollen shedding occurs, no pollen is released from anthers of MS plants due to premature breakdown of the tapetum at the tetrad stage, hypertrophy of the tapetum at the dyad stage or abnormally long retention of the tapetum (Monosmith, 1925; Holford et al., 1999b). Further, unlike T-cytoplasm of maize, sunflower there are no differences in number or structure of mitochondria in the tapetum of N-and S-cytoplasmic onion. In other words, there are differences in the mtDNAs among N-fertile and MS cytoplasm of maize and sunflower. S-cytoplasm of onion does not possess small circular DNA molecules (episome) like the S-cytoplasm of CMS in maize. Additionally, the MS of the S-cytoplasm is not transmissible by grafting and virus-like particles are not found. CMS is conditioned by the interaction between cytoplasmic and nuclear factors. S-cytoplasm with ms/ms (male sterility locus in recessive homozygous form) gives rise to male sterile plant. There is single male fertility restorer locus (Ms). Advantages with CMS system in onion is that the nuclear male fertility is a simple inherited trait and that there is stable expression of MS across a range of temperature. The second source of male sterility in onion (bulb onion) is T-cytoplasm. Male sterility in T-cytoplasmic plants is resored by dominant alleles at one locus (A-) or at both of two complementary loci (B-C-). Potential useful source of CMS is A. galanthum, need to be transferred to bulb onion, shallots (A. cepa)-Aggregatum group and Japanese bunching onion. Fertility restorer, dominant allele, Rf, originated from A. galanthum, restores the galanthum-CMS bulb onion. Hybrid seed production in leek is by genetic male sterility (Schweisguth, 1970). Asexual propagation of genetic male sterile plant is currently used to develop hybrids. Interspecific hybridization between CMS onion and leek is being done to transfer CMS from onion to leek.

Crop Evolution and Genetic Resources

10.102

In chives CMS is as a result of interaction of the S-cytoplasm and a single nuclear fertility restorer locus (X) (Tatlioglu, 1982). Microspores die in the MS plants. Male sterility is sensitive to chemical and environmental factors. Tetracyclin restores male fertility. In case of CMS in A. fistulosum, male fertility restoration is inherited in a more complex manner than in either bulb onion or chives. CMS is conditioned by interaction of cytoplasm-S with two nuclear restoration loci, MS1 and MS2 (Moue and uehara, 1985). Male sterility occurs when both of these nuclear fertility restorer loci are homozygous recessive Onion  In case of T-cytoplasm (Schweisguth, 1973) the male sterility is due to interaction between T-cytoplasm and three recessive genes, one independent gene, a and two complementary genes, b and c. This type of male sterility is restored by MSMS as in case of S-cytoplasm (Jones and Clarke, 1943). As the heterotic advantage of F1 hybrid over better parent has been in the range of 4-13% and so it is not clear whether or not one should for development of hybrids in onion. In case of onion the following cross be used for the production of hybrids using male sterility. Smsms × Nmsms

F1 Smsms (male sterile)

As bulb is harvested in onion so it does not matter whether F1 produces seed or not. When a crop is vegetatively propagated or where seed is not eaten this method of using cytoplasmic male sterility for the development of hybrids can be used. For example, in case of forage crops where means of propagation is vegetative, it can be used for developing hybrids. In case of flowers where part (s) other than seed are important, this method can be employed. Using self incompatibility, hybrids can be produced in two ways. 1. SI × Self fertile cross or 2. SI × SI cross (e.g. S1S1 × S2S2). The problem with SI system is that SI is incomplete in the sense that 1. SI depends on developmental stage of the plant, 2. on external factors (environmental factors) and 3. hybrids produced contain some selfed seeds because of selfing. Bud pollination is done to produce inbreds and it is done 3-4 days before bud opens. At that time the style and stigma are both receptive and SI factor has not yet developed. And so open the flower 1-4 days before they would naturally open. SI may be overcome by CO2 enrichment (plants are put in a closed chamber with higher concentration (5%) of CO2, the most efficient method of overcoming self incompatibility), electicity aided pollination, wire brush pollination, temperature aided pollination and spraying with NaCl (spraying of 3-4% NaCl solution onto the open flower and after 20-30min remove the excess salt, the salt removes the inhibitor from the stigma). Caulifower is predominantly self compatible. Thus it is better to go for use of genetic male sterility system. The problem with genetic male sterility system is that from the female line (row) in the crossing block male fertile plants need to be rouged out. Those

Origin and Genetic Resources of Vegetable Crops

10.103

crops such as tomatoes, lettuce, bean whose flowers lack nectarines, self incompatibility is a more efficient mechanism for facilitating cross pollination than male sterility. The two mechanisms, self incompatibility and male sterility facilitate outcrossing and thus hybrids can be developed. Hybrids have advantage of being uniformity in plant size, shape and maturity. Older hybrid varieties will continue to use SI mechanism (cabbage, cauliflower, broccoli, Brussels sprouts, kale) but presently CMS is being used to develop hybrids because of many advantages in Brassicas. For details on method of developing hybrids using these mechanisms see Roy, 2000, 2012. The problem associated with single cross hybrid development using eith SI or MS mechanism is that seed produced on inbred parent is low because of the fact that inbred parents are less productive and thus emphasis is now on the development of three way cross or double cross hybrids. Large quantity of hybrid seed is harvested from the F1 female parent. Alternatively, one can go for production of top cross cross in which inred parent is crossed with open pollinated line used as male and seed is saved from the female inbred parent. In order to develop single cross hybrid in Brassica species it is a must to develop vigorous inbred parents which can be done through the use of population improvement. First through various recurrent selection schemes improved populations should be developed and from which subsequently inbred lines be extracted. Method of producing double cross: S1S1 × S2S2  S3S3 × S4S4 S1S2 × S3S4 S1S3, S1S4, S2S3, S2S4

Triple cross: S1S1 × S2S2 S4S4 × S5S5 S1S2 × S3S3 S4S5 × S6S6 S1S3, S2S3 × S4S6, S4S6 F1 hybrid

10.104

Crop Evolution and Genetic Resources

Development of composites/synthetics  In cauliflower, cabbage, radish, carrot, onion, etc. in which the flowers are small and difficult to hand pollinate one can employ polycross mating to develop improved population or develop synthetic/composite varieties. It does so by providing the estimate of general combining ability of inbred parent and open pollinated varieties. Polycross is also used when a suitable tester variety is not available for developing top cross progenies. Also in spice such as coriander which attracts honeybees, use of polycross can be made to determine general combining ability and to develop synthetics. Synthetics can also be synthesized in niger and safflower which attract lots of honey bees. Polycross is also employed in the development of grasses. In this method propagules from each selected clone/inbred are planted at random into smaller compact plots in a replicated (usually 4-10) and isolated polycross nursery. Seed from each line is collected which is supposed to have been outcrossed with other lines/clones growing in the same nursery. Volumes of the pollen produced, time of anthesis, differential cross compatibilities, level of inbreeding, plant height and lodging affect random pollination. Equal amounts of seed harvested from each entry from all replications are bulked to constitute the polycross seed which is then raised in the subsequent generation for evaluation. Use of cloth or plastic screen pollination cages is made for ensuring cross pollination. Flies or bees are released in the pollination cage to transfer pollen or pollen is transferred between plants by hand or brush. In case of carrots flowers are small and only generate up to two seeds per pollination. Inbred lines to be evaluated for general combining ability are isolated with a set of male sterile testers to allow development of hybrid progenies for evaluation from a single cage. Synthetic varieties are primarily used in forage species like grasses and clovers. 5-10 highly heterozygous parental clones form the basis of a synthetic variety. In case of onion synthetic variety is developed through S1 selection. Plants of OPV/F1 are selfed and selfed generation S1 is evaluated in the second year. Between and within family selection is practised within S1 lines. Intercrossing is allowed in the third year and in the fourth year the reconstituted population is grown and individual bulb selection is practised and this process is repeated. After 4-5 cycles of S1 family selection bulked seed is used as synthetic variety. Synthetic or composite varieties can be developed in sweet corn. In all those cross fertilizing vegetables and those self fertilizing species which allow more than 25% cross pollination synthetic varieties can be developed. Production of doubled haploid (DH) lines  In crops likes onion which shows high inbreeding depression and selfing can not be continued for more than 2-3 times, the inbreds so produced are partially inbreds and thus the F1(hybrid) developed shows considerable phenotypic variability. In that situation it will be better to develop DH lines showing high genetic uniformity. In case of onion DH is produced through gynogenic embryo induction and not through the more efficient microspore culture technique. Flower buds are used as explants in onion. The problem with DH production is that the haploid induction is genotype dependent and further chromosome doubling is also a problem as only 10% of the embryo develops into DH. Finally, the DH lines so developed are showing severe

Origin and Genetic Resources of Vegetable Crops

10.105

inbreeding depression. These problems of genotype dependency is can be solved by using line(s) showing high hapoid induction and problem of inbreeding depression can be solved through crossing between DH lines or sib mating. Another method of for production of haploids is the use of polyembryonic seeds which are produced in asparagus, pepper, etc. For more on genetics and production of DH lines see Roy, 2000, 2012. Improvement of dioecious vegetables  In case of spinach, pointed gourd and Asparagus one breeding strategy would be to improve male and female line separately and then plant seeds from both parents for commercial crop. Further, as is done in case of papaya, a dioecious fruit crop, the breeding aim should be to develop variety with hermaphrodite flowers so that fruit yield can be increased. Further, hybrids can be developed. Male and female lines can be improved separately.

Improvement of Tree Spices and Vegetables Cloves, cinnamon, drumsticks, jack fruit are tree species and thus those breeding methods which can be applied for the improvement of fruit crops (see chapter 9) can also be applied in here. They will all be heterozygous and crossing followed by individual plant selection in the segregating population and multiplication of best selection through vegetative method will the method of choice. Further, tissue culture method for mass propagation and adventitious bud technique for mutation breeding will be another methods. Besides these, use of rootstock can be made to solve problems of soil borne pathogens (biotic stress), abiotic stress (soil salinity, alkalinity, water logging, marshy land, etc.) and improve other traits. A list of minor vegetabls is given in the table a below 10.50. There is nothing like minor or major vegetable. A vegetable is a minor vegetable at a place (or location, region/ country, environment) but a major vegetable at some other place (location, region/country or environment) depending on the liking or preference of the consumer, its market, etc. Yield components  Yield components of some vegetable crops are given in the Table 10.50. Table 10.50  Showing yield components of some vegetable crops Crop

Yield components/breeding objectives

Asparagus

Number of spears, Average diameter, Average weight/spear

Cabbage

Head size, head weight, Number of heads per unit area

Broccoli

Head size, head compactness

Carrot

Length and shape of the root, average root weight, number of plants per unit area, percent useable roots

Quality traits

Conformation, exterior and interior leaf colour, core length, density of head, no growth cracks Orange colour, same colour of both cortex and core xylem, texture-crisp, absence of secondary root, low oil content Contd...

Crop Evolution and Genetic Resources

10.106 Contd...

Crop

Yield components/breeding objectives

Quality traits

Cucumber

Higher number of pistillate flowers, more vigorous vegetative phase, total yield, total number of fruits/plant

Winter squash

Total yield/plant, yield of mature fruits/plant, average fruit weight, number of fruits/plant

Brinjal (aubergines)

Size of plants, number of primary branches, number of fruits/plant, average weight of fruit

Pepper (Capsicum)

Number of fruits/plant, Average fruit weight

Spinach

Petiole and leaf tissue (weight of single leaf), leaf dimensions

Tomato

Number of fruits/plant, average fruit weight, solid content

Onion

Bulb yield per unit area, average bulb size, average bulb weight

Sweet potato

High yield and good culinary qualities. Root yield, growth cracks, dry matter, skin colour, high sprouting, vine length, leaf type, flower buds/cyme, good storage characteristics, flooding resistance

Flesh colour, skin color, fibre, crude protein, flesh oxidation

Watermelon

Yield/acre-number of melons and total weight, small size, thinner but tougher rind, firm flesh and small seed size is the requirement in present times.

Flesh color-intense red preferred over paler red or pink. Sweetness (soluble solids), flesh texture and firmness. Flesh could be melting or fine grained flesh or fibrous (and/or coarse grained) flesh, high proportion of edible flesh and dense seed packing in the center of the fruit (small cavities without empty spaces between carpels are preferred). Seeds are located in central cavity of the fruit surrounded by the edible flesh.

Capsicum

Earliness, yield, fruit shape and size

Flavor compounds, pigment content and Vit. C content. Fruits having strong pleasing and high sugar/acid ratio are desirable

Tomato

Yield/plant, number of fruits/plant, fruit size, fruit weight

Flavor, aroma, texture and fresh market and processing product quality parameters

Bell pepper-Uniform block shape, smooth and shiny surface, strong uniform color (green (unripe), red, yellow and purple), thick and firm pericarp and good storage quality (higher shelflife, > 1-2 weeks)

Earliness is the economically most valuable character and fruits should be free from insect infestation and diseases. Further, breeding objective in vegetables will be to reduce the ‘juvenile phase’ (planting to opening opening of the first pistillate flower and ‘ripening phase’ (anthesis to maturity of the first fruit).

Origin and Genetic Resources of Vegetable Crops

10.107

Table 10.51  Showing minor vegetables, its origin and breeding system Crop Asparagus

Annual/perennial,Botanical name, family A. officinale, perennial

Amaranth Globe artichoke

Perennial, herb

Cross pollinated Cross pollinated

Jerusalem artichoke Brussels sprouts Broccoli Beet Basella

Perennial

Cross pollinated

Chives Chinese chives Celery Celeriac Chicory Chekkurmanis

Perennial Perennial Biennial, herb Biennial, tuber, Umbelliferal Perennial Perennial, shrub, Sanropus androgynus, Euphorbiaceae, other species include S. assimilis, S. retroversus, S. rigidus, S. quandrangularis, Annual, herb Annual, herb, Cassia alata, Caesalpinaceae, other species-C.angustifolia, C.obovata, C. tora, C. obtusifolia, C. senna and C.tomentosa Perennial/annual Biennial

Cassia Coleus

Welsh onion Swiss chard

Ploidy level, center of origin

Breeding sytem Dioecious,

Annual/biennial Annual Annual/biennial Perennial,

Cross pollinated

2n = 22, Origin-Europe Indo-Berma

2n = 24, Tropics

Dendelian

Perennial, Taraxicum officinale

2n = 16, 24, 48, Temperate

Endive Horseradish

Biennial Perennial, Armoracia rusticana, Cruciferaea

2n = 32, SE Europe and WAsia

Cross pollinated Cross pollinated (monoecious), protogyny

Characteristics, method of propagation Seed, crown (one year old) seed Offshoots, seed/division of old crowns Tuber or pieces of tuber approx. 2oz seed seed seed Climbing vine, stem and root cuttings Seed/plant division seed seed seed seed Stem cuttings/seed

seed Vine cuttings/seed

Seed/division Cross pollinated, seed SI and protandry Seed, several crops can be taken in a season, better green salad than lettuce, celery and endive seed Cross pollinated Root cuttings Contd...

Crop Evolution and Genetic Resources

10.108 Contd...

Crop

Annual/perennial,Botanical name, family Leek Biennial Mint Perennial Orach (Mountain Annual, Atriplex hortensis, spinach) Chenopodiaceae Shallots Perennial Parsely Biennial Parsnip Biennial, Pastinacea sativa Rosemary Rozella Rhubarb Salisify Rumex Sage

Perennial, evergreen shrub Rosmarinus officinalis Annual Perennial Biennial, Tragopogon porrifolius Annual/biennial Perennial, evergreen aromatic shrub, Salvia officinalis, Lamiaceae, other species include S. lavandulaefolia, L. triloba and S. sclarea

Swede/rutabaga Thyme Perennial,shrub, evergreen, Thymus vulgare, Lamiaceae (Labiatae), other species include T. zygis (white or Spanish thyme), T. serpyllum (white or creeping thyme), T. capitatus (Spanish origanum, T. citriodorus (Lemon thyme), T. satureioides (Moroccon thyme) and T. pulegioides (Broad leaf thyme) Kale/collards Perennial Lettuce Garden cress Curry leaf

Annual Annual/perennial Perennial, shrub or small tree, Morraya koenigii, Rutaceae

Ploidy level, center of origin

2n = 18

Mediterranean 2n = 24, Mediterranean

2n = 12, Mediterranean 2n = 14, North East Mediterranean

2n = 30, Mediterranean (Souther Europe)

2n = 16, 32, Ethopia 2n = 18, India

Breeding sytem

Characteristics, method of propagation Seed Seed/cuttings Seed

Seed (bulb) seed Cross pollinated, seed protandrous Seed, stem and root cuttings seed Seed/crown seed Seed, root cuttings Seed, stem cuttings

seed Stem cuttings, root division, seed

Cross pollinated, seed SI Self pollinated seed seed Self pollinated seed

Contd...

Origin and Genetic Resources of Vegetable Crops

10.109

Contd...

Crop Sorrel

Annual/perennial,Botanical name, family Perennial, Rumex acetosa

Ploidy level, center of origin 2n = 21, 22, 29, British origin

Breeding sytem

Characteristics, method of propagation seed

Spinach Broad bean

annual

Dioecious

seed seed

New Zea land spinach

Annual, Tetragonia expanse, New Zea land

2n = 32

seed

Chard or leaf beet

Biennial, Beta vlgaris var. cicla

2n = 18, 36, Italy origin

seed

Rakkyo

Perennial, herb

Purslane

Kulfa sag, Annual, herb, Portulacea oleracea, Portulacaceae

Water leaf

Ceylone spinach, Talinum 2n = 48, 72, Brazil triangulare, other species include T. arnotti, T. caffrum, Tportulacifolium, T. patents, T. crassifolium, T. cuneifolium and T. indicum

Yam bean

Annual

Chervil

Annual/biennial, Anthriscus cerefolium

Water cress

Perennial

seed

Sea kale

Perennial

Seed/cuttings

Cassava

Perennial

stem

Bulb 2n = 54, Indian origin

seed

Self pollinated

Seed/stem cuttings

seed 2n = 18, Europe, SW and N. Aisa

seed

10.44  ‘DISEASES AND PESTS OF SOME VEGETABLE CROPS’ The table 10.52 given below shows important diseases and pests of some vegetable crops. While carrying out crop improvement program these constraints must be made as breeding objectives. Table 10.52  Showing important diseases and pests in some vegetable crops. Crop

Diseases and pests Fungus

Asparagus

Bacterium

Virus

Insect and nematodes

Fusarium wilt (F. oxysporum f. sp.aspargi), Stemphyllum leaf spot (S. vesicarium), Phytophthora rot (Phytophthora megasoerma, Rust (Puccinia aspargi) Contd...

Crop Evolution and Genetic Resources

10.110 Contd...

Lettuce

Downy mildew (Bremia lactucae), lettuce drop (Sclerotinia minor), Verticillium wilt, Fusarium wilt

Spinach

Downy mildew (Peronospora farinosa f. sp. spinaceae), white rust (Albuigo occidentalus), anthracnose (Colletotrichum dematium). Cercospora beticola, Fusarium oxysporum, Rhizoctonia solani, Phytophthora aphanidermatum

Cucumber

Scab (Cladopsorium cucumeriosum), Downy mildew (Pseudopernosperma cucubensis, Anthracnose (Colletotrichum lagenarium, Fusarium wilt

Cauliflower and Broccoli

Downy mildew (Pernospora farinose f. sp. spinaceae, White rust (Albuigo occidentalis), Fusarium wilt (F. oxysporum f. sp. spinaceae)

Watermelon (It is one of the most susceptible Cucurbit species to gummy stem blight and also it is one of the most resistant Cucurbit species against powdery mildew.

Fusarium wilt (F. oxysporum f.sp. niveum), Anthracnose (Colletortichum lagenarium), Gummy stem blight, Powdery mildew (Spaerotheca fuliginea)

Carrot

Leaf blight (Alternaria dauci, Xanthomonas campestris pv.carotae), Cercospora carotae, Powdery mildew (Erysiphe heraclei), Carrot spot (Phythium spp.)

Corky root of lettuce- LMV (Lettuce mosaic Lettuce aphidSphingomonas virus) vectored by Nasonovia ribisnigri suberifaciens green peach aphidsMyzus persicae, Big vein (Mirafiori lettuce big vein virus, MLBVV vectored by soil borne fungus, Olpidium brassicae Green peach aphid(Myzus persicae), leaf minor (Liriomyza spp.)

Bacterial wilt (Erwinia tracheiphila)

Cucumber mosaic virus (CMV), WMV, Poty virus, ZYMV, GMMV (Green motle mosaic virus)

Bacterial rind necrosis (Erwinia spp.), bacterial fruit blotch

PRSV-PRSV-W

Root knot nematode (Meloidogyne spp.)

Carrot fly (Psila rosae), Nematode (Meloidogyne spp. (M. incognita, M. javanica and Heterodera carotae Contd...

Origin and Genetic Resources of Vegetable Crops

10.111

Contd...

Cabbage and Kale

Black rot (Xanthomonas campestris pv.campestris), club root (Plasmodiophora brassicae). Alternaria spp, Leptosphaeria macularis and Peronospora parasitica are of world wide importance

Cabbage worm (Pieris rapae), Cabbage looper (Trichoplusiani), diamond backmoth (Plutella xylostella), cabbage fly (Delia radicum), cabbage aphid (Brevicoryne brassicae), Flea beetles (Phyllotreta spp.)

Melon

Powdery mildew (Podosphaera xanthii and Golovinomyces cichoracearum, downy mildew (Pseudoperonospora arbensis), Fusarium wilt (F. oxysporum f. sp. melonis), Gummy stem blight (Didymella bryoniae)

Summer squash

Powdery mildew (Podosphaera xanthii and downy mildew (Pseudoperonospora cubensis)

Zuchini YMV(ZYMV). CMV – the most damaging disease, white flies transferred through aphids, white flies transfers SLCV (squash leaf curl begomovirus), beetles transfer squash mosaic virus)

Onion

Downy mildew (Peronospora destructor), Fusarium basal rot, Pink rot (Pyrenochaeta terrestris or Phoma terrestris)

Onion fly (Delia antiqua)

Pea

Foot and root rots (Aphanomyces enteiches, downy mildew (Peronopspora viciae), pea blight (a complex of Mycospaerella pinodes var. pinodella and Phoma medicaginis)

Bacterial wilt (Erwinia trucheiphila)

Polero virus, Aphids (Aphis Cucumovirus, Tobamo gossypii), Root knot virus, Crinivirus, nematode (M. spp.) polyvirus

Contd...

Crop Evolution and Genetic Resources

10.112 Contd...

Snap beans

Alternaria leaf spot (Alternaria alternata), Phythium spp. Fusarium root rot, Root and stem disease (Rhizoctonia solani)

Bacterial brown spot (Pseudomonas syringae), bacterial wilt (Corynebacterium flaccumfaciens)

Common mosaic virus, beet curly top virus (BCTV), beet green mosaivc virus(BGMV) and beet yellow mosaic virus (BYMV)

Aphidae, Hemiptera and Coleoptera, Root knot nematode (Meloidogyne spp.).

Pepper

Phytophthora root and stem rot (Phytophthora capsici), powdery mildew (Laveillula taurica)

Bacterial leaf spot (Xanthomonas campestris pv.vesicatoria)

Tobacco mosaic virus (TMV-transferred by meachanical means and by seeds), Potyvirus (PVY , TEV), Cucumber mosaic virus (CMV- the most destructive virus in Asia), Bagamovirus (vectored by white flies) and tospovirus (transferred by thrips and beetles)

Root knot nematode (Meloidogyne spp.)

Egg plant

Fusarium wilt (F. oxysporum Bacterial wilt f. sp. melongena), (Pseudomonas verticillium wilt (V. dahliae solanacearum) and V. albo-album), Fruit anthracnose (Colletotrichum gloeosporioides),

Virus (Tomato spotted Fruit and shoot borer virus and pot virus),) (Leucinodesorbonalis)the major pest in Asia. Nematode (M. incognita)

Tomato

Alternaria blight (Alternaria solani)

TMV (transmitted by contact), TSWV (vectored by thrips), Tomato leaf curl virus (TYLCD, vectored by Bemissia tabaci), white flies transmit gemini viruses, Phids (Aphis gossypii) –vector of several non-persistent virus such as C (cucumber) MV, A (alfalfa) MV and potato virus (PVY)

Bacterial leaf spot (Xanthomonas), Bcaterial wilt (Ralstonia solanacearum), Pseudomonas syringae)

10.45  DESCRIPTION OF DIFFERENT VEGETABLES Chard/Swiss chard/leaf beet is a variety of Beta vulgaris cicla with large succulent leaves and thick stalks used as vegetable. Kale is a cultivated variety of cabbage, B. oleracea acephala with crinkled leaves.

Origin and Genetic Resources of Vegetable Crops

10.113

Collards is a variety of cabbage, B. oleracea acephala having a crown of edible leaves, eaten as vegetable. Garden cress is a pungent tasting Cruciferous plant Lepidium sativum, cultivated for salads, as a garnish. Scallion has a small bulb and long leaves and eaten in salads. Chive/Chives has long, slender, hollow leaves and are used in cooking to flavor soups, stews, etc. Broccoli is a cultivated variety of cabbage, B. oleracea italica, having branched, greenish flower heads. Muskmelon is any of the varieties of C. melo (Cantaloupe, Honey dews, etc, see Table) having a ribbed or warty rind and sweet, yellow, white or green flesh with a musky aroma. Pumpkin are plants of C. pepo and C. maxima and has thick orange rind, pulpy flesh with numerous seeds. Squash are plants of C. pepo and C. maxima which has hard rind surrounding edible flesh. It is a green vegetable eaten green. Celery is an umbelliferous Eurasian plant (Apium graveolens dulce)’ whose blanched leaf stalks are used in salads or cooked as vegetable. Parsnip  A strongly scented plant of Patinaca sativa is cultivated for its long whitish root, eaten as vegetable. Parsley(Petroselinum crispum) is an European umbelliferous plant widely cultivated for its curled aromatic leaves which are used in cooking. French bean/green bean is a twining, bushy, annual plant of Phaseolus vulgaris. Its slender green pods are edible. It has white or lilac flowers. Lima bean  It is cultivated in U.S.A. for its flat pods containing pale green edible seeds. There are two species of lima bean, P. lunatus (climbing, small seeded, annual) and P. limensis(large seeded type). Scarlet bean/runner bean/string bean  It is a climbing perennial plant of P. multiflorus or P. coccineus. It is having scarlet flowers. It is widely cultivated for its long green edible pods(unripe pods)containing edible seeds. Mint  It is a perennial herb with rhizomes and belongs to genus Mentha. It is having aromatic leaves and spikes of typically mauve flowers. Leaves of some species of genus Mentha(M. arvensis, field mint/corn mint/Japanese mint, M. piperita) are used for seasoning and flavouring. Peppermint, Mentha piperita is cultivated for its downy leaves which yields pungent oil, methanol. Spearmint, M. spicata syn M. viridis is cultivated for its leaves which yields an oil for flavouring. For more on mentha see chapter. Dandelian  A plant of Taraxacum officinale, belongs to Compositae, native to Europe and Asia and which has deeply notched basal leaves which are used for salad or wine. Purslane  A plant of Portulaca oleracea whose fleshy leaves are used in salads and as a pot herb.

10.114

Crop Evolution and Genetic Resources

Salsify  A plant of Tragopogon porrifolius, a Mediterranean plant which has long white edible tap root and tastes like oyster and eaten as a vegetable. Sage  A plant of Salvia officinalis, Mediterrean perennial whose leaves are use in cooking for flavouring. Thyme  A small herb of temperate genus Thymus, having a strong mint like odour with small leaves. Chervil  An aromatic umbelliferous Eurasian plant, Anthriscus cerefolium having small white flower with aniseed flavored leaves used as herb in soups and salads. Basil  A Eurasian plant of Ocimum basillicum with aromatic leaves used as herbs for seasoning. Celeriac  A variety of celery, Apium graveolens rapaceum, an umbelliferous Eurasian plant with a large turnip-like root used as vegetable. Celery is an umbelliferous Eurasian plant, Apium graveolens dulce whose blanched leafstalks are used in salads. Horseradish  A Eurasian cruciferous plant, Armoracia rustica cultivated for its thick white pungent roots used for making sauce. Rosemarry  An aromatic European shrub Rosmarinus officinalis which is widely cultivated for its grey green evergreen leaves used in cookery for flavouring or for extraction of oil for making perfume. Rutabaga/swede  A plant of cruciferous Brassica napobrassica cultivated for its bulbous edible roots, eaten as vegetable and as cattle fodder. Sea kale  It is an European cruciferous plant of Crambe maritime with broad fleshy leaves and cultivated for its asparagus-like shoots. Sorrel  A polygonaceous plant of genus Rumex sp. Rumex acetosa of Eurasia and North America having acid tasting leaves used in salads and sauces. Turnip  A widely cultivated cruciferous plant of B. rapa with a large yellow or white edible roots, eaten as vegetable. Rhubarb  A polygonaceous, temperate and subtropical plant of Rheum rhaponticum, has long green and red acid tasting edible leaf stalks, usually eaten sweetened and cooked. Water cress  It is a cruciferous plant, Rorippa nasturtium-aquaticum (or Nasturtium officinalis) having pungent leaves which are used in salads and as a garnish. Chinese chives  Leaves and young flowers are edible.

References Accarri, N., Schiavi, M., Vitelli, G., Maestrelli, A., Forni, E. and Giovanessi, L. 1997. Breeding of green curded cauliflower for fresh market and freezing. Intl. Symposium on Brassica, Acta Hort., 459, 403-410. Ambrose, M. 2008. Garden Pea. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.1-26.

Origin and Genetic Resources of Vegetable Crops

10.115

Andres, T.C. 1990. Biosystematics, theories on the origin and breeding potential of Cucurbita ficifolia, In: Biology and Utilization of the Cucurbitaceae. D.M. Bates, R.W. Robinson and C.Jeffrey(eds.), Cornell University press, new York, pp.102-119. Andres, T.C. 2004a. Diversity in tropical pumpkin(Cucurbita moschata): cultivar, origin and history, In: progress in Cucurbit Genetics and Breeding Research, Proc. of Cucurbitaceae 2004, the 8th Eucarpia meeting on Cucurbit genetics and Breeding. A. Lebeda and H.S. Paris(ed.) Palaky University Press, Olomouc, pp.113-118. Andres, T.C. 1987. Cucurbita fraternal, the closet wild relative and progenitor of C. pepo. Cucurbit Genet. Coop. Rep., 10, 69-71. Anido, F.L. and Cointry, E. 2008. Asparagus. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.87-119. Bannerot, H., Boulidard, L., Caudero, Y. and Tempe, J. 1974. Transfer ofcytoplasmic male sterility from Raphanus sativus to Brassica oleracea. Proc. Eucarpia Cruciferae meeting, Dundee, 52-54. Barcaccia, G., Varotto, S., Soattin, M., Lucchin, M and Parrini, P.2003. Genetic and molecular studies of self-incompatibility in Cichorium intybus L. proc. Of the Eucarpia meeting on Leafy Vegetables Genetics and Breeding, March, 19-21, 2003. Noordwijerhout, The Netherland. Bassett, M. J.(ed.). 1986. Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut. Bates, D.M. and Robinson, R.W. 1995. Cucumbers, melons, and water-melons: Cucumis and Citrullus(Cucurbitaceae). In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants, Longman Scientific and Technical, Harlow, UK. Bauman, U.; Juttner, J.; Bian, X. and Langridge, P.2000. Self incompatibility in the grasses. Annals of Botany 85:203-209. Bemis, W.P. and Wilson, G.B. 1953. New hypothesis explaining the genetics of sex determination in Spinacea oleracea L. J. Hered. 44, 90-95. Benjamin, L.R., McGarry, A. and Gray, D. 1997. The root vegetables: beet, carrot, parsnip and turnip. In: Wein, H. C. (ed.) The physiology of vegetable crops. CAB International. Ben-Zeev, N. and Zohary, D. 1973. Species relationships in the genus Pisum. Israel Journal of Botany 22:73-91. Beyers, R.E., Baker, L.R., Dilley, D.R. and Shell, H.M. 1972. Ethylene: a natural regulator of sex expression of Cucumis melo L. Proc. Natl. Acad. Sci., U.S.A. 69, 717-720. Bhatt, K.L. 2007. Minor Vegetables- Untapped Potential. Kalyani Publiskers. Bliss, F and Gableman, W.H. 1965. Inheritance of male sterility in beet. Crop Sci., 5, 403-406. Bond, D.A. 1995. Faba bean: Vicia faba(Leguminosae-Papilionoide. In: Smartt, J and Sommond, N.W.(eds.) Evolution of Crop Plants, Longman Scientific and Technical, Harlow, UK, pp:312-316. Bosemark, N. O. 1993. Genetics and Breeding. pp.67-119. In: The sugar beet crop: science into practice. D.A. Cook and R.K. Scott(eds.). Chapman and Hall, London.

10.116

Crop Evolution and Genetic Resources

Bragdo, M. 1962. Breeding of polyploidy spinach. Euphytica, 11, 143-148. Branca, F. 2008. Cauliflower and Broccoli. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.151-188. Brewster, J.L.(ed.). 1994. Onions and other Vegetable Alliums. CAB International. Buck, P.A. 1956. Origin and taxonomy of broccoli. Eco. Bot., 10, 250-253. Campbell, G.K.G. 1976. Sugar beet. In: Evolution of crop plants. N. W Simmonds( ed.) Longman, London. Chailakhyan, M.K.H. 1979. Genetic and hormonal regulation of growth, flowering and sex expression in plants. Am. J. Bot., 66, 717-736. Chen, J.; Isshiki, S.; Tashiro, Y. and Miyazaki, S. 1997. Biochemical affinities between Cucumis hystrix Chakr and two cultivated Cucumis species (Cucumis sativus L.a nd C. melo) based on isozyme analysis. Euphytica 97:131-141. Coyne, D.P. 1970. Effect of 2-chloroethylphosphonic acid on sex expression and yield in Butternut squash and its usefulness in producing hybrid seed. Hort Science, 5, 227-228. Crisp. P and Tapsell, C.R. 1993. Cualiflower, Brassica oleracea L. 157-178. In: Kaloo, G and Berg, B. O.(eds.) Genetic improvement of vegetable crops. Pergamon Press, Oxford. Crosby, K.M. 2008. Pepper. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.221-248. Daunay, M.C. 2008. Eggplant. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.163-220. De Vries, I.M. 1997. Origin and domestication of Lactuca sativa L. Genet. Resour. Crop Evol. 44, 165-174. Deb, D. B. 1989. Solanum melongena, Solanum incanum versus S. insanum (Solanaceae). Taxon, 38, 138-139. Decker, D.S. 1988. Origin(s), evolution and systematic of Cucurbita pepo. (Cucurbitaceae). Econ. Bot., 42, 4-15. Decker, D.S. 1988. Origin(s), evolution and systematic of Cucurbita pep (Cucurbitaceae). Economic Botany 42:4-15. Decker-Walters, D.; Staub, J.; Lopez-Sese, A. and Nakata, E. 2001. Diversity in landraces and cultivars of bottle gourd (Lagenaria siceraria; Cucurbitaceae) as assessed by random amplified polymorphic DNA. Genetic Resources and Crop Evolution 48:369-380. Decker-Walters, D.S and Walters, T.W. 2000 Squash, In: The Cambridge World history of Food, K.F.Kipple and K.C. Ornelas(eds.) Cambridge University Press, New York, pp.335-351. Decker-Walters, D.S. 1990. Evidence for multiple domestications of Cucurbita pepo. In: Bates, D.M.(ed.) Biology and Utilization of the Cucurbitaceae. Cornell university Press, Ithaca, NY. Den Nijs, A.P.M. and Visser, D.L. 1985. Relationships between African species of the genus Cucumis L. estimated by the production, vigor and fertility of F1 hybrids. Euphytica 34 279-290.

Origin and Genetic Resources of Vegetable Crops

10.117

Dickson, M.H. and Wallace, D.H. 1986. Cabbage Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp.396-435. Diez, M.J. and Nuez, F. 2008. Tomato. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.249-323. Dixon, G.R.(ed.). 2007. Vegetable Brassicas and related Crucifers. CAB International. Dowker, B.D. and Gordon, G.H. 1983. Heterosis and hybrid cultivars in onion. In: HeterosisReapraissal of theory and practice. (Ed.) Frankel, R. Springer-Verlag, Berlin. Dressler, O. 1958. Cytogenetical investigations on diploid and polyploidy spinach (Spinacea oleracea L.) with special consideration of the inheritance of sex as the basis of inbredheterosis breeding. Z. Pflanzenzuecht, 40, 385-424. Eenink, A.H. 1981. Compatibility and incompatibility in witloof-chicory (Cichorium intybus L.). 2. The incompatibility system. Euphytica, 30, 77-85. Ellison, J.H. 1986. Asparagus Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp.523-570. Eshbaugh, W.H.; Guttman, S.I. and McLeod, M.J. 1983. The origin and evolution of domesticated Capsicum species. Journal of Ethnobiology 3:49-54. Eshbaugh, W.H. 1980. The taxonomy of the genus Capsicum (Solanaceae)-1980. Phytologia 47:153-166. Esquinas-Alcazar, J.T. and Gulick, P.J. 1983. Genetic Resources of Cucurbitaceae. Int. Board for Plant genet. Res., Rome, pp.101. Fahey, J.W., Zhang, Y. and Talalay, P. 1997. Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against carcinogens. Pro. Natl. Acad. Sci., U.S.A., 94, 10367-10372. Ferriol, M. and Pico, B. 2008. Pumpkin and Winter squash. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.317-350. Ford-Lloyd, B. V. 1995. Sugarbeet and other cultivated beets. In: Evolution of crop plants. 2nd ed. Smartt, J. and Simmond, N. W(eds.) Longman. Foster, R.E. 1968. F1 hybrid muskmelon. V. Monoecism and male sterility in commercial seed production. J. Hered., 59, 205-207. Franken, A.A. 1970. Sex characteristics and inheritance of sex in asparagus. Euphytica, 19, 277-287. Galun, F. 1973. The use of genetic sex types for hybrid seed production in Cucumis. In: Moav, R.*ed.) Agricultural Genetics, Wiley and Sons, New York, pp.23-56. Goldman, I.L. and Navazio, J.P. 2008. Table Beet. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.219-240. Gray, A. R. 1982. Taxonomy and evolution of broccoli (Brassica oleracea var. italic). Eco. Bot., 36(4), 397-410. Gray, A.R. 1982. Taxonomy and evolution of broccoli (Brassica oleracea var. italic). Economic Botany 36:397-410.

10.118

Crop Evolution and Genetic Resources

Greenleaf, W.H. 1986. Pepper Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 69-134. Gritton, W.T. 1986. Pea Breeding. Pp. 284-321. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 1-36. Heiser, C.B. and Smith, P.G. 1953. The cultivated capsicum peppers. Economic Botany 7:214-227. Heiser, C.B. 1995a. Peppers: Capsicum (Solanaceae). In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants. Longman Scientific & Technical, Harlow, UK, PP:449-451 Hodgkin, T. 1995. Cabbage, kales, etc., In: Evolution of Crop Plants. 2nd ed., J. Smart and N.W.Simmonds, eds. Longman. Hoser-Krauze, J. 1979. Inheritance of self incompatibility and the use of it in the production of F1 hybrids of cauliflower. Genet. Pol. 20, 431-357. Hume, R.J. and Lovell, P.H. 1983. The control of sex expression in cucurbits by ethephon. Ann. Bot., 52, 689-695. Hyams, E. 1971. Cabbages and Kings. In: Plants in service of man, 33-61. London. Isshiki, S. , Okubo, H. and Fujieda, K. 1994a. Phylogeny of egg plant and related Solanum species constructed by allozyme variation. Sci. Hort.(59), 171-176. Janick, J. 1955a. Inheritance of sex in tetraploid spinach. Proc. Am. Soc. Hortic. Sci., 66, 361363. Janick, J. 1955b. The effects of polyploidy on sex expression in spinach. J. Hered. , 46, 150-156. Janick, J. and Stevenson, E.C. 1955a. Environmental influence on sex expression in monoecious lines of spinach. Proc. Am. Soc. Hortic. Sci., 65, 416-422. Jenkins, J.A.1948. The origin of cultivated tomato. Economic Botany 2:379-392. Jobst, J.; King, K. and Hemleben, V. 1998. Molecular evolution of the internal transcribed spacers(IST1 and IST2) and phylogenetic relationships among species of the family Cucurbitaceae. Molecular Phylogenetics and Evolution 9:204-219. Jones, A., Dukes, P.D. and Schalk, J.M. 1986. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 1-36. Karihaloo, J. L. and Gottlieb, L.D. 1995. Allozyme variation in the eggplant, Solanum melongena L.(Solanaceae). Theor. Appl. Genet. 90, 578-583. Karihaloo, J.L., Brauner, S. and Gottleib, L.D. 1995. Random amplified polymorphic variation in the eggplant, Solanum melongena L.(Solanaceae). Theor. Appl. Genet. 90, 767-770. Kaukis, K. and Davis, D.W. 1986. Sweet Corn Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 477-522. Kesicki, E. 1979. New type of functional male sterility. Symp. on production of tomatoes for processing. Evora, Purtugal. Kihara, H. 1951. Triploid watermelons. Proc. Amer. Soc. Hort. Sci., 58, 217-230. Koutsika-Sotiriou, M. and Traka-Mavrona, E. 2008. Snap Bean. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables II. Springer, pp.27-83.

Origin and Genetic Resources of Vegetable Crops

10.119

Ladizinsky, G. and Adler, A. 1976a. Genetic relationships among the annual species of Cicer. Theoretical and Applied Genetics 48:197-203. Ladizinsky, G. and Adler, A. 1976b. The origin of chickpea Cicer arietinum. Euphytica 88:181-188. Ladizinsky, G. 1995. Chickpea, Cicer arietinum (Leguminosae-Papilionoideae) In: Smartt, J and Simmond, N.W.(eds.) Evolution of Crop Plants, Longman Scientific and Technical, Harlow, UK, pp:258-261. Ladizinsky, G. 1999. Cytogenetic relationships between Avena insularis (2n = 28) and both A.strigosa (2n = 14) and A. murphi (2n = 28). Genetic Resources and Crop Evolution 46:501-504. Ladizinsky, G. 1999. Identification of lentil’s wild genetic stock. Genetic Resources and Crop Evolution. 46:115-118. Ladizinsky, G. and Zohary, D. 1971. Notes on species delimination, species relationships and polyploidy in Avena. Euphytica 20:380-395. Ladizinsky, G.; Braun, D.; Goshen, D. and Muehlbauer, F.J. 1984. The biological species of the genus Lens. Botanical Gazette 145:253-261. Laggett, J.M. and Thomas, H. 1995. Oat evolution and cytogenetics. In: Welch, W.(ed.) The Oat Crop. Production and Utilization. Chapman & Hall, London, pp:121-149. Laizinsky, G. 1975. On the origin of the broad bean, Vicia faba L. Israel Journal of Botany 24:80-88. Lanteri, S. and Portis, E. 2008. Globe Artichoke and Cradoon. . In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp. 49-74. Larson, R.E. and Paur, S. 1948. The description and inheritance of functional male sterile flower in tomato and its possible value in hybrid tomato seed production. Proc. Am. Soc. Hortic. Sci., 52, 355-364. Larter, E.N. 1995. Triticale: Triticosecale spp. (Gramineae-Triticinae). In: Smartt, J and Sommond, N.W.(eds.) Evolution of Crop Plants, Longman Scientific and Technical, Harlow, UK, pp:181-183. Leggett, J.M. 1992. Classification and speciation in Avena: In: Marshall, H.G. and Sorrells, M.E. (eds.) Oat Science and Technology. Agronomy Monograph 33, ASA and CSSA, Madison, Wisconsin, pp:29-53. Leggett, J.M. 1996. Using and conserving Avena genetic resources. In: Scoles, G.J. and Rossnagel, B.G.(eds.) Barley Chromosome Coordinators Workshop at the V International Oat Conference and VII International Barley Genetics Symposium. University of Saskatchewan, Canada, pp:128-132. Lester, R.N. 1997. Typification of nineteen names of African Solanum species described by A.Richard and others, including S.campylanthum and S.panduriforme. Bot. J. Linnaean Soc. 125, 273-293. Lester, R.N. and Hasan, S. M. Z. 1991. Origin and domestication of the brinjal-egg plant, Solanum melongena, from S. incanum in Africa and Asia. P. 369-387. In: J.G. Hawkes et al.(eds.) Solanaceae III: Taxonomy, Chemistry, Evolution. Royal Botanic Gardens, Kew, UK.

10.120

Crop Evolution and Genetic Resources

Lester, R.N. and Hawkes, J.G. 2001. Solanaceae. P. 1790-1856. In: P.Hanelt(ed.)., Mansfeld’s Encyclopedia of Agricultural and Horticultural Crops. Springer Verlag. Lindqvist, K.1960a. On the origin of cultivated lettuce. Heriditas, 46, 319-350. Lower, R.L. and Edwards, M.D. 1986. Cucumber Breeding. In: Bassett, M. J.(ed.). Breeding Vegetable Crops. AVI Publishing Company , INC, Conneticut, pp. 173-209. Loy, J.B., Natti, T.A., Zack, C.D. and Fritts, S.K. 1979. Chemical regulation of sex expression in a gynomonoecious line of muskmelon. J. Am. Soc. Hortic., 104, 100-101. Lucchin, M., Varotto, S., Barcaccia, G. and Parrini,. 2008. Chicory and Endive. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.3-48. MacLeod, M.J. , Eshbaugh, W.H. and Guttman, S.I. 1982. Early evolution of chili peppers (Capsicum). Economic Botany 36:361-368. Mangelsdorf, P.C. 1974. Corn: Its origin, Evolution and Improvement. Harvard University Press, Cambridge, Massachusetts. Mangelsdorf, P.C. 1986. The origin of corn. Scientifi American 255:80-86. Mangelsdorf, P.C. and Reeves, R.G. 1939. The Origin of Indian Corn and its Relatives. Bulletin 549, Texas Agricultural Experiment Station, Colege Station. McNaughton, I.H. 1995a. Turnip and relatives. Brassica napus (Cruciferae). In: Smartt, J. and Simonds, N.W. (eds.) Evolution of crop plants, Longman group, U.K. McNaughton, I.H. 1995b. Swedes and rapes. Brassica napus (Cruciferae). In: Smartt, J. and Simonds, N.W. (eds.) Evolution of crop plants, Longman group, U.K. Mehra, K.L. 1963a. Differentiation of cultivated and wild Eleusine species. Phyton 20:189-198. Merrick, L.C. 1995. Squashes, pumpkins and gourds: Cucurbita (Cucurbitaceae). In: Smartt, J and Simmond, N.W.(eds.) Evolution of Crop Plants, Longman Scientifi and Technical, Harlow, UK, pp: 57-105. Merrick, L.C. 1990. Systematics and evolution of a domesticated squash, Cucurbita argyrosperma and its wild and weedy relatives, In: Biology and Utilization of Cucurbitaceae, D.M. Bates, R.W. Robinson and C. Jeffrey(eds.) Cornell University Press, New York, pp.77-95. Miles, P.G. and Chang, S.T. 1997. Mushroom Biology. Concise Basics and Current Developments. World Scientific. Singapore. Mohr, H.C. 1986. Watermelon Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 37-68. Morelock, T.E. and Correll, J.C. 2008. Spinach. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.189-218. Mou, B. 2008. Lettuce. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.75-118. Nee, M. 1990. The domestication of Cucurbita (Cucurbitaceae). Eco. Bot., 44(3, suppl.), 56-68. Nee, M. 1990. The domestication of Cucurbita (Cucurbitaceae). Economic Botany 44:56-68. Nieuwhof, M. and Garretsen, F. 1975. Hybrid breeding in early spring cabbage II. Euphytica, 24, 87-97.

Origin and Genetic Resources of Vegetable Crops

10.121

Ordas, A. and Cartea, M.E. 2008. Cabbage and Kale. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.119-150. Owens, K.W., Peterson, C.E. and Tolla, G.E. 1980. Induction of perfect flowers on gynoecious muskmelon by silver nitrate and amino ethoxy vinyl glycine. HortScience, 15, 654-655. Paris, H.S. 2008. Summer Squash. 2008. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.351-380. Paris, H.S. and Brown, R.N. 2005. The genes of pumpkin and squash. HortScience, 40, 16201630. Paulet, P. 1985. Cichorium intybus and C.endiva. In: A.H. Harvey(ed.). CRC Handbook of Flowering. Vol. ii. CRC Press Inc., Boca Raton. Pearson, E.H. 1983. Heterosis in vegetable crops. In: Heterosis-Reapraissal of theory and practice. (Ed.) Frankel, R. Springer-Verlag, Berlin. Peterson, C.E. and Anhder, L. 1960. induction of staminate flowers on gynoecious cucumbers with gibberellins. Science, 131, 1673-1674. Peterson, C.E. and Simon, P.W. 1986. Carrot Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 322-356. Pike, L.M. 1986. Onion Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 357-395. Pike, L.M. and Peterson, C.E. 1969. Gibberellin A4/A7 for induction of staminate flowers on the gynoecious cucumber. Euphytica, 18, 106-109. Pink, .D.A.C. 1992. Beetroot, In: Breeding vegetable crops, G. Kaloo(ed.) AVI Press, Westport, pp.473-477. Pitrat, M. 2008. Melon. 2008. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.283-316. Prakash, S. and Hinata, K. 1980. Taxonomy, cytogenetics and origin of crop Brassica, a review. Opera Bot. 55, 1-57. Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables I. Springer. Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer. Putz, F.E. and Mooney, H.A. 1992. Green in leaf and tendril- the biology of vines. Science 256:1339-1343. Rabinowitch, H.D. and Currah, L.(eds.). 2002. Allium Crop Science: Recent Advances. CAB I Publishing. Rhodes, B and Zhang, X. 1999. Hybrid seed production in watermelon. In: A.S. Basra(ed.) Food products press, New York, pp.69-88. Rick, C.M. 1995. Tomato: Lycopersicon esculentum(Solanaceae) In: Smartt, J. and Simmonds, N.W.(eds.) Evolution of Crop Plants, Longman Scientific and Technical, Harlow, UK. pp:452-457. Robinson, R.W. and Decker-Walters, D.S. 1997. Cucurbits. CAB International, New York.

10.122

Crop Evolution and Genetic Resources

Robinson, R.W. and Reiners, S. 1999. Parthenocarpy in summer squash. HortScience, 34, 715-717. Rudich, J., Kedar, N. and Halevy, A. H. 1970. Changed sex expression and possibilities for F1 hybrid seed production in some cucurbits by application of ethrel and alar. Euphytica, 19, 47-53. Ryder, E.J. 1986. Lettuce Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp.436-476. Ryder, E.J.1999. Lettuce, Endive and Chicory. CABI Publishing, new York. Sakata, Y., Nishio, T., and Matthews, P.J. 1991. Chloroplast DNA analysis of eggplant (Solanum melongena) and related species for their taxonomic affinity. Euphytica, 55, 21-26. Sakata,Y. 1992. Taxonomic relationships between Solanum melongena (eggplant) and its related species S incanum and S. marginatum. Euphytica, 80, 1-4. Sanjur, O.L., Piperno, D.R., Andres, T.C., and Wessel-Beaver, L. 2002. Phylogenetic relationships among domesticated and wild species of Cucurbita (Cucurbitaceae) inferred from a mitochondrial gene: implications for crop plant evolution and areas of origin, proc. Natl. Acad. Sci., U.S.A., 99, 535-540. Shigyo, M. and Kik, C. 2008. Onion. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.121-159. Silbernagel, M.J. 1986. Snap Bean Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company, INC, Conneticut, pp. 244-283. Simmonds, N.W. 1995b. Potatoes: Solanum tuberosum (Solanaceae). In: Smartt, J. and Simonds, N.W. (eds.) Evolution of crop plants, Longman group, U.K. pp:466-471 Simon, P.W., Freeman, R.E., Vieira, J.V., Boiteux, L.S., Briard, M., Nothnagel, T., Michalik, B. and Kwon, Y.S. 2008. Carrot. In: Prohens, J. et al.(eds.). 2008. Handbook of Plant Breeding. Vegetables II. Springer, pp.327-357. Singh, S.P. and Hymowitz, T. 1995. The genomic relationships among six perennial species of the genus Glycine subgenus Glycine. Euphytica 33:337-345. Sneep, J. 1953. The significance of andromonoecy for the breeding of Asparagus L. Euphytica, 2, 89-95. Snogerup, S. 1980. The wild forms of the Brassica oleracea group (2n = 18) and their possible relations to the cultivated ones., In: Brassica Crops and Wild Allies, S. Tsunoda, K. Hinata and C.Gomez-Campo(eds.), Japan Scient. Soc. Press, Tokyo. Staub, J.E., Robbins, M. D. and Wehner, T.C. 2008. Cucumber. In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.241-282. Swarup, V. and Brahmi, P. 2005. Cole crops, In: Plant Genetic Resources: Horticultural Crops, B.S Dhillon, R.K. Tyagi, S. Saxena and G.J. Randhawa(eds.), Narosa, new Delhi. Thompson, D. J. 1961. Studies on inheritance of male sterility in the carrot, Daucus carota L. var. sativa. Proc. Am. Soc. Hortc Sci., 78, 332-338. Thompson, K.F. 1979. Cabbage, kales, etc. Brassica oleracea(Cruciferae). In: Simmonds, N.E.(ed.). Evolution of Crop Species. Longman, London, pp: 49-52.

Origin and Genetic Resources of Vegetable Crops

10.123

Tigchlaar, E.C. 1986. Tomato Breeding. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company , INC, Conneticut, pp. 135-172. Tronichkova, E. 1962. Ausnutzung der mannlichen Sterilitat in der Hybridisaatgutproduktion bei Tomaten. In: Daskaloff Ch(ed.) Internationale Wissensachftlich Heterosis-Tagung Academy press, Sofia, pp. 37-44. Varotto, S., Pizzoli, L., Lucchin, M. and Parrini, P.1995. The incompatibility system in Italian red chicory(Cichorium intybus L.). Plant Breeding, 114, 535-538. Webb, R.E. and Thomas, C.E. 1976. Development of F1 spinach hybrids. HortScience, 11, 546. Wehner, T.C. 1998. Heterosis in vegetable crops. In: J.G. Coors and S. Pandey(eds.) Genetics and exploitation of heterosis in crops. Amer. Soc. Agron., Madison. Wehner, T.C. 2008.Watermelon. 2008. . In: Prohens, J. et al.(eds.) Handbook of Plant Breeding. Vegetables I. Springer, pp.381-418. Welch, J.E. and Grimball, E.L. Jr. 1947. Male sterility in the carrot. Science, 106, 594. Whitaker, T.W. and Davis, G. N. 1962. Cucurbits: botany, cultivation and utilization. Interscience Publishers, Inc., New York. Whitaker, T.W. and Robinson, R.W. 1986. Squash Breeding. Pp.210-243. In: Bassett, M. J.(ed.) Breeding Vegetable Crops. AVI Publishing Company , INC, Conneticut, pp. 1-36. Whiteker, T.W. and Bemis, W.P. 1976. Cucurbits, In: Evolution of Crop Plants, , N.W Simmonds(ed.) Longman, pp. 64-69. Wijnheijmer, E.H.M. , Brandenburg, W.A. and TerBorg, S.J. 1989. Interactions between wild and cultivated carrots(Daucus carota L.) in the Netherlands. Euphytica 40:147-154 Winner, C. 1993. History of the crop. In: The sugarbeet crop: science into practice. Cook, D.A. and Scott, R.K.(eds.)., Chapman and Hall, London. Wuest, P.J. ; Royse, D.J. and Beelman, R. B. 1987. Cutivating Edible Fungi. Elsevier. Yordanov, M. 1983. Heterosis in tomato. In: Heterosis-Reapraissal of theory and practice. (Ed.) Frankel, R. Springer-Verlag, Berlin. Zhiyuan, F., Wang, X., Dongyu, Q., and Guangshu, L. 1999. Hybrid seed production in cabbage. J.New Seeds, 1, 109-129.

Origin and Genetic Resources of Floricultural Crops

C H A P T E R

11

11.1  INTRODUCTION Common names of different flowers, their botanical names, basic chromosome number, ploidy levels, and breeding system and method of propagation are given in the table 11.1 below. Interspecific hybridization has played an important role in the varietal development in ornamentals and a high proportion of perennial herbs and shrubs, for example, orchids, roses, cannas, dahlias, gladioli, poppies, are hybrid in origin. Further, wide hybridization including intergeneric hybridization has been frequent in ornamentals especially roses, orchids and lilies (Emsweller et al., 1937). Interspecific hybrids have been obtained in cosmos, kalanchoe, primula and begonia with the use of embryo rescue technique. Somatic hybrids have been produced in Dianthus and Primula based on successful plant regeneration system from protoplast. Also, successful genetic transformation system has been established in orchids(Phalaenopsis, Cymbidium, Debdrobium. Cattleya, Vanda), rose, chrysanthemum, carnation, snapdragon, Nierembergia, Petunia, Lilium, Dahlia, Begonia, Primula, and Matthiola. Wide hybridization has been used to combine various traits such as colors, the multiflorus state and heavier flower. Most important cut flowers include rose, carnations, chrysanthemum. gladioli, gerbera, orchids, lilies, tulips, aster, gypsophila, anthurium, freesias, etc. Important bedding plants include geranium, pansies, fuschia, petunia, impatiens, begonias, tagetes, salvia, dianthus, verbena, lobelia, torenia, etc. Important foliage plants include ficus, dracaena, palms, hedera, yucca, schefflera, etc. Pot flowers include begonia, cyclamen, pelargonium, saintpaulia, kalanchoe, poinsettias, dendranthema, cyclamen, primula spp, spathiphyllum, etc.

Rosa sp.

Rose

Antirrhinum (Snapdragon)

Anthurium

Gerbera

Dahlia Amaryllis

Jasmine Tuberose

Chrysanthe-mum

Carnation

Polyploids

Orchidaceae

Iridaceae

Diploid to octaploid

Diploid

Ploidy level

Rosaceae

Nymphaceae

Family

8

15,16,22

25

8 11

Compositae Amaryllidaceae Diploid and Triploids

9

15

15

20

7

8

13 30

x

Oleaceae Amaryllidaceae

Gerbera Compositae Diploid jamesonii Anthurim spp. Araceae Diploid A. scherzerianum, A. andreanum Antirrhinum spp. Plantaginaceal Diploid

Jasminum spp. Polianthes tuberose Dahlia spp. Amaryllis spp.

Diathus Caryophyllaeae Diploids & caryophyllus Tetraploids Dendrathema sp. Compositae

Orchid-Cymbidium hybrids, Dendrobium hybrids, Phalaenopsis hybrids Gladiolous sp. Gladiolous

Nelumbo lutea

Botanical name

Lotus

Common name

Table 11.1  Showing flower crops, their ploidy level and breeding systems. Breeding system

Pollination agent

8-16 Southern Europe

Cross Insects pollinated

16-64 Mexico 22,23 Tropical & subtropical America 50 South Africa & Asia Cross Insects pollinated 30 Central & south Cross Insects America pollinated

30-120 Africa & Asia Minor Self – pollinated 30-60 Mediterranean region 18-72 China Cross Insects pollinated 26-52 India 60 Mexico

Primary centre of origin

Contd...

Winter season, seed

Vegetative, seed culiflower

Winter season

Winter & Summer season

Season of flowering, seed/ vegetative propagation 16 India, china, japan insect,wind Honeybees Throughout year cross pollinated 14-56 Himalayan Region Cross Insects Throughout pollinated year, vegetative propagation Indo-Malaya & Cross Insects & Through out year, Tropical America pollinated Birds vegetative

2n

11.2 Crop Evolution and Genetic Resources

Tagetes spp.

Delphinium hybrids (Larkspur) Verbena Nemesia Alyssium

Corn flower

Linum Ageratum

Clianthus Wall flower

Lagiminosae

Cruciferae

Verbena erinoides Verberaceae

A. houstanianum A. conyzoides Centaurea Compositae cyanus

Cheiranthus cheiri

Papilionaceae Crueiferae

I. balsamina

Balsam

Lathyrus odoratus

Gloriosa superbu Liliaceae

Gloriosa

Lupin Sweet pea

Lilium sp.

Lilium

Diploid & Teraploid

Diploid & Tetraploid Amaryllidaceae Diploid & Triploids Tetraploid Liliaceae Diploid & Tetraploid

Compositae

Callistephus chinensis Mattihola incana Cruciferae

Narcissus (Daffodils) Narcissus spp.

Marigold

Stock

China Aster

Contd...

11

12

South Africa

24-36 Northern hemisphere up to south Canada & Siberia 22-88 Tropical Africa & Asia

7(predominant), 14-28 Spain & Portugal 10, 11 (Europe)

12

Mediterranean region 24-48 Mexico

China

Insects

Insects & wind Insects

C.P. C.P. C.P.

C.P.

C.P.

Often C.P. C.P.

S.P. Often C.P.

Cross Insects pollinated Self pollinated S.P. S.P.

Cross Insects pollinated

Cross pollinated Cross pollinated Cross pollinated

seed

Contd...

Seed, vegetative

seed

Winter

Winter season

vegetative

Winter season, seed Throughout the year Throughout year

Origin and Genetic Resources of floricultural Crops 11.3

Dracaena spp.

Begoniaceae

Begonia Aster spp.

Primulaceae (funnel or bell shaped flower) Gesneviaceae Diploid

Palmale (monocot)

Lobeliaceae Solanaceae

Compositae Solanaceae

Labiatae

Callistephus chinenses

P. vulgaris

P. hybrida

Senecio cruentus Compositae

Compositae

Salvia Alstroemeria hybrids

Saintpaulia (S. ionanthax S. confuisa)

Lobelia erinus Nicotiana sanderae hybrids PalmsChamaedorea spp, Chrysalidocarpus tutescens, Howea, Phoenix Primula

Limonium spp

Arctotis Calendula (Pot marigold) Cineraria Gazania Zinnia Petunias

Contd...

Diploid, Triploid and Tetraploid

16

South America

28, 30 East Africa

South American

Canary Island

C.P. C.P. C.P. C.P GSI

C.P. C.P.

vegetative Contd...

Seed, vegetative Vegetative

Seed Vegetative

Vegetative

seed

Seed propagated

Seed and vegetative Seed seed

11.4 Crop Evolution and Genetic Resources

Iridaceae Crassulaceae

Iris hollandrica hybrids

Kalanchoe blossfeldiana

Diploid Tetroploid

SP = Self pollinated; CP = Cross pollinated; GSI = Gametophyhc self incompatibility

Primulaceae Liliaceae

Oenotheraceae

Fuschia hybrids

Catharanthus roseus Cyclamen persicum Tulipa gesneriana

Iridaceae

Pteridophyte order filicales

Dendranthema grandiflorum Ferns-Nephrolepis, Asplenium Ficus Freesia hybrids

Contd...

2x = 34, 4x = 68

seed Seed

vegetative spores formed in sori Vegetative Seed, Vegetative, cut flowers Vegetative (short cutting) Vegetative (Bulb) Vegetative

Vegetative

Origin and Genetic Resources of floricultural Crops 11.5

Crop Evolution and Genetic Resources

11.6

Seasonal flowers  There are flowers which can be grown in summer, another group of flowers can be grown in winter and yet another group that can be raised in rainy season. These flowers are mostly propagated by seeds. Annuals flowers can be grown in summer/rainy season or winter season and thus there are summer annuals or winter annuals. Summer annuals  Table 11.2 given below shows flowers grown in summer season and the same can be grown in rainy season as well. Others include cleime, coleous. Table 11.2  Showing list of summer annuals and their methods of propagation. Common name

Botanical name

Common name

Seed seed

Amaranthus

Amaranthus tricolor

Balsam

Impatiens balsamina, I. walleriana, I. hawkerii

Busy lizzie, touch-me-not, Presence of a continuous genome (chromosomes are connected).

Cocks comb

Celosia cristata

Found in various attractive colors

Cosmos

Cosmos bipinnatus, C. sulphureus

Gaillardia

Gaillardia grandiflora

Evolved from G. aristata and G. pulchella

Gomphrena

Gomphrena globosa

Purple globe amaranth, Fresh excellent cut flower

Sun flower

Helianthus annuus

Marigold

Tagetes spp.

Sadabahar

Vinca alba, Vinca rosea

Periwinkle, Indian origin

Zinnia

Zinnia elegans, Z. angustifolia

Bedding plant and cut flower

Portulaca

P. oleracea, P. amilis, P. grandiflora, P. umbraticola

Moss rose or sun rose

Kochia

Kochia scorparia

Vegetative propagation Vegetative

In vitro propagation more rapid and possibility of producing disease free plant Seed

seed seed

Winter annuals  Table 11.3 given below shows winter annual flowers that are raised during this season. Others include Delphinium, statice, poppy Table 11.3  Showing list of winter annulas and their methods of propagation. Name

Botanical name

Everlasting daisy

Acroclinium album

Hollyhock

Althea rosea

Sweet alyssum

Alyssum maritimum

Ageratum

Ageratum houstonianum

Common name

Seed propagated

Vegetatively popagated

Seed Contd...

Origin and Genetic Resources of floricultural Crops

11.7

Contd...

Name

Botanical name

Common name Snapdragon

Seed propagated

Antirrhinum

Antirrhinum majus

Aster

Aster spp.

Brachycome

Brachycome iberidifolia

Calendula

Calendula officinalis

Candytuft

Iberis umbellate

Carnation

Dianthus caryophyllus

Sweet Sultan

Centaurea imporialis

Chrysanthemum

Chrysanthemum coronaria

Coreopsis

Calliapsis tnctoria

Cineraria

Cineraria grandiflora

Clarkia

Clarkia elegans

Dianthus

Dianthus noblis or D. chinensis

Cape marigold

Dimorphotheca aurantiaca

Californian poppy

Eschcholzia californica

Gaillardia

Gaiallardia drummondii

Godetia

Godetia grandiflora

Paper rose

Halichrysum bracteatum

Larkspur

Delphinium spp.

Sweet pea

Lathyrus odoratus

Linaria (Toad flax)

Linaria bipartite

Flax

Linum grandiflorum

Lobelia

Lobelia erinus

Lupine

Lupines hartwegii

Nasturtium

Tropaeolum minor

Pansy

Viola wittrockiana hybrids

seed

Petunia

Petunia hybrid

seed

Nemetia

Nemetia strumosa

Phlox

Phlox drummondii

Corn poppy

Poppy shirloy, P. rhoeas

Cone flower

Rudbeckia bicolour

Vegetatively popagated

seed Vegetatively propagated

seed

vegetative

Vegetative

Contd...

Crop Evolution and Genetic Resources

11.8 Contd...

Name

Botanical name

Common name

Seed propagated

Sage

Salvia salendens

Stocks

Matthiola incane

seed

Verbena

Verbena hybrid

seed

Venidium

Venidium fastuosum

Wall flower or Gilli

Cheiranthus cherii

Dahlia hybrids

Dahlia varibilis

Sweet William

Dianthus barbatus

Barberton daisy

Gerbera jamesonii

Flowering tobacco

Nicotiana tabacum

Vegetatively popagated

seed

Cape daisy Seed (single flower) Vegetative (double flower) seed

Vegetative

Devil-in-bush, love-in-mist Nigella damascena Evening prime rose

Oenothera odarata

Geranium

Pelargonium grandiflorum

Lady’s lace

Pimpinella moniea

Velvet flower

Salpiglosis spp.

Saponaria (Soapwort)

Saponaria calabrica

Morning bride (Scabiosa)

Scabiosa spp.

Schizanthus or Poor man; s orchid

Schizanthus wisetonensis

Mismaranthum (ice plant) Mesembryanthemum edule syn. Carpobrotus edulis

South Africa

Gazania

Cross pollinated

seed

vegetative

Linum Corn flower

Centaura cyanus

Various methods of natural vegetative propagation are given in the table 11.4 below. Table 11.4  Showing various methods of vegetative propagation. Types of vegetative propagation

Plant part/Organ

Example

Natural methods of vegetative propagation

Leaf tips

Walking ferns (Adiantum caudatum)

Underground stem

Rhizome-ginger, Tuber-potato, bulbonion, garlic, tuberose, most lilies, etc., Corm-Galdiolus, Amorphophallus, saffron (Corcus)

Contd...

Origin and Genetic Resources of floricultural Crops

11.9

Contd...

Types of vegetative propagation

Artificial method of vegetative propagation

Asexual reproduction

Plant part/Organ

Example

Sub-aerial stem

Runner-wood sorrel, Stolon-wild strawberry, Offset-water lettuce, suckerChrysanthemum, rose, mint, pineapple, banana, dagger plant (Yucca)

Adventitious bud

AB produced on leaf margin-Bryophyllum pinnatum, Kalanchoe, AB on the surface of leaf-Begonia, AB on the root-sweet potato

Bulbils

American aloe, garlic, Dioscorea bulbifera, wood sorrel(Oxalis), Pine apple

Cuttings

Stem cutting- rose, sugarcane, tapioca, croton, China rose,drumstick, Duranta, Coleus, Root cutting-Lemon, citron, tamarind

Grafting

Layering , gootee, Inarching, approach grafting, bud grafting, whip or tongue grafting, wedge grafting, crown grafting. Fruits-Mango, litchi, guava, lemon, Flowers-Magnolia, Michelia, Ixora

Spores

Ferns(Sporophyte(diploid)- asexual spores(haploid)- gametophyte- sexual reproduction-sporophyte) and mosses

11.2  MARIGOLD It belongs to family compositae or daisy. It is a cross pollinated flower crop, entomophilious. There are two genera-1. Tagetes, 2. Calendula. Homeotic mutants, double flowered (variety with extra petals, e.g., found in roses, camellias, carnations, marigold), apopetalous are found. Propagation is through seed or though vegetative means, i.e., cuttings. When some stamens or all the stamens are replaced by petals-they are called homeotic mutants (double flowered, when the flower has more than one row of petals), they are usually recessive. Tagetes erecta (2n = 24), is African tall marigold and T. patula (2n = 48), an alloletraploid is French, dwarf marigold (6 to up to 12 tall). T. patula originated from the cross between T. erecta and T. tenuifolia (Towner, 1956). They have Mexican origin. T. erects x T. patula produces triploid, (12 to 18 high) the sterile marigold. Triploid does not ptoduce seeds. Triploid marigold produces flower repeatedily throughout the summer and thus shows tolerant / resistant to hot weather. Another species is T. tenuifolia (2n = 24), the signet marigold and T. lucida is called sweet scented marigold. T. lucida persists as perennial. Signet marigolds produce small single flower, yellow to orange gold or bicolored flower. Plants of signet marigold are bushy. Other species include T. filifolia, T. remolifolia, T. jaliscensis (2n = 24) T. minuta (2n = 48), T. grandulifera, T. pusilla and

Crop Evolution and Genetic Resources

11.10

T. corymbosa. T. lemmonii (2n = 24) is a shrubby plant. Flowers give lemon fragrance and flowers are edible. The bud of the main stem is plucked 30-45 days after planting (pinching) in order to have many branches coming up with bud / flowers. Planting is done in Feb-March, June-July and September-October. Marigold kills root knot nematodes. Marigold can be used for extraction of dye or food colorant.

11.3  GERBERA It can be grown in open in tropical and subtropical condition. It is used as cut flower. Flowers are solitary daisy like. It belongs to family Compositae. There are three types of flowers-outer ring of ray florets, middle ring of trans florets and central ring of disc florets. Trans florets are female and length of petals vary among varieties. Ray flowers are females and have anthers in the beginning but abort later during development. There is pappus, the hair like structure on flowers. It is diploid with 2n = 50. The genus contains 30-40 species (Asiatic and African species). Modern gerbera (G. hybrida) arose from the cross-G. jamesonii (native of Africa) x G. viridfolia (Bremmer, 1994; Harisen, 1999). The other African species are G. linnaei (white), G. wrightii (red, coppery or white), G. crocea (dull green), etc. Propagation is through seeds, stem cutting and suckers. Tissue cultured plants are only used for the production of cut flowers. After one year of planting side roots (suckers) start developing from the mother plants. Multiplication is through sexual or asexual means. Sexual propagation is through seeds but takes longer time to flower. Vegetative propagation is through division of clumps. It can be propagated through cuttings as well. Also, micropropagation is possible through shoot tip, inflorescence bud, flower bud, flower head, mid ribs. It is grown in soil. It can be grown as pot flower which is annual. The cut flower is perennial and grown for commercial cultivation in green house. Production and size of flower is more in cut flower under protected cultivation. There are four types of flower, namely, cup shaped, double or single, spider and mini. Each type is typified by characteristic enlarged or diminished say, trans or disc florets. Three alleles Crd, Cr and Sp determine the floral types with incomplete dominance. Dc a single dominant gene controls disc color. The following eight species given in the table 11.5 are used in breeding program. Table 11.5  Showing species of Gerbera, its characteristics and origin Species G. aurantiaca G. ambigua G. piloselloides G. viridifolia G. jamessonii G. kraussii G. kunzeana G. tomemtosa

Cultivated / wild

Only cultivated species

Characteristics Pink, orange Pink, white Dirty white, small flower Single and double flowered

Origin South Africa

Origin and Genetic Resources of floricultural Crops

11.11

The package of parches Size of bed for planting  Bed width-1 m, Length-less than 25 m, Bed height-35 cm. Row to row spacing  50 cm, plant to plant spacing-40-50 cm and planting is done in a zig zag fashion. Density of plants is 5 plants/mt sq area and there should be two rows per bed. Cultural operation  It is very important to keep in mind that 25-30 leaves/plant are maintained. Older and infected leaves are removed in order to keep plant healthy. Fertigation (irrigation plus fertilization) schedule is as given below in the table 11.6. Table 11.6  Showing various nutrients and its dose for raising gerbera for cut flower production in protected condition Tank-1

100 litres of water

Calcium sulphate

10 kg

Ammonium sulphate

5 kg

Iron

100 g

Tank-2 Mono potassium phosphate

8 kg

Potassium sulphate

2 kg

Magnesium sulphate

10 kg

Manganese sulphate

70 gm

Zinc sulphate

65 g

Borax

100 g

Copper sulphate

20 g

Sodium molybdate

10 g

1.7 litres of solution from tank-1 and equal quantity of solution (1.7 liters) from tank-2 are mixed with 1000 litres of water. This solution is applied on alternate day, e.g. Monday, Wednesday and Friday. Flowering starts four months after planting and continues up to 5-6 years. After that it is not profitable from commercial view point. Under protected cultivation flowers can be obtained round the year. Shelf life in winter is about 15-20 days whereas during summer it is around 12 days. When temperature goes up above 38°C, production of flower goes down. Pink, red, yellow and white color flowers are preferred in India. Flower is head or capitulum consisting of inner ring of ray florest, middle ring of trans florets and central ring of disc florets. Flowers are of three types-single flowered, double flowered and spider or crested types. Each type is typified by characteristic enlarged or diminished ray, trans or disc flowers. A single dominant gene controls disc color. Three alleles Crd, Cp and Sp with incomplete dominance determine the floral type.

11.4  TUBEROSES (Polyanthes tuberosa, rajnigandha) Polyanthes tuberosa is the cultivated species. It is perennial, belongs to Amaryllis family, gown for fragrance. It is also one of the most

Crop Evolution and Genetic Resources

11.12

important fragrant cut flowers in tropical and subtropical regions. The natural oil comprises of geraniol. There is high concentration of sapogenein (saponins) in the rhizome and tuberous roots which is used for making soap. There are about 12 species as shown in the table. There are three genera, namely, Manfreda, Polyanthes and Prochnyanthes and genus Prochnyanthes is very closely related to genus Polyanthes. Further there are two subgenera in the genus Polyanthes: Bravoa and Polyanthes. Flower is white and small. It is a diploid with 2n = 60. Vegetative propagation is through bulb and bulblets. Vegetative propagation is through corm of size of 2 cm diameter. Sexual propagation is through seeds. Plants obtained from seeds take long time to reach maturity. There are four groups of cultivar considering the density of flower-single flower, flower with one row of petal (mostly grown for perfume), double flower, flower with three rows of petals (preferred as cut flower), semi double, GVB54 variegated. Planting is done during March-April. In most species pollination is carried out by hawkmoth whereas in P. geminiflora it is carried out by humming birds. Flowers of all known cultivars are white and thus breeding objectives include developing cultivar with a range of colour. Use of wild species can be made to develop cultivars with novel colors in tuberose. Interspecific crosses have been successful in developing hybrids with different flower colours. 1. P .x blissii derived from the cross, P . geminiflora × P . tuberosa and has orange-red flower. 2. P .x bundrantii derved from the cross, P . howardii × P . tuberosa and has wine or purple internally and red-pink externally. 3. Hybrid P. “Sunset” derived from the cross, P. sp. 2 × P. tuberose. Intergeneric crosses have also been found successful. 1. P. geminiflora × Prochnyanthes. 2. Manfreda elongate × P. geminiflora. 3. P. tuberose × Manfreda elongata. Root knot nematode is the major problem associated with cultivation of this flower. Micropropagation is through axillary shoot culture. Different specis of genus polyanthes are given in Table 11.7. Table 11.7  Showing subgenera and genera and flower colour of Polyanthes. Genus/subgenus Polyanthes-subgenus Bravoa

Species

Unique trait

Flower color

P. howardii P. bicolor P. graminifolia P. geminiflora

Source of saponins

Reddish-orange flower

P. oaxacana P. zapopanensis P. multicolot P. Montana Contd...

Origin and Genetic Resources of floricultural Crops

11.13

Contd...

Genus/subgenus Subgenus Polyanthes

Species

Unique trait

Flower color Yellow flower

P. densifolia P. platyphylla P. venustuliflora P. palustris P. tuberose P. longiflora P. nelsonii P. sessiflora

11.5  CHRYSANTHEMUM Chrysanthemum indicum (or C. morifolium or C. x hortorum) is an important cut flower and pot plant. It belongs to family Asteraceae. The genus comprises about 50 species. The centre of diversity is China. Chinese chrysanthemum can be divided into two groups-C. zawadskii found in northern China and C. indicum found in southern China. This genus shows a lot of variation in ploidy level which ranges from 2n = 2x = 18 (diploid) to 2n = 36, 54, 72, up to 90. Evolutionary history of Chrysanthemum is less understood because of hybridization and polyploidy. The compound inflorescence is an array of several flower heads. Each flower consists of ray and disc florets and can produce seed. Ray florets are female whereas the disc florets are bisexual. The genus contains several hybrids. The most important hybrid is Chrysanthemum × morifolium (syn. C. grandiflorum) derived from interspecific cross involving C. indicum as one of the parents. Red, purple, pink, yellow and white flowers are found but bright red and blue color chrysanthemum varieties are not found. The other cultivated species include C. boreale, C. maximum, C. carinatum, C. frutescens, C. corocium, and C. segatum (Table 11.8). There are two groups of chrysanthemum cultivars-garden hardy and exhibition. The former produces large number of small flowers and the plant does not require any support. Exhibition type variety requires support (staking). Further, flower heads can occur in various forms such irregular incurves or regular incurves, reflex form (mop head), pompon form (double flower) or button form, anemone form or spider form. C. morifolium is grown for extraction of oil and sesquiterpenoid alcohol. C. morifolium is a hexaploid and highly heterozygous. In this crop a spontaneous mutant can be commercialized within 1.5 to 2 years. Table 11.8  Showing species of chrysanthemum and its characteristics Species

Characteristics

C. boreale

Thought to be involved in the evolution of florists’ chrysanthemum,

C. carinatum

Tricolour chrysanthemum, winter season

C. coronarium

Winter season, used for making garland

C. cinerariifolium

Temperate, Grown for extracting insecticide pyrethrum Contd...

Crop Evolution and Genetic Resources

11.14 Contd...

Species

Characteristics

C. coccineum

Painted daisy, perennial

C. frutescens

Popular as pot plant

C. japonicum C. maximum

Perennial, used as cut flower

C. morifolium

Perennial, composite inflorescence

C. ornatum

Supposedly Progenitor

C. rubellum

Hardiness

C. satsumense

Possible ancestor

C. sibiricum

Supposedly parent of Korean hybrid

C. sinense

One of the supposedly sources of modern day chrysanthemum

Planting is done in August-September. Propagation is through cutting and puttal. When the plant is about 15-20 cm in height then the upper vegetative bud is plucked (Pinching). It is used as cut flowers. It takes 70 days to flower. Pinched parts are used for vegetative multiplication (propagation through cuttings). Mother plants survive for six months only. The package of practices for cut flower production is as follows. Bed size  Bed width-1mt, Bed height-20cm and Bed to Bed distance-40 cm. Planting density and method of planting  Row to row distance-20 cm, Plant to plant distance-20cm, four rows per bed, zig zag planting and density of 20 plants/mt sq net area. Before planting one layer of carnation net of size 10cm × 10cm sq or grid size be laid on each bed at ground level and planting be done on it.

Pinch and Half Method Pinching  Side buds are to be pinched leaving terminal bud in the standard types of chrysanthemum. In the spray types chrysanthemum terminal bud is pinched leaving the lateral buds. Fertigation  Fertigation schedule is given in Table 11.9. Table 11.9  Showing nutrients/chemicals, its dose for raising chrysanthemum (cut flower) in protected condition Tank-1

100 litres

Calcium ammonium nitrate

5 kg

NPK-19A11

10 kg

Iron

150 g

Tank-2

100 litres Contd...

Origin and Genetic Resources of floricultural Crops

11.15

Contd...

Tank-1

100 litres

Potassium sulphate

4 kg

Ammonium sulphate

12 kg

Diammonium phosphate

2 kg

Msgnesium sulphate

1 kg

Borax

50 g

Librasol

300 g

1 litre from tank-1 and 1 litre from tank-2 are mixed with 1000 litres of water and then applied.

11.6  DAHLIA It is a genus of tuberous, herbaceous, shade intolerant and perennial plant. It belongs to family Asteraceae or compositae. There are about 36 wild species and most of the species (except D. australis, D. cocinea, D. imperialis) are native to Mexico. Hybrids are usually grown as garden plant and cultivated hybrids might have evolved from wild x wild cross or cross between naturally occurring species. Cultivars have been derived from D. pinnata and D. coccinea. The genus contains a range of chromosome numbers with x = 16, 17 and 18. Some are diploid with 2n = 32 (wild Dahlia) but others are tetraploid (cultivated Dahlia), octoploids. Plant height can vary from 30 cm (D. tenuis, D. scapigera) to 2 m (D. tenuicaulis and D. macdougallii with 2n = 32). D. tenuis and D. barkeriae are shade tolerant. Flower size can range from 5 cm to 30 cm. Most of the varieties grown are octoploids and some are diploids. Garden dahlia, D. variabilis is an autotetraploid with 2n = 64. Other species include D. pinnata, D. rosa, D. coccinea. Hybridization and/or polypoidization are the process through which new varieties are developed. All colors except blue are found in this genus. Further, presence of transposons creates enormous variability. There are different types of cultivars considering the inflorescence shape, colors and size because of high polyploidy. One can find anemone (tubular floret) type, single flowered, star cupid shaped, collarets, paeony flowered, pompon. Cactus dahlia are fully double flowered. Cross pollination is through bees. Propagation is through seeds, tuberous roots and cuttings. Pinching is done to promote branching in dahlia. In case of massive branching genotype pruning is done to keep the center of bushes open. Disbudding is done to obtain the largest flower. All buds except the central bud and all lateral branches are to be removed.

11.7  ORCHID it is a monocot and has 600-800 genera and has about 25000-35000 species. This flower can be grown in tropics, subtropics and temperate regions. It requires 60-1100 cm rainfall and can be grown at up to 5000 mts. It can be used as cut flower. Cultivars vary according to the climate. In India there are about 140 genera and 1300 species found in

Crop Evolution and Genetic Resources

11.16

North Eastern region to Eastern and Western Ghats. Multiplication is through division of large clumps, cutting and air layering. Although orchids produce large number of seeds, the germination is very very low (0.2 to 0.3%). It is self incompatible. Orchid is associated with endotrophic mycorrhiza. There is one set of fungi which helps in seed germination as seeds of orchids are tiny with limited nutrient supply. Another set of fungi get established in young plant as young plant cant photosynthesize and this requires association of fungi. Orchids can be epiphytic (grown in tropical and subtropical climate) and terrestrial, i.e. grown in soil and generally grown in temperate condition (in Sikkim). In tropical and subtropical climate cut flowers of orchids include cultivars from the genera such as Dendrobium, Vanda, Cattleya, Cymbidium and Renanthera. Dendrobium is sympodial in nature in the sense that it produces offshoots horizontally. Pseudostems die after producing flowers. Thus it is deciduous in nature. One pseudostem produces 3-4 spikes and one spike produces 15-18 flowers. Commercial cultivation of cut flowers can be taken for four years. Cut flowers are bigger in size and heavier. One spike with 6-7 flower fetches a price of Rs. 375 in the market. Shelf life is more than 22 days. Temperate and terrestrial species include Cymbidium and Phaelonopsis. Flowers from Makora species fetch more price than Dendrobium. This species is have hanging roots. They absorb moisture and nutrients from 2-3 away from the shade net containing cocohusk and charcoal. The genera such as Aerides, Cattleya, Renanthera, Cymbidium, Vanda and Phaelonopsis are monopodial in nature. In other words, they are evergreen, pseudostems will not die and they grow vertically. New shoots will arise from the collar region. Indigenous orchids are small flowered with short spike length and with very short shelf life. Cymbidioid phylad includes Cymbidium, Odontoglossum, Miltonia, Oncidium. These are pantropical epiphytic species. They have chromosome number varying from 2n = 10 (Psygmorchis pusilla) to 2n = 168 (Oncidium varicosum). All Phalaenopsis species orchids are diploid with 2n = 2x = 38. Genus Sacoila which is a smaller genus with three species are diploid with 2n = 2x = 46. Dendrobium is the third largest genus comprising diploid and polyploid species (2n = 38-40). It is epiphytic. Basic chromosome number of terrestrial orchids is X = 7. There is predominance of polyploidy series, 7, 14, 21, 28, 42 with a dysploid variation of + or – 1 (aneuploid). Besides interspecific hybrids, bigeneric, trigeneric and quadrigeneric hybrids have been produced in orchids. The various genera with different species are given in Table 11.10. Table 11.10  Showing genera and species of orchids and its characteristics Genera

Species

Characteristics

Aerides

crispum, A. falcatum, A. fieldingii, A. japonicum, A. lawrenceae, A. maculosum, A. mitratum, A. multiflorum, A. odoratum, A. radicosum, A. vandarum, etc.

Monopodial epiphyte, stem long, inflorescence drooping

Cattleya

aurantiaca, C. bicolor, C. bowringiana, C. citrina, C. dowiana, C. intermedia, C. labiata, C. leopoldii, C. luteola C. maxima, C. schilleriana, C. skinneriC. violacea, C. warsceriezii, etc.

Sepals are spreading and crisped petals away from the large different colored lip, monopodial

In vitro propagation

Tissue culture

Contd...

Origin and Genetic Resources of floricultural Crops Genera

Species

11.17 Characteristics

In vitro propagation

Cymbidium

C. aloifolium, C. devonianum, C. eburneum, C. insigne, C. giganteum, C. grandiflorum, C. longifolium, C. pendulum, C. loweianum, C. madidum, C. mastersii, C. simonsianum, C. tigrinum, C. tracyanum, etc.

Long spikes, excellent for decoration, monopodial

Dendrobium

D. aggregatum, D. amplum, D.D. bigibbum, D. bellatulum, D. bensoniae, D.D. canaliculatum, D. chrysanthemum, D. densiflorum, D. devonianum, D. ddraconis, D. falconeri, D. farmer, D. fimbriatum, D. gibsoni, D. gouldii, D. grantii, D. moschatum, D. nobile, D. parishii, D. sulcatum, D. thrysiflorum, D. uncdulatum, etc.

Lip in various shapes, sizes and color, large showy flowers, sympodial

Miltonia

M. anceps, M. candida, M. spectabilis, M. stenoglossa, M. vexillaria, M. warscewiczii, etc.

Epiphyte, flowers are borne singly Tissue or in clusters culture

Oncidium

O. ampliatum, O. auriferum, O. cavendishiaum, O. cheirophorum, O. crispum, O. divariacatum, O. forbesii, O. lanceanum, O. macrathum, O. marshallianum, O. papilio, O. sacodes, O. varicosum, O. variegatum, etc.

Mostly epiphytes, disc on the mid lobe bears prominent crests or tubercles.

Tissue culture

Phalaenopsis P. amabilis, P. fuscata, P. mannii, P. parishii, Short stemmed epiphyte, grown P. schilleriana, P. speciosa, P. stuartiana, P. violacea, etc for cut flower, monopodial

Tissue culture

Renanthera

R. cccinea, R. imschootiana, R. storiei, R. elongta, R. pulchella

Tall growing orchids, mostly epiphytic, horizontally spreading

Vanda

V. amesiana, V. bensonii, V. coerulea, V. coerulescens, V. cristata, V. hookeritina, V. denisoniana, V. teres, V. tessellate, etc

Most popular of all orchids, monopodial, epiphytic

Tissue culture

Orchids are having flowers of unusual shapes and beautiful colors. Purple-fringed orchid is either of the two North American species, Habenaria psychodes and H. fimbriata having flowers purple fringed. Spider orchid is any of the several European orchids, Ophrus esp. O. sphegodes having yellow, green or pink sepals. Bee orchids are having flowers with shape and colour of bumble bees. Splash-petaloid orchids is the most common example of peloric(homeotic) mutation. Package of practices for cut flower production of orchids  The package of practices for production of cut flower in orchids are as follows. Growing benches  60-70 cm height from ground level. Walking way (Isle)-1 mt, either GI pipes or concrete pillars can be used. Growing media is cocohusk blocks. Planting density is 1000 plants/100 mt sq and 4 plants/cocohusk block. Fertigation:  1. First two weeks of planting NPK-19:19:19 plus micronutrients. 2. Third week with NPK in the ratio 10:20:30 plus micronutrients. 3. Fourth week with NPK in the ratio 10:45:15 plus micronutrients. Dose: 500 g of complex fertilizer and 100 g of micronutrients mixed in 1000 litres of water and applied at an interval of three days (e.g. Monday and Friday).

11.18

Crop Evolution and Genetic Resources

Methods of propagation  Cut flower production is taken using tissue culture plants. Plantlets or Kei-kis (offsets) can also be used for propagation. Flowering starts after four months of planting. Pinching  2-3 times pinching of spike is done in order to get more pseudostems and more vigorous vegetative growth. Initially spike length is smaller, 10-15 cm and that is why pinching is done. Pinching allows to produce more vigorous vegetative growth. Paphiopedilum  It is the most primitive form of the Orchidaceous taxon and belongs to family Orchidaceae(Karasawa, 1979). The genus contains about 60 species. Chromosome number in the genus varies from 2n = 20, 26, 28, 30, 32, 34, 36, 38, 40 to 2n = 42. Variation in chromosome numbers is due to occurrence of centric fusion in metacentric chromosomes or shifting of the position of centromere as median to submedian to subterminal. This species P. insigne is discussed because of following two unique characteristics. 1. Presence of bi-modal karyotypes 2. Presence of sub-haploid pollengrains Bi-modality in a karyotype refers to a situation where the difference in length between longest and shortest chromosome is more than 4-5 times. Yucca is a classical example of bi-modal karyotypess having five large and five small chromosomes in the haploid set (0’Mara, 1932). Another example is Hypochaeris (Stebbins, 1971). Bi-modality is also observed in other orchids like Dendrobium. In Listera and Cymbidium chromosomes can be arranged in several well separated length. Sub-haploid pollen grains  There are two classes of sub-haploid pollen grains-hypoploid pollen grains and hyperploid pollen grains. Subhaploid pollen grains with chromosome number varying from n = 5-12 has been observed in cultivar of P. insigne (2n = 26). Also observed were the hyperploids pollen grains with n = 18, 20. Sub-haploidy results from some form of non-disjunction. The higher percentage (81%) of sub-haploid pollen grains may be due to high degree of segregational irregularities during meiosis or to split spindle or failure of cell wall formation. It has been observed in Allium (Ved Brat, 1971), Amaranthus (Pal and Khoshoo, 1972) and Zephyranthes (Raina and Khoshoo, 1971).

11.8  ANTIRRHINUM Antirrhinum(Snapdragon)  It belongs to family Plantaginceae. Its origin is Europe and North America. It is annual, biennial, grown in tropical, subtropical and temperate climate. Receme is borne on tall spike. A. majus is the cultivated species which is self fertile. Wild species include A. valentinum, A. subbaeticum, A. siculum, A. hispanicum. There are three subsections in the genus. 1. Antirrhinum-A, majus subspecies litigiosum 2. Subsection-Kickxiella-A. pulverulentum and 3. Subsection-Streptosepalum-A. meonanthum. Out of some 25 species in the genus Antirrhinum only one species A. majus is domesticated as ornamental species. It is a diploid with 2n = 16. Tetraploid cultivars are also found. Majority of the species show gametophytic system of self incompatibility with single locus, multiple allelic S-system. There is also presence of male sterility in this crop. This is the most well genetically and molecularly investigated species and used

Origin and Genetic Resources of floricultural Crops

11.19

as a model flowering plant. Interspecific crosses with A. molle, A. glutinosum, A. barrelieri and A. latifolium have been studied. Floral scent is due the presence of chemicals such as phenylpropanoids and isoprenoids. Propagation is through seeds and cuttings. Flowers can be obtained after 3-4 months of sowing. There are transposons, namely, Tam 3 (similar to Ac of maize), CACTA (similar to Spm/Em) and MITEs present in the genome. Regulating genes such as MYB or basic helix-loop-helix (bHLH) transcription factors are affecting the intensity or pattern of pigmentation (Schwin et al, 2006). Transposon induced mutation is required for the synthesis of anthocyanin magenta which is structurally related to yellow aurones. Location and effect of genes can be studied through the production of Trisomics. First triploid is generated by the cross, 4n(female) × 2n(male). The triploid thus produced is backcrossed to diploid parent as 3n(female) × 2n(male). 5-20% progeny in the cross will be trisomics. Thus eight trisomics can be produced and gene can be studied (Sampson et al., 1961). Study of flower pigments has shown that all pigments have the same basic formula, i.e. they are all derived from flavon. The flavon has three rings, A, H and B. The differences between flavones, flavonols and anthocyanidins are in the radicals in the positions 3rd and 4th of the heterocyclic ring (H). In anthocyanidin and flavonols different sugars can be added in positions 3. Within each group of pigments the same differences in the radical in the positions 3 and 4 are there in the B ring. Apigenin and pelargonidin have only one OH group in position 3. Luteolin, quercetin and cyaniding have a second OH group in the position 4. Hydroxy-cinnamic acid under the influence of gene, niv+ gets converted as precursor of the flower pigments. The precursor under the influence of gene, nic+ is converted to anthocyanins. The gene, Pal series of genes is involved in the synthesis of cyaniding-3-rutinoside (Harte, 1974).

11.9  ANTHURIUM It is not grown in soil. It is an epiphytic crop i.e. grows on tree. Sometimes it grows epilyptically (on rocks) or terrestrially (on the ground). It belongs to family Araceae. The genus contains some 500-600 species. Some of the important cultivated species include species from flowering and foliage groups. Flowering group species include A. andraeanum, A. bakeri, A. brownie, A. x ferrierense, A. ornatum, A. regale, A. regnellianum, A. robustum and A. scherzerianum of which A. andraeanum and A. schizerianum are the widely cultivated species for flower production. The present day hybrids involved A. andraeanum or A. schizerianum as one of the two parents. The basic chromosome numbers of Anthurium vary as n = 15, 16 and 22. A.andraeanum is a diploid with 2n = 30. Sexual propagation is through seeds and vegetative propagation is through division of offshoots and cuttings. Tissue cultured plants are obtained from Holland as well as from India. It can be grown in pot or as cut flower in green house. The crop survives for 6-7 years. Flowers can be obtained round the year. Tissue cultured plants are used to start cut flower production. Inflorescences are cup shaped and have a spadix and a spathe. Stalk height ranges from 35 cm to 70 cm. Shelf life of cut flower is around 25 days. Colors of flowers range from white, green, red (light, dark), pink (light, dark).

Crop Evolution and Genetic Resources

11.20

It is a major cut flower of tropical and subtropical countries. Anthurium consists of about 1000 species (Croat, 1992). It is available in red, pink, orange, coral and white color. It is a diploid with 2n = 30 (Sheffer and Kamemoto, 1976). Basic modes of propagation are through seeds and cuttings but now a days propagation through tissue culture is commercially used. It belongs to family Araceae. The two cultivated species, A. schrzerianum and A. andraeanum have bright red spathes. A. crystallinum f peltifolium is used as household plant or can be raised under shade. A. aminicola is a miniature species with lavender spathes. Other species include A. formosum with very large, creamy white spathe, A. kamemotoanum with dark magenta spathe and A. lindenianum with white spathe.

Package of Practices Bed size  Bed width-1.2 m and Bed height-40 cm. Beds are either with bricks on the ground or with shade net in hanging design. The media constituents include Cocopeat, Cocohusk, sand, perlite and charcoal pieces. Imported plants are 5-6 cm in height and 4-5 months old. These plants are kept in the green house for hardening for 8-9 months (12-15 cm). After that they are shifted to green house and flowers are formed after 1 and 1/2 years to 2 years. Planting density and method of planting  30 × 20 cm, zig zag planting, density is 25 plants/mt sq net area and five rows are there in one bed. Fertigation  schedule is given below in the table 11.11. Table 11.11  Showing nutrients and its dose for raising Anthuroum for cut flower in protected condition Tank-1

100 litres

Calcium nitrate

4 kg

Urea

6 kg

Iron

100 g Tank-2

100 litres

Potassium nitrate

8 kg

Diammonium phosphate (DAP)

5 kg

Magnesium sulphate

1 kg

Librasol

50 g

1 litre from tank-1 and 1 litre from tank-2 are mixed in 1000 litres of water and applied. At temperature less than 15°C the growth of plants and production of flowers are adversely affected. This flower crop is highly temperature sensitive. Even the water temperature affects production as lower temperature affects roots and the nutrient supply.

11.10  CARNATION Dianthus caryophyllus belongs to family Caryophyllaceae. It is a diploid with 2n = 20, annual or perennial. Three most common kinds of carnations are: 1. Annual carnations 2. Border carnations 3. Perpetual carnations. D. caryophyllus belongs to the perpetual type

Origin and Genetic Resources of floricultural Crops

11.21

of carnation. It is number one cut flower. It is highly heterozygous and thus propagation through seed will not produce true to type plant. Annual carnations tend to be propagated by seeds. There are three distinct groups of polyploid. There are diploid (2n = 2x = 30), triploid (2n = 45), tetraploid (D. chinensis), hexaploid and 12x = 180. D. broteri, the Iberian carnation shows the highest diversity. There is production of unreduced gametes in D. caryophyllus. The genus Dianthus contains about 300 species. D. caryophyllus. D. barbatus, D. chinensis, D. plumarius, D. superbus and their hybrids are used as cultivars. Carnations are double-flowered cultivars evolved from interspecific hybridization between two or more species, one of which is likely to be D. caryophyllous. Propagation is through seed and cutting. In order to get large sized flower main stem and other branches are cut from about plant of 20-25 cm heigh (pinching). Only 3-4 branches per plant are kept. The centre of diversity is southern Europe and greatest range of Dianthus species are found in south eastern European countries. Pigmentation in carnation is mainly due to anthocyanin and chalcone derivatives and due to absence of F3, 5 H, a key enzyme involved in the synthesis of delphinidin, blue or violet color have never occurred in carnation (see section). Transfer of F3, 5H gene from pansy or petunia has led to development of blue or violet transgenic carnation. Carnations can also be propagated by tissue culture-shoot tip culture and single node explants. Like chrysanthemum plants should be replaced after 4 years. For cut flower production tissue cultured plants are used. This crop gives flower for four years and round the year. It takes five months to flower. It is a very sensitive to temperature. If temperature goes beyond 34°C, roots die. Cut flower production can be taken under protected cultivation. Other species of Dianthus include D. alpinus, D. arenarius, D. attenua, D. caesius, D. callizonus, D. capitatus, D. carthusianorum, D. cruentus, D. deltoids, D. diadematus, D. fimbriatus, D. giganteus, D. glacialis, D. grandiflorus, D. heddewigii, D. hybridus, D. knappi, D. laciniatus, D. latifolius, D. monspessulanus, D. nobilis, D. pancicii, D. petraeus, D. plumarius, D. squarrosus, D. sylvestris, D. versicolor, D. winteri, etc.

Package of Practices Under Protected Condition The package of practices is as follows. Bed size  Bed length-1mt, Bed height-20-25 cm and Bed to Bed distance-45 to 50 cm. Planting density and method of planting  Row to row distance-20 cm, plant to plant distance-20 cm, four rows per bed, zig zag planting and density of 20 plants/mt sq net area is maintained. Heights of netting and net size are as follows (Table 11.12). Table 11.12  Showing net sizes used in the production of cut flower in Dianthus Nets 1st net (ground level) 2nd net 3rd net 4th net

Height 10 cm 25 cm 45 cm 65 cm

Size 10 × 10 cm 12 × 12 cm -do-do-

Crop Evolution and Genetic Resources

11.22

Pinching  First pinching is done at 3 pairs of fully developed leaves, second pinching is done on the bottom most two side branches. The top two branches should be allowed to grow for flowering. Fertigation  The fertigation schedule is given in Table 11.13. Table 11.13  Showing nutrients and chemicals, its dose for cut flower production in Dianthus. Tank-1 Calcium nitrate Ammonium sulphate Iron Tank-2 Potassium nitrate Mono ammonium phosphate Borax Microsal

100 litres 8 kg 6 kg 150 g 100 litres 12 kg 11 kg 200 g 5 kg

Vase life of cut flowers or flower longevity is most important characteristic of carnation. Carnation flowers are highly sensitive to ethylene (Woltering and Van Doorn, 1988) which induces autocatalytic ethylene production and wilting in carnation petals. Senescence of Tradescantia, Ipomea and Hibiscus is also strongly influenced by ethylene whereas petal senescenceof Chrysanthemum, Narcissus and Zinnia seem not to be affected be ethylene. Thus like fruits floricultural crops can be grouped as climacteric or non-climacteric depending on whether the senescence is sensitive or insensitive, respectively to ethy-lene. Flower longevity is a quantitative trait, i.e. polygenes are involved in ethylene production and ethylene sensitivity and conventional cross breeding method is used to improve vase life. Vase life can be improved by chemical treatment with aminooxyacetic acid and aminoethoxyvinylglycine which are inhibitors of ACC synthase as well as by silverthiosulfate, an inhibitor of ethylene binding to its acceptor (Wang and Baker, 1980). In other words, ethylene climacteric during senescence can be checked by inhibiting either synthesis of hormone or its binding to receptor.

11.11  ROSE Roses are important cut flower. The genus Rosa contains about 200 species. Rosa chinensis and R. gigantia (wild tea rose) are diploid. Modern day roses have evolved from crosses of these species. Other species are R. damascene, R. moschata, R. multiflora R. wichurariana, R. gallaica and R. foetida. Most of the species are native to Asia (China, Japan). A small number is from Europe, North America and North West Africa. Asia is the gene center. Modern day roses have evolved from crosses of these species. R. damascene, R. centifolia, R. gallaica, R. alba and R. borboniana are used for producing perfume, attar of rose, oil. Tea rose blossoms only once in a year and is single flowered. Floribunda rose are multiflower cut roses. Grandiflora hybrids are tetraploid (2n = 4x = 60). Dutch roses are sold as cut flowers. They are known for fragrance and come in different colors like red, yellow, pink,

Origin and Genetic Resources of floricultural Crops

11.23

orange and white. Red is the most preferred color in the market. The today’s cultivated roses, Rosa hybrida evolved as a result of interspecific hybridization involving wild species involving yellow-flowered (producing carotenoids) and orange flowered (producing pelargonidin related anthocyanins) species. As Rosa can not produce delphinidin-based anthocyanin, so it does not have any varieties having bluish range of color. Three types of rose are commercially grown in India. 1. Hybrid tea 2. Floribunda 3. Spray (Floribunda or Polyantha). Hybrid tea produces larger size single flower and has 50-120 cm stem length. Floribunda produces small size single flower with 30-70 cm stem length. Spray type produces smaller flowers, the number of which can be less than three with a stem length of 40-70 cm. There is positive correlation between bud size and stem length, bigger the bud the lager the stem. Species or wild rose and their hybrids are large erect shrubs, climbers or trailing with stem like roses with single flower. Garden roses are hybrid roses. Old garden roses include Tea, Alba (R. x alba), China (R. chinensis), centifolia (R. x centifolia), Moss, Rumblers, etc. Modern rose (has spicy sweet scent and grown for smell) includes hybrid tea, climbing Polyantha, Floribunda, hybrid rugosa, grandiflora, etc. Polyantha was derived from R. chinensis x R. multiflora cross. Grandiflora was derived from backcrosses between Hybrid Tea and Floribunda. Species roses (wild roses) are the parents of modern day roses. Floribunda is a hybrid between hybrid tea x polyantha. Hybrid tea is developed from the cross hybrid tea x hybrid tea and hybrid perpetual x Tea cross. Hybrid perpetuals were derived from the cross between Asian rose and European rose. The hybrid had the reblooming characteristic. Centifolia evolved from R. gallica, R. R. moschata, R. canina and R. damascene. Borsault was derived from R. pendulina and R. chinensis. Alba originated from the cross of R. canina and R. damascene. English rose was derived from old garden rose x Hybrid Tea or Floribunda cross. Tea rose (R. x oderata) was derived from the cross of R. chinensis and R. gigantia. Japan has a large number of Rosa species such as R. multiflora, R. lutea and R. rugosa. These species have been utilized to breed Rose hybrid which is tetraploid whereas wild roses are diploids. Hybrid tea roses have vase like shape and fragrant, lower part of the plant is rather bare and is repeat bloomers if dead headed. Grandiflora type rose is the largest the roses, upright and very tall plant. Floribunda type has bushy shape and is smaller than hybrid tea roses and is suitable for wetter climate. Polyantha type is similar to floribunda but there is profusion of small sized flowers and blooms all season long (blooming non-stop) and perfect for container roses. Shrub rose bushes lack the traditional perfect bud found in hybrid teas. Miniature rose is perfect for container. Rugosa roses are fit for rose hedges and seaside gardens, Finally there are thornless roses which are almost or virtually thornless. Wild rose  any of the numerous roses including dog rose (Rosa cannina, scentless flower) and sweetbrier (Rosa rubiginosa) which grow wild and have flowers with only one whorl of petals. Rose petals from scented rose are used for making gulkand after extraction of oil. Rose hips are fruits of rose (red to orange in color) which are rich source of Vit. C (contain 50% more Vit. C than orange) and cancer preventing compounds. It is also used for making wine, vinegar, jams, syrup and tea. Rosa canina , the climbing wild dog rose is famous for its rose hips. There are about 20-30 species in the section Canina in the

11.24

Crop Evolution and Genetic Resources

genus Rosa. R. rugosa, R. amblyotis, R. acicularis, R. davuriaca, R. pendulina and R. glauca are also used for rose hips production. and Rosa canina has permanent odd polyploidy. Dog roses are mostly pentaploid but tetraploids or hexaploids may occur although the basic chromosome number in the genus Rosa is x = 7. Regardless of ploidy level only seven bivalents are formed leaving the other chromosomes as univalents. Univalents are included in the egg cell but not in pollen. R. damascene and R. centifolia are commercially used for extraction of rose oil for use in perfume industry. Rose oil contains citronellol, phenyl ethyl alcohol, geraniol, nerol, etc. Besides these two species R. sempervirens and R. moschata are also known for aromatherapy. Most of the recurrent flowering cultivars are tetrasomic tetraploid with 2n = 4x = 28 (R. gallica, R. centifolia, R. foetida, R. R. damascene) and originated from 10 to 15 mostly diploid species with 2n = 2x = 14 (R. moschta, R. gigantean, R. multiflora, R. chinensis, R. wichuraiana). Heterozygosity and crosspollination are the obstacles in rose improvement. Remove or cut the upper portion of the branch, leaving the lower side of braches with 4-5 buds (pruning). Further wintering is done in which after pruning digging of the soil surrounding the root of the plant, about 45 cm in diameter and 15-20 cm in depth, is done. Candied rose (gulkand) is prepared from rose petals after extracting oil. In addition to species grown for perfume, R. pomifera and R. chinensis are also grown for preparing gulkand. Rose water is also prepared from rose. Rose species being used as rootstocks include R. borboniana, R. canina, R. indica var. odorata, R. laxa, R. rugosa, R. moschata, R. multiflora, R. rubiginosa, R. chinensis, R. sempervirens, etc.

Method of Production of Cut Roses in Protected Condition Package of practices adopted for cut flower production in rose is as follows. Only Dutch roses are used for cut flower production. It is propagated through I/patch budding. China rose is vegetatively propagated by cutting and can be grown in pot as well under open field condition. China rose is of no commercial value. Bed size  Width-1m, height of bed-35-40 cm and bed to bed distance – 40cm. Planting density and method of planting  Spacing 40 × 20 cm, 2 rows per bed, zig zag planting and density of 7 plants/mt sq net area. Cutting and pruning: 1. Bending-Bending of lateral branches is done after 4 to 6 months of planting (just near the attachment). Bending helps in maintaining enough leaf area in plants which is required for a strong root system. Bending breaks apical dominance of the plant. It is a continuous process and should be continued throughout life cycle. 2. After two months pinching of the new basal shoots. First flower is pinched so that 2-3 eyes bud will sprout on main branch to grow as branches. 3. 20 days after pinching cut the productive stem starts flower production.

Origin and Genetic Resources of floricultural Crops

11.25

There are two types of pinching-soft also called disbudding and hard pinching. Bending in mature plants provides photosynthates to incoming shoot. Weak productive stems are disbudded which results in production of axillary shoots and it grows thicker. Disbudding refers to removal of side buds. All varieties produce one center bud along with some side buds. When bud attains pea size and shows some color, it is the right time of disbudding. In case of spray varieties center crown bud is removed. Pinching is removal of unwanted vegetative growth from the axil of the leaf below the terminal bud. It leads to break of apical dominance. It is done to produce quality flower. Wild shoots (root stock) are also removed. It is removal of unwanted growth at the union on the rootstock. Fertigation  The fertigation schedule is given below in the table 11.14. Table 11.14  Showing nutrients and chemical, its dose applied in production of cut flower of rose Tank-1 Calcium ammonium nitrate Urea Iron Tank-2 NPK-19A11 Potassium nitrate DAP Magnesium sulphate Borax Librasol

100 litres 14 kg 3 kg 200 g 100 litres 5 kg 6 kg 8 kg 2 kg 100 g 4 kg

800 ml from tank-1 and equal quantity from tank-2 are mixed with 1000 litres of water and applied.

11.12  GLADIOLUS It is a bulbous plant, highly heterozygous and widely cultivated as cut flowers. It is also good for bedding. Planting is done during September-November. Vegetative propagation is through corm of size of greater than 3-4 cm. The genus Gladiolus contains around 300 species. It is a bulbous flowering plant. It belongs to family Iridaceae. The centre of diversity is Cape Floristic Region. Inflorescence contains one to several flowers, varying in size from very small to 40mm across. Flower spike is large, one sided. Flowers are bisexual. Cross pollination is through insects. Flowers vary in color. Most of the species of the genus are diploid with 2n = 30. But then there are tetraploid species with 2n = 24 = 60, pentaploid, hexaploid and octaploid. Grandiflora hybrids are tetraploid because its parent, Gladiolus dalenii is a tetraploid. Breeding at polyploid level is widely used in interspecific hybridization. The evolution of modern day cultivars involved about 20 or more species and even few related genera. Vegetative propagation is through cormlets which are produced as offsets by the parent corms. Clumps should be dug up

11.26

Crop Evolution and Genetic Resources

and divided every few years in order to keep plant vigorous. Cultivated species include G. primulinus, G. alatus, G. cardinalis, G. undulates, G. dalenii, G. imbricatus, G. x hortulans, G. carneus, etc., African species G. tristis is white and G. segetum is having magenta color.

11.13  LILY-WATER LILY It is a monocot, bulbous crop and belongs to family Liliaceae. The genus Lilium contains over 80 species. It is spread in mountaneous area of Nothern hemishphere (Asia, North America, Europe). There are three sections in the genus, namely, Leucolirion (white trumpet shaped flower), Sinomartagon (containing a variety of flower colors) and Archelirion (containing white and pink flower). Thus there are three most important groups of hybrid varieties, Longiflorum hybrids, Asiatic hybrids and Oriental hybrids respectively. Varieties in these groups are mostly diploid with 2n = 2x = 24. Within section cultivars hybridize easily but it is difficult to hybridize cultivars belonging to different sections and here in vitro techniques are employed. Longiflorum is a common easter lily. Asiatic and LA hybrids (Longiflorum/Asiatic) have slight or no fragrance whereas oriental, LO (Longiflorum/Oriental) and OT (Oriental/Trumpet, Orient) are fragrant.

Oriental hybrids include L. auratum, L. speciosum and L. rubellum and Asiatic hybrids include L. tigrinum, L. bulbiferum, L. maculatum, L. dauricum and L. davidii. Other species include L. x formolongi, L. japonicum, etc. There is not always direct relationship between complexity and genome size. Human genome is made up of 6 billion bps. Lily produces fewer different proteins than human but has 18 times more DNA.

11.14  LOTUS Lotus (Nelumbo nucifera) is a symbol of spiritual purity and longevity. It is an aquatic perennial. It has got the genes contributing to longevity and repairing genetic defects. This flower may hold secrets about aging. Its petal and leaves act as anti-depressant. Its flower generates heat to attract cold-blooded insect pollinator. Its flower, seed, young leaves and roots (rhizomes) are all edible. The genus Nelumbo contains two species. 1. Nelumbo nucifera, the sacred or Indian lotus and 2. Nelumbo lutea, the American lotus. Both are diploid with 2n = 16 (Wang et al., 1985). It belongs to family Nelumbonaceae. N. nucifera is distantly related to Nymphaea caerulea (water lily). Hybrids have been derived from

Origin and Genetic Resources of floricultural Crops

11.27

the cross, N. nucifera x N. lutea. Flowers are fragrant and show a range of colors such white, yellow, pink and even bicolor. Flowers open in the morning and petals fall in the afternoon. N. nucifera is cultivated for edible rhizome and seed and thus is a food crop as well. Rhizome is used for making pickles. In N. nucifera there are three groups of varieties, namely flower lotus, rhizome lotus and seed lotus. Seed lotus are phylogenetically close to wild lotus. Seeds remain viable for about 1300 years. Sexual propagation is through seeds, the most simple and common method. Seeds show long dormancy. Vegetative propagation is through division of rhizome.

11.15  PANSY It is known for its colorful and patterned flowers. It is a winter flower, almost heart shaped with overlapping petals. Four petals point outwards and only one is directed downwards. It prefers slightly acidic soil (pH-6.0-6.2). Modern day pansy is garden pansy, Viola x wittrockiana which is a hybrid between V. tricolor (garden pansy, annual and biennial) x V. lutea (mountain pansy, creeping, perennial). V. wittrockiana is annual or biennial and base of lower petal is always yellow. V. tricolor is a native of Europe. V. wittrockiana is an autoallo octoploid with 2n = 6x = 48, have thicker, wider, greener leaves, greater stomatal size and larger flowers. Different species of the genus Viola are given in the Table 11.15 along with chromosome number. There are two types of flowers. 1. Chasmogamous (not strictly autogamous) and 2. Cleistogamous (invariable autogamous). Like Viola Oxalis and Commelina also produce these two types of flowers. Breeding objectives in pansy include stocky, bushy and genotype with plenty of buds. This flower is largely self fertilizing but cross pollination also occurs through insects. Flower size can be large, medium, small or multiflora. Color can be pure or multicolored. It is hermaphrodite, self fertile. Cross pollination is through bumble bees (Bombus spp.) and moth (Plusia gama) Traditional (untreated) and primed seeds are sold in the market. Priming is done to enhance germination, higher percentage of germination and less sensitivity to high temperature during germination. Table 11.15  Showing species of Pansy, its ploidy level and characteristics Species

Ploidy level

V. altaica

n=?

V. cornuta

n = 11

V. lutea

n = 24 n = 13 2n = 48

V. tricolor V. wittrockiana V. arvensis V. ocellata V. odorata V. patrini

Characteristics Horned pansy, evergreen and perennial Widely cultivated Modern pansy

Size of plant flower Small plants with smaller flower

11.28

Crop Evolution and Genetic Resources

11.16  ZINNIA It is used as bed, border or pot flower plant. It flowers throughout the year. It is native to Mexico. It belongs to the family Asteraceae (Compositae). There are 20 species in the genus, Zinnia. The species grown includes Z. elegans (2n = 24), Z. haageana (Z. angustifolia) (2n = 22), Z. linearis, Z. acerosa, Z. zamudiana. Z. elegans and Z. angustifolia are widely grown for their attractive flowers. Autotetraploids have been synthesized. Z. marylandica has 2n = 4x = 46 and Z. violacea has 2n = 4x = 48 or 2n = 2x = 24. There is presence of SI (Self incompatibility) and male sterility in this flower crop. Propagation is through seeds.

11.17  BIRD OF PARADISE Strelitzia reginae belongs to the family Strelitziaceae. It is an evergreen perennial plant. Plants are rhizomatous. The genus includes 5 species, namely, S. augusta, S. kewensis, S. nicolai (2n = 22), S. candida, S. reginae. S. reginae is popular orange-colored flower species, called bird of paradise or crane flower. The basic chromosome number is reported as n = 11 or n = 7. It is a crosspollinated crop and pollination is by bird. Propagation is through seeds, division of clumps and separation of offsets. Vegetative propagation through rooted suckers is the common method. The plant from offsets takes 3-5 years for flowering.

11.18  ALSTROEMERIA It is an important cut flower. It is bulbous, perennial and used as bedding, border or plot plant. The genus Alstroemeria contains about 60 species. Some important species include A. aurea syn. A aurantiaca, A. brasiliensis, A. campaniflora, A. caryophyllea, A. hookeri, A. ligtu, A. pelegrina, A. pulchella, A. spathulata, A. versicolor, A. violacea. All species are diploid with 2n = 16. There has been report of presence of diploid with 2n = 12, triploid with 2n = 3x = 24, tetraploid and various types of aneuploids. Present day Alstroemeria hybrids have been developed from inter specific hybridization involving A. pelegrina, A. violacea and A. aurantica. Various polyploidy form evolved through the process of sexual polyploidization involving production of 2n gametes.

11.19  STOCK It is an annual or biennial flower, raised as border or pot flower, also cultivated for cut flowers. It belongs to family Cruciferae. There are about 55 species in the genus Matthiola. Important species include M. fructilosa, M. incana, M. longipetala subsp. Bicornis syn M. bicornis, M. odoratissima, M. sinuata, M. tristis, M. tricuspidata, M. vallesiaca, M. pademontana and M. fenestralis. It is propagated by seeds.

Origin and Genetic Resources of floricultural Crops

11.29

11.20  CHINA ASTER Callistephus chinensis is an annual flower. It is a self pollinated crop which allows up to 10% outcrossing. It is also used as cut flower. It belongs to family Asteraceae. The genus contains single species, C. chinensis. It is propagated through seeds.

11.21 STATICE It is also sold as cut flower. Limonium belongs to family Plumbaginaceae. The genus is native to Europe. Limonium are annual, biennial or evergreen perennial. There area about 150 species in this genus. Some of the annual species include L. sinuatum-a major cut flower species, L. suworowii whereas perennial species include L. latifolium and L. vulgar. L. profusum is cultivated for extracting medicine. Other species include L. tataricum, L. bonduelli, L. aureum. It is propagated through seeds. It can also be propagated vegetatively through division of clumps.

11.22  ZANTEDESCHIA It is known as calla lily. Z. aethiopica is a perennial herb, used as cut flower in Newzealand and pot plant. It propagates through offset production. The genus contains 6 species. It belongs to family Araceae. It has African origin. Z. aethiopica is an evergreen species whereas others are winter-dominant species. Z. aethiopica is a diploid whereas species from winter-dominant section are tetraploids. There is presence of SI (Self in compatibility) in this species. The different species include Z. albomaculata syn. Z. melanoleuca, Z. elliottiana, Z. oculata, Z. pentlandii, Z. rehmannii, Z. odorata, Z. There are other species which have evolved as a result of interspecific hybridization such as Richardia aurata (Z. albomaculata x Z. oculata, R. lathamiana) (Z. ellittiana x Z. albomaculata and R. taylori) (Z. elliottiana x R. aurata) (Bailey, 1963). Arhul  Hibiscus rosa–sinensis- It is a flowering shrub and belongs to family Malvaceae. It flowers throughout the year. It has basic chromosome number x = 18 and chromosome number can vary from 2n = 36 to 2n = 144 (36, 38, 40, 44, 52, 70, 76, 84, 90, 92, 118, 144). Aneuploids arose by hybridization between species belonging to presence of two groups of species described below.

11.23  HIBISCUS There are four main species of Hibiscus having ornamental vale. These include H. rosasinensis, H. syriacus, H. schizopetalous and H. mutabilis. Hibiscus represents auto-polyploidaneuploid complex. Chromosome numbers in cultivars of H. rosa-sinensis vary from 2n = 46, 54, 63, 68, 72, 77, 84, 90, 96, 112, 132, to 144. H. rosa-sinensis is thought to have evolved from H. rosa-sinensis (Sensu strict) and a number of species such as H. schizopetalous (2n = 40), H. liliflorus (2n = 42), H. fragilis, H. boryanus, H. kokio (2n = 80), H. arnottianus (2n = 80), H. waimae (2n = 80), H. denisonii and H. storckii in addition to other unknown species (Palmer and Palmer, 1954).

11.30

Crop Evolution and Genetic Resources

The centre of origin is China. There are two groups of species in this genus. One is South Indian Ocean island, East African coast which includes H. schizopetalus, H. liliiforus, H. fragilis, H. boryanus and the another group called Pacific islands which include H. arnottianus, H. kokio, H. stockii, H. denisonii. They are fully intercompatible. Flower color includes white, pink, red to yellow. Further, flowers can be single or double flowered and large or small. Flowers are bisexual. Popagation is through cuttings. Seed setting is rare due to male or female sterility and self incompatibility. Sthalkamal  Hibiscus is the most important ornamental shrub. Hibiscus mutabilis is another important species. Flower color changes from white to pink to dark red.

11.24  BUGAMBILIA Bougainvillea is grown in tropical and subtropical climate. It grows best in full sun, under high light intensity. It has South American origin. It is a paper flower. It is a diploid with 2n = 34. It is a thorny woody, evergreen vine but deciduous where there is dry season. It belongs to family Nyctinaginaceae. It can be used as hedge, barrier and slope covering. It can be used as shrub, bushes and ground cover. It can also be trained as ‘Standard’, a small flowering tree with a single trunk. Further, bonsai can be made. Regular pruning is essential. Flowers occur in cluster. Each cluster contains three flowers, surrounded by 3 or 6 bracts. There are 14 species in this genus of which three species are horticulturally important. These species include B. spectabilis (hairy leaves and stem, 2n = 34), B. glabra (2n = 34, climbing, evergreen, can tolerate slightly cooler condition, hairless, blooming several times a year and B. peruviana with green bark. Interspecific crosses have produced important hybrids such as B x buttiana derived from the cross B. glabra and B. peruviana and B x spectoglabra derived from B. glabra and B. spectabilis. The former is the most common hybrids grown. A wide range of color variation exists such as pink, magenta, red, purple, yellow, orange and white. Vegetative propagation is through soft wood cuttings.

11.25  JUHI, BELA AND CHAMELI Jasminum is a genus of shrub and vines. It is native to tropical and subtropical regions of Asia, Africa and Australia. Juhi  (Jasminum auriculatum) or Indian jasmine is a shrub or climber. It grows well under 15 to 40°C. Flowers appear in bunches. The white flowers are very strong scented. It is used for making scent. Bela  J. sambac is an evergreen shrub or vine. It is called Arabian jasmine. It is native to India. Leaves are ovate. It blooms throughout the year. Flowers are white, small star shaped very attractive and sweetly fragrant and used for making perfume and tea. Vegetative propagation is through cuttings, layering, marcotting. Chameli  Jasmine grandiflorum is closely related to J. officinale. It is a tropical deciduous shrub. Flowers open in cyme. Leaves are arranged in opposite fashion. It belongs to family Oleacea. It is native to South Asia, India. Jasmine oil contains methyl jasmonate.

Origin and Genetic Resources of floricultural Crops

11.31

Most of the species in the genus Jasminum are diploid with 2n = 26. But then polyploidy exists in this species of this genus such as J. sambac (2n = 39), J. flexile (2n = 52), J. primulinum (2n = 39), J. angustifolium (2n = 52). The centre of diversity is South Asia and South East Asia. Other species include J. fluminense, J. dichotomum, J. polyanthum (found in Australia with white flower). There is autoployploidy, lots of spontaneous mutation and there is occurrence of natural hybridization between species. Some of species with their distribution are given below in the table 11.16. Table 11.16  Showing species of Jasmine, its origin and characteristics Species J. auriculatum J. calophyllum J.dispersum J. flexile J. parkeri J. pubigerum J. rigidum J. sambac J. beesianum J. dichotomum J. favreri J. floridum J. fluminense J. fruticans J. grandiflorum J. multiflorum J. nitidum J. nudiflorum J. officinale J. polyanthum J. rex J. revolutum J. trinerve J. volubile J. wallichiamum J. humile J. pubescens

Origin India India India India India India India India China, U.S.A. Africa, U.S.A Myanmar China U.S.A. Mediterrenean Subtropical Himalayan region India, U.S.A., China, Myanmar U.S.A. China, U.S.A. Iran, India, China China, U.S.A. U.S.A. Himalaya, Afganistan Java Australia Nepal Tropical Asia

Scented / nonscented Scented

Cultivated / wild cultivated

scented

Arabian Jasmine, cultivated

Scented

Spanish Jasmine, cultivated

scented

Common white Jasmine or Royal Jasmine

scented scented

Crossandra  It is an important commercial flower, grown in India. It produces flower throughout the year. Flowers are popular because of attractive bright colour (orange, deep orange or orange–yellow). This flower is used in combination with jasmine flowers.

Crop Evolution and Genetic Resources

11.32

It belongs to family Acanthaceae. There are about 50 species in this genus. The cultivated species include C. infundibuliformis, C. guineensis, C. mucronata, C. nilotica and C. subacaulis of which C. infundibuliformis is the only commercially cultivated species as pot plant. Crossandra is a diploid with 2n = 20 and is highly homozygous. It produces lots of seeds and breeds true. There is also a triploid variety which produces deep orange bright color. Propagation is through seeds and soft-wood and semi-hardwood cuttings (FebruaryMarch or July-August planting). Pruning of plant improves quality of flower and plant vigor. Plant requires lots of irrigation for good yield. Raatrani  Cestrum nocturne is an evergreen flowering bush. It is a nigh blooming Jasmine. It is native to West Indies. It is adapted to subtropical region. Flowers are greenish white. It is heavily perfumed at night. It belongs to family Solanaceae. The plant contains alkaloid called solanine. Perfume causes respiratory problem and shows feverish symptom after inhalation. Harshringar  Nyctanthes arbor-tristis is a night flowering Jasmine. It belongs to family Nyctanthes, Oleaceae. It is native to Southern Asia. It is a shrub or small tree with fragrant flowers. Flowers are white with orange stem. Flowers bloom in the evening and fall throughout the night. Extracts from seeds, leaves and flowers are have medicinal properties. Further, yellow dye for clothing can be produced from the flower. Fuchsia  It is an out breeding shrub species, highly heterozygous and diploid (2n = 22) and is propagated vegetatively. Flower colors range from red through purple to pink and white and only a few species are predominant (F . magellanica (2n = 44), F . fulgens (2n = 22), F . boliviana, F . triphylla (2n = 22) and F . splendens) in the gene pool. The genus contains over 100 species. Interspecific crosses have yielded transgressive segregants for flower color. The other different species include F. arborescens (2n = 22), F . trumpetor, F . hatschbachii, F . glazioviana, etc., (Talluri and Murray, 2014).

11.26  PETUNIA Petunia belongs to family Solanaceae. The genus Petinua contains 30 species (Sink, 1984) and is distributed in South America. Petunia hybrid is flower crop which can tolerate aneuploidy (Rick, 1971). P. hybrida arose from the cross of two wild species, namely, P. axillaris and P. violaceae. Progenies of aneuploid can range from 15 to 20 chromosomes. Some of the species of Petunia along with their ploidy levels are given in the Table 11.17 below. Table 11.17  Showing some species of Petunia Species P. inflata P. axillaris P. violacea P. parodi P. parviflora P. linearis P. calycina P. hybrida P. hybrida var.Superbissima

Ploidy level 2x = 14 2x = 14 2x = 14 2x = 14 2x = 18 2x = 18 2x = 18 2x = 14 4x

Common name

Garden petunia Gigas garden petunia

Origin and Genetic Resources of floricultural Crops

11.33

11.27  CACTUS It is a xerophytic, flowering plant. There are about 200 species and approximately 2000 varieties. Cacti are for gardens as ornamental plants, for fodder or foliage, for fruit (food), eaten fresh (cactus pads) or cooked as vegetable or pickled or for industrial purpose, preparation of jam or for extraction of dye (Cochineal dye) carmic acid used in textile industry or for medicinal purpose. The insect, Dactyloptus coccus feeds on cladodes. It refers to any spinny, succulent plant of the family Cactaceae of arid region. It is a dicot and insect pollinated. Bat (Leptonycteris curasoae) and Choeronycteris Mexicana (Glossophaginae) also do the pollination. Most cacti are hermaphrodite but a few are dioecious. Flower is solitary. Some populations are trioecy (consisting of male, female and hermaphrodte plants) and some are gynodioecious (hermaphrodite and female plants). There is presence of herkogamy (spatial separation of anthers and stigmas, distyly, heterostyly) or dichogamy (temporal separation, i.e. pollen produced when the stigma of the same flower is not receptive) and self incompatibility. It is born on axillary bud (called areoles) which also gives rise to new plant. Method of propagation is through seeds, offsets or by rooting of body parts. Parthenocarpy is also found in Opuntia. Cactus is mainly night blooming. Cacti are diploids (2n = 2x = 22), tetraploids (2n = 4x = 44), hexaploids (2n = 6x = 66) or octoploids (2n = 8x = 88). Polyploidy is widespread in Opuntia species. Further there are reports of autotetraploids and allotetraploids in Opuntia (Prrofitt, 1980). Cactuses have swollen, tough stems, leaves reduced to spines or scales and have large brightly colored flowers. Phylloclade is used for storing water and food. Stomata are fewer in numbers and remain sunken in grooves and occluded. CAM is found in cacti. The different genera of Cactus include Opuntia, Cereus, Nopalia, Pereskin, etc. Cactus species of horticultural importance include Cereus, Echinocacatus, Opuntia, Oreocereus, Schlumbergera. Species from Genus Opuntia have long, sharp spines whereas Christmas cactus from genus Sclumbergera have fewer or no spines. Genus Pereskia is considered close to ancestral species from which all cacti have evolved. Cacti from Cephalocereus, Fero cactus and Mammillaria are used as fodder. Cactus from Lophophora genus, saguaro cactus(Carnegia gigantia), Trichocereus pachanoi, Peyote cactus, Caratema fimbriata are raised for medicinal purpose. Opuntia ficus indica is used for culinary purpose. Opuntia and Thore are used for jam and pickles. Cactus is a source of gene determining temperature resistance/tolerance (high temperature, drought or cold). Opuntia species is most cold tolerant. The breeding objectives in cactus include development of variety with compact growth habit, increased number of flowers per leafy segment (phylloclade) and flower colour. Propagation is through tuberous roots and cuttings. Tubers harvested are divided and tubers should be separated from the old clumps with at least one eye at the stem end. And these are planted. A single tuber gives rise to 5-6 true to type plants. From 6-10 tall plants cuttings are obtained with 2-4 leaves and these cuttings are planted in small container. Rooting takes place in 2-3 weeks time and these plants are then transferred for planting in pot.

Crop Evolution and Genetic Resources

11.34

11.28  FOLIAGE PLANTS Other commercially important indoor foliage plants include, Calathea, Chlorophytum, Cordyline, Monstera, Paperomia, Philodendron, Scindapsus, Codiaeum, Spathiphyllum, Dieffenbachia, Aglaonema (A. commutatum). Other foliage pot species include Aloe spp., Asparagus fern (A densiflorus), Aspidistra elatior (Cast-iron plant), Codiaeum variegatum var. pictum (Croton), Epipremnum aureum (Pothos), Fittonia verschaffeltii (Nerve plant), Maranta leuconeura (Prayer plant), Pletramthus australis (Swedish ivy), Sansivieria trifasciata (Snake plant), Tradescantia spp. such as T. albillora, T. blossfeldiana, T. fluminensis, T. zebrina (Wandering Jew or Inch plant). The species of various foliage plants along with their characteristics are given in Table 11.18. Table 11.18  Showing different attractive foliage pot plants and its method of propagation. Common name Aloe spp.

Method of propagation Division of rootstock

Characteristics Family Rosette forming succulent plant

Asparagus Fern

Species A. aristata, A. variegata, A. humilis, A. vera (medicinal) Asparagus densiflorus

Division or seed

Aglaonema

A. commutatum

Division or tip cuttings

Cast-iron plant

Aspidistra elatior

Division of rhizomes

Spider plant

Chlorophytum comosum var. variegatum

Offsets

Croton

Codiaeum variegatum var pictum Cordyline terminalis

Tip (stem) cutting or air layering Stem cuttings

Dracaena draco, D. deremensis, D. fragrans, D. marginata. Epipremntum aureum F. elastica (rubber tree), F. benjamina, F. lyrata, F. pumila, F. black, F. nuda, F. panda, F. reginald, F. triangularis Fittonia verschaffeltii, F. gigantea, F. albivenis Hedera

Tip or stem cuttings, seed or suckers

Shrubby plants with fine textured needle like leaves Marked foliage, shade loving Large, shinny, dark green, leathery leaves Long grass like leaves, yellow shoots and tuberous roots Leathery leaves, vary in shape and colour Very similar to Dracaena, leaf sword shaped, Indoor plant Shade loving

Ti plant

Dragon tree

Pothos Ficus spp.

Nerve pant English ivy

Tip or stem cuttings Tip cuttings, air layering

Araceae

Liliaceae

Liliaceae

Dracaenaceae

Indoor/shady

Cuttings or rooted portion of creeping stem Tip or stem cutting with Rootlet climber aerial roots. Contd...

Origin and Genetic Resources of floricultural Crops

11.35

Contd...

Common name Prayer plant

Species Maranta leuconeura

Peperomia spp. Philodendron spp.

Swedish ivy Snake plant Peace lily Wandering Jew

P. scandens with heart shaped leaves, P. x red princess, P. selloum, P. cordatum, P. radiatum, P. domesticum P. squaferum Plectranthus australis Sansevierria trifasciata Spathiphyllum spp. Tradescantia albivera, T. blossfeldiana, T. fluminensis, T. zebrina, T. virginiana, T. navicularis, T. sillamontana

Caladium Syngonium Calathea Euonymous Yucca

Method of propagation Division

Family

House/green house plant Shade living Most popular foliage plant,Perennial, garden plant Most popular foliage plant

Marantaceae

Tip, stem or leaf cuttings and division Tip or stem cuttings, air layering, seed

Tip cutting Division of offsets Division Tip cuttings.

Division, stem cutting

Schefflera Callistemon(Bottle brush)

Characteristics Bushy plants with large attractive foliage with beautiful markings

Liliaceal

Cuttings

11.29  HEDGE PLANTS Important hedge plants include herbs, shrubs, trees, climbers, palms, etc. Duranta (Duranta variegata), Lawsonia (Lawsonia inermis), Inga dulcis, Dodonea and Acacia modrata. Henna or Mehendi belongs to Lythraceae and this plant has thorns. Lawsone-a reddish brown or brown dye is obtained from the powdered leaves of this plant. Lowering hedge includes Jasminim pubescens, Coffea bengalensis, Ixora. Rosa multiflora, Many of the cacti such as Cereus and Opuntia are also used. Trees as hedge include Polyalthea longiflora.

11.30  LAWN / TURF GRASS Warm season grass species include Bermuda grass, St. Augustine grass, Buffalo grass, Zoysia grass and Bahia grass(Paspalum). There are three species of Zoysia grass, namely, Z. japonica (Japanese lawn grass, Z. matrella (Manila grass) and Z. tenuifolia (Korean grass).

Crop Evolution and Genetic Resources

11.36

The latter two species are multiplied vegetatively whereas Japanese grass is multiplied through seeds but now variety with vegetative means of propagation is also available. The Korean grass is wiry with fine texture and mostly used as ground cover. Cool season grasses include Kentucky blue grass, Fescue and perennial rye grass (Lolium perene). Other lawn grasses include Agrostis tennis, A. cannina, Cynosurus cistatus and Poa nemorals. Centipede and selection number-1 are also grown as lawn grass. The problem with use of Cynodon dactylon is that the maintenance cost is very high and requires frequent cutting. Grasses belong to family Gramineae. Very few grasses are vegetatively propagated either by apomictic seeds or by runner, stolons oe other vegetative parts. Apomixis can be obligate or facultative. In case of obligate apomicts (hexaploid D. annulatum) mutation (spontaneous or induced) is the source of variability whereas in case of facultative apomicts (tetraploid D. annulatum) advantages of both sexual and asexual embryosacs and reproduction could be combined. In case of obligate apomicts the crop is completely dependent on spontaneous mutation and thus the objective in mutation breeding would be to overcome apomixis. Breeding objectives in grasses include changing growth habit and development of dwarf variety besides characteristics such as width of leaves, colour and resistance to wear and resistance to certain diseases.

Section B

11.31  GENETICS AND PLANT BREEDING Biochemistry of floral pigment and color variation in flowers  Various colors in plant are conferred by anthocyanins. These pigments protect plants against solar exposure, U.V. rays. They are free radical scavenging (works as molecular scavenger), have antioxidative capacity and are involved in defense against plant pathogens, symbiosis and signaling cascade. There are three major classes of pigments that produce flower color-flavonoids, carotenoids and betalains. Of these flavonoid is most abundant and contributes most to the range and type of colored pigments in plants. Flavonoids contain two classes of pigments-co-pigments (flavanones, flavones and chalcones) and anthocyanin (petunidin, pelargonidin and cyanidin). Anthocyanins confer orange, red, magenta, violet and blue colors. Aurones and chalcones are yellow pigments whereas flavones and flavonoids are colorless. Anthocyanin accumulates in vacuoles of epidermal or subepidermal cells and produce pink, magenta, red, blue and violet flower. Co-pigments produce pale yellow, ivory, near white or colorless flower in the absence of other pigments. Under many circumstances flower color is positively correlated with the types (s) of anthocyanidin (s)-anthocyanin without sugar. Flower color is also affected by abiotic factors such as light intensity, temperature and water stress. Further, biotic factors such as vacuolar pH, presence of metal ions (Fe, Mg, Ca), co-pigmentation, cell shape also affect flower color. Thus anthocyanin, its structure, type and concentration, co-pigments, metal ion type and concentration, pH of the vacuoles, anthocyanin localization and shapes of the surface cells all determine final flower color. Anthocyanins are water soluble pigment. At acidic pH (less than 7), pink color develops, at neutral pH (= 7), purple color develops, at alkaline pH (greater than 7) there is development of greenish-yellow color. At very

Origin and Genetic Resources of floricultural Crops

11.37

alkaline pH the pigment is completely reduced and it becomes colorless. Anthocyanin and betalains are never found in the same plant. Cactus, beets and Amaranth do not contain anthocyanin. Anthocyanin is found in all tissues (flowers, fruits, foliage, seeds and roots) of higher plant. Anthocyanin is derived from anthocyanidins. Anthocyanins are glycosides and acylglycosides of anthocyanidins. Unlike carotenoids anthocyanins are not present in leaf tissue throughout the growing season. Though there are hundreds of anthocyanins but they are based on six common anthocyanidins (chromophores of anthocyanins) pelargonidin, cyanidin, peonidin, delphinidin, petunidin and malvidin. As peonidin is derived from cyanidin and petunidin and malvidin are both derived from delphinidin and so there are only three major anthocyanidins. Delphinidin and its derivatives determine blue flower color whereas red flowers have pelargonidin. Rose petals have predominantly cyanidin or pelargonidin. Delphinidin based anthocyanins are present in both ornamental as well as food plants such as blueberries, black currants, grapes, egg plants, red currants, cherry and craneberries. Petunia does not produce pelargonidin pigments whereas maize and snapdragon are capable of producing this pigment. The precursors for the synthesis of all flavonoids including anthocyanins are malonyl-CoA and p-coumaroyl-CoA. Floral pigments are primarily flavonoid and carotenoid compounds which are produced by phenylpropenoid (which produces anthocyanin) (Fig. 11.1, 11.2) and isoprenoid pathways (Fig. 11.4), respectively. Carotenoids are of two major types-carotene (hybrocarbons) and xanthophylls (alcoholic). Carotenoids include lutein (found in petal of marigold), beta carotene, violaxanthin, neoxanthin and zeaxanthin. Color is due to carotene and xanthophylls. Carotenes are fat soluble and insoluble in water in contrast to other carotenoids, the xanthophylls. Chlorophyll and carotene are attached to cell

Fig. 11.1  Showing anthocyanin, flavonoids and flavonols synthesis pathway

11.38

Crop Evolution and Genetic Resources

Fig. 11.2  Anothocyanic and flavonal biosynthetic pathway

Origin and Genetic Resources of floricultural Crops

11.39

membrane whereas anthocyanins are free and water soluble. Levels of carotenoids and their profiles in fruits, flowers and seeds vary considerable depending on the developmental stage, environment, stress or a combination of these. Carotenoid’s catabolism products such as beta-ionnes are involved in plant-insect interactions. Carotenoids are isoprenoid molecules consisting of forty carbons and are synthesized in plastids such as chloroplast and are found in bacteria, fungi, algae and yeast. Apocarotenoids are also accumulated in chromoplast-plastids that accumulate pigments in flowers, fruits and storage roots. There are three types of plastids, namely, leucoplasts, chloroplasts and chromoplasts. Chloroplasts change to chromoplasts (a colored plastid containing red or yellow pigment). Carotenoids are precursors for apocarotenoids such as abscisic acid, ABA and stringolactones. Some caotenoids (beta carotene) are precursors of Vitamin A. Anthocyanins are synthesized via the flavonoid pathway (Figs. 11.1, 11.2). Flavonoids are often produced in vegetative cells under normal condition as well as under stress conditions such as high light intensity, cold temperature, nutrient deficiency, pathogen attack or senescence. Anthocyanins affect the quality of fruits and there is developmental and environmental regulation of anthocyanin biosynthesis in fruits. Manipulation of anthocyanin biosynthesis pathway is possible. Down-and up regulation of flavonoid and anthocyanin pathway is possible and predictable. The seven genes involved in anthocyanin biosynthetic pathway are CmCHS, CmF3H, CmF3’H, CMDFR, CmANS, CmCHI and Cm3GT (Figs. 11.1, 11.2). Petunia, tobacco and torrenia are the model species for studying flower color variation through genetic engineering because they are easy to transform (Fig. 11.3). Petunia does not accumulate pelargonidin based anthocyanin. Transgenic plants with white flowers have been obtained in many plant species by down regulating anthocyanin synthesizing genes. In torrenia RNA interference (RNAi) has been found to be more effective to down regulate a target gene than antisense or sense suppression (co-suppression). Anthocyanins are ubiquitous in nature and present in both ornamental and common food plants. Flavonoids biosynthesis  The main precursor of all flavonoids is phenylalanine which is converted into 4-coumaroyl CoA by the enzymes phenylalanine ammonialyase (PAL), cinnamic acid 4-hydroxylase (CH4) and 4-coumarate-CoA ligase(4CL) as shown in Fig. 11.1. Chalcone synthase (CHS) is the key enzyme in flavonoid biosynthesis which condenses 4-coumaryl CoA with three molecules of malonyl CoA to 4, 2’, 4’, 6’-tetrahydroxy chaclone which is further converted into flavonone naringenin by the enzyme chaclone isomerase (CHI). The naringenin is further converted into dihydrokaepferol by flavones-3-hydroxylase (FTH). The hydroxylation of the B-ring by F3’H (flavonoid 3’-hydroxylase and further by falvonoid 3’, 5’-hydroxylase results in formation of two dihydroflavonols dihydroquercetin and digydromyricetin. These dihydroflavonols are further converted into flavonols by enzyme flavonol synthase (FLS) and into anthocyanins by a cascade of enzymes, the first enzyme being dihydrofalvonol 4-reductase (DFR). The genes involved in anthocyanin biosynthesis can be classified into four following groups (Cornu and Maizonnier, 1983). 1. Those involved in anthocyanin and flavonol production. 2. Those involved in hydroxylation and methylation of the anthocyanin.

11.40

Crop Evolution and Genetic Resources

Fig. 11.3  Genetic control of anthocyanin modifications in petunia

3. Those involved in glycosylation and acetylation of the anthocyanin. 4. Those involved in modification of colour in different parts of flower without changing the chemical composition of the anthocyanin. Flower colour variation can be through either intensification or elimination of pigmentation. The genetic engineering strategies for intensification of pigmentation are as follows. 1. Over expression of a gene product. 2. Use of regulatory gene for controlling the expression of the entire pigment biosynthesis pathway. The elimination of pigmentation can be achieved through two strategies The mechanism involved is suppression of gene expression which can be through the use of

Origin and Genetic Resources of floricultural Crops

11.41

Geranylgeranyl pyrophosphate (GGPP) Phytoene synthase (PSY) Phytotene Phytoene desaturase (PDS) z-carotene zcarotene desaturase (ZDS)

Lycopene Lycopenee-cyclase (LCYe)

LCYb (Lycopene b-cyclcase

g-carotene

d-carotene LCYb

b-carotene

a-carotene a-ring hydroxylase ( HYe) a-cryptoxanthin

b-ring hydroxylase (Hyb ) b-cryptoxanthin

Hyb Lutein

Hyb Zeaxanthin

Fig. 11.4  Showing biosynthesis of carotenoids

1. Sense RNA. 2. Antisense RNA. Both sense and antisense RNA constructs yield plants showing irratic phenotypes and stability of such phenotypes varies considerably. Flower colour  Flowers with unique appearance, i.e., color or shape are highly desired by consumers. A very attractive flower on small, branched stem is a good fit for pot plant but not for putting in vase and thus not as cut flower. Branched flowering stem is also a problem in packing and transportation and thus an ideal cut flower should have a long, unbranched stem with a solitary flower or compact inflorescence. Indeed, most cut flowers such as Rose, Tulip, Gerbera, Carnation, Chrysanthemum, etc fulfill these requirements.

11.42

Crop Evolution and Genetic Resources

Final flower color  Final flower color in ornamental crops is affected by a number of factors. It is controlled by light, temperature, hormones, biotic and abiotic stresses as all these non-genetic factors affect the expression of flavonoids biosynthetic genes (Weiss, 2000). Other factors such as vacuolar pH, metal ions, co-pigmentation, optical properties of the cell (cell shape) also affect flower colour. Besides these factors, substrate availability is another factor which affects pigment composition, the ratio of anthocyanins and flavones and flavonols. The two strategies to be adopted for changing flower colour are as follows. 1. By modulating up-and down regulation of genes involved in anthocyanin biosynthetic pathway 2. By introducing foreign gene(s) encoding enzyme missing in the biosynthetic pathway.

Development of New Flower Color Cultivar Creation of novel flower colors in commercially important ornamental plants is the requirement of the day. Blue flower varieties are missing from a number of important ornamental species such as carnation, chrysanthemum and roses. None of these flower crop species is capable of producing blue delphinidin pigment. Color changes can be created by either manipulating the levels of a particular pigment or by synthesizing novel pigment. In other words, flower color can be changed in a highly directed fashion through genetic engineering technique by introducing genes encoding novel enzyme activities and inactivation of endogenous genes. Controlled expression of the appropriate regulatory genes may lead to increase in anthocyanin synthesis in important cut flower species.

Breeding methods in floricultural crops Flowers are raised for its aesthetic appeal. This trait, aesthetic quality is very subjective and are perceived differently by different individuals but be considered along with production and quality traits which are judged objectively. Visual appeal (eye catching) must be considered at all stages of selection processes in the breeding program. Any and every part of the plant can contribute to aesthetic beauty. So variation in any trait is welcome. Ornamental crops can be perennial or annual. In perennial (long duration crop) there is regular harvesting of flowing stems over one or more years, for example, rose, carnation, gerbera, alstroemeria, etc. On the other hand, in short duration crop one flowers are harvested over a brief period of one of a few weeks, e.g., chrysanthemum, freesia, pot plant species, etc. In case of former total production is a function of yield in terms of stems harvested and quality of the flower, harvested over time and space (or area) used. Production characteristics will vary from time to time of the year and with levels of maintained inputs such as temperature, CO2, etc. In case of later as only one product is harvested from each propagule planted, so the term yield is not applied. It can be trees, shrubs or herbs runners or climbers. It can be grown for its flower, fragrance or foliage. It can be sexually propagated through seeds or can be asexually propagated. Seeds can be dicot or monocot. Asexual propagation can be through runner, stolen,

Origin and Genetic Resources of floricultural Crops

11.43

rhizome, tuber, bulb or corms. Artificial vegetative propagation can be through cuttings, layering, etc. Majority of the cut flower ornamentals and pot plants are vegetatively propagated. Breeding system can be self fertilizing or cross fertilizing. Ornamental foliage plants are predominantly cross fertilizing species. Further, most annual flowers are cross pollinated. Overall, most of the ornamental crops are cross pollinated and only a few are obligate self pollinated (inbreeders). Variety can be pure breeding line or clone or hybrid. Many floricultural crops include three types of varieties- clonal variety, open pollinated variety and hybrid variety. Selection of a breeding method depends on the type of cultivar required, breeding system of the crop, mode of inheritance of the trait and the ploidy level. Where exists polyploidy, diploid and polyploidy cultivars are developed. Tree or shrub flower crops are heterozygous like fruit crops. Traits to be improved are different flower characteristics in flower crops but in case of foliage crops plant leaf attributes (color, texture, shape and overall beauty of the foliage) are to be improved. Traits to be improved in food crops revolve round improving yield and yield components besides disease and pest resistance. In flower crops every trait except seed yield is important, be it plant height-dwarf or tall, leaf characteristics such as leaf size, shape, color, orientation of leaves on the plant, leaf variegation, flowering time-extra early, mid flowering, late flowering, flower attributes such as flower shape, size and color, fragrance. In case of annual, seed propagated flower crops depending on the breeding system conventional methods of plant breeding can be employed (See Allard, 1960; Hallauer and Miranda, 1980; Roy, 2000, 2012). This crop differs from food and vegetable crops in that the economically important traits are the flower color, size, shape, fragrance and attractiveness of plants which include leaf characteristics and plant architecture. Further, breeding objectives could include tolerance to heat, cold hardy, drought, salinity and alkalinity, resistance to damage by vain or wind (all abiotic stresses and biotic stresses). Changing plant habit- use as garden plant, indoor plant or as cut flower will be another objective. In comparison to field, fruit or vegetable crops there is more variability in floricultural crops. In case of Narcissus there are more than 25000 varieties, in Lilium more than 7000 and in Tulipa more than 1000 cultivars are there. In floricultural crops there are four types of products. 1. Inbred lines / pure breeding lines. 2. Outbreeding populations. 3. Hybrid varieties. 4. Clones. Thus breeders aim at developing these types of varieties considering the breeding system, method of propagation, growth habit, etc. Breeding system can be either self fertilizing or cross fertilizing. Flowering crops are mostly outbreeders. Autogamous flower crops include Matthiola incana, double flowered varieties of Callistephus or Tagetes in which the single flowered genotypes were allogamous. In pansy hercogamy (position of male and female organs which prevents self pollination) eliminated the need of hand emasculation.

11.44

Crop Evolution and Genetic Resources

The growth habit can be annual / biennial or perennial. Further, flowers can be annual, biennual or perennial herbs or perennial shrubs (Rose, Jasmine, Azalea, Poinsettia, Hibiscus, Camellia, Bougainvillea, Crossandra, Barleria, Hydrangea, Cassia, Adenium, Acalypha, Allamanda) or trees. Bedding plants, cut flowers and pot plants are herbaceous annual, biennial and perennial. Aquatic flowers include Nelumbo, Nymphaea, etc. Further, ornamental crops can be grown for either, flower or attractive foliage. Further, some flower crops can be used as ‘fillers’ in flower arrangement. Propagation can be either through seeds or by vegetative means. Ornamental crops can be used as commercial garden plants (Pelargonium, Viola, Osteospermum, Petunia, Fuschia, Hydrangena, Rosa, Hellebones) bedding plants, pot plants or hedge plant or as lawn grass. Further, flower crops can be diploid, tetraploid (Pelargonium), hexaploid (Chrysanthemum), octaploid (Dahlia, Pansies, Oxalis). Then there are flower species in which a variety of ploidy levels exist (e.g. diploid and triploid in Tulip and Lilies). Fibrous rooted Begonias as bedding plant and tuberous as pot plant, are used.

Plant introduction Plant acquisition and introduction has played an important role in the development and growth of flower industry. New genera, species, intergeneric or interspecific or novel varietal hybrids or mutants are being introduced, evaluated and commercialized.

Breeding Objectives-Traits to be Improved in Flower Cut flowers  Traits to be considered in cut flowers include number and/or size of flowers, stem length and strength, leaf size, appearance, pedicel length, etc., Besides these quality traits there is requirement of uniformity. In case of vegetatively propagated flowers one will have to consider the clone (rhizome, pseudostem, buded/grafted plant, etc.) uniformity with respect to vigor. Now a days tissue cultured plant are being grown in order grow virus free material and to have more uniformity. Yield  Yield in cut flower is a function of a number of yield component traits. For example, in gerbera yield is associated with lateral shoot production. Further it will depend on the environmental factors such as time of the year, light integral, photoperiod, etc. Breeding for cultivars ideal for raising in different seasons such as winter season or summer season or protected condition must be started. Besides yield, one will have to consider the plant throughput per unit area and time. In other words, one will have to consider the cropping time as growers think in terms of net profitability. Flower yield can be increased through either through environmental or genetic manipulation. Environmental manipulations include pinching to break apical dominance, forcing the plants for several flowering cycles, delaying flowering to produce additional vegetative growth, changing fertilization and irrigation levels, and changing to green house cultivation. Flower color, flower and leaf longevity, flowering time, flower size and architecture and disease resistance are the important characters to be improved.

Origin and Genetic Resources of floricultural Crops

11.45

Changing Method of Propagation, a Breeding Objective There are crops which are grown commercially through seeds, e.g. Antirrhinum or alternatively through vegetative means or seed, e.g., freesia, gerbera, pelargonium (geranium) and so switching from clonal propagation to seed propagation is an important objective. Selection during breeding program be based on developing new generation through seed but the selected plant be multiplied through clonal multiplication which has the advantage of quickly fixing the genotype. Flower color  Flower color is one of the most important traits in breeding program. Many plants do not produce flowers in the full color spectrum because of lack of certain flavonoids. The three main pigment classes are flavonoids, caarotenoids and betanoids. Flavonoids produce pale yellow to red to blue flowers whereas carotenoids and betanoids produce yellow and orange color flowers. Flavonoids pathway of Petunia hybrid are divided into anthocyanins (giving pink, red, violet and blue colors), flavones and flavonols are colorless co-pigments which enhance color and contribute to blueing of anthocyanins and aurones which give yellow color (Chandler and Bruglierra, 2011). Scarlet verbena and violet petunia contain pelargonidin and delphinidin based anthocyanin. Yellow color of many flowers including rose and chrysanthemum have been derived from carotenoids. In marigolds yellow color is due to carotenoid plus 6-hybdroxy flavonol and orange color is due all the three types of pigments, carotenoids, 6-hydroxy flavonol and cyaniding based anthocyanin. Non-transgenic torentia mainly accumulate delphinidin based anthocyanin. Flower and leaf longevity  The vase life of cut flower or the flowering period of a flowering pot plant is of interest to plant breeders. These traits are highly influenced by growing conditions prior to harvest, stage of flowering at harvest and environmental conditions prevailing during transport, distribution and after sale. There is presence of sufficient genetic variation for this trait of vase life. In gerbera a 14-day vase life is a realistic breeding goal. Vase life  Genetic engineering is another strategy to increase vase life in ethylene sensitive flowers. It involves transfer of etr1-1, a recessive gene with reduced ability to bind ethylene and thus results in disruption of EST pathway and ultimately increase in the vase life. Ethylene binding to a receptor is encoded by gene, ETR1(dominant) which activates ethylene signal transduction pathway. This strategy is more efficient then the other ones and gives 105 to 129% increase in vase life (Bovy et al., 1999). Flower longevity  Senescence occurs naturally or is induced through environmental stress(gene activation pathway). It also occurs through independent transcription circuits invoking response to pathogens. Certain pathogens defense related genes are found to be expressed in senescing leaves and there it serves to combat infections that might disrupt nutrient salvaging. Senescence entails regulation phase(gene activation and synthesis of protein)and execution phase which involves nutrient salvaging and cell death. Membrane fatty acid de-esterification and lipid phase separation leading to leakiness appearance are a common feature of both natural and prematurely induced senescence.

11.46

Crop Evolution and Genetic Resources

Fig. 11.5  Showing regulation of ABA biosynthesis

There are different types of senescence. 1 Mono-carpic senenscence refers to senescence of whole plant (annual) observed in the final stage of develop-ment. 2. Senescence of aerial shoots is seen in herbaceous perennials, for example, haldi. 3. Seasonal leaf senescence in deci-duous trees. 4. Sequential leaf senescence in leaves after attaining physiological maturity. Then we see senescence of fleshy fruit and dry fruits, senescence of storage cotyledons and floral organs. We see flower senescence in floriculture and leaf senescence is negatively affects the quality and vase life of several cultivars. Oldest leaves at the bottom are to senesce first followed by upper leaves. Senescence is accompanied by reduced photosynthesis and is associated with nutrient remobilization. There is a role of ABA in senescence (Fig. 11.5). Pyrabactin is antagonist of certain ABA receptors. Drought induces stomata closure which decreases the photosynthetic rate and thus growth is adversely affected. Closure of stomata leads to reduction in the concentration of CO2 in mesophyll which results in accumulation of NADPH. In the limiting condition of NADP, O2 acts as an alternative acceptor of electron from the thylakoid electron transport chain thereby resulting in the formation of superoxide radicals O2 (ROS, reactive oxygen species). Superoxide radicals and its reduction product H2O2 formed are toxic compounds. ROS causes lipid degradation, membrane injuries, protein degradation and enzyme inactivation which cause death of plants. Adverse effects of ROS can be overcome by molecular scavengers such as enzymes (SOD, Catalase, Glutathione peroxidases and antioxidants such as Vit. C (Ascorbic acid), E (Tocopherol), uric acid and glutathione. This trait is very important in case of cut flower and pot plants. Leaf and flower senescence is mainly regulated by hormones, ethylene and cytokinin. Ethylene biosynthetic

Origin and Genetic Resources of floricultural Crops

11.47

Fig. 11.6  Showing hormone, ethylene bio-synthesis pathway and its regulation.

pathway is shown in the Fig. 11.6. Ethylene production is a three step process and it can be controlled by ACC synthase, ACC oxidase, ACC deaminase and SAM hydrolase. Insertion of ACC oxidase in sense and / or anisense orientation in Torenia resulted in flowers showing greater longevity than the wild type (Aida and coworkers, 2008). Thus one method is to stop ethylene production and another method is to reduce ethylene sensitivity in flowers and this can be achieved by mutating the ethylene receptors. Five ethylene receptors have been found and mutating even the binding site of one receptor will result in ethylene insensitivity (Hall et al, 1999). Ethylene insensitivity has been obtained using mutated ethylene receptor etr1-1 from Arabidopsis in Kalanchoe, Campanula, Rhipsalidopsis, Oncidium and Odontoglossum (Mibus et al., 2009). Ethylene is involved in various processes such as disease sensitivity in plants and regulation of vegetative propagation. A mutated receptor m DG-ERS1 receptor similar to ert1-4 from Arabidopsis resulted in reduced leaf senescence in chrysanthemum occurring before flower senescence. This transgenic lines showed reduced ethylene sensitivity and leaves stayed green longer in comparison to wild type (Narumi et al., 2005). These techniques will not work in ethylene insensitive flowers.

11.48

Crop Evolution and Genetic Resources

Fruits, vegetable and floral products (cut flowers, flowers, bulbs, cuttings, rootstocks) produce ethylene and releases it into air. Further, as mentioned above they all contain receptors which serve as binding sites for absorption of free atmospheric molecule. This results in hastening the ripening, aging and eventually spoilage of fruits, vegetables and floral products. The different changes include bud and leaf abscission, leaf yellowing, loss of deep color, flower or petal dropping, irregular bud opening (sleepy carnations) and premature death. Thus fruits and flowers can go together. Thus inhibition of ethylene production and / or ethylene binding (whether in selected variety or by treatment with chemicals) result in longer-lived cut flower (e.g. carnation). In other words, short life is due to rise in ethylene production and respiration. Reduction in respiration and ethylene production rates will slow down changes related to ripening and senescence. The ethylene sensitive types flowers include Cymbidium, Dendrobium, Lily, Gladiolus, Helianthus, Phlox, Mini carnation, Snapdragon, Sweet pea, Veronica, Allium, Delphinium, Carnation, Orchids and Roses. Fig. 11.7  showing giberrellin synthesis pathway. In case of orchids and roses not all varieties are ethylene sensitive, i.e. there are ethylene sensitive as well as ethylene non-sensitive cultivars. There is thus a need for treating cut flowers with anti-ethylene compound to ensure longer life. Further, there is a need to establish ‘Cold Chain’ at all levels of flower production and distribution. This controlled atmosphere storage (CAS which contains O2, CO2 and high humidity) or modified atmosphere packaging (MAP) combined with low temperature is used for storage of fruit, vegetable and floral products. Low temperature is the most important factor in maintaining quality and extending the shelf life of fruits and vegetables. Ethylene sensitivity is less of a problem at low temperature (less than 4°C). Flowering time  Flowering time can be controlled by either genetic manipulation or through environmental manipulations (photoperiod, chilling and/or use of growth regulators). Genetic manipulation is through two types of genes. Meristem identity genes and floral organ identity genes regulate floral development. The former encode transcription factors which regulate the the induction of organ identity genes. This type of genes include AP1 (APETALA1 and LFY (LEAFY) and SOC1 (SUPPRESSOR OF CONSTANS) also called as AGAMOUS from Arabidopsis. These genes are activated to

Origin and Genetic Resources of floricultural Crops

11.49

establish apical meristem identity. Floral identity genes determine where the different organs within a plant will be formed. In Arabidopsis five homeotic genes determining floral organ identity are AP1, AP2, AP3, AG and PI (PISTALLATA). The homeotic genes are divided into three categories (as described in ABC model of floral development and discussed below). Finally, insertion of Arabidopsis FLOWERING LOCUS T (FT) gene which encodes flowering hormone, ‘Florigen’ reduces flowering time in ornamental gentian (Natkasuka et al., 2009). Manipulation of flowering time  Most annual flowering plants are autonomous flowering plants that produce flowers after producing a certain number of leaves. In such plants flowering times can be controlled by changing the sowing date or growing conditions. Increase in light intensity or temperature will enhance vegetative growth and thus advance flowering time. But there are perennial autonomous flowering plants in which it is difficult to manipulate flowering time. In such crops production can be increased by extending the flowering season. We know that flowers are required at certain time of the year and thus plants are required to be forced to flower during that period of great demand of the market. Some plants flower once a year for a very short period and there the objective should be to extend the flowering period. Further, some plants flower sporadically round the year and in such cases the objective would be to concentrate the flowering periods. Temperate flower crops require long day length for flowering whereas tropical and subtropical plants require short days for flowering. Further, many plants require vernalization (exposure to low temperature, 0-4°C) for flower induction. In such cases seeds of those plants or bulbs, crown or roots in case of geophytes be stored at low temperature before flowering. In case of deciduous plants low temperature is required for breaking flower bud dormancy. As we see in food crops that there flowering (early or late) depends on the genotype of the plant as well as on the environment. Stress induces early flowering. Keeping this in mind it would be worth while to develop early maturing variety through genetic manipulations or modify flowering time through environmental manipulation. Further, plants raised from seeds will be late maturing but plants obtained by cuttings will not show such delay. Likewise plants developed through grafting will also show earliness. This type of difference in seedling plant and its clone derivatives will be observed for plant height and other traits as well.

ABC model of floral organ specification Specification of flower and floral organ identity, leaf and flower asymmetry and pollen component of gametophytic self-incompatibility are conserved in flowering plants. ABC model of floral organ specification was proposed by Bowman et al. 1991 and it is working in Antirrhinum and Arabidopsis. In this model combination of genes is expressed in each of the four whorls to determine the identity of the floral organ such as A genes (APETALA2 gene, AP2) work in whorl 1 and specify sepals, genes A (AP2) + B genes (APETALA3 and PISTILLATA, AP3/P) specify petals, B + C genes (AP3/PI and AG) specify stamens and

11.50

Crop Evolution and Genetic Resources

C gene (AGAMOUS, AG) function in whorl 4 and specify the carpels. Genes functioning in the A and C fields, AP2 and AG are mutually antagonistic. Recent advances in this model are as follows. 1. All genes except AP2 encode MADS transcription factors (Weigel and Mayerowitz, 1994). 2. Another A function gene APETALA1 exists in Arabidposis (Bowman et al., 1993) This gene, AP1, like CAL in Cauliflower arrest the development of inflorescence meristem stage. AP1 mutation results in loss of sepals and petals with leaf like structure whereas CAL dates mires the specification of flower stem identity. 3. Four other MADS genes (SEPALLATAs) are involved in establishimg floral nature of floral organs in Arabidopsis (Pelaz et al., 2000). 4. SEP proteins are likely to act in multimeric combination with A, B and C function MADS protein (Melzer and Theissen, 2009). 5. AP2 transcripts are regulated post-transcriptionally by miRNAs (Chen, 2004). 6. AP2 is a direct negative regulator of AG expression (Dinh et al., 2012). Thus in Arabidopsis, A genes (AP1 and AP2) control organ identity in sepal and petals and loss of A results in formation of carpels instead of sepals in the first whorl and of stamens instead of petals in the second whorl. B genes (AP3 and PI) controls organs in second and third whorls and loss of B results in formation of sepals instead of petals in the second whorl and carpels instead of stamens in the third whorl. Type C determines functions of third and fourth whorl. Loss of C results in formation of petals instead of stamens. Without C which normally conditions carpel, there is formation of new flower.

Genetics of double flower Double flowers are sexually sterile containing no nectar and propagated through cuttings. In the double flower some or all stamens are replaced by petals. It is a homeotic mutant. This trait is under control of one gene, which can be be recessive (Antihirrhinum, Callistephus chinensis, Eschscholtzia californica, Dianthus barbatus, Matthiola incana, Papver rhoeas and Salpiglossis) or dominant (Cyclamen persicum, Dianthus caryophyllus, Gerbera, Pelargonium, Petunia, Rosa, Saintpaulia ionantha, Sinnigera and Tagetes). A gene affects sepal and petal, B gene affects petal and stamen and C gene affects stamen and carpel. Agamous is a C class gene (a double flower gene), a transcription factor involved in activating genes determining stamen and carpel development. When both copies of this double flower gene are deleted or made non-functional, no stamen and carpel segment formation takes place. Instead stamen forms petal and carpel develops into a new flower resulting in sepal-petal-petal pattern. In pelargonium doubleness is under control of three loci and in Cosmos bipinnatus two genes are involved, one of which is heterozygous. Senescence  Senescence of flower can be controlled by the following two genetic engineering strategies

Origin and Genetic Resources of floricultural Crops

11.51

1. By blocking the synthesis of ethylene which will delay the petal senescence. 2. Flowers are also sensitive to exogenous ethylene and senescence can occur in response to as little as 10ppb and here the strategy will be to change the tissue responsiveness to ethylene. In other words, disruption of ethylene receptor function is required. There are two approaches to achieve this. Cloning of mutated gene from Arabidopsis thaliana conferring ethylene insensitivity and second approach is through controlled expression of ipt gene from Agrobacterium tumefaciens which encodes enzymes capable for cytokinin synthesis. It results in increase in the level of cytokinin and thereby altering the phenotype (Medford et al., 1989). Flower size and plant architecture  Plant size can be controlled by using dwarfing rootstock, use of chemical, different management practices, through environmental manipulation and through genes. Controlling plant height in potted plants is done by pruning which breaks apical dominance, chemical growth retardant, climate control and other strategies such as reduced water or nutrient availability and mechanical stress. Another strategy to reduce the plant height is to introduce genes such as rolC genes (root loci genes) from Agrobacterium rhizogenes, GAI and GA2 oxidase. Trangenics with this gene were obtained in different plant species such as Antirrhinum, Datura, Eustoma grandiflorum, Gentiana sp., Kalanchoe and Pelargonium. Besides reduction in plant height other traits changes were increase or decrease in flowering time, increase in number of flowers, decreased flower size, altered flower shape and reduced fertility and seed set as well as change in leaf morphology and leaf color. Plant height can also be reduced by manipulating gibberellins pathway since plant height is mainly controlled by gibberellins and regulation of GA biosynthesis would be a better way to control plant size (Fig. 11.7). Use of PcGAox1 gene encoding GA2 oxidase isolated from runner bean has produced dwarf plants in Solanum malanocearasum, Solanum nigrum, Petunia sp, Triticum estivum and Oryza sativa. It works by degradation of GA1 and GA4 and thus active form of GA is reduced. It is involved in GA catabolic pathway through 2beta-hydroxylation. Dwarfism can also be induced by insertion of antisense of GA20, through interference of microRNA (RNAi) and through insertion of GA insensitive genes (GAi). GA20-oxidase in rice catalyzes the three steps in GA biosynthesis. GAi determines how the plant responds tothis hormone. Altered version of this gene is less sensitive to gibberellins and thus dwarf plant is produced. Dwarfing genes in wheat are Rht-B1b and Rht-D1b. They encode DELLA protein which repress GA responsive growth. In rice the semi-dwarf-1 (sd-1) results in loss of function of GA biosynthetic enzymes. The chemical, paclobutrazol also induces dwarfess by inhibiting GA biosynthesis. Floral Scent  Volatiles are emitted from flower and leaves. There are three major classes of compound determining the floral scent. 1. Terpenes 2. Phenylpropanoid 3. Fatty acid derivatives. Other volatiles are derived from various amino acids. A single gene encoding enzyme converts phenylalanine into phenylacetaldehyde, a compound found in scent of rose, petunia and many other species. Eugenol, a phenylpropanoid class of compound is formed as a result of two step process from coniferyl alcohol, an intermediate formed

11.52

Crop Evolution and Genetic Resources

in the lignin biosynthesis. Volatile mono-terpenes and sesquiterpenes are formed from geranyl diphosphate and farnesyl diphosphate which are intermediates in the primary metabolites such as sterols, carotenoids, chlorophylls, gibberellic acid and absicic acid (ABA) through a single step process. Finally, non-volatile compound can be converted into volatile compounds through methylation, acetylation and decaoxylation (Pichersky and Dudareva, 2007). Thus scent can be modified though introduction of single gene, multiple genes (formation of new compound), elimination of some compounds, down regulation of transcription factors and blocking of competitive pathways. There is a common regulatory mechanism determining scent production in different plant species. Volatiles are synthesized de novo in the epidermal cells from which are emitted. Regulation of production of volatiles and their emission (spatial and temporal regulation) occurs at transcription level. Quantitative and / or qualitative changes can bring about modified scent composition and new aroma. What is required is to see first that whether not the substrate for volatile is produced in the specific plant, if produced then see the concentration of that substance. If not produced then bioengineering of metabolic pathway is required to be done to produce that substrate. If formed in low concentration then genetic engineering is required for enhancing the concentration. There could be three breeding objectives as far as this trait is concerned. 1. To increase the production of volatiles 2. To modify the scent composition 3. To produce all together a new scent. Finally, aim could be to develop a scented variety in plant species which is traditionally non-scented. Aroma in plants (fruits, vegetables, flowers and other plants)  Although some aromas are predominanty defined by a single molecule, for example, cinnamaldehyde in cinnamon but most aromas consist of mixture of voltiles (in other words as a result of interaction between different volatiles). Metabolic pathways involved in the biosynthesis of main aroma components are: 1. Degradation of lipids resulting in formation of short chain alcohols and aldehydes such as n-hexanol or cis-3 hexanol-the compounds imparting fresh and green notes in plants 2. The shikimic acid pathway leading to biosynthesis of eugenol in cloves, t-anethole in anise and estragole in basil 3. The terpenoid pathway leading to synthesis of geraniol in rose, 1, 8-cineole in eucalyptus and menthol in peppermint Components of aroma of many flowers and fruits are synthesized through terpenoid pathway. The terpenoid pathway is partly involved in the synthesis of many metabolites such as phytol chain of chlorophyll and growth regulators such as gibberellins, abscisic acid, photosynthetic pigments, chromophores, and vitamins which are derived from carotenoids and tocopherols). Monoterpenes (e.g. S-linalool), diterpenes (such as gibberellins and tocopherols) and tetrapenes (such as carotenoids) are synthesized in plastids from glyceraldehydes-3-phosphate/deoxyxylulose phosphate through isopentenyl

Origin and Genetic Resources of floricultural Crops

11.53

diphosphate. Linalool is an acyclic monoterpene alcohol which has an aroma with a sweet floral note. It is a major component of the scent of many flowers and is also present in many fruits such as guava, peach, plum, pineapple and passion fruit. Thus metabolic engineering of terpenoid pathway could lead to production, modification or reduction of aroma in plants. Geraniol synthase catalyzes geranyl diphosphate into geraniol, emitted from rose(Rao et al., 2000). Linalool synthase can catalyze geranyl diphosphate into linalool where in genranyl diphosphate is an intermediate in the carotenoid biosynthesis.

Development of Seedless Cultivar Development of seedless cultivars with improved ornamental characteristics is needed in foliage plants. The breeding objectives should include the traits such as growth, flowering, pollination and seed setting for improvement besides attractive and novel foliage. In context of seed setting factors such as temperature, relative humidity, diurnal cycles are to be studied which are critical in some genera. Besides these traits stress resistance, chilling resistance and disease resistance are to be incorporated. Further, ability to grow well under indoor condition need to be improved in foliage plants. Disease resistance  Conventional plant breeding methods for resistance breeding requires presence of source (s) of gene (s) determining race-specific or race-nonspecific resistance to be present in primary (GP1) and secondary gene pool (GP2). Identification of gene for disease resistance is a problem in ornamental crops as large diversity of flora and nursery crop species are susceptible to an equally large group of different pathogens and also because many genera of ornamental plants do not have a gene pool that has disease resistance gene as we find in case of food crops described earlier. Further, ornamental crop varieties differ from food crop varieties in that the former have limited life span (period of commercial cultivation) as new and more attractive varieties are introduced every year and thus resistance breeding is difficult to employ. Also, backcross method of transfer of gene for resistance is time consuming and it suffers from the problem of linkage drag. Another problem with traditional method of breeding is that many ornamental crops are vegetatively propagated as they can not produce viable seeds. So one can look towards production of transgenic plants but again the problem of finding resistance gene and the cost of developing transgenic at commercial level be considered. The following breeding methods can be employed in the development of variety in ornamental crops. 1. Hybrid development  As one flower produces lots of seed so one can go for hand emasculation and pollination for developing hybrids. Table 11.19 shows different methods employed in the development of hybrids. Methods of developing F1 hybrids in flowers  The first hybrid developed was in Begonia, B. cucullata var. hookeri (syn. B. semperflorens) × B. schmidtiana.

Crop Evolution and Genetic Resources

11.54

Table 11.19  Showing different methods of developing hybrid cultivars in flowers. Method of hybridization

Types of incompatibility

Mechanism

Flower species Pelargonium zonale, Antirrhinum majus, Cyclamen persicum, Sinningia speiosa, Impatiens walleriana, Petunia hybrid, Dianthus caryophyllus, and D. chinensis (Diploid × Diploid cross or Tetraploid × Tetraploid cross)

Hand emasculation and pollination-economical to produce hybrids with this method

Self incompatibility Gametophytic SI

Nicotiana, Petunia, Antirrhinum

Sporophytic homomorphic SI

Bellis perennis, Heliotropium peruvianum, Ageratum houstonianum, Gerbera

Sporophytic heteromorphic SI

Primula

Genetic male sterilitymonogenically or digenically controlled

Antirrhinum, Delphinium, Salvia splendens, Impatiens walleriana, Calceolaria

Cytoplasmic male sterility

Petunia, Ageratum, Helianthus(Zinnia)

Male sterility

Male sterility

1.male organs change to pistil like structure(Cindrella character)2. male sterility due to absence of petals, stamens and anthers

1. Begonia semperflorensdiploid, fibrous rooted begonia 2. in Tagetes erecta

Double flower character(transformation of anthers into petals)- a source of male sterility, requires insects for carrying out pollination as pistils are hidden by the petals

Dianthus caryophyllus

*Both GMS and SI can be used in the production of hybrids in Ageratum houstonianum, Petunia

Development of Inbreds Followed by Hand Emasculation and Pollination Monoecious (separation of male and female flower on the same inflorescens) Begonias and Petunias can be easily inbred and cross pollination is easy and further spontaneous

Origin and Genetic Resources of floricultural Crops

11.55

self pollination can be prevented and thus first hybrids were produced in Begonias and Petunias. After cross pollination facilitating mechanisms such as SI (self incompatibility) or MS (male sterility) were used for developing hybrids.

Development of hybrids using SI/MS Gene action in Self-incompatibility  The modes of action of SI vary greatly but they are all regulated by tightly linked multigene complexes referred to as haplotypes (McCubbin and Kao, 2000). In case of sporophytic SI in Brassica germination of self pollen is inhibited through interaction of two pollen proteins(SP11 / SCR), a stylar receptor kinase(SRK), a glycoprotein (SLG, S-locus receptor kinase) and several other proteins. Self pollen‘s rejection may involve hydration of the pollen grains. In case of gametophytic SI in poppy, self pollen tube growth on the stigmatic surface is inhibited by the interaction of a stigmatic S protein, a pollen S receptor(SBP), a Ca-dependent protein kinase (CDPK) and a glycoprotein. Pollen tube growth is arrested by a cascade of events linked to an increase in cytosolic calcium and a disruption of cytoskeleton. In case of tobacco, tomato, petunia and potato and fruit crops such as apple, cherry, pear with gametophytic system of SI, self pollen tube growth is inhibited within styles through a pistil released ribonuclease(S-RNAse) which selectively destroys the RNA of self pollen tube (incompatibility a consequence of recognition). Thus pollen S proteins are thought either to selectively allow self S-RNAs to enter the pollen tube or to inhibit non-self S-RNAs. Self incompatibility has been found in Ageratum, Bellis, Heliotropium, Lilium, Petunia, Nemesia, Oenothera, Chryanthemum, Nictotiana, sanderae, Cosmos bipinnatus, Iberis amara. Primula. Self incompatibility can be overcome through various means such as bud pollination, end of season pollination, or by a high temperature treatment. Heterostyly occurs in Primula, Limonium, Pentas and Lythrum (Tristylic, Von Ubisch, 1991). Heterostyly is under control of one locus, S with two alleles (S, s) system. The long styled pin genotype (short stamen) is ss, homozygous recessive whereas the thrum genotype (short style and long stamen) is heterozygous, Ss. Pin x Pin or thrum x Thrum mating will be incompatible whereas Pin x Thrum or Thrum x Pin mating will be compatible. Male sterility has been used to develop hybrids in Antirrhinum, Impatiens walleriana. Heterostyly, a heteromorphic self incompatibility has been used to develop hybrids in Primula. SI has also been used to develop hybrids in Ageratum. Hybrid development used apopetalous (male sterile) female parent in Tagetes and Zinnia. During development of hybrids, inbred seed (male sterile line) and pollen parents are often vegetatively propagated mainly through micropropagation. Male sterility is also found in marigold, petunia, Dianthus, Geranium and snapdragon. 2. Intergeneric / Interspecific hybridization Heterosis  Hybrid vigor or heterosis is more in interspecific / intergeneric crosses in comparison to intervarietal crosses (at below species level) as has been observed in fodder crops such as elephant grass (Pennisetum purpureum × P. typhoideum), Bermuda grass

11.56

Crop Evolution and Genetic Resources

(Cynodon transvalensis × C. dactylon) Fesue and rye grass (F. pratensis × Lolium multiflorum, Lolium multiflorum × Festuca aundinaca or F. pratensis. And the same type of wide crosses can be made to exploit hybrid vigor in floricultural crops. In Alstroemeria the first cultivar was an interspecific diploid hybrid (2n = 2x = 16) between two Chilean species. The large-sized irises (2n = 31) were developed by interspecific hybridization between Spanish iris, Iris xiphium (2n = 34) and I. tingitana (2n = 28). The English iris is I. xiphoides with 2n = 42 and the bearded irises are complex hybrids involving a number of species (I. chamaeiris, pallid and variegata). In irises there are diploid, triploid and tetraploid cultivars. In Lilium Asiatic and Oriental hybrid groups have been developed from interspecific crosses within the sections Sinomartagon and Archelirion, respectibvely. Commercial cultivars have been developed through interspecific hybridization involving L. longiflorum and Asiatic hybrids. In case of orchids, besides species or their hybrids within the genus intergeneric hybrids are serving as commercial cultivars. There are examples of intergeneric crosses involving two genera and three genera, respectively. For example, Aranda was developed from the cross between Vanda and Arachnis, Ascocenda from Ascocentrum and Vanda, Vandaenopsis from Phalaenopsis and Vanda and Holttuumara from Archnis, Renanthera and Vanda. Some of the genera of interest are Catleya, Dendrobium, Cymbidium, Vanda, Oncidium and Phalaenopsis, among others. In Tulipa the triploid, sterile hybrid was developed from an interspecific cross, T. gesneriana × T. fosteriana. New interspecific hybrid cultivars have been developed from crosses, T. gesneriana × T. praestans and T. gesneriana × T. agenensis. Complex inter-specific crosses have resulted in broad range of shapes and colors of plants and flowers. Wide crosses can give rise to new colors or color combinations. In other words, wide cross can yield novel hybrids. Larger flower than either parent was found in interspecific cross, Nicotiana longsdorfii x N. alata. Antirrhinum crosses show bizarre appendages (Hagedoorn, 1921). In cross of two species of snapdragon, Antirrhinum majus and A. molle Bour (1924) found F2 population showing considerable variability and a few individual had unique characteristics showing the transgressive segregation. There was appearance of new flower color, white in interspecific cross of primula, P. veris x P. julia (Halden, 1959). Interspecific crosses in Viola resulted in increased adaptiveness and faster growth. In lotus new pigments appear in interspecific hybrids (Harney and Grant, 1964). In Zinnia interspecific hyridization yielded a novel hybrid (Z. angustifolia var. angustifolia x Z. violacea). Further, Rosa, Narcissus, Crocus, Iris and Chrysanthemum are of interspecific hybrid origin and secondly they are mostly polyploids. Reciprocal crosses and other types of crosses failed to the desired flower color trait coupled with disease resistance and plant habit. There are many ornamental plants in which traits of interest could not be transferred. One good example is the transfer of yellow color from Lathyrus belinensis into its hybrids. In case of Fuchsia and Lathyrus species the interspecific hybrids (F1) showed a wide range of phenotypic expression ranging from being intermediate through to the wild type flower color and to the extent that hybrids did not resemble either parent. Transgressive segregants were not only found in the interspecific hybrids (in F1) but also in the subsequent generation which can be explained due to occurrence of mutations,

Origin and Genetic Resources of floricultural Crops

11.57

epistasis or complementary gene action. Such type of generation of variation has also been reported in interspecific crosses in primrose and oxlip (Valentine, 1947). There are other examples, in which F1 between interspecific cross shows an intermediate level of expression for traits. There are sexual barriers preventing interspecific hybridization. The problems of pre-hybridization barriers can be overcome through use of mixed and mentor pollen (mixed pollen refers to mixture of compatible and incompatible pollen and mentor pollen refers to compatible pollen inactivated by irradiation but still capable of pollen tube growth together with incompatible pollen) (Kunishige and Hirata, 1978), bud pollination, chemical treatment (use of lipids such as trilinolein which promotes the growth and penetration of pollen tube into pistil, Wolters-Arts etal., 1998), application of growth regulators such as auxin, cytokinins, gibberellins to peduncle and ovary, cut style pollination (removal of stigma and part of style or all of the style and pollination of the cut end) and grafting of style (pollen grains are deposited on a compatible stigma and after one day the style of the pollen donor is cut 1 to 2 mm above the ovary and grafted onto the ovary of another incompatible parent. Style and stigma are joined in vivo using a piece of straw filled with Lilium longiflorum exudates in case of Lilium). Post-hybridization barriers which results in failure of endosperm development and abortion of embryo can be overcome through ovary culture (ovary slice culture), ovule culture and embryo culture. Ovary culture has been applied in Lilium, Nerine and Tulipa. In the ovary culture technique, ovary is harvested 7-14 days after cut-style pollination. Ovule culture technique is applied where fruit aborts before embryo culture can be taken. It has been applied in Alstroemeria. It is an easy and rapid alternative. Embryo culture is employed where flower remains on the plant for a considerable length of time after pollination. In this technique embryo is rescued when it is in globular stage. This technique has been applied in flower bulbs such as Allium, Alstroemeria, Freesia, Lilium, Tulipa and Zantedeschia. An integrated approach of in vitro pollination and fertilization (Zenkteler, 1990) which brings pollen grains in direct contact with ovules followed by embryo rescue has been applied in many interspecific and intergeneric crosses, e.g., Lily. This technique takes care of both pre and post-hybridization barriers. Barriers occurring after embryo rescue include hybrid break down and F1 sterility. Hybrid breakdown results in loss of hybrid before flowering due to the formation of unbalanced genome combination. F1 sterility results from reduced chromosome pairing during meiosis. Intergeneric hybridization has been successful in Polyanthes. Thus in vitro breeding techniques such as embryo rescue, in vitro pollination, protoplast fusion and mutagenesis will lead to development of novel type.

Overcoming F1 sterility a. By mitotic polyploidization-somatic chromosome doubling through use of colchicine or oryzalin. It does not allow homeologous recombination. Breeding at polyploidy levels is widely used in bulbous flower crop such as Alstroemeria, Freesia, Gladiolus and Lilium.

11.58

Crop Evolution and Genetic Resources

b. By meiotic polyploidization-through 2n gametes production. There are two mechanisms of 2n gametes production. 1. First division restitution (FDR) and 2. Second division restitution (SDR). In the former whole chromosome complement divides equationally before telophase I followed by cytokinesis which leads to formation of dyad without further division. In case of SDR the chromosomes divide reductionally at anaphase I and telophase I and cytokinesis occurs thereby producing a dyad. However, in the second division the chromatids divide but the nuclei restitute in each of the two cells of dyad. The Indeterminate meiotic restitution (IMR) combines the two, FDR and SDR. Some of the univalents divide equationally (as in FDR) and some bivalents disjoin reductionally (as in SDR) before telophase leading to dyad without further division. It permits homeologous recombination. If FDR occurs without homoeologous recombination then the cross between two diploids, say A × B cross will yield allotetraploid wich will be similar to the amphidiploids produced using the two diploids, A and B. But if there is FDR with homoeologous recombination then in that case F1 produced will be a segregating generation population and selection can be practised. For desirable genotype (s) improvement through use of 2n gametes has been done in case of Tulip, Lily, Hyacinth, Narcissus, Gladiolus, Iris, Crocus, Allium and Zantedeschia. Sexual polyploidization is also found in Fuchsia. Pollengrains are of different sizes and shapes. Genetically unbalanced gametes are produced as a result of random non-disjuncrion of chromosomes at anaphase I (FDR). These unreduced gametes are viable. Selection should be carried out for isolation crop (s) and genotype (s) within a crop (Potato, Alstromeria) which produce high frequency of 2n gametes. Meiotic doubling has been successfully practiced in Lilium and Alstromeria. Triploid block  In case of cross, 2x (diploid) x 4x (tetraploid) the 3x progeny are not viable because of triploid block because of embryo-endosperm imbalance. Normal endosperm development takes place when the ratio of maternal to paternal EBN contribution to their progeny is 2:1. This ratio is based on the fact that 2n polar nuclei or central nucleus fuses with n male gamete to form endosperm (double fertilization). Any deviation from this ratio will result in no seed development. In case of 4x (4EBN) × 2x (2EBN) or 2x (2EBN) × 4x (4EBN) when reduced gametes are produced, no triploid progeny will result because of EBN hypothesis. But in the cross, 4x (4EBN) × 2x (2EBN) when the female produces reduced gamete and male produces unreduced gamete and there will be generation of triploid. Triploid block operates in Lilium and this trait can be used for selection of 2n eggs. Methods of improvement in rose  In case of rose wild diploid can be made tetraploid through the use of colchicine and tetraploid x tetraploid crosses can be attempted and different cultivars are crossed in each cycle in backcrossing program in order to improve/transfer quantitative trait. Polyploidization can be done with chemical such as oryzalin and trifluralin. In the second method of rose improvement wild (diploid) × wild (diploid) crosses are made and F1 is amphiliploidized through colchicine and thus tetraploids are synthesized.

Origin and Genetic Resources of floricultural Crops

11.59

This tetraploid is now crossed with tetraploid cultivated variety and selection is practiced for improved genotype (s). Besides improvement through somatic polyploidization use of meiotic polyploidization can be made to improve this crops described above. Further, meiotic polyploidization is carried out in roses for improving this crop. 3. Mutation a. Use of physical and chemical mutagens b. Use of transposon Use of gamma rays and heavy ion beams can be used to create variation irrespective of in vivo or in vitro method in vegetatively propagated ornaments. Seed can be treated with either physical or chemical mutagens which induce gene mutation. As flower color is under control of gene (s), mutants differing in intensity of color or mutant with a different color can be obtained. Similarly, as we will see in the following that leaf color variation is also controlled genetically. Mutation breeding is more important in the improvement of ornamental foliage plants. Mutation breeding techniques using physical and chemical mutagens can be employed to simulate production of sports in various genera or species which do not normally hybridize easily. The problem with chemical mutagens for use ‘in vivo’ is the lack of uniform penetration of the target meristem when larger plants are used. In case of ornamental crops a growth reduction rate of nearly 30% (LD30) rather than 50% (LD50 as in case of field crops) has generally given the best result. In case of vegetatively propagated crops adventitious bud technique will produce solid mutants. In vivo single cell adventitious bud technique will be a more suitable method in vegetatively propagated ornamentals. Adventitious shoots that develop at the base of petiole of detached leaves (explants) are single cell origin and if the detached leaf is irradiated then the single mutated cell situated in a multicellular tissue will produce non-chimeric or solid mutants. Leaf color variation  There are ornamental plants such as Dracaena, croton, coleus, etc. which are grown for their attractive leaf color. In Coleus the character solid purple (P), solid green (P G ) or pattern (p) is under control of single allelic series and P and PG are dominant over p. Intense or dilute green (I, i ) do not appear to be linked to P/p. Crinky leaves or smooth leaves are determined by single gene. Deep lobed is associated with male sterility. There is great variation in leaf color and very less variation in form and flower type. Maternal inheritance  There is maternal inheritance for leaf color in 4   o’clock (Mirabilis jalapa) plant. Egg cell is many times larger than pollen cell and contains both mitochondria and chloroplasts and thus contain all the organelle DNA from the female parent. Depending on the phenotype of the mother plant there will be three types of egg-chloroplast with chlorophyll, chloroplast without chlorophyll and a mixture of the two. In case of pollen which is small and is devoid of organelles and thus does not contain organelle DNA. Reciprocal differences can be due maternal inheritance or sex linkage. Maternal inheritance can be biparental or maternal or paternal. A cross of two parents, one having

Crop Evolution and Genetic Resources

11.60

green plastids (G) and another having white plastids (W), will yield the progeny in these three types as follows. 1. Maternal inheritance

G (Female)

×







F1 (G)



W (Female) × G (Male)

RF1 (W)

2. Paternal inheritance



G (Female)

×







F1 (W)



W (Male)

W (Male)

W (Female) × G (male)

RF1 (G)

3. Biparental inheritance



G (Female)

×

W (Male)







F1 ( G, V and W)

W (Female) × G (Male)

RF1 (G, V and W)

In fact, only V(variegated plastids) progeny are strictly biparental. Sometimes, only two types of progeny, namely, G + V, W + V or G + W are obtained in biparental inheritance. Use of transposon mutagenesis  Variation in flower color can be obtained through use of transposable elements which constitute even up to 84 per cent of the genome. Flower color variegation in Antirrrhinum is conferred by mutant alleles of pigmentation genes that carry transposon insertion. TE (Transposable element) can be excised somatically or in the germ line with different consequences. Transposon can affect genes encoding anthocyanin pigmentation. A transposon altered phenotype differs from other bicolored forms such as chimeras or plants with a gene controlled coloration pattern, in the coloration pattern as well as the variability of the pattern. All individuals show a different color pattern and their progeny will show a whole range of appearance. Colored phenotype (wild type) upon mutation in a pigmentation gene will give rise to colorless phenotype which will breed true. But when a colored phenotype is mutated with the insertion of a TE, mutant will be colorless in the first generation but subsequently may give progeny with variegation in color. Flower color variegation is due to unstable mutant alleles of pigmentation genes that carry transposon insertions. Pigmentation gene (wild type color) upon insertion of TE will produce colorless phenotype. Plants with variegated flowers upon insertion of TE can generate clonal patches of pigmented cells on the colorless

Origin and Genetic Resources of floricultural Crops

11.61

background if there is somatic excision of TE. Excision in germ line tissue will generate some progeny with fully red colored flowers (a case of reversion). Experiment can be done for identification of a pigmention gene which is specifically impaired in variegation flower color and this gene can be a candidate gene for transposon trapping study. Here the objective would be to study the genetic behavior of plants with variegated flower color. In other words, see whether or not these plants show germinal instability. Now search for transposon insertion in the candidate gene. Determine whether transposon activity at the candidate gene is responsible for mutant phenotype. Determine whether phenotypic reversion either somatic or germinal is attributable to transposon excision. Development of variety with variegated flower pattern  Insertion and excision of transposons in genes involved in biosynthetic pathway or regulatory genes will produce a mosaic or variegated phenotype whose pattern will be dependent on the frequency and timing of excision (Lui et al., 2001). Examples of variegation involving biosynthetic genes are observed in snapdragon where insertions of transposons, Tam1, Tam2 and Tam3 into the CHS and DHFR resulted in floral sectors generated by excision of the element (Coen and Carpener, 1986). A variegated petunia was developed through insertion of a transposon in the An1 gene involved in anthocyanin biosynthesis (Dooderman et al., 1984). These studies show that it is possible to engineer variegated floral phenotype by placing anthocyanin biosynthetic or regulatory genes under control of a TE. 4. Polyploidization Polyploidy method of breeding  Poyploids show gigas effect. Polyploidy offers three advantages. 1. It can shift the reproductive system to asexual mode of propagation. 2. It can break down the self incompatibility. 3. It can change plant-animal pollination. Besides all these it helps in adaptation and speciation (evolution). Polyploidy occurs in a number of floricultural crops such as Ageratum, Antirrhinum, Aster, Begonias, Carnation, Cosmos, Chrysanthemum, Cyclamen, Dahlia, Delphinium, Dendranthema, Dianthus, Freesia (both diploid and tetraploid cultivars), Fuschia, Gladiolus, Impatiens, Iris, Kalanchoe, Lilium, Limonium, Lobelia, Narcissus, Orchids, Pelargonium, Primula, Petunia, Rosa, Tulip, etc. This shows that emphasis should be given on the synthesis of new auto, allo, autoallo polyploids besides increasing the levels of ploidy (triploid, tetraploid, penta, hexa, septa, octo, etc). It offers a number of advantages. Autoployploidy results in increase in the size of flowers and vegetative parts of plants. They are more compact and vigorous than corresponding diploids. Their internodes in inflorescences of flower species such as hyacinths, gladioli or primulas are shorter than diploids. Polyploids particularly auoployploids reduces number of flowers / plant and sexual fertility. For example, triploids are sterile but them it lengthens the blooming period and thus been developed in Tagetes, Begonia and Ageratum. Tetraploid cultivats have replaced the diploid cultivars over the years in crops such as Freesia, Begonias, Cyclamen, Primula and geranium. Cochiploids have been successful in Antirrhinum, Cosmos, Dimorphotheca sinuate, Helipterum roseum, Nemesia, Tanacetum parthenium. Allopolyploids (Amphidiploids) have been synthesized to restore sterility in begonias, Impatiens, Kalanchoe, lily and others. Similarly, allotetraploid

Crop Evolution and Genetic Resources

11.62

(Tagetes patula), autoallooctoploid (Pansies) and allohexaploids (Delphinium) have been developed. Aneuploids are found in Alstromeria and Hibiscus spp. Table 11.20 shows the flower species and occurrence of polyploidy. Spontaneous polyploids are common in rose, chrysanthemum, gladiolus, dahlia, iris, hyacinth, tulip, petunia and gloriosa. Self pollinated flower crops such as Matthiola incana or double flowered varieties of species like Callistephus or Tagetes which were originally cross pollinated in the early single flowered genotypes. Table 11.20  Showing different flower species, their mode of multiplication and occurrence of polyploidy (Adapted from Horn, 2002). Species

Ageratum houstonianum

Y

Alostroemeria hybrids Anemone coronaria

Occurrence of polyploidy

seed

Vegetative

Method of vegetative propagation

Y

Y

Y

Y, Bulb

Y

Anthurium scherzerianum, A. andreanum Antirrhinum majus

Method of propagation

Bulb Y

Perennial

Y

Annual/Biennial,

Y

Y

Annual

Y

Y Bulb

Y

Aster spp.

Annual/perennial

Begonia spp. Tuberous

Y

Calcelaria integrifolia, C. hybrids

Y

Callistephus chinensis

Y

Cosmos bipinnatus, C. sulphueus

Y

Y

Y

Cyclamen persicum

Y

Y

Y Bulb

Dahlia hybrids

Y

Y

Y Bulb

Delphinium hybrids

Y

Y

Y

Y

Y

Annual, Perennial

Y

Y

Perennial

Dendrathema grandiflorum Dianthus spp.

Y

Dracaena spp.

Y

Euphorbia pulcherrima, E. fulgens

Y

Ferns Nephrolepsis Asplenium

Annual

Perennial Y Perennial

Y Y Contd...

Origin and Genetic Resources of floricultural Crops

11.63

Contd...

Species

Method of propagation

Occurrence of polyploidy

seed

Vegetative

Method of vegetative propagation

Perennial

Ficus spp. Y

Y, Bulb

Freesia hybrids

Y

Y Bulb

Fuchsia hybrids

Y

Y

Freesia spp.

Gazania hybrids

Annual/perennial

Y

Y

Gerbera jamesonii hybrids

Annual

Y Y

Bulb

Herbaceous, Perennial

Y, Bulb

Gladiolus hybrids

Annual or Perennial

Gypsophila paniculata, G.elegans

Y

Hedera helix

Y

Y

Y

Y

Iris hollandca hybrids

Y

Y

Klanchoe blossfeldiana hybrids

Y

Y

Lilium hybrids

Y

Y Bulb

Perennial

Y

Y

Annual, Perennial, herb, shrub

Y

Annual

Impatiens walleriana, I. hawkeri hybrids

Y

Limonium spp.

Y

Lobelia erinus

Y

Matthiola incana

Y

Narcissus spp. Nicotiana sanderae hybrids

Y

Palms Chamaedorea spp. Chryalidocarpus lutescens Howea Phoenix

Y Annual

Y

Orchid Cymbidium hybrids Dendrobium hybrids Phalae hybrids

Annual

Y Y Y

Y Y Y

Herbaceous, Perennial

Perennial Y Y Y Y Contd...

Crop Evolution and Genetic Resources

11.64 Contd...

Species

Method of propagation

Occurrence of polyploidy

seed

Vegetative

Method of vegetative propagation

Annual/perennial

Y

Herbaceous, Perennial

Y

Herbaceous, Perennial

Y

Y

Annual

Rosa hybrids

Y

Y, Shrub

Perennial

Rhododendron simsii hybrids

Y

Y

Saintpaulia ionantha hybrids

Y

Pelargonium hybrids Primula spp.

Y

Petunia hybrids

Y

Salvia splenddens

Y

Spathiphyllum hybrids

Y

Tagetes spp.

Y

Tulipa hybrids

Annual Y Annual

Y Y

Y, Bulb

y

Y

Annual

Verbena spp.

Y

Viola wittrickiana hybrids

Y

Y

Annual

Zinnia elegans, Z.angustifolia

y

y

Annual

Bird of paradise

y

y

Perennial

Y = Yes.

Development of triploid cultivars in floricultural crops  The advantage of triploid cultivar is that there is no seed set and so there is continuous blooming instead of normal termination of flowering after fertilization. Table 11.21 shows development of triploid cultivars in different species. Table 11.21  Showing production of triploids in different species (adapted from Reimann–Philipp, 1983). Triploid production

Frequency

Exceptionally

Rarely

Cyclamen, Antirrhinum

Petunia, Gerbera

Freely Ageratum, Begonia(B. socotrona with 2n = 4x = 52 × B. degrei with 2n = 2x = 26), Rosa × multiflora, Tagetes, Viola tricolor

Origin and Genetic Resources of floricultural Crops

11.65

Role of Aneuploidy in floriculture  Aenuploidy is found in the genera Hibiscus, Petunia, etc. Aneuploid cultivars are found in Chrysanthenum, Begonia, Hyacinth, Crocus, Nerine, Iris, Tulipa and Japanese flowering cherry (Tomino, 1963; Saito, 1969). Iris is a diploid with 2n = 2x = 24. In the Japanese garden iris the trisomic with 2n = 25(24 + 1) is a very attractive flowering type plant. Primary trisomic (2n + 1) can be produced by crossing diploid (2n = 24) with triploid (2n = 36). Problems with polyploidy method of plant breeding-Problems in carrying out traditional plant breeding programme in floricultural crops are due to their polyploid nature and / or have quite long generation time as shown in the table 11.22 below. Table 11.22  Showing ploidy level and generation time of some important ornamental crops(Adapted from Dons et al., 1991). Species

Ploidy level

Generation time(Years)

Rose

Hexaploid

1

Chrysanthemum

Hexaploid

0.5

Carnation

Diploid or tetraploid

1

Tulip

Diploid or tetraploid

4-7

Lily

Diploid or tetraploid

2-5

Sexual polyploidization-Use of 2n gamete sin developing variety A. AA × BB (2X-2X CROSSING) AA × F1-AB × BBBB (2X-4X CROSSING) AAB ABBB Types of gametes produced by F1 of interspecific hybrid Tetrads-results from reduction and equational division (Normal meiosis) 1 PMC (pollen mother cell)-4x n gametes Triad- Results from reductional and restitution only one part by SDR 1 × 2n gametes or 2 × n gamtes Dyad- Results from FDR OR SDR OR IMR 2 × 2n gametes Monad- Results from double restitution via both FDR and SDR 1 × 4n gametes

(2x) AA × BB (2x)



AB

AA × AABB × BBBB

AAB ABBB

Crop Evolution and Genetic Resources

11.66

Use of colchicine  Doubling of chromosomes can be obtained with colchicine. In case of marigold the alloplyploid has been developed in the following manner. T. erecta × T. tenuifolia

F1 Colchicine treatment Allopolyploid (T. patula) Doubling of chromosomes (allopolyploidy) has been used to restore fertility and this technique has been employed in Begonias, Impatiens, Kalanchoe, Lily and others. Pansies (Viola wittrockiana) are autoallooctploid (Horn, 1956). Perennial Delphinium hybrids are allohexaploid (2x D.grandiflorum × 4x D. elatum). Tetraploid cultvars have now replaced diploids in Freesia. Proportion of polyploidy varieties has increased in Begonias, Cyclamen, Primula malacoides and Geranium. Triploids which are sterile is a boon as it lengthens the flowering period, in Begonia, Ageratum and Tagetes. Polyploids are being developed to get large flower type in Antirrhinum, Cosmos, Dimorphotheca sinuata, Nemesia and Helipterum roseum. In tulip triploid with 2n = 3x = 36 has been produced from the cross, T. gesneriana × T. fosteriana. 5. Haploidization/dihaploidization Chromosomes can be doubled either spontaneously during the regeneration process or artificially induced by colchicine. Spontaneous doubled haploid plants could result from nuclear fusion in the early division of the microspores, endomitosis, endoreduplication or multipolar mitosis during the in vitro culture. Haploid and double haploid have been produced in Coffea arabica (anther culture, organogenesis), Coffea canephora (haploid embryoculture, embryogenesis), Musa accuminata (anther culture, indirect embryogenesis), Musa balbisiana (anther culture, indirect somatic embryogenesis), Sainpaulia ionantha (anther culture, somatic embryogenesis), Spathiphyllum wallisii (ovule culture, embryogenesis and Zinger officinale (anther culture and organogenesis). Dihaploidy  Dihaploidy production can be tried in the following species. Cyclamen, Begonia semperflorens gracilis(Gracilis growth always occurs in only triploid or tetraploid), Viola tricolor maxima, most of garden rose. Although it is a success in Palargonium and Saintpaulia. 6. Somatic hybridization Where hybrids can not be produced by sexual crossing, somatic hybridization can be used for improving traits. Protoplast fusion of mature cells has been used to generate hybrids

Origin and Genetic Resources of floricultural Crops

11.67

in Lilium, Gypsophila and Sandersonea. And this can be confirmed by polymerase chain reaction (PCR) or flow cytometry. In the somatic hybridization protoplasts from different species are fused and plant is regenerated from the hybrid protoplast. This method can be employed as diseases caused by bacteria, fungi and viruses are common and some species or wild relatives possess disease resistant traits. Further, protoplast can be used for genetic transformation either by direct DNA uptake (direct DNA electrophoresis) or through other mediated means. The application of conventional methods of plant breeding is limited to variations contained in the gene pool of the parent species. It we want to expand the available gene pool then we will have to go to the application of in vitro techniques such as embryo rescue. Now if the crosses do not produce a surviving embryo then one should attempt the technique of somatic hybridization, i.e. protoplast fusion. Polyethylene glycol (PEG) cell fusion technique is used for protoplast fusion in symmetric hybridization. Further, use of dimethyl sulfoxide (DMSO) results in higher fusion rate and higher percentage of viable fusion products (heterokaryons). The heterokaryons are isolated mechanically by micromanipulation (Menczel and Wolfe, 1984) or cell sorting or by genetic mutants controlling metabolic differences or those naturally occurring with regard to growth differences in culture. Protoplast fusion technique has led to the development of new varieties in a number of flower crops such as Gypsophilia, Lilium and Sandersonia. In case of asymmetric hybridization only a few chromosomes, subchromosome fragment(s) or small pieces of chromosomes are transferred from the donor parent to the recipient. Fragmentation of the chromosomes of the donor parent is done through irradiation and this promotes organelle transfer and generate cybrids (Zelcer et al., 1978). This technique has been used in Solanaceous plant. 7. Genetic Engineering As the economically important trait in ornamental crops is not the food product so production of genetically modified crop employing genetic engineering technique can be permitted to develop with new flower color and disease resistance against different pathogens. Methods for developing transgenics are described in detail elsewhere (see Biotechnology, Roy (2010). Majority of the floricultural plants are dicotylednous and the stem and leaf are the preferred explants in adult tissue and hypocotyls or cotyledons from seedling tissue. In case of orchid protocorm like bodies are the preferred explants. Transformation technique used is either Agrobacterium tumefaciens mediated transformation or direct transformation through particle bombardment. A. rhizogenes can be been used where dwarfing and increased root production are desirable characteristics, for example, rose and pelargonium. The most frequently used vectors include AGLO, LBA4404, and EHA101 but other can be used as well. Most common selection marker used is kenamycin (nptII) resistance but for use of transgenic in European countries where bacterial resistance is required another marker can be used. Majority of the transformation systems in ornamental crops use CaMV35S as promoter for dicots and

11.68

Crop Evolution and Genetic Resources

maize ubiquitin 1 as promoter for monocots. For protocol development the marker gene uidA encoding beta-glucuronidase (GUS) is often inserted in the absence of any gene of interest. But it must be deployed with gene of interest which includes gene for flower color, shape, size, disease resistance, etc. The traits such as flower color, fragrance, plant architecture, cut flower-vase life. Disease resistance, abiotic stress and herbicide tolerance have been modified through genetic engineering technique. Transgenic flowers  There are problems with conventional methods of plant breeding and in vitro techniques. One will have to carry our several(at least 6) backcrosses to transfer a desirable trait from a donor parent into an otherwise desirable variety(the recipient parent) and thus it takes many years to transfer a desirable gene. Further, the variability is limited in the gene pool which is available to the plant breeder. These problems of presence of limited variability in the gene pool and the necessity for successive backcrossing can be over come through production of transgenics. Most of the floricultural crops that have been transformed are cut-flower crops and Agrobacterum-mediated transformation is the most widely used technique followed by microprojectile bombardment(gene gun). Gene gun is less precise in transgene integration pattern. It requires destructive tissue sampling and an expensive substrate(X-GLUC) to detect gene expression and transgenic status. A. rhizogenes has also been used where dwarfing and increased root production are most desirable traits. Direct DNA electrophoresis into plant meristem is now being used to generate transgenic poinsettias. GM cultivars with commercial potential have been produced in Carnation, chrysanthemum, and petunia. Carnation is at present in commercial cultivation. The insertion of rolC in ornamental plants such as carnation and petunia has led to increased branching, better rooting of stem cuttings and precocious flowering(Casanova et al., 2003). Further insertion of rolC in strawberry has led to improved productivity and fruit quality(Landi et al., 2009). Down-and up-regulation of flavonoids and anthocyanin pathways are possible and predictable. The Florigen Moon Series transgenic carnation produces delphinidin based anthocyanins which can not be produced by carnation. The difference in color intensity between varieties is due to variation in the amount of anthocyanin present. Transgenic rose with blur color flower is producing delphinidin. Non-transgenic torenis accumulates mainly delphinidin based anthocyanin. In transgenic Tagetes anthocyanins are derived from delphinidin. Down regulation of anthocyanin synthase gene yielded white and partly white flowers whereas down regulation of flavonoid 3, 5, -hydroxylase and F3H and expression of an heterologous dihydroflavonol reductase produced pink flower accumulating pelargonidin anthocyanins. In snapdragon, tetrahydroxychalcone 4¢ glucosyl transferase and aureusidin synthase genes and down regulation of anthocyanin pathway led to aureusidin accumulation with a yellow color. Accumulations of delphinidin based anthocyanins in transgenic plants pose no threat. Transgenic Kalanchoe with short internode has been obtained by inserting shi (short internode) mutant gene from Arabidopsis placed under control of both a 35S promoter and gene’s own promoter (Lutke et a., 2010).

Origin and Genetic Resources of floricultural Crops

11.69

In another strategy to obtain dwarf plant (reduced plant height), rol genes (root loci) from Agrobacterium rhizogens have been inserted into a number of ornamental plants such as Antirrhinum, Datura, Eustoma, Gentiana, Kalanchoe and Palargonium sp. Besides changing plant height, insertion of this gene led to change in other traits such increase or decrease of flowering time, increase of number of flowers, reduction in flower size, change of flower shape and reduction in fertility and seed set, change in leaf morphology and leaf color. Although genetically modified cultivars with commercial potential have been produced in Carnation, Chrysanthemum and Petunia but only Carnation is in commercial cultivation. USE OF RNAi  For rebuilding delphinidin pathway CmF3’H was down regulated using RNAi and over expressed Senecio cruentus F3’, 5’H (PCFH) gene in chrysanthemum which resulted in accumulation of cyaniding thereby production of bright red but did not accumulate delphinidin. S. cruentus F3’, 5’H did not rebuild delphinidin pathway. Biosafety measures in transgenic development and production  First transgenic crop variety was introduced for commercial cultivation in U.S.A. in 1994. In India the first transgenic variety was Bt cotton, introduced in 2002. Transgenic varieties have been globally commercialized in maize, soybean, cotton, canola, squash, papaya, alfalfa and sugarbeet. People from all quarters-farmers’ organization, activist groups, institutions, scientist, politicians, governments, administrators have made lots of hue and cry since the inception of the transgenic technology. Critics or opponents of this technology say that this technology will have unknown effects on our ecosystem and farming practices. It could lead to loss of diversity, development of super race of insect / pathogen and adverse effects on non-target and beneficial insects(honeybees, bumblebees and earthworms). However, the proponents say that this technology is quicker and more efficient in the sense that a variety can be developed in comparatively short time and it will help in understanding fundamental biological processes by switching gene on and off. In other words, it will help in understanding the gene function. Transgenic technology of transfer of genes bypass the reproductive process, transfers genes in a single generation, overrides the incompatibility barriers, allows gene transfer not only in related species but between widely diverse taxon(from bacteria to tree). There are a number of biosafety concerns which people must know so that people’s perception about this technology can be changed. Transgenic variety contains selection marker, left and right border of vector besides the foreign gene of interest. Marker-free transgenics are now being developed. Marker elimination strategies include the following(Kondrak et al., 2007). 1. Co-transformation with a simple binary vector, dual binary vector and modified 2 border Agrobacterium transformation vector. 2. Use of Ipt(Isopentyl transferase (gene). 3. Recombination methods-Use of site-specific recombinases under control of inducible promoters to excise the markers. Cre / lox, FLP / FRT and R / Rs systems have been employed to obtain marker-free transformants. For details see Biotechnology(Roy, 2010).

11.70

Crop Evolution and Genetic Resources

Non-toxic chemicals such as glucorinidase, xylose isomerase, phosphomannose isomerase, dexamethasone inducible promoter genes have been used for selection of transformants (a case of positive selection). Selection marker is used because of the low frequency of transgene integration. Negative selection (by killing of non-transgenic tissue) can be also be practiced. Preventing the gene flow to other commercial varieties, weeds or wild relatives is the prime concern. It has been observed that in poplar more than 50% pollen comes from >1km to 10km away from the mother tree and so the biological issues involves destruction of wild and weedy species, exotic and native species. Further, in case of insect or disease resistant transgenic there should be high dose of genes and secondly, 20% of the area in a locality where transgenic variety is being commercially cultivated, be under normal variety (the susceptible one). Transgenic variety should not be allowed to be raised in a locality which is supposed to the reservoir of genetic diversity. This is particularly true in case of introduction of transgenic brinjal in Bihar. West Bengal, Bihar and part of contain lots of genetic resources of brinjal. Social issues include the effect on market value of organic and other products, cost of regulation and reinforcement of international treaty. Mitigation strategy  There are a number of mitigation strategies (Al-Ahmad and Gressel, 2005). 1. Risk of transgene introgression could be reduced if the transgene is inserted into the unshared genome, i.e., by utilization of partial genomic incompatibility with crops having multiple genomes derived from different progenitors. This strategy proved ineffective in oilseed rape, B. napus 2. Integration of the transgene into the plastid or mitochondrial genome results in limiting gene flow due to maternal inheritance (Daniel, 2002; Maliga, 2004). However, this strategy does not preclude the possibility of pollen influx from the relative to the transgenic crops. Further, leakage of ct-encoded genes via pollen occurs in more than 0.03% (Wang, 2004). 3. Introduction of plastome–inherited traits into varieties with complete male sterility would vastly reduce the risk of transgene outflow. 4. Seed sterility utilizing the genetic use restriction technology (GURT) and recoverable block of function for controlling volunteer seed dispersal. 5. Repressible seed lethal system Association of transgene with a chemically induced promoter will allow expression of transgene upon chemical induction but still there is a possibility of an inducible promoter mutating to become constitutive (Jepson, 2002). All these mechanisms prevent either gene flow or influx but not both which is required. Mitigator gene  Transplastomic and male sterility systems suppress the transgene flow but not the influx of pollen from relatives, requiring mitigation. Its transgene is coupled with mitigator gene such as dwarfing, non-bolting, no secondary dormancy, no seed shattering or poor seed viability it would be a double fail-safe. Dgai(gibberellic

Origin and Genetic Resources of floricultural Crops

11.71

acid-insensitive)gene from Arabidposis thaliana driven by its own promoter induces male sterility in transgenic Nicotiana tabacum which is chemically reversible by application of kinetin. It is a dwarfing mitigator gene which renders the rare transgenic hybrids unfit and unable to compete with its wild type but female reproduction is not affected. There are a number of male sterility systems which can be used. 1. Barnase-barstar system(Mariani et al. 1990). This barnase-barstar system has now been modified (Kempt et al., 2014) which does not require the fertility restorer, barstar. The hybrid produced is male fertile as in case of the barnase-barstar system. The split-gene system is based on the modification of female crossing partner, the parent with barnase. In this system, barnase coding information (barnase gene) is divided and distributed at two loci (A1, A2) that are located on allelic position in the host chromosome and are linked in repulsion. Functional complementation of the loci is achieved through the co-expression of barnase fragments and intein-mediated ligation of the barnase protein fragments. This system permits growth and maintenance of male sterile female parent. The male sterile line is heterozygous, A1A2. The male sterile is maintained by crossing with homozygous male fertile line(maintainer line) with genotypic constitution, A1A1 or A2A2. The crossing results in 50% male sterile progeny (A1 and A2). The allelic position of the complementary barnase fragments enforces 100% segregation during meiosis and this results in male fertility and seed set in the hybrid progeny as all segregants carrying only an inactive barnase fragment (either A1 or A2) but the two together produce intact cytotoxic barnase protein. 2. Constitutive expression of Agrobacterium rhizogenes rolC sterility gene. Fertility is restored by putting rolC in antisense orientation (Schonulling, 1993). 3. An alternate strategy relies on site-specific recombination to remove the transgene from pollen (Keenam and Stemmer, 2002). Also, the researchers, lab technicians and students working in the lab engaged in developing transgenic crop variety must strictly follow these biosafety measures. This subject is presented in the form of following slides. Biosafety measures for laboratory workers

1. Types of laboratory worker • Agronomy • Soil Science • Molecular Biology and genetic engineering

2. Types of work to be done in Lab. • Production of transgenic crop variety • Development of new agriculturally important microbial strains-Trichoderma, Pseudomonas, VAM, etc • Microorganism pathogenic to human/animal (Ebola virus, B. anthrcis, Yersinia pestis) Contd...

11.72

Crop Evolution and Genetic Resources

Contd...

3. Level of threat/risk/hazard • Low • Medium • High

4. Mehtods of developing varieties 5. Source of gene(s) in conventional methods • Conventional methods-Hybridization, recombination, selection, mutation, • Different varieties of the same haploidy, polyploidy, all natural species reproductive processes. • Related wild and weedy • Non-conventional methods (Genetic species–GP1A and GP1B engineering) • Different species–GP2 and GP3

6. Source of Gene(s) in Trangenic plant and method of transfer • GP4 Organism • Use of genetic engineering methods • Agrobacterium-mediated • Direct gene transfer-gene gun, biolistics

7. Kinds of gene being used in the development of transgenic • Herbicide resistance-Glyphosate, glufosinate • Insect resistance- Bt gene • Virus resistance • Improved quality- Beta- carotene, golden rice • Vaccine-rice based oral vaccineCholera toxin B-subunit(CTB)

9. Biosafety concerns • Conventional varieties-Ecofriendly variety • Trangenic variety-Raises biosafety concerns • During product development and testing-lab • During evaluation and after release for commercial cultivation

10. Biosafety concerns after release of 11. Human/Animal health safety transgenic • Food/Food product, oil/Feed• Human/Animal health concernsanalysis of seed composition problem of toxicity and allergenicity (carbohydrate, protein, fatty acid, etc) • Environmental concerns-Losss of biodiversity, development of super • Test for toxicity and allergenicity weed, super race of insect/pathogen using all available toxins/ proteins • Socio-economic and ethic (legal and trading difficulties)

12. Where these genes will go? • Seed-food, feed • Pollen dispersalatmosphere, on to other plants, soil, water • Seed dispersal, • Vegetative parts • Residue-Soil-Soil microorganism

13. Environmental concerns-gene flow • GM Crop to non-GM crop-loss of biodiversity • GM crop to wild species• GM crop to weedy speciesdevelopment of super weedherbicide res. and insect res. • To soil bacteria (part. Selection marker genehorizontal gene transfer)-development of antibiotic resistant microorganism • Development of super race of insects/pathogen • Adverse effect on non-target or beneficial insects/microorganisms

8. Types of genetic elements transferred in transgenic • Foreign gene • Selectable marker-kanamycin, hygromycin, methotrexate • L and R-border of Vector

14. Study of pollen and gene flow • Pollen biology-pollen quantity, weight, size, stickyness, dispersal distance, nectar • Estimation of the frequency of gene flow • Determing the expression level of Transgene • Measuring the fitness of transgenecompetive ability, aggressiveness

Contd...

Origin and Genetic Resources of floricultural Crops

11.73

Contd...

15. Conclusion from research work 16. Recommendation for a locality 17. Advancement in Transgenic technology • No toxicity or allergenicity• Which area/region to adopt gene product does not • Production of marker-free • Presence of wild and weedy relatives resemble any known toxin or tansgenic • Chance of out crossing allergen • Use of mitigator gene to reduce • Adoption of special farming • Crops possessing HT the fitness of T-gene. practices-High dose/refuge crop conferring proteins does not pose any envtal risk • Selectable markers (kanamycin, hygromycin) proven safe • Shows little evidence of enhance persistence or invasiveness 18. Safety concerns • Will differ from corp to cropbreeding system, • Should differ form trait to trait

19. Biosafety concerns in Lab • research worker/scientists, lab technician • Lab-Machine/instruments • Genetic meterials- Foreign gene, selection marker, Reporter gene, Vector • Chemical-Enzymes, radio isotopes, X-ray-mutagenic and carcinogenic • Green house/Net house facility • Storage and disposal facility

20. Safety measures in Laboratory • Physical containmentbiocontaiminant, monitoring facility-bacteria, fungi, virus insects, rodents. • Restricted entry, No eatables, no smoking, no paan, tobacco chewing, no gutkha • Mechanical pipetting • Laboratory coat, protective gloves • Double door, changing clothing (street clothing) • Safety of workers-radiation, hazardous chemical, genetic material not to move out

21. Storing and disposal facility • Disposal of waste and byproducts-solid waste and liquid waste • Chemical disinfectant to treat liquid waste • Solid waste-autoclaving or steam sterilization • Leak proof container- for disposal of radioactive material away form the institution

22. Green house/net house 23. Tissue culture facility and green house experiment • Required size for conducting small scale field trials • Tissue culture and regeneration of plant • specially designed green house • Stability, transmission/heredity • Controlled and filtered air flow and expression of transgene • System to control and disinfect water • Assess viability of GMO under leaving the facility field condition • Autoclaves for on site sterilization of • Adaptive or evolutionary plant material and equipments potential of GMO under varying • Restricted entry environments • Lab work must precede field trials. Contd...

Crop Evolution and Genetic Resources

11.74 Contd...

24. Requirement of technical staff • Oversee the integration of facilities, instruments, tools governing the ambient biosafety condition • Monitoring viable and nonviable counts in water, air, surface • Biosafety committee

Development of Male and Female Sterility Engineering male sterility in ornamental plants will facilitate hybrid variety development, eliminate pollen allergen, reduce the need of deadheading for extending the flowering period, redirect resources from seed to vegetative growth, increase flower longevity and prevent gene flow between genetically modified and related native plants. Process of pollination and fertilization causes senescence of petals in flowers through the action of or precursors. Thus ethylene is involved in the regulation of senescence in ethylene sensitive flowers whereas abscisic acis (ABA) is involved in ethylene non-sensitive flowers in the regulation of senescence. Prevention of pollination delays senescence. Production of male and female sterility can be used to increase flower longevity where pollination or fertilization is a trigger for petal senescence. Male sterility (CMS) can be derived from interspecific cross, Brassica nigra × B. oleracea (in Brasssicas) and intergeneric cross, B. oleracea × Raphanus sativus and mutation breeding. Disturbance of normal interaction between the cytoplasm and nuclear genes when both are not closely related leads to male sterility. Use of apomixis  Male sterile line (female parent) as one of the parents of the hybrids can be maintained or hybrids can breed true to their types using apomixis. In the various forms of apomixis such as parthenogenesis, apospory or diplospory the seeds are identical with genotype of the mother. In other words, there is permanent fixation of heterosis by simply harvesting the seeds of apomictic hybrids. Apomixis can be either obligate or facultative. It can be dominant or recessive. It can be found in diploid or polyloid. Following methods using apomictic lines can be used for the production of hybrids. 1. Apomictic parent × Facultative apomicts

F1 hybrid



or

Origin and Genetic Resources of floricultural Crops



11.75

2. Apomict × Sexual plant



F1(selection of more vigorous apomictic hybrid)

Facultative apomictic parents need to be emasculated before crossing and pollination of a large number of flowers is required. The use of apomixis in the development of hybrid is based on the reasoning that even though vegetative multiplication is easy, it often more expensive and less convenient then seeding. But the problem with hybrid is that it can not breed true and it hybrid seed needs to be produced afresh every year. Many of the subtropical grasses such as Panicum maxicum, P. notatum, Melinis minutiflora, Urochloa mosambicensis and Heteropogon controtus are obligate apomicts (Burton, 1970).

Multiplication of floricultural crops In vitro culture method of vegetative propagation of vegetatively propagated flowers is most practical and commercially efficient. Micropropagation has been successfully commercialized for mass multiplication of a genotype, true to type and disease, pest free clone. Where seed is not available or seed is not produced in the absence of pollinator (where seed production is poor) or where seed germination is very low as in case of orchids and nepenthes and where many plants are to be produced in short time, microproagation can be employed. Further, plants with virus free or free from any infection can be produced. From research view point tissue culture generates somaclonal variation which provides an opportunity for regeneration of somaclonal variants, isolation, characterization and selection of variant (s) and this has resulted in development and subsequent release of a large number of new varieties of flowers. Various methods of micropropagation include shoot tip with proliferation of lateral shoots, single node culture, axillary bud, meristem culture, adventitious organ formation and callus systems. Inflorescence is used as explants for micropropagation of Tulip, Nerine and Hippeastrum. Flowers such as orchids (apical and axillary bud of Cymbidium, Cattleya, Phalaenopsis), ferns (apical meristem, rhizome segments or tips, leaf tissue), foliage plants, bulbous species (bulbs, corms, fleshy rhizomes), herbaceous materials, trees and shrubs have been successfully micropropagated. Micro grafting has been used for obtaining ring spot virus free plant by way micrografting of plant obtained through shoot apex culture of kinnow mandarin (C. nobilis × C. deliciosa) on decapitated rootstock seedling of rough lemon (C. jambhiri).

Concept of ideotype in floricultural crops Like field crops concept of ideotype has been applied in the imporovement of flower crops. Ideotype breeding refers to construction and selection of plant which combines predetermined morphological and physiological traits in order to maximize yield or

11.76

Crop Evolution and Genetic Resources

quality in a particular environment. Langton and Cackshull (1976) proposed ideotype with following traits for spray Chrysanthemum for summer flowering. 1. Quick rooting 2. Large, horizontally arranged leaves 3. High leaf initiation rate in long days condition 4. High internode extension 5. Low leaf number in short days 6. Rapid flower bud development 7. Little or no flowering delay at above or below optimum temperature 8. Low competitive ability 9. Strong apical dominance 10. High leaf number In long days season 11. Moderate peduncle length 12. Pink flowers

11.32  MUTATION BREEDING IN VEGETATIVELY PROPAGATED CROPS Mutation breeding  Mutation can be spontaneous or induced. Spontaneous mutation gives rise to ‘bud sports’. The bud sports can result from genetic changes in one or a few genes. It can also result from changes in ploidy level called ‘ploidy chimeras(or cytochimeras) and it leads to ‘giant sports’. It is induced by colchicine and irradiation. Majority of the bud sports are periclinal chimeras. If natural variation in a crop is large then there is no need for induced mutation. Further, if mutation breeding is chosen then rapid vegetative production seems necessary. Solid mutants are easier to transfer to the next generation in contrast to periclinal chimeras which are obtained after seed to tuber irradiation. The materials to be treated to mutagens are important. It ranges from whole plant (seedling) to seed, pollen, plant part(explants), rhizome, tuber, bulb, corm, cuttings, scions, bud, etc. Isolation of mutant(s) depends on the type of material used for radiation. Method for isolation of mutant in case of seed propagated plants would be different than in case of vegetatively propagated material. Where in vivo or in vitro adventitious bud technique is available it is easier to obtain solid mutant. In vivo bud can arise from single cell or multi cells and in case of former solid mutant can be isolated easily. In case of cuttings we can have rooted cutting or unrooted cuttings available. Rooted cutting are more appropriate for irradiation. In case of rhizome, tuber, bulb or corm, we can treat either dormant material or freshly harvested material and the most appropriate material would be freshly harvested material, i.e. material having bud in the ontogenetically young stage of development as in case of Dahlia, tulip, Iris and other tuber crops. Freshly harvested tubers upon irradiation give rise to chimeras as well as apparently solid mutant in the ratio 50:50. After storage tuber carry relatively large sprouts. Similarly, irradiating buds should be the most appropriate stage of development

Origin and Genetic Resources of floricultural Crops

11.77

in order to ensure large mutated sectors and easy recovery of stable periclinal chimeras through successive vegetative propagation. Repeated back cuttings or several prunings will lead to isolation of solid mutant. Repeated cut back will lead to increase in sector size of the chimera and ultimately promote the formation of stable chimeras. Decapitated seedlings are another important material to be treated for isolation of solid mutant. Buds on decapitated seedlings originate from one of a few cells of hypocotyls and thus results in higher percentage of solid mutants. Irradiation in this case be just before or immediately after decapitation (Broertjes and van Harten, 1988). This system can be applied in Borago, Cucumis, Luffa, Phaseolus and Pisum (Kowalewska, 1927) to obtain useful mutants. Table 11.23 shows material/explants to be treated with optimum dose of radiation in order to obtain desirable mutants in different crops. In some case there is application of recurrent dose of mutagen in few successive generations. Table 11.23  Showing types of materials to be treated with different mutagens and their optimum doses in different crops. Crops

Streptocarpus, Acimenes Cassava Garlic Potato

Mode of vegetative Optimum dose of Optimum dose propagation/Materials to X-rays (in Gy) of Gamma-rays be treated with mutagen (in Gy) Leaf Stem cutting Cloves, inflorescence bulbils Tubers, Vegetative parts

Optimum dose of chemical mutagen

30

Reference

Broertjes, 1963 30 150

Crocus

Freshly harvested tuber

10-15(best dose)

Dahlia

Freshly harvested tuber

20-30

Gladiolus

Corm

75(Selection carried out in 2 or 3 rd vegetative generation

Broertjes and Bellego, 1967, 1968, 1969: Boertjes and Bakker, 1984

Lilium

Bud scales

2.5

Boertjes and Alkema, 1970

25-125

0.010.0%5(NMU) 0.1-0.4%(DES)

Contd...

Crop Evolution and Genetic Resources

11.78 Contd...

Muscari

Leaf pieces

10

Polyanthes Tulipa

Bulb Diploid bulb, Triploid bulb, 5 Freshly harvested bulb >5 4 Anthurium Callus 7.5 Begonia 20-30 Bougainvillea Stem cutting 5-10 Cactus Freshly harvested 15 segments Calathea Healthy plant/stem 11 cutting Crossandra Rooted or unrooted 20 cutting Cyclamen Seed Tuber 90-100 Saintpaulia Leaf petiole(True to type 30 vegetative propagation of variegated cultivar) Hibiscus 30 Euphorbia 2 × 20 Kalanchoe Rooted cutting(stem 30 or leaf cutting) In vitro propagation Pelargonium Plant 10-12.5 Peperomia Leaves 20-30 Rhododendron 40-60 or 2 , 3 × 20 Codiaeum(Croton) 5-10 Fern Adiantum scutum Asplenium nidus Platycerium alcicorne Pteris cretica albo lineata Hedera Schefflera Alstroemeria Diploid Triploid Chrysanthemum Rooted cuttings Explant

3.3-4.0 Gy of fast neutron 20

5-10 15 11

5(fast neutron)

Nakornthap, 1974

40-60, 2, 3 × 20

100-500 200 100 >500 300

40 Around 10 3 4 10-20 8

Around 10

10-20 8 Contd...

Origin and Genetic Resources of floricultural Crops

11.79

Contd...

Carnation Gerbera

Orchids

unrooted cutting Seed in vitro micropropagation of axillary bud( on commercial scale) Large scale in vitro propagation (protocorms, leaf or pedicel explants, callus)

80 10-25 with 10-25 with highest number highest number of mutants at 20 of mutants at 20 10-40

Rose Bud wood 45 Portulaca Woody ornamentals Forsythia 50-60 Poplar and other Cutting, AB in callus broad leaved trees (Pupulus can be propagated by splitting a branch into two parts or by making a long cut through it which under warm and humid condition develops callus from which adventitious plantlets are produced) Morus Rooted cutting Grafted plants Fruits Apple Dormant bud, Dormant 40-75 scion, young tree, seed, seedling, cuttings

Pear

Dormant bud

Cherry

Pollen, Dormant scion, 25-50 with 40 Bud (at the earliest optimum possible ontogenic stage)

Olive

Young tree, Dormant and rooted scions

10-40

40

0.5-1.5Gy/ day(0.5-0.7Gy/ day-optimum dose)

50-100

Compact or spur types and improved fruit colour traits are aimed to obtain through mutation breeding 40-75 Induction of fertility by applying irradiated pollen to incompatible female parent. 30-40 optimum

Main objective is to produce spur type growth habit Contd...

Crop Evolution and Genetic Resources

11.80 Contd...

Peach

Young seedling Bud, Bud 30(Repeated sticks to be T-budded treatment of onto seedling stock after X-rays) irradiation

Almond

20

Figs

Seed Axillary bud

50-70

Brambles (Raspberry, blackberry)

Plant(recurrent irradiation), irradiation of roots

Blue berry and Crane burry

In vitro irradiation

Currants

Irradiation of cuttings

30

Grapes

Seed, Rooted cutting, scions

20-60

Banana

Rhizomes, Seed, Shoot apex explant