The Mango Botany Production and Uses [2 ed.] 9781845934897, 2008029843

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The Mango, 2nd Edition

Botany, Production and Uses

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The Mango, 2nd Edition Botany, Production and Uses

Edited by

Richard E. Litz Tropical Research and Education Center and Center for Tropical Agriculture University of Florida 18905 SW 280 Street Homestead, FL 33031-3314 USA

CABI Head Office Nosworthy Way Wallingford Oxfordshire OX10 8DE UK

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© CAB International 2009. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data The mango : botany, production and uses/edited by Richard E. Litz. -- 2nd ed. p. cm. Includees bibliographical references and index. ISBN 978-1-84593-489-7 (alk. paper) 1. Mango. I. Litz, Richard E. SB379.M2M35 2009 634’.44--dc22

2008029843

ISBN-13: 978 1 84593 489 7 Typeset by AMA Dataset Ltd, Preston, UK. Printed and bound in the UK by the MPG Books Group, Bodmin. The paper used for the text pages in this book is FSC certified. The FSC (Forest Stewardship Council) is an international network to promote responsible management of the world's forests.

Contents

Contributors

vii

Preface

ix

Acknowledgements

xi

1. Introduction: Botany and Importance S.K. Mukherjee and R.E. Litz

1

2. Taxonomy and Systematics J.M. Bompard

19

3. Important Mango Cultivars and their Descriptors R.J. Knight, Jr, R.J. Campbell and I. Maguire

42

4. Breeding and Genetics C.P.A. Iyer and R.J. Schnell

67

5. Reproductive Physiology T.L. Davenport

97

6. Ecophysiology B. Schaffer, L. Urban, P. Lu and A.W. Whiley

170

7. Fruit Diseases D. Prusky, I. Kobiler, I. Miyara and N. Alkan

210

8. Foliar, Floral and Soilborne Diseases R.C. Ploetz and S. Freeman

231

9. Physiological Disorders V. Galán Saúco

303 v

Contents

vi 10. Pests J.E. Peña, M. Aluja and M. Wysoki

317

11.

Crop Production: Propagation S. Ram and R.E. Litz

367

12. Crop Production: Mineral Nutrition I.S.E. Bally

404

13. Crop Production: Management J.H. Crane, S. Salazar-García, T.-S. Lin, A.C. de Queiroz Pinto and Z.-H. Shü

432

14. Postharvest Physiology J.K. Brecht and E.M. Yahia

484

15. Postharvest Technology and Quarantine Treatments G.I. Johnson and P.J. Hofman

529

16. World Mango Trade and the Economics of Mango Production E.A. Evans and O.J. Mendoza

606

17. Fruit Processing L.C. Raymundo, M.T. Ombico and T.M. de Villa

628

18. Biotechnology R.E. Litz, M.A. Gómez-Lim and U. Lavi

641

Index

671

The colour plate section can be found following page 372.

Contributors

N. Alkan, Department of Technology and Storage of Agricultural Products, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, Bet Dagan 50250, Israel. M. Aluja, Instituto de Ecología AC, Km 2.5 Antigua Carretera a Coatepec No. 357, Congregación El Haya, Apartado Postal 63, CP 9100 Xalapa, Veracruz, Mexico. E-mail: [email protected] I.S.E. Bally, Horticulture and Forestry Sciences, Department of Primary Industries and Fisheries, 28 Peters Street (PO Box 1054), Mareeba, QLD 48890, Australia. E-mail: [email protected] J.M. Bompard, Les Mazes, 34160 Montaud, France. E-mail: [email protected] J.K. Brecht, 1143 Fifield Hall, Department of Horticultural Sciences, University of Florida, Gainesville, FL 32611-0690, USA. E-mail: [email protected]fl.edu R.J. Campbell, Fairchild Tropical Botanic Garden, 10901 Old Cutler Rd, Miami, FL 33156-4296, USA. E-mail: [email protected] J.H. Crane, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu T.L. Davenport, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu E.A. Evans, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu S. Freeman, Department of Plant Pathology and Weed Research, Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan 50250, Israel. E-mail: [email protected] V. Galán Saúco, Departamento de Fruticultura Tropical, Instituto Canario de Investigaciones Agrarias, Apartado Correos 60, 38200 La Laguna, Tenerife, Canary Islands, Spain. E-mail: [email protected] M.A. Gómez-Lim, Centro de Investigacion y de Estudios Avanzados del IPN (CINVESTAV), Apartado Postal 629, Irapuato GTO, Mexico 36500. E-mail: [email protected] P.J. Hofman, Department of Primary Industries and Fisheries, PO Box 5083, SCMS Nambour, QLD 4560, Australia. E-mail: [email protected] C.P.A. Iyer, Indian Institute of Horticultural Research, Hessaraghatta Lake Post, Bangalore 560089, India. E-mail: [email protected] G.I. Johnson, Horticulture 4 Development, PO Box 412, Jamison, ACT 2614, Australia. E-mail: greg. [email protected] R.J. Knight, Jr, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu vii

viii

Contributors

I. Kobiler, Department of Technology and Storage of Agricultural Products, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, Bet Dagan 50250, Israel. E-mail: [email protected] U. Lavi, Department of Horticulture, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, Bet Dagan 50250, Israel. E-mail: [email protected] T.-S. Lin, 111 Room, No. 4 Hall, Department of Horticulture, National Taiwan University, No. 1 Sec. 4 Roosevelt Road, 106 Taipei, Taiwan. E-mail: [email protected] R.E. Litz, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: relitz@ufl.edu P. Lu, EWL Sciences, PO Box 39443, Winnellie, NT 0821, Australia. E-mail: ping.lu@ewlsciences. com.au I. Maguire, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: imaguire@ufl.edu O.J. Mendoza, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. I. Miyara, Department of Technology and Storage of Agricultural Products, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, Bet Dagan 50250, Israel. S.K. Mukherjee (deceased), Department of Agriculture, Calcutta University, 35 Ballygunge Circular Road, Calcutta 700 019, India. M.T. Ombico, Fruit and Vegetable Laboratory, Food Science Cluster, College of Agriculture, University of the Philippines Los Baños, Laguna, 4031, Philippines. J.E. Peña, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu R.C. Ploetz, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu D. Prusky, Department of Technology and Storage of Agricultural Products, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, Bet Dagan 50250, Israel. E-mail: [email protected] A.C. de Queiroz Pinto, Private Consultant Tropical Fruits, SHCGN 706 Bloco P Casa 13, 70740716, Brasilia-DF, Brazil. E-mail: [email protected] S. Ram (deceased), Department of Horticulture, GB Pant University of Agriculture and Technology, Pantnagar 263 145, India. L.C. Raymundo, Fruit and Vegetable Laboratory, Food Science Cluster, College of Agriculture, University of the Philippines Los Baños, Laguna, 4031, Philippines. E-mail: [email protected] S. Salazar-García, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Campo Experimental Santiago Ixcuintla, Km. 6 Carret. Intnal. Tepic-Mazatlán, Apartado Postal 100, Santiago Ixcuintla, Nayarit 63300, Mexico. E-mail: [email protected] B. Schaffer, Tropical Research and Education Center, University of Florida, 18905 SW 280 Street, Homestead, FL 33031-3314, USA. E-mail: [email protected]fl.edu R.J. Schnell, United States Department of Agriculture (USDA) Agriculture Research Service (ARS), Subtropical Horticultural Research Unit/National Germplasm Repository, 13601 Old Cutler Road, Miami, FL 33158, USA. E-mail: [email protected] Z.-H. Shü, Department of Biological Science and Technology, Meiho Institute of Technology, 23 Ping Kuang Road, Neipu, Pingtung, 91202, Taiwan. E-mail: [email protected] L. Urban, Directeur de l’UR Génétique et écophysiologie de la qualité des agrumes (GEQA), Centre INRA de Corse, 20230 San Giuliano, France. E-mail: [email protected] T.M. de Villa, Fruit and Vegetable Laboratory, Food Science Cluster, College of Agriculture, University of the Philippines Los Baños, Laguna, 4031, Philippines. A.W. Whiley, Sunshine Horticultural Services Pty Ltd, 287 Dulong Road, Nambour, QLD 4560, Australia. E-mail: [email protected] M. Wysoki, Department of Entomology, Institute of Plant Protection, The Volcani Center, Bet Dagan 50250, Israel. E-mail: [email protected] E.M. Yahia, Facultad de Química, Universidad Autónoma de Querétaro, Querétaro, 76190 Qro, Mexico. E-mail: [email protected]

Preface

The first edition of The Mango: Botany, Production and Uses appeared in 1997, and went into an unprecedented second printing in the following year. Despite the worldwide importance of the mango, this was the first book that was devoted solely to this fruit crop species since the publication of The Mango by Gangolly et al. in 1957 and The Mango: Botany, Cultivation and Utilization by L.B. Singh in 1960. The appearance of The Mangoes: their Botany, Nomenclature, Horticulture and Utilization by Kostermans and Bompard in 1993 had provided a much-needed taxonomic and systematic revision of mango and the related Mangifera species; the Kostermans and Bompard book also stimulated interest in the Mangifera spp. germplasm for breeding and rootstock development. The Mango: Botany, Production and Uses (Litz, 1997) provided a fresh perspective of the mango. The authors represented several countries, including India, Australia, Israel, the UK, France, USA, Mexico, Pakistan and South Africa, and reflected the expansion of mango production outside its traditional areas of cultivation during the mid-20th century and the development of new technologies in these new lands. The worldview of the first edition was unique, and the authors were at the forefront of the advance of science in support of mango production. I wish to particularly acknowledge L.A. Milne (South Africa), R.V. Mosqueda-Vazquez (Mexico), S.K. Mukherjee (India) and S. Ram (India), who contributed to the first edition, and who have passed away since then. Since 1997, other mango books have appeared: El Cultivo del Mango by V. Galán Saúco in 1999 (Spain), Mango Cultivation edited by R.P. Srivastava in 1998 (India), A Cultura da Mangueira edited by P.J. de Carvalho Genu and A.C. de Queiroz Pinto in 2002 (Brazil) and El Mango by E. Yahia Kazuz, J. de J. Ornelas Paz and R. Ariza Flores in 2006 (Mexico). These books have generally targeted audiences in specific mango-producing countries. Drs Galán Saúco, Pinto and Yahia are also contributors to the second edition of The Mango: Botany, Production and Uses. ix

Preface

x

Much has happened in the decade following the appearance of the first edition of The Mango: Botany, Production and Uses. China has emerged as the second largest producer of mango fruit; India’s production is now less than half of the world total. Fresh mangoes are now consumed worldwide and are available year-round in the European Union (EU), North America and Japan. The availability of fruit of a range of mango cultivars is increasing. Mango products, including fruit nectars, leather, dried fruit slices, preserves, yogurt, etc. have become widely popular outside the tropics. The authorship of the second edition of The Mango: Botany, Production and Uses represents the USA, Mexico, Brazil, Australia, the Philippines, Taiwan, India, Israel, France and Spain, and includes leading authorities in each field. The subject matter of this book ranges from the most basic to the applied, and is designed to be a compendium that will remain highly relevant for researchers and growers for many years. I would like to express my appreciation and thanks to all of the authors for their persistence during the 3-year gestation period. I would like to express my gratitude to Ian Maguire of the Tropical Research and Education Center of the University of Florida for his photographic assistance. Financial assistance provided by Dr Yungcong Li, also of the Tropical Research and Education Center, for reproduction of colour plates is gratefully acknowledged. Special thanks to Pamela A. Moon, Guillermo Padilla and Irene Perea who tolerated me while I worked on this project. Richard E. Litz

References de Carvalho Genu, P.J. and de Queiroz Pinto, A.C. (eds) (2002) A Cultura da Mangueira. EMBRAPA Informacao Tecnologica, Brasilia DF. Galán Saúco, V. (1999) El Cultivo del Mango. Mundi-Prensa, Madrid. Gangolly, S.R., Singh, R., Katyal, S.L. and Singh, D. (1957) The Mango. Indian Council for Agricultural Research, New Delhi, India. Kostermans, A.J.G.H. and Bompard, J.M. (1993) The Mangoes: their Botany, Nomenclature, Horticulture and Utilization. Academic Press, London. Litz, R.E. (ed.) (1997) The Mango: Botany, Production and Uses. CAB International, Wallingford, UK. Singh, L.B. (1960) The Mango: Botany, Cultivation and Utilization. Leonard Hill, London. Srivastava, R.P. (1998) Mango Cultivation. International Book Distributing Co, Lucknow, India. Yahia Kazuz, E., de J. Ornelas Paz, J. and Ariza Flores, R. (2006) El Mango. Editorial Trillas, S.A. de C.V., Mexico.

Acknowledgements

The assistance provided by Ian Maguire is gratefully acknowledged. Artwork for the covers was provided by Ian. Special thanks to Campbell, Penelope and Anna.

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1

Introduction: Botany and Importance S.K. Mukherjee1 and R.E. Litz2 1Calcutta

University, Calcutta, India of Florida, Florida, USA

2University

1.1 Introduction 1.2 Description of Mango The tree Flowers The fruit The seeds and polyembryony 1.3 History of Cultivation Origin of Mangifera indica Domestication of mango Distribution 1.4 Germplasm Conservation Genetic erosion Collection and documentation of Mangifera germplasm Relevance of germplasm resources to mango improvement 1.5 Importance of Mango Cultivars 1.6 Production and Uses

1 2 2 2 3 4 5 5 9 10 11 11 12 12 12 12 14

1.1 Introduction Mango has become a major fruit crop of the tropics and subtropics, particularly in Asia, where the mango has always been the most important fruit crop and where it has been considered the ‘king of fruits’ (Purseglove, 1972). A generation ago, the Green Revolution culminated, creating surpluses of staple and horticultural crops in many developing countries. The Green Revolution was the result of nearly a century of effort of applying Mendelian genetics to crop improvement (i.e. conventional breeding) together with the optimization of agronomic and horticultural practices and the successful management of insect pests and diseases. However, improvement of tree © CAB International 2009. The Mango, 2nd Edition: Botany, Production and Uses (ed. R.E. Litz)

1

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S.K. Mukherjee and R.E. Litz

crops has lagged far behind field crops for several reasons: their heterogeneity, polyploidy, lengthy juvenile period, time required for evaluation of trees in the field, and the relatively high cost of maintaining tree plantings. For the most part, fruit cultivars continue to be ancient selections, many of which have serious problems, including alternate bearing, lack of disease resistance, low yields, etc. The rapid growth of mango production in recent years has been due to its expansion into new growing regions of the New World, China and parts of Africa; the planting of regular bearing selections; and the adoption of modern field practices, which include irrigation management, control of flowering, etc. Agricultural practices are currently undergoing another revolution, as integrated pest and disease management replaces the earlier reliance on agrichemicals, and emerging fields within biotechnology begin to impact cultivar development.

1.2 Description of Mango The tree The mango tree is believed to have evolved as a canopy layer or emergent species of the tropical rainforest of South and South-east Asia (Kaur et al., 1980; Bompard, Chapter 2, this volume). Mature trees can attain a height of 40 m or more, and can survive for several hundred years. Mango trees that have been domesticated by selection from openly pollinated seedling populations show variation in tree architecture (i.e. shape and size). The tree is an arborescent evergreen. Leaves are simple and alternate, with petioles that range in length from 1 to 12.5 cm. Leaf morphology is highly variable, depending on the cultivar: leaves can be lanceolate, oblong, ovate and intermediate types involving these forms. Leaf length ranges from 12 to 38 cm and width can be between 2–13 cm. Young leaves are copper-coloured, changing gradually to light and then dark green with age. The leaves are spirally arranged in whorls and are produced in flushes. The canopy is normally oval, elongated or dome shaped. The juvenile period of seedling trees can range from 3 to 7 years. The root system consists of a long, vigorous taproot and abundant surface feeder roots.

Flowers Mango flowers are borne on terminal pyramidal panicles, and are glabrous or pubescent; the inflorescence is rigid and erect, up to 30 cm long, and is widely branched, usually tertiary, although the final branch is always cymose. The inflorescence is usually densely flowered with hundreds of small flowers, which are 5–10 mm in diameter. The flowers are either monoecious or polygamous, and both monoecious and polygamous flowers are borne within a single inflorescence (Plate 1). The pistil aborts in male flowers. The ratio of monoecious to polygamous flowers is strongly influenced by

Introduction: Botany and Importance

3

environmental and cultural factors. The flowers have four or five sepals and petals that are ovate to ovoid to lanceolate and also thinly pubescent. The floral disc also is four- or five-lobed, fleshy and large and located above the base of the petals. There are five large, fleshy stamens, only one or two of them being fertile; the remaining stamens are sterile staminodes that are surmounted by a small gland. In addition, two or three smaller filaments arise from the lobes of the nectaries. The stamens are central. The ovule is anatropous and pendulous. It is believed that the flowers are cross-pollinated by flies (see Davenport, Chapter 5, this volume). Mukherjee (1951a, 1953) investigated the pollen morphology of mango and 12 other Mangifera species. Their pollen grains were tricolpate of almost the same size. Mondal et al. (1982, cited in Kostermans and Bompard, 1993) attempted to correlate pollen morphology with taxonomic relationships of 17 Mangifera species based upon different characteristics of the exine and sporoderm. They demonstrated that all of the species of section II (subgenus Limus) possess coarse exine; whereas there was no clear correlation with pollen type in species within section I (subgenus Mangifera).

The fruit Description The mango fruit is a large, fleshy drupe, containing an edible mesocarp of varying thickness. The mesocarp is resinous and highly variable with respect to shape, size, colour, presence of fibre and flavour. The flavour ranges from turpentine to sweet. The exocarp is thick and glandular. There is a characteristic beak that develops laterally on the proximal end of the fruit. A sinus is always present above the beak. Fruit shape varies, including elongate, oblong and ovate or intermediate forms involving two of these shapes. Fruit length can range from 2.5 to > 30 cm, depending on the cultivar. The endocarp is woody, thick and fibrous; the fibres in the mesocarp arise from the endocarp. The mango fruit is climacteric (see Brecht and Yahia, Chapter 14, this volume), and increased ethylene production occurs during ripening. Chlorophyll, carotenes, anthocyanins and xanthophylls are all present in the fruit. The skin is generally a mixture of green, red and yellow pigments, although fruit colour at maturity is genotype dependent. During ripening the chloroplasts in the peel become chromoplasts, which contain yellow and red pigments (Krishnamurthy and Subramanyam, 1970; Akamine and Goo, 1973; Salunkhe and Desai, 1984; Mitra and Baldwin, 1997). Peel colour obviously is cultivar dependent (see Knight et al., Chapter 3, this volume). Fruit of ‘Bombay Green’ is green; ‘Carabao’, ‘Manila’, ‘Mulgoa’ and ‘Arumanis’ are greenishyellow; ‘Dashehari’ and ‘Alphonso’ are yellow; and ‘Haden’, ‘Keitt’ and ‘Tommy Atkins’ have a red blush. The red blush is due to the presence of anthocyanins (Lizada, 1991). The pulp carotenoids in ripe fruit also vary with respect to cultivar (Mitra and Baldwin, 1997).

S.K. Mukherjee and R.E. Litz

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Flavour Flavour of the mango mesocarp is a function of carbohydrates, organic acids, lactones, monoterpene hydrocarbons and fatty acids (Mitra and Baldwin, 1997). During fruit maturation, starch that accumulates in the chloroplasts is hydrolysed to sucrose, glucose and fructose (Medlicott et al., 1986; Selvaraj et al., 1989; S. Kumar et al., 1994); sucrose is present in slightly higher concentrations than either fructose or glucose. Organic acid content decreases during ripening (Krishnamurthy and Subramanyam, 1970). The dominant organic acid is citric acid, but glycolic acid, malic acid, tartaric acid and oxalic acids are also present (Sarker and Muhsi, 1981; Medlicott and Thompson, 1985). The peach-like flavour of mangoes is attributed to the presence of lactones (Lakshminarayana, 1980; Wilson et al., 1990). Nutrition Mango fruit contain amino acids, carbohydrates, fatty acids, minerals, organic acids, proteins and vitamins. During the ripening process, the fruit are initially acidic, astringent and rich in ascorbic acid (vitamin C). Ripe mangoes contain moderate levels of vitamin C, but are fairly rich in provitamin A and vitamins B1 and B2. Perry and Zilva (1932) determined the vitamin A, C and D content of the fruit of three Indian mango cultivars, and found that the pulp of mangoes is a concentrated source of vitamin C. The pulp of mango fruit contains as much vitamin A as butter, although vitamin D is not present in a significant quantity. Fruit acidity is primarily due to the presence of malic and citric acids. In addition, oxalic, malonic, succinic, pyruvic, adipic, galacturonic, glucuronic, tartaric, glycolic and mucic acids are also present (Jain et al., 1959; Fang, 1965). Acidity is cultivar related; for example, immature Florida cultivars have low acidity (0.5–1.0%) in comparison with ‘Alphonso’ (3%). During ripening, acidity decreases to 0.1–0.2%. Following fruit set, starch accumulates in the mesocarp. Free sugars, including glucose, fructose and sucrose, generally increase during ripening; however, the sucrose content increases three- to fourfold due to the hydrolysis of starch. Sucrose is the principal sugar of ripe mangoes. The sucrose content of ripe fruit of three Indian cultivars, ‘Alphonso’, ‘Pairie’ and ‘Totapuri’, ranges from 11 to 20% representing 15 to 20% of the total soluble solids (Popenoe, 1932).

The seeds and polyembryony Mango seeds are solitary, large and flat, ovoid oblong and surrounded by the fibrous endocarp at maturity. The testa and tegumen are thin and papery. Embryos are dicotyledonous. Seeds of monoembryonic mango types contain a single zygotic embryo, whose cotyledons can be unequal in size or lobed in shape. The seeds of polyembryonic mango types contain one or more embryos (Plate 2); usually one embryo is zygotic, whereas the remaining embryos are derived directly from the nucellus, a maternal tissue. Nucellar embryos apparently lack a suspensor. Polyembryony has also been reported in Mangifera casturi, M. laurina and M. odorata (Bompard, 1993). Certain

Introduction: Botany and Importance

5

polyembryonic cultivars reportedly can produce seeds with adventitious nucellar embryos only, for example ‘Strawberry’ (Juliano, 1934), ‘Carabao’ and ‘Pico’ (Juliano and Cuevas, 1932) and ‘Olour’ and ‘Cambodiana’ (Maheshwari et al., 1955). Early studies suggested that polyembryony appeared to be a polygenic trait (Juliano, 1934; Sturrock, 1968), segregating as a recessive character in the progeny of controlled crosses. Recent studies, however, have demonstrated that the polyembryony trait is inherited as a dominant character (Aron et al., 1998). Several studies have shown that nucellar seedlings can be distinguished from the single zygotic seedling of polyembryonic seeds by isozymes (Schnell and Knight, 1992; Degani et al., 1993) and DNA markers, for example single sequence repeats (SSRs) (Eiadthong et al., 1999a), amplified fragment length polymorphisms (AFLPs) (Kashkush et al., 2001) and inter-simple-sequence-repeats (ISSRs) (Gonzalez et al., 2002). Mango seeds are considered to be recalcitrant, and cannot survive for more than a few days or weeks at ambient temperatures (Parisot, 1988). This important characteristic of mango seeds would have inhibited the long distance dispersal of mango by seed until recent times.

1.3 History of Cultivation Origin of Mangifera indica The largest number of Mangifera species occurs in the Malay Peninsula, the Indonesian archipelago, Thailand, Indochina and the Philippines (Mukherjee, 1985; Bompard, 1989; see Bompard, Chapter 2, this volume). The most recent classification of Mangifera species was based upon floral morphology (Kostermans and Bompard, 1993) and included 69 species, most of which are included in two subgenera Mangifera and Limus with another 11 species occupying an uncertain position (Table 1.1). Eiadthong et al. (1999b) described the phylogenetic relationships among Mangifera species using genomic restriction fragment length polymorphisms (RFLPs) and amplification of chloroplast DNA (cpDNA), and suggested that the Mangifera species should be classified using molecular data. In the next few years, it is likely that molecular biology will have a major impact on phylogenetic studies involving mango and its relatives. Mangifera species with a single fertile stamen are distributed in northeastern India, Myanmar, Thailand and the Malay Peninsula. Many of the mango relatives have small fruits with thin, acidic flesh, large seeds, abundant fibre and astringent resinous substances that are localized near the skin. In addition to M. indica, edible fruit is produced by at least 26 other species in the genus, primarily species found in South-east Asia (Gruezo, 1992). Mangifera caesia, known as ‘binjai’ or ‘kemang’ in South-east Asia, is cultivated in Java, where it bears fruit in the mango off-season (Bompard, 1992a). Mangifera foetida is less commonly cultivated due to its highly astringent fruit; however, the fruit is widely used for pickling and as a substitute for tamarind (Bompard, 1992b). Mangifera kemang and M. altissima are consumed

6

Table 1.1. Classification of Mangifera species according to Kostermans and Bompard (1993). Subgenus

Section

Species

Mangifera

Mangifera

Marchandora Pierre Euantherae Pierre

M. gebede Miq M. caloneura Kurz M. cochinchinensis Engler M. pentandra Hooker f. M. andamanica King M. gracilepes M. griffithii Hooker f. M. merrillii Mukherji M. microphylla Griff. ex Hooker f. M. altissima Blanco. M. applanata Kosterm. M. austro-indica Kosterm. M. austro-yunnanensis Hu M. casturi Kosterm. M. collina Kosterm. M. dewildei Kosterm. M. dongnaiensis Pierre M. flava Evard. M. indica L. M. lalijiwa Kosterm. M. laurina Bl. M. linearifolia (Mukherji) Kosterm. M. longipetiolata King M. magnifica Kochummen M. minor Bl. M. monandra Merr.

Rawa Kosterm.

Mangifera Ding Hou

M. minutifolia Evard. M. nicobarica Kosterm. M. paludosa Kosterm. M. parvifolia Boerl. & Koorders M. mucronulata Bl. M. oblongifolia Hooker f. M. orophila Kosterm. M. pedicellata Kosterm. M. pseudo-indica Kosterm. M. quadrifida Jack M. rigida Bl. M. rubropetala Kosterm. M. rufocostata Kosterm. M. similis Bl. M. sulauesiana Kosterm. M. sumbawaensis Kosterm. M. sylvatica Roxb. M. swintonioides Kosterm. M. timorensis Bl. M. torquenda Kosterm. M. zeylanica (Bl.) Hooker f.

S.K. Mukherjee and R.E. Litz

Genus

Limus (Marchand) Kosterm.

Species of uncertain position

M. leschenaultii Marchand M. macrocarpa Bl. M. odorata Griff. M. pajang Kosterm. M. superba Hooker f. M. persiciformis Wu & Ming M. subsessifolia Kosterm. M. taipa Buch.-Hamilton M. transversalis Kosterm. M. utana Utana

Introduction: Botany and Importance

M. blommesteinii Kosterm. M. caesia Jack M. decandra Ding Hou M. foetida Lour. M. kemanga Bl. M. lagenifera Griff. M. acutigemma Kosterm. M. bompardii Kosterm. M. bullata Kosterm. M. campospermoides Kosterm. M. hiemalis Liang Jian Ying M. maingayii Hooker f.

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as fresh fruit or used green as a salad (Angeles, 1992; Bompard, 1992a). Mangifera pajang has the largest fruit in the genus, and is an attractive fruit. Mangifera odorata is grown in the Philippines and Indonesia, and has occasionally been used as a rootstock for mango (Ochse, 1931; Bompard, 1992c). Mangifera odorata is widely grown in the humid lowlands of South-east Asia in areas that are unsuitable for mango as a mango substitute. Mangifera laurina and M. pentandra are appreciated as salad ingredients (Bompard, 1992d). In addition, M. griffithii, M. minor, M. monandra, M. quadrifida and M. similis have palatable fruit that are considered to have great potential (Gruezo, 1992). All mango cultivars belong to the species M. indica. According to De Candolle (1884), ‘It is impossible to doubt that it (the mango) is a native of south Asia or of the Malay Archipelago, when we see the multitude of varieties cultivated in those countries, the number of ancient names, in particular a Sanskrit name, its abundance in the gardens of Bengal, of Deccan peninsula, and of Ceylon even in Rheede’s time (i.e. 1683).’ Although the centre of origin and diversity of the genus Mangifera is now firmly established as being in South-east Asia, the origin of M. indica has been a matter of speculation for many years. The fossil record provides few clues, as only a single fossil bearing the imprint of a leaf of M. pentandra has ever been found (Seward, 1912). Mangifera indica is believed to have first appeared during the Quatenary period (Mukherjee, 1951b). Blume (1850) considered that mango might have originated from several related species, primarily located in the Malay archipelago. On the basis of ancient accounts of travellers and the written historical record, it was believed for many years that mango must have originated in India and spread outwards from there to South-east Asia and thence to the New World and Africa. Because north-eastern India is at the northernmost edge of the distribution of the Mangifera species, Hooker (1876) suggested that mango might have been naturalized in India. The historical record provides a sometimes conflicting account of the distribution of mango. Miquel (1859) did not record it as being wild in the Indonesian archipelago. According to Rumphius (1741), the mango was introduced into certain islands of the Indonesian archipelago within recent times; however, the mango was in cultivation in Java at least as early as ad 900–1100, when the temple at Borobodur was built and faced with carvings of the Buddha in contemplation under a mango tree (Plate 3). Based upon taxonomic and recent molecular evidence, it is now apparent that the mango probably evolved within a large area including north-western Myanmar, Bangladesh and north-eastern India (see Bompard, Chapter 2, this volume). Polyembryonic and monoembryonic M. indica Within M. indica, there are two distinct types that can be distinguished on the basis of their mode of reproduction and their respective centres of diversity: a subtropical group with monoembryonic seed (Indian type) and a tropical group with polyembryonic seed (South-east Asian). A few polyembryonic cultivars occur along the west coast of India; however, they may have been introduced into Goa from South-east Asia, perhaps by the Portuguese from

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their colonies of Malacca in the Malay Peninsula or Timor in the Indonesian archipelago. Kumar et al. (2001) estimated the genetic relatedness among ten polyembryonic and monoembryonic cultivars from the west coast of southern India using genomic and chloroplast DNA RFLP analysis. The cultivars could be grouped on the basis of embryo type (i.e. monoembryonic and polyembryonic) and had distinctly different genetic backgrounds. They concluded that polyembryonic mangoes could not have originated in India, and must have been introduced, probably from South-east Asia.

Domestication of mango Historical record It is probable that mango cultivation originated in India, where De Candolle (1884) estimated that mango cultivation appeared to have begun at least 4000 years ago. In the early period of domestication, mango trees probably yielded small fruit with thin flesh. Such fruit can be found today in north-eastern India and in the Andaman Islands (Anonymous, 1992). Folk selections of superior seedlings over many hundreds of years would have resulted in larger fruit with thicker flesh. Mukherjee (1950a, b) described many of these primitive selections from Orissa in north-eastern India; they demonstrated great variation in fruit shape and size. The mango is a very important cultural and religious symbol of India. Buddhist pilgrims Fa-Hien and Sung-Yun mentioned in their travel notes that the Gautama Buddha was presented with a mango grove by Amradarika (c.500 bc) as a place for meditation (Popenoe, 1932). According to Burns and Prayag (1921), a mango tree is depicted in friezes on the stupa of Bharut, which was constructed c.100 bc. Other travellers to India, including the Chinese Hwen T’sung (ad 632–645), the Arabs Ibn Hankal (ad 902–968) and Ibn Batuta (ad 1325–1349) and the Portuguese Lurdovei de Varthema (ad 1503– 1508), all described the mango. The Indian subcontinent was the birthplace of some of the earliest highly developed civilizations, and over the centuries, India exerted strong cultural, religious and commercial influence over South and South-east Asia. In successive waves, Hinduism, Buddhism and Islam were introduced into South-east Asia from India. To this day, many commonly used words in Indonesia are derived from both Sanskrit and Tamil. One of the most widely used words for mango in Malaysia and Java (Indonesia) is ‘mangga’, which is derived from the Tamil ‘manga’. Traders and monks from India possibly introduced superior selections of mango into South-east Asia; however, vegetative propagation was unknown in India until after the arrival of the Portuguese in Goa in the 15th century. Moreover, the most important mango selections of Thailand, Cambodia, Vietnam, Malaysia, Indonesia and the Philippines historically have all been of the polyembryonic type, and have traditionally been seed propagated. Until the establishment of Portuguese enclaves on the coast of India beginning in the late 15th century, mango cultivars did not exist in India, as there was no known method for vegetatively propagating superior selections (see Iyer and Schnell,

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Chapter 4, this volume). However, under the Moghul emperor Akbar (1556– 1605), the best selections of seedling mangoes were propagated by approach grafting and were planted in large orchards. The ‘Lakh Bagh’, a mango orchard of 100,000 trees, was planted near Darbhanga in Bihar. Perhaps nothing more eloquently attests to the importance of this fruit and the esteem in which it was held than this vast mango orchard. The Ain-i-Akbari, an encyclopedic work that was written during the reign of Akbar, contains a lengthy account of the mango, and includes information about the quality of the fruit and varietal characteristics. There was evidently a strong body of information about mango cultivation that had accumulated up to that time. Most of the mango cultivars of India had their origin in those years, and have been maintained under cultivation for over 400 years by vegetative propagation. ‘Alphonso’, ‘Dashehari’, ‘Langra’, ‘Rani Pasand’, ‘Safdar Pasand’ and other mango cultivars were selected during that time. Relics of orchards from the time of Akbar are found in different parts of India, and it has been suggested that they could still provide valuable material for selection of superior mango cultivars.

Distribution Spreading from the centres of domestication The global spread of mangoes and their cultivation outside their original centres of domestication probably did not occur until the beginning of the European voyages of discovery and colonialization in the 15th and 16th centuries. Because mango seeds are recalcitrant, and cannot survive for more than a few days or weeks, mango germplasm in the early days must have been transported as ripe fruit, seedlings or, later on, as grafted plants. It is believed that the Portuguese transported the mango from their colonies in India to their African colonies, although Purseglove (1972) suggested that it might also have been introduced to Africa via Persia and Arabia in the 10th century by Arab traders. The Portuguese later introduced the mango into Brazil from their African colonies of Mozambique and Angola. Spaniards, who encountered a mango-growing civilization in the Philippines after Magellan’s passage across the Pacific Ocean, introduced polyembryonic mango types to their New World colonies through the Pacific trading ports of Mexico and Panama. The most important, traditional mango cultivar in Mexico remains the ‘Manila’, reflecting its Philippine origin. ‘Carabao’ and ‘Manila’ are probably identical. The mango was introduced to the West Indies in the mid- to late 18th century, probably from Brazil. The first introductions of mango into Florida (USA) occurred in 1861, and involved the ‘No. 11’ polyembryonic seedling from Cuba. Seven years later, another polyembryonic selection, ‘Peach’ was introduced into the state (Knight and Schnell, 1993). Many of the early introductions into Florida proved to be unproductive, although ‘Mulgoba’ was planted on a small commercial scale (this cultivar is referred to as ‘Mulgoa’ in India, ‘Mulgoba’ in the USA and ‘Malgoa’ in Malaysia).

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Secondary ‘centres of diversity’ In 1910, a seedling of ‘Mulgoba’ came into production in Florida. Its fruit had a highly attractive red blush, and appeared to bear more heavily than its parent(s) (Wolfe, 1962). This selection was named ‘Haden’. Although ‘Haden’ was not superior with respect to fruit quality in comparison to the imported germplasm from India, its genetic base was much wider. During the 20th century, more introductions of mango germplasm into Florida occurred from South-east Asia (the Philippines, Cambodia), India and elsewhere. It was at one time believed that these introductions of mango germplasm created a secondary centre of diversity of the species (Knight and Schnell, 1993). ‘Eldon’, ‘Glenn’, ‘Lippens’, ‘Osteen’, ‘Parvin’, ‘Smith’, ‘Springfels’, ‘Tommy Atkins’ and ‘Zill’ are progeny of ‘Haden’. ‘Saigon’ seedlings were selections made from ‘Cambodiana’, a polyembryonic introduction from Indochina. From ‘Saigon’ seedlings, ‘Alice’, ‘Herman’ and ‘Florigon’ were selected. Based upon more recent genetic analysis involving microsatellite markers, it is now estimated that the majority of Florida cultivars are descended from only four monoembryonic Indian mango cultivar accessions, i.e., ‘Mulgoba’, ‘Sandersha’, ‘Amini’ and ‘Bombay’, together with the polyembryonic ‘Turpentine’ from the West Indies (Schnell et al., 2006). The Florida mango cultivars have been found to be highly adaptable to many agroecological areas and bear regularly, whereas many of the outstanding Indian cultivars have been unproductive outside their centre of domestication, and are alternate bearing. These selections also have a highly attractive red blush at maturity, firm flesh, a high flesh to seed ratio and a regular bearing habit. Some of the Florida cultivars, for example ‘Tommy Atkins’, ‘Keitt’, etc. are also moderately resistant to anthracnose, the most important production and postharvest problem of mango in many areas. In the latter half of the 20th century, plantings of Florida cultivars have been established in many countries and now form the basis of international trade of mangoes. Current distribution The mango is cultivated commercially throughout the tropics and in many subtropical areas. It is grown at the equator and at a latitude of 35–37q in southern Spain. According to Knight and Schnell (1993), ‘The process that began in Florida – introduction of superior germplasm from abroad followed by selection of improved cultivars adapted to local conditions – is now underway in many areas.’

1.4 Germplasm Conservation Genetic erosion The Mangifera species have their centre of diversity and origin in South-east Asia, a region that has experienced great economic development in recent years. Vast wooded areas have been completely or partially deforested either for expanding agriculture or for removal of tropical hardwoods for export.

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This has caused great genetic erosion within many species and genera. The Mangifera species, like many other tropical fruit trees, are canopy and emergent trees of the tropical rainforest (Kaur et al., 1980). These trees are widely scattered in the tropical rainforest, flower erratically and reproduce from large seeds that deteriorate rapidly. As such, they are particularly vulnerable and in danger of extinction.

Collection and documentation of Mangifera germplasm The International Plant Genetic Resources Institute (IPGRI), formerly known as the International Board for Plant Genetic Resources (IBPGR), commissioned an ecogeographical study of known Mangifera genetic resources (Mukherjee, 1985). Based upon this documentation, a joint IBPGR-International Union for the Conservation of Nature (IUCN)-World Wildlife Fund (WWF) project was initiated to collect wild mangoes on the island of Borneo and in the Malay Peninsula (Bompard, 1989), the regions that held the highest concentrations of Mangifera species. Kostermans and Bompard (1993), in the latest revision of the taxonomy of Mangifera, recognized 69 species, many of which were collected during the course of this project (Table 1.1). Because of the loss of natural habitat, the establishment of in situ and ex situ germplasm collections of Mangifera species was considered to be imperative.

Relevance of germplasm resources to mango improvement The genetic improvement of mango hitherto has depended on the utilization of the genetic variability found within a single species, M. indica. According to Mukherjee (1985), ‘A concerted sampling strategy should be devised for ex situ samples to meet urgent needs for use in research for improvement of the crop through breeding or as rootstocks. Sources of resistance to mango malformation, anthracnose, powdery mildew, gall midge are urgently needed.’

1.5 Importance of Mango Cultivars A partial list of the principal mango cultivars has been provided in Table 1.2. This list includes many cultivars that were identified in a survey of world mango production compiled by Watson and Winston (1984). The distribution of mango cultivars outside their centres of domestication can be attributed primarily to three historical events: (i) the movement of Indian varieties (monoembryonic) along the trade routes of the Portuguese to Africa and South America; (ii) the spread of South-east Asian varieties (polyembryonic) across the Pacific Ocean to Central and South America by the Spaniards; and (iii) the identification of improved mango cultivars initially in Florida and

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Table 1.2. Most important mango cultivars in major producing countries. Continent

Country

Cultivars

Africa

Cote d’Ivoire Egypt

‘Amelie’, ‘Kent’ ‘Alphonso’, ‘Bullock’s Heart’, ‘Hindi be Sennara’, ‘Langra’, ‘Mabrouka’, ‘Pairie’, ‘Taimour’, ‘Zebda’ ‘Boubo’, ‘Ngowe’, ‘Batawi’ ‘Amelie’, ‘Kent’ ‘Fascell’, ‘Haden’, ‘Keitt’, ‘Kent’, ‘Sensation’, ‘Tommy Atkins’, ‘Zill’ ‘Aswina’, ‘Fazli’, ‘Gopal Bhog’, ‘Himsagar’, ‘Khirsapati’, ‘Langra’ ‘Gui Fei’, ‘Tainong No. 1’, ‘Keitt’, ‘Sensation,’ ‘Zill’, ‘Zihua’, ‘Jin Huang’ ‘Alphonso’, ‘Banganapalli’, ‘Bombay’, ‘Bombay Green’, ‘Chausa’, ‘Dashehari’, ‘Fazli’, ‘Fernandian’, ‘Himsagar’, ‘Kesar’, ‘Kishen Bhog’, ‘Langra’, ‘Mallika’, ‘Mankurad’, ‘Mulgoa’, ‘Neelum’, ‘Pairi’, ‘Samar Behisht’, ‘Suvarnarekha’, ‘Totapuri’, ‘Vanraj’, ‘Zardalu’ ‘Arumanis’, ‘Dodol’, ‘Gedong’, ‘Golek’, 'Madu’, 'Manalagi’ ‘Haden’, ‘Tommy Atkins’, ‘Keitt’, ‘Maya’, ‘Nimrod’, ‘Kent’, ‘Palmer’ ‘Apple Rumani’, ‘Arumanis’, ‘Golek’, ‘Kuala Selangor 2’, ‘Malgoa’ ‘Aug Din’, ‘Ma Chit Su’, ‘Sein Ta Lone’, 'Shwe Hin Tha’ ‘Anwar Ratol’, ‘Began Pali’, ‘Chausa’, ‘Dashehari’, ‘Gulab Khas’, ‘Langra’, ‘Siroli’, ‘Sindhri’, ‘Suvarnarekha’, ‘Zafran’ ‘Carabao’, ‘Manila Super’, ‘Pico’ ‘Irwin’, ‘Jin-hwung’, ‘Keitt’, ‘Tommy Atkins’, ‘Tainong No. 1’, ‘Tsar-swain’ ‘Nam Doc Mai’, ‘Ngar Charn’, ‘Ok Rong’, ‘Keow Savoey’, ‘Pimsen Mum’ ‘Calypso’, ‘Kensington Pride’ ‘Haden’, ‘Irwin’, ‘Keitt’, ‘Mora’, ‘Tommy Atkins’ ‘Haden’, ‘Keitt’, ‘Kent’, ‘Tommy Atkins’

Kenya Mali South Africa Asia

Bangladesh China India

Indonesia Israel Malaysia Myanmar Pakistan

The Philippines Taiwan Thailand Australia North and Central America

South America

Costa Rica Dominican Republic Guatemala Haiti Mexico USA Brazil

Colombia Ecuador Peru Venezuela

‘Haden’, ‘Keitt’, ‘Kent’, ‘Tommy Atkins’ ‘Francine’, ‘Madame Francis’ ‘Ataulfo’, ‘Haden’, ‘Keitt’, ‘Kent’, ‘Manila’, ‘Palmer’, ‘Sensation’, ‘Tommy Atkins’, ‘Van Dyke’ ‘Keitt’, ‘Kent’, ‘Tommy Atkins’ ‘Bourbon’, ‘Coite’, ‘Coquinho’, ‘Coracao’, ‘Espada’, ‘Haden’, ‘Itamaraca’, ‘Keitt’, ‘Mamao’, ‘Palmer’, ‘Rosa’, ‘Tommy Atkins’, ‘Uba’, ‘Van Dyke’ ‘Vallenato’ ‘Haden’, ‘Keitt’, ‘Kent’, ‘Tommy Atkins’ ‘Haden’, ‘Keitt’, ‘Kent’, ‘Tommy Atkins’ ‘Haden’, ‘Keitt’, ‘Kent’, ‘Tommy Atkins’

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later in other new mango-producing areas, as a result of open and controlled pollination among local and introduced mango germplasm from India and South-east Asia. Further information about many of the mango cultivars, including their fruit characters, is available in Knight et al. (Chapter 3, this volume), and in publications by Burns and Prayag (1921) for mangoes of Maharashtra, Naik and Gangolly (1950) for south Indian mangoes, Singh and Singh (1956) for Uttar Pradesh mangoes, Mukherjee (1948) for Bengal mangoes and Campbell (1992) for Florida mangoes. Because many clonally propagated mango cultivars have unique local and/or regional names, there is considerable confusion in nomenclature. The Indian Agricultural Research Institute (IARI), New Delhi, has been recognized by the International Society for Horticultural Science (ISHS) as the International Registration Authority for Mango, whose mission is to consolidate superfluous names of mango cultivars. The potential for molecular, for example randomly amplified polymorphic DNA (RAPD), markers, to resolve much of this confusion has been demonstrated by Schnell and Knight (1992), Degani et al. (1993), Schnell et al. (1995), Eiadthong et al. (1999a), Kashkush et al. (2001) and Gonzalez et al. (2002) (see Bompard, Chapter 2 and Iyer and Schnell, Chapter 4, this volume). There is little variation among seedlings derived from polyembryonic mangoes. None the less, a certain amount of variability does occur, probably as a result of somatic mutation. Thus, in Indonesia there are several ‘Arumanis’ selections that are denoted numerically, for example ‘Arumanis 1’, ‘Arumanis 2’, etc. In addition, although Philippine mango cultivars are distinguished by different names, for example ‘Carabao’, ‘Manila’, ‘Philippine’, etc., the differences among them are quite subtle.

1.6 Production and Uses The mango is the most important fruit of Asia, and currently ranks fifth in total production (in metric tonnes) among major fruit crops worldwide, after Musa (bananas and plantains) (105,815,354 t), Citrus (all types) (105,440,168 t), grapes (65,584,233 t) and apples (59,444,377 t) (FAOSTAT, 2006). According to the Food and Agriculture Organization of the United Nations (FAO) database (FAOSTAT, 2006), world mango production has increased from 16,903,407 t in 1990 to 28,221,510 t in 2005. Much of this new production has occurred outside the traditional centres of mango culture of South and South-east Asia. In 1990, India produced approximately 51% of the world’s mangoes, but by 2005, India’s share had declined to approximately 38%, despite the substantial increase in mango production since 1990 (from 8,645,405 to 10,800,000 t between 1990 and 2005). The current leading producing nations after India include (in metric tonnes) China (3,450,000), Thailand (1,800,000), Pakistan (1,673,900), Mexico (1,600,000), Indonesia (1,478,204), Brazil (1,000,000) and the Philippines (950,000). Although world production has increased by 67% between 1990 and 2005, mango exports have increased almost sixfold

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from 158,030 to 907,782 t, with total export value estimated to be US$583,763,000 (FAOSTAT, 2006). The major exporting countries are (in metric tonnes) Mexico (212,505), India (156,222) and Brazil (111,181). As a result, mangoes are widely available as fresh fruit and as processed products (i.e. dried fruit, dairy products, juice, pickles, etc.). Mangoes are an important component of the diet in many less developed countries in the subtropics and tropics. In regions of the world that have experienced low living standards and serious nutritional deficiencies, their attractiveness and flavour have also enhanced the quality of life. Surplus production has increasingly been processed and fruit of certain cultivars is destined for export as fresh fruit. Approximately 1% of mango production is utilized for processing for juice, nectars, preserves (including chutney), fruit leather, dried fruit slices, frozen pulp and as a flavouring for baked goods, ice cream, yoghurt, etc. (see Raymundo et al., Chapter 17, this volume). No part of the fruit is wasted. In India and the subcontinent, the seed is used for extraction of starch ‘amchur’, and the peels (skin) have been used as a source of anacardic acid. Mango wood is a low quality timber, and the bark of the tree is an important source of tannins for curing leather.

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S.K. Mukherjee and R.E. Litz Burns, W. and Prayag, S.M. (1921) The Book of Mango. Bulletin 103, Department of Agriculture, Bombay, India. Campbell, R.J. (1992) A Guide to Mangoes in Florida. Fairchild Tropical Garden, Miami, Florida. De Candolle, A.P. (1884) Origin of Cultivated Plants. Hafner, London. Degani, C., Cohen, M., Reuveni, O., El-Batsri, R. and Gazit, S. (1993) Frequency and characteristics of zygotic seedlings from polyembryonic mango cultivars, determined using isozymes as genetic markers. Acta Horticulturae 341, 78–85. Eiadthong, W., Yonemoni, K., Kanzaki, S., Sugiura, A., Utsunomiya, N. and Subhadrabandhu, S. (1999a) Amplified fragment length polymorphism (AFLP) analysis for studying the genetic relationships among Mangifera species in Thailand. Journal of the American Society for Horticultural Science 125, 160–164. Eiadthong, W., Yonemoni, K., Sugiura, A., Utsunomiya, N. and Subhadrabandhu, S. (1999b) Analysis of phylogenetic relationship in Mangifera by restriction site analysis of an amplified region of cpDNA. Scientia Horticulturae 80, 145–155. Fang, T.T. (1965) Chromatographic fractionation of nonnitrogenous organic acids of mango and guava fruits by silica gel column. Memoirs of the College of Agriculture, National Taiwan Museum 8, 236. FAOSTAT (2006) Available at: http://faostat.fao.org/site/340/default.aspx (accessed 22 October 2006). Gonzalez, A., Coulson, M. and Brettell, R. (2002) Development of DNA markers (ISSRs) in mango. Acta Horticulturae 575, 139–143. Gruezo, W.S. (1992) Mangifera L. In: Verheij, E.W.M. and Coronel, R.E. (eds) Plant Resources of South-east Asia No.2: Edible Fruits and Nuts. Pudoc-DLO, Wageningen, the Netherlands, pp. 203–206. Hooker, J.D. (1876) The Flora of British India 2. Reeve, London. Jain, N.L., Krishnamurthy, G.V. and Lal, G. (1959) Nonvolatile organic acids in unripe pickling mangoes and salted mango slices by paper chromatography. Food Science 8, 115–117. Juliano, J.B. (1934) Origin of embryos in the strawberry mango. Philippine Journal of Science 54, 553–563. Juliano, J.B. and Cuevas, N.L. (1932) Floral morphology of the mango (Mangifera indica L.) with special reference to the Pico variety from the Philippines. Philippine Agriculturist 21, 449–472. Kashkush, K., Jinggui, F., Tomer, E., Hillel, J. and Lavi, U. (2001) Cultivar identification and genetic map of mango (Mangifera indica). Euphytica 122, 129–136. Kaur, A., Ha, C.O., Jong, K., Sands, V.E., Chan, H.T., Soepadmo, E. and Ashton, P.S. (1980) Apomixis may be widespread among trees of the climax rain forest. Nature 271, 440–442. Knight, R.J., Jr and Schnell, R.A. (1993) Mango (Mangifera indica L.) introduction and evaluation in Florida and its impact on the world industry. Acta Horticulturae 341, 125–135. Kostermans, A.J.G.H. and Bompard, J.M. (1993) The Mangoes: Botany, Nomenclature, Horticulture, Cultivation and Utilization. Academic Press, London. Krishnamurthy, S. and Subramanyam, H. (1970) Respiratory climacteric and chemical changes in the mango fruit Mangifera indica L. Journal of the American Society for Horticultural Science 95, 333–337. Kumar, N.V.H., Narayanaswamy, P., Prasod, D.T., Mukunda, G.K. and Sondhu, S.N. (2001) Estimation of genetic diversity of commercial mango (Mangifera indica L.) cultivars using RAPD markers. Journal of Horticultural Science and Biotechnology 76, 529–533.

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Kumar, S., Das, D.K., Singh, A.K. and Prasad, U.S. (1994) Sucrose metabolism during maturation and ripening of mango cultivars. Plant Physiology and Biochemistry 21, 27–32. Lakshminarayana, S. (1980) Mango. In: Nagy, S. and Shaw, P.E. (eds) Tropical and Subtropical Fruits. AVI Publishing Co., Westport, Connecticut, USA, pp. 184–257. Lizada, M.C. (1991) Post harvest physiology of mango – a review. Acta Horticulturae 291, 437–449. Maheshwari, P., Sachar, R.C. and Chopra, R.N. (1955) Embryological studies in mango (Mangifera indica L.). In: Proceedings of the 42nd Indian Scientific Congress, Baroda, India, p. 233. Medlicott, A.P. and Thompson, A.K. (1985) Analysis of sugars and organic acids in ripening mango fruit (Mangifera indica L. var. Keitt) by high performance liquid chromatography. Journal of the Science of Food and Agriculture 36, 56–566. Medlicott, A.P., Bhogol, M. and Reynolds, S.B. (1986) Changes in peel pigmentation during ripening of mango fruit (Mangifera indica var. Tommy Atkins). Annals of Applied Biology 109, 651–656. Miquel, F.A.G. (1859) Flora van Nederlandsch Indie 1, 627–634. Mitra, S.K. and Baldwin, E.A. (1997) Mango. In: Mitra, S.K. (ed.) Postharvest Physiology and Storage of Tropical and Subtropical Fruits. CAB International, Wallingford, UK, pp. 85–122. Mukherjee, S.K. (1948) The varieties of mango (M. indica L.) and their classification. Bulletin of the Botanical Society of Bengal 2, 101–133. Mukherjee, S.K. (1950a) Wild mangoes of India. Science and Culture 15, 469–471. Mukherjee, S.K. (1950b) Mango. Its allopolyploid nature. Nature 150, 196–197. Mukherjee, S.K. (1951a) Pollen analysis in Mangifera in relation to fruit set and taxonomy. Journal of the Indian Botanical Society 30, 49–55. Mukherjee, S.K. (1951b) Origin of mango. Indian Journal of Genetics and Plant Breeding 11, 49–56. Mukherjee, S.K. (1953) Origin, distribution and phylogenetic affinities of the species of Mangifera L. Journal of the Linnean Society, Botany 55, 65–83. Naik, K.C. and Gangolly, S.R. (1950) A Monograph on Classification and Nomenclature of South Indian Mangoes. Government Press, Madras, India. Ochse, J.J. (1931) Fruits and Fruiticulture in the Dutch East Indies. G. Kolff, Batavia, (Jakarta), Indonesia. Parisot, E. (1988) Etude de la croissance rhythmique chez de jeunes manguiers (Mangifera indica L.). Description, germination et conservation de graines polyembryonnees de manguier. Fruits 43, 97–105. Perry, E.O.V. and Zilva, S.S. (1932) Preliminary Report on Vitamin Content of the Mango. Empire Marketing Board, London. Popenoe, W. (1932) Manual of Tropical and Subtropical Fruits. Macmillan Co., New York. Purseglove, J.W. (1972) Mangoes west of India. Acta Horticulturae 24, 107–174. Rumphius, G.E. (1741–1750) Herbarium Amboinense. Vol. 1–6. Den Haag, Amsterdam. Salunkhe, D.K. and Desai, B.B. (1984) Mango. In: Postharvest Biotechnology of Fruits, Vol. 1. CRC Press, Boca Raton, Florida, pp. 77–94. Sarker, S. and Muhsi, A.A. (1981) A study on the content and interconversions of organic acids of mango (Mangifera indica L.) at various stages of fruit development. Bangladesh Journal of Agricultural Science 8, 69–75. Schnell, R.J. and Knight, R.J., Jr (1992) Frequency of zygotic seedlings from five polyembryonic mango rootstocks. HortScience 27, 174–176.

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S.K. Mukherjee and R.E. Litz Schnell, R.J., Ronning, C.M. and Knight, R.J., Jr (1995) Identification of cultivars and validation of genetic relationships in Mangifera indica L. using RAPD markers. Theoretical and Applied Genetics 90, 269–274. Schnell, R.J., Brown, J.S., Olano, C.T., Meerow, A.W., Campbell, R.J. and Kuhn, D.N. (2006) Mango genetic diversity analysis and pedigree inferences for Florida cultivars using microsatellite markers. Journal of the American Society for Horticultural Science 13, 214–224. Selvaraj, Y., Kumar, R. and Pal, D.K. (1989) Changes in sugars, organics, amino acids, lipids, lipid constituents and aroma characteristics or ripening mango (Mangifera indica L.) fruit. Journal of Food Science and Technology 26, 306–311. Seward, A.C. (1912) Dictyledonous leaves from Assam. Records of the Geological Survey of India 42, 100. Singh, L.B. and Singh, R.N. (1956) A Monograph on the Mangoes of UP. Superintendent of Printing, Uttar Pradesh Government, Lucknow, India. Sturrock, T.T. (1968) Genetics of mango polyembryony. Proceedings of the Florida State Horticultural Society 81, 311–314. Watson, B.J. and Winston, E.C. (1984) Plant genetic improvement. In: Proceedings of the First Australian Mango Research Workshop. Commonwealth Scientific and Industrial Research Organization (CSIRO), Canberra, pp. 104–138. Wilson, C.W., Shaw, P.E. and Knight, R.J., Jr (1990) Importance of some lactones and 2,5-dimethyl-4-hydroxy-3-(2H)-furanone to mango (Mangifera indica L.) aroma. Journal of Agricultural Food Chemistry 38, 1556–1559. Wolfe, H.S. (1962) The mango in Florida – 1887 to 1962. Proceedings of the Florida State Horticultural Society 75, 387–391.

2

Taxonomy and Systematics J.M. Bompard Les Mazes, Montaud, France

2.1 Introduction 2.2 The Genus Mangifera L. Distribution Ecology and habitat 2.3 Taxonomy and Systematics Taxonomic history 2.4 Phytogeography Species distribution Subgenera and section distribution 2.5 Interspecific Molecular Characterization 2.6 Region of Origin of the Genus 2.7 Origin of the Common Mango The common mango in South-east Asia 2.8 Conclusion Potential contribution of wild species to mango cultivation Source of rootstock Hybridization Potential of wild species

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2.1 Introduction The genus Mangifera is one of the 73 genera (c.850 species) belonging to the family of Anacardiaceae, in the order of Sapindales. Anacardiaceae is a family of mainly tropical species, with a few representatives in temperate regions. Malesia, which is the phytogeographic region extending from the Malay Peninsula south of the Kangar-Pattani line to the Bismarck Archipelago east of New Guinea (Whitmore, 1975) contains more species in the Anacardiaceae than any other area. Within Malesia occurrence is mainly in Western Malesia (Ding Hou, 1978b). © CAB International 2009. The Mango, 2nd Edition: Botany, Production and Uses (ed. R.E. Litz)

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Apart from mango, several other cultivated fruit trees belong to the family, for example the ambarella or Otaheite apple (Spondias dulcis Forst.) probably from Melanesia, and the yellow and purple mombins (Spondias mombin L. and S. purpurea L., respectively) from tropical America, the Bouea species from IndoMalesia, dragon plums (Dracontomelum spp.) from IndoMalesia and the Pacific region, kaffir plum (Harpephyllum caffrum Bernh. ex K. Krause) and the marula plum (Sclerocarya caffra Sond.) of southern Africa. The cashew (Anacardium occidentale L.) is from tropical America and the pistachio (Pistacia vera L.) from Iran and Central Asia. Anacardiaceous species also yield other valuable products: wood (several genera), gums and resins (Pistacia spp.), varnishes (Rhus spp. and Melanorrhoea spp., ‘lacquer trees’) and tanning materials (Rhus spp. and Schinopsis spp.). It is also a family well known for the dermal irritation produced by some of its members, such as the poison ivies and oaks (Rhus spp.) in North America, rengas (Gluta spp.) in Southeast Asia and other species including some Mangifera species whose resinous sap may induce a mild to strong allergic reaction.

2.2 The Genus Mangifera L. Distribution The range of natural distribution of the 69 Mangifera species is mainly restricted to tropical Asia, and extends as far north as 27° latitude and as far east as the Carolines Islands. Wild mangoes occur in India, Sri Lanka, Bangladesh, Myanmar, Sikkim, Thailand, Kampuchea, Vietnam, Laos, southern China, Malaysia, Singapore, Indonesia, Brunei, the Philippines, Papua New Guinea and the Solomon and Carolines Islands. The highest species diversity, c.29 species, occurs in western Malesia, especially in peninsular Malaysia and in Borneo and Sumatra, which represent the heart of the distribution range of the genus (Fig. 2.1).

Ecology and habitat The majority of Mangifera species occur as a rule as scattered individuals in tropical lowland rainforests on well-drained soils. The species are distributed mostly below 300 m, but can occur up to c.1000 m above sea level, on well-drained soils (44 species), in periodically inundated areas (ten species) and in certain types of swamp forest (i.e. M. gedebe, M. griffithii and M. parvifolia). Three species are mainly found in sub-montane forests above 1000 m and occasionally up to 1700 m above sea level (M. bompardii, M. dongnaiensis and M. orophila). There are also species that are adapted to seasonally dry climates in deciduous or semi-deciduous forests (e.g. M. caloneura, M. collina, M. timorensis and M. zeylanica). A few species occur north of the Tropic of Cancer, for example M. austro-yunnanensis and M. persiciformis in China, M.

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Fig. 2.1. Distribution of Mangifera species in the range of the genus. Numbers shown indicate the number of wild species in each area: Sri Lanka, India and Sikkim, Andaman and Nicobar Islands, Myanmar, Thailand, Indochina, China, peninsular Malaysia, Sumatra, Borneo, Java, Lesser Sunda Islands, Sulawesi, Moluccas, the Philippines, New Guinea, and Solomon Islands (the Caroline Islands not represented).

sylvatica Roxb. in Sikkim and southern China, at altitudes of 600–1900 m above sea level; apparently wild M. indica can also be found outside the tropics. Wild mangoes are large trees, 30–40 m (occasionally 54 m) in height, with tall columnar boles. Several species are exploited for their timber. The majority of wild mangoes occur as scattered individuals at very low densities in lowland forests on well-drained soils. Some of these are very rare; there are normally one to three trees above 40 cm in diameter/10 ha. Only a few species (M. gedebe, M. griffithii and M. parvifolia) are gregarious in certain types of swamp forest. Most species are evergreen although a few are deciduous in the rainforests following a dry period, and stand bare for a short time before flushes of new leaves appear. A deciduous habit that is not linked to a seasonal climate also occurs in other genera of Anacardiaceae (Ding Hou, 1978b). In the rainforest of western Malesia, Mangifera species flower and fruit very irregularly. As with many other genera in the region, mast or general fruiting at intervals of 3–8 years is the dominant pattern. In mast years, the ground beneath the trees can be covered with mangoes, whose strong smell attracts many animals. Isolated flowering may occur after a dry period and is generally followed by a poor fruit crop. The occurrence of flowering of a few species, for example the ‘lanjut’ (M. lagenifera) is only once every 5–10 years. There seem to be clear reproductive barriers between species in the wild, although limited hybridization among cultivated species has been reported (see section 2.8, Conclusion, this chapter).

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These widely scattered towering tree species, often with an inaccessible crown, are undercollected and poorly represented in herbarium collections (Bompard, 1995). Because of their irregular flowering, the flowers and fruits of a few species are still unknown. Collecting plant material is consequently very difficult, and plant explorations are still yielding new records or new species. Many species have been recently recorded for the first time, even from peninsular Malaysia, a country that has already been rather well combed by botanists, having one of the highest collecting indices in the Malesian region. Other species still await to be discovered. Sadly some species of very limited range may already have been lost to posterity by deforestation. Our very meagre knowledge of the wild mangoes is due to the fact that identification at the species level from leaves only is often difficult because of intraspecific variation in vegetative characters. Moreover, many of the original species were based on very poor specimens. Consequently, frequent misidentification of herbarium material has resulted in much confusion, requiring a critical revision of all the specimens in these collections. It is not uncommon that the same species has been described from different places under different names. For instance, M. inocarpoides described by Merrill and Perry from New Guinea in 1941, M. camptosperma and M. reba (recorded by Pierre in South Vietnam in 1897) are now recognized to be a single species M. gedebe Miquel, a species initially named in 1861 from a specimen collected in Sumatra. Mangifera longipes Griffith is now treated as M. laurina Blume, because this name takes precedence as it was validly published 4 years earlier. After thorough study of herbarium collections and field collections, a number of species have been newly described. Sixty-nine species are now recorded, including 13 species of uncertain affinities, in contrast with the 49 species recognized by Mukherjee (1949). As more collections are made, there will doubtless be further taxonomic adjustments made to the genus Mangifera.

2.3 Taxonomy and Systematics Taxonomic history Subdivision of the genus An historical review of the subdivisions of the genus Mangifera shows that two major groups have been rather consistently recognized in taxonomic treatments. Hooker (1862) was the first to recognize two sections based on the characters of the flower disc: section I with a disc broader than the ovary, and section II with a disc stalk-like or wanting. These sections were later named by Marchand (1869) Amba, an Indian name for the common mango, and Limus, a Sundanese name for M. foetida in West Java, respectively. He also added a section Manga for M. leschenaultii, which in fact belongs to the section Limus. In his monograph of the Anacardiaceae, Engler (1883) maintained Hooker’s sections, and subdivided group A (Hooker’s section I) into two groups,

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one group with four or five petals and the other group with four petals. He considered the following sequence of morphological characters to be important for classification: (i) texture of the leaves; (ii) number of fertile stamens; (iii) prominence of veins; (iv) pilosity of inflorescences; and (v) leaf shape. Pierre (1897) further divided the genus Mangifera into five sections based on flower characters, i.e. number of stamens, the attachment of stamens to the disk, and the style. Two of these five sections – namely section I Euantherae, with a short thick flower disc and 4–12 fertile stamens, and section V Marchandora then consisting of M. camptosperma (currently considered a synonym of M. gedebe) are still maintained as they form clear-cut sections. In his monograph, Mukherjee (1949) recognized two unnamed sections, conserving Hooker’s subdivision. Ding Hou (1978a) adopted the same method in his revision of the Malesian Anacardiaceae recognizing only Hooker’s two original sections and providing them with proper names and synonyms: section Mangifera (section I Hooker, section Amba Marchand, group A Engler, sections Euantherae and Marchandora Pierre) and section Limus (section II Hooker, sections Limus and Manga Marchand, group B Engler, and sections Eudiscus and Microdiscus Pierre). Most recent classification of the genus The taxonomic classification referred to herein follows that proposed by Kostermans and Bompard (1993). This treatise includes the results of collections and surveys carried out between 1986 to 1998 in Borneo and peninsular Malaysia, which were initiated and sponsored by the International Institute for Genetic Resources (now Biodiversity International) and the World Wide Fund for Nature.1 It was published under the auspices of the International Board for Plant Genetic Resources (now International Plant Genetics Resources Institute) and the Linnean Society of London. The most recent treatment of Mangifera reflects the current status of what is still fragmentary knowledge. It can provide a basis for further studies involving all aspects of the wild relatives of mango, but particularly their potential in mango breeding. Determining phylogenetic affinities based upon molecular markers could change our thinking about relationships among Mangifera species and among the cultivated forms of M. indica (see Interspecific Molecular Characterization section, this chapter). The morphological characters used for identification have been placed in the following sequence of importance: 1. Shape of the floral disc (see section Subdivision of the genus). 2. Number of fertile stamens. 3. Seed labyrinthine or not. 4. Shape of secondary branches of the inflorescences: open or lax panicle, flowers glomerulate or sub-glomerulate, the ramifications racemoid or spike like. 5. Pubescence of the inflorescence. 6. Shape, number and attachment of the nerves (ridges or fingers) at the inner surface of the petals.

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7. Shape and size of the petals. 8. Flowers tetra- or pentamerous (not a very constant character and often overlapping). 9. Reticulation of the leaves, especially of the lower surface. 10. Shape of the leaf (only fully grown leaves of sterile branches can be used). 11. Texture of the leaves. 12. Deciduous or non-deciduous trees. 13. Colour of the flowers. 14. Shape, colour and smoothness of the fruit. 15. Number and size of the stone fibres. Kostermans (Kostermans and Bompard, 1993) raised the sections to the rank of subgenus, i.e. subgenus Limus (Marchand) Kosterm., having a disc narrower than the base of the ovary, stalk-like or even lacking and subgenus Mangifera (Ding Hou) Kosterm., having a disc broader than the base of the ovary, cushion-like, often divided in four or five lobes. SUBGENUS LIMUS (MARCHAND) KOSTERM. Mangifera species of the subgenus Limus are quite distinctive and show only remote affinity with the common mango. This taxon is more primitive than the subgenus Mangifera and may be ancestral to it, although the two subgenera may have originated from two different ancestors. The subgenus Limus consists of 11 species, which are native to the rainforests of western Malesia (peninsular Thailand, Malay Peninsula, Sumatra, West Java and Borneo), with the exception of M. foetida, which extends to the east, possibly as far as New Guinea, and M. odorata which is only known in cultivation. Kostermans divided the subgenus Limus into two sections: (i) section Deciduae for deciduous trees (i.e. M. caesia, M. kemanga, M. pajang, M. superba and possibly M. blommesteinii, M. decandra and M. lagenifera); and (ii) section Perennes for non-deciduous species (i.e. M. foetida, M. leschenaultii, M. macrocarpa and M. odorata) (Kostermans and Bompard, 1993). In deciduous trees, the bracts enclosing the buds leave a characteristic collar of dense, narrow scars, which persist on old twigs and are especially prominent in M. caesia and M. kemanga. Mangifera lagenifera and M. decandra have ten stamens, five of which are fertile. The other nine species have only one (and rarely two) fertile stamen(s) and two to four staminodes. The two species with five fertile stamens (M. decandra and M. lagenifera) and M. superba, M. caesia, M. kemanga and M. blommesteinii, whose leaves are apically aggregated into rosettes at the end of massive twigs are particularly distinctive. The fruits of these species are broadly ellipsoid or pear shaped, not compressed, and have dirty whitish or pinkish mesocarp and lanceolate, and fibrous, non-ligneous leathery endocarp. Mangifera subsessilifolia shows some affinity with M. lagenifera and M. blommesteinii; however, it has been placed among the species of uncertain taxonomic position due to a lack of complete study material. This is not a very rare species, but flowering and fruiting seem to occur at intervals of, or > 5 years, similar in this respect to M. lagenifera, which can be found growing

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in old orchards in peninsular Malaysia. The flowers and fruits of M. subsessilifolia are still unknown. Mangifera foetida, M. odorata, M. caesia and M. kemanga are widely cultivated in the humid lowlands of the Malay Peninsula, Sumatra, Borneo, Java and Bali. They have also been introduced elsewhere in South-east Asia; M. caesia, M. foetida and M. odorata are grown in the southern part of the Philippines, M. foetida is grown in Myanmar, and M. odorata is found in Indochina. They have been described in general reviews of tropical fruit (Ochse and Bakhuizen, 1931; Ochse et al., 1961; Molesworth, 1967; Verheij and Coronel, 1991). Mangifera pajang, an endemic and commonly cultivated species in Borneo, is hardly known outside its native island. This deciduous tree has very stout twigs, with leaves more or less aggregate at the apices. The globose fruits, up to 20 cm in diameter, are the largest known fruits in the genus. The rough, potato-brown rind (0.5–1 cm thick) can be peeled off like that of a banana. Its bright, deep yellow, thick and fibrous flesh is sweet with a distinctive taste (Kostermans, 1965; Bompard, 1991a). In orchards in Borneo where M. foetida and M. pajang are both cultivated, forms with leaves and fruits having intermediate characters are occasionally found. Mangifera caesia, M. foetida, M. pajang and especially M. odorata are important in tropical humid regions where the common mango cannot be grown satisfactorily. Mangifera pajang has potential as an ornamental tree, having brilliant rose-red blossoms (Philipps et al., 1982). SUBGENUS MANGIFERA.

The subgenus Mangifera contains most of the species (47), and is divided into four sections: (i) section Marchandora Pierre; (ii) section Euantherae Pierre; (iii) section Rawa Kosterm.; and (iv) section Mangifera Ding Hou.

Section Marchandora Pierre. This section has only one species, M. gedebe Miquel (syn. M. camptosperma Pierre, M. inocarpoides Merr. and Perry, M. reba Pierre). The labyrinthine seed is unique to this species, wherein the inner integuments penetrate the cotyledons and form numerous irregular folds. The flat, discus-like fruit has only a very thin mesocarp. Mangifera gedebe grows in inundated places along rivers or lakes. The seed floats in water and is dispersed during periods of high water, and this may explain its wide distribution, from Myanmar through Malesia to New Guinea and the Bougainville Island. Section Euantherae Pierre. The three species in this section (M. caloneura Kurz (syn. M. duperreana Pierre), M. cochinchinensis Engler and M. pentandra Hook. f.) appear to be the most primitive among the species of the subgenus Mangifera. The flowers are characterized by the presence of five fertile stamens. The three species are mainly confined to Myanmar, Thailand, Indochina and the north of the Malay Peninsula. The region is in the transition zone from the humid tropical rainforest to monsoon forest, and these species show an adaptation to low rainfall. Mangifera cochinchinensis, which occurs in south-eastern Thailand and in Vietnam, has small oblong fruits with a thin seed; the fruits are much relished by local people in southern Vietnam, although they are very acidic. Mangifera caloneura and M. pentandra are closely

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related, and can be mistaken for M. indica. However, their leaves are more leathery, have a more conspicuously dense reticulation, and the panicles are much more hirsute than the common mango. Mangifera caloneura occurs from Myanmar through Thailand to Indochina, in lowland evergreen forests, as well as in semi-deciduous forests. It is cultivated for its acidic-sweet fruit, and has been planted along the streets of Vientiane and Ho Chi Minh City (Saigon). Mangifera pentandra, apparently native to the northern Malay Peninsula close to the Kra isthmus transition zone, is found in old orchards, in scattered locations, especially in Kedah and possibly also in peninsular Thailand. It is also grown in the Anambas Islands and in Sabah, where it might have been introduced in early times. It is a prolific bearer, with small mangoes, c.8 cm length, and ripening green or yellow. The pale orange, watery pulp has a sweet taste and few fibres. Section Rawa Kosterm. This group, consisting of nine species, is not well delimitated. Most species have thick twigs and rather coriaceous leaves seated on protruding pedestals. The small, hardly flattened ovoid or ellipsoid fruits that are black or partly red at maturity in several species are also characteristic. ‘Rawa’ is the Malay word for marsh, indicating that these species usually are found in periodically or permanently inundated areas. The five species that occur in west Malesia (M. gracilipes, M. griffithii, M. microphylla, M. paludosa and M. parvifolia) grow primarily in the swamps of south peninsular Malaysia, in central coastal areas of east Sumatra and western Borneo, and occasionally in peripheral uplands. It has also been reported from the Andaman Islands and from Thailand (Sreekumar et al., 1996; Eiadthong et al., 2000a). Mangifera andamanica and M. nicobarica are endemics from the Andaman and Nicobar Islands, respectively. Mangifera merrillii is a rare species endemic to the Philippines and M. minutifolia is known solely from a single collection from southern Vietnam. Mangifera griffithii and M. microphylla are the only cultivated species within section Rawa. The former species is considered to be representative of the section, and is cultivated along the eastern coast of peninsular Malaysia and in western Borneo, and rarely in Sumatra. The fruits are small (3–5 cm long) and oblong or ovoid; the skin is rose-red, turning purplish black at maturity. The rind is thin and easily removed from the orange-yellow pulp, which is juicy and pleasantly sweet. Different forms are recognized by local people, according to the size and taste of fruits. Mangifera microphylla is a related, but less well-known species, having thinner leaves and a rather similar fruit. Section Mangifera Ding Hou. With more than 30 species, section Mangifera is by far the largest. The common mango and the related M. laurina belong here. Species within the section have the same distribution range as the genus. The section may be divided into three groups based on floral structure and organ number variation: (i) those having pentamerous flowers; (ii) those having tetramerous flowers; and (iii) an intermediate group of species having both pentamerous and tetramerous flowers. Within these three groups, it is possible to distinguish species with either puberulous or glabrous panicles.

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Only characteristics of representative species within each group, especially those found in cultivation, are described below. Pentamerous flowers (14 species): Three species, M. laurina, M. minor and M. sylvatica, show affinity with the common mango. Mangifera laurina is a species of the lowland forests of Malesia, where it is also under cultivation in old orchards. It can be distinguished from the common mango by having lax and widely pyramidal, glabrous or sparingly puberulous panicles. The flowers are smaller and are not glomerulate; the petals have a different shape, texture and colour. The fruit resemble those of a small common mango, with orange-yellow pulp, which is almost liquid at maturity. It is generally consumed when unripe. Several forms are in cultivation; however these are now becoming rare. Mangifera laurina is well suited to the humid tropical lowlands, fruiting well in areas where the common mango cannot be grown satisfactorily; moreover, it appears to be highly resistant to anthracnose (Bompard, 1991b). Mangifera minor occurs east of Wallace’s line, from Sulawesi to New Guinea (east Malesia) and to the Carolines Islands in the east. It is adapted to a wide range of ecological conditions, growing equally well in dry savannahs and in tropical rainforests up to 1300 m. The fruit is obliquely oblong, 5–10 cm long, much narrowed, the tip obtuse, with a distinct beak and sinus. It is found in cultivation, although the yellowish fruit pulp is acidic and scant. Mangifera sylvatica is found from Sikkim (up to 1200 m) to northern Myanmar and Thailand, and apparently also in Yunnan up to 1900 m. The fruit is obliquely ovate, 8–10 cm long, much compressed distally forming a hook, has scanty whitish-yellow pulp which is almost fibreless. Other species are occasionally found in cultivation, for example M. rufocostata, which is esteemed by the Banjarese people of South Kalimantan for its very sour fruits that are used to prepare a spicy condiment with chilli. Tetramerous flowers (15 species): Mangifera altissima is apparently endemic to the Philippines, where it occurs mainly at low elevations in the forests from northern Luzon to Mindoro (Brown, 1950). The fruit is mango shaped, ovoid or ellipsoid, slightly compressed, up to 8 cm length, green or somewhat yellow when ripe, with whitish, sweetish-acidic flesh. It is commonly found in dooryards, and thrives in regions with distinct wet and dry seasons (Angeles, 1991). Mangifera torquenda occurs wild in west Malesia, and is cultivated in south Sumatra and in Borneo, where it is common in the forests and orchards of eastern Kalimantan. The sub-globose fruit, c.7.5 cm long and 6.5 cm in diameter, is yellow-green with darker spots at maturity, and has a thin rind. The pale yellow pulp has a rather pleasant sweet-acid, slightly resinous taste and a light turpentine smell. Short fibres are attached to the seed. It is closely related to M. longipetiolata. Mangifera magnifica is a common species in the rainforests of western Malesia, occasionally cultivated in central Sumatra and in West Kalimantan, where it has a special importance in the myths of Land Dayak peoples. The fruit is ovoid oblong, up to 12 cm long, 10 cm in diameter, only slightly compressed, greyish green with brown spots. The pulp is whitish, soft at

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maturity, sweetish acid. Sweeter forms are reported in central Kalimantan (J.J. Afriastini, personal communication). The stone is unique in the genus in that it lacks fibres adhering to it. Mangifera quadrifida is found from peninsular Malaysia to the Moluccas. The fruit is ellipsoid-globose, 6–8 cm long, green covered with black dots turning completely black at maturity, and has a pale yellow, sweet-acid pulp. Another form is recognized by its more coriaceous leaves, smaller fruits, c.4 cm long, having dark yellow pulp, purplish around the stone, and a sweet, palatable taste, somewhat like prunes. Both forms are cultivated in old orchards. Tetra- and pentamerous flowers (four species, and also M. indica): Mangifera casturi is related to M. quadrifida, from which it can be distinguished by leaf and fruit characters. It has never been collected in the wild, and is a favourite among the Banjarese people in south Kalimantan. The fruits are small, a little compressed and up to 6 cm in length, becoming completely black at maturity. The orange pulp is very sweet and palatable, and resembles ‘honey mango’ or ‘mangga madu’ grown in East Java. Although M. casturi bears heavily, it has a strong- to alternate-bearing habit. It is an excellent fruit for the humid tropical lowlands, and appears to be resistant to anthracnose. Several differently named forms exist; these have polyembryonic seeds. Mangifera rubropetala is also only known in cultivation, and may be a primitive race of M. indica. SPECIES OF UNCERTAIN TAXONOMIC POSITION. There is a group of 11 disparate species of uncertain taxonomic position that cannot be placed with certainty due to the absence of adequate material. There are three species only known in China.

2.4 Phytogeography Species distribution An examination of the present distribution of the genus shows that the largest number of Mangifera species in either subgenera is found in western Malesia on the Sunda shelf. A decreasing number of species occurs towards the genus boundary east of Wallace’s line in east Malesia, and in its northern and western range of distribution. While peninsular Malaysia and the islands of Sumatra and Borneo have the highest diversity of species, the number of species becomes gradually lower in east Malesia, especially in the Lesser Sunda Islands, Moluccas and New Guinea. This is explained by the geologic and paleogeographic features of the Malesian region which spans two large partly submerged continental shelves, the Asiatic shelf (Sunda Shelf linking the Malay Peninsula with the islands of Sumatra, Java, Borneo and Palawan) and the Australasian shelf (Sahul Shelf linking the Aru islands and New Guinea with Australia). During the last glaciation period (c.22,500–11,000 bp) the shelves were regions of land uncovered by the lowering of sea level, and present day peninsular Malaysia, Sumatra and Borneo were connected by

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land bridges during the late period of maximal sea lowering. During the cool periods of glacial maxima, the Malesian forest was reduced in extent, but there is no evidence that it was reduced to isolated island forests. The Sundaland and Papuasian rainforest blocks are therefore comparable to refugia in terms of species richness and the high degree of endemism (Whitmore, 1981). Mangifera has undergone major species development in west Malesia, which has remained relatively stable over a long period of time. The current vegetation of west Malesia probably differs very little from that at the end of the Tertiary (van Steenis, 1950). A lower number of Mangifera species is found in Java and the Philippines, regions less often connected with Asia during the Pleistocene. Only three species occur in New Guinea, which is largely covered with rainforest. These include M. minor, M. mucronulata and the widely distributed M. gedebe. Mangifera foetida also occurs, but may have been introduced. Mangifera minor occurs from Celebes and the Philippines to the Solomon Islands; M. mucronulata is found in the Moluccas, New Guinea and the Solomon Islands. The distribution of these species suggests a late immigration of a Laurasian genus from Sundaland via the Philippines, Sulawesi and the Moluccas into New Guinea, which is supported by the geological history of the region. No Mangifera species have ever been recorded from northern Australia. Very few species are found in peninsular India and Sikkim. From presentday distribution, there is little evidence of migration of species into the subcontinent of India after its collision with Eurasia in the middle Eocene (Audley-Charles et al., 1981). According to Mehrotra et al. (1998), fossil leaves described as Eomangiferophyllum damalgiriensis Mehr. from the Upper Palaeocene in north-eastern India are an analogue of the modern genus Mangifera. Mangifera sylvatica occurs along the northern limit of the range of Mangifera, with more or less discontinuity, from Sikkim to northern Thailand and to the southern part of Yunnan, where it is reported in mountains up to 1900 m above sea level (Anonymous, 1980). The few species that grow in southern China are very poorly known: M. austro-yunnanensis from western Yunnan, M. persiciformis from south-eastern Yunnan and southern Guizhou at latitudes up to 26°N and M. hiemalis, the ‘winter mango’ from Guangxi near the northern border Vietnam. In the revised Flora of China (Min and Barfod, 2008), M. austro-yunnanensis is considered to be conspecific with M. indica, M. hiemalis is treated as a synonym of M. persiciformis, and M. laurina is recorded from the lowland forests of south Yunnan.

Subgenera and section distribution The species distribution is especially meaningful when the ranges of the species of each subgenus and section are considered separately. Subgenus Limus All species of the subgenus Limus are restricted to the Malesian area (M. foetida and M. macrocarpa occurring in peninsular Thailand), whereas all the species

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with five fertile stamens, considered the most primitive condition, are confined to west Malesia (M. decandra in Sumatra and Borneo; M. lagenifera in the two latter areas and in peninsular Malaysia). Only M. caesia, M. foetida and closely related M. leschenaultii occur in east Malesia. Subgenus Mangifera In the subgenus Mangifera, M. gedebe is the only species belonging to the section Marchandora, and has the widest range within the genus, extending from Myanmar through Malesia to New Guinea and Bougainville Island. Section Euantherae is centred in the region from Myanmar to Vietnam. Mangifera pentandra is only known from peninsular Malaysia, the Anambas Islands and Borneo. Section Rawa is mainly in western Malaysia and shows notable diversification in the swamps and peripheral uplands in the south of peninsular Malaysia, east central Sumatra (notably the Riau province) and west Borneo. During the glacial period this area, termed the ‘Riouw pocket’ (Corner, 1978), formed a vast plain connecting the Malay Peninsula, Sumatra and Borneo, and is believed to have been filled with swamps. Mangifera merrillii is an endemic of the Philippines, M. minutifolia is an endemic of Vietnam, M. andamanica and M. nicobarica are endemics of the Andamans and Nicobar Islands. None of the species of section Mangifera occurring in mainland South-east Asia, north of the isthmus of Kra, are found in eastern Malesia; however, it would be interesting to assess the genetic relatedness of M. sylvatica and M. minor, and also M. laurina, which may prove to be phylogenetically very closely related.

2.5 Interspecific Molecular Characterization Molecular biology techniques now make it possible to assess genetic relatedness in a more precise way. Published data support some of the groupings based on anatomical characters (Kostermans and Bompard, 1993) but not entirely. RAPD (random amplification of polymorphic DNA) markers were first used in mango by Schnell and Knight (1993) and Schnell et al. (1995). Nine Mangifera species were analysed and compared to the traditional taxonomic groupings. The unweighted pair group method of arithmetic averages (UPGMA) cluster analysis for the subgenus Limus was not supportive of the separation between sections Perennes and Deciduae, which, admittedly, has a weak taxonomic basis. It confirmed the relatedness between M. foetida and M. pajang. The UPGMA cluster analysis of the subgenus Mangifera supported the current taxonomy based on flower morphology. It showed the relatedness between M. quadrifida and M. torquenda (both placed in the group of species with tetramerous flowers), but also with M. casturi, although the latter species has tetra- and pentamerous flowers. One of the most significant results was the evidence for the existence of interspecific hybridization within the studied species of the section Mangifera (see also Yonemori et al., 2002). Phylogenetic relationships among 14 Mangifera species of Thailand were analysed by comparing amplified fragment length polymorphism (AFLP)

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markers (Eiadthong et al., 2000b), and by comparing sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) (Yonemori et al., 2002). They demonstrated that the common mango was closely related to M. laurina, M. sylvatica and M. oblongifolia of subgenus Mangifera to which M. indica belongs. A close relationship between M. indica and M. sylvatica has been corroborated by Nishiyama et al. (2006), who compared signal intensity of genomic in situ hybridization (GISH) on somatic metaphase chromosomes of M. indica, using labelled DNA of eight wild Mangifera species. Furthermore, Eiadthong et al. (2000b) and Yonemori et al. (2002) have demonstrated that M. odorata, M. foetida and M. macrocarpa (of subgenus Limus) were related to M. indica. It is not surprising in the case of M. odorata whose hybrid origin (M. foetida × M. indica) has now been established, but this calls into question the position of the section Perennes. Results of molecular studies do not permit a comprehensive view of the phylogenetic relationships among the genera. So far, they are rather supportive of the groupings based on phenotype within the subgenus Mangifera (notably sections Rawa and Euantherae), but not for the subgenus Limus which will need to be redescribed, and likely restricted to the group of species related to M. caesia (M. kemanga, M. lagenifera, M. superba and possibly M. decandra). More studies will be needed to infer phylogenetic relationships within the section Mangifera. Keeping in mind the frequent misidentifications in collections and botanic gardens, herbarium specimens of studied material must be deposited in the national herbaria so that its taxonomic position can be ascertained in case of doubt.

2.6 Region of Origin of the Genus Based on morphological, phytogeographical and fossil evidence, Mukherjee (1953) argued that: although the highest number of species of both sections is concentrated in the Malay Peninsula [19 were then recorded], the centre of origin of the genus cannot be restricted to that area alone, as both the phylogenetically older species, i.e. with pentacyclic flowers (M. duperreana, now reduced to M. caloneura, and M. lagenifera), occur in Siam and Indochina, and the former is absent from Malay Peninsula.

He concluded that the genus had its origin somewhere in the Myanmar– Thailand–Indochina area or in the Malayan area. Careful identification of the greatest part of herbarium materials available has allowed a more accurate delimitation of the distribution ranges of the Mangifera species, notably of the subgenus Limus, and has revealed, among other things, that M. lagenifera does not occur north of Kra isthmus contrary to Mukherjee’s assertions. Furthermore, the ten-stamen species, M. decandra, which was described by Ding Hou in 1972 and hence was unknown to Mukherjee, is confined to Borneo and Sumatra, and to date has not been recorded from peninsular Malaysia.

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Without overemphasizing the present great species diversity of subgenera in the Malay Peninsula, Borneo and Sumatra, the available evidence points to a Sundaic origin for the genus. This, however, must not minimize the particular importance of the region stretching from Myanmar to Indochina as another centre of diversification, as attested by the range of species belonging to the section Euantherae. Unfortunately, many of the species of this region remain poorly known, and it can be expected that plant collecting in the region will yield interesting new findings. The speciation that occurred in this region with a likely radiation centre today traced by the range of the section Euantherae, is of special significance as it has given rise to the common mango.

2.7 Origin of the Common Mango The common mango apparently originated in regions on the western border of the secondary centre of diversification mentioned above. Truly wild mango trees have been recorded in Bangladesh (Chittagong Hill tract, c.23°N), northeastern India (‘undoubtedly indigenous in the evergreen tracts of valley of Assam’ according to Kanjilal et al., 1937), and in Myanmar where it was reported as ‘not unfrequent in the tropical and lower mixed forests all over Burma from Arracan and Pegu down to Tenasserim’ (Kurz, 1877). It would be desirable to assess its affinity with the species of the section Euantherae, as well as with species of other sections of the subgenus Mangifera that occur in the same area and region. It is also believed to be wild ‘in the sub-Himalayan tract, in deep gorges of the Baraitch and Gonda hills in Oudh, and the outer hills in Kamaon and Garhwal’ (Brandis, 1874). The common mango has been grown and disseminated for such a long time in India that semi-wild trees can be found in the forests throughout the subcontinent. The fruits of wild trees are said to be small and of poor quality. Watt (1891) mentioned two socalled ‘almost unaltered wild varieties’ existed under cultivation in Tirhoot, ‘one originating from Kangra, a very variable one, and the other from Sikkim which was evidently the progenitor of the varieties cultivated in Malda’.

The common mango in South-east Asia The Linnean binomial (Mangifera indica) indicates in this instance the place where the common mango was selected and improved, and not necessarily its place of its origin. It has been traditionally accepted that mango was domesticated several millennia ago in India (see Mukherjee and Litz, Chapter 1, this volume); however, it cannot be excluded that domestication occurred independently in several areas, possibly in the south-western and south-eastern regions of its centre of origin, or later differentiated in those two regions. This hypothesis would account for the differences that exist between the local polyembryonic cultivars of Myanmar, Thailand, Indochina and Indonesia, and the monoembryonic Indian cultivars. Note that polyembryony occurs

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also in the cultivated M. casturi, M. laurina and M. odorata. Aron et al. (1998) have demonstrated that polyembryony in mango is under the control of a single dominant gene. According to Juliano (1937), Bijhouwer suggested that there were two main centres of domestication of mango, ‘one in India with monoembryonic mangoes, the other in the Saigon area, Indonesia and the Philippines with polyembryonic mangoes’. The ‘Saigon’ area must in fact be extended to southern Vietnam, other parts of Indochina, Thailand and Myanmar, which were recognized by Valmayor (1962) as homes of polyembryonic mangoes. Notwithstanding, the origin of polyembryonic mangoes is probably better placed in Myanmar, and possibly the eastern part of Assam. According to Brandis (1874), ‘in Burma, the mango is not generally grafted, and seeds of a good kind, as a rule, produce fruit of a similar description’. There are only a few polyembryonic mango cultivars in India. They are restricted to the southwestern coastal region, and geographically isolated from the polyembryonic mangoes of Myanmar and South-east Asia. Analysis of genetic relatedness using RAPD markers among polyembryonic and monoembryonic cultivars grown in the west coast of southern India suggest that the polyembryonic types are unlikely to have originated from India and might have been introduced from South-east Asia (Ravishankar et al., 2004). Indian Buddhist monks might have introduced the common polyembryonic mango to South-east Asia, first along land trade routes through Myanmar, where they might have found better races, and from there into insular South-east Asia. It is well established that some local names of the common mango currently used in parts of Indonesia are of Sanskrit origin (‘ampelam’ and its cognates), and are sometimes used to designate M. laurina, which is a truly native species. Vernacular names do not always travel with a plant, and even if they did so in the case of the common mango, it is very unlikely that these introductions were the first ones and that they came obligatorily from India. In the absence of a comprehensive classification of the innumerable South-east Asian cultivated forms of the common and wild mangoes, including the countless primitive races, we have to rely on linguistics and the rich history and prehistory of this region. Vernacular names The different local names of the common mango in Indonesia (‘pauh’, ‘ampelam’ and its variants, and ‘mangga’) bear evidence of a long history of contacts with mainland Asia and India, and point to possible introduction at different times from different places. In some parts of Indonesia, the vernacular names ‘paoh’ or ‘pauh’ refer either to primitive races of the common mango, or to native species, as a rule the ones most closely resembling the common mango, for example: ‘pauh asal’ (= native mango) for M. pentandra in peninsular Malaysia; ‘pahohutan‘ or ‘pahutan’ (= forest mango) for M. altissima in the Philippines; and ‘pao pong’ (= forest mango) for M. minor in Flores, Lesser Sunda Islands. ‘Pau’ is a word belonging to Austronesian languages, nowadays spoken over a very wide area from Madagascar to the Easter Islands by people who originate from mainland Asia. These languages

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are still spoken by certain minority populations in Vietnam, Cambodia and the Mergui Archipelago off the coast of Myanmar (Bellwood et al., 1995). In Cambodia, which was occupied by the Chams from about the 3rd to the 15th century ad, ‘pa:uh’ is a Chamic word. ‘Sva:y’, used by the Khmers (as in ‘sva:y srok’ meaning mango of the village (M. indica), and ‘sva:y prey’, wild mango (i.e. M. caloneura) as attested in pre-Angkorian Khmer inscriptions dating from the 6th to the 8th century ad (Pou and Martin, 1981)) is of AustroAsiatic origin. ‘Sva:y’ has cognates in south Vietnam (‘xoay’) and in Asian languages spoken by aboriginal people in peninsular Malaysia. ‘Wai’, another cognate, is a vernacular name of M. minor in several parts of New Guinea. Pawley and Ross (1995) proposed ‘wai’ and ‘pau(q)’ as the reconstructed Proto-Oceanic terms referring, respectively, to a generic name for mango, and a species that is probably M. indica. Nowadays, these two words are generic terms for mango fruits that rather closely resemble M. indica. In the same way, ‘thayet’ which is the common vernacular name referring to M. indica in Myanmar (‘sinnin thayet’ and ‘taw-thayet’ for M. caloneura and M. sylvatica, respectively), or ‘mamuang’ in Thai languages are probably generic names. Obviously, linguistic evidence alone provided by these vernacular names is not sufficient to prove the time and place of an introduction. None the less, it is significant that in mainland South-east Asia none of the vernacular names of the common mango exhibits signs of an Indian influence, moreover, cognates of these names are also applied to primitive races in some parts of insular South-east Asia. Evidence of early trade in South-east Asia The history of plant domestication in mainland South-east Asia has undoubtedly involved introduction of plants by people migrating from the mainland into insular South-east Asia. In more recent times, there is evidence of contacts and sea trade since at least the first centuries ad between mainland and insular South-east Asia to indicate that there have been numerous opportunities for introduction of the common mango from different places at different times prior to the 4th century (before the Indianization of early South-east Asian states) into present-day Malaysia and Indonesia. Recent studies based on archaeological evidence stress the long unrecognized importance of South-east Asian trade (emanating from South-east Asia) between ports established along the Java Sea, those of mainland Asia, and India, back to the 1st century ad, and possibly earlier (Walker and Santoso, 1984). Trade routes connected the developing population centres of the mainland, such as the earliest known South-east Asian political entity, Funan, an advanced agrarian society located on the southern Vietnam coast, which became influenced by the Indians and reached the zenith of its commercial prosperity in the middle of the 3rd century (Hall, 1985). Increasingly, kingdoms organized according to the Indian concept of royalty were established in the Indonesian archipelago, for example Kutai in East Kalimantan (4th century) and Central Java (8th to 9th century), the latter being famous for the Buddhist temple at Borobudur, where sculptures depict the mango tree.

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It is highly probable that the eventual introductions of superior cultivars of polyembryonic mangoes from the south-west coast of India, ‘between the 6th and 14th century, the height of classical South-east Asian civilization and also the golden age of early south Indian civilization’ (Hall, 1985), were not the first ones. During the 16th and 17th centuries, the Portuguese and Spaniards contributed to the widest distribution of superior varieties in the archipelago, especially to the east. The name mango itself derives from the Tamil ‘man-kay’ or ‘man-ga’ (see Mukherjee and Litz, Chapter 1, this volume), which the Portuguese adapted as ‘manga’ and ‘mangueira’ when they colonized west India. Superior Philippine cultivars originated through introduction of cultivars from Indonesia, for example ‘Dodol’ into Mindanao, and from Indochina, for example ‘Carabao’ and ‘Pico’ in Luzon, the Visayas and northern Mindanao (Wester, 1920; Bondad et al., 1984). However, these introductions dating from the first half of the 17th century were also preceded by the introduction of primitive races of the common mango as well as other species into the Sulu Archipelago and Mindanao through contacts with north Borneo, as attested by their local names quoted by Wester (1920), that is mampalam (M. indica, and possibly also M. laurina), baonoh (M. caesia) and wannih (M. odorata). The South-east Asian M. indica germplasm includes many races that defy classification. Natural cross-pollination has undoubtedly occurred with native species, such as M. laurina, which was also brought into cultivation in several areas before the introduction of M. indica.

2.8 Conclusion Potential contribution of wild species to mango cultivation To date, the improvement and breeding of common mango has depended on the use of genetic variability within a single species, M. indica. Mukherjee (1957) observed that ‘similarity in chromosome number and pollen morphology in different species suggests close compatibility during hybridization and stock-scion relationship if other species are used as stock for the common mango’. Biotechnology opens new perspectives for mango improvement (Litz, 2004). As noted by Litz et al. (Chapter 18, this volume), the transformation of mango with genes from other species could address a number of plant breeding objectives.

Source of rootstock Grafting experiments between M. indica and other species are reported in the literature, for example budding of M. indica on M. foetida and M. odorata in Java (Ochse and Bakhuizen, 1931), M. odorata on M. indica in the Philippines (Wester, 1920), and M. indica on M. zeylanica in Sri Lanka (Gunaratman, 1946).

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Mangifera indica ‘Madu’ in Java, and M. laurina in Sabah have been used as rootstocks for M. casturi. Trials of grafted M. caesia on M. indica (Wester, 1920) and M. indica on M. kemanga or M. caesia (Ochse and Bakhuizen, 1931) were unsuccessful, as these two species have distinct bark features and only remote affinity with the common mango. Better compatibility can be expected using species more closely related to the common mango within the subgenus Mangifera. In West Kalimantan, M. laurina is occasionally used as a rootstock for the common mango on periodically inundated riverbanks. It has been tried as a rootstock by the Department of Agriculture in Sabah (Lamb, 1987). Campbell (2004) reported that M. casturi, M. griffithii, M. laurina, M. odorata, M. pentandra and M. zeylanica grafted on M. indica had a high percentage of success. Several species that can grow in permanently inundated areas (i.e. M. gedebe, M. quadrifida, M. griffithii and other species of the section Rawa) represent a potential source of rootstock for the development of mango cultivation on poorly drained soils or in areas liable to prolonged flood. Other species may be a source of dwarfing rootstocks.

Hybridization From our observations in Borneo, natural interspecific hybridization involving various cultivated Mangifera species can occasionally occur. Suspected hybrids were observed between wild M. gedebe and cultivated M. laurina in the lakes area along the Mahakam River in East Kalimantan, where important populations of M. gedebe occur; between cultivated M. foetida and M. pajang, two species showing close affinity, in different areas of Kalimantan where both species are grown together; and between closely related M. caesia and M. kemanga in cultivation. A hybrid origin has been suggested for M. odorata (M. indica × M. foetida), which is unknown in the wild (Ding Hou, 1978a). Based on AFLP analysis, Teo et al. (2002) and Kiew et al. (2003) have confirmed that M. odorata is a hybrid between M. foetida and M. indica. The index of similarity showed that M. odorata is closer to M. foetida (76% similarity) than it is to M. indica (66%). Yamanaka et al. (2006) showed a high genetic similarity among 11 landraces of M. odorata from the Malaysian Agricultural Research and Development Institute (MARDI) gene bank. Higher variability can be expected from Sumatra and Java samples. Existing information about experimental interspecific hybridization is scarce. According to Mukherjee et al. (1968), successful crosses between M. odorata and M. zeylanica were made in India.

Potential of wild species There is little doubt that wild mangoes are potentially valuable in breeding programmes. Some species have important horticultural implications as they demonstrate many desirable characteristics (Bompard, 1993). Fairchild (1948)

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noted that crosses between the common mango and related five-stamen species of the section Euantherae might produce hybrids with better pollinating quality. Mangifera pentandra, which is grown in peninsular Malaysia and Sabah, is a prolific bearer, due to its high proportion of hermaphrodite to male flowers. Stress resistance In the Malesian rainforests, wild mangoes thrive well under an ever-humid climate, without a prolonged dry season, i.e. is in areas with an annual rainfall > 4000 mm and no monthly mean < 100 mm and where the common mango cannot be grown satisfactorily. Species, occurring in subtropical areas, including primitive races of the common mango, or in high altitude tropical forests, should be evaluated for cold tolerance, opening up the possibilities for mango production in subtropical and Mediterranean areas. Mangifera laurina and other species related to the common mango that grow in the rainforest (e.g. M. minor in New Guinea) are apparently immune to anthracnose. Sharma and Choudhury (1976) also observed that trees of an unknown wild race found in the Tripura State (north-eastern India) were free from mango malformation. Potential new fruits Extensive, yet largely unrecorded variability also exists among the non-indica species under cultivation. Sadly, this gene pool is barely represented in existing collections, and is rapidly vanishing. An increasing number of horticulturists are demonstrating a keen interest in the wild relatives of the mango. It is hoped that local peoples who have contributed to the recognition and maintenance of these species can benefit from future innovative mango breeding. Since early times, local peoples have planted seeds collected from trees that were observed to produce better quality fruits in the forests around their settlements. In areas now completely devoid of lowland primary forest, especially in Sumatra and Borneo, the only wild relatives still found are those which have been integrated into indigenous agroforests which represent gene banks for an amazing diversity of fruit trees. A tenuous but constant selection pressure over many centuries has resulted in improved selections of several species. Today, some of these selections hold economic importance for their intrinsic characteristics. In Malesia, forms of M. odorata and M. foetida with sweeter and less fibrous flesh have been identified. The ‘wani’, a form of M. caesia from Bali and Borneo, has green-skinned fruit with milky white soft flesh and a sweet taste quite different from the fruit of common forms of M. caesia. In addition, there are many interesting selections of M. casturi, M. griffithii and M. torquenda. Further improvement of these wild mangoes is especially desirable owing to their local economic importance in the wet tropical regions. Use of vegetative propagation methods must be encouraged. With proper selection, there is every reason to believe that other Mangifera species can become valuable commercial fruits.

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Acknowledgement Thanks are due to Dr Dawn Frame who assisted in correcting the text.

Note 1Surveys

were carried out in Kalimantan in cooperation with the Indonesian Institute of Science (LIPI) and the Indonesian Commission on Germplasm, and in Malaysia with the Forest Research Institute of Malaysia (FRIM).

References Angeles, D.E. (1991) Mangifera altissima Blanco. In: Verheij, E.W.M. and Coronel, R.E. (eds) Plant Resources of South-east Asia No.2: Edible Fruits and Nuts. Pudoc-DLO, Wageningen, the Netherlands, pp. 206–207. Anonymous (1980) Mangifera L. In: Cheng, M. and Ming, T.L. (eds) Flora Reipublicae Popularis Sinicae. Vol. 45(1). Science Press, Beijing, Peoples Republic of China, pp. 73–78. Aron, Y., Czosnek, H., Gazit, S. and Degani, C. (1998) Polyembryony in mango (Mangifera indica L.) is controlled by a single dominant gene. HortScience 33, 1241–1242. Audley-Charles, M.G., Hurley, A.M. and Smith, A.G. (1981) Continental movements in the mesozoic and cenozoic. In: Whitmore, T.C. (ed.) Wallace’s Line and Plate Tectonics. Clarendon Press, Oxford, UK, pp. 9–23. Bellwood, P., Fox, J.J. and Tryon, D. (eds) (1995) The Austronesians, Historical and Comparative Perspectives. The Australian National University, Canberra. Bompard, J.M. (1991a) Mangifera caesia Jack and Mangifera kemanga Blume, Mangifera foetida Lour. and Mangifera pajang Kostermans. In: Verheij, E.W.M. and Coronel, R.E. (eds) Plant Resources of South-east Asia No.2: Edible Fruits and Nuts. PudocDLO, Wageningen, the Netherlands, pp. 207–211. Bompard, J.M. (1991b) Mangifera laurina Blume and Mangifera pentandra Hooker f.; Mangifera odorata. In: Verheij, E.W.M. and Coronel, R.E. (eds) Plant Resources of South-east Asia No.2: Edible Fruits and Nuts. Pudoc-DLO, Wageningen, the Netherlands, pp. 216–220. Bompard, J.M. (1993) The genus Mangifera re-discovered: the contribution of wild species to mango cultivation. Acta Horticulturae 341, 69–77. Bompard, J.M. (1995) Surveying Mangifera in the tropical rain forests of South-east Asia. In: Guarino, L., Ramanatha Rao, V. and Reid, R. (eds) Collecting Plant Genetic Diversity. Technical Guidelines. CAB International, Wallingford, UK, pp. 627–637. Bondad, N.D., Rivera, F.N., Agcopra, D.B. and Minh Tam Aurin (1984) Philippine mangoes and their relationship to South-east Asian cultivars. Philippine Geographical Journal 28, 59–71. Brandis, D.D. (1874) Forest Flora of North West and Central India. Allen, London, pp. 125–127. Brown, W.H. (1950) Useful Plants of the Philippines. Vol. 2. Bureau of Science, Manila, the Philippines, pp. 336–340. Campbell, R.J. (2004) Graft compatibility between Mangifera species and Mangifera indica L. ‘turpentine’ rootstocks and their subsequent horticultural traits. Acta Horticulturae 645, 311–313.

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Corner, E.J.H. (1978) The Freshwater Swamp-forest of South Johore and Singapore. Botanic Gardens, Parks and Recreation Department, Singapore. Ding Hou (1972) A new species of Mangifera. Reinwardtia 8, 323–327. Ding Hou (1978a) Flora Malesiana Praecursores 56 (Anacardiaceae). Blumea 24, 1–41. Ding Hou (1978b) Anacardiaceae. 4. Mangifera. In: van Steenis, C.G.G.J. (ed.) Flora Malesiana I. Vol. 8. Rijksherbarium, Leiden, the Netherlands, pp. 423–440. Eiadthong, W., Yonemori, K., Sugiura, A., Utsunomiya, N. and Subhadrabandhu, S. (2000a) Records of Mangifera species in Thailand. Acta Horticulturae 509, 213–224. Eiadthong, W., Yonemori, K., Sugiura, A., Utsunomiya, N. and Subhadrabandhu, S. (2000b) Amplified fragments length polymorphism analysis for studying genetic relationships among Mangifera species in Thailand. Journal of the American Society for Horticultural Science 125, 160–164. Engler, A. (1883) Anacardiaceae. In: de Candolle, A.P. (ed.) Monographiae Phanerogamarum. Vol. 4. Masson, Paris, pp. 195–215. Fairchild, D. (1948) The mango relatives of Cochin China; those with five-stamen flowers. Proceedings of the Florida State Horticultural Society 61, 250–255. Gunaratman, S.C. (1946) The cultivation of mango in the dry zone of Ceylon (part II). Tropical Agriculturist 102, 23–30. Hall, K.R. (1985) Maritime Trade and State Development in Early South-east Asia. Allen and Unwin, Sydney. Hooker, J.D. (1862) Mangifera. In: Bentham, G. and Hooker, J.D. (eds) Genera Plantarum. Vol. I. Reeve and Co., London, p. 420. Juliano, J.B. (1937) Embryos of Carabao mango (Mangifera indica Linn.). Philippines Agriculturist 25, 749–760. Kanjilal, U.N., Kanjilal, P.C. and Das, A. (1937) Mangifera. Flora of Assam 1(2), 335–336. Kiew, R., Teo, L.L. and Gan, Y.Y. (2003) Assessment of the hybrid status of some Malesian plants using Amplified Fragment Length Polymorphism. Telopea 10, 225–233. Kostermans, A.J.G.H. (1965) New and critical Malesian plants VII. Reinwardtia 7, 19–46. Kostermans, A.J.G.H. and Bompard, J.M. (1993) The Mangoes. Botany, Nomenclature, Horticulture, and Utilization. Academic Press, London. Kurz, S. (1877) Forest Flora of British Burma. Vol. 1. Burma Government Printers, Calcutta, pp. 304–305. Lamb, A. (1987) The potential of some wild and semi-wild fruit trees in Sabah and the progress made by the Department of Agriculture, Sabah in establishing a germplasm pool. Paper presented in Forest Research Institute Malaysia, Kepong, Malaysia. Litz, R.E. (2004) Biotechnology and mango improvement. Acta Horticulturae 645, 85–92. Marchand, L. (1869) Révision du Groupe des Anacardiacées. Baillière, Paris. Mehrotra, R.C., Dilcher, D.L. and Awasthi, N. (1998) A palaeocene Mangifera-like leaf fossil from India. Phytomorphology 48, 91–100. Min, T. and Barfod, A. (2008) Anacardiaceae, Mangifera. In: Wu, Z.Y., Raven, P.H. and Hong, D.Y. (eds) Flora of China. Vol. 11. Missouri Botanical Garden Press, St Louis, Missouri and Science Press, Beijing, pp. 338–339. Available at: http://flora.huh. harvard.edu/china/mss/volume11/index.htm#alphabetical_list (accessed 5 August 2008). Molesworth, A.B. (1967) Malayan Fruits. An Introduction to the Cultivated Species. Donald Moore Press, Singapore. Mukherjee, S.K. (1949) A monograph of the genus Mangifera L. Lloydia 12, 73–136. Mukherjee, S.K. (1953) Origin, distribution and phylogenetics affinities of the species of Mangifera L. Journal of the Linnean Society, Botany 55, 65–83.

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J.M. Bompard Mukherjee, S.K. (1957) Cytology of some Malayan species of Mangifera. Cytologia 22, 239–241. Mukherjee, S.K., Singh, R.N., Majumder, P.K. and Sharma, P.K. (1968) Present position regarding breeding of mango (Mangifera indica L.) in India. Euphytica 17, 462–467. Nishiyama, K., Choia, Y.A., Honshoa, C., Eiadthong, W. and Yonemori, K. (2006) Application of genomic in situ hybridization for phylogenetic study between Mangifera indica L. and eight wild species of Mangifera. Scientia Horticulturae 110, 114–117. Ochse, J.J. and Bakhuizen, R.C. (1931) Fruits and Fruitculture in the Dutch East Indies. G. Kolff, Batavia (Jakarta), Indonesia. Ochse, J.J., Soulé, M.J, Dijkman, M.J. and Wehlburg, C. (1961) Tropical and Subtropical Agriculture. Vol. 2. MacMillan, New York. Pawley, A. and Ross, M. (1995) The prehistory of Oceanic languages: a current view. In: Bellwood, P., Fox, J.J. and Tyron, D. (eds) The Austronesians. The Australian National University, Canberra, pp. 39–74. Philipps, A., Philipps, S.M. and Philipps, C. (1982) Some ornamental plants of Sabah. Nature Malaysiana 7(4), 20–27. Pierre, L. (1897) Flore Forestière de la Cochinchine. Vol.1, fasc. 23. Doin, Paris. Pou, S. and Martin, M. (1981) Les noms des plantes dans l’épigraphie ancienne khmère. Asie du Sud Est et Monde Insulindien 12, 3–70. Ravishankar, K.V., Chandrashekara, P., Sreedhara, S.A., Dinesh, M.R., Lalitha, A. and Saiprasad, G.V.S. (2004) Diverse genetic bases of Indian polyembryonic and monoembryonic mango (Mangifera indica L) cultivars. Current Science 87, 870–871. Schnell, R.J. and Knight, R.J., Jr (1993) Genetic relationships among Mangifera spp. based on RAPD markers. Acta Horticulturae 341, 86–92. Schnell, R.J., Ronning, C.M. and Knight, R.J. (1995) Identification of cultivars and validation of genetic relationships in Mangifera indica L. using RAPD markers. Theoretical and Applied Genetics 90, 269–274. Sharma, D.K. and Choudhury, S.S. (1976) Occurrence of an unknown wild race of Mangifera in Tripura. Current Science 45, 305–306. Sreekumar, P.V., Veenakumari, K. and Padhye, P.M. (1996) Mangifera griffithii (Anacardiaceae): an addition to the Indian mangoes, from Andaman Islands, India. Malayan Nature Journal 50, 85–87. Teo, L.L., Kiew, R., Set, O., Lee, S.K. and Gan, Y.Y. (2002) Hybrid status of kuwini, Mangifera odorata (Anacardiaceae) verified by amplified fragment polymorphism. Molecular Ecology 11, 1465–1469. Valmayor, R.V. (1962) The Mango, its Botany and Production. University of the Philippines, Laguna, the Philippines. van Steenis, C.G.G.J. (1950) The delimitation of Malaysia and its main plant geographical divisions. In: van Steenis, C.G.G.J. (ed.) Flora Malesiana. Series I. Sijthoff and Noordhoff Publishers, Groningen, the Netherlands, pp. 70–75. Verheij, E.W.M. and Coronel, R.E. (eds) (1991) Plant Resources of South-east Asia No.2: Edible Fruits and Nuts. Pudoc-DLO, Wageningen, the Netherlands. Walker, M.J. and Santoso, S. (1984) Romano-Indian pottery in Indonesia. In: van de Velde, P. (ed.) Prehistoric Indonesia, a Reader. Foris, Dordrecht, the Netherlands, pp. 376–383. Watt, G. (1891) A Dictionary of the Economic Products of India. Vol. 5. Office of the Superintendent, Government Printing, Calcutta; W.H. Allen, London, pp. 146–157. Wester, P.J. (1920) The Mango. Bureau of Agriculture Bulletin No. 18. Bureau of Agriculture, Manila, the Philippines. Whitmore, T.C. (1975) Tropical Rain Forests of the Far East. Clarendon, Oxford, UK.

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Whitmore, T.C. (1981) Paleoclimate and vegetation history. In: Whitmore, T.C. (ed.) Wallace’s Line and Plate Tectonics. Clarendon, Oxford, UK, pp. 36–42. Yamanaka, N., Hasran, M., Xu, D.H., Tsunematsu, H., Idris, S. and Ban, T. (2006) Genetic relationship and diversity of four Mangifera species revealed through AFLP analysis. Genetic Resources and Crop Evolution 53, 949–954. Yonemori, K., Honsho, C., Kanzaki, S., Eiadthong, W. and Sugiura, A. (2002) Phylogenetic relationships of Mangifera species revealed by ITS sequences of nuclear ribosomal DNA and a possibility of their hybrid origin. Plant Systematics and Evolution 231, 59–75.

3

Important Mango Cultivars and their Descriptors R.J. Knight, Jr,¹ R.J. Campbell² and I. Maguire¹ 1University

of Florida, Florida, USA ²Fairchild Tropical Botanic Garden, Florida, USA

3.1 Introduction 3.2 Criteria for Cultivar Description 3.3 Mango Cultivars ‘Alfa’ (Brazil) ‘Alphonso’ (India) ‘Amelie’ (West Africa) ‘Arumanis’ (Indonesia) ‘Ataulfo’ (Mexico) ‘B74’ (‘Calypso’™) (Australia) ‘Banganpalli’ (India) ‘Beta’ (Brazil) ‘Bombay Green’ (India) ‘Cambodiana’ (Vietnam) ‘Carabao’ (Philippines) ‘Chausa’ (India) ‘Cogshall’ (Florida, USA) ‘Coração de Boi’ (Brazil) ‘Dasheheri’ (India) ‘Espada’ (Brazil) ‘Ewais’ (Egypt) ‘Excellent Succari’ (Egypt) ‘Extrema’ (Brazil) ‘Fajri’ (India) ‘Fernandin’ (India) ‘Genovea’ (Egypt) ‘Glenn’ (Florida, USA) ‘Golek’ (Indonesia) ‘Haden’ (Florida, USA) ‘Himsagar’ (India) ‘Hindi Besennara’ (Egypt) ‘Hindi Khassa’ (Egypt) 42

43 44 45 45 45 46 46 46 47 47 47 47 48 48 48 49 49 49 49 50 50 50 50 51 51 51 51 52 52 52 52

© CAB International 2009. The Mango, 2nd Edition: Botany, Production and Uses (ed. R.E. Litz)

Mango Cultivars and Descriptors ‘Irwin’ (Florida, USA) ‘Julie’ (West Indies) ‘Keitt’ (Florida, USA) ‘Kensington’ (Australia) ‘Kent’ (Florida, USA) ‘Khanefy’ (Egypt) ‘Kyo Savoy’ (Thailand) ‘Langra’ (India) ‘Mabrouka’ (Egypt) ‘Madame Francis’ (Haiti) ‘Mallika’ (India) ‘Manila’ (Mexico) ‘Manzanillo’ (Mexico) ‘Mesk’ (Egypt) ‘Mulgoa’ (India to Florida, USA) ‘Nabeel’ (Egypt) ‘Nam Doc Mai’ (Thailand) ‘Neelum’ (India) ‘Nuwun Chan’ (Thailand) ‘Okrung’ (Thailand) ‘Osteen’ (Florida, USA) ‘Pairi’ (India) ‘Palmer’ (Florida, USA) ‘Rosa’ (Brazil) ‘Sensation’ (Florida, USA) ‘Suvarnarekha’ (India) ‘Tahar’ (Israel) ‘Taimour’ (Egypt) ‘Tommy Atkins’ (Florida, USA) ‘Totapuri’ (India) ‘Turpentine’ (West Indies) ‘Vallenato’ (Colombia) ‘Van Dyke’ (Florida, USA) ‘White Succari’ (Egypt) ‘Zebda’ (Egypt) 3.4 Conclusion

43 53 53 53 54 54 54 55 55 55 55 56 56 56 56 57 57 57 58 58 58 59 59 59 59 60 60 60 61 61 61 62 62 62 62 63 63

3.1 Introduction The mango (Mangifera indica L.) has traditionally been grown in an area that extends southwards and eastwards from India through Myanmar and Vietnam to Indonesia. It probably is not indigenous to the Philippines, where it has long been cultivated (Valmayor, 1962), but Mangifera species are endemic there (Bondad, 1982). This crop is best adapted to a warm tropical monsoon climate, with a pronounced dry season followed by rains. Fruit of the best quality is usually produced in such areas, but specific races are known to fruit in humid regions. For example, some Mangifera species bear dependably on the island of Borneo, where most standard cultivars do not mature normal crops of fruit. Numerous Mangifera species closely related to the common mango are indigenous to

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Borneo and nearby parts of Malaysia and Indonesia, and this region is the probable centre of diversity for this genus (see Bompard, Chapter 2 this volume). Most crops long cultivated over an extended time and area show considerable diversity, reflecting different selection criteria in different regions of culture as well as genetic responses to varied environmental influences. Certainly this is true of the mango. Indian cultivars differ markedly from those grown in South-east Asian countries and in Egypt. An additional factor that has promoted genetic diversity in the group recently has been the widespread introduction of this crop into new areas of cultivation, many in the western hemisphere, over the last 500 years. In this manner, genetically diverse germplasm has been brought from widely dispersed areas of the original range of the species and grown in mixed plantings where, through the cross-pollination natural to the species, new genetic combinations have been made and selected under many varying conditions of microclimate. In Florida, since the late 18th century, enough such importations and genetic recombinations have occurred to qualify the southern part of this state as a secondary centre of diversity for the crop. A new group of mango clones designated the Florida cultivars has been exported to Brazil, Israel, Australia and other places where the process of increasing diversity under new and varying cultural and environmental conditions continues (Knight and Schnell, 1994; Schnell et al., 2006). Some Florida cultivars, most notably ‘Haden’, have been important in aiding the establishment of a modern mango industry in other parts of the world (Knight and Schnell, 1994), and the phenomenon first observed in Florida is now occurring elsewhere; we are presented with the prospect of the importation of cultivars of outstanding merit from their countries of origin to be grown, first experimentally and then commercially, in new regions. For this reason it is important to become familiar with the characteristics of a group of cultivars that currently are known in the commerce and/or horticulture of one or more countries, and that may have potential for expanded culture or use in breeding.

3.2 Criteria for Cultivar Description In the recent past, efforts to assemble lists of mango descriptors produced two publications that cover the subject (Mukherjee, 1985; IBPGR (now International Plant Genetic Resources Institute, IPGRI), 1989) and provide people who manage collections with morphological criteria to identify cultivars. The Descriptor List used by IPGRI documents passport data (identifying the accession and information recorded by collectors), characterization (recording characters considered to be highly heritable which can easily be seen in the field and are expressed in all environments) and preliminary evaluation, which records a limited number of additional traits thought desirable by a consensus of users of the crop. Plant data are important in preliminary evaluation, and include for the tree, habit and height of the mature tree; for the leaf, shape, length and width, and colour of the young leaf; and for the inflorescence, position, shape, density of flowers, length, colour, hairiness, presence or absence of leafy bracts, and percentage of flowers in an average inflorescence. (Some research indicates

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that both leafy bracts and number of perfect flowers are influenced by local conditions and vary in their expression with differing environments.) Additional plant data used in initial evaluation include those for the flower, diameter in millimetres, type (pentamerous, tetramerous or both), nature of disc (swollen, broader or narrower than ovary, reduced or absent) and number of stamens; fruit, length, width and thickness, weight, shape, skin colour (which may be compared with reference cultivars), skin thickness, skin texture, ratio of pulp to skin and stone, texture of pulp, adherence of skin to pulp, fibre in pulp and its quantity and length, and stem insertion; and stone, length, weight, veins and pattern of venation, presence or absence of fibres and their length. Additional plant data for leaves, inflorescence and fruit have been collected and some of these, notably season (maturity period), productivity, eating quality and attractiveness are quite important. Unfortunately, from the viewpoint of those who expect to apply these criteria outside the Indian subcontinent, reference cultivars are for the most part Indian and many are not readily available outside India. Other important characters that have been evaluated or proposed for evaluation include susceptibility to stress (drought, wind, flooding), susceptibility to specific diseases and pests, molecular markers, cytological characters and identified genes. Because of the extreme comprehensiveness of this list and the limited availability of many of the proposed descriptor evaluations at this time, we have tried to utilize such information as is available to make the comparison, identification and evaluation of specific well-known cultivars a practical possibility.

3.3 Mango Cultivars A list of mango cultivars that are of interest in areas other than their places of origin, with descriptions intended to help differentiate them, follows (see Plates 4–40). Spelling and name variants in some cases represent efforts to transliterate from other orthographies to the Roman alphabet, and in others reflect regional differences in usage. ‘Alfa’ (Brazil) A monoembryonic cultivar developed by EMBRAPA Cerrado, Brazil, from crossing ‘Mallika’ × ‘Van Dyke’. The tree is semi-dwarf in habit and highyielding, resistant to Oidium mangiferae and malformation, and moderately resistant to anthracnose (Colletotrichum gloeosporioides); the fruit is large (435 g), pink-red, firm, medium fibrous and of good quality (16% total soluble solids (TSS), 0.23% acidity) (Pinto et al., 2004). ‘Alphonso’ (India) Also known as ‘Appus’, ‘Badami’, ‘Gundu’, Haphus’, ‘Kagdi’, ‘Khader’ and ‘Khader Pasand’. The tree is moderately large, with broadly rounded, dense

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canopy; the fruit (Plate 4) is yellow, ovate-oblique, averaging 6 cm long by 5 cm broad, weighing 225–325 g (mean 226 g); the skin is thin; the flesh is firm to soft, low in fibre, yellow, sweet with characteristic aroma and with a very pleasant taste preferred by many who know this cultivar, bringing premium prices on Indian and international markets. Seed is monoembryonic in a large, woody stone; the quality is excellent; ripening fruit in late to midseason. Bearing is irregular, medium to heavy in India, but light and irregular in Florida (Prasad, 1977; R.J. Knight, Jr, personal communication, 1995).

‘Amelie’ (West Africa) Also known as ‘Gouverneur’ in the Caribbean. The tree is tall with a rounded, dense canopy; the fruit is green to orange-yellow with the advance of the season, rounded, 10–15 cm long by approximately 10 cm broad by approximately 7.8 cm thick and weighing 300–600 g (average 360 g). The skin is thick and separated with difficulty; the flesh is soft, juicy, melting, without fibre, a deep orange colour, sweet and perfumed, free from turpentine, and provides the best of mango tastes. Seed is monoembryonic in a medium-sized, elongate, narrow stone that adheres to the flesh, having a few short, pliable fibres that are not objectionable; the quality is excellent; the season early. The fruit closely resembles that of ‘Julie’. ‘Amelie’ is exported to France, along with ‘Kent’, from Burkina Faso, Ivory Coast and Mali. ‘Amelie’ is increasing in popularity on the French market, chiefly in Paris and the surrounding area. It brings lower prices than cultivars with blushed fruit because the consumer is not always aware when it is ripe (Naville, 1985, 1986; R. LePrette, personal communication, 1996).

‘Arumanis’ (Indonesia) Also referred to as ‘Harumanis’. The tree is vigorous and tall with a slightly open canopy. The fruit (Plate 5) is greenish yellow with large, light-yellow dots, elongate oblong with rounded base, 11–14 cm long by 6.6–7.5 cm broad by 4.75–6.5 cm thick, weighing 200–350 g. The skin is thick, tough and easily separated, the flesh firm and juicy with little fibre, lemon yellow, sweet, slightly insipid with a strong aroma, of poor to fair quality. Seed is polyembryonic in a thick, woody stone; this cultivar ripens midseason and bears regularly. Relatively easy to propagate by graftage, scionwood survives well; widely planted in humid parts of the world where many better-quality cultivars fail to fruit (R.J. Knight, Jr, personal communication, 1995).

‘Ataulfo’ (Mexico) A polyembryonic cultivar sold in North American markets under the name ‘Ataulfo’ and as ‘Champagne’™. Originated in Tapachula, Chiapas, Mexico reportedly from seed brought from Costa Rica in about 1930. The tree is

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vigorous and upright, a mid-range producer with production averages of 10–20 t/ha possible. The tree is not highly adaptive to different climatic/ edaphic conditions. It is moderately resistant to anthracnose disease. The fruit (Plate 6) is small (200–300 g), elongate, of good quality, sweet with slight acidity, yellow, firm, standing shipping stress well, and ripens from early to midseason (Campbell et al., 2002; Magallanes-Cedeño, 2004).

‘B74’ (‘Calypso’™) (Australia) A monoembryonic cultivar that originated from the controlled cross of ‘Sensation’ × ‘Kensington’. The tree is upright, with low to moderate vigour and is highly productive, with good tolerance of flower and fruit diseases; the fruit (Plate 7) is moderately large (457.4 ± 38.1 g), ovate (10.12 ± 0.27 cm long by 9.13 ± 0.28 cm wide), fibre-free and firm, bright yellow overlaid with red blush, with extended shelf life and potential for shipment to overseas markets; ripens late in the season; patented (Whiley, 2001; Whiley and Hofman, 2006).

‘Banganpalli’ (India) Also called ‘Beneshan’ and ‘Chappatai’. The tree is medium sized with a rounded canopy; the fruit is primrose-yellow, ovate-oblique, large and the skin smooth, thin and shiny, flesh firm to meaty with juice moderately abundant, without fibre, maize-yellow, with pleasant aroma and sweet taste. Seed is monoembryonic, in an oblong stone covered with sparse fibres; quality good; ripens midseason and bears heavily (Singh, 1960).

‘Beta’ (Brazil) A cultivar developed by EMBRAPA Cerrado, Brazil, from crossing ‘Amrapali’ × ‘Winters’ (M20222 United States Department of Agriculture (USDA)). The tree is moderately vigorous and free of malformation, high-yielding but irregular, moderately resistant to anthracnose and Oidium; the fruit is small (310 g), yellow, firm with low fibre, of excellent quality (24.8% TSS, 0.16% acidity) (Pinto et al., 2004).

‘Bombay Green’ (India) Also called ‘Bhojpuri’, ‘Bombai’, ‘Hiralal Bombai’, ‘Kali Bombai’, ‘Laile Alipur’, ‘Malda’, ‘Sarauli’ and ‘Sheeri-Dhan’. The tree is tall and erect; the fruit (Plate 8) is apple green with ochre blush at the base and on some exposed parts, dots abundant, with brown specks in the middle, ovate with beak almost missing, medium sized, with tough, thick, non-adhering smooth skin; the flesh is cadmium-orange, firm and juicy with scanty fibre just under the skin,

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very sweet with pleasant aroma, of very good quality; seed is monoembryonic in a full, thick, medium-sized stone. This cultivar ripens early in the season and is a medium bearer. ‘Bombay Yellow’ is said to be practically identical to this cultivar but for a slight difference in fruit colour. The present ‘Bombay Green’ is said to be a degenerate form of the original one (Singh, 1960). In Jamaica it is sometimes called ‘Peter’, which suggests a confusion with ‘Pairi’, but the Jamaican ‘Peter’ is without the bright red blush normal to ‘Pairi’.

‘Cambodiana’ (Vietnam) Also known as ‘Xoai Voi’. The tree is moderately vigorous, with a dense, rounded canopy; the fruit (Plate 9) is greenish yellow, unblushed with a few small white dots, oblong to ovate, 9–11.5 cm long by 6.5–7.5 cm broad by 5–6 cm thick, weighing 220–340 g; the skin is thin, tender and adherent; the flesh contains little fibre, is tender and melting, lemon yellow, sweet and mildly subacid with a pleasant aroma; the seed is polyembryonic in a thick, woody stone. Ripens early in the season. Brought to Florida in 1902, where it gave rise to the ‘Saigon’ landrace (Campbell, 1992).

‘Carabao’ (Philippines) The tree is vigorous, forming a large and dense canopy; the fruit (Plate 10) is greenish to bright yellow, brushed with a few small green dots, long and slender, with base rounded to slightly flattened, 11–13 cm long by 6.5–7 cm broad by 6–6.5 cm thick, weighing 270–440 g; the skin is thick, medium tough and easily separated; the flesh is without fibre, tender and melting, lemon yellow, spicy and sweet with a mild aroma, of good to excellent quality; seed is polyembryonic in a thin, papery stone. Ripens early in the season (Campbell, 1992). This is a heavy bearer that may alternate; however, it can be induced to fruit by potassium nitrate treatment in the tropics (Bondad and Linsangan, 1979). It is highly resistant to bacterial black spot (Xanthomonas campestris pv. mangiferaeindicae) in Queensland (Mayers et al., 1988). It was introduced to Florida in 1909. ‘Carabao’ is important in commerce between the Philippines and Japan and is increasingly imported into the USA.

‘Chausa’ (India) Also called ‘Samar Bahisht Chausa’ and ’Khajari’. The tree is tall and spreading; the fruit is canary yellow to raw sienna when fully ripe, with numerous obscure medium-sized dots with minute specks inside them, oblong with prominent beak, obtuse to rounded, medium sized; the skin is thin and somewhat adhering, pulp raw sienna, soft and juicy with scanty fine, long fibres near the skin; the fruit is very sweet with a luscious, delightful aroma, of excellent quality; seed is monoembryonic in a thick, medium-sized oblong

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stone with fine, short fibres all over the surface and a tuft of long fibres on the ventral edge. Ripens late in the season and is a light bearer (Singh, 1960).

‘Cogshall’ (Florida, USA) A monoembryonic cultivar that originated on Pine Island in Lee County. The tree is relatively small, forming a rounded canopy, moderately susceptible to anthracnose and consistently productive; the fruit is medium to large, averaging about 350 g, yellow with a bright crimson blush, oblong (11–14 cm long by 7.5–8.5 cm broad by 6.2–8 cm thick) of excellent quality, rich and sweet in taste, with tender skin and soft flesh. Ripens early to midseason over about 4 weeks, a season longer than some cultivars. It is recommended for the home garden, not commercial planting, in Florida but is now grown commercially on Mauritius and marketed in France. Seedling of ‘Haden’ (Campbell and Campbell, 1995; Schnell et al., 2006).

‘Coração de Boi’ (Brazil) The tree is vigorous, precocious and productive; the fruit is greenish yellow and intense red on the side exposed to the sun, cordiform, medium sized, pulp yellow and fibrous. The seed is polyembryonic. There are two seasons in São Paulo, January–February and September–December. This is one of the best-known commercial cultivars in São Paulo state (Sampaio, 1980; A.C. Pinto, personal communication, 1996; L.C. Donadio, personal communication, 1996).

‘Dasheheri’ (India) Also known as ‘Dasheri’ and ‘Aman Dusehri’. The tree is of medium height and moderate vigour, spreading, with a rounded, medium-dense canopy; the fruit is primrose to canary yellow with abundant light-yellow dots, oblong to oblong-oblique with base rounded to obliquely rounded, medium sized, skin smooth, medium thick, tough and non-adhering; the flesh is yellow, firm, with almost no fibre, scanty juice and a delightful aroma, very sweet taste, of excellent quality; seed is monoembryonic in a thick, medium-sized stone. Ripens midseason and is heavy bearing; fruit keeps well (Singh, 1960).

‘Espada’ (Brazil) The tree is tall and develops rapidly, with a dense canopy, very productive; the fruit is intense green or greenish yellow, oblong-elongate with a concave base, medium sized, with smooth, thick skin; the flesh has much fibre, is eggyellow, with a strong aroma of turpentine. The quality is considered good for fresh consumption. The polyembryonic seed is in an oblong stone, covered

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with soft fibres and many nerves. There are two seasons per year in São Paulo, January–February and November–December (Sampaio, 1980; A.C. Pinto, personal communication, 1996).

‘Ewais’ (Egypt) A polyembryonic cultivar of major commercial importance. The tree is vigorous, the fruit small (275 g), yellow with no blush, with small, light-brown slightly corky dots, ovate-oblong in shape (11.7 cm long by 7.2 cm wide by 6.3 cm thick), with adherent skin of intermediate thickness, relatively free of disease; flesh orange, juicy but susceptible to jelly seed, with no objectionable fibre, sweet and agreeable in taste, of very good quality. The stone is large (38.5 g). Fruit ripens midseason (Knight and Sanford, 1998). In warm subtropics this cultivar has shown a tendency for flowering in the warm season, with fruit ripening during the cool winter. It has good anthracnose tolerance.

‘Excellent Succari’ (Egypt) A polyembryonic mango of minor commercial importance. The tree is vigorous, ripening fruit in late midseason. The fruit is small (280 g), green with a yellow overlay and small, yellow smooth dots, ovate-oblong in shape (11 cm long by 7 cm wide by 6.4 cm thick), with non-adherent skin of intermediate thickness quite free of surface disease; the flesh is orange, melting (without jelly seed) and juicy with no objectionable fibres, a delightfully sweet taste and excellent quality; stone large (36.6 g) (Knight and Sanford, 1998). It has moderate to good anthracnose tolerance in the warm subtropics.

‘Extrema’ (Brazil) The tree is upright, vigorous and productive. The fruit is yellow with greenish areas, ovate-reniform, weighing 350–400 g, with smooth and thin skin, and yellow, watery flesh with almost no fibres with a moderately resinous, agreeable taste. The quality is considered good for fresh consumption and processing. The polyembryonic seed is in a large, fibrous stone. Ripens early in the season (Sampaio, 1980; A.C. Pinto, personal communication, 1996).

‘Fajri’ (India) Also spelled ‘Fazli’. The tree is of medium size and moderately vigorous, with rounded, open canopy. The fruit is light chrome yellow with small, dark-coloured fairly sparse dots, obliquely oval with base slightly rounded and beak distinct to slightly prominent, large (averaging 14.3 cm long by 9.8 cm broad, weighing 500 g on average) with a medium-thick skin that is

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smooth with some inclination to be warty, and firm to soft, fibreless flesh of a light cadmium yellow with a pleasant aroma and a sweet taste, having juice that may be scanty to moderately abundant, of good to very good quality. The seed is monoembryonic in a large, oblong stone that is covered with a sparse, short and soft fibre. Ripens midseason to late (Gangolly et al., 1957; N. Balasundaram, India, personal communication, 1990). ‘Fernandin’ (India) The tree is moderately vigorous with a dense, rounded canopy; the fruit is bright yellow with an attractive bright-red blush, ovate-oblique, averaging 12.2 cm long by 8.5 cm broad, weighing 450 g; the skin is rough and warty, thick and adherent, flesh bright yellow, moderately to abundantly juicy, thick, with no objectionable fibre, with delightful to piquant aroma and sweet to very sweet, delicious taste, of superior quality; seed is monoembryonic; season late (Gangolly et al., 1957; Singh, 1960). ‘Genovea’ (Egypt) A polyembryonic cultivar of minor commercial importance. The fruit is small (234.5 g), green with a yellow overlay and medium-sized smooth yellow dots, ovate-oblong in shape (11 cm long by 6 cm wide by 5.6 cm thick), a thin adherent skin relatively free of surface disease; flesh orange, firm (no jelly seed) and juicy with no objectionable fibres, a sweet agreeable taste of acceptable quality; stone large (53 g) (Knight and Sanford, 1998). ‘Glenn’ (Florida, USA) The tree is moderately vigorous, small to medium with dense, rounded canopy of compact growth; the fruit (Plate 11) is bright yellow with orange-red blush, with numerous small yellow and white dots, oval to oblong with a rounded base, 9.5–12.5 cm long by 7.5–8.5 cm broad by 7–8 cm thick, weighing 400–620 g; the skin is thin, tough and easily separated, flesh soft and juicy, with little fibre, deep yellow, rich and spicy with a strong, pleasant aroma, of excellent quality; seed is monoembryonic in a thick, woody stone. Ripens early in the season and is a regular bearer. This is a seedling of ‘Haden’ (Campbell, 1992; Schnell et al., 2006). ‘Golek’ (Indonesia) The tree is moderately vigorous with an upright, open canopy; the fruit (Plate 12) is greenish yellow with an orange overlay and prominent white dots, oblong with rounded base, 9.5–12.5 cm long by 6–8 cm broad by 5.5– 6.5 cm thick, weighing 200–365 g; the skin is thin, tough and easily separated;

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the flesh is soft and juicy with abundant fibre (not objectionable), deep yellow, sweet, insipid with a mild aroma, of poor to fair quality; the seed is polyembryonic in large, woody stone with abundant fine fibre. Ripens midseason (R.J. Knight, Jr, personal communication, 1995). ‘Haden’ (Florida, USA) The tree is vigorous, with a large, spreading canopy; the fruit (Plate 13) is bright yellow with a deep crimson or red blush and numerous large yellow dots, oval with a rounded base, 10.5–14 cm long by 9–10.5 cm broad by 8.5– 9.5 cm thick, weighing 510–680 g; the skin is thick, tough and adherent; the flesh is firm and juicy with abundant fibre, deep yellow, rich and sweet with a pleasant aroma, of good to excellent quality; the seed is monoembyonic in a medium-thick woody stone. Ripens early to midseason and bearing is sometimes irregular. This is a seedling of ‘Mulgoba’ × ‘Turpentine’ and is the first of the Florida mango cultivars, introduced in 1910 and since grown in many other countries. It is the seed parent of numerous other cultivars (Campbell, 1992; Knight and Schnell, 1994; Schnell et al., 2006). ‘Himsagar’ (India) The tree is vigorous, tall, with a dense, spreading canopy; the fruit (Plate 14) is greenish yellow to bright yellow with no blush, with light-yellow dots, ovate with a flattened base, 12–15 cm long by 8.5–9.5 cm broad by 7.5–8.5 cm thick, weighing 465–585 g; the skin is thin, tough and easily separated; the flesh is firm and juicy with no fibre, orange, rich and sweet with a mild aroma, of good to excellent quality; the seed is monoembryonic in a thick, woody stone. This is a late midseason cultivar that bears well (R.J. Knight, Jr, personal communication, 1995). ‘Hindi Besennara’ (Egypt) A polyembronic cultivar of major commercial importance. The tree is of medium vigour, ripening fruit early to midseason. The fruit (Plate 15) is of small to medium size (319 g), green with orange overlay, with small white corky dots, oblong-cylindrical in shape (15.4 cm long by 6.7 cm wide by 6.5 cm thick) with thick, non-adherent skin relatively free of surface disease; the flesh is orange, yielding and juicy with no objectionable fibres, pleasantly sweet in taste, of very good quality; the stone is large (47.2 g) (Knight and Sanford, 1998). ‘Hindi Khassa’ (Egypt) A polyembryonic cultivar of major commercial importance. The tree is vigorous, ripening fruit in late midseason. The fruit is of medium size (461 g),

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yellow with no blush, with intermediate-sized smooth, light-yellow dots, oblong-cylindrical in shape (16 cm long by 6.6 cm wide by 6.9 cm thick), with thick, adherent skin relatively free of surface disease; flesh is orange, firm and juicy with no objectionable fibres, of mediocre taste and a quality not suitable for export; stone is large (55 g) (Knight and Sanford, 1998).

‘Irwin’ (Florida, USA) The tree is small to medium, moderately vigorous, with open canopy. The fruit (Plate 16) is bright yellow with a crimson or bright red blush, numerous large white dots, ovate with rounded base, 11.5–13 cm long by 8–9 cm broad by 6.5– 7.5 cm thick, weighing 340–450 g; the skin is medium-thick, tender and adherent; the flesh is soft, tender, melting and juicy without fibre, lemon yellow, sweet and mild with a pleasant aroma, of good quality; the seed is monoembryonic in a thin, papery stone. The stone may be seedless following cool weather at flowering time. This is an early, regular and heavy bearer. The fruit is usually soft with a short postharvest life, but it is often exported from tropical America to Europe. It is a seedling of ‘Lippens’ × ‘Haden’ (Campbell, 1992; Schnell et al., 2006). ‘Julie’ (West Indies) Also called ‘St Julienne’. The tree is compact (dwarf), with a dense canopy; the fruit (Plate 17) is greenish yellow with a light pink to maroon blush and numerous small white dots, rounded with flattened apex, pronouncedly compressed laterally, 7–9.5 cm long by 4–7.5 cm broad by 2–5.5 cm thick, weighing 200–325 g with a thin, tender skin and soft, melting, juicy, orange flesh with scanty fibre, of a rich, spicy flavour with a strong, pleasant aroma, of good quality; seed is monoembryonic in a thin, papery stone. This cultivar ripens midseason and is a regular producer of small crops. The fruit is often severely infected with anthracnose disease, but its unique taste is preferred by many West Indians, and it is exported to the London market (C.W. Campbell, personal communication, 1996).

‘Keitt’ (Florida, USA) The tree is medium sized, moderately vigorous, upright with open canopy; the fruit (Plate 18) is greenish yellow, with a pink or red blush, numerous small white or yellow dots, oval, with rounded base, 13–15 cm long by 9–11 cm broad by 8.5–10 cm thick, weighing 510–2000 g; the skin is thick, tough and adherent; the flesh is firm and juicy, with little fibre, lemon yellow, sweet and mild with a pleasant aroma, of good to excellent quality; the seed is monoembryonic in a thick and woody stone. This cultivar ripens late in the season. It is a seedling of ‘Brooks’. After ‘Tommy Atkins’ it is the most commercially important cultivar in the export mango industry of the western

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hemisphere. It is resistant to anthracnose disease, packing and shipping stress and is heavily productive (Campbell, 1992; Schnell et al., 2006). It is highly susceptible to bacterial black spot in Queensland (Mayers et al., 1988).

‘Kensington’ (Australia) Also known as ‘Kensington Pride’ and ‘Bowen’. ‘Kensington’ has a large, vigorous tree with spreading canopy; the fruit (Plate 19) is yellow with an orangered blush on the shoulder, round ovate with a flattened base and a slight beak, 10.5–13 cm long by 8.5–9.6 cm broad by 7.5–8.5 cm thick, weighing 350–750 g; the skin is thick, tender and adherent; the flesh is soft and juicy, with moderate to little fibre, sweet with a characteristic flavour that makes it the most popular cultivar in Australian markets, of excellent quality; seed is polyembryonic in a moderately thick, woody stone. This cultivar ripens midseason and it bears well. It is unusually susceptible locally, in Florida, to damage by redbanded thrips (Selenothrips rubricinctus (Giard.)), and may be killed by this pest without adequate countermeasures (R.J. Campbell, personal communication, 1994; R.J. Knight, Jr, personal communication, 1995). It is moderately susceptible to anthracnose and bacterial spot (Mayers et al., 1988).

‘Kent’ (Florida, USA) The tree is large and vigorous with a dense, upright canopy; the fruit (Plate 20) is greenish yellow with a red or crimson blush, numerous small yellow dots, oval, with rounded base, 11–13 cm long by 9.5–11 cm broad by 9.9.5 cm thick, weighing 600–750 g; the skin is thick, tough and adherent; the flesh is firm, tender, melting and juicy with little fibre, deep yellow to orange-yellow, sweet with a rich flavour and pleasant aroma, of excellent quality; the seed is monoembryonic in a thick, woody stone. Fruit ripens late midseason to late and bearing may be alternate. It is a seedling of ‘Haden’ × ‘Brooks’, which is a seedling of ‘Totapuri’ (‘Sandersha’) (Schnell et al., 2006). ‘Kent’ is not commonly commercial in Florida because it is prone to storage disease, but is a successful commercial cultivar in drier parts of Mexico, Central and South America and West Africa (Campbell, 1992). It is highly susceptible to bacterial black spot in Queensland (Mayers et al., 1988).

‘Khanefy’ (Egypt) A cultivar of minor commercial importance. The fruit is large (475 g), green with a yellow overlay and large, brown, smooth dots, ovate in shape (10.7 cm long by 8.3 cm wide by 8.6 cm thick), with an adherent skin quite free of surface disease; the flesh is yellow, often with jelly seed, juicy, with no objectionable fibres and a bland flavour unacceptable to many Western palates. The stone is moderately large (53 g) (Knight and Sanford, 1998).

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‘Kyo Savoy’ (Thailand) The tree is large, vigorous, with an open canopy made up of long branches; the fruit is green when harvested (before the ripening process begins) turning to greenish yellow, oblong, 11.5–12.5 cm long by 5.5–6.5 cm broad by 5–6 cm thick, weighing 230–340 g; the skin is thin, tender and adherent; the flesh is medium firm, tender and not very juicy with no fibre, pale yellow, very sweet with an insipid taste and a mild, pleasant aroma, of fair to good quality; the seed is highly polyembryonic in a medium-thin stone. This is a regular producer (C.W. Campbell, personal communication, 1995). The fruit is often consumed green. ‘Langra’ (India) Also called ‘Darbhanga’, ‘David Ford’, ‘Hadialaziz’, ‘Hajipur Langra’, ‘Hardoi Langra’, ‘Lan Garhi’, ‘Langra Faquirwala’, ‘Sylhet’ and ‘Tikari’. The tree is moderately vigorous, forming a dense canopy; the fruit is greenish yellow with medium to big dark-green dots, ovalish to oblong, 8–10.5 cm long by 6.5–7.5 cm broad by 6–7 cm thick, weighing 235–375 g; the skin is medium smooth, thick; the flesh is firm to soft, fibreless, lemon yellow, very sweet with a strong, pleasant aroma, juice moderately abundant; seed is monoembryonic in a medium-sized, flattened stone covered with dense, short and soft fibre; quality is very good. Fruit ripens early to midseason (Gangolly et al., 1957; R.J. Knight, Jr, personal communication, 1995). ‘Mabrouka’ (Egypt) A major commercial cultivar considered to have been originally introduced from India. The tree is moderately vigorous; the fruit (Plate 21) is large (481 g), yellow with an orange to red blush and small, light-yellow, smooth dots; ovate-oblong in shape (13.7 cm long by 8.9 cm wide by 8.2 cm thick) with a thick, non-adherent skin relatively free of surface disease; the flesh is yellow, firm and juicy with no objectionable fibre, moderately agreeable in taste, of acceptable quality. The monoembryonic seed is in a moderately large (51 g) stone. Fruit ripens late midseason, ships well and has been marketed in Poland (Singh, 1960; Knight and Sanford, 1998). ‘Madame Francis’ (Haiti) The tree is moderately vigorous, medium sized, forming an open canopy; the fruit (Plate 22) is greenish to bright yellow, with no blush and a few large russet dots, oblong, sigmoid with rounded base, 15–17 cm long by 8.5–11 cm broad by 5.5–7.5 cm thick, weighing 370–520 g; the skin is thin, tender and adherent; the flesh is soft and juicy with medium fibre, orange, rich spicy and sweet with a pleasant aroma, of fair to good quality; seed is polyembryonic

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in a thin, papery stone. This cultivar ripens early to midseason and bears well. Shipped to North American markets from Haiti nearly 10 months of the year (R.J. Campbell, personal communication, 2007). ‘Mallika’ (India) The tree is a moderately vigorous dwarf with a dense canopy; the fruit (Plate 23) is bright yellow with no blush and numerous small, light-yellow dots, oblong with rounded base, 10–12 cm long by 6.5–7.5 cm broad by 5–5.5 cm thick, weighing 280–450 g; the skin is thick, tough and easily separating; the flesh is soft, tender and juicy with little fibre, deep yellow to orange, rich, strongly aromatic and sweet, of excellent quality; seed is monoembryonic in a medium-thick and woody stone. This cultivar ripens midseason and is an irregular producer. This cultivar came from crossing ‘Neelum’ and ‘Dashehari’ (Singh et al., 1972; Campbell, 1992). ‘Manila’ (Mexico) The tree is large, vigorous, with an upright, open canopy; the fruit (Plate 24) is bright yellow, sometimes with a light-pink blush, a few small reddish dots, long and slender with rounded base and bluntly pointed apex sometimes with a small beak, 12.5–14 cm long by 5.5–6 cm broad by 5–5.5 cm thick, weighing 180–260 g; the skin is thin, medium tough and easily separating; the flesh is medium firm and juicy, with little to abundant fibre, deep yellow, sweet, rich and spicy in taste with a pleasant aroma, of good to very good quality; seed is polyembryonic in a medium-thick and woody stone. This cultivar ripens early midseason and crops fairly dependably. For a long time ‘Manila’ has been the most popular mango in Mexico. ‘Manzanillo’ (Mexico) The tree is large, of medium vigour with an upright canopy; the fruit is yellowish orange with 75% of the surface blushed an intense dark red with numerous dots, oval with moderately flattened base, averaging 12 cm long by 10 cm broad by 7.5 cm thick, and 660 g in weight; the flesh is low in fibre, slightly subacid and very palatable, quality high; seed is monoembryonic in a relatively small stone. This cultivar ripens early in the season but spread over a 60-day harvest period. It bears heavily without pronounced alternation and the fruit stores and ships well (Núñez-Elisea, 1984). ‘Mesk’ (Egypt) A major commercial cultivar. The tree is vigorous, the fruit small to medium sized (312.5 g), yellow with a red blush, with small, corky yellow dots;

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ovate-oblong (11.3 cm long by 7.4 cm wide by 6.5 cm thick) with adherent skin intermediate in thickness and fairly free of surface disease; the flesh is orange, frequently jelly-seeded, with no objectionable fibres and a sweet, agreeable taste of very good quality. The polyembryonic seed is in a moderately large (52.5 g) stone. Fruit ripens late in the season (Knight and Sanford, 1998).

‘Mulgoa’ (India to Florida, USA) Also spelled ‘Mugoba’ and ‘Mulgova’. The tree is large, vigorous with open, spreading canopy; the fruit (Plate 25) is bright yellow with a pink blush and numerous large white dots, oval to ovate with flattened base, 8.5–10.5 cm long by 6.5–7.5 cm broad by 5–6 cm thick, weighing 340–450 g; the skin is thick, medium tough and adherent; the flesh is soft, tender, melting and juicy, with little fibre, lemon yellow, rich spicy and sweet with strong, pleasant aroma, of good to excellent quality; seed is monoembryonic in a thick, woody stone. This cultivar ripens midseason to late and is a shy, irregular bearer. Introduced to Florida in 1889 and called ‘Mulgoba’, this is the seed parent of ‘Haden’, first of a series of cultivars known as the Florida group. A question exists whether the cultivar known in Florida is identical with the Indian cultivar or is a seedling rootstock that survived after the scion was killed by cold. In either case its superior quality ensured its retention and propagation (Campbell, 1992). Literature serves to compound the nomenclatural confusion, as illustrated by Gangolly et al. (1957) whose ‘Mulgoa’ fruit, yellow overall and roundish oblique with a deeply depressed stem insertion, does not resemble the cultivar introduced to Florida. Singh (1960), on the other hand, portrays a rounded, lightly blushed greenish yellow fruit that closely resembles the Florida mango. Furthermore, vegetative propagation of selected chance seedlings has resulted in a variety of clonal types carried under this name in India (Ratnam and Chellapa, no date, post-1954).

‘Nabeel’ (Egypt) A minor commercial cultivar. The fruit is large (495 g), green with small yellow dots that are smooth; ovate-oblong (14 cm long by 9 cm wide by 7 cm thick), with adherent skin relatively free of surface disease; the flesh is orange, firm and juicy, without objectionable fibre, with a passable but not outstandingly pleasing taste and acceptable quality. The seed is polyembryonic in a large (56.6 g) stone (Knight and Sanford, 1998).

‘Nam Doc Mai’ (Thailand) The tree is vigorous, medium sized with upright, dense canopy; the fruit (Plate 26) is greenish to bright yellow with a slight pink blush and numerous

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small green dots, long and slender, sigmoid in shape with a rounded base, 17–19 cm long by 7.5–8.5 cm broad by 6.5–7.5 cm thick, weighing 340–580 g; the skin is medium thick, tender and easily separated from the flesh which is soft, tender and juicy with no fibre, lemon yellow, rich, spicy and very sweet with pleasant aroma, of excellent quality; seed is polyembryonic in a thin, papery stone. This cultivar ripens early midseason, fruits regularly and may have multiple crops in one season (Campbell, 1992). It is highly resistant to foliar infection, and resistant to fruit infection by bacterial black spot in Queensland (Mayers et al., 1988).

‘Neelum’ (India) The tree is moderately vigorous with a small, compact canopy; the fruit is bright yellow with no blush and numerous small white dots, oval with flattened or slightly rounded base, 9.5–11 cm long by 7.5–8.5 cm broad by 6–6.5 cm thick, weighing 230–300 g; the skin is thick, tender and easily separating; the flesh is soft, melting and juicy with no fibre, deep yellow, mild and sweet with a delightfully pleasant aroma, of good to excellent quality; seed is monoembryonic in a medium-thick, woody stone. This cultivar is a late, heavy bearer (Campbell, 1992).

‘Nuwun Chan’ (Thailand) The tree is moderately vigorous, small, upright with a dense canopy; the fruit (Plate 27) is greenish yellow with a pink to red blush, numerous small green dots, long and slender with a flattened base, 16–18 cm long by 7–8 cm broad by 6–6.5 cm thick, weighing 340–500 g; the skin is thick, tough and easily separating; the flesh is soft, melting, juicy with little fibre, pale yellow, mild and sweet with a faint, pleasant aroma, of good eating quality; seed is polyembryonic in a thick, woody stone. This cultivar is an early, regular bearer. Fruit is often eaten green (Campbell, 1992).

‘Okrung’ (Thailand) The tree is moderately vigorous, medium sized and upright, forming a dense canopy; the fruit (Plate 28) is green to greenish yellow with no blush and numerous small white dots, oblong and sigmoid with a rounded base, 11–13 cm long by 5–6 cm broad by 4.5–5.5 cm thick, weighing 160–240 g; the skin is thick, tough and medium adherent; the flesh is soft and juicy with abundant fibre, yellow or greenish, mild, somewhat insipid and very sweet with a pleasant aroma, of good quality; seed is polyembryonic in a thick, woody stone. This cultivar ripens midseason, is a heavy producer and sometimes bears more than one crop/year (Campbell, 1992).

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‘Osteen’ (Florida, USA) The tree is vigorous, medium sized, forming a dense canopy; the fruit (Plate 29) is yellow-orange with a purple or lavender blush and numerous small white dots, oblong with rounded base, 12–15.5 cm long by 9–10.5 cm broad by 8.6–9.5 cm thick, weighing 500–760 g; the skin is thick, tough and easily separating; the flesh is firm and juicy, with little fibre, lemon yellow, mild and sweet with a pleasant aroma, of good quality; seed is monoembryonic in a thick and woody stone. This cultivar ripens late midseason to late and is a regular producer. It is a ‘Haden’ seedling (Campbell, 1992; Schnell et al., 2006).

‘Pairi’ (India) Also written ‘Pairie’, ‘Paheri’ and ‘Pirie’; synonyms are said to be ‘Peter’, ‘Peter Pasand’, ‘Grape’, ‘Gohabunder’, ‘Nadusalai’, ‘Rasjuri’ and ‘Yerra Goa’. The tree is moderately vigorous, forming a dense, rounded canopy; the fruit (Plate 30) is medium sized, green to yellow with a bright red blush, roundish, skin smooth, thick, flesh golden yellow, slightly juicy, fibreless, with a delicious subacid taste, of excellent quality; the thick stone covered with short, bristly fibre encloses monoembryonic seed (Popenoe, 1927; Singh, 1960). This cultivar has long been popular as a dooryard fruit tree in Hawaii.

‘Palmer’ (Florida, USA) The tree is moderately vigorous, forming a large, upright, tight canopy; the fruit (Plate 31) is yellow-orange with a dark-red to crimson blush and a few small white dots, oblong with rounded base, 12–15 cm long by 8.5–10 cm broad by 6.5–7.5 cm thick, weighing 510–850 g; the skin is medium thick, tough and adherent; the flesh is firm and melting with little fibre, orangeyellow, mild and aromatic, of good quality; seed is monoembryonic in a medium-thick woody stone. This is a late midseason cultivar and is a regular bearer. It is a seedling of ‘Haden’ (Schnell et al., 2006). In Florida it is of minor commercial importance (Campbell, 1992). It is grown in Israel and is the seed parent of ‘Naomi’. It is attracting increased attention in the western hemisphere export market as a result of its superior eating quality.

‘Rosa’ (Brazil) The tree is medium sized, of slow growth with a rounded canopy; the fruit (Plate 32) is yellow to rose-red on the side exposed to sun, oblong-cordiform and medium sized; the skin is thick and smooth; the flesh is firm and moderately juicy, fibrous, golden yellow, moderately sweet with a turpentine aroma, of ordinary quality, susceptible to anthracnose disease; the seed is polyembryonic in a small, oblong stone. This cultivar ripens midseason to

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late. It is one of the most important commercial cultivars in the Federal District of Brazil, used for juice as well as fresh consumption, and is one of the most well-known cultivars in Brazil (Sampaio, 1980; L.C. Donadio, personal communication, 1996; A. Pinto, personal communication, 1996).

‘Sensation’ (Florida, USA) The tree is vigorous, with a moderately open, symmetrical canopy; the fruit (Plate 33) is dark yellow with a prominent dark-red to purple blush that covers most of its surface, oval with rounded base and rounded apex, 9–11.5 cm long by 7–8 cm broad by 6.5–7 cm thick, weighing 280–340 g; the skin is medium thick, tough and easily separating; the flesh is firm and medium juicy, fibreless, deep yellow, mild and sweet with a weak, pleasant aroma, of fair to good quality; seed is monoembryonic in a thick, woody stone. This cultivar ripens midseason to late (Campbell, 1992). It is a seedling of ‘Haden’ × ‘Brooks’ (Schnell et al., 2006), and the seed parent of ‘B74’. It alternates severely, and in ‘on’ years the fruit may be clustered so heavily that it becomes diseased before maturity, thus ‘Sensation’ is not of commercial importance. It is highly resistant to bacterial black spot in Queensland (Mayers et al., 1988), but often has severe internal breakdown (browning, water soaking) (A.W. Whiley, personal communication, 1996).

‘Suvarnarekha’ (India) Also called ‘Swarnarekha’ and ‘Sundri’. The tree is moderately vigorous and tall, with a rounded, dense, spreading canopy; the fruit is light cadmium yellow with a blush of jasper red and abundant small, light-coloured dots, ovate oblong with a base slightly flattened, of medium size, 11 cm long by 8.2 cm broad, weighing 400 g; the skin is medium thick, easily separated, flesh soft, fibreless, primrose yellow with a pleasant aroma, sweet taste and abundant juice, of medium to good quality; seed is monoembryonic in an oblong-oval stone covered with soft, short fibre. Ripens early in the season early and is heavy bearing (Gangolly et al., 1957).

‘Tahar’ (Israel) The tree is vigorous, medium sized, with an upright, dense canopy; the fruit is bright yellow with a dark-red blush and numerous small white dots, ovate with flattened base, 11.5–13 cm long by 8.9–9.5 cm broad by 7.5–8 cm thick, weighing 360–520 g; the skin is thick, tough and easily separating; the flesh is soft and juicy with little fibre, deep yellow, mild, aromatic and slightly insipid with a strong odour not appreciated by many, of fair to good quality; seed is monoembryonic in a medium-thick woody stone. This cultivar ripens in late midseason and bears well in Israel (Campbell, 1992).

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‘Taimour’ (Egypt) A major commercial cultivar. The tree is vigorous; the fruit (Plate 34) is large (500 g), ripening late in the season, dark green with large light-brown dots, smooth in texture, ovate-oblong (12.8 cm long by 8.4 cm wide by 8 cm thick), with non-adherent skin of intermediate thickness, quite free from surface disease; flesh is orange, firm (free of jelly seed) and juicy with no objectionable fibre, of a delightfully rich, sweet taste and excellent quality. The seed is polyembryonic in a medium-sized (50.8 g) stone (Knight and Sanford, 1998).

‘Tommy Atkins’ (Florida, USA) The tree is vigorous, with a dense, rounded canopy; the fruit (Plate 35) is orange-yellow, with a crimson or dark-red blush and numerous small, white dots, oval to oblong, with broadly rounded base, 12–14.5 cm long by 10–13 cm broad by 8.5–10 cm thick, weighing 450–700 g; the skin is thick, tough and adherent; the flesh is firm and medium juicy; with a medium amount of fibre, lemon to deep yellow, mild and sweet with a strong pleasant aroma, of fair to good quality; seed is monoembryonic in a thick, woody stone. This cultivar ripens early to midseason. It is a ‘Haden’ seedling (Schnell et al., 2006). ‘Tommy Atkins’ is the most important commercial cultivar in the western hemisphere export mango market; it is highly resistant to anthracnose disease and handling and shipping stress, and a consistent, heavy producer (Campbell, 1992). ‘Jelly seed’ (internal breakdown) is a serious problem in the moist subtropics and tropics outside Florida, where the mango is grown on calcareous, well-drained soil (A.W. Whiley, personal communication, 1996).

‘Totapuri’ (India) Also called ‘Bangalora’, ‘Collector’, ‘Kallamai’, ‘Killi’ (‘Gilli’), ‘Mukku’, ‘Sandersha’ and ‘Thevadiyamuthi’. The tree is of medium size, vigorous, spreading with an open canopy; the fruit (Plate 36) is greenish yellow with a pink blush and a few small, white dots, oblong, base rounded, apex rounded to bluntly pointed with a large beak, 17.5–20 cm long by 9–11.5 cm broad by 8.5–10.5 cm thick, weighing 800–1100 g; the skin is thick, tough and adherent; the flesh is firm and medium juicy with a weak, somewhat repugnant aroma, of poor to fair quality; seed is monoembryonic in a thin, papery stone. This cultivar ripens late midseason, is productive and regular bearing. Fruit cracks when exposed to heavy rains at ripening time. ‘Totapuri’ was imported to Florida twice, as ‘Sandersha’ in 1901 and as ‘Totapuri’ in the early 1960s. It is the seed parent of ‘Anderson’ and ‘Brooks’, which is itself the parent of ‘Kent’. It is called ‘Totapuri’ in Bangalore, and ‘Bangalora’ in much of the rest of India (Gangolly et al., 1957; Campbell, 1992).

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‘Turpentine’ (West Indies) The tree is vigorous, with a large, spreading, rounded canopy; the fruit (Plate 37) is bright yellow with a few large white dots, occasionally with a pink blush, oval with a flattened base, 7.5–8.5 cm long by 6.5–7.5 cm broad by 6–6.5 cm thick, weighing 140–200 g; the skin is thick, tough and easily separating; the flesh is firm and juicy, with abundant coarse fibre, lemon yellow, rich, aromatic, spicy, resinous and sweet with a strong, pleasant aroma, of poor to fair quality; seed is polyembryonic in a thick, woody stone. This cultivar ripens early midseason to late midseason and is a heavy producer but may alternate. It is commonly used as a grafting stock (Campbell, 1992).

‘Vallenato’ (Colombia) The tree is vigorous, with an upright, dense canopy; the fruit (Plate 38) is bright yellow, with a crimson blush, oblong with flattened base, 8–9 cm long by 7–8 cm broad by 6–7 cm thick, weighing 195–340 g; the skin is thin, tough and adherent; the flesh is firm, juicy with abundant fine fibre (not objectionable), pale yellow, mild and sweet with a strong, pleasant aroma, of good to excellent quality; seed is monoembryonic. This cultivar ripens in early midseason (R.J. Campbell, personal communication, 1995).

‘Van Dyke’ (Florida, USA) The tree is moderately vigorous, with a large, open canopy; the fruit (Plate 39) is bright yellow with a bright red or crimson blush, oval with rounded base, 9–11.5 cm long by 7.5–9.5 cm broad by 7–8 cm thick, weighing 250– 520 g; the skin is thick, tough and easily separating; the flesh is quite firm, melting and juicy with little fibre, orange-yellow, rich, spicy and sweet with a strong, pleasant aroma, of good to excellent quality, but susceptible to internal breakdown; seed is monoembryonic in a medium-thick, woody stone. This cultivar ripens in late midseason and is a regular, heavy producer. It is a seedling of ‘Haden’ (Campbell, 1992; Schnell et al., 2006).

‘White Succari’ (Egypt) A cultivar of major importance. The tree is vigorous; the fruit is medium large (410 g), greenish yellow with yellow overlay and small, brown dots of smooth texture, ovate-oblong in shape (11.25 cm long by 8.3 cm wide by 8.0 cm thick), with thin adherent skin reasonably free of surface disease; flesh is orange, yielding and juicy with no objectionable fibres, of an agreeable sweet taste and very good quality. The seed is polyembryonic in a moderate to large-sized stone (49 g), the season early (Knight and Sanford, 1998).

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‘Zebda’ (Egypt) A cultivar of major importance. The tree is vigorous and regularly productive; the fruit (Plate 40) is large (660 g), green with no overlay and small, brown dots of smooth texture, oblong-cylindrical in shape (14.6 cm long by 9.7 cm wide by 8.3 cm thick), with non-adherent skin quite free of surface disease; flesh is deep orange, firm and juicy, with no objectionable fibre and a mild, sweet taste, of acceptable quality. The seed is polyembryonic in a moderately small (52 g) stone. This cultivar is of late-midseason maturity (Knight and Sanford, 1998). It is highly tolerant of anthracnose and resistant to malformation (R.C. Ploetz, personal communication, 2007).

3.4 Conclusion The mango fruit’s nutritional value, aesthetic and gustatory appeal have assured its growing importance in non-traditional markets since the late 1950s, as it has been introduced to consumers previously unacquainted with it. Furthermore, the migration of large populations from South-east Asia and other regions where this fruit is a traditional crop to metropolitan centres where it has not been well known has created a permanent demand for it in these new markets. An additional factor permitting market expansion has been the growing mango production in areas previously unimportant in world commerce such as Mexico, Brazil, Australia, West Africa, Israel, Florida and the Canary Islands. The fact that most new markets are remote from areas of production has necessitated selection of cultivars for fresh market sale that are dependably productive and resistant to harvest, handling and shipping stress, with relatively long shelf life, for example ‘Tommy Atkins’, ‘Keitt’ and ‘Madame Francis’. The fruit quality of mango cultivars well suited to packing and shipping has been a secondary consideration, and is generally not so high as that of cultivars acknowledged to be superior for eating. Economic factors obviously must dictate what is grown for the fresh market. The commercial market for processed mango products permits other cultivars to be utilized, and these may vary with the product that is marketed. Cultivars chosen for purée or juice preparation are likely to be quite different from those used for manufacture of chutney or other products requiring pulp that maintains its integrity after it is cooked. ‘Totapuri’ (‘Sandersha’) or ‘Turpentine’, for example, considered mediocre for fresh consumption, can be used to prepare excellent chutneys, as can many ‘criollo’ types in the West Indies. ‘Tommy Atkins’ makes outstandingly good dried fruit sections, sweet and aromatic, even though its fresh-fruit quality is generally conceded not to be high. Mango butter and mango leather are other products that are appreciated by many who know them (see Raymundo et al., Chapter 17, this volume; Campbell and Campbell, 1983; Campbell and Smith, 1987). As more fruit that is wholesome, but not of export quality, becomes available in areas of increasing production, it is likely that processed mango products will become more common.

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Table 3.1. Ratings of selected mango cultivars grown in Florida (Source: Knight, 1993). Shapea Sizeb Firmnessc Colourd Anthracnosee Fibref Tasteg Yieldh Scorei

Cultivar ‘Alphonso’ ‘Boribo’ ‘Carabao’ ‘Haden’ ‘Keitt’ ‘Kensington’ ‘Langra’ ‘Pope’ ‘Tommy Atkins’ ‘Van Dyke’

3 3 5 3 4 3 2 3 3

5 8 6 9 10 8 6 9 9

7 8 7 8 9 7 8 5 9

2 4 3 8 6 7 3 7 9

3 7 5 5 8 7 5 2 9

7 9 9 7 9 8 8 8 6

9 5 8 7 8 7 8 8 6

1h 6 6h 3h 8 6 3h 1 7

x x x x /// / x x ///

3

7

10

9

7

8

7

6

///

aRatings

of 1 (round) to 5 (long) indicate fruit shape, not its desirability. below 6 justify discard; those of 7 and above show size only, not merit. cRatings of 1–10 where 1 = least and 10 = most. dRatings of 1–10 where 1 = least and 10 = most. eRatings of 1–10 where 1 = most and 10 = least susceptible. fRatings of 1–10 where 1 = most and 10 = least. gRatings of 1–10 where 1 = worst and 10 = best. hTrends markedly towards alternate bearing. iOne or more checks (/) show overall value; (x) indicates no commercial acceptability. bRatings

Despite the recognized high quality of many well-known mango cultivars, considerable cultivar improvement is still needed in most regions of culture before anything approaching perfection is likely to be achieved (Table 3.1). For any given area, cultivars that combine adequate resistance to disease and packing and shipping stress, regular heavy production, high quality, and attractive appearance throughout a long bearing season are all requisites. Production of seedlings from controlled crossing of different parents having desired characters, followed by vigorous selection and evaluation of the resultant selections, can produce such improved cultivars. Pursuit of common goals, including the cooperative exchange and testing of elite germplasm in different regions of production, can accelerate progress towards this objective (Lavi et al., 1989, 1993; Knight, 1993). Such interregional and international activities are to be encouraged because of their potential for advancing mango production and utilization in the world.

Acknowledgements For their help in reviewing portions of this chapter and/or contributing vast quantities of information on mango cultivar descriptors and attributes, the authors are profoundly grateful to the following: Dr N. Balasundaram, Head, Sugarcane Breeding Institute, Regional Centre, Karnal, India 132001; the late Dr Carl W. Campbell, Tropical Research and Education Center, 18905 SW 280

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Street, Homestead, Florida 33031 USA; Luis C. Donadio, Universidade Estadual Paulista, Rodavia Carlos Tonanni KM5, Jaboticabal, 14870, São Paulo, Brazil; Dr Shmuel Gazit, Department of Horticulture, Hebrew University of Jerusalem, Rehovot 76100, Israel; Mr Remy LePrette, Directeur, Interfel, 155 Rue F.G. Poissonierre, Paris 75009, France; Dr Alberto C. Pinto, Lider de Projeto/CPAC, EMBRAPA, Caixa Postal 08 223, CEP 73301-970, Brasilia, DF, Brazil; Dr Eli Tomer, Department of Fruit Trees, the Volcani Centre, Institute of Horticulture, PO Box 6, Bet Dagan 50-250, Israel; Dr Anthony W. Whiley, Maroochy Horticultural Research Centre, PO Box 5093 SCMC, Nambour, Queensland 4560, Australia.

References Bondad, N.D. (1982) Mango and its relatives in the Philippines. Philippine Geographic Journal 26, 88–100. Bondad, N.D. and Linsangan, E. (1979) Flowering in mango induced with potassium nitrate. HortScience 14, 527–528. Campbell, B.A. and Campbell, C.W. (1983) Preservation of tropical fruits by drying. Proceedings of the Florida State Horticultural Society 96, 229–231. Campbell, B.A. and Smith, J. (1987) An overview of tropical fruit uses in Florida. Proceedings of the Florida State Horticultural Society 100, 408–411. Campbell, C.W. and Campbell, R.J. (1995) ‘Cogshall’, a mango for the home garden. Proceedings of the Florida State Horticultural Society 108, 369–370. Campbell, R.J. (ed.) (1992) A Guide to Mangos in Florida. Fairchild Tropical Garden, Miami, Florida, USA. Campbell, R.J., Ledesma, N. and Campbell, C.W. (2002) Tropical Mangos: How to Grow the World’s Most Delicious Fruit. Fairchild Tropical Garden, Miami, Florida, USA. Gangolly, S.R., Singh, R., Katyal, S.L. and Singh, D. (1957) The Mango. Indian Council of Agricultural Research, New Delhi, India. International Board for Plant Genetic Resources (IBPGR) (1989) Descriptors for Mango. International Board for Plant Genetic Resources, Rome. Knight, R.J., Jr (1993) Evaluating important fruit characters in mango germplasm. Fruit Varieties Journal 47, 25–30. Knight, R.J. and Sanford, R.L. (1998) Mango Cultivar Evaluation. Publication No. 42. (USAID (United States Agency for International Development) Project No. 263–0240). ATUT (Agricultural Technology Utilization and Transfer) /Ronco, Giza, Egypt. Knight, R.J. and Schnell, R.J. (1994) Mango introduction in Florida and the ‘Haden’ cultivar’s significance to the modern industry. Economic Botany 48, 139–145. Lavi, U., Tomer, E. and Gait, S. (1989) Inheritance of agriculturally important traits in mango. Euphytica 54, 5–10. Lavi, U., Sharon, D., Tomer, E., Adato, A. and Gazit, S. (1993) Conventional and modern breeding of mango cultivars and rootstocks. Acta Horticlturae 341, 146–151. Magallanes-Cedeño, R. (2004) Area-wide assessment of the ‘Ataulfo’ mango cultivation in the Soconusco region of Chiapas, Mexico. Acta Horticulturae 645, 361–363. Mayers, P.E., Whiley, A.W., Hutton, D.G. and Saranah, J.B. (1988) Integrated control of bacterial black spot (Xanthomonas campestris pv. mangiferaeindicae) of mango. 1. Evaluation of 23 cultivars of mango for foliar and fruit resistance to bacterial black spot under orchard conditions at Childers, south east Queensland. Maroochy Horticultural Research Report 5, 100–101.

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R.J. Knight et al. Mukherjee, S.K. (1985) Systematic and Ecogeographic Studies of Crop Gene Pools. 1. Mangifera L. International Board for Plant Genetic Resources, Rome. Naville, R. (1985) Les fruits tropicaux et subtropicaux sur le marche français en 1984. Fruits 40, 345–356. Naville, R. (1986) Les importations françaises de fruits tropicaux et subtropicaux en 1985. Fruits 41, 409–420. Núñez-Elisea, R. (1984) ‘Manzanillo-Núñez’: a new Mexican mango cultivar. Proceedings of the Florida State Horticultural Society 97, 360–363. Pinto, A.C.Q., Andrade, S.R.M., Ramos, U.H.V. and Cordeiro, M.C.R. (2004) Intervarietal hybridization in mango (Mangifica indica L.): techniques, main results and their limitations. Acta Horticulturae 645, 327–330. Popenoe, W. (1927) Manual of Tropical and Subtropical Fruits. Macmillan, New York. Prasad, A. (1977) Bearing behaviour and fruit quality of south Indian varieties of mango in northern India. Indian Journal of Horticulture 34, 372–376. Ratnam, L.V. and Chellappa, T. (no date, post-1954) Mulgoas of Hyderabad. In: Rao, B.U. (ed.) The Mango a Souvenir. Department of Agriculture, Neo Silver Jubilee Press, Hyderabad, India. Sampaio, J.M.M. (1980) Características gerais de algumas cultivares e tipos de mangueiras no Brasil. In: Donadio, L.C. (ed.) Anais do I˚ Simposio Brasileiro sobre a Cultura da Mangueira. Departamento de Fitotecnia, Faculdade de Ciencias Agrarias e Veterinarias, Universidade Estadual de Jaboticabal, São Paulo, Brazil, pp. 35–50. Schnell, R.J., Brown, J.S., Campbell, R.J., Kuhn, D.N., Meerow, A.W. and Olano, C.T. (2006) Mango genetic diversity analysis and pedigree inferences for Florida cultivars using microsatellite markers. Journal of the American Society for Horticultural Science 131, 214–224. Singh, L.B. (1960) The Mango: Botany Cultivation and Utilization. Leonard Hill, London. Singh, R.N., Majumder, P.K., Sharma, D.K. and Mukherkjee, S.K. (1972) Some promising mango hybrids. Acta Horticulturae 24, 117–119. Valmayor, R. (1962) The Mango: its Botany and Production. University of the Philippines, Laguna, the Philippines. Whiley, A.W. (2001) Mango (Mangifera indica) ‘B74’. Plant Varieties Journal 14, 45–46. Whiley, A.W. and Hofman, P.J. (2006) ‘Calypso’™ Best Practices Manual. (On CD). Horticulture Ltd, Nambour, Australia.

4

Breeding and Genetics C.P.A. Iyer1 and R.J. Schnell2

1Indian 2USDA

Institute of Horticultural Research, Bangalore, India ARS, National Germplasm Repository, Miami, Florida, USA

4.1 Introduction 4.2 Origin of Cultivars and Distribution Mangifera species and mango History of cultivation Impact of Florida mangoes 4.3 Reproductive Mechanisms Polyembryony Floral biology and pollination Incompatibility Cytology 4.4 Inheritance of Characters Dwarfness, regular bearing and precocity Flesh colour Skin colour Flowering time Beak Disease resistance Other horticultural traits 4.5 Breeding Objectives General objectives Specific objectives 4.6 Methods of Breeding Selection from open-pollinated seedlings Controlled pollination 4.7 Handling of Hybrid Populations and Selection Criteria for initial selection Pre-selection Potential for marker assisted selection (MAS) Molecular markers 4.8 Minimizing Problems in Breeding Heavy fruit drop

68 68 68 69 70 70 70 71 72 72 73 73 74 74 74 74 74 75 75 75 76 78 78 79 80 80 81 81 81 83 83

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Long juvenile phase Polyembryony 4.9 Achievements of Conventional Breeding India Other countries 4.10 Mutations Somatic mutations Induced mutations 4.11 Breeding Potential of Wild Species 4.12 Conclusions

83 84 84 85 86 87 87 88 88 89

4.1 Introduction Mango has been considered to be a difficult plant species to improve in breeding programmes because of certain inherent characteristics including: (i) a long juvenile phase; (ii) a high level of heterozygosity resulting in unpredictable outcomes in hybridization; (iii) only one seed per fruit; (iv) heavy fruit drop leading to low retention of crossed fruits; (v) polyembryony in many cultivars; and (vi) the large area required for a meaningful assessment of hybrids. Despite these drawbacks, mango breeding can be successful because of its wide range of genetic variation and the ease with which a selected hybrid can be vegetatively propagated. Barring a few hybrid varieties resulting from planned hybridization programmes, which are now gaining increased attention, almost all known cultivars have resulted from the selection of chance seedlings from natural cross-pollinations. However, in Florida, a number of cultivars have resulted from the screening of seedlings from known mother plants. Most of the present-day mango cultivars were selected on the Indian subcontinent; these selections were made based mainly on fruit quality, with very little emphasis on modern horticultural and industrial requirements. These requirements include precocity, dwarfness, heavy and regular bearing, absence of physiological disorders, resistance to disease and pests and good shipping qualities. With decreasing land availability and the rising cost of labour, tree architecture requirements have also changed. The need for new cultivars to meet these requisites pinpoints the importance of planned hybridization rather than merely depending on chance seedlings. Current knowledge of hybridization techniques, inheritance patterns, management of hybrid populations and the development of genetic markers have greatly reduced the uncertainty in mango breeding.

4.2 Origin of Cultivars and Distribution Mangifera species and mango Almost all the commercial cultivars belong to Mangifera indica. However, a few commercial varieties of South-east Asia belong to other species, i.e. M. altissima, M. caesia, M. foetida, M. griffithi, M. odorata, M. pentadra, M. sylvatica,

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M. zeylanica, M. laurina, M. lagenifera, M. cochinchinensis, etc. The monoembryonic mango (M. indica) originated in north-eastern India (Assam), the Indo-Myanmar border region and Bangladesh (Chittagong Hill tract), where it is still found as a wild tree, with very small fruits. It may also occur in the lower Himalayan tract, near Nepal, Bhutan and Sikkim. Polyembryonic mangoes are considered to have originated in South-east Asia. Wild mangoes, representing different Mangifera species, can be found in tropical Asia, particularly north-eastern India, Sri Lanka, Myanmar, Thailand, Indo-China, southern China, Malaysia, Indonesia, Papua New Guinea, the Philippines and as far as the Solomon and Caroline Islands in the east. There are more than 60 species worldwide. The highest specific diversity is found in the heart of the distribution area of the genus Mangifera; the Malay Peninsula, Borneo and Sumatra (Bompard, 1993).

History of cultivation Mango has been cultivated in India for at least 4000 years and over 1000 varieties are recognized there (Mukherjee, 1953). Almost all of them are selections made from naturally occurring, open-pollinated seedlings. However, based on random amplification of polymorphic DNA (RAPD) analysis, Ravishankar et al. (2004) felt that the mono- and polyembryonic types of Indian mango cultivars have a different genetic base, and that the polyembryonic types might have been introduced from South-east Asia and are unlikely to have originated in India. Mango culture gradually spread to tropical and subtropical countries throughout the world, where selections were made that were adapted to particular growing conditions. Thus, selection by man has played the most significant role in the development of new mango cultivars. The explorers who tasted the mango in the regions of its origin were enchanted with its aromatic qualities, ambrosial flavour and creamy, smooth and silky texture, and introduced the fruit to other tropical regions. The spread of Hinduism and Buddhism assisted in the distribution of mangoes in South-east Asia. The Chinese traveller Hwen T’sang who visited India in the first half of the 7th century ad returned to China with the mango. The mango was known in Baghdad in the 7th century. The Persians or Omanis may have taken mangoes to East Africa around the 10th century ad. The fruit was introduced to East and West Africa in the early 16th century by the Portuguese and thence into Brazil. After being established in Brazil, the mango was carried to the West Indies, being first planted in Barbados by about 1742 and later in the Dominican Republic and Jamaica (about 1782). The mango was introduced into Mexico from the Philippines by the Spanish and also from the West Indies (Morton, 1987). Duval et al. (2006) developed microsatellite markers for studying the genetic variability of Caribbean mangoes and concluded that there were two routes of mango to the French West Indies, namely, cultivars grown in Central America (Mexico) and South America (Colombia) introduced from South-east Asia and also from former French colonies in the Indian Ocean. As the mango

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adapted to new locales, new cultivars were selected based on local adaptation and fruit preferences.

Impact of Florida mangoes The first recorded successful introduction of mango into Florida (USA) was made in 1861 (Knight, 1980). The earliest introductions were from the West Indies and India, followed by the introduction of several hundred accessions in the 20th century from South-east Asia, India and from other mango-growing areas of the world (Florida Mango Forum, 1951). The introduction of mangoes into Florida and subsequent development of a Florida group of mangoes has been reviewed by Knight and Schnell (1994). The Florida mango cultivars are unique in that they are hybrids between Indian cultivars (primarily monoembryonic) and the South-east Asian cultivars (primarily polyembryonic) selected under south Florida conditions. The mango breeding system favours out-crossing. Therefore, the proximity of numerous genotypes of disparate geographical origins led to the production of many new seedlings by interpollination in Florida (Knight and Schnell, 1993). Florida selections are therefore not the result of a formal breeding programme. Early Florida selections were made by growers and enthusiasts and historical information is often anecdotal. The Florida Mango Forum, established in 1938 for the advancement of mango production, documented historical information on the parentage of Florida cultivars in their proceedings. In addition to the United States Department of Agriculture (USDA) Germplasm Resources Information Network (GRIN) database, several sources compile information on Florida mango selections and introduction of accessions to Florida (Ruehle and Ledin, 1956; Singh, 1960; Campbell and Campbell, 1993; Schnell et al., 2006). With the exception of South-east Asia, Australia and some African countries, which cultivate mostly locally selected varieties, the majority of countries produce cultivars developed in Florida, i.e. ‘Haden’, ‘Tommy Atkins’ and ‘Keitt’ (Galan Sauco, 1997). These Florida selections are now widely grown commercial cultivars affording production stability across many environments (see Mukherjee and Litz, Chapter 1, this volume).

4.3 Reproductive Mechanisms Polyembryony Nucellar embryos Mangoes can be classified into two groups, monoembryonic and polyembryonic, based on their mode of reproduction from seeds. In general, monoembryonic seeds are found in the sub-tropical group (Indian type) and the polyembryonic seeds in the tropical group (South-east Asian). Monoembryonic mango seeds each contain a single zygotic embryo, and hence only one seedling per seed that is of probable hybrid origin. Polyembryonic mango

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seeds can contain one or more embryos, one of which is usually, but not always zygotic. Adventitious embryos develop from the nucellus, a maternal tissue surrounding the embryo sac, and consequently the seedlings of polyembryonic mangoes are genetically identical to the maternal parent. Adventitious embryos can also originate by direct budding from the cotyledons and hypocotyls of other nucellar embryos (Juliano, 1934). According to Maheshwari and Rangaswamy (1958), the nucellar cells destined to form adventitious embryos are recognizable by their dense cytoplasm and starchy contents. They gradually push into the embryo sac cavity where they divide and differentiate into embryos. Inheritance of polyembryony Polyembryony is genetically determined. Leroy (1947) considered that adventive embryony probably reflects the effect of one or more recessive genes. This view was supported by Sturrock (1968), whose study of the progenies of monoembryonic mango hybridized with polyembryonic cultivars indicated that monoembryony was possibly a dominant trait. In contrast, Aron et al. (1998) and Brettell et al. (2004) observed that polyembryony in mango is controlled by a single dominant gene. Schnell et al. (2006) reported that 58 of the Florida cultivars had been classified with 50 being monoembryonic and eight polyembryonic. Information from the Florida cultivars parentage analysis using 25 microsatellite markers supported the findings of Aron et al. (1998) where polyembryony was found to be dominant. ‘Haden’ is a cross of the monoembryonic ‘Mulgoba’ and the polyembryonic ‘Turpentine’. If we assume that a single dominant gene controls this trait, all of the Indian cultivars in Florida must be homozygous recessive and the ‘Turpentine’ parent of ‘Haden’ must have been heterozygous. The evidence suggests that ‘Haden’ inherited the recessive allele from ‘Turpentine’, as all identified progeny of ‘Haden’ are monoembryonic with the exception of ‘Winters’. The most probable pollen parent of ‘Winters’ is ‘Ono’, a polyembryonic cultivar from Hawaii. The frequency of this dominant allele is low in the Florida population and absent from the Indian cultivars in Florida. In view of these interesting findings, and since a thorough knowledge of inheritance of polyembryony is essential for speculating the origin of M. indica, more work on these lines is warranted.

Floral biology and pollination The mango inflorescence is primarily terminal, although axillary and multiple panicles may also arise from axillary buds. Both perfect (hermaphrodite) and staminate (male) flowers occur in the same inflorescence. The total number of flowers in a panicle may vary from 1000 to 6000, depending on the cultivar (Mukherjee, 1953). Initial fruit set in mango is directly related to the proportion of perfect flowers, although the final fruit set does not necessarily depend on this ratio (Iyer et al., 1989). It appears that the proportion of perfect flowers in a cultivar becomes critical for optimum fruit set only when the proportion drops to 1%.

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Flowers begin to open early in the morning and anthesis has generally been completed by noon. The greatest number of flowers opens between 9 and 10 a.m. Although the receptivity of the stigma continues for 72 h after anthesis, it is most receptive during the first 6 h; however, there are reports that the stigma can become receptive even before anthesis has occurred (Singh, 1960). The minimum time required for pollen grains to germinate is 1.5 h (Sen et al., 1946; Singh, 1954; Spencer and Kennard, 1955). Singh and Singh (1952) observed 98% pollen viability after 11 months in storage at 7°C and 25% relative humidity (RH), and 65.7% viability after 24 months of storage at 0°C and 25% RH. Mango is cross-pollinated, which is carried out by insects such as the common housefly, honeybees and thrips, and possibly by other insects al-though to a lesser extent. Pollination by wind and gravity has been suggested to occur in mango (Popenoe, 1917; Maheshwari, 1934; Malik, 1951). In nature, > 50% of flowers do not receive any pollen. Some workers had suggested that self-pollination in certain cultivars can also occur quite frequently (Dijkman and Soule, 1951). Studies by Issarakraisila and Considine (1994) have shown that for polyembryonic ‘Kensington’, a night temperature of < 10°C results in pollen grains with low viability (< 50%). The optimum temperature for normal meiosis is between 15 and 33°C with 70–85% viability.

Incompatibility Although the existence of self-sterility in mango was suspected several years ago (Ruehle and Lynch, 1948, cited in Sharma and Singh, 1970; Dijkman and Soule, 1951), the prevalence of self-incompatibility was clearly established in monoembryonic ‘Dashehari’ by Singh et al. (1962). Subsequently, detailed studies indicated that the four popular monoembryonic cultivars of northern India (i.e. ‘Dashehari’, ‘Langra’, ‘Chausa’ and ‘Bombay Green’) were selfincompatible (Mukherjee et al., 1968; Sharma and Singh, 1970). Embryological studies have shown that although fertilization takes place after self-pollination, degeneration of endosperm occurs 15 days after pollination involving self-incompatible parents (Mukherjee et al., 1968). The selfincompatibility system operating in mango appears to be of the sporophytic type. Instances of cross-incompatibility among certain mango cultivars have also been reported (Ram et al., 1976), necessitating the identification of suitable pollinizers for mango. Using an approach involving isozyme analysis, Dag et al. (2006) have initiated studies in many commercial mango cultivars in Israel and concluded that self-pollination is not a yield-limiting factor in monoembryonic ‘Maya’ and the practice of planting ‘Maya’ in solid blocks is sound. They had obtained similar results earlier with monoembryonic ‘Tommy Atkins’ (Dag et al., 1997).

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Cytology Chromosome number Information on the cytology of mango is quite limited. Only a few Mangifera species (i.e. M. indica, M. caloneura, M. sylvatica, M. foetida, M. caesia, M. odorata and M. zeylancia) have been studied, and were found to have chromosome numbers of 2n = 2x = 40 and n = x = 20 (Mukherjee, 1950, 1957; Roy and Visweswariya, 1951). Chromosome numbers and ploidy status of other species are yet to be studied. The only exception to this chromosome number that has been reported to date (Roy and Visweswariya, 1951) involves ‘Vallikolamban’, which was reported to be tetraploid (2n = 4x = 80), although subsequent studies have indicated that it is only a diploid (Majumder and Sharma, 1990). Polyploidy Mango has been referred to as an allopolyploid. Due to the presence of secondary associations at metaphase of meiosis, Mukherjee (1950) suggested that the basic chromosome number of Mangifera is n = 8. In addition, the high number of somatic chromosomes and the correspondingly high number of nucleolar chromosomes led him to conclude that mango is an allopolyploid. However, the evidence used to arrive at this conclusion is not unequivocal. In fact, the molecular marker evidence is antithetical to this conclusion. Results from Duval et al. (2005), Viruel et al. (2005) and Schnell et al. (2005, 2006) using microsatellite markers all indicate that M. indica is diploid. Although many wild Mangifera species are potentially valuable for crop improvement, they are yet to be exploited. Mukherjee (1963) felt that the different Mangifera species could intercross easily, based on the success obtained with interspecific crosses between M. zeylanica and M. odorata.

4.4 Inheritance of Characters High heterozygosity in the cultivars that are used in hybridization and the inadequate number of hybrid progenies realized has made accurate genetic analysis in mango very difficult. However, based on limited data, some indications are available which would be useful in selecting parents in breeding programmes designed with specific objectives. In studies of the distribution of different traits in seedlings derived from open-pollination (where the pollen parent is unknown), Lavi et al. (1989) observed: (i) there is no maternal effect on juvenile period and fertility; (ii) there is a slight effect of the female parent on fruit taste and size; (iii) there is a maternal parent effect on harvest season and fruit colour.

Dwarfness, regular bearing and precocity An analysis based on observations of more than 1000 hybrids, involving several combinations, has revealed that dwarfness, regular bearing and precocity

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are controlled by recessive genes (Sharma and Majumder, 1988a). Regularity of bearing appears to be linked with precocity. Characters contributing to biennial bearing are dominant over those governing regular bearing habit. Flesh colour Sharma (1987) considered that additive gene action may be involved in the inheritance of flesh colour; however, studies involving monoembryonic ‘Alphonso’ and ‘Neelum’ have indicated that light yellow is dominant over orange-yellow (Iyer, 1991). Skin colour With regard to skin colour of fruit, Sharma (1987) observed that when red cultivars were crossed with green cultivars, the F1 seedlings exhibited various gradations of red. Iyer and Subramanyam (1987) also found a wide array of colours in the hybrids when the coloured monoembryonic ‘Janardhan Pasand’ was crossed with green-fruited cultivars, indicating that colour is mediated by a number of loci. Flowering time The flowering response of mango cultivars in subtropical and tropical environments differs greatly (see Davenport, Chapter 5 this volume). Trees can be stimulated to flower under certain conditions in tropical environments using ethephon; however, this is ineffective in subtropical environments. Schnell and Knight (1998) investigated the repeatability of flowering using eight cultivars over six harvest cycles (years), collecting data weekly. Three characters were evaluated: days to bloom (DTB) (from 1 November in each year), days in bloom (DIB), and days in bloom and fruit (DIBF). Significant differences were detected for all three characters for both years and cultivars. Significant differences were not detected for replicate trees within cultivars. Repeatability (R) of the flower phenology characters was high (R = 0.73, 0.88 and 0.77 for DTB, DIB and DIBF, respectively). This indicates that much of the variation is heritable and useful for extending flowering times in subtropical environments. Beak The presence of a beak on mango fruit appears to be a dominant character since most of the hybrid plants had this feature when monoembryonic ‘Bangalora’ (‘Totapuri’) was used as one of the parents in controlled crosses (Iyer and Subramanyam, 1979). Bunch bearing was found to be a dominant character, as indicated in many crosses (Sharma et al., 1972) involving bunchbearing types with single-fruited cultivars.

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Disease resistance Bacterial canker (Xanthomonas campestris pv. mangiferaeindicae) resistance appears to have cytoplasmic inheritance. Whenever ‘Neelum’, a susceptible cultivar, is used as the female parent, susceptibility is transmitted to all the hybrids, irrespective of the male parent (Sharma and Majumder, 1988a). It has been suggested that internal breakdown (spongy tissue) is mediated by recessive genes (Iyer, 1991). Susceptibility to ‘mango malformation’ appears to be dominant, since crosses involving resistant ‘Bhadauran’ did not yield any resistant hybrids (Sharma and Majumder, 1988a).

Other horticultural traits The genetics of inheritance of various horticultural traits appears to be unclear. More knowledge will be forthcoming only when large-scale controlled hybridization experiments are undertaken at different mango research centres. However, the information now available for some of the characters is very useful in deciding which parental genotypes ought to be used in hybridization programmes. Brettell et al. (2004) subjected the large number of mango hybrids obtained from the Australian National Mango Breeding Programme to a biometrical analysis. Their data indicated that many of the important fruit quality aspects, including fruit weight, fruit shape, ground skin colour, fruit width and pulp depth have high heritabilities and can therefore be readily selected in a breeding programme. Of particular interest is the observation that a high frequency of hybrids with a red or burgundy blush can be recovered from crosses where one parent has an intense red blush. Similarly, while the unique flavour compounds associated with ‘Kensington Pride’ are also found in nearly 50% of the hybrids involving ‘Kensington Pride’, leaf fragrance was not found to be a reliable predictor of fruit flavour.

4.5 Breeding Objectives General objectives Breeding objectives vary from region to region, depending on the specific trait(s) for which improvement is sought. However, they can be broadly generalized to consist of the development of cultivars with: (i) regular bearing; (ii) dwarf tree habit; (iii) precocity; (iv) attractive, good sized (300–500 g), good quality fruits (appealing flavour and firm flesh without fibres); (v) resistance to major diseases and pests; (vi) freedom from physiological disorders; and (vii) good shipping qualities and shelf life. While it would be hard to combine all these characteristics within a relatively short time, especially resistance to all major diseases and pests, all of these characteristics are basic for commercial success.

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With regard to the improvement of rootstocks by breeding, the main desirable features are: (i) polyembryony; (ii) dwarfing; (iii) tolerance of adverse soil conditions (high pH, calcareous soil, etc.); and (iv) good scioncompatibility.

Specific objectives In addition to improving general characters such as yield and quality, breeding has also been undertaken for certain specific purposes. Dwarfness Because of the obvious benefits of comparatively dwarf trees for orchard management and fruit quality, attempts have been focused on obtaining hybrids with a dwarf tree framework. Breeding for dwarfness is important in mango, since a consistent dwarfing effect of any rootstock has not been established to date. The Indian cultivars that could be useful as a source for dwarfness include ‘Kerla Dwarf’, ‘Janardan Pasand’, ‘Manjeera’, ‘Amrapali’, ‘Creeping’ (Iyer and Subramanyam, 1986) and ‘Nileswar Dwarf’ (Singh, 1990). Regular bearing The causes of irregular bearing vary from region to region. In general, the main reason for alternate bearing, particularly in subtropical India, is the lack of initiation of vegetative growth soon after fruiting. However, two cultivars, ‘Neelum’ and ‘Bangalora’ (‘Totapuri’), which are regular bearers, have been extensively used as either of the parents in a hybridization programme to transfer the regular bearing habit to hybrids. ‘Neelum’ has been observed to be a good combiner and has contributed to the evolution of many regularbearing Indian hybrid cultivars. However, ‘Bangalora’ is not a suitable parent since the hybrids possess very prominent beaks and their fruit quality is invariably poor. The regular bearing Florida cultivars (i.e. ‘Tommy Atkins’, ‘Keitt’, etc.) also have potential as parents. Fruit colour Most of the commercial cultivars in South-east Asia possess green skin. Efforts are underway to produce new hybrid cultivars that retain the good qualities of these fruits together with attractive skin colour, so that they will occupy a better position in international trade. Since good skin colour has been shown to be transmissible to hybrids from suitably coloured parental cultivars, a number of cultivars with coloured skin are being used for hybridization. In general, the attractively coloured Florida cultivars have been found to be suitable parents. In addition, there are several Indian cultivars (e.g. ‘Janardan Pasand’, ‘Suvarnarekha’, etc.) that would be suitable for use as parents for this purpose. In Florida, the skin colour of the mango is an important factor and red skin is considered essential for mangoes shipped to northern markets. In the past, the evaluation of mango colour has been subjective and based on visual

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ratings. Large errors are associated with these types of ratings, which makes evaluation based on fruit colour difficult. Ayala-Silva et al. (2005) used a colorimeter to quantify fruit colour, quality and differentiation among cultivars. Mango colour was measured with a Minolta Chroma Meter CR-400 (Osaka, Japan) portable tristimulus colorimeter and fruit chromaticity was recorded in Commission Internationale de l’Eclairage (CIE) L*, a* and b* colour space coordinates. In this system of colour representation the values L*, a* and b* describe a uniform three-dimensional CIE colour space. If the L*, a* and b* coordinates are known, then the colour is not only described, but also located in quantifiable space. Maternal half-sib families (MHS) of the mango cultivars, ‘Keitt’, ‘Tommy Atkins’, ‘Tyler Premier’, ‘Mamita’, ‘White Alfonso’ and ‘Sandersha’ were evaluated along with two parental check clones, ‘Tommy Atkins’ and ‘Keitt’. Significant differences were found for each of the L*, a* and b* colour space coordinates. Further work is underway to estimate the heritability of these traits to estimate their usefulness for breeding and selection. Disease resistance MANGO MALFORMATION. Although no breeding work has been reported that specifically addresses disease or pest resistance/tolerance, cultivars are known to show varying degrees of susceptibility to biotic stress (see Ploetz and Freeman, Chapter 8, this volume ). Mango malformation, caused by Fusarium subglutinans, is a very serious disease that has threatened the very survival of the mango industry in many subtropical mango-growing regions. As there are no reliable cultural and chemical control measures available, breeding for resistance/tolerance has been attempted using ‘Bhadauran’ as the resistant parent; however, all of the F1 hybrids were susceptible to the disease (Sharma and Majumder, 1988a). In this respect, the observations of Ram et al. (1987) are very encouraging. Out of 102 cultivars screened, three of them, namely, ‘Bhydayam Dula’, ‘Samar Bahist Rampur’ and ‘Mian Sahib’, were free of malformation and could be tried as one of the parents in hybridization. BACTERIAL CANKER. Bacterial canker is a serious problem with many cultivars. The only cultivar possessing true resistance to canker is ‘Bombay Green’ (Prakash and Srivastava, 1987) and hence could be a potential gene donor. ANTHRACNOSE.

Anthracnose, caused by Colletotrichum gloeosporioides Penz., is the most widespread disease in all mango-growing countries, manifesting itself in blossom blight, peduncle blight, leaf spot, twig blight, wither tip, fruit russetting and fruit rot. ‘Tommy Atkins’ is moderately tolerant of anthracnose and coupled with its other desirable qualities (i.e., regular bearing, fruit colour, etc.) should be a good parent in breeding programmes. In addition, ‘Parish’ and ‘Fairchild’ have been reported to be relatively resistant (Yee, 1958).

POWDERY MILDEW. Powdery mildew caused by Oidium mangiferae Berthet, has been reported to cause heavy loss of crops in years when RH is very high and accompanied by cool nights during flowering. Cultivar differences with respect to susceptibility are recognized, and ‘Pairi’ (‘Raspuri’) is highly susceptible.

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Gupta (1976) has listed those cultivars that are most tolerant of this disease – ‘Neelum’, ‘Zardalu’, ‘Bangalora’, ‘Totapuri-Khurd’ and ‘Janardan Pasand’ – and hence could be valuable in breeding programmes. PEST RESISTANCE. Considerable variation is also known to occur among mango cultivars with respect to their susceptibility to attack and injury by insect pests. Although no resistant genotypes have been reported for the mango hopper (Idiocerus spp.), the insect has been observed to avoid colonizing open plant types where free movement of wind is possible, an observation that could be useful in selection. Although complete resistance is not known to either fruit fly (Bactrocera spp.) or seed weevil (Stenochetus mangiferae), variation in the degree of susceptibility has been reported (Iyer, 1991). Rossetto et al. (2006) observed that resistance to fruit fly is compatible with fruit quality and productivity and advocated that resistance to fruit fly should be one of the objectives of all mango breeding programmes. Their results also indicated that the main factors for resistance of mangoes to fruit flies lie in the fruit peel and not in the fruit pulp.

4.6 Methods of Breeding Selection from open-pollinated seedlings In India, almost all cultivars are selections that were made from naturally occurring open-pollinated seedlings. All of the Florida cultivars were selected from open-pollinated seedling progenies; none has come from a controlled breeding programme. Among the 64 Florida cultivars evaluated in the parentage analysis by Schnell et al. (2006), the genetic background was found to be based on as few as four Indian cultivars and the polyembryonic cultivar ‘Turpentine’. Two Indian cultivars, ‘Mulgoba’ and ‘Sandersha’, are in the background of most Florida types with ‘Amini’, ‘Bombay’, ‘Cambodiana’, ‘Long’, ‘Julie’ and ‘Nam Doc Mai’ making lesser contributions. In the parentage analysis ‘Turpentine 10’ was identified as a most probable paternal parent for ‘Haden’. The polyembryonic seedling races of Cuba and Florida were considered the same by Popenoe (1920) who called them the West Indian race (commonly known as ‘Turpentine’ in Florida). ‘Haden’ was reported as the maternal parent for ten cultivars included in the analysis, but based on the parentage analysis, 31 cultivars were found to have ‘Haden’ as one of the most likely parents. Likewise, the other important early Florida selection ‘Brooks’ is the parent of seven cultivars. ‘Haden, ‘Brooks’ and seedlings of ‘Haden’ and ‘Brooks’ have contributed disproportionately to the Florida group. In Florida, modern selection and breeding programmes for mango have focused on cultivars with exceptional production, red skin, disease resistance and extended shelf life. Methodology for crop improvement consists of collecting seeds from selected maternal parents with desired characteristics and growing them in close proximity to desirable male parents. Seedlings are screened by leaf aroma and horticultural traits, leading to a field population of thousands of candidate seedlings (Campbell and Zill, 2006).

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In the Canary Islands, Spain, breeding mainly involves selection of openpollinated seedlings of ‘Lippens’. Lavi et al. (2004) indicated that mother trees should not be chosen entirely on the basis of their phenotypes and trees with inferior performance could also be included since progeny performance is quite unpredictable. They observed that most of the variance components of the agriculturally interesting traits are non-additive (Lavi et al., 1998) and most of these traits result from dominant and epistatic interactions. The Israel mango-breeding programme therefore relies on open-pollination involving many mango cultivars from various parts of the world and screening approximately 100 seedlings from each mother tree. The seedlings are grown on their own roots in the nursery for about a year and then planted in the field at spacings of 2 × 6 m. Fruiting occurs after 3–6 years and first selection is carried out based on field and laboratory data. Fruit characteristics at this stage are good skin colour, fruit weight of 400–600 g and high fruit quality (good taste, absence of fibres and small seed). Where a long harvest season is desired both early and late harvest seedlings are selected and a general idea about shelf life of these seedlings is obtained. The second selection is carried out under commercial conditions by several experienced farmers using grafted plants. Plants that successfully pass this stage are planted in semi-commercial plots for a final assessment before recommendation to farmers. The two selection stages are aimed at shortening the breeding programme and minimizing both the false negatives (loss of interesting seedlings which were not identified) and the false positives (wrong identification of interesting seedlings which should actually be rejected). New mango cultivars have also been selections made from open-pollinated seedlings. ‘Maya’ and ‘Nimrod’ are seedlings of the same mother tree (Oppenheimer, 1967); ‘Tahar’ is a seedling of ‘Irwin’ (Slor and Gazit, 1982) and ‘Naomi’ is a seedling of ‘Palmer’ (Tomer et al., 1993). The other promising selections include ‘Shelly’ (late season), ‘Tango’ (early season), ‘Selection 20/1’ (large fruit with aborted seeds) and ‘Selection 1/5’ (shiny red colour). The South African mango-breeding programme also places a major emphasis on open-pollinated seedling selection. The screening of seedlings, besides undergoing tests for various plant and fruit characters, also includes shipping quality tests in which fruits are packed in 4 kg crates and stored at 11°C for 28 days to simulate shipping conditions. After storage the fruits are allowed to ripen at room temperature (25 ± 2°C) and screened thoroughly. Promising seedlings are again field-tested with ‘Sabre’ as rootstock with a row of 40 trees along with ten trees of commercial varieties. Two cultivars, ‘Joa’ (‘Palmer’ seedling) and ‘Chene’ (‘Kent’ seedling), were released from the breeding programme in 1996. Another high yielding selection ‘A2-CD28’ (‘Fascell’ seedling) is a midseason clone with an attractive pink blush (Human et al., 2006) and has been recommended for Plant Breeders’ Rights in 2005. The other promising selections are ‘Osteen’ (‘Haden’ seedling) and ‘Neldica’ (‘Palmer’ seedling). The 'R2E2' cultivar developed in Australia is a seedling progeny of the Florida cultivar 'Kent', and is now the second most popular mango grown in Australia.

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Controlled pollination Hand pollination The traditional, cumbersome method involving the continued pollination of flowers on a panicle over several days when the flowers are open has now been replaced in India with more efficient methods. The current method involves the pollination of a limited number of flowers per panicle (maximum of ten), utilizing a larger number of panicles since it is very rare that a panicle bears more than one fruit to maturity. Using this method, fruit set as high as 3.85% can be achieved compared to the 0.23–1.57% efficiency involving other methods (Mukherjee et al., 1968; Singh et al., 1980). Caging The enclosure of two desirable parents of synchronous flowering in a screen house with pollinating insects provides a more practical method of hybridization. This method has been used in Israel (Degani et al., 1993), Brazil (Pinto and Byrne, 1993) and South Africa (Cilliers et al., 1996). A standardized caging technique for mango breeding was previously used in India following the discovery of self-incompatibility in some of the most popular commercial cultivars (Sharma and Singh, 1970). This procedure involves the planting of self-incompatible (female) and male parents in specially prepared breeding plots, and are enclosed in an insect-proof cage into which freshly reared houseflies, or any other suitable pollinator, are introduced to effect cross-pollination (Sharma et al., 1972). Polycross mating A polycross is simply the use of a number of advanced selections or current commercial clones planted in a design that maximizes the chance for cross-pollination. The polycross design has been extensively used in sugarcane breeding where small flower size and low numbers of seedlings per cross make controlled pollinations difficult. At USDA Subtropical Horticulture Research Station (SHRS) in Miami the clones ‘Haden’, ‘Tommy Atkins’, ‘Kent’, ‘Keitt’ and ‘Nam Doc Mai’ have been used to produce new seedlings for selection. Five clones of each genotype were planted, with at least one plant of each genotype next to all other genotypes. Over 1000 seedlings from known mother trees are planted as maternal half-sib families. The pollen parent of superior selections is determined using microsatellite markers.

4.7 Handling of Hybrid Populations and Selection Criteria for initial selection Primary selection from the hybrid progeny is based on: (i) precocity; (ii) fruit size and shape; (iii) skin colour; (iv) fruit characteristics (high pulp to stone ratio and freedom from fibre and physiological disorders); and (v) fruit quality. Following this preliminary evaluation, selected hybrids are retained for

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further screening. It is important to graft the hybrids onto proper rootstocks as early as possible, as grafted plants are precocious. At least ten grafted plants of each selected hybrid are used in the final selection, which is based on yield, regularity in bearing and response to diseases and pests, in addition to other desirable fruit characters. At least 3 consecutive years’ performance data should be collected before deciding on their suitability for release as new cultivars.

Pre-selection Trees have a long juvenile phase, and the development of pre-selection methods is important for discarding inferior seedlings at a very early stage, obviating the need for maintaining a large number of seedlings for long periods. This can save time, land and labour. Leaf flavour has been reported to be directly correlated with fruit flavour (Majumder et al., 1972; Whiley et al., 1993). Emergence of new growth flushes, simultaneously with fruiting or immediately after harvest, is indicative of regular bearing (Sharma et al., 1972). A higher phloem to xylem ratio, associated with dwarfing, has been used effectively as a pre-selection criterion. Genotypes in which the ratio exceeds 1.0 are least vigorous, those with a ratio between 0.6 and 1.0 are of medium vigour and those with a ratio of less than 0.6 are most vigorous (Kurian and Iyer, 1992). In addition, higher levels of phenolics in the apical bud is associated with reduced vigour and dwarfing (Iyer, 1991). Although Majumder et al. (1981) indicated that low stomatal density is an indicator of dwarfness this has not been confirmed by other workers (Iyer, 1991). Regular bearing mango cultivars have low polyphenol oxidase (PPO) activity (catecholase and cresolase) compared to alternate bearers (Sharma, 2003). Sharma et al. (2000) observed that a strong positive correlation existed between the incidence of floral malformation and both enzyme activity (catecholase and cresolase) and phenolic content and speculated that PPO activity can be used as a biochemical index for screening mango germplasm against malformation disease.

Potential for marker assisted selection (MAS) More than 65 microsatellite markers have been developed for mango and these are easily used to verify parentage using a software package such as cervus (Marshall et al., 1998). When caging trees or using the polycross mating design it is possible to identify the male parent from a set of potential male parents. This has been useful in cacao breeding where mistakes in pollination have lead to the estimation of unreliable breeding values for parental clones. The development of linkage maps and identification of quantitative trait loci (QTL) for productivity and quality traits has led to a very successful MAS in cacao (Schnell et al., 2007). This could serve as a model for future mango breeding and selection efforts.

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Molecular markers Molecular markers can be used for estimating genetic relationships among clones, for parentage analysis and for the development of a saturated linkage map. Isozymes were the first markers to be used for fingerprinting mango cultivars, to determine self- versus cross-pollination and to estimate genetic relationships (Degani et al., 1990; Knight and Schnell, 1994). RAPD markers were also used to fingerprint cultivars and estimate genetic relationships in mango (Schnell et al., 1995). A group of ‘Haden’ seedlings and a random group of seedlings were evaluated using 11 RAPD primers. This study supported the ‘Haden’ parentage of ‘Eldon’, ‘Lippens’, ‘Tommy Atkins’ and ‘Zill’; however, the parentage of ‘Glenn’ and ‘Osteen’ was questioned. Adato et al. (1995) used DNA fingerprinting (DFP) to evaluate genetic relationships between 26 mango cultivars and 14 rootstocks. They provided a pedigree that further confirmed the relationship between many of the ‘Haden’ seedlings. Lopez-Valenzuela et al. (1997) used RAPD markers to estimate genetic diversity among 15 rootstock cultivars using 13 markers, and identified a specific RAPD band associated only with the polyembryonic types. Eiadthong et al. (1999) utilized anchored simple sequence repeat markers to analyse 22 mango cultivars; they were able to distinguish genotypes, but were unable to find markers unique to either monoembryonic or polyembryonic types, or for the Thai cultivars selected for green harvest (crispy mango) from the cultivars selected for ripe fruit production. Kashkush et al. (2001) utilized amplified fragment length polymorphisms (AFLP) to estimate genetic relationships between 16 cultivars and seven rootstock cultivars. They also analysed 29 progeny from a cross of ‘Tommy-Atkins’ and ‘Keitt’ and produced a crude linkage map that identified 13 of the 20 linkage groups. Viruel et al. (2005) developed the first reported set of 16 microsatellite markers for mango, of which 14 produced the expected one or two amplification products per genotype. These 14 microsatellites were used to evaluate 28 mango genotypes that included 14 Florida cultivars. Discrimination of all 28 genotypes was possible and the average number of alleles per locus was 5.3. Previously known pedigree information for the ‘Haden’ family of mangoes was confirmed and was in agreement with previously published RAPD and DFP analyses (Adato et al., 1995; Schnell et al., 1995) with one exception. Viruel’s clone of ‘Zill’ was not resolved as a seedling of ‘Haden’. Schnell et al. (2005) developed a second set of 15 microsatellite markers and analysed 59 Florida cultivars and four related species. Two of the microsatellites were monomorphic among the Florida cultivars; the other 13 had an average number of alleles per locus of 4.2 with polymorphism information content (PIC) values varying from 0.21 to 0.63. Schnell et al. (2006) used 25 microsatellite loci to estimate genetic diversity among 203 unique mangoes (M. indica L.), two M. griffithii Hook. f. and three M. odorata Griff. accessions maintained at the National Germplasm Repository (NGR) and by Fairchild Tropical Botanic Garden (FTBG) in Miami, Florida. The 25 microsatellite loci had an average of 6.96 alleles per locus and an average PIC value of 0.552 for the M. indica population. The total

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propagation error in the collection (i.e. plants that had been incorrectly labelled or grafted) was estimated to be 6.13%. When compared by origin, the Florida cultivars were more closely related to Indian than to South-east Asian cultivars. Unbiased gene diversity (Hnb) of 0.600 and 0.582 was found for Indian and South-east Asian cultivars, respectively, and both were higher than Hnb among Florida cultivars (0.538). When compared by horticultural type, Hnb was higher among the polyembryonic types (0.596) than in the monoembryonic types (0.571). To date 63 microsatellite markers have been developed for mango (Duval et al., 2005; Honsho et al., 2005; Schnell et al., 2005; Viruel et al., 2005). This number is more than adequate for genetic diversity studies and for parentage analysis as has been demonstrated by Schnell et al. (2006); however, it is not enough to develop a saturated linkage map for the 20 linkage groups of mango. Developing an additional 200 microsatellite or single nucleotide polymorphic markers is a major objective of the USDA Agriculture Research Service (ARS) programme in Miami over the next 2 years. Three experimental populations have been developed and planted in the field as mapping populations. The first population is an F2 population derived from self-pollination of ‘Tommy Atkins’ consisting of 168 seedlings that was planted in the field in 1995. The second population is an F2 population derived from selfpollination of ‘Haden’. A total of 224 seedlings from a single isolated ‘Haden’ tree have been in the field for 3 years. Phenotypic data collection is in progress for both of these populations. The development of a saturated linkage map and the identification of QTL for important traits are objectives for the USDA-ARS programme in Miami for the next 5 years.

4.8 Minimizing Problems in Breeding Heavy fruit drop Heavy fruit drop ultimately results in few hybrid fruits, despite the large number of flowers used for cross-pollination. While many recommendations are available to minimize mango fruit drop with growth regulators, these have not been very useful in breeding programmes where the number of flowers remaining in a panicle is very low. Iyer and Subramanyam (1972) suggested that embryo culture could be used to rescue hybrid embryos, and Sahijram et al. (2005) developed in-vitro techniques to rescue immature mango embryos from controlled crosses and recovered hybrid plants.

Long juvenile phase Normally, mango seedlings require 3–10 years to flower, thereby prolonging the breeding programme. Grafting individual hybrids on the proper rootstocks at the earliest possible stage and growing them in a location where climatic stress (particularly cold weather) prevails, induces precocious

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flowering. Iyer (1991) has reported significant differences between seedlings on their own roots and grafted plants of the same genotype with respect to fruit size, quality and even colour in the early years. However, different results have been reported in a recent study of the effect of rootstocks on the performance of seedling scions with respect to ten horticultural traits (Lahav et al., 1995). No difference of practical importance was found between the original seedlings and their grafted duplicates. Singh (1969) has suggested that young mango seedlings can be induced to flower and fruit if they are grafted onto comparable shoots of a bearing tree (a few days before flowering). The scions are defoliated and girdled. Using this technique, it has been reported that the fruit characteristics of F1 hybrids can be determined within 2 years and F2 hybrids within 4 years, thus eliminating at least 10 years from the period required to raise and evaluate F2 populations (Singh, 1963). Ethephon (Chacko et al., 1974) and paclobutrazol (Anonymous, 1984) have flower-inducing properties in mango and could also be utilized for shortening the juvenile phase. However, they must be used with caution since chemical induction of flowering can alter fruit size and this could lead to errors in judgement when making selections within the hybrid progeny.

Polyembryony Seeds of polyembryonic mango cultivars characteristically contain several nucellar embryos, and may also contain a zygotic embryo. While nucellar seedlings are preferred as rootstocks for mango because of their uniformity, the breeder, on the other hand, is generally interested in sexual seedlings for the selection of improved rootstocks. Until recently, crosses involving polyembryonic cultivars as the maternal parents were generally not performed, since reliable methods for identifying zygotic seedlings were not available. The use of polymorphic enzyme systems (isozymes) (Degani et al., 1990, 1992) to identify zygotic seedlings (Schnell and Knight, 1992; Truscott, 1992; Degani et al., 1993) is based on the fact that nucellar seedlings should have the same isozyme alleles as the maternal parent. A variation at a locus coding for an enzyme indicates that the plant has originated by sexual reproduction. Zygotic seedlings arising from self-pollination are distinguished from nucellar seedlings by being homozygous at one or more loci at which the female parent is heterozygous. Statistically, when three or four heterozygous loci are examined, up to 88 or 94%, respectively, of the selfed zygotic seedlings are identifiable (Moore and Castle, 1988). Cross-pollination by another cultivar of the same genotype is equivalent to self-pollination. Zygotic seedlings from cross-pollination are distinguishable from those resulting from self-pollination if they express an allele not carried by the female parent. The frequency of occurrence of zygotic seedlings varies among the polyembryonic mango cultivars, i.e. 22% with ‘13-1’ (Degani et al., 1993), 20 and 24% with ‘Turpentine’ (Degani et al., 1993 and Schnell and Knight, 1992, respectively), 2 and 4% with ‘Sabre’ (Truscott, 1992 and Schnell and Knight,

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1992, respectively) and 36 and 64% with ‘Madu’ and ‘Golek’, respectively (Schnell and Knight, 1992).

4.9 Achievements of Conventional Breeding Despite the many problems associated with mango breeding for cultivar development, many useful hybrids have been released. The earliest attempts were probably made in the West Indies to combine the good qualities of the Indian mango with the indigenous types by controlled pollination (Brooks, 1912).

India Intervarietal hybridization in India has resulted in the release of many cultivars. The work at Sabour initially yielded two promising hybrids: ‘Mahmood Bahar’ and ‘Probashanker’, both combinations of ‘Bombay’ and ‘Kalapady’ (Roy et al., 1956). Subsequently, four more hybrids have been developed. These are: ‘Sundar Langra’ (‘Sardar Pasand’ × ‘Langra’) having ‘Langra’ quality and regular bearing habit; ‘Alfazli’ (‘Alphonso’ × ‘Fazli’) with ‘Fazli’ quality and early ripening; ‘Sabri’ (‘Gulabkhas’ × ‘Bombai’) having ‘Bombai’ fruit shape and colour of ‘Gulabkhas’ with regular bearing habit; and ‘Jawahar’ (‘Gulabkhas’ × ‘Mahmood Bahar’) having high pulp and early bearing habit (Hoda and Ramkumar, 1993). Developed in Kodur, the hybrid ‘Swarnajehangir’, combining the high quality of ‘Jehangir’ and the attractive colour of ‘Chinnaswarnarekha’, is a prolific bearer and is the best of all hybrids developed at this centre. The other hybrids released from Kodur are ‘Neeludin’ (‘Neelum’ × ‘Himayuddin’), ‘Neelgoa’ (‘Neelum’ × ‘Yerra Mulgoa’) and ‘Neeleshan’ (‘Neelum’ × ‘Baneshan’). Two excellent, regular-bearing hybrids, ‘Mallika’ and ‘Amrapali’, were developed and released by the Indian Agricultural Research Institute (IARI), New Delhi (Singh et al., 1972). ‘Mallika’ is a hybrid between ‘Neelum’ and ‘Dashehari’ with a high total soluble solids (TSS) content, a higher percentage of pulp, fibreless flesh and a fruit size of about 300 g. ‘Amrapali’ (‘Dashehari’ × ‘Neelum’) is precocious, distinctly dwarf and hence amenable to high-density planting, a regular bearer with excellent quality and is also very rich in vitamin A. Recently, two more cultivars, ‘Arunima’ (‘Amrapali’ × ‘Sensation’) and ‘Pusa Surya’ (a selection from ‘Eldon’) have been released from the IARI. A promising mango hybrid ‘Ambika’, a cross between ‘Amrapali’ and ‘Janardhan Pasand’, having a yellow colour with red blush, firm flesh and scanty fibre was released from the Central Institute of Sub-Tropical Horticulture, Lucknow. Four hybrid cultivars were released from the Indian Institute of Horticultural Research in Bangalore: ‘Arka Aruna’ (‘Banganapalli’ × ‘Alphonso’), ‘Arka Puneet’ (‘Alphonso’ × ‘Banganapalli’), ‘Arka Anmol’ (‘Alphonso’ × ‘Janardhan Pasand’) and ‘Arka Neelkiran’ (‘Alphonso’ × ‘Neelum’). ‘Arka Aruna’ is dwarf, and large fruited with a high percentage of pulp and high TSS content. It is ideal for homesteads. ‘Arka Puneet’ is very similar to

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‘Alphonso’ but free of ‘spongy tissue’, has a good shelf life and is not susceptible to fruit fly attack. ‘Arka Anmol’ is a heavy bearer with good keeping quality (Iyer and Subramanyam, 1993). ‘Arka Neelkiran’ is free of spongy tissue and has excellent skin colour. ‘Ratna’ is a cross between ‘Alphonso’ and ‘Neelum’ that was carried out at the Fruit Research Station, Vengurla, Maharashtra; it has a larger fruit size, fruit quality similar to ‘Alphonso’ and is free of ‘spongy tissue’ (Salvi and Gunjate, 1988). A parthenocarpic mango cultivar, ‘Sindhu’, has been developed at this station as a result of back-crossing ‘Ratna’ with ‘Alphonso’ (Gunjate and Burondkar, 1993). Two hybrid cultivars were released from the Fruit Research Station in Sangareddy, Andhra Pradesh. ‘Au-Rumani’ (‘Rumani’ × ‘Mulgoa’) is a regular and prolific bearer with fibreless flesh. ‘Manjira’ (‘Rumani’ × ‘Neelum’) is a dwarf, regular and prolific bearer with good quality fruits. The Paria Research Station in Gujarat developed three mango hybrids, ‘Neelphonso’ (‘Neelum’ × ‘Alphonso’), ‘Neeleshan Gujarat’ (‘Neelum’ × ‘Baneshan’) and ‘Neeleshwar’ (‘Neelum’ × ‘Dashehari’). These hybrids are superior in TSS, total sugars and vitamin C, in addition to their dwarfing habit, with respect to their parents (Sachan et al., 1988).

Other countries USA Mango hybridization was reported from Hawaii in the 1920s, but no outstanding problem appears to have been addressed or solved (Pope, 1929). A number of crosses have been reported in Florida (Young and Ledin, 1954; Sturrock, 1969), but all of the Florida cultivars are chance seedlings and none came from controlled pollinations. Israel There is an extensive breeding programme in Israel aimed at producing higher yielding cultivars with good quality, attractive fruit and with longer harvest periods. Several hundred seedlings from open and controlled pollinations have been evaluated, and 14 of them have been identified as being of interest (Lavi et al., 1993). The rootstock breeding programme is aimed at developing rootstocks resistant to or tolerant of soil stresses, i.e. calcareous soils, saline irrigation water and heavy non-aerated soils that predominate in the mango-growing regions of Israel. Several interesting monoembryonic and polyembryonic rootstocks have been selected (Lavi et al., 1993), but none has performed better than ‘13-1’, the currently preferred rootstock in Israel (Gazit and Kadman, 1980). Australia A breeding programme to develop a new cultivar which retains the characteristic flavour of ‘Kensington’, but with improved productivity, greater disease resistance, enhanced skin colour and better postharvest performance,

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was initiated in Queensland, Australia. These features are found in many Florida cultivars (i.e. ‘Irwin’, ‘Sensation’ and ‘Tommy Atkins’) which are being used as maternal parents in crosses with ‘Kensington’ (Whiley et al., 1993). Promising hybrids have been identified in crosses involving ‘Sensation’, for example ‘Calypso’™ (see Knight et al., Chapter 3, this volume). ‘Calypso’™ has increased shelf life, firmer fruit, extra blush for cosmetic appeal, a higher flesh-to-seed ratio and consistent yields of high-quality fruit. The Australian mango breeding programme was strengthened since 1994 by launching a major effort involving various organizations located in different agro-climatic zones in hybrid production, as well as regional testing. Brazil Breeding has been initiated in the tropical savannah of Brazil to develop cultivars that are dwarf and with good quality fruit. Hybridizations have involved local, Indian and Florida cultivars. ‘Amrapali’ and ‘Imperial’ were good male parents to confer dwarfing in the progeny (Pinto and Byrne, 1993). Out of 2088 seedlings in the field, 209 seedlings were selected in the first year and 42 of these were later identified as promising, from which four have been released as new cultivars (Pinto et al., 2004). These four are: ‘Alfa’ (‘Mallika’ × ‘Van Dyke’), which is semi-dwarf, high yielding and regular bearing; ‘Beta’ (‘Amrapali’ × ‘Winter’), high yielding and moderately resistant to anthracnose and Oidium; ‘Roxa’ (‘Amrapali’ × ‘Tommy Atkins’), with excellent fruit quality; and ‘Lita’ (‘Amrapali’ × ‘Tommy Atkins’), high yielding with excellent fruit quality. South Africa The South African breeding programme at the Citrus and Subtropical Fruit Research Institute (CSFRI) is based on introductions, open-pollination and mass selection. Four new cultivars have been released: ‘Heidi’, ‘Neldawn’, ‘Neldica’ and ‘Ceriese’. In addition, 12 promising selections have been identified for further evaluation (Marais, 1992).

4.10 Mutations Somatic mutations Asexual propagation enables the preservation of accumulated mutations (macro and micro), which would normally be eliminated during sexual propogation. In many fruit crops, bud mutations and chimeras occur rather frequently and can provide an additional source of variability for selection. However, such reported instances are relatively few in mango. Roy and Visweswariya (1951) observed mutants of ‘Puthi’ in which the number of palisade cell layers differed from the original cultivar. Naik (1948) observed significant variation among trees of the same clone with respect to fruit shape, size, colour and quality, which was ascribed to bud mutations. ‘Davis Haden’, a sport of ‘Haden’, is larger than ‘Haden’ and its season of maturity is about

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a month earlier (Young and Ledin, 1954). ‘Rosica’ from Peru, is a bud mutant of ‘Rosado de lca’. Unlike its parent, ‘Rosica’ is high yielding and regular bearing, and does not produce seedless fruits (Medina, 1977). Oppenheimer (1956), after a survey of many orchards in India, reported wide variability in the performance of trees of the same clone within a single orchard. Mukherjee et al. (1983) conducted a survey of mangoes in eastern India and identified some superior clones. Singh and Chadha (1981), in a study of orchards of ‘Dashehari’, located four clones which were superior in performance. Singh et al. (1985) isolated two high-yielding clones from orchards of ‘Langra’. Within ‘Kensington’, strains have also been identified that show improved resistance to bacterial black spot (Whiley et al., 1993). Roy (1950) observed a mutant of ‘Alphonso’ with respect to fruit shape, and suspected it to be a mericlinal chimera. Pandey (1998) has described seven clones of ‘Alphonso’: ‘Alphonso Behat’ and ‘Alphonso Bihar’ from Bihar, ‘Alphonso Batli’, ‘Alphonso Black’ and ‘Alphonso Bombay’ from Maharashtra, ‘Alphonso Punjab’ from Punjab and ‘Alphonso White’ or ‘Bili Ishada’ from the North Canara district of Karnataka. Rajput et al. (1996) assembled several ‘Dashehari’ variants and after 14 years of observation, reported that the clone ‘Dashehari 51’ was superior with respect to yield and regular bearing. Other somatic mutants include: ‘Cardozo Mankurad’ with large fruits of attractive colour and high yields from ‘Mankurad’ of Goa; dwarf selections from the ‘Rumani’ and ‘Bangalora’ (Ramaswamy, 1989); development of ‘Paiyur’, a dwarf selection from ‘Neelum’ (Vijaya Kumar et al., 1991); ‘Rati Banganapalli’ and ‘Nuzuvid’ from ‘Banganapalli’ (Anonymous, 1999); and ‘MA-1’, regular bearing and high yielding with resistance to ‘spongy tissue’ from ‘Alphonso’ (Mukunda, 2003). In Thailand, Chaikiattiyos et al. (2000) selected clone ‘SKoo7’ (now known as ‘Kaew Sisaket’) from 320 ‘Kaew’ plants; ‘SKoo7’ has higher yield and superior quality. Jintanawongse et al. (1999) also made superior selections for yield and fruit quality from ‘Nam Dok Mai’, ‘Khiew Sawoey’, ‘Rad’ and ‘Nang Klang Wau’ and DNA fingerprints of all these clones were made for comparison with the parental clone. For these studies, it is important to conduct a replicated cultivar evaluation trial against standard commercial cultivars to establish that these variations are stable and not due to environmental responses. The use of genetic markers should be explored to confirm that the new clones are genetically distinct from the original cultivar.

Induced mutations Mutation induction using ionizing radiation was attempted by Siddiqui et al. (1966). Siddiqui (1985) irradiated dormant buds of ‘Langra’ with high doses of J rays, and grafted them onto 1-year-old seedlings. A bud graft exposed to 3.0 kR bore fruits which were heavier, larger and had a more cream-yellow pulp than the control. This variability was stable over three seasons. Sharma and Majumder (1988b) irradiated bud sticks, topworked them onto 10-year-old

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seedlings, and found that dosages above 5 kR are lethal for mango and that the lethal dose required for 50% mortality (LD50) lies between 2 and 4 kR. Effective dosages of the chemical mutagens, ethane methyl sulfonate (EMS) and N-nitroso methyl urea (NMU), were 1.5 and 0.05%, respectively. The spectrum of mutations induced by physical and chemical mutagens was observed to be more or less the same, indicating the high sensitivity of certain loci. The mutants included dwarfness, changes in shape and serration of leaves and in TSS content in ‘Dashehari’. As in other perennial crops, mutagenesis techniques that can allow useful traits to be targeted, as well as isolating mutated sectors from a chimera, are essential.

4.11 Breeding Potential of Wild Species Bompard (1993; see Bompard, Chapter 2, this volume) has made a comprehensive study of the wild Mangifera species and enumerated their potential use in breeding. Mangifera laurina, which has subglabrous and laxly flowered panicles and is well adapted to areas with perpetual wet climates, is resistant to anthracnose. Mangifera orophila from Malaysia and M. dongnaiensis from Vietnam are both restricted to mountain forests 1000–1700 m above sea level and their hybrids with mango could extend cultivation into temperate zones. Mangifera magnifica is completely free of fibres; M. rufocostata and M. swintonioides have an off-season bearing habit; M. pajang (endemic to Borneo) and some strains of M. foetida have good quality fruits. Similarly ‘Wani’ from Bali and Borneo, the best variety of M. caesia, has a distinctive taste. Mangifera casturi from South Kalimantan is a prolific bearer with small, black, sweet fruits having good potential. Mangifera altissima is reportedly resistant to mango pests, such as hoppers, tip borers and seed borers (Angeles, 1991). Sharma and Choudhury (1976) observed that wild Mangifera trees identified in Tripura State (north-eastern India) were free of mango malformation. The wild species could also contribute to higher productivity. Fairchild (1948) observed that crosses between five-stamened mango and the Indian mango (only one fertile stamen) could produce hybrids having better pollinating quality. The interspecific compatibility of these species with M. indica must be verified before they can be utilized in hybridization programmes (as suggested by Bompard, 1993; Kostermans and Bompard, 1993; see Bompard, Chapter 2, this volume).

4.12 Conclusions Until recently, all mango cultivars arose as chance seedlings or as seedling selections from known mother trees. Enthusiasm for controlled hybridization by means of hand pollination waned because of the tedious nature of the task and heavy fruit drop, resulting in only very few hybrids. This low hybrid population was inadequate for selection and hence not many outstanding hybrids were obtained. However, improvements in pollinating techniques

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and more rapid screening of hybrid populations have enabled the release of many hybrid mango cultivars of commercial value. Because of the world market’s demand for mangoes with specific qualities, the synthesis of new cultivars has become imperative. Rapid strides in molecular biology and in other aspects of biotechnology have opened up new approaches in plant breeding. The development of polymerase chain reaction (PCR)-based genetic markers, specifically microsatellites, and their application to classical breeding offer tremendous potential for mango improvement. The development of a saturated linkage map and the identification of QTL for important traits will allow the implementation of a MAS programme. The introduction of specific genes for disease resistance from cultivars and wild species into popular cultivars should soon be a reality. Without resorting to these new technologies, mango breeding will continue to be a slow process.

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Lopez-Valenzuela, J.A., Martinez, O. and Paredes-Lopez, O. (1997) Geographic differentiation and embryo type identification in Mangifera indica L. cultivars using RAPD markers. HortScience 32, 1105–1108. Maheshwari, P. (1934) The Indian mango. Current Science 3, 97–98. Maheshwari, P. and Rangaswamy, N.S. (1958) Polyembryony and in vitro culture of embryos of Citrus and Mangifera. Indian Journal of Horticulture 15, 275–282. Majumder, P.K. and Sharma, D.K. (1990) Mango. In: Bose, T.K. and Mitra, S.K. (eds) Fruits: Tropical and Subtropical. Naya Prokash, Calcutta, pp. 1–62. Majumder, P.K., Singh, R.N., Sharma, D.K. and Mukerjee, S.K. (1972) Preliminary studies on inheritance in Mangifera indica L. Acta Horticulturae 24, 101–106. Majumder, P.K., Sharma, D.K. and Singh, R.N. (1981) Breeding for dwarfness in mango (Mangifera indica L.). National Symposium on Tropical and Subtropical Fruit Crops, Horticultural Society of India, Bangalore, p. 3. Malik, P.C. (1951) Morphological and biology of the mango flower. Indian Journal of Horticulture 14, 1–23. Marais, Z. (1992) Mango evaluation for breeding. Citrus and Subtropical Fruit Research Institute (CSFRI) Information Bulletin 234, 7. Marshall, T.C., Slate, J., Kruuk, L. and Pemberton, J.M. (1998) Statistical confidence for likelihood-based paternity inference in natural populations. Molecular Ecology 7, 639–655. Medina, J.P. (1977) ‘Rosica’ – a new mango variety selected in Ica, Peru. Fruit Varieties Journal 31, 88–89. Moore, G.A. and Castle, W.S. (1988) Morphological and isozymic analysis of openpollinated citrus rootstock population. Journal of Heredity 79, 59–63. Morton, J.F. (1987) Fruits of Warm Climates. Creative Resource Systems, Winterville, North Carolina, pp. 221–237. Mukherjee, S.K. (1950) Mango; its allopolyploid nature. Nature 166, 196–197. Mukherjee, S.K. (1953) The mango – its botany, cultivation, uses and future improvements, especially as observed in India. Economic Botany 7, 130–162. Mukherjee, S.K. (1957) Cytology of some Malayan species of Mangifera. Cytologia 22, 239–241. Mukherjee, S.K. (1963) Cytology and breeding of mango. Punjab Horticultural Journal 3, 107–115. Mukherjee, S.K., Singh, R.N., Majumder, P.K. and Sharma, D.K. (1968) Present position regarding breeding of mango (Mangifera indica L.) in India. Euphytica 17, 462–467. Mukherjee, S.K., Chakraborty, S., Sadhukhan, S.K. and Saha, P. (1983) Survey of mangoes of West Bengal. Indian Journal of Horticulture 40, 7–13. Mukunda, G.K. (2003) Studies on the performance of certain clones of mango cv. Alphonso. PhD thesis, University of Agricultural Sciences, Bangalore, India. Naik, K.C. (1948) Improvement of the mango (Mangifera indica L.) by selection and hybridization. Indian Journal of Agricultural Science 18, 35–41. Oppenheimer, C. (1956) Study tour report on subtropical fruit growing and research in India and Ceylon. Special Bulletin No.3 State of Israel Ministry of Agriculture. Agricultural Research Station, Rehovot, Israel. Oppenheimer, C. (1967) Nimrod – a new mango variety selected in Israel. Proceedings of the Florida State Horticultural Society 80, 358–359. Pandey, S.N. (1998) Mango cultivars. In: Srivastava, R.P. (ed.) Mango Cultivation. International Book Distributing Co., Lucknow, India, pp. 39–99. Pinto, A.C.Q. and Byrne, D.H. (1993) Mango hybridization studies in tropical savannah (‘Cerrados’) of Brazil Central region. Acta Horticulturae 341, 98–106.

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C.P.A. Iyer and R.J. Schnell Pinto, A.C.Q., Andrade, S.R.M., Ramos, V.H.V. and Cordeiro, M.C.R. (2004) Intervarietal hybridization in mango: techniques, main results and their limitations. Acta Horticulturae 645, 327–331. Pope, W.T. (1929) Mango Culture in Hawaii. Hawaii Agricultural Experiment Station Bulletin 58. Hawaii Agricultural Experiment Station, Hawaii. Popenoe, W. (1917) The Pollination of the Mango. US Department of Agriculture (USDA) Bulletin 542. USDA, Washington DC. Popenoe, W. (1920) The mango. In: Manual of Tropical and Subtropical Fruits. The Macmillan Co., New York, p. 135. Prakash, O. and Srivastava, K.C. (1987) Mango Diseases and their Management – a World Review. Today and Tomorrows Printers, New Delhi, India. Rajput, M.S., Chadha, K.L. and Negi, S.S. (1996) Dashehari – 51, a regular bearing and high yielding clone of mango cv. Dashehari. (Abstract). The Fifth International Mango Symposium, 1–6 September, Tel Aviv, Israel, p. 42. Ram, N., Kamalwanshi, R.S. and Sachan, I.P. (1987) Studies on mango malformation. Indian Journal of Mycology and Plant Pathology 17, 29–33. Ram, S., Bist, L.D., Lakhanpal, S.C. and Jamwal, I.S. (1976) Search of suitable pollinizer for mango cultivars. Acta Horticulturae 57, 253–263. Ramaswamy, N. (1989) Survey and isolation of ‘plus trees’ of mango. Acta Horticulturae 231, 93–96. Ravishankar, K.V., Chandrasekhar, P., Sreedhar, S.A., Dinesh, M.R., Anand, L. and Saiprasad, G.V.S. (2004) Diverse genetic bases of Indian polyembryonic and monoembryonic mango cultivars. Current Science 87, 870–871. Rossetto, C.J., Bortoletto, N., Carvalho, C.R.L., Walder, J.M.M., Nogueira, N.L., Arthus, V. and Lopes, L.A. (2006) Mango resistance to fruit flies: 1. Varietal selection and mechanism of resistance. (Abstract). The Eighth International Mango Symposium, 5–10 February, Sun City, South Africa, p. 22. Roy, B. (1950) A mango chimera. Current Science 19, 93. Roy, B. and Visweswariya, S.S. (1951) Cytogenetics of mango and banana. Report of Maharashtra Association for Cultivation of Science, Pune, India. Roy, R.S., Mallik, P.C. and Sinha, R.P. (1956) Mango breeding in Bihar, India. Proceedings of the American Society for Horticultural Science 68, 259–264. Ruehle, G.D. and Ledin, R.B. (1956) Mango Growing in Florida. Florida Agricultural Experiment Station Bulletin 574. Florida Agricultural Experiment Station, Florida. Sachan, S.C.P., Katrodia, J.S., Chundawat, B.S. and Patel, M.N. (1988) New mango hybrids from Gujarat. Acta Horticulturae 231, 103–105. Sahijram, L., Bollamma, K.T., Naren, A., Soneji, J.R., Dinesh, M.R. and Halesh, G.K. (2005) In vitro hybrid embryo rescue in mango (Mangifera indica L.) breeding. Indian Journal of Horticulture 62, 235–237. Salvi, M.J. and Gunjate, R.T. (1988) Mango breeding work in Konkan region of Maharashtra state. Acta Horticulturae 231, 100–102. Schnell, R.J. and Knight, R.J., Jr (1992) Frequency of zygotic seedlings from five polyembryonic mango rootstocks. HortScience 27, 174–176. Schnell, R.J. and Knight, R.J., Jr (1998) Phenology of flowering among different mango cultivars. Proceedings of the Florida State Horticultural Society 111, 320–321. Schnell, R.J., Ronning, C.M. and Knight, R.J., Jr (1995) Identification of cultivars and validation of genetic relationships in Mangifera indica L. using RAPD markers. Theoretical and Applied Genetics 90, 269–271. Schnell, R.J., Olano, C.T., Quintanilla, W.E. and Meerow, A.W. (2005) Isolation and characterization of 15 microsatellite loci from mango (Mangifera indica L.) and

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cross-species amplification in closely related taxa. Molecular Ecology Notes 5, 625–627. Schnell, R.J., Brown, J.S., Olano, C.T., Meerow, A.W., Campbell, R.J. and Kuhn, D.N. (2006) Mango genetic diversity analysis and pedigree inferences for Florida cultivars using microsatellite markers. Journal of the American Society for Horticultural Science 131, 214–224. Schnell, R.J., Brown, J.S., Kuhn, D.N., Cervantes-Martinez, C., Borrone, J.W., Olano, C.T., Motamayor, J.C., Phillips, W., Johnson, E., Monteverde-Penso, E.J., Amores, F. and Lopes, U. (2007) Current challenges of tropical tree crop improvement: integrating genomics into an applied cacao breeding program. Acta Horticulturae 738, 129–144. Sen, P.K., Mallik, P.C. and Ganguly, B.D. (1946) Hybridization of the mango. Indian Journal of Horticulture 4, 4–15. Sharma, D.K. (1987) Mango breeding. Acta Horticulturae 196, 61–67. Sharma, D.K. and Choudhury, S.S. (1976) Occurrences of an unknown wild race of Mangifera in Tripura. Current Science 45, 305–306. Sharma, D.K. and Majumder, P.K. (1988a) Further studies on inheritance in mango. Acta Horticulturae 231, 106–111. Sharma, D.K. and Majumder, P.K. (1988b) Induction of variability in mango through physical and chemical mutagens. Acta Horticulturae 231, 112–116. Sharma, D.K. and Singh, R.N. (1970) Self incompatibility in mango (Mangifera indica L.). Horticultural Research 10, 108–115. Sharma, D.K. Majumder, P.K. and Singh, R.N. (1972) Inheritance pattern in mango (Mangifera indica L.). In: Proceedings of the Symposium on Recent Advances in Horticulture. Uttar Pradesh Institute of Agricultural Sciences, Kanpur, Uttar Pradesh, India, pp. 66–68. Sharma, R.R. (2003) Catecholase and cresolase activity as biochemical index for screening mango seedlings at nursery stage for bearing behaviour in their future reproductive life. Plant Genetic Resources (PGR) Newsletter 133, 31–34. Sharma, R.R., Singh, C.N., Chbonkar, P., Goswami, A.M. and Singh, S.K. (2000) Polyphenol oxidase activity as an index for screening mango (Mangifera indica) germplasm against malformation. Plant Genetic Resources (PGR) Newsletter 124, 41–43. Siddiqui, S.H. (1985) Induced somatic mutation in mango. Mangifera indica L. cv. Langra. Pakistan Journal of Botany 17, 75–79. Siddiqui, S.H., Mujeeb, K.A. and Vati, S.M. (1966) Evolution of new varieties of mango (Mangifera indica L.) through induced somatic mutations by ionizing radiations. In: Proceedings of the First Agricultural Symposium. Atomic Energy Commission, Dacca, Bangladesh, pp. 34–37. Singh, H. and Chadha, K.L. (1981) Improvement of Dashehari by clonal selection. (Abstract). National Symposium on Tropical and Subtropical Fruit Crops. Horticultural Society of India, Bangalore, p. 5. Singh, L.B. (1960) The Mango – Botany, Cultivation and Utilisation. Leonard Hill, London. Singh, L.B. (1963) A new technique for inducing early fruiting in mango hybrids based on movement of hormones. Proceedings of the Florida State Horticultural Society 75, 410–412. Singh, L.B. (1969) Mango. In: Ferwerda, F.P. and Wit, F. (eds) Outlines of Perennial Crop Breeding in the Tropics. Veenen and Zonen, Wageningen, the Netherlands, pp. 309–327. Singh, R.N. (1954) Studies on floral biology and subsequent developments of fruit in the mango varieties, Dashehari and Langra. Indian Journal of Horticulture 11, 69–88. Singh, R.N. (1990) Mango. Series No. 3. Indian Council of Agricultural Research (ICAR), New Delhi, India.

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C.P.A. Iyer and R.J. Schnell Singh, R.N., Majumder, P.K. and Sharma, D.K. (1962) Self-incompatibility in mango var. Dashehari. Current Science 31, 209. Singh, R.N., Majumder, P.K., Sharma, D.K. and Mukherjee, S.K. (1972) Some promising mango hybrids. Acta Horticulturae 24, 117–119. Singh, R.N., Sharma, D.K. and Majumder, P.K. (1980) An efficient technique of mango hybridization. Scientia Horticulturae 12, 299–301. Singh, R.N., Gorakh, S., Rao, O.P. and Mishra, J.S. (1985) Improvement of Banarsi Langra through clonal selection. Progressive Horticulture 17, 273–277. Singh, S.N. and Singh, S.P. (1952) Studies on the storage and longevity of some fruits and vegetables. Journal of Agriculture and Animal Husbandry Uttar Pradesh 2, 3–11. Slor, E. and Gazit, S. (1982) ‘Tahar’, a new mango cultivar. Alon Honotea 36, 807. (In Hebrew) Spencer, J.L. and Kennard, W.C. (1955) Studies on mango fruit set in Puerto Rico. Tropical Agriculture 32, 323–330. Sturrock, D. (1969) Final report on some mango hybrids – 1969. Proceedings of the Florida State Horticultural Society 82, 318–321. Sturrock, T.T. (1968) Genetics of mango polyembryony. Proceedings of the Florida State Horticultural Society 81, 311–314. Tomer, E., Lavi, U., Degani, C. and Gazit, S. (1993) ‘Noami’: a new mango cultivar. HortScience 28, 755–756. Truscott, M. (1992) Biochemical screening of polyploidy mango seedlings. Citrus and Subtropical Fruit Research Institute (CSFRI) Information Bulletin 237, 17–18. Vijaya Kumar, M., Ramaswamy, N. and Rajagopalan, R. (1991) Exploiting natural variability in mango. In: Proceedings of the National Seminar on Irregular Bearing in Mango – Problems and Strategy, Pusa, Bihar, India. Rajendra Agricultural University, Sabour, Bihar, India, pp. 55–56. Viruel, M.A., Escribano, P., Barbieri, M., Ferri, M. and Hormaza, J.I. (2005) Fingerprinting, embryo type and geographic differentiation in mango (Mangifera indica L., Anacardiaceae) with microsatellites. Molecular Breeding 15, 383–393. Whiley, A.W., Mayers, P.E., Saranah, J. and Bartley, J.P. (1993) Breeding mangoes for Australian conditions. Acta Horticulturae 341, 136–145. Yee, W. (1958) The Mango in Hawaii. Hawaii Agricultural Experiment Station Series Circular No. 388. Hawaii Agricultural Experiment Station, Hawaii. Young, T.W. and Ledin, R.B. (1954) Mango breeding. Proceedings of the Florida State Horticultural Society 67, 241–244.

5

Reproductive Physiology T.L. Davenport University of Florida, Florida, USA

5.1 Introduction 5.2 Phenology 5.3 Shoot Development Vegetative shoots Reproductive shoots 5.4 Flowering Mechanisms Shoot initiation Induction Florigenic promoter (FP) or stimulus Vegetative promoter (VP) 5.5 Environmental Influence on Vegetative and Reproductive Development Temperature Water relations Effect of N on flowering Photoperiod 5.6 Hormonal Influence on Flowering Ethylene Auxin Cytokinins Gibberellins Plant growth retardants 5.7 Photoassimilate Influence on Flowering 5.8 Horticultural Manipulation of Flowering 5.9 Conceptual Flowering Models Carbohydrate-regulated flowering models Hormone-regulated flowering models 5.10 Floral Management 5.11 Floral Biology Sex ratio Environmental determinants of sex ratio Physiological determinants of sex ratio © CAB International 2009. The Mango, 2nd Edition: Botany, Production and Uses (ed. R.E. Litz)

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5.1 Introduction Flowering and fruit set are the most critical of all events occurring after establishment of a tree crop. Given favourable growth conditions, the timing and intensity of flowering greatly determine when and how much fruit are produced. Many important details about flowering are becoming clearer, especially in herbaceous plants, at the physiological, biochemical and molecular levels (see reviews by Searle, 1965; Zeevaart, 1976, 2006; Bernier et al., 1981, 1993; Halevy, 1985–1986; Bernier, 1988; Kinet, 1993; Boss et al., 2004; Komeda, 2004; Putterill et al., 2004; Corbesier and Coupland, 2005). Cool temperatures in the subtropics stimulate mango flowering and age of the last vegetative flush has an important bearing on its ability to flower in marginally cool or warm temperatures of the tropics (van der Meulen et al., 1971; Davenport, 2000, 2003). Consequently, mango flowering can be enhanced during its normal season or manipulated to occur at other times of the year in the tropics. For example, potassium nitrate (KNO3) can stimulate out-of-season flowering in mangoes in tropical latitudes (Barba, 1974; NúñezElisea, 1985; Davenport, 1993; Protacio, 2000), although this treatment has not always been dependable. Various aspects of mango flowering and/or fruit set have been reviewed (Singh, 1958a, 1979; L.B. Singh, 1960, 1977; Chacko, 1986, 1991; Chadha and Pal, 1986; Davenport, 1993, 2000, 2003; Davenport and Núñez-Elisea, 1997; Singh et al., 2005), and M.J. Soule (1950) published an extensive annotated bibliography of the older literature related to mango reproduction. Understanding mango flowering is essential to efficiently utilize management systems that extend the flowering and crop production seasons. Recent studies of mango flowering have resulted in conceptual models that help explain the physiological basis of flowering (Chacko, 1991; Cull, 1991; Kulkarni, 1991, 2004; Whiley et al., 1991; Davenport and Núñez-Elisea, 1997; Davenport, 2000, 2003). Control of flowering allows growers to harvest their crops at the most profitable times. Increasing the season of availability improves competitiveness in the international marketplace, and promotes the most efficient use of resources as costs of inputs continue to rise. This chapter addresses the physiology of mango flowering, early fruit set and retention. Cultivar names and type of embryony (i.e. monoembryonic or

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polyembryonic) are purposefully left out to focus on the physiological aspects of reproduction regardless of whether they are tropically or subtropically adapted or from Indian or South-east Asian origin. Cultivars are selected for their productivity in specific environments. Transfer of a cultivar to a different environment often results in some alteration in performance. It is reasonable to assume that the underlying mechanisms by which all cultivars respond to their environment within the framework of their genetic limitations are similar. The concepts described herein, therefore, apply to all cultivars, regardless of origin.

5.2 Phenology Growth of mango and other tropical trees is not continuous (Nakasone et al., 1955; Halle et al., 1978; Verheij, 1986; Davenport, 1993, 2000, 2003). Apical buds spend most of the time in rest. Growth occurs as intermittent, ephemeral flushes of shoots from apical or lateral buds (Naik and Mohan Rao, 1942; Singh, 1958a, b). Stems are quiescent or resting terminal vegetative structures on branches from which shoot growth occurs. Shoots are elongating vegetative or reproductive structures that emerge from apical or lateral buds of stems. Vegetative shoots develop a prescribed number of nodes during growth before entering a resting state as a stem. Depending on environment, periods of stem rest are generally short in young plants but usually last several months between episodes of growth in mature trees. Vegetative growth generally occurs up to three or four times a year on individual branches, depending upon cultivar and growth conditions. Development of the vegetative shoot from initiation of growth to full elongation requires 3–6 weeks, depending on the cultivar and climatic conditions (Whiley et al., 1991). During this period, 10–20 new leaves are generally produced before returning to a resting state. These rhythmic episodes of extension growth are recorded on each branch as segments consisting of compressed internodes interspersed with long internodes, that is articulate growth (Tomlinson and Gill, 1973). Davenport (1992, 2003, 2006) referred to regions of compressed internodes as intercalations and the entire segment of long internodes terminating in an intercalation as an intercalary unit. The number of intercalations between each branching point indicates the number of vegetative growth episodes or flushes that have occurred between each flowering flush. Flushes of vegetative growth occur on groups of stems borne on scaffolding branches in isolated sections of tree canopy. Flushing stems are usually connected at some common branch point within the tree limbs. Asynchronous flushes of growth at various times in random portions of a tree canopy may appear to be continuous growth but are simply flushes occurring in various parts of the total canopy over time. Flowering flushes generally occur after extended periods of stem rest in the low-latitude tropics or during cool winter months in the high-latitude tropics and subtropics. Like vegetative flushes, reproductive flushes are usually asynchronous in tropical climates

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(Verheij, 1986). In the subtropics, however, trees exposed to cold temperatures (3–10°C) display synchronized flowering flushes throughout the tree canopy approximately 1 month later. Subsequent vegetative flushes also tend to be synchronous for one or two growth cycles depending upon the number of retained fruit. Less intense, cool weather (10–18°C), however, results in asynchronous reproductive flushes in responsive stems as is typical of trees growing in the tropics. The timing of flowering flushes of cultivars in various locations has been reviewed by L.B. Singh (1960), Chadha and Pal (1986) and Pandey (1989). Variations in flowering patterns occur in all cultivars depending on their age and whether they are growing in dry or humid tropics or subtropics (L.B. Singh, 1960).

5.3 Shoot Development Flushes of vegetative extension growth of mango stems terminate with formation of determinate panicles. Several weeks to a few months after separation of the last flower or fruit from these panicles are required for the central axis of the panicle or rachis to dry and mechanically separate from the supporting stem, depending on the longevity of attached fruit. Five to ten lateral vegetative shoots typically develop from axillary buds located at the terminal intercalation positioned in a compact whorl surrounding the panicle scar of each stem (see Fig. 1 of Reece et al., 1949). These lateral shoots become the branch points of stems. These branching shoots form 10–15 leaves before the apical buds return to a resting state to establish them as individual stems. Initiation of these lateral vegetative shoots may occur 2–3 months after desiccation of panicles which fail to set fruit. Fruit-bearing stems do not initiate new lateral shoots until several months after separation of fruit and rachis from the stem (Kulkarni and Rameshwar, 1989). Such delayed vegetative growth can reduce the potential for new shoots to flower during the next flowering season (Singh and Khan, 1939; L.B. Singh, 1960, 1972; Monselise and Goldschmidt, 1982). The apical bud of stems is at rest for most of the year in mature trees. Stems on centennial trees typically produce only one vegetative flush during the year (N. Golez, personal communication, the Philippines, 1989). The apical resting bud of each newly established lateral stem (intercalary unit) is surrounded by a compact whorl of 10–12 leaves with short internodes (intercalation) (Fig. 5.1). Protective bud scales are green but may be brown at the tips due to desiccation (Sen and Mallik, 1941; Mustard and Lynch, 1946; Singh, 1958b; Ravishankar et al., 1979). Resting buds possess a number of pre-formed nodes, each of which contains a leaf bract or leaf primordium and a lateral meristem (Fig. 5.2; see Figs 7–12 in Chaikiattiyos et al., 1994). The outermost, proximally located dried leaf bracts (bud scales) protect the more distal interior leaf bracts, leaf primordia and lateral meristems from mechanical damage and desiccation. Leaf bracts are vestigial nondeveloped leaves. Scales abort upon evocation of new shoots. Proximally located bracts in apical buds fail to further develop beyond some enlargement and also abort with elongation of shoots.

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Fig. 5.1. Apical bud of resting mango stem.

Lateral meristematic primordia

Apical dome (includes meristem)

Leaf primordia (bracts)

Fig. 5.2. Stylized cross-section of apical bud showing positions of apical meristem, lateral meristems and leaf primordia.

If apical buds are initiated during vegetatively inductive conditions, bracts develop as small leaves and the leaf primordia develop as the fullsized leaves of vegetative shoots. Additional leaves result from nodes formed by renewed activity of the apical meristem. The number of leaves (nodes) is dependent upon the mean temperature during initiation, and increases as temperatures rise (Whiley et al., 1989). The lateral meristems of the apical bud develop as axillary buds at the base of petioles in the elongating vegetative shoot, each bearing protective bracts, leaf primordia and lateral meristems (Fig. 5.3; see Fig. 1 of Reece et al., 1949). In contrast, if shoot growth is initiated under floral inductive conditions, the leaf bracts and primordia fail to fully develop, but the lateral meristems

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Stem

Fig. 5.3. Axillary bud of resting mango stem. Leaf petioles (arrows).

begin to elongate and branch at each node forming secondary, tertiary and quaternary lateral meristems. Each branch point in the lateral inflorescence from the panicle axis to the floral pedicels bears a floral bract (i.e. partially developed vestigial leaf primordium) (Fig. 5.4). The distal half of the panicle structure is derived from newly formed nodes laid down by cell divisions in the apical meristem prior to returning to a resting state. Mixed shoots, bearing both leaves and inflorescences at each node, result from development of both the primary leaf primordia and the lateral meristems, which form the inflorescences in the same nodes as leaves. Vegetative shoot induction, thus, involves stimulating development of leaf primordia from resting buds while repressing development of lateral meristems. Leaf primordia then follow a predetermined cascade of genetic signals resulting in leaf development at each node. Because all shoots emerge from resting buds, a vegetatively induced event does not involve simply inhibition of flowering. The putative inductive signal directing differentiation of leaf primordia onto leaves upon initiation is termed a vegetative promoter (VP) rather than a floral inhibitor. Shoots bearing only inflorescences (generative shoots) result from inductive development of lateral meristems and suppression of leaf primordial development. A predetermined cascade of flowering gene signals is activated in lateral meristems resulting in lateral cymose inflorescences terminating with flowers. A distinct florigenic promoter (FP) may be responsible for specific activation of the lateral meristems of mango. Mixed shoot induction results in combined development of leaf primordia and lateral meristems. Vegetative shoots Vegetative shoots bear only leaves (Fig. 5.5). The anatomy of mango vegetative shoot development has been described (Singh, 1958b; Chaikiattiyos

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2° º

1°

5°

1 Bract 1°

Axis

1° Pedicel 1° Bract

1° Pedicel

3° Bract 2° Bract 2° Pedicel

1° Bract Axis

1° Pedicel

2° Bract

1° Pedicel

Fig. 5.4. Diagram and photos of mango inflorescence depicting the panicle axis and primary (1°), secondary (2°) and succeeding levels of pedicel and cymose floral architecture. Vestigial leaf promorida (floral bracts) are depicted at the base of each level of pedicel architecture.

et al., 1994). Vegetative shoots may arise either from axillary buds, if no apical bud exists due to flowering in the previous flush, or from the apical bud when present. The latter is considered extension growth or addition of an intercalary unit on the existing stem, but the developmental events during shoot formation from either apical or lateral buds are basically the same. Cells in the leaf primordia of initiating buds begin to form individual leaves in the proximal portion of the vegetative shoot. Soon thereafter, the apical meristem activates to form more nodes bearing leaf primordia and lateral meristems. These newly formed leaf primordia develop as the distal portion of the vegetative shoot if environmental conditions remain vegetatively inductive (Núñez-Elisea et al., 1996). Newly elongating vegetative shoots are green in most cultivars but may be bronze or red in others. Fully expanded

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VEGETATIVE

GENERATIVE

GENERATIVE

CHIMERIC

MIXED

V/F TRANSITION VEGETATIVE

CHIMERIC

MIXED

V/F TRANSITION

F/V TRANSITION

F/V TRANSITION

Fig. 5.5. Stylized diagrams and photomontage of shoot types found in mango. Transition shoots shift from vegetative to floral (V/F) or floral to vegetative (F/V). Arrow ( ) represents individual leaves; floral diagram ( ) represents lateral inflorescences.

leaves are a shade of red, depending upon cultivar and cultural conditions and are thin and limp from lack of lignification. The apical buds of vegetative shoots generally become quiescent before completion of the limp, red-leaf stage (Núñez-Elisea and Davenport, 1995). Internodes are compressed at the apex, and leaf development is arrested thereby forming a bud with protective outer scales, inner leaf primordia, lateral meristems and the apical meristem. Fully expanded leaves become light green and stiff as they become lignified and suberized. Vegetative shoots are mature when leaves become dark green, which occurs when they are c.2 or 3 months old.

Reproductive shoots Two types of reproductive shoots typically occur in mango. Generative shoots display only flowers and have floral bracts or non-developed leaves at the base of each lateral inflorescence (Fig. 5.5). Terminal inflorescences, i.e. panicles or thyrsoids (Weberling, 1989), develop from dormant apical buds. The anatomy of panicle development has been described (Juliano and Cuevas, 1932; Musahib-ud-din, 1946; Mustard and Lynch, 1946; Singh,

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1958b; L.B. Singh, 1960; Sturrock, 1966; Ravishankar et al., 1979; Scholefield, 1982; Scholefield et al., 1986). The complexes of primary to quaternary branching lateral structures of the inflorescence each terminate with three cymose flowers. The terminal flower opens first, followed by two subtending lateral flowers. These complexes form the lateral inflorescence structures emerging from the central axis of the panicle. The central axis extension also terminates in a similar fashion. Morphological stages of floral buds and panicle development were described by Shu (1981) and Oosthuyse (1991a). Reece et al. (1949) described the development of inflorescences initiated in lateral buds when the terminal bud is missing. There are more nodes in dormant apical buds and their bracts are more developed than in axillary buds; however, floral evocation is indistinguishable. Generative shoot development in apical buds initially involves swelling of the lateral meristems and their bud scales. Each axillary meristem develops as an inflorescence on a primary peduncle. The apical meristem then forms new lateral meristems and leaf primordia for the distal portion of panicle development if floral inductive conditions persist (Núñez-Elisea et al., 1996). Panicles may be open or compact, depending upon internode elongation, which is cultivar dependent (L.B. Singh, 1960), but the architecture generally conforms to that in Fig. 5.5. Mixed shoots develop under weak floral inductive conditions (i.e. in the low-latitude tropics). Both leaves and primary pedunculate inflorescences develop from the same nodes (Fig. 5.5). Leaf primordia and lateral meristems develop as leaf and floral structures, respectively.

5.4 Flowering Mechanisms Mango stems undergo varying periods of rest between episodes of growth, depending on tree age and environmental influences. Resting mango buds must, therefore, respond to two distinctly different signals for shoots to occur. The first signal initiates growth of the shoot and the second determines if it will be vegetative or reproductive. The signals that regulate initiation of shoot growth in resting buds differ from the inductive signals that regulate shoot type.

Shoot initiation Initiation is the onset of shoot development, regardless of the type of shoot evoked. It involves cell division and elongation of cells in leaf primordia (vegetative shoots), lateral meristems (generative shoots) or both (mixed shoots) in the nodes of the resting buds, and is followed by cell divisions in the apical meristem to form more nodes. Shoot initiation is stimulated by pruning, defoliation and irrigation during dry conditions, or transition from the dry to rainy season in the tropics. Application of nitrogen (N)-containing fertilizers, exposure to ethylene, or a shift from cool to warm temperatures

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also stimulates shoot initiation. Reece et al. (1946, 1949), Mustard and Lynch (1946), Núñez-Elisea and Davenport (1992b), Núñez-Elisea et al. (1996) and Davenport et al. (2006a) observed that the vegetative or reproductive fate of mango buds remains undetermined until after shoot growth is initiated. Reece et al. (1949) proposed that a putative signal that triggers initiation of shoot development is separate and different from the inductive signal, which determines the fate of the shoot. Removal of apical buds by pruning stimulates initiation of axillary shoots (Singh and Singh, 1956; Núñez-Elisea and Davenport, 1992b; Núñez-Elisea et al., 1996; Davenport et al., 2006a). Defoliation of the apical whorl of five to ten leaves also stimulates shoot initiation in dormant apical buds (Núñez-Elisea et al., 1991; Núñez-Elisea and Davenport, 1995). The fate of shoots that emerge in response to these initiation stimuli, however, is determined by other factors that are prevalent at the time of initiation. Tip pruning, for example, during warm summer months results in initiation of vegetative shoots from axillary buds, whereas pruning during cool winter months usually results in initiation of axillary inflorescences.

Induction Induction in mango is the temporary commitment of buds to evoke a particular developmental pathway (i.e. vegetative shoot, generative shoot or mixed shoot) when growth is initiated. Initiation of herbaceous plant flowering refers to the onset of floral bud growth in actively growing vegetative shoots after the floral inductive event (Bernier et al., 1981, 1993; Halevy, 1985– 1986; Bernier, 1988; Huala and Sussex, 1993; Kinet, 1993). The inductive signal is formed in leaves, but the responsive buds are in continuous vegetative growth at the time of floral induction in herbaceous plants and floral initiation follows; whereas mango buds are in rest. Although the mango bud must be initiated to grow, that growth is induced according to forces already present. Whereas the floral inductive signal in mango may be present prior to bud initiation, it must be present at the time of initiation for flowering to occur (Kulkarni, 1988a; Núñez-Elisea and Davenport, 1995; Núñez-Elisea et al., 1996; Davenport and Núñez-Elisea, 1997; Davenport et al., 2006a). The inductive signal can be shifted from floral (F) to vegetative (V) or vegetative to floral, forming F/V or V/F transition shoots, by altering temperatures during early shoot development (Batten and McConchie, 1995; Núñez-Elisea et al., 1996) (Fig. 5.5). This shift in morphogenic responses during shoot development demonstrates the plasticity and temporal nature of induction, indicating that cells of the apical meristem do not become irreversibly determined under inductive conditions. These results demonstrate that, rather than being irreversibly committed to a vegetative or reproductive fate at the onset of shoot initiation, the mango apical meristem provides progenitor cells, some of which differentiate into specific target cells at each node in the apex. The apical meristem, therefore, may not be directly involved in the flowering process.

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Target cells within leaf primordia and lateral meristems are competent to respond to inductive signals; for example when initiated to grow under vegetatively inductive conditions, individual leaf primordia develop as leaves and subtending lateral meristems associated with each developing leaf develop as dormant axillary buds with protective bracts. These axillary buds may develop in subsequent flushes as vegetative shoots when initiated in vegetatively inductive conditions or as axillary inflorescences under floral inductive conditions. Under strongly floral-inductive conditions, leaf primordia fail to develop beyond the bract stage, become dormant, and lateral meristems develop. Each lateral meristem forms nodes consisting of leaf primordia and meristems that are influenced by the putative floral-inductive stimulus, which suppresses development of newly formed leaf primordia. Subsequently formed meristems form pedunculate structures that terminate in cymose inflorescences borne on each tertiary peduncle (Fig. 5.4). Formation of the primary, secondary, tertiary and quaternary peduncles, as well as pedicels of inflorescences are always accompanied by a subtending, aborted bract or vestigial leaf at each node (Fig. 5.4). Such development is attributed to a sequence of gene expression (Coen et al., 1990; Coen and Meyerowitz, 1991; Weigel et al., 1992; Coen and Carpenter, 1993; Lumsden, 1993; Yanofsky, 1995). Shoot initiation during weakly floral-inductive conditions activates growth of leaf primordia to develop leaves and the lateral meristems to produce peduncles bearing lateral inflorescences in each node of mixed shoots. The bases of each pedicel branch within each lateral inflorescence also bear a vestigial leaf. Upon termination of cell divisions in the apical meristem at the end of a flushing period, no more nodes are formed. The apical bud of vegetative shoots becomes quiescent, and the resting leaf primordia, bracts and lateral meristems are poised to resume growth at a later date. When reproductive or mixed shoots become quiescent, the lateral meristems ultimately develop determinant cymose inflorescences. The most distally located meristem is possibly the determinant extension of the central axis forming the terminal cymose floral group. Chimeric shoots (Fig. 5.5) can occur in mango trees when shoot initiation occurs during floral inductive conditions. They display inflorescences on one side of the longitudinally bisected shoot and leaves on the other. The shoot axis is red on the floral side of red fruiting cultivars (typical of panicles) and green on the vegetative side (typical of vegetative shoots). This difference in the two sides extends to the apical bud, which bears an undeveloped inflorescence on the floral side and leaf bracts on the vegetative side. The explanation for this spatial differentiation is that target nodes on each side of the apical bud respond to the different inductive signals at the same time. The apical meristem is not implicated except to form more nodes for the lateral inductive responses on each side in the second portion of growth. Differences in inductive signals on each side of an existing shoot probably cause the differential response. This phenomenon indicates that the fate of nodes on each side of the shoot cannot be attributed to a single mother cell in the apical meristem. The inductive response must involve cells formed in later

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cell divisions and would be determined by their location within nodes of the bud.

Florigenic promoter (FP) or stimulus Early flowering work provided evidence for the presence of a graft transmissible floral stimulus (i.e. florigen) that was induced in leaves and was translocated to buds to stimulate floral development (Chailakhyan, 1936; Zeevaart and Boyer, 1987). Florigen was functionally conserved across plant species (Lang, 1965, 1984; Zeevaart, 1976; Lang et al., 1977). Floral induction in most plants involves sensing of some environmental cue (i.e. daylength, water stress or vernalizing temperature) in some organ (e.g. leaves). A putative floral stimulus or alteration in the ratio of florigenic to anti-florigenic components may be translocated to target cells in meristems (Bernier et al., 1981). Photoassimilate movement from leaves in phloem facilitates its transport to buds where it can interact to initiate flowering (King and Zeevaart, 1973). Until recently, a floral stimulus could not be identified. Alternative hypotheses were proposed that nutrient diversion to the meristems could be involved (Sachs and Hackett, 1983) or that floral induction might be controlled by multiple factors, including the putative floral stimulus, photoassimilates and phytohormones (Bernier et al., 1993). Molecular biology of flowering in the facultative, long-day, model plant, Arabidopsis thaliana (reviewed in Zeevaart, 2006 and Aksenova et al., 2006), has provided insight into the nature of the floral stimulus (FP). A network of four interacting genetic signalling pathways may result in flowering in response to photoperiodic, vernalization, gibberellin and autonomous environmental cues (Perilleux et al., 1994; Mouradov et al., 2002; Perilleux and Bernier, 2002; Boss et al., 2004; Komeda, 2004; Putterill et al., 2004; Corbesier and Coupland, 2005). The photoperiodic pathway involves activation of the CONSTANS (CO) gene that encodes a zinc-finger protein, which in turn induces expression of the FLOWERING LOCUS T (FT) gene in the phloem tissue of leaves. FT is the terminal, integrating gene of the four pathways regulating flowering in Arabidopsis. Its transcribed mRNA was initially thought to be the FP that is transported in phloem to buds (Huang et al., 2005); however, evidence indicates that the translated protein product of FT is translocated to Arabidopsis buds (Corbesier et al., 2007). Analogous proteins encoded by Hd3a, an ortholog of FT in rice (Tamaki et al., 2007), and the aspen ortholog, PtFT1, which along with CO regulates the timing of flowering and growth cessation of Populus trichocarpa (Bohlenius et al., 2006), appear to be the FP. In the buds, the protein product of FT is thought to combine with the bZIP transcription factor (FD) protein to activate transcription of floral identity genes (i.e. APETALA1) to begin floral expression (Abe et al., 2005; Wigge et al., 2005). Similar mechanisms are likely to exist in mango. Zhang et al. (2005) and Davenport et al. (2006b) isolated a CONSTANSlike gene (MiCOL) from mango leaf DNA. CO is a circadian expression gene interacting with the photoperiodic pathway in Arabidopsis (Putterill et al.,

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2004), and is central to activation of the FT gene in Arabidopsis during long days. Its role in mango flowering is unclear. The mango ortholog has 79%, 76% and 62% homology with two apple CO genes, MdCOL2 and MdCOL1, and the Arabidopsis CO gene (AtCO), respectively. Isolation of the FT or homologous gene responsible for synthesis of the FP has been unsuccessful. Studies with mango indicate that a FP is synthesized in leaves during exposure to cool, floral-inductive temperatures and moves to buds to induce flowering (Reece et al., 1946, 1949; Singh and Singh, 1956; L.B. Singh, 1959, 1962, 1977; R.N. Singh, 1961; Sen et al., 1972; Núñez-Elisea and Davenport, 1989, 1992b; Davenport and Núñez-Elisea, 1990; Davenport et al., 1995, 2006a). Unlike receptor sites in buds of Thlaspi arvense (Metzger, 1988) and other plants requiring vernalization for floral induction (Zeevaart, 1976; Bernier et al., 1981), mango leaves appear to be where the putative floral stimulus is produced. Complete defoliation of girdled branches during inductive conditions results in vegetative shoots instead of generative shoots (Reece et al., 1949; Sen et al., 1972; Núñez-Elisea and Davenport, 1989, 1992b; NúñezElisea et al., 1996; Davenport et al., 2006a). It appears to be transported over long distances from leafy branches to defoliated branches (Sen et al., 1972; Núñez-Elisea et al., 1996). The putative, temperature-regulated FP is short-lived in situ (NúñezElisea and Davenport, 1989, 1992b; Davenport et al., 1995; Núñez-Elisea et al., 1996). Leafless cuttings from trees during cool, floral inductive conditions produce inflorescences when stimulated to grow within 7 days of transfer to warm, non-inductive conditions; the influence of the removed leaves lasts for 13 days when cuttings are stored at cool temperatures (Davenport et al., 2001a). The same cuttings produce only vegetative shoots in both storage conditions after the initial loss of reproductive shoot production. There are more leaves on mango stems than are necessary for floral induction in cool temperatures. Stems bearing as little as one-quarter of a cross-sectioned leaf induce 95% generative shoots (Davenport et al., 2006a); the remaining shoots are vegetative. Half of a leaf or more resulted in 100% generative shoots. Thus, the limiting amount of leaf necessary for floral induction is less than a quarter of a leaf per stem. Davenport et al. (2006a) demonstrated the quantitative movement of mango FP from half to five leaves on a donor stem to five leafless receiver stems located as far as 100 cm from the donor stem in isolated branches during exposure to cool, floral inductive temperatures. The FP moves with photoassimilates in phloem from donor leaves to buds in the receiver stems. The mango floral stimulus is graft transmissible (L.B. Singh, 1959, 1962; Kulkarni, 1986, 1988b, 1991). Flowering of seedling stems is stimulated by grafting onto mature trees or by grafting mature stems onto juvenile plants (L.B. Singh, 1959, 1962). Some mango cultivars selected in the tropics can flower at higher temperatures than others and are not restricted to winter flowering (Kulkarni, 1991). Transfer of the FP from tropical to subtropical selections was accomplished using reciprocal grafts between the two cultivar types (Kulkarni, 1986, 1988b, 1991). Subtropical cultivars that seldom flower in warm temperatures flower in the ‘off’ season using these techniques. Three conditions

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were essential for summer flowering to occur in the low-temperature-requiring cultivars (receptors) when grafted to the summer flowering type (donors): (i) the summer-flowering donor cultivar stocks or scions were in a flowering cycle; (ii) buds on the receptor scions or stocks of grafted plants had initiated shoot growth during this cycle; and (iii) receptor stocks or scions had been completely defoliated for transfer and/or expression of the floral stimulus. The presence of any leaves on the receptor plants resulted in vegetative shoots. Girdling experiments to isolate treated mango branches from the rest of the tree suggest that the FP is translocated via phloem to apical buds (King and Zeevaart, 1973; Bernier et al., 1981; Núñez-Elisea and Davenport, 1989, 1992b; Núñez-Elisea et al., 1996; Davenport et al., 2006a). Shading experiments to reduce photosynthate loading into the phloem also support this (Kulkarni, 1991). Reduced flowering responses were observed in isolated leafy branches that were provided with 90% and complete shading, which stopped photosynthate production entirely, mimicked defoliation during cool, floral inductive conditions, resulting in a vegetative growth response (R. Núñez-Elisea, T.L. Davenport and B. Schaffer, Florida, 1991, unpublished results).

Vegetative promoter (VP) An independently regulated VP probably contributes to induction of vegetative shoots as opposed to a floral inhibitor or expression of a default vegetative status in the absence of sufficient FP at the time of shoot initiation. Grafting studies (L.B. Singh, 1959, 1962; Kulkarni, 1986, 1988b, 1991, 2004) demonstrated that complete removal of leaves from receptor stems is required to express flowering of those receptors when they are grafted to flowering donor stems. Kulkarni (1986, 1988b, 1991, 2004) considered that a putative floral inhibitor in leaves of the non-induced receptor stems might antagonize the influence of the floral stimulus from donor leaves. Others have noted a relationship between leaf age and the ability of shoots to be reproductive (Singh et al., 1962a; Scholefield et al., 1986). KNO3-stimulated early flowering in the tropics is successful only on stems that are at least 4 (Davenport, 2003) to 7 months old (Astudillo and Bondad, 1978; Bondad and Apostol, 1979; Núñez-Elisea, 1985). Young stems often produce vegetative shoots when initiated under conditions that are floral inductive for more mature stems (Núñez-Elisea and Davenport, 1995; Davenport, 2003). The putative VP appears to be most active in leaves of young stems and slowly dissipates over time to allow expression of the FP when shoots are initiated to grow in warm conditions. The VP may be a gibberellin or closely associated with the gibberellin synthesis pathway as indicated by enhanced flowering responses of trees to plant growth retardants. Mangoes growing in wet and humid, low-latitude tropics tend to produce frequent vegetative flushes and flower sporadically, perhaps due to higher levels of the VP in the young stems combined with low levels of the putative FP when shoot initiation occurs. Paclobutrazol

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(PBZ) reduces the time in rest necessary to allow floral induction during warm temperature conditions by c.1 month (Davenport, 2003), thus increasing the potential to produce reproductive shoots in younger stems when initiated to grow. PBZ and uniconazole, triazole compounds that inhibit kaurene oxidase in the gibberellin-synthesis pathway (Dalziel and Lawrence, 1984; Rademacher, 1991), stimulate production of flowering shoots during weakly inductive conditions (Burondkar and Gunjate, 1991, 1993; Tongumpai et al., 1991a; Voon et al., 1991; Nartvaranant et al., 2000; Yeshitela et al., 2004a). Application of PBZ to mango trees bearing 1-month-old stems produced inflorescences when bud break was initiated 3 months later by foliar application of KNO3 (Davenport, 2003). Vegetative or reproductive induction at the time of shoot initiation is governed by the ratio of the putative floral promotive to inhibitory components (Lang et al., 1977; Lang, 1984; Kulkarni, 1988a; see Bernier et al., 1981 for additional references). The mango floral inhibitor should be viewed as an age-dependent VP. The presence of an age-regulated VP in mango leaves, which moves with the temperature-regulated FP and photoassimilates in phloem, may explain the induction of specific receptors by this promoter in targeted leaf primordia to cause development of leaves in vegetative or mixed shoots. A gradual decrease in the level or influence of the VP may cause vegetative shoots to develop when initiation occurs on 2-month-old stems, and generative or mixed shoots when initiation occurs in stems from 4- to 7-month-old stems, given the constantly warm daily temperatures maintaining a low level of FP in both situations.

5.5 Environmental Influence on Vegetative and Reproductive Development The effects of temperature and water relations on determinating vegetative and reproductive growth of mango have been addressed (Davenport and Núñez-Elisea, 1997; Davenport, 2000; Kulkarni, 2004; Bangerth, 2006). This section focuses on the impacts of temperature, plant water relations, mineral nutrition and photoperiod on shoot initiation and induction. Temperature The developmental fate of mango buds is strongly influenced by temperature (Davenport and Núñez-Elisea, 1997). Cool night temperatures < 15°C in combination with day temperatures < 20°C typically induce flowering if shoot initiation occurs when plants are exposed to these conditions (Ou, 1980, 1982; Wolstenholme and Mullins, 1982a, b; Shu and Sheen, 1987; Whiley et al., 1988, 1989, 1991; Núñez-Elisea et al., 1993; Núñez-Elisea, 1994; Núñez-Elisea and Davenport, 1994a, b). The physiological and molecular basis for temperature perception in leaves with respect to floral induction is not understood (Samach and Wigge, 2005). Whiley et al. (1988, 1989, 1991)

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described the vegetative growth and flowering responses of several monoembryonic and polyembryonic cultivars to four temperature regimes ranging from vegetatively inductive (30°C day/25°C night) to floral inductive (15°C day/10°C night). The effect of temperature on marcotted, container-grown plants that were tip pruned or defoliated in order to stimulate shoot initiation was also studied (Davenport, 1987; Núñez-Elisea et al., 1991, 1993, 1996; Núñez-Elisea and Davenport, 1994b). Mango trees develop vegetative shoots when shoot initiation occurs in warm temperatures (30°C day/25°C night), whereas inflorescences develop when shoots initiate growth in cool temperature conditions (18°C day/10°C night; or 15°C day/10°C night) (Whiley et al. 1989; Núñez-Elisea and Davenport, 1991b, 1995; Núñez-Elisea et al., 1993, 1996; Batten and McConchie, 1995). Bangerth et al. (2004) reported changes in the major phytohormones in stems of containerized mango trees during exposure to cool, floral inductive temperatures. The minimum leaf age and time of exposure to a low temperature regime (18°C day/10°C night) required by stems for floral induction was examined (Núñez-Elisea and Davenport, 1995). Leaves are competent to respond to cool temperatures at 7 weeks, forming a small percentage of generative shoots. As they age, higher proportions of generative shoots are induced and warmer temperatures can stimulate floral induction. The response to temperature is moderated by age of the previous flush. Stems that are 4–5 months beyond the limp, red-leaf stage of development will be induced to form generative shoots if initiated to grow at 25–30°C (Davenport, 2003). Whiley et al. (1988, 1989, 1991) observed that at least 17 weeks are required for initiation of reproductive shoots on non-clipped stems of trees maintained at 15°C day/10°C night. In similar experiments with different cultivars without previous clipping of distal leaves to stimulate initiation, inflorescences were observed after 5 weeks at 15°C day/10°C night (Chaikiattiyos et al., 1994). Although inductive conditions were present in each of these studies, shoot initiation was delayed by the presence of distal leaves. The earlier initiation of inflorescence development in tip-pruned or tip-defoliated stems compared to intact ones demonstrates that the floral stimulus may be present, but the buds are not induced until initiation occurs. It demonstrates the importance of stimulating initiation of stems by tip defoliation or pruning at the onset of incubation in controlled environment conditions so that the inductive response can be observed within a reasonable length of time. The variable delays in shoot initiation in these studies occurred because the experimental protocols depended on the plants’ internal initiation cycle to initiate shoots. This cycle slows down when plants are exposed to lower temperatures (Whiley et al., 1988, 1989, 1991). Floral or vegetative induction occurs when shoots are initiated. Resting buds of plants that are exposed to cool temperatures (18°C day/10°C night) for > 3 weeks and then transferred to a warm temperature (30°C day/25°C night) before initiation, produce only vegetative shoots (Núñez-Elisea et al., 1996). Thus, the stems do not ‘remember’ that they had been exposed to floral inductive conditions while still in rest. They responded to warm conditions present when shoot initiation occurred.

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This response to temperature conditions at the time of shoot initiation extends to the formation of transition shoots if conditions change during early shoot development. First reported by Naik and Mohan Rao (1943), transition shoots are an unusual transition in expression of shoot type during a single growth flush (Kulkarni, 1988b; Núñez-Elisea and Davenport, 1989, 1992b; Batten and McConchie, 1995). The transition typically occurs near the middle of the extending shoot. Resting buds possess preformed nodes, each of which contains a primordial leaf or bract and a lateral meristem. The apical meristem initiates cell division at the same time or soon after the nodal target tissues begin development (Mustard and Lynch, 1946; L.B. Singh, 1960; Núñez-Elisea et al., 1996). Vegetative or inflorescence development in the pre-formed primordia is underway before the apical meristem begins to produce differentiating cells. Transfer from a warm, vegetatively inductive condition to a cool, floral inductive environment at early bud break results in formation of V/F transition shoots (Fig. 5.5). Transfer from cool to warm conditions at the same stage of bud break results in formation of F/V transition shoots (Batten and McConchie, 1995; Núñez-Elisea et al., 1996). The flowering response to temperature occurs in mangoes growing in subtropical latitudes where cool temperature is the dominant induction factor. Many cultivars flower erratically in the low-latitude tropics, providing continuously warm temperatures with high soil and atmospheric moisture. Under such conditions, the age of stems is the dominant inductive factor (Buell, 1954; Nakasone et al., 1955; Ravishankar et al., 1979; Ou and Yen, 1985; Issarakraisila et al., 1992), and occasional cool night temperatures in the upper latitude tropics have a positive moderating effect (Davenport, 2003).

Water relations In the absence of cool temperatures, mango trees in the tropics may flower in response to irrigation or rain following periods of water stress lasting 6–12 weeks or more (Pongsomboon, 1991). Plant water stress has been presumed to provide the stimulus for flowering (reviewed in Whiley, 1993; Chaikiattiyos et al., 1994; Schaffer et al., 1994; Davenport and Núñez-Elisea, 1997); however, most of these studies have failed to substantiate prolonged tree water deficit as a successful agent for floral induction. Experiments with container-grown trees fail to produce inflorescences after 8 weeks of water deficit (Wolstenholme and Hofmeyr, 1985). Under glasshouse conditions (27°C day/22°C night; relative humidity (RH) ≥ 90%), container-grown, monoembryonic cultivars were water stressed through deficit irrigation for 14 days, resulting in an average leaf xylem water potential of −3.9 MPa (Davenport, 1992; Núñez-Elisea and Davenport, 1992a, 1994b). Following resumption of irrigation, all trees grew vegetatively. Similarly, only vegetative growth was obtained when container-grown trees were deprived of irrigation for 36 days during summer, although leaf xylem water potentials of −3.78 MPa were attained (Núñez-Elisea and Davenport, 1994b). Water stress imposed on plants during the cool autumn months

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(night temperatures < 15°C) do not increase the proportion of apical buds forming inflorescences, but expedited shoot initiation after rewatering (Núñez-Elisea and Davenport, 1994b). These results demonstrated that cool temperatures provide inductive conditions, whereas relief of water stress accelerated shoot initiation under cool, inductive temperatures. Flowering was delayed when container-grown monoembryonic mangoes were waterstressed at 18°C day/15°C night (Chaikiattiyos et al., 1994). Water-stressed trees held at 29°C day/25°C night did not flower. Mango trees growing in the low-latitude tropics may flower after an extended period of mild water stress (Harris, 1901; Collins, 1903; Kinman, 1918; Gangolly et al., 1957; Gangolly, 1960; L.B. Singh, 1960). Pongsomboon et al. (1991) observed flowering in field-grown trees in the tropics following 6 weeks of withholding water. The primary impact of water stress appears to be prevention of shoot initiation during stress. The accumulating age of stems is greater in water-stressed trees than in trees maintained under well-watered conditions that promote frequent vegetative flushes (Davenport, 1992, 1993; Schaffer et al., 1994). This delay in flushing may provide more time for accumulation of a putative FP (Schaffer et al., 1994) or reduction in the level of a putative VP (Davenport and Núñez-Elisea, 1997; Davenport, 2000). Some cultivars appear to be better adapted to such delays in growth and perform better in dry environments in the tropics.

Effect of N on flowering Subsequent to the discovery of ethephon to stimulate mango flowering (Gonzalez, 1923; Alcala and San Pedro, 1935), Barba (1974), Bueno and Valmayor (1974), Astudillo and Bondad (1978), Bondad et al. (1978), Bondad and Apostol (1979), Pantastico and Manuel (1978) and Bondad and Linsangan (1979) reported that KNO3 could be used for the same purpose. This has been exploited in the low- and mid-latitude tropics (Mosqueda-Vázquez and de los Santos de la Rosa, 1981; Mosqueda-Vázquez and Avila-Resendiz, 1985; Núñez-Elisea, 1985, 1986; Ou and Yen, 1985; Winston and Wright, 1986; Tongumpai et al., 1989; Goguey, 1993; Ravishankar et al., 1993; Sergent et al., 1996; Yeshitela et al., 2004b, 2005). The nitrate (NO3–) anion is the active component of KNO3 (Bueno and Valmayor, 1974), and ammonium nitrate (NH4NO3) is twice as effective as KNO3 (Núñez-Elisea, 1988; Núñez-Elisea and Caldeira, 1988). In the low- and mid-latitude tropics, receptive trees respond by developing visible reproductive buds within 2 weeks after application. The effective spray concentration is 1–10% KNO3, depending on the age of the trees and climate. Two to four per cent KNO3 or calcium nitrate (Ca(NO3)2) and 1–2% NH4NO3 are effective for stimulating flowering in most conditions. The physiological and temporal timing of application is important. Old trees, non-vigorous trees, and trees in which vegetative flushes have been discouraged by low water potentials produce the best response to NO3– induction (N. Golez, personal communication, the Philippines, 1989).

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Chemical bud forcing is most effective in the tropics where distinct wet and dry seasons prevail. The response to chemical bud forcing by NO3− and ethephon diminishes at latitudes > 22° N or S (Mosqueda-Vázquez and de los Santos de la Rosa, 1981). Their effect may involve the decline of night temperatures from ≥ 20°C around the equator to ≤ 10°C between 22° and 27° N or S latitude during winter months or by late summer vegetative flushes. Trees in the wet or dry subtropics at 25° N or S have not responded to treatments (Davenport, 1993). Stems must be sufficiently mature, dark green with a minimum age of 4 months since the previous limp, red-leaf stage in easily induced cultivars and 5 months for more recalcitrant cultivars to obtain a reproductive shoot response in the low-latitude tropics (Davenport, 2003). Bueno and Valmayor (1974) indicated that leaves must be brittle when hand-crushed. NúñezElisea (1986, 1988) reported that stems must be at least 6 months old. Trees that experience autumn dry periods become responsive to treatments as early as October (northern hemisphere). Groups of stems within tree canopies are produced through asynchronous flushes of growth, and vary in age; only a few are responsive to the first inductive spray. Subsequent biweekly applications cause flowering in canopy sectors as they reach the age-dependent requirement for initiation. Early and out-of-season flowering and fruiting can thereby be achieved. KNO3 may be floral inductive in mango (Barba, 1974); however, trees in the upper latitude tropics typically flush vegetatively rather than produce bloom when either KNO3 or NH4NO3 is sprayed between June and September (N. Golez, personal communication, the Philippines, 1989). The warm, rainy season producing frequent flushes of growth during this period is conducive to a vegetative response to the sprays. These results indicate that KNO3 and NH4NO3 stimulate shoot initiation but do not determine bud morphogenesis. In buds released after KNO3 or NH4NO3 treatments, the ratio of leaf-generated FP to VP and not NO3– causes initiating buds to become reproductive. Kulkarni (1988b, 2004) suggested that the floral stimulus is present in stems when buds are forced in response to KNO3 and suggested that KNO3 may also sensitize buds to the floral stimulus. Davenport (2003), T.L. Davenport and J. Oleo (2006, unpublished data) and F. Ramirez and T.L. Davenport (submitted for publication) observed 100% vegetative shoots when 4% KNO3 was foliar applied to 2-month-old stems; whereas, application of the same spray treatment to 4.5-month-old stems on trees in the same orchards resulted in 100% reproductive shoots. Trees with high leaf N levels rarely flower in the tropics. Lack of flowering is always due to frequent vegetative flushes of growth, especially during the rainy season. Mango trees must have leaf N levels of 1.4% or less in order to suppress frequent flushes of vegetative growth (Davenport, 2003). Leaf N levels of < 1.1% suppress frequent flushes but also provide insufficient nutrition to support good cropping. Thus, 1.1–1.4% N levels in leaves appear to be optimum for good commercial production and control of flowering time in a managed orchard. The application of KNO3 to the foliage of the resting stems 4–5 months after the limp, red-leaf stage will cause a flowering response.

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Photoperiod Flowering in most trees does not appear to be under photoperiodic control (Kozlowski et al., 1991). Mango cultivation is concentrated between 27° N and 27° S where the shortest annual photoperiod is c.10.5 h and the longest photoperiod is c.13.5 h. Cultivars in the upper-latitude tropics and subtropics flower during the winter when photoperiods are short; however, trees in the low-latitude tropics, where a 12-h photoperiod is nearly constant, can flower at any time of the year. Furthermore, flowering on spring-initiated shoots in the subtropics occurs during summer (Schaffer et al., 1994). Studies have failed to demonstrate a correlation between 8-h photoperiods and flowering (Maiti, 1971; Maiti and Sen, 1978; Maiti et al., 1978). Núñez-Elisea and Davenport (1995) studied the effects of 11-, 12-, 13- and 24-h photoperiods at 18°C day/10°C night, or 11- and 13-h photoperiods at 30°C day/25°C night on flowering of container-grown trees. Photoperiod had no effect on the fate of buds, and the promotive effect of cool temperatures on flowering was independent of photoperiod. Photoperiods of 11-, 12- or 13-h with 18°C day/10°C night, caused flowering in trees within 40 days. The 24-h photoperiod with 12-h thermoperiods of 18°C and 10°C caused flowering of trees within 35 days. Photoperiods of 11- or 13-h at 30°C day/25°C night resulted in vegetative growth only. With warm temperatures, vegetative shoots were produced in 17 days. These results confirm that floral induction is caused by cool temperatures and not by short photoperiods and that warm temperature, not a long photoperiod, caused vegetative induction.

5.6 Hormonal Influence on Flowering FP is a protein product of the FT gene in Arabidopsis (Corbesier et al., 2007) and the Hd3a gene in rice (Tamaki et al., 2007) and moves in phloem from leaves to buds; there is little evidence that phytohormones are directly involved as the FP. Phytohormones appear to be responsible for shoot initiation in conditions that are floral inductive.

Ethylene Smudging has been utilized to stimulate mango flowering in the Philippines. Only branches that attain sufficient age respond to smudging by forming reproductive shoots (Acala and San Pedro, 1935; Bueno and Valmayor, 1974). Rodriguez (1932), investigating smoke-induced flowering of pineapple, proposed that ethylene, generated by burning material, may stimulate flowering. Dutcher (1972) confirmed that smoke from smudge fires contained ethylene. Smudging and the use of ethephon in 1968 by F. Manuel (Barba, 1974) and others (Bondad, 1972, 1976) to promote mango flowering suggested that endogenous ethylene is integral for floral induction (Barba, 1974; Bondad, 1976; Chadha and Pal, 1986). Ethephon effectively promotes flowering

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of mangoes under specific conditions in the low-latitude tropics (Davenport and Núñez-Elisea, 1997). The involvement of endogenous ethylene in flowering is supported by observations that indirectly link it to symptoms of ethylene production. Extrusion of latex from terminal buds occurs at the time of inflorescence initiation, and epinasty of mature leaves near the apex during expansion of the panicle has been observed (Davenport and Núñez-Elisea, 1990, 1991). Both are symptoms of plants exposed to high ethylene levels (Abeles, 1973). Indirect support also comes from reports that KNO3-stimulated flowering of mango is mediated by increased levels of endogenous ethylene (Thuck-Thye, 1978; Lopez et al., 1984). Mosqueda-Vázquez and Avila-Resendiz (1985) reported that the efficacy of KNO3 was negated by cobalt chloride (CoCl2) and silver nitrate (AgNO3), which inhibit the synthesis and action of ethylene, respectively, when sprayed 1–4 h after KNO3. Saidha et al. (1983) reported a gradual increase in endogenous leaf ethylene production as the season of floral initiation approached. Ethylene production by stems producing reproductive shoots was up to fivefold that of resting stems. Inconsistent (Pandey et al., 1973; Sen et al., 1973; Winston and Wright, 1986) or non-responsive results with ethephon (Pandey and Narwadkar, 1984; Ou and Yen, 1985; Pandey, 1989) or smudging (Sen and Roy, 1935), especially during warm, non-inductive conditions, have been reported. Davenport and Núñez-Elisea (1990, 1991) reported elevated ethylene production in mango stems in response to ethephon sprays without an accompanying floral response. Experiments were conducted during floral-inductive and non-inductive periods. Unlike Saidha et al. (1983), they observed no increase in ethylene production rates prior to or during panicle development. The effect of ethylene on flowering is unresolved. It is likely that ethylene stimulates shoot initiation by inhibiting auxin transport from leaves to buds and stems (Morgan and Gausman, 1966; Beyer and Morgan, 1971; Riov and Goren, 1979, 1980; Ramina et al., 1986). This may increase the ratio of cytokinin to auxin in buds and stimulate shoot initiation (Davenport, 2000). Other factors (i.e. cool temperatures or aged leaves) may be responsible for floral induction (Ona and de Guzman, 1982; Davenport, 1993).

Auxin Although auxin may have a critical role in floral induction of mango (Chadha and Pal, 1986; Hegele et al., 2006), there is little supporting evidence. The application (L.B. Singh, 1961; Singh and Singh, 1963; Bakr et al., 1981; Pandey and Narwadkar, 1984) and analysis of auxin in leaves (Paulas and Shanmugavelu, 1989; Sivagami et al., 1989), stems (Chen, 1987) and shoots (Chacko et al., 1972b) have been reported in relation to mango flowering. These studies are inconclusive due to inconsistencies in purification and analytical methodologies (Davenport and Núñez-Elisea, 1997). Auxin may indirectly stimulate root-produced cytokinins through initiation of new root growth. Auxin is transported basipetally from growing

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shoots and leaves to roots (Goldsmith, 1968; Cane and Wilkins, 1970; Wilkins and Cane, 1970; Goldsmith and Ray, 1973; Lomax et al., 1995) and stimulates root initiation (Hassig, 1974; Wightman et al., 1980). The efficacy of various auxins for stimulating adventitious rooting of mango marcots and cuttings was reviewed by Davenport and Núñez-Elisea (1997). Auxin inhibits shoot initiation (Davies, 1995) and confers apical dominance by preventing axillary bud break. Leaf-produced auxin and petiolar auxin transport capacity declines as leaves age (Veen, 1969; Veen and Jacobs, 1969; Davenport et al., 1980). The interaction of decreasing auxin and accumulating cytokinins in resting buds may explain the cyclic nature of shoot initiation. The ratio of cytokinin to auxin levels in buds regulates shoot initiation (Skoog and Miller, 1957; Bangerth, 1994; Cline et al., 1997; Beveridge et al., 2003).

Cytokinins Relationships between mango flowering and the endogenous levels of cytokinins in leaves (Paulas and Shanmugavelu, 1989; Kurian et al., 1992), stem tips (Agrawal et al., 1980) and xylem sap (Chen, 1987) and the effect of cytokinin applications on bud break and shoot development have been reported. Chen (1985) described precocious flowering of mango shoots in response to early October application of 6-benzylaminopurine (BA). Flowering was observed 1 month following application and 3 months later on non-treated trees. Núñez-Elisea et al. (1990) reported numerous reproductive shoots per stem in response to the synthetic cytokinin, thidiazuron, during cool, floral inductive conditions; however, numerous vegetative shoots per stem were initiated when thidiazuron was applied during warm, vegetatively inductive conditions. Early bud break was not achieved following foliar application of Promalin (commercial formulation of BA and gibberellins A4+A7) (Oosthuyse, 1991b), BA (A.K. Singh and Rajput, 1990) or kinetin (Singh and Singh, 1974). Chen (1987) reported the lowest levels of putative trans zeatin and its riboside were translocated from roots during the vegetative shoot growth and resting stages, whereas the highest levels occurred during early flowering and full bloom. Paulas and Shanmugavelu (1989) observed no significant difference in cytokinin levels of the fourth and fifth leaves during resting bud and flowering. Cytokinin levels in mango stem buds increased during exposure to cool, floral inductive temperatures (Bangerth et al., 2004). Agrawal et al. (1980) described 11 cytokinin-like substances isolated from stem tips of an alternate-bearing cultivar in ‘on’ and ‘off’ years. Kurian et al. (1992) reported a link between PBZ applications and reduction in cytokinins in mango leaves with treatments, perhaps caused by reduction in feeder root development and formation of thick, blunt roots (Bausher and Yelenosky, 1987; Peng et al., 1991; Burrows et al., 1992; Yelenosky et al., 1993). Concurrent with this response was suppression of bud initiation and reduced internode lengths for c.2 years.

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The role of cytokinins in flowering is unresolved due to sampling of different organs at non-comparable times or conditions. The elevated cytokinin levels found prior to and during flowering and the flowering response to applied BA led to the conclusion that cytokinins are involved in flowering of mango (Chen, 1985, 1987; Bangerth, 2006); however, such responses can be explained if cytokinins are involved in stimulation of bud break (i.e. shoot initiation) during floral inductive conditions. A well-documented role for cytokinins in higher plants, especially evident in vitro, is bud organogenesis (Skoog and Miller, 1957; Miller, 1963; Takahashi, 1986; Salisbury and Ross, 1992; Davies, 1995; Haberer and Kieber, 2002). The primary cytokinins in higher plants are trans zeatin, dihydrozeatin, isopentenyl adenine and their ribosides. They are translocated from roots and accumulate in resting buds (Hendry et al., 1982a, b) or can possibly be synthesized in nearby tissues as regulated by auxin (Nordstrom et al., 2004; Tanaka et al., 2006). Their rate of accumulation may relate to periodic root flushes that alternate with shoot flushes (Krishnamurthi et al., 1960; Bevington and Castle, 1986; Cull, 1987, 1991; Parisot, 1988; Williamson and Coston, 1989).

Gibberellins Gibberellins are tetracyclic diterpenoid compounds that vary in biological activity according to the type and location of substituted side groups on a basic ent-gibberellane skeleton. The number of known gibberellins is > 100 (Pearce et al., 1994). Reproductive shoot initiation is suppressed in many woody angiosperms by gibberellic acid (GA3) (Pharis and King, 1985). GA3 inhibits mango flowering (older literature reviewed in Davenport and Núñez-Elisea, 1997; Núñez-Elisea and Davenport, 1998). GA3 inhibition of mango flowering is correlated with the applied concentration (Kachru et al., 1971, 1972) and may cause buds to develop vegetatively under floral-inductive conditions. Núñez-Elisea and Davenport (1991a, 1998) reported a delay in initiation of axillary shoots when GA3 was foliar applied to deblossomed stems during cool, floral inductive temperatures. Higher concentrations caused longer delays in shoot initiation. GA3 did not inhibit floral induction, so long as cool, inductive temperatures were present during axillary shoot initiation. Late initiating buds, which grew during warm, spring temperatures, however, formed vegetative shoots. Similar delays in reproductive shoot initiation in response to GA3 application was reported by Shawky et al. (1978) and Turnbull et al. (1996). Multiple applications, even at lower rates, are more effective than a single application (Tomer, 1984; Turnbull et al., 1996; Davenport and Smith, 1997). GA3 treatment has been recommended in the Canary Islands to delay flowering until the danger of frost has passed (Galán-Saúco, 1990). In the subtropics of Australia, it is used to prevent flowering in newly planted trees during the spring so that the full growing period can be utilized for vegetative growth, thereby hastening orchard establishment (A.W. Whiley, personal communication, Queensland, 1996).

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Response to GA3 varies among cultivars, growing conditions and timing of application (Tomer, 1984; Oosthuyse, 1995a; Turnbull et al., 1996; SánchezSánchez et al., 2004). GA3 can delay shoot initiation beyond the floral inductive window, resulting in a vegetative flush when shoots develop in warm weather (Kachru et al., 1971, 1972; Núñez-Elisea and Davenport, 1991a, 1998; S. Gazit, personal communication, Israel, 1993). The variable response to GA3 may be related to levels of active gibberellin in buds at the time of application, inconsistent uptake or differential sensitivity of buds, depending on their position (apical versus axillary) or age (Núñez-Elisea and Davenport, 1991a, 1998). Efficacy is related to the timing of application; immediately prior to normal shoot initiation appears to be most effective (Davenport and Smith, 1997). Reports of endogenous gibberellins in mango tissues, especially in buds, are difficult to interpret with respect to a regulatory role in bud break or flowering. Problems include sampling of tissues other than apical buds, i.e. whole stems (Tongumpai et al., 1991b), leaves (Paulus and Shanmugavelu, 1989; Sivagami et al., 1989) and xylem sap (Chen, 1987), or at times when developing shoots may contribute to the overall result (Chen, 1987). Pal and Ram (1978) tentatively identified the presence of gibberellins A1, A3, A4, A5, A6, A7 and A9. Chen (1987) identified gibberellins A1/3, A4/7, A5, A17, A20 and A29. The estimated levels of gibberellins in apical buds for 6 months prior to the flowering season were reported to be higher in the ‘off’ year than in the ‘on’ year of an alternate-bearing cultivar (Pal and Ram, 1978). Chen (1987) reported the highest levels of gibberellins in xylem sap during leaf differentiation and lower concentrations during rest, panicle emergence and full flowering. Tongumpai et al. (1991b) observed increasing levels of gibberellins in whole stems over the 16 weeks prior to vegetative shoot emergence and decreasing levels over the same period prior to panicle development. Gibberellins A1, epi-A1, A3, A19, A20 and an unidentified gibberellin in buds and leaves from shoot and stem tips of different ages have been quantified (Davenport et al., 2001b). The detected gibberellins are members of the early 13-hydroxylation pathway of gibberellin synthesis (Takahashi, 1986; Pearce et al., 1994). Gibberellins A3 and A19 were the most abundant gibberellins in apical stem buds. The concentration of GA3 increased within buds with increasing age of stems, although concentrations of other GAs were variable. The concentration of GA3 did not change significantly with age in leaves, whereas that of most of the other GAs declined. Davenport et al. (2001b) concluded that elevated GA3 levels in buds may enhance or maintain the synthesis or activity of endogenous auxin to maintain low cytokinin/auxin ratios and enhance inhibition of shoot initiation (Jacobs and Case 1965; Scott et al., 1967; Pharis et al., 1972; Ross et al., 1983; Law 1987; Law and Hamilton, 1989). The roles of gibberellins and other phytohormones in shoot initiation and induction is unclear. Endogenous levels in buds and leaves must be correlated with physiological events in individual stems. Experimental approaches should include examination of resting buds up to both vegetative and reproductive shoot initiation to avoid misinterpretation of results. Experiments

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should utilize plants grown under defined conditions with specific environmental controls for evaluation of cause and effect. Finally, extraction and purification protocols should include quantifiable internal standards and use of sensitive unambiguous analytical techniques.

Plant growth retardants Plant growth retardants have been evaluated to stimulate early or more intense flowering, especially in the ‘off’ year of alternate-bearing cultivars (Davenport and Núñez-Elisea, 1997). They are in three main classes: (i) the gibberellin transport inhibitor, daminozide (N-dimethylamino-succinamic acid), known as alar or B-Nine; (ii) the onium type, chloremquat chloride (2-chloroethyl trimethylammonium chloride), known as cycocel and CCC; and (iii) the steroid-synthesis-inhibiting triazoles, for example PBZ (PP-333), known as Cultar®, and uniconazole, known as XE-1019 or Sumagic (Rademacher, 1991, 2000a). The latter two classes of compounds inhibit ent-kaurene synthetase, an enzyme in the gibberellin synthesis pathway (Nickell, 1983; Dalziel and Lawrence, 1984; Rademacher, 1991, 2000a). Applying daminozide results in increased gibberellin levels, perhaps due to the inability to distribute it properly (Rademacher, 1991). Plant responses may depend upon whether target tissues are near the site of gibberellin synthesis or sufficiently removed from it to be affected by the inhibited translocation. Daminozide and cycocel The efficacy of daminozide and cycocel for increasing flowering in the ‘off’ season of alternate-bearing cultivars has been studied (Maiti et al., 1972; Mukhopadhyaya, 1978; Rath and Das, 1979; Suryanarayana, 1980; Rath et al., 1982; Ou and Yen, 1985), together with their ability to stimulate early flowering (Suryanarayana and Rao, 1977; Chen, 1985; Kurian and Iyer, 1993a, b). Enhanced, inconsistent flowering occurs in response to these compounds, especially cycocel. Triazoles PBZ is being used (except in the USA where it has not been cleared for use) to stimulate enhanced or early flowering. It is best applied to the soil due to its low solubility, long residual activity and lack of efficient foliar uptake (Rademacher, 2000b). PBZ applied as a soil drench (1–20 g active ingredient (ai)/tree) reduces internode lengths and causes earlier and enhanced flowering in mango trees (Hasdiseve and Tongumpai, 1986; Haw, 1986; Hongsbhanich, 1986). Depending on climate, residual activity lasts for c.2 years (Kulkarni, 1988a). These results have been confirmed in different locations in the tropics (Davenport and Núñez-Elisea, 1997; Yeshitela et al., 2004a, b). Nartvaranant et al. (2000) recommended soil application of PBZ at 1–1.5 g ai/m of canopy diameter to achieve flowering in 90–120 days if the trees are stimulated to flush. Davenport (2003) observed that such treatments allowed a reduction of c.1 month in the time required for stem rest before stimulating them to initiate reproductive shoots using KNO3. PBZ also reduces alternate

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bearing of some cultivars (Hillier and Rudge, 1991; Burondkar and Gunjate, 1993; Rao, 1997; Rao et al., 1997; Rao and Srihari, 1998; Vijayalakshmi and Srinivasan, 1999). Cultivars that tend to flower with minimal inductive impetus are more responsive and can be induced to flower out-of-season using PBZ (Tongumpai et al., 1989). Núñez-Elisea et al. (1993) demonstrated that application of PBZ and uniconazole advanced bud break of containerized trees in controlled environment chambers, but cool temperatures were necessary to induce flowering. Initiated shoots were induced to be vegetative in warm temperatures. The greater proportion of purely reproductive panicles in treated plants (compared with controls) suggests that triazoles impact the level of a putative VP, probably a gibberellin. Whiley (1993) suggested a secondary mechanism for the floral promotive action of PBZ on mangoes, noting inconsistent responses in the literature between cultivars, environments and application times. Application of PBZ reduces the number of panicles, despite increased fruit set (Goguey, 1990). Davenport (1987, 1994) observed neither growth inhibition nor enhanced or early flowering in response to root drenches or bark banding with uniconazole (1–5 g ai/tree) in trees growing in alkaline, calcareous soil. He reported that new shoot growth was stunted with extremely short internodes when trees were severely pruned soon after or as long as 3 years after treatment. Yield was severely reduced due to the lack of normal growth flushes. The growth stunting effect continued for 7 years after pruning. Davenport (1994) warned that use of triazole plant growth retardants for control of tree growth, flowering or yield must be done with considerable caution, especially if severe pruning of the trees is anticipated. Residual uniconazole or PBZ applied as a soil drench or bark band is apparently retained in high concentrations in main scaffolding branches. In Central and South America, growers utilize PBZ annually to stimulate early flowering. A test tree should be severely pruned to determine if the trees are affected by PBZ to anticipate the orchard response to later severe pruning. Certain gibberellins (i.e. GA1) are necessary for shoot elongation. Inhibition of bud break and shoot elongation in response to application of the growth retardants cycocel (Maiti et al., 1972) and triazoles (Kulkarni, 1988a; Burondkar and Gunjate, 1991, 1993; Tongumpai et al., 1991a; Kurian et al., 1992; Winston, 1992; Kurian and Iyer, 1993a, b; Núñez-Elisea et al., 1993; Werner, 1993) have been reported. Elongation of panicles is inhibited, especially by high levels of triazoles (Kulkarni, 1988b; Winston, 1992; Davenport, 1994; Salomon and Reuveni, 1994). Inflorescences in treated trees may become compact, improving opportunities for disease and insect attack (Winston, 1992). Kurian et al. (1992) associated reduced cytokinin levels in leaves with inhibition of shoot initiation in plants treated with soil drenches of PBZ. Elevated, concentration-dependent levels of phenolic compounds were also found in resting apical buds of PBZ-treated trees (Kurian et al., 1994). They suggested that low cytokinin activity and high phenolic levels in buds contributed to inhibition of shoot initiation. The combined impact of the gibberellin synthesis-inhibiting triazoles on shoot initiation, induction, and elongation implies that several different

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gibberellins regulate specific activities in mango plants. This is supported by the inhibitory effect of GA3 on shoot initiation in contrast with early initiation of flowering in triazole-treated trees. Compression of reproductive and vegetative shoot internodes may involve inhibition of GA1 synthesis. Stimulation of flowering instead of vegetative growth during early initiation in triazole-treated plants in marginal or non-floral inductive conditions, suggests that the putative VP, a gibberellin other than GA3 or GA1, is reduced when gibberellin synthesis is inhibited.

5.7 Photoassimilate Influence on Flowering Flowering may be regulated by C:N ratios with high levels being conducive to flowering (Kraus and Kraybill, 1918). Photoassimilates reaching the apical bud from leaves was central to several theories of floral induction (Sachs, 1977; Bernier and Sachs, 1979; Bernier et al., 1981, 1993; Bernier, 1988) including mango (Mallik, 1951; L.B. Singh, 1960; Chacko and Ananthanarayanan, 1982; Rameshwar, 1989) and other species (Allsopp, 1965; Sachs, 1977; Mishra and Dhillon, 1978; Ramina et al., 1979; Bernier et al., 1981; Sachs and Hackett, 1983). The theory of photoassimilate diversion to the apical bud (Sachs et al., 1979) is the basis for the carbohydrate-regulated flowering models (see below). Sugars are utilized during panicle development (Ravishankar and Mohan Rao, 1982). Starch reserves and C:N ratios have been correlated with flowering (Mishra and Dhillon, 1978; Suryanarayana, 1978a, b, c; Chacko and Ananthanarayanan, 1982; Whiley et al., 1988, 1989, 1991; Robert and Wolstenholme, 1992; Shivashankara and Mathai, 1995), and the subject has been reviewed (L.B. Singh, 1960, 1972; Singh, 1979; Chacko, 1986, 1991; Chadha and Pal, 1986; Pandey, 1989). Starch accumulation during extended periods of canopy rest prior to flowering provides supportive evidence, but there is little consensus regarding the role of carbohydrates and N in flowering. Photoassimilates may be necessary for floral induction. If a florigenic promoting gene product is synthesized in leaves in small amounts, it must be able to move to those buds via phloem. Due to the requirement for high solute concentrations to motivate phloem flow, the low concentration of the FP could not cause fluid movement through sieve tubes of the phloem on its own. The much higher concentrations of photoassimilated sugars carried by water loading into the phloem in leaves passively transports the FP towards the various sinks, including respiring buds, where they are utilized for floral induction.

5.8 Horticultural Manipulation of Flowering Mango flowering can be stimulated by trunk or branch girdling, defoliation and deblossoming (Pandey, 1989). Responses vary with cultivar and environment. Trunk girdling of mango trees to promote flowering is inconsistently effective (Kinman, 1918; Gaskins, 1963; Winston and Wright, 1986) and

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can be detrimental to trees, especially if done in subsequent years. It has been shown to increase flowering in the ‘off’ year of alternate-bearing cultivars; however, it either has no effect or is only marginally beneficial in the ‘on’ year (Mallik, 1951; Rath and Das, 1977, 1979; Rath et al., 1982; Rameshwar, 1989). Girdling in late summer or early autumn usually results in less vegetative flushing prior to flowering, which is enhanced in trees exposed to marginally inductive conditions. Tree response is dependent on the width of the girdle. Narrow cuts result in either a short-term or no response; whereas, girdles that are too wide can kill trees if they do not close within a reasonable time. Girdling cuts phloem transport, starves roots of photoassimilates and interrupts auxin transport to roots (Morris and Thomas, 1978; Hegele et al., 2004). These are detrimental to root development and can alter the bud cytokinin:auxin ratio due to reduced cytokinin translocation from roots. This results in delayed shoot initiation, which can impact the level of the age-dependent, putative VP when shoot initiation occurs. The delay in flushing, therefore, enhances flowering. Defoliation of trees stimulates flushing, possibly by altering the cytokinin:auxin ratio in buds because leaves are the primary source of auxin. Bloom delay is useful where recurring temperatures < 15°C stimulate flowering, but continued low temperatures hamper pollination, fertilization and early fruit development (Young and Sauls, 1979; Wolstenholme and Mullins, 1982a, b; Whiley et al., 1988; Galán-Saúco et al., 1991). Low temperatures cause production of seedless, underdeveloped fruit. Deblossoming stimulates growth of dormant axillary buds, which produce inflorescences if initiation occurs under conditions conducive to floral morphogenesis (Singh et al., 1974). Late blooms can also be promoted with ethephon (Chadha and Pal, 1986; Galán-Saúco et al., 1993) and cycloheximide (Pal and Chadha, 1982; Shu, 1993). Sprays of these compounds cause abscission of apical panicles, thereby releasing dormant axillary buds that will produce inflorescences under cool, floral-inductive conditions of the subtropics.

5.9 Conceptual Flowering Models Several conceptual models have been proposed that attempt to explain the physiological basis of mango flowering. Each model should be viewed as a collection of integrated ideas, which require rigorous testing for validity within the context of the models. A useful model should explain how flowering and vegetative growth is regulated in all cultivars and races in both humid and dry climates in the tropics and subtropics. It should also be supported by the preponderance of research evidence. The flowering models are either carbohydrate-regulated or hormone-regulated.

Carbohydrate-regulated flowering models Cull (1987, 1991) presented a holistic approach for tree crop research and management to maximize sustainable fruit production. This concept is based

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on the axiom of genotype/environment adaptability expressed through the annual phenological cycle and is an alternative to the traditional reductivebased approach to crop research and development. He proposed that productive cultivars follow ‘normal’ phenological patterns from year to year due to gene expression in specific environments. A significant departure from this pattern results in reduced or total crop failure. Annual variations in climatic conditions that alter tree phenology can be countered by strategic applications of nutrients, water, plant growth regulators and canopy manipulation. The model does not attempt to explain the intricacies of shoot initiation or induction, but takes a broader approach in detailing temporal relationships between reproductive and vegetative growth that lead to reliable cropping. The fundamental principle underlying this model is that yield is the product of photoassimilate (carbohydrate) accumulation and subsequent redistribution during the annual growth cycle. Accumulated photoassimilates would drive critical growth events that require higher levels of resources than are available from current photoassimilate supplies. Cultivars that proceed with balanced reproductive, vegetative and rest phases are more likely to have sufficient carbon resources to meet periods of critical demand and therefore will sustain high yields. The model illustrates floral initiation as occurring after a 2- to 3-month rest period during autumn/winter when a critical threshold level of carbohydrate is reached in buds together with a putative floral stimulus. Bud break during cool weather results in a high percentage of flowering stems (> 90%; Searle et al., 1995) with fruit set and retention suppressing vegetative flushing on individual fruiting stems until after they have matured and harvested. Shortly after harvest, vegetative buds are released and a flush of growth occurs during the summer, which is followed by a period of strong root growth. The regenerated canopy becomes a source for rebuilding photoassimilate reserves that are stored in the roots, bark and resting stems. In the tropics, growth events are less orderly, and cultivar and management skills are of greater importance. The pre-flowering rest period is usually achieved by drought as temperatures remain above the critical threshold for shoot growth (15°C) (Whiley et al., 1989). Other practices used with some success to enforce canopy quiescence are girdling and the application of growth retardants. The principles of phenological modelling have been advanced into working pheno/physiological models for avocado (Whiley, 1994) and mango (Searle et al., 1995). The advantage of this approach is that the annual progression of growth cycles with associated physiological changes is studied concurrently, adding a further dimension to our understanding of tree growth and development. Information gathered in this way provides opportunities to identify and assess critical yield-limiting events, which in the case of mangoes largely relates to the success or failure of flowering. Chacko (1991) proposed a flowering model driven by assimilate supply and diversion to apical meristems (Fig. 5.6). Environmental conditions, such as water stress, cool temperatures, high evaporative demand, flooding, girdling and other events that inhibit vegetative growth result in a shift in

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FLORAL INHIBITION

FLORAL INDUCTION · Water stress · Low temperature · High VPD · Flooding

KNO3 (cultivar and location specific) Exogenous gibberellin

? High starch

· Stem girdling · Root pruning

MISSING LINK

· Mild nitrogen stress

· Growth retardants · Inhibitors

ASSIMILATE DIVERSION from SHOOT APEX

GROWTH STIMULATION and high gibberellin

· High temperature · High humidity · High soil moisture

Sugar High nitrogen

· High reserves · Efficient assimilate partitioning Dwarf/precocious cultivars e.g. ‘Irwin’

· Low reserves · More wood formation Over vigorous cultivars e.g. ‘Kensington’

HEREDITY

Frequent flushing of roots and shoots

High gibberellin levels

JUVENILITY

Fig. 5.6. Chacko’s Assimilate Supply and Diversion Flowering Model, a carbohydrate-regulated flowering model (Source: Chacko, 1991).

T.L. Davenport

INCREASED ASSIMILATE supply to SHOOT APEX

GROWTH CHECK

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carbohydrate partitioning and a diversion of soluble assimilates to stem apices. The elevated carbohydrate status in buds, together with a floral stimulus, results in floral induction. Vigorously growing cultivars and juvenile plants have low starch reserves (Whiley et al., 1988, 1989, 1991) and a diversion of soluble assimilates from stem apices results in floral inhibition. Conditions that promote vegetative growth, i.e. high temperature and moisture, high gibberellins and N, also lead to floral inhibition. Experiments involving chemical girdling of trees are based on this model (Blaikie et al., 1999).

Hormone-regulated flowering models Tri-factor Hypothesis of Flowering Extensive work on movement of the putative floral stimulus across grafts from donor to receptor stems (Kulkarni, 1986, 1988b) and the inhibitory influence of fruit on subsequent flowering (Kulkarni and Rameshwar, 1989) form the basis of a flowering model proposed by Kulkarni (1991): the Tri-factor Hypothesis of Flowering in mango (Kulkarni, 2004). This theory (Fig. 5.7) proposes an interactive role for a putative, cyclically produced floral stimulus in leaves, a floral inhibitor in leaves and fruits, and bud activity during the floral cycle. During dormancy following a vegetative cycle, genetic and

Genetic and Environmental Factors

Flowering promoter synthesized in the leaves in the floral cycle

Pure panicles

Flowering inhibitor and vegetative promoter synthesized in the leaves and possibly other organs

Mixed leafy panicles

Bud activity in synchrony with the floral cycle

Vegetative flush

Fig. 5.7. Kulkarni’s Tri-factor Hypothesis of Flowering in mango, a hormone-regulated flowering model (Source: Kulkarni, 2004).

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Mango flowering model PHOTOASSIMILATES

VEGETATIVE SHOOT AUXIN GIBBERELLINS GA3 GA1 GAx FREQUENT VEGETATIVE GROWTH

FRUIT

MIXED SHOOT

INDUCTION

AUXIN GIBBERELLINS A3 Ax GENERATIVE SHOOT

PROMOTER IN LEAVES

CHILLING TEMP. OTHER FACTORS?

WATER STRESS SHOOT INITIATION

PRUNING DEFOLIATION NITRATE SPRAY ETHYLENE STORAGE CARBOHYDRATES

CHILLING TEMP. ROOT INITIATION ROOTS

GIRDLING CYTOKININS

Fig. 5.8. Davenport’s Comprehensive Conceptual Hormone-regulated Flowering Model (Source: Davenport and Núñez-Elisea, 1997; Davenport, 2000). Single lines indicate promotive impact. Double lines indicate inhibitory impact.

environmental factors determine the level of synthesis of the putative floral stimulus. Flowering occurs only if certain correlative factors are present, for example if the receptor bud becomes active. If fruits are or have been recently present on the stem, vegetative growth will result. Presence of the putative floral inhibitor in leaves interferes with expression of the floral stimulus resulting in vegetative growth. The level of the floral stimulus determines the response: high levels give rise to normal panicles, intermediate levels give rise to mixed panicles and low levels result in vegetative growth. Comprehensive Conceptual Flowering Model This is a model of flowering involving the various classes of phytohormones (Davenport, 1992, 1993, 2000, 2003; Davenport and Núñez-Elisea, 1997) (Fig. 5.8) based on many lines of experimental evidence as well as on research of other tropical and subtropical fruit crops with similar phenological cycles (Menzel, 1983; Davenport, 1990, 1992; Menzel et al., 1990; Menzel and Simpson, 1994; Davenport and Stern, 2005). Focusing on events occurring in individual buds, it is applicable to monoembryonic and polyembryonic cultivars in the tropics and subtropics and attempts to explain the physiological basis for the annual progression of the phenological cycle. SHOOT FORMATION. Two distinct events must occur for vegetative or reproductive growth to occur in resting apical or lateral buds of mango: (i) the

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bud(s) must be initiated to grow (shoot initiation); and (ii) at the time of initiation, shoot development (i.e. vegetative, mixed, or generative) is determined (induction). Although conditions for floral induction may be present prior to shoot initiation, determination of that inductive condition in buds is not made until initiation occurs. Initiation and induction events are regulated by different signals and each may be manipulated by different stimuli. Removing the apical whorl of leaves or tip pruning physiologically mature stems stimulates shoot initiation in apical or lateral buds, respectively. If containerized plants are maintained in warm temperatures (30°C day/25°C night) following initiation, vegetative shoot growth is induced. If they are kept under cool conditions (18°C day/10°C night), initiating shoots are induced to be generative. In either of the two temperature regimes without pruning, they do not initiate shoots until the natural flushing event occurs much later. They become vegetative or reproductive according to the temperature at the time of shoot initiation. If transferred from cool to warm temperatures before shoot initiation, new shoot growth is induced to be vegetative. Induction is therefore determined at the time of shoot initiation, and plants rapidly lose their floral inductive potential when removed from the cool environment. Determination of shoot type can be reversed during morphogenesis by transferring containerized trees from warm-to-cool or cool-to-warm conditions (Batten and McConchie, 1995; Núñez-Elisea et al., 1996). INITIATION CYCLE. The cyclic initiation of vegetative or reproductive shoots is common to all mango cultivars. Developing vegetative shoots are rich sources of auxins and gibberellins, which may be inhibitors in an internal cycle that regulates shoot initiation. Auxins are actively transported basipetally to roots from production sites in stems (Goldsmith, 1968; Cane and Wilkins, 1970; Wilkins and Cane, 1970; Goldsmith and Ray, 1973), and they stimulate adventitious root growth in mango and other crops (Hassig, 1974; Wightman et al., 1980; Sadhu and Bose, 1988; Rajan and Ram, 1989; NúñezElisea et al., 1992). Elevated auxin synthesis in periodically flushing shoots is likely to form a concentrated pulse of auxin, which inhibits recurring bud break and moves basipetally to the roots. This pulse of elevated auxin may stimulate initiation of new root flushes following each vegetative flush. Alteration of root and shoot growth occurs in mango (Krishnamurthi et al., 1960; Cull, 1987, 1991; Parisot, 1988) and other tropical and subtropical trees (Bevington and Castle, 1986; Williamson and Coston, 1989; Ploetz et al., 1991, 1993). Timing of the root flush may depend on the distance from stems to roots, the physiological condition of the transport path, and environmental conditions (i.e. temperature or water relations). New roots that develop following growth stimulation are a primary source of cytokinins (Davies, 1995). Cytokinins are transported passively to stems via the xylem sap in all plants and are active in bud break (Went, 1943; Kende and Sitton, 1967; Sitton et al., 1967; Itai et al., 1973; Haberer and Kieber, 2002). Cytokinins stimulate shoot initiation in mango (Chen, 1985; NúñezElisea et al., 1990) and other plants (Oslund and Davenport, 1987; Belding and Young, 1989; Williamson and Coston, 1989; Davenport, 1990; Davies, 1995;

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Henny, 1995). Auxin inhibits shoot initiation (Davies, 1995) and confers apical dominance by preventing axillary bud break. Leaf-produced auxin and petiolar auxin transport capacity declines as leaves age (Davenport et al., 1980). Auxin and cytokinins may therefore be involved in the periodic cycle of bud break. A critical balance of these two phytohormones, possibly modulated by GA3, may regulate shoot initiation. During a rest period, the inhibitory action of auxin transported to buds decreases with time; whereas, cytokinin levels in buds increase (Chen, 1987). When a critical cytokinin/auxin ratio is achieved, the buds are stimulated to grow, thereby resetting the cycle with initiation of new shoots. The interaction of auxin and cytokinin to control bud break in plants is a concept that is supported by molecular studies (see review by Nordstrom et al., 2004). Moreover, initiation of shoot growth occurs following pruning, defoliation or the application of thidiazuron (NúñezElisea et al., 1990). Vigorous cultivars (Whiley et al., 1989) and young, small trees under vegetatively promotive conditions flush frequently with only short periods of rest; however, this cycle slows with age. Old centennial trees flush infrequently (N. Golez, personal communication, the Philippines, 1989). Foliar or soil-applied NO3− stimulates initiation of reproductive shoots only if applied after resting stems have attained an age to overcome any vegetatively inductive influence. In contrast, high N in soils leads to high N levels in leaves resulting in frequent vegetative flushes. The mechanism whereby NO3− stimulates shoot initiation is unknown. Seeds are rich sources of auxin and gibberellins, which contribute to the strong inhibition of bud break commonly observed on fruit-bearing mango stems. The longer that fruit are attached to stems, the longer the postharvest inhibition may last in the stem (Kulkarni and Rameshwar, 1989; Kulkarni, 1991). Water stress inhibits shoot initiation by its direct impact on cell division and elongation possibly by interfering with translocation of cytokinins from roots. There is little evidence that water stress is directly involved in inductive processes. During water stress, roots continue to grow and produce cytokinins (Itai and Vaadia, 1965; Itai et al., 1968; Wu et al., 1994). Reduced xylem flux due to limited soil hydration, and transpiration due to increased stomatal resistance during water stress may reduce the amount of cytokinins reaching stems. After rewatering, the increased levels of cytokinins in roots may translocate to and accumulate in buds. Auxin synthesis and transport from leaves are reduced during water stress (Davenport et al., 1980) and may require several days for correction after rewatering. This rapid shift in the cytokinin/auxin ratio of buds may explain the shooting response that occurs soon after relief of water stress. GA3 may act with auxin to inhibit shoot initiation (Davenport et al., 2001b). Early flowering in plants treated with PBZ may be a response to lowered gibberellin levels, thus lowering the level of initiation inhibitor. This model could explain why sectors of tree canopies flush in the tropics. Mango trees flush often and synchronously throughout the canopy when they are young. With advancing age, the frequency of flushing is reduced

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and synchrony is lost, resulting in sporadic flushes of vegetative or reproductive growth in sections of the canopy. As the distance between stems and roots increases, the time required for transport of the putative pulses of elevated auxin levels to roots, formed during a vegetative flush, is increased. Groups of stems exhibiting simultaneous flushing ultimately connect to a common branch. Dye trace studies indicate that water transport remains in strict phylotaxic alignment from secondary roots to the canopy, even in large trees (T.L. Davenport, unpublished results, Florida, 1991). Unless disturbed by girdling or by pruning of branches or roots, specific branches in the canopy communicate only with those roots in phylotaxic alignment with them. The hormone transport time may vary among sections of the canopy as the tree grows. This generates individual initiation cycles in sections of the canopy that are separately maintained unless resynchronized with the rest of the tree following a canopy-wide environmental trigger. Synchronization of growth throughout trees occurs following exposure to low temperature, water stress, light pruning of the entire tree and any condition that would increase the postulated cytokinin/auxin ratio in buds throughout the canopy. An increased ratio may occur by inhibiting auxin transport from leaves to buds, or increasing cytokinin translocation from roots to stems. Winter in the subtropics would reduce auxin transport; whereas, water stress in the tropics may impact the availability of cytokinins from roots and auxin from leaves. The intensity of the initiation response (i.e. synchronization of flushes in the canopy) may be regulated by decreased auxin transport at low temperatures, the base level of which may be determined by the age of individual stems. Passage of a strong, extended cold front during subtropical winters produces synchronized flowering. Milder winters with weak cold fronts result in asynchronous flowering in sections of trees. The oldest sectors of canopies flower first, followed by sectors bearing sequentially younger flushes in subsequent cold fronts. Vegetative flushes occur when night temperatures are > 18°C for significant periods between cold fronts. INDUCTION SWITCH.

Floral or vegetative induction is possibly governed by the interactive ratio of a FP that is up-regulated in low temperatures to an ageregulated VP in leaves at the time of shoot initiation. High FP:VP ratios would be conducive to induction of generative shoots, low ratios conducive to vegetative shoots and an intermediate ratio of the two would be conducive to mixed shoots. Regardless of the endogenous levels of the two components perceived in buds at the time of initiation, flowering and vegetative growth responses can best be explained by the ratio of the two. Although the putative FP seems to be up-regulated during leaf exposure to cool temperatures (< 18°C), there appears to be a basal level present at all times in leaves exposed to higher temperatures. Flowering of mango occurs in low-latitude tropics lacking cool night temperatures when stems become sufficiently aged so that the ratio of the basal level of resident FP to decreasing VP increases to a critical threshold to provide floral induction when shoots are initiated. This could explain how flowering on non-synchronized

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branches may occur at any time of the year in trees growing in low-latitude tropics. High proportions of mixed shoots are commonly found in these conditions, indicating the marginally floral-inductive ratios present under these conditions. In contrast, flowering in younger stems having higher levels of VP is observed only when initiation occurs in cool, floral-inductive temperatures. More flowering occurs throughout the canopy when stems are exposed to cool temperatures, attributable to the higher ratio of up-regulated FP to resident VP. Genetic differences in base levels of the putative FP and/or VP or the receptors of these components could explain the range in flowering responses in tropical and subtropical cultivars and why a cultivar grown in an environment different from that in which it was selected is less productive. Cultivars selected in the subtropics usually flower as well in the low-latitude tropics as those selected in the tropics. Cool temperatures in the subtropics sometimes cause earlier flowering in tropical cultivars than those selected in the subtropics. Kulkarni (1991) demonstrated that several multi-flowering cultivars can induce flowering in receptor graft plants and cause a range of the flowering response of the receivers to donors. Some cultivars may produce higher base levels of putative FP than others. These are the same cultivars that readily flower under warm temperatures and flower early during cool winter months. The Comprehensive Conceptual Flowering Model suggests that flowering can occur at any time in any cultivar regardless of origin so long as stems are sufficiently old to reduce the VP level to below the critical FP/VP ratio when initiation occurs. Although the putative FP, perhaps a product of an ortholog of the Arabidopsis FT gene, has not been identified, the VP may be a gibberellin. Triazoles and other plant growth retardants that inhibit gibberellin synthesis, promote strong and out-of-season flowering under conditions that would normally be marginally or non-floral inductive. PHOTOASSIMILATES. Photoassimilates produced by leaves provide carbohydrates essential for development of roots and other plant organs, including fruit. They are either used immediately by the nearest sinks (Finazzo et al., 1994) or are stored in locations throughout the tree to be used when demand for carbon resources exceeds the existing photosynthetic supply (Whiley et al., 1988, 1989, 1991). A direct role for carbohydrates in shoot initiation or induction is not part of this model, although they facilitate mass flow in phloem from leaves to passively carry the FP to buds. ALTERNATE BEARING.

High levels of auxin and gibberellins produced in seeds possibly inhibit shoot initiation on fruit-bearing stems for weeks or months following fruit removal. Rapid production of new shoots following light pruning of fruit-bearing stems after harvest indicates that residual levels of auxin and gibberellins linger only in the rachis and last intercalary unit. If fruit are not set on the lingering rachis, there is less inhibition. Heavy fruit set in 1 year impacts the timing of subsequent shoot initiation on the large number of fruit-bearing branches. Substantial delays in subsequent vegetative

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flushes until close to the normal flowering period impact the flowering ability of young shoots. This may explain the occurrence of chronic alternate bearing in some cultivars.

5.10 Floral Management The Comprehensive Conceptual Flowering Model is consistent with growth and development patterns of mango trees in the tropics and subtropics. It provides a reasonable explanation for the various events in the phenological model of Cull, predicts what will happen under a defined set of circumstances and is being used to develop strategies for consistent mango flowering. Flowering can be obtained at any time of the year in a flowering management programme (Davenport, 2003). The flowering management programme begins each season with tip pruning of the entire canopy of orchard trees. Tip pruning can be done immediately after harvest to move production forward in the following year or c.1–2 months after harvest, depending upon cultivar, in order to achieve harvest at the same time as the previous year. If sufficient soil water is available at the time of pruning, a vegetative flush will occur on all pruned stems c.1 month later. The number of new shoots that will mature to become stems will be five- to eightfold greater than the original number of pre-pruned stems due to initiation of many lateral vegetative shoots on each stem. This increase in terminal stem number in the canopy will be reflected in a concomitant increase in yield. The frequent flushes that can cause an early second flush of vegetative growth tend to be suppressed. The new stems must not flush a second time until at least 5 months after pruning (Davenport, 2006). If they flush within 3–4 months after pruning, they will be induced to be vegetative. Pre-prune leaf N levels in the stems must be 1.1–1.4% in order to suppress a second flush of vegetative growth during the rainy season. Mild water stress after the post-prune flush during the dry season will suppress a second, undesired vegetative flush when leaf N levels are above the optimum range. Pruning near the end of the dry season in non-irrigated or furrow-irrigated trees should be avoided. Transition from dry to wet season 2–3 months after pruning causes a rain-stimulated vegetative flush prior to achieving sufficient age of stems from the last flush. Test sprays of 4% KNO3 on two to three representative trees should be applied 5 months (for easily induced cultivars) and 6 months (for more difficult to flower cultivars) after pruning. If no developing shoots occur within 2 weeks, the spray is repeated. A flowering response is usually evident after the second application. The other trees that were pruned on or near the same date can then receive the foliar spray and will respond by synchronized flowering. Although Davenport (2003) described the appropriate timing of PBZ in a flowering management programme, it is not recommended because flowering can be achieved without it. For orchard trees to be amenable to tip pruning, efficient spray application of KNO3 and easy harvesting, they should be no taller than 4 m. Pruning to rejuvenate large mango trees and

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properly shape trees for the annual flowering management programme is recommended (Davenport, 2006).

5.11 Floral Biology Detailed descriptions of generative shoots were reviewed in Davenport and Núñez-Elisea (1997). Juliano and Cuevas (1932) described ovary development.

Sex ratio Sex ratio (i.e. the proportion of perfect to staminate flowers) is a variable component within panicles, trees and among cultivars. This ratio varies with cultivar, but is usually < 50% (Davenport and Núñez-Elisea, 1997). Most perfect and staminate flowers are borne in the proximal portion of panicles due to their architecture (Musahib-ud-din and Dinsa, 1946; Cobin, 1950). The variability in the perfect/staminate flower ratio may be governed by physiological and environmental conditions. Most studies indicate that although the total number of flowers is substantially less in the distal half of panicles, there is a greater proportion of perfect flowers in this region (Davenport and Núñez-Elisea, 1997); however, this condition may be reversed in some cultivars (Hussein et al., 1989). Perfect flowers tend to form in the terminals of individual inflorescences while staminate flowers are displayed in the earlier forming flowers located closer to the panicle axis. When panicles begin to elongate in the lower inflorescences, only staminate flowers form and the perfect flowers form at the terminus of each lateral inflorescence. As more distally located lateral inflorescences begin elongation and anthesis, they too first display staminate flowers before perfect flowers. These inflorescences are progressively shorter than previously formed proximal inflorescences, and there are fewer staminate flowers. The final vertical spike of the panicle is composed almost exclusively of perfect flowers. Flowers abscise soon after anthesis, thereby shifting the sex ratio. The sex ratio should include sex type of all flowers in each panicle; however, sex ratios are normally determined at some arbitrary moment during panicle development. Thus, the sex ratio is naturally variable, increasing from extremely low to extremely high values so that timing of observations during panicle development is critical.

Environmental determinants of sex ratio Tropical cultivars yield poorly in the subtropics due to a small proportion of perfect flowers on inflorescences (Singh and Singh, 1959; Singh et al., 1965; Singh, 1971). Cool weather during inflorescence development contributes to fewer perfect flowers (Naik and Mohan Rao, 1943; Singh et al., 1965, 1966).

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Inflorescences that emerge during the middle and end of the flowering season produce two and seven times more perfect flowers, respectively, than the early breaking inflorescences (Majumder and Mukherjee, 1961; Singh et al., 1966). This response correlates with higher temperatures later in the flowering season. In controlled-environment studies, low temperatures (15°C day/10°C night) reduced the proportion of perfect flowers, particularly in tropical, polyembryonic cultivars relative to subtropical, monoembryonic cultivars (Sukhvibul et al., 1999).

Physiological determinants of sex ratio Endogenous factors affect the ratio of perfect to staminate flowers. Bajwa et al. (1956), Majumder and Mukherjee (1961) and Joubert et al. (1993) reported that lateral inflorescences on mixed shoots carried higher proportions of perfect flowers. Inflorescences on older trees produce higher proportions of perfect flowers than those on young trees (Naik and Mohan Rao, 1943; Majumder and Mukherjee, 1961; Chacko and Randhawa, 1971; Pandey, 1989). This also occurs in inflorescences borne on grafted compared with seedling trees (Musahib-ud-din and Dinsa, 1946). The effect of tree maturity or rootstocks on sex ratio of flowers is not understood. Panicles carried within the canopy of some cultivars (Majumder and Mukherjee, 1961; Singh et al., 1966) or on particular sides of the canopy (Mukherjee, 1953; Majumder and Mukherjee, 1961) have been reported to have higher proportions of perfect flowers. Application of some hormones and growth regulators alters the sex ratio of inflorescences. GA3, applied at concentrations of 50–100 mg/l just prior to inflorescence shoot initiation, substantially reduces the proportion of perfect flowers (Maiti, 1973), as do combination sprays of urea (0, 3 and 6%) and GA3 (0, 15 and 30 mg/l) (Rajput and Singh, 1989). Soil-applied PBZ (10 g ai/tree) significantly increases the ratio of perfect/staminate flowers (Kurian and Iyer, 1993a). Increases in floral ratio also occur with daminozide, whereas maleic hydrazide either had no effect or lowered the ratio (Singh et al., 1965; Subhadrabandu, 1986). Foliar application of 50 mg/l BA with 2% calcium ion (Ca2+) increased the proportion of perfect flowers (Singh and Rajput, 1990). Naphthalene acetic acid (NAA) at concentrations of 50, 100 and 200 mg/l increased the perfect/staminate flower ratio (Mallik et al., 1959; Singh et al., 1965). Other factors influencing sex ratios of inflorescences include stem age and mineral nutrients. Gunjate et al. (1983), Desai et al. (1986) and Hussein et al. (1989) reported that inflorescences from stems that grew at different times during the previous summer/autumn period had significantly different perfect/staminate flower ratios. Singh and Dhillon (1987) found that boron (B) levels affect sex ratio. Sex ratios can be manipulated with growth regulators, but has no commercial advantage (A.W. Whiley, personal communication, Queensland, 1996). Increases in fruit yield resulting from chemically increased perfect/ staminate flower ratios have not been observed, suggesting that perfect flower numbers are not the primary limitation to crop performance (Schaffer

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et al., 1994). If only one or two fruits were set on each terminal, the tree would carry an unusually heavy crop. It is unlikely that reduced perfect flower numbers due to cool temperatures during inflorescence development is directly responsible for poor fruit set and yields. Pollen viability, growth and ovule fertilization are probably the main factors contributing to low fruit set under these conditions.

Anthesis and dehiscence Floral anthesis generally occurs at night in polyembryonic cultivars (Wagle, 1929; Torres, 1931; Galang and Lazo, 1937; Pimentel et al., 1984) and at night or early morning in monoembryonic types (Popenoe, 1917; Musahib-ud-din and Dinsa, 1946; Singh, 1954a; Randhawa and Damodaran, 1961a, b). Subsequent dehiscence of the four-lobed anthers occurs during the daylight morning hours revealing pale blue pollen grains (Torres, 1931; Galang and Lazo, 1937; Mallik, 1957; L.B. Singh, 1960). Anthesis and anther dehiscence are delayed by low temperatures or overcast days (Singh, 1954a; De Wet and Robbertse, 1986a). Dehiscence is also delayed by high RH, and pollination occurs primarily around midday (Mallik, 1957; Randhawa and Damodaran, 1961a, b). Stigmas are receptive from c.18 h prior to anthesis to at least 72 h after anthesis with optimum receptivity within 3 h from anthesis (Popenoe, 1917; Wagle, 1929; Sen et al., 1946; Singh, 1954a; Spencer and Kennard, 1956; Randhawa and Damodaran, 1961a, b; Gunjate et al., 1983; Pimentel et al., 1984; Robbertse et al., 1994). Receptive stigmas are shiny and white-green, whereas non-receptive stigmas are desiccated and yellow-brown. Pollen germination generally occurs within 90 min of deposition, although the percentage germination of pollen deposited on stigmas is relatively poor (Singh, 1954a; S.N. Singh, 1961). Pollination is initiated by the formation of two unusual protuberances that meet to form a bridge or ponticulus connecting the dorsal side of the ovule with the ovary wall in line with the base of the style (Joel and Eisenstein, 1980). The ponticulus may guide the elongating pollen tube to the ovule. Ovule fertilization occurs 48–72 h after pollination (S.N. Singh, 1961; Ram et al., 1976). Both zygote cell and endosperm nuclear division appear to rest for about 2 weeks following pollination despite cell division and growth of the ovary (Sharma and Singh, 1972; Ram et al., 1976). A description of embryo development is presented by U.R. Singh (1961). Application of B may improve stigma receptivity, pollen tube germination and growth and ovule fertilization (De Wet and Robbertse, 1986b; Robbertse et al., 1988; De Wet et al., 1989) as well as fruit development (Chen, 1979; Robbertse et al., 1990); however, Jutamanee et al. (2002) could not verify the effect of B.

Pollen Pollen grains are 20–45 Pm long and are oblong when dry and more spherical when hydrated (Popenoe, 1917; Jivanna Rao, 1923; Bijhouwer, 1937;

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Mukherjee, 1950; Singh, 1954a; Randhawa and Damodaran, 1961b; S.N. Singh, 1961). There are generally three equilateral, tapering furrows along the longitudinal sides of dry pollen that give hydrated grains a roughly triangular shape when viewed on end (Popenoe, 1917; Singh, 1954a; S.N. Singh, 1961; U.R. Singh and A.P. Singh, 1973). Each furrow has a germpore in its centre (Mukherjee, 1950; S.N. Singh, 1961). Anthers produce c.250–650 pollen grains with a mean of 410 grains per anther (Popenoe, 1917, 1920; Spencer and Kennard, 1955). In vitro germination of mango pollen has been reported (Popenoe, 1917; Spencer and Kennard, 1955; Young, 1958; Randhawa and Damodaran, 1961b; S.N. Singh, 1961). Germination on stigmas was c.10% less than that on artificial media, that is 78% across cultivars (Spencer and Kennard, 1955), although lower rates of germination have been reported (Mukherjee, 1950). Mango pollen is most viable soon after anther dehiscence and rapidly degrades (Sen et al., 1946; Spencer and Kennard, 1955; Mallik, 1957; S.N. Singh, 1963). Although the initial percentage of viable pollen is generally ≥ 90% during warm weather (Popenoe, 1917; Mukherjee, 1949a, b; Singh, 1954a; S.N. Singh, 1961), cool temperatures early in the flowering season result in abnormal, non-viable pollen grains (Popenoe, 1917; U.R. Singh and A.P. Singh, 1973; Shu et al., 1989; Gazit et al., 1992; Issarakraisila et al., 1992). The pre-vacuolate stage of meiosis during microsporogenisis is the most sensitive period to temperatures < 10°C (Issarakraisila and Considine, 1994). Germination and pollen tube growth are reduced by cool temperatures (S.N. Singh, 1961; Mullins, 1986; Robbertse et al., 1988; Whiley et al., 1988; De Wet et al., 1989) and completely inhibited at temperatures < 15°C (Popenoe, 1917; Young, 1955; Sukhvibul et al., 2000).

Pollination Pollination is a major yield-limiting constraint, due to the large number of flowers on trees and low fruit set. Unlike polyembryonic cultivars, which produce nucellar embryos, pollination is necessary for fruit set with monoembryonic cultivars (Popenoe, 1917; Young, 1942; Spencer and Kennard, 1955; Gunjate et al., 1983; Pimentel et al., 1984; Robbertse et al., 1994). Pollen compatibility within and between cultivars has been widely investigated. Complete or partial self-incompatibility has been reported (Mukherjee et al., 1961; Singh et al., 1962b; Sharma and Singh, 1970, 1972; Ram et al., 1976; De Wet et al., 1989; Robbertse et al., 1993). Incompatibility is evident by degeneration of embryonic and nucellar tissues and excessive loss of fruitlets. Cross incompatibility between some cultivars has also been noted (Saha and Chhonkar, 1972; Ram et al., 1976; Robbertse et al., 1993). Wind Early investigators concluded that the species is wind pollinated (Hartless, 1914). Initially wet pollen dries to a powdery consistency on anthers soon after anthesis in dry conditions (Pimentel et al., 1984), whence it is likely to be liberated in moving air or via gravity to adjacent stigmas on the same and

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nearby flowers (Naik and Mohan Rao, 1943; Mallik, 1957). Singh (1954a) and S.N. Singh (1961) suggested, however, that the amount of pollen moving in air streams was too low for wind to be a pollination vector. They did not report the location of pollen-collecting slides or take into account the close proximity of flowers within inflorescences or numbers of open flowers in the canopy. Panicles bagged to exclude pollinating insects were reported to set fruit (Free and Williams, 1976), which were retained to maturity, thereby confirming that mango pollen can be transferred by air movement or gravity (Bijhouwer, 1937; Mallik 1957). The tacit assumption that open-pollinated flowers are exclusively crossed is likely to be incorrect, although mango may favour cross-pollination. Insect Popenoe (1917) reasoned that pollen transfer occurs primarily within flowers by insects. Panicles bagged to exclude insect visitation generally result in less fruit set than on panicles in the open (Popenoe, 1917; Musahib-ud-din and Dinsa, 1946; Mallik, 1957; Free and Williams, 1976; Jiron and Hedstrom, 1985). Insects working mango flowers include Diptera, Hymenoptera, Lepidoptera and Coleoptera (Popenoe, 1917; Simao and Maranhao, 1959; Randhawa and Damodaran, 1961b; McGregor, 1974; Anderson et al., 1982; Jiron and Hedstrom, 1985). Flies of various genera are common on mango flowers (Popenoe, 1917; Burns and Prayag, 1921; Bijhouwer, 1937; Singh, 1954a; Spencer and Kennard, 1955; Eardley and Mansell, 1993). Polistes wasps are observed on mango flowers but are considered to be ineffectual for pollen transfer (Spencer and Kennard, 1955; Free and Williams, 1976; Wolfenbarger, 1977). Honeybees (Hymenoptera) are occasional visitors (Young, 1942; Simao and Maranhao, 1959; Smith, 1960; Morton, 1964; Jiron and Hedstrom, 1985; MacMillan, 1991; Du Toit and Swart, 1993, 1994; Eardley and Mansell, 1993, 1994), but only if other more inviting flowers are not present (Spencer and Kennard, 1955; Free and Williams, 1976; McGregor, 1976). They are assumed to be the most effective pollinators of mango and may be more effective if hives are placed in orchards during flowering (Du Toit and Swart, 1993, 1994). Anderson et al. (1982) recorded actual pollen transfer on mango flowers by insects and found, in order of importance, the most efficient pollinators to be wasps, bees, large ants and large flies. With few exceptions (Mallik, 1957), pollen deposition rates are generally low (Naik and Mohan Rao, 1943; Mukherjee, 1951). Differences in pollination rates can be attributed to environmental conditions during flowering, differing attraction of insects to specific cultivars, proximity of more attractive flowering species or a combination of the above. Young (1942) observed that insects visit only 10–12% of available flowers. Depending on weather conditions, insect activity on mango flowers is usually continuous from early morning to late afternoon, but nocturnal activity of some species has also been reported (Jiron and Hedstrom, 1985). The role of insects in cross-pollination is not understood. Anderson et al. (1982) observed various insects carrying pollen to and from flowers and noted pollination subsequent to those visits; however, they made no distinction

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between actual pollen depositions by visiting insects and pollen transferred by other means. Wester (1920) considered that pollination is facilitated by wind and to a lesser extent by insects, and this conclusion is probably correct in most environments. Self-pollination within flowers by insects while the pollen is still damp is likely to occur. Use of isozyme (Degani et al., 1990; Robbertse et al., 1993) and microsatellite DNA markers (Adato et al., 1995; Schnell et al., 2005) to discern ratios of cross- versus self-pollinated fruitlets and offspring is the most accurate procedure to confirm self- and cross-pollination. Initial fruit set of pollinated flowers is inconsequential since most of these fruitlets abscise before reaching maturity (Lynch and Mustard, 1950; Singh, 1954a; Randhawa and Demodaran, 1961a).

5.12 Fruit Development Fruit growth is correlated with several growth regulating substances. Enlargement is sigmoidal reaching a constant size c.2–3 weeks before maturity (Singh, 1954a; Randhawa and Damodaran, 1961a, b; Ram, 1983; Prakash and Ram, 1984). The highest rates of fruit growth have been correlated with peak levels of putative endogenous auxins found in seeds (Chacko et al., 1970a, b; Singh and Singh, 1974; Chen, 1981; Ram, 1983; Prakash and Ram, 1984). Baghel et al. (1987a, b) reported increased fruit mass with a combination spray of NAA and urea to pre-anthesis panicles. Free and bound gibberellins, especially in seeds (Ogawa, 1963; Ram, 1983), peak similarly to putative auxins during fruit development (Chacko et al., 1970c, 1972a; Ram and Pal, 1979; Chen, 1981). Cytokinins tentatively identified as zeatin and zeatin riboside and other active fractions appear to vary in concentration in seeds and pericarp with two distinct peaks of activity. No particular relationship to growth was evident (Ram, 1983; Ram et al., 1983). Seeds produced more cytokinin activity than did the pericarp. In contrast, Chen (1983) found only one peak of cytokinin activity in seeds and pulp occurring at about half full size of both seed and pericarp. Seed tissues contain the highest cytokinin activity. Levels of endogenous auxin, gibberellins and cytokinins in leaves during fruit set were compared to production in leaves during other periods without conclusive results (Paulas and Shanmugavelu, 1989).

5.13 Stenospermocarpy Abscission of non-fertilized and fertilized flowers is normal. Fruitlet abscission from pea size on is often associated with embryo abortion (Chandler, 1958; U.R. Singh, 1961; Singh, 1964; Lakshminarayana and Aguilar, 1975; Ram et al., 1976) and is referred to as stenospermocarpy (Soule, 1985). Stenospermocarpy in mango is unusual (Chacko and Singh, 1969a) but occurs regularly in some cultivars (Núñez-Elisea and Davenport, 1983; Whiley et al., 1988). Stenospermocarpic fruitlets have slower growth rates than seeded fruit, generally become misshapen and fail to reach full size.

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Stenospermocarpy in some cultivars has been correlated with low temperatures during flowering and early fruit set in the subtropics (Lakshminarayana and Aguilar, 1975; Young and Sauls, 1979; Whiley et al., 1988; Schaffer et al., 1994). Núñez-Elisea and Davenport (1983) reported that stenospermocarpic fruit often occur distal to seeded fruitlets within panicles and suggested that embryo abortion is associated with high temperatures when these latter fruit set. Secondary spring flowering of some monoembryonic cultivars under high temperatures has resulted in high proportions of stenospermocarpic fruit (E.K. Chacko, personal communication, Australia, 1995). Application of auxins, gibberellins and cytokinins produce seedless fruit in some cultivars, suggesting that the abscission zone is protected by these hormones despite the loss of the endogenous supply from the aborted seed (Venkataratnam, 1949; Chacko and Singh, 1969a, b; Kulkarni and Rameshwar, 1978).

5.14 Fruit Set and Retention Fruit set and retention of mango was recently reviewed by Singh et al. (2005). Abscission of flowers and fruitlets is accomplished by rapid formation of a separation layer in the abscission zone in the pedicel-peduncle junction (Barnell, 1939). U.R. Singh (1961) described formation of the abscission zone during floral ontogeny and of the separation layer during abscission of flowers and fruitlets. The majority of panicles lose all fruitlets (Núñez-Elisea and Davenport, 1983). The pattern of fruitlet abscission is asymptotic with the greatest losses occurring during the first weeks after anthesis (Núñez-Elisea and Davenport, 1983; Prakash and Ram, 1984; Searle et al., 1995). Except for the tendency to retain fruit in the distal portion of panicles, abscission of flowers and fruitlets is random. It can involve fruitlets regardless of size or location. Of the 8–13% of perfect flowers setting fruit, < 1% reach maturity (Bijhouwer, 1937; Sen, 1939; Naik and Mohan Rao, 1943; Mukherjee, 1949b; U.R. Singh, 1960; Randhawa and Damodaran, 1961a; Singh, 1978; Gunjate et al., 1983; Prakash and Ram, 1984). Generally, most fruit are set on the most distal spike portion of panicles (Chadha and Singh, 1963; Núñez-Elisea and Davenport, 1983). Fruit loss has been associated with embryo abortion, resulting in blackened or shrivelled embryos (Singh, 1954a, 1964; Chandler, 1958; U.R. Singh, 1961; Sharma and Singh, 1972; Ram et al., 1976) after the fruit is separated from the tree (Núñez-Elisea and Davenport, 1983).

Sex ratio The perfect/staminate floral ratio in panicles may influence fruit set and productivity (Naik and Mohan Rao, 1943; Singh, 1954b; Singh and Singh, 1959; U.R. Singh, 1960). Mallik (1957) noted that more perfect flowers are formed in ‘on’ than ‘off’ years of alternate-bearing cultivars. Other studies, however,

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have demonstrated that the number of perfect flowers does not correlate with subsequent yield (Randhawa and Damodaran, 1961a) so long as the proportion of perfect flowers is not < 4% (Singh, 1964, 1971). Most fruit are borne in the distal portion of panicles (Shawky et al., 1977), which may be correlated with the high ratio of perfect to staminate flowers there. Scholefield and Oag (1984) estimated that one mature fruit is harvested for each 169 perfect flowers in the distal half of the panicle; whereas 592 perfect flowers are required to produce one fruit in the proximal half. Therefore, intrinsic factors other than sex ratio regulate fruit set.

Mineral nutrients Boron is one of seven micronutrients required for normal plant growth. The physiological function of B is unknown (Hu and Brown, 1994), although it is essential for floral development, pollen germination, pollen tube growth, embryo development and growth of organs (i.e. fruit) (Vasil, 1963; Agarwala et al., 1981; Dell and Huang, 1997; Shorrocks, 1997). Deficient soils are commonly found in mango-producing areas of Australia, Thailand, Central and South America and Africa where symptoms are common (Aitken et al., 1987; Singh et al., 2005). Boron applications to deficient mango trees increase normal fruit set (Robbertse et al., 1990; Raja et al., 2005). Fruitlet abscission in mangoes has also been attributed to zinc (Zn) deficiency (Jiron and Hedstrom, 1985).

Hormonal control Auxin Research demonstrating improved fruit set and retention following application of several auxin analogues to pre-anthesis panicles or to panicles bearing fruitlets of various sizes has been reviewed (Davenport and Núñez-Elisea, 1997; Singh et al., 2005). NAA is the most effective auxin analogue for improving fruit retention (Prakash and Ram, 1986; Khan et al., 1993). Initial fruit set was substantially increased when sprays of 200 mg/l indole acetic acid (IAA) were applied to developing panicles (Singh et al., 1965). A 300–400% increase in fruit set resulted when NAA (40 or 50 mg/l) was sprayed at the pre-anthesis stage (Ram, 1983; Singh and Ram, 1983; Prakash and Ram, 1986). Chen (1981) reported no effect on fruit retention when 5 mg/l of either naphthaleneacetamide or β-naphthoxoyacetic acid were applied three times at 2-week intervals to panicles in which fruit had reached 4 mm in diameter. Despite increased fruit retention of mango using exogenous applications of auxins, few studies have examined endogenous auxins in fruit as related to retention (Chacko et al., 1970a, b; Ram et al., 1983; Prakash and Ram, 1984). Singh and Singh (1974) were unable to detect significant differences in endogenous auxins or inhibitors when comparing alternate and regular bearing cultivars. Chen (1981) observed lower levels of auxin-like substances in

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mesocarp and calyx tissues of abscised fruits than those of intact fruits. Similar decreases in auxin and gibberellins with an increase in abscisic acid as fruitlets abscised were reported by Bains et al. (1999). The interaction of auxin in fruit and abscission zones to maintain mango fruit retention is not clear. Continuous auxin synthesis and basipetal transport to the abscission zone is critical for maintenance of plant organs, including fruit (Crane, 1964; Nitsch, 1965; Morgan et al., 1977; Davenport et al., 1980; Roberts and Osborne, 1981). Increased mango fruit set and retention in response to exogenously applied auxins confirms this requirement; however, other hormonal factors also appear to be involved. Developing seeds are rich sources of all the known classes of phytohormones, including auxins (Crane, 1964; Nitsch, 1965; Chacko et al., 1970a, b, c; Chen, 1981). Hence, exogenous enrichment of auxin in the presence of other seed-produced phytohormones facilitates increased fruit retention. In contrast, NAA (10 and 20 mg/l) spray-applied to bagged, selfpollinated flowers, does not result in development of stenospermocarpic fruits beyond the marble size (Venkataratnam, 1949; Chacko and Singh, 1969a, b). Similarly, applications of 250 or 500 mg/l GA3 or 250 mg/l BA alone to panicles does not promote production of stenospermocarpic fruits (Chacko and Singh, 1969a, b). Supplying exogenous β-naphthoxyacetic acid (10 mg/l), BA (250 mg/l) and GA3 (250 and 500 mg/l) together in multiple sprays until half grown, however, resulted in retention of several seedless fruit to maturity. Chen (1983) and Oosthuyse (1995b) observed that gibberellin, cytokinin and auxin reduce fruit drop of open-pollinated fruitlets of some cultivars. Thus, although auxin is important for maintaining the abscission zone, the presence of other phytohormones appears to be important for fruitlet development (Chacko et al., 1970a, b; Ram, 1983; Ram et al., 1983). Cytokinins Although cytokinins are not generally thought to be associated directly with abscission, Ram (1983) and Ram et al. (1983) concluded that low cytokinin levels during fruit development might contribute to fruit loss. Chen (1983) observed a correlation of low cytokinin levels in stenospermocarpic fruits with abscission at the marble stage of growth. Application of 250 mg/l BA to bagged panicles does not promote production of seedless fruits (Chacko and Singh, 1969a, b). The synthetic cytokinin, N-(2-chloro-4-pyridyl)-N’-phenylurea (CPPU) also does not improve fruit set when applied alone at a rate of 10 mg/l to post-anthesis panicles (Oosthuyse, 1995b). The role of cytokinins in separation events remains inconclusive. Gibberellins Gibberellins do not appear to be directly linked to the onset of abscission (Chacko et al., 1970c, 1972a; Ram and Pal, 1979; Chen, 1981; Ram, 1983). Spray applications of GA3 to pre- and post-anthesis panicles to increase fruit set and retention have been inconsistent. Increased yield (Teaotia et al., 1967; Singh and Ram, 1983; Rajput and Singh, 1989) and production of seedless fruit (Kulkarni and Rameshwar, 1978) have been reported from these treatments, but Chacko and Singh (1969a, b) observed no such effects. Chen (1983) and

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Oosthuyse (1995b) investigated the effects of several foliar applications of GA3 starting at the 4 mm diameter stage, but were unable to improve fruit set. Several classes of gibberellin-synthesis inhibitors have been tested for reducing fruit drop. The growth retardants, daminozide and cycocel, increased fruit set when applied to post-anthesis panicles (Singh and Ram, 1983). The authors suggested that increased fruit retention might have been mediated through increased cytokinin-like activity of the growth retardants. Although initial fruit set was promoted by PBZ, yield was not improved (Kurian and Iyer, 1993a). It is not clear whether the contrasting results of increased yield (Kurian and Iyer, 1993b) were due to reduced fruit loss or more intense flowering in response to treatment. Goguey (1990) reported increased fruit set and retention using soil-applied PBZ at 5 g ai/tree. Spray application of uniconazole, a more biologically active triazole (500–2000 mg/l), reportedly increased fruit set and yield (Galila and El-Masry, 1991). It is difficult to resolve the contradictory results demonstrating enhancement of fruit retention by GA3 and inhibitors of its synthesis. Inhibitors Abscisic acid (ABA) is possibly involved in fruitlet abscission. Although correlations exist between certain inhibitors and abscission of mango fruitlets, no clear cause and effect relationships have been established. Fruit drop was correlated with levels of an acidic inhibitor, possibly ABA (Chacko et al., 1970b, 1972a; Singh and Singh, 1974; Ram, 1983; Prakash and Ram, 1984). Chen (1981) reported similar changes in putative ABA with maximum levels occurring during early fruit drop and with advancing age of fruits. Putative ABA levels in abscised and retained fruits were compared and were highest in the calyx and mesocarp of abscised fruitlets. Ethylene Ethylene has the greatest immediate impact on flower and fruitlet abscission. Van Lelyveld and Nel (1982) reported higher levels of ethylene in abscised fruitlets compared with those retained on trees. Núñez-Elisea and Davenport (1983, 1984, 1986) examined the dynamics of ethylene production in intact and excised fruitlets from onset to separation. Increased production began in explants about 26 h postharvest and increased logarithmically until fruit separation. Abscission of the fruitlets began 48 h after the onset of enhanced ethylene production. Similar results with avocado fruitlet abscission experiments (Davenport and Manners, 1982) indicate that the onset of ethylene production in intact fruitlets is spontaneous in individual fruitlets followed by abscission 48 h later. The pericarp provided the bulk of ethylene for induction of abscission processes; the pedicel produced no ethylene. There was reduced fruit drop in response to inhibitors of ethylene production and action (Singh and Ram, 1983; Naqvi et al., 1990, 1992). Whereas increased peroxidase (Van Lelyveld, 1978) and polyphenol oxidase activities have been reported in abscissed mango fruitlets (Van Lelyveld and Nel, 1982), NúñezElisea and Davenport (1984) observed no changes in peroxidase activity or protein levels prior to separation of fruitlets.

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Abscission of stenospermocarpic fruits has been associated with small increments in ethylene production (Núñez-Elisea and Davenport, 1983). Sensitivity to low levels of endogenous ethylene may reflect the absence of seedproduced auxins. Protection of the abscission zone depends on a constant supply of auxin, and ethylene production levels in tissues correlate with endogenous auxin levels (Roberts and Osborne, 1981). Despite their roles in cell division, cell enlargement and maintenance of the abscission zone in developing fruit, a specific recommendation for exogenous application of plant growth regulators, either alone or in combination, to improve yield of mango has not been adopted. Phytohormones have little residual effect on fruit development, and multiple applications of products to counteract the short-term responses are prohibitively expensive. Photoassimilates Wolstenholme and Whiley (1995) discussed the ecophysiology of the mango as a basis for preharvest management. They proposed that the adaptive survival strategies of the mango explain its notoriously poor cropping performance. Mechanisms that impart tolerance to heat, drought and flood stresses, which the tree has developed for survival in harsh environments, have come at considerable carbon cost with the resultant diversion of photoassimilate resources away from fruiting. There is abundant evidence that heavy cropping in tree crops exhausts stored reserves (Jones et al., 1975; Kaiser and Wolstenholme, 1994; Whiley et al., 1996) and that current photosynthate is often unable to satisfy the demands of fruit set and fruit growth after heavy and prolonged flowering (Chacko et al., 1982). There are significant genotypic differences in photoassimilation rates between low- and high-yielding cultivars growing in both the tropics and the subtropics of Australia (Chacko et al., 1995; Searle et al., 1995). At each location, photoassimilation rates were considerably greater on the higheryielding cultivar, and this difference was maintained from flowering through to fruit maturation. 14C studies during the fruit set and abscission period also demonstrated strong discrimination in the movement of assimilates, which was dominated by randomly located fruit on panicles of the low-yielding cultivar (Chacko et al., 1995). In contrast, assimilate discrimination to fruitlets was less severe in the high-yielding cultivar with a more even distribution of photoassimilates. It was concluded that the availability and distribution of photoassimilates during the fruit set and establishment stages was largely responsible for the yield differences between the cultivars. Supporting evidence for the role of photoassimilates in fruit set and retention also comes from enrichment studies (Schaffer et al., 1999). Containergrown plants that flowered in the open were transferred to controlledenvironment glasshouse rooms immediately after the completion of anthesis. Temperatures were 28°C day/20°C night while the atmospheric carbon dioxide (CO2) concentrations were 350 or 600 Pmol/mol. Photoassimilation of trees in the CO2-enriched rooms was approximately 60% greater than those held at partial pressures of 350 Pmol/mol CO2. Fruit retention and final yield were significantly higher on those trees grown at the partial pressure of

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600 μmol/mol CO2. Higher levels of available assimilates during the fruiting cycle appear to benefit fruit retention and yield.

5.15 Alternate Bearing Alternate bearing of certain mango cultivars has plagued growers (Hartless, 1914; Rao, 1997). Lack of production in the ‘off’ year is usually a result of lack of floral initiation (R.N. Singh, 1959), and has been reviewed (Mukherjee, 1953; Gangolly et al., 1957; L.B. Singh, 1960, 1972; Chadha and Pal, 1986; Pandey, 1989). Shoot initiation and induction described in this chapter perhaps offers a clearer understanding of this phenomenon.

5.16 Conclusions This chapter has provided a comprehensive review of investigations of various factors potentially involved in mango flowering, fruit set and retention. Many of the reports cited are contradictory. Such variable results reflect: (i) the different experimental approaches utilized, especially in field experiments; (ii) the range of environments in which experiments have been conducted; and (iii) differences in the responses of cultivars to treatments. As a consequence, it is difficult to draw unambiguous conclusions with respect to the role of specific factors on flowering, fruit set and retention. More research is clearly needed in these areas, particularly in controlled environments. For example, although KNO3 is utilized with great success to stimulate flowering in tropical conditions, confusion remains as to whether it effects initiation or floral induction. Future studies on flowering research should include results of the proportion of stems that remain in rest and those that produce vegetative shoots as well as the proportion of reproductive shoots. Providing this information allows an analysis of the impact of treatments on initiation and inductive events. This chapter also presents several hypothetical models for shoot development and flowering. Each of the proposed models consists of a series of hypotheses that invite further study to test their validity. Future research should challenge these models so that flowering and crop yield can be better understood in both the tropics and the subtropics.

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T.L. Davenport Sitton, D., Itai, C. and Kende, K. (1967) Decreased cytokinin production in the roots as a factor in shoot senescence. Planta 73, 296–300. Sivagami, S., Vijayan, K.P. and Natarajaratnam, N. (1989) Effect of nutrients and growth regulating chemicals on biochemical aspects and hormonal balance with reference to apical dominance in mango. Acta Horticulturae 231, 476–482. Skoog, F. and Miller, C.O. (1957) Chemical regulation of growth and organ formation in plant tissues cultured in vitro. Symposium of the Society of Experimental Biology 54, 118–130. Smith, F.C. (1960) Beekeeping in the Tropics. Longmans, London, 265 pp. Soule, J. (1985) Glossary for Horticultural Crops. Wiley, New York, 898 pp. Soule, M.J. (1950) A Bibliography of the Mango (Mangifera indica L.). Florida Mango Forum and University of Miami, Coral Gables, Florida, 89 pp. Spencer, J.L. and Kennard, W.C. (1955) Studies on mango (Mangifera indica L.) fruit set in Puerto Rico. Tropical Agriculture 32, 323–330. Spencer, J.L. and Kennard, W.C. (1956) Limited stigmatic receptivity may contribute to low fruit-set in the mango. Proceedings of the American Society for Horticultural Science 67, 287–289. Sturrock, T.T. (1966) The mango inflorescence. Proceedings of the Horticultural Society 53, 366–369. Subhadrabandu, S. (1986) Studies of plant growth regulator effects on tropical and subtropical tree fruits of Thailand. Acta Horticulturae 175, 291–297. Sukhvibul, N., Whiley, A.W., Smith, M.K., Hetherington, S.E. and Vithanage, V. (1999) Effect of temperature on inflorescence development and sex expression of monoand poly-embryonic mango (Mangifera indica L.) cultivars. Journal of Horticultural Science and Biotechnology 74, 64–68. Sukhvibul, N., Hetherington, S.E., Whiley, A.W., Smith, M.K. and Vithanage, V. (2000) Effect of temperature on pollen germination, pollen tube growth and seed development in mango (Mangifera indica L.). Acta Horticulturae 509, 609–616. Suryanarayana, V. (1978a) Amino acid changes in mango shoots in relation to flowering. Plant Biochemistry Journal 5, 50–57. Suryanarayana, V. (1978b) Seasonal changes in ribonucleic acid and protein contents in mango shoots in relation to flowering. Plant Biochemistry 5, 9–13. Suryanarayana, V. (1978c) Seasonal changes in sugars, starch, nitrogen and carbonnitrogen ratio in relation to flowering in mango. Plant Biochemistry Journal 5, 108– 117. Suryanarayana, V. (1980) Amino acid changes in mango shoots as affected by growth retardants in relation to flowering. Plant Biochemistry Journal 7, 78–82. Suryanarayana, V. and Rao, V.N.M. (1977) Ascorbic acid changes in shoots of mango cv. Mulgoa as affected by growth retardants in relation to flowering. Indian Journal of Plant Physiology 20, 88–90. Takahashi, N. (ed.) (1986) Chemistry of Plant Hormones. CRC Press, Boca Raton, Florida, 277 pp. Tamaki, S., Matsuo, S., Wong, H.L., Yokoi, S. and Shimamoto, K. (2007) Hd3a protein is a mobile flowering signal in rice. Science 316, 1033–1036. Tanaka, M., Takei, K., Kojima, M., Sakakibara, H. and Mori, H. (2006) Auxin controls local cytokinin biosynthesis in the nodal stem in apical dominance. The Plant Journal 45, 1028–1036. Teaotia, S.S., Singh, R.N., Upadhyay, S.K. and Srivastava, V.S. (1967) Effect of growth substances on fruit retention in mango (Mangifera indica L.) varieties ‘Langra’ and ‘Dashehari’. International Symposium on Sub-tropical and Tropical Horticulture. New Delhi, pp. 224–229.

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Thuck-Thye, L. (1978) Ethylene and the induction of flowering by potassium nitrate in mango (Mangifera indica L.). MSc thesis, University of the Philippines, Los Banos, the Philippines. Tomer, E. (1984) Inhibition of flowering in mango by gibberellic acid. Scientia Horticulturae 24, 299–303. Tomlinson, P.B. and Gill, A.M. (1973) Growth habits of tropical trees: some guiding principles. In: Meggers, B.J., Ayensu, E.S. and Duckworth, W.D. (eds) Tropical Forest Ecosystems in Africa and South America: a Comparative Review. Smithsonian Institution, Washington, DC, pp. 124–143. Tongumpai, P., Hongsbhanich, N. and Voon, C.H. (1989) ‘Cultar’ – for flowering regulation of mango in Thailand. Acta Horticulturae 239, 375–378. Tongumpai, P., Jutamanee, K. and Subhadrabandhu, S. (1991a) Effect of paclobutrazol on flowering of mango cv. Khiew Sawoey. Acta Horticulturae 291, 67–70. Tongumpai, P., Jutamanee, K., Sethapakdi, R. and Subhandrabandu, S. (1991b) Variation in level of gibberellin-like substances during vegetative growth and flowering of mango cv. Khiew Sawoey. Acta Horticulturae 291, 105–107. Torres, J.P. (1931) Some notes on Carabao mango flowers. Philippine Journal of Agriculture 2, 395–398. Turnbull, G.C.N., Anderson, K.L. and Winston, E.C. (1996) Influence of gibberellin treatment on flowering and fruiting patterns in mango. Australian Journal of Experimental Agriculture 36, 603–611. van der Meulen, J.H.E., Smith, T., van den Boom, I.B., Kok, A., Schwartz, C. and Jacobs, J. (1971) Mango Growing in South Africa. Leaflet No. 48. Citrus and Subtropical Fruit Research Institute, Nelspruit, South Africa, 40 pp. Van Lelyveld, L.J. (1978) Peroxidase activity and isozymes in abscised and normal mango (Mangifera indica L.) fruits. Zeitschrift für Pflanzenphysiologie 89, 453–456. Van Lelyveld, L.J. and Nel, E. (1982) Ethylene concentration and polyphenol oxidase activity in mango (Mangifera indica L.) fruit abscission. Zeitschrift für Pflanzenphysiologie 107, 179–182. Vasil, I.K. (1963) Effect of boron on pollen germination and pollen tube growth. In: Linskens, H.F. (ed.) Pollen Physiology and Fertilization. North Holland, Amsterdam, pp. 107–119. Veen, H. (1969) Auxin transport, auxin metabolism and ageing. Acta Botanica Neerlandica 18, 447–453. Veen, H. and Jacobs, W.P. (1969) Transport and metabolism of indole-3-acetic acid in coleus petiole segments of increasing age. Plant Physiology 44, 1157–1162. Venkataratnam, L. (1949) Hormone induced set and parthenocarpy in mango. Current Science 18, 409. Verheij, E.W.M. (1986) Towards a classification of tropical tree fruits. Acta Horticulturae 175, 137–150. Vijayalakshmi, D. and Srinivasan, P.S. (1999) Morpho-physiological changes as influenced by chemicals and growth regulators in alternate bearing mango cv. Alphonso. Madras Agricicultural Journal 86, 485–487. Voon, C.H., Pitakpaivan, C. and Tan, S.J. (1991) Mango cropping manipulation with Cultar. Acta Horticulturae 291, 219–228. Wagle, P.V. (1929) A preliminary study of the pollination of the Alphonso mango. Agriculture Journal of India 24, 259–263. Weberling, F. (1989) Morphology of Flowers and Inflorescences. Cambridge University Press, Cambridge, UK. Weigel, D., Alvarez, J., Smyth, D.R., Yanofsky, M.F. and Meyerowitz, E.M. (1992) LEAFY controls floral meristem identity in Arabidopsis. Cell 69, 843–859.

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6

Ecophysiology

B. Schaffer,1 L. Urban,2 P. Lu3 and A.W. Whiley4 1University

of Florida, Florida, USA INRA de Corse, San Giuliano, France 3EWL Sciences, PO Box 39443, Winnellie, Northern Territory, Australia 4Sunshine Coast Horticultural Services Pty Ltd, Nambour, Queensland, Australia 2Centre

6.1 Introduction 6.2 Photosynthesis Introduction Light Leaf temperature Elevated atmospheric CO2 concentration Humidity Flooding Internal factors Photosynthetic contributions by fruit 6.3 Plant Water Relations 6.4 Tree Growth and Development Light Temperature Drought Flooding Wind Salinity Elevated atmospheric CO2 concentration 6.5 Crop Production Temperature limitations to crop production Light interception and orchard design 6.6 Conclusions

170 172 172 177 179 181 182 182 184 187 188 190 190 192 193 194 195 196 197 198 198 199 200

6.1 Introduction The genetic composition of mango cultivars is the primary determinant of yield potential. However, actual yield, as well as tree growth and development, are mediated by several endogenous factors including previous fruit load, postharvest vegetative growth, preflowering maturity of terminal shoots, 170

© CAB International 2009. The Mango, 2nd Edition: Botany, Production and Uses (ed. R.E. Litz)

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production and mobilization of carbohydrates, nutritional status, plant growth substances and carbon to nitrogen ratios (Schaffer et al., 1994). These factors are either directly or indirectly affected by environmental variables such as light, temperature and water availability. Environmental conditions outside the range for optimum growth may also impose stress which results in physiological changes that reduce growth or cause permanent damage to mango trees. For example, major climatic events (i.e. extended drought, floods, wind storms, heat waves and freezes) can cause severe damage to crops due to development of excessive stress. However, mediated stress and the release from stress imposed by normal seasonal changes provide conditions that result in the progression of cropping cycles due to phenological changes in the plants. An example of beneficial stress in mango is the improved synchrony and reliability of flowering in subtropical climates due to cool winter temperatures. Thus, understanding the impact of the environment on tree physiology and growth, and the particular adaptive strategies developed through the processes of evolution, can provide a framework to manage the crop to maximize genetic yield potential (Schaffer et al., 1994). Physiological responses of mango to environmental variables can be related to the evolutionary centre of origin of a specific cultivar. Mango cultivars are classified into two ecotypes based on embryony (see Mukherjee and Litz, Chapter 1, this volume). A race with a single zygotic seed, monoembryonic types, evolved in the dry subtropical, monsoonal regions of the Indian subcontinent with very hot summers but cooler winters. The polyembryonic types, produced through nucellar embryony, largely evolved in the consistently hot, humid tropics of South-east Asia where the monsoonal pattern still predominates but the dry season is shorter than that of the Indian subcontinent (Mukherjee, 1972). Hybridization occurs freely within and between the two ecotypes and has led to a proliferation of cultivars of widely varying genetic composition. Differences in growth and flowering responses to temperature have been observed between the two embryonic ecotypes (Whiley et al., 1989) and selection and breeding offer potential for increasing the cropping performance of this notoriously low-yielding and recalcitrant tree across a wider range of environmental conditions (Schaffer et al., 1994). Inevitably, the many unique features of the mango tree represent its evolutionary response to an indigenous environment that is particularly hostile, with sustained extreme heat and high evaporative demand for much of the year. This chapter provides an overview of the impact of environmental factors on physiology, growth and productivity of mango. Plant responses will be considered in the context of the evolutionary origin and adaptability of the mango tree. Responses to light, temperature and water are emphasized, while the effects of atmospheric carbon dioxide (CO2) concentration, wind and salinity are also discussed. Photosynthesis and plant water relations are closely associated with environmental conditions and directly affect plant growth and productivity. The principles of leaf gas exchange and plant water relations are discussed to provide a theoretical basis for interpreting physiological responses to the environment. The impact of photosynthesis and tree water relations on

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growth and development under different environmental conditions is discussed. Pollination, fertilization, flowering and fruit set, which are strongly influenced by environmental factors, have been addressed elsewhere (see Davenport, Chapter 5, this volume; Schaffer et al., 1994). In the final section of this chapter, mango crop production is integrated with aspects of ecophysiology.

6.2 Photosynthesis Introduction The net CO2 assimilation rate (Anet) in C3 plants is a function of the carboxylation rate (Vc), the oxygenation rate (Vo) and the rate of CO2 evolution in light that results from processes other than photorespiration, sometimes called ‘day respiration’ (Rd): Anet = Vc – 0.5Vo – Rd

(6.1)

Rd is usually inferred from measurements of leaf CO2 exchanges after 5 min in the dark (i.e. ‘night respiration’ Rn). However, it has been repeatedly shown that Rd is lower than Rn (see Atkin et al. (2000) for review), so that light is known to inhibit respiration, with a Rd/Rn value ranging from 30 to 100% (see Peisker and Apel (2001) for review). Urban et al. (2008) established the following linear regression for Rd of mango leaves: Rd = 0.35Rn – 0.21, which may be used to infer Rd from Rn for photosynthetic photon flux (Q) values above 170 Pmol photons/m2/s. Currently, modelling of Anet often uses the Harley et al. (1992) version of the Farquhar et al. (1980) model. According to this model, Anet can be expressed as: Anet = (1 – 0.5O/(WCi))min(Wc, Wj, Wp) – Rd

(6.2)

where O represents the partial pressure of oxygen (O2) in the intercellular air spaces (Pa), W the specificity factor of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco). Ci is the partial pressure of CO2 in the intercellular air spaces (Pa), Wc the carboxylation rate limited by the amount, activation state or kinetic properties of Rubisco (Pmol CO2/m2/s), Wj the carboxylation rate limited by the rate of ribulose bisphosphate regeneration (Pmol CO2/m2/s), and Wp the carboxylation rate limited by triose phosphate utilization in sucrose and starch synthesis (Pmol CO2/m2/s). Usually O is set as 21 kPa (21%). The variable W, which characterizes the ratio of the affinities of CO2 and O2 for ribulose-1,5-bisphosphate in the active site of Rubisco, can be calculated from the CO2 compensation point ** (the CO2 concentration at which photosynthesis equilibrates with respiration): W = 0.5O/* *

(6.3)

where W = 2220 mol CO2/mol O2 at 25°C for ‘Cogshall’ mango leaves (Urban et al., 2008), which is lower than those given by Epron et al. (1995): 2100–2900

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mol CO2/mol O2. Rubisco’s large subunit is encoded by a single gene in the chloroplast genome, and no post-transcriptional modifications have been discovered so far. It is thus very unlikely that W can change in the short term (Spreitzer and Salvucci, 2002). The internal partial pressure of CO2 (Ci) is one of the two major variables of photosynthesis (with the photosynthetically active photon flux density). It may be calculated from the supply function: Ci = Ca – Anet/gb – Anet/gs

(6.4)

where Ca is the partial pressure of CO2 (Pa) in ambient air, gb represents the leaf boundary layer conductance (mol H2O/m2/s), and gs is the stomatal conductance of water (H2O) (mol H2O/m2/s). Stomatal conductance is the major factor controlling Anet. It ranges from c.0.02 to c.0.4 mol H2O/m2/s in ‘Cogshall’ mango leaves and may be linearly related to Anet (Urban et al., 2002, 2003, 2006). The slope of the relationship between gs and Anet however is affected by drought (Fig. 6.1). Variations in the slope of this relationship reflect changes in photosynthetic water use efficiency and are not well understood. It must be stressed that using Ci as the driving variable of photosynthesis is much debated. It has been advocated that Cc, the partial pressure of CO2 at the site of carboxylation, should be utilized instead. Using Ci implies that the following assumptions have been made: Cc = Ci and gm = 0, where gm represents mesophyll conductance, also called liquid phase resistance, which

0.50 0.45 0.40

gs (mol H2O/m2/s)

0.35 Wet y = 0.025x + 0.028 R2 = 0.86

0.30 0.25 0.20 0.15

Dry y = 0.009x + 0.024 R2 = 0.695

0.10 0.05 0

0

5

10 Anet (μmol CO2/m2/s)

15

20

Fig. 6.1. The relationship between stomatal conductance (gs) and net photosynthesis (Anet) in mango leaves from well-irrigated (■) and drought-stressed (▲) 12-year-old ‘Cogshall’ trees (Source: redrawn from Urban et al., 2006).

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encompasses diffusion from the intercellular leaf spaces to the carboxylation sites in the chloroplasts. There is a growing body of evidence that gm is not negligible in most species. The average value of gm in unstressed mango leaves (0.21 Pmol CO2/m2/s) (Urban et al., 2008), calculated using the method of Epron et al. (1995), is within the range of values for broadleaf species surveyed by Ethier and Livingston (2004) and Manter and Kerrigan (2004). The carboxylation rate (in Eqn 6.2) limited by the amount, activation state or kinetic properties of Rubisco (Wc) can be calculated as: Wc = VcmaxCi/(Ci + Kc(1 + O/Ko))

(6.5)

where Vcmax represents the maximum rate of carboxylation (Pmol CO2/ m2/s), and Kc (Pa CO2) and Ko (Pa O2) are the Michaelis constants of Rubisco carboxylation and oxygenation, respectively. The Vcmax values of wellexposed mango leaves at a leaf temperature of 30°C are typically in the range of 80–100 Pmol CO2/m2/s (Urban et al., 2006). Specific values of Kc and Ko for mango leaves have not been estimated and are approximated using data from other species (i.e. cotton or tobacco). The carboxylation rate limited by the rate of ribulose bisphosphate regeneration (Wj) is controlled by the rate of electron flow J (Pmol electrons/m2/s): Wj = JCi/(4(Ci + O/W))

(6.6)

with J = DT Q/(1 + D2T 2Q2/Jmax2)0.5

(6.7)

where Q is the photosynthetically active photon flux density (Pmol quanta/ m2/s), T represents leaf absorbance (no units), D is the apparent efficiency of light energy conversion (mol electrons/mol photons) and Jmax is the lightsaturated rate of electron transport (Pmol electrons/m2/s). Leaf absorbance of mango leaves, measured from 390–760 nm using an integrating sphere, was found to be close to 0.81 (Urban et al., 2008) and is in the normal range of T values of the literature (Bauerle et al., 2004). Leaf absorbance, which is positively correlated with leaf chlorophyll content, may increase as a consequence of paclobutrazol treatments (Gonzalez and Blaikie, 2003). The apparent efficiency of light energy conversion in mango reaches 0.32 Pmol electrons/ Pmol photons (Urban et al., 2004b), in the absence of photoinhibition or photodamage. This value corresponds to the mean value of operational D (Singaas et al., 2001). The Jmax values of well-exposed mango leaves at a leaf temperature of 30°C are typically in the 120–150 Pmol CO2/m2/s range. The Jmax as well as the Vcmax values are rather low when compared to values from other species and partly explain why maximal rates of leaf photosynthesis (Amax) are rather low, typically 12–15 Pmol CO2/m2/s. The carboxylation rate limited by triose phosphate utilization during sucrose and starch synthesis (Wp in Equation 2), can be calculated by: Wp = 3TPU + Vo/2 = 3TPU + Vc0.5Ci /(CiW)

(6.8)

where TPU is the rate of phosphate release in triose phosphate utilization during starch and sucrose production. The TPU is usually not included in

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most studies on photosynthetic capacity because of methodological difficulties. However, Urban et al. (2003) found that TPU = 8–12 Pmol CO2/m2/s at a leaf temperature of 30°C in well-exposed ‘Cogshall’ mango leaves. The variables Vcmax and Jmax are temperature dependent and their dependency is described by: Parameter (Vcmax, Jmax, TPU) = exp(c – 'Ha/(RTl)) /(1+exp(('STl – 'Hd)/(RTl)))

(6.9)

where c is a scaling factor, 'Ha (J/mol) the activation energy of the given parameter, R the gas constant (8.3143 J/°K/mol), Tl (°K) the leaf temperature, 'S (J/mol) an entropy term and 'Hd (J/mol) the deactivation energy of the given parameter. Similarly, the temperature dependency of Rd, W, Kc and Ko is described by: Parameter (Rd, W, Kc, Ko) = exp(c – 'Ha/(RTl))

(6.10)

Proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen (N). Therefore, photosynthetic capacity is strongly related to leaf N content expressed on an area basis (Na) (Field and Mooney, 1986; Evans, 1989; Kellomäki and Wang, 1997; Walcroft et al., 1997). To account for the relationship commonly observed between the parameters defining photosynthetic capacity (Vcmax, Jmax, TPU and Rd mainly) and Na (Field and Mooney, 1983; Harley et al., 1992) (Fig. 6.2), scaling factors c of Vcmax, Jmax, TPU and Rd may be related to Na, either linearly or slightly non-linearly. In summary, leaf net photosynthesis depends on five major classes of factors, either variables (external or internal factors) or parameters (more or less constant factors), provided that plants are not exposed to too extreme conditions; we may consider the internal factors as genetic factors. The five classes of factors are: 1. The photosynthetically active photon flux density (Q), which is the major driving variable of photosynthesis. Gross photosynthesis is determined by Q while Ci determines the proportion of photorespiration, and thus net photosynthesis. One of the major environmental factors affecting Ci is water availability in the root zone through its effect on gs. 2. Leaf nitrogen concentration (Na), which is not a rate-determining factor of photosynthesis, unlike Q, but may be considered as a rate-limiting factor. In other words, Na sets the photosynthetic potential of a leaf (i.e. photosynthetic capacity). We shall see below which factors influence Na in mango leaves. 3. Leaf temperature influences leaf photosynthesis. Net photosynthesis is positively correlated with leaf temperature in a normal range. Leaf temperature (Tl) is not a driving variable of photosynthesis but it is the single most important rate-determining factor after Q. In addition, extreme temperatures may influence photosynthesis through their damaging effects. Kinetics of enzymes involved with photosynthetic reactions collectively comprise an additional set of factors that influence leaf net photosynthesis.

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176 140

Vcmax (μmol CO2/m2/s)

120 100 80 y = 41.52x – 15.52 R2 = 0.87 y = –201.64x–1 + 173.41 R2 = 0.88

60 40 20 0 1.0

1.5

2.0

(a)

2.5 Na (g N/m2)

3.0

3.5

4.0

250

Jmax (μmol/m2/s)

200 150 100 y = 66.94x – 15.40 R2 = 0.83 y = –330.44x–1 + 291.55 R2 = 0.86

50 0 1.0 (b)

1.5

2.0

2.5

3.0

3.5

4.0

Na (g N/m2)

Fig. 6.2. Relationship between (a) the maximum rate of carboxylation (Vcmax) and (b) the light-saturated rate of electron transport (Jmax), and nitrogen concentration per unit leaf area (Na). Measurements were performed on mango leaves of 3-year-old ‘Cogshall’ trees (●), standard leaves ({) and leaves close to developing fruits (…) of 11-year-old ‘Cogshall’ trees. Best fit lines for pooled data correspond to the linear (_) and the ax–1 + b (…) models (Source: redrawn from Urban et al., 2003).

4. Several parameters related to enzymes include the specificity factor of Rubisco (W), the Michaelis constants of Rubisco carboxylation and oxygenation, Kc and Ko, the activation and deactivation energies of the different parameters 'Ha and 'Hd, the entropy terms 'S, c factors and leaf absorbance (T). With the exception of Kc and Ko, the specific values of all these parameters have been estimated for ‘Cogshall’ mango (Urban et al., 2003). 5. The apparent efficiency of light energy conversion (D). This factor belongs to a category of its own since it should theoretically not differ from one

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species to another and may be considered as a constant in the absence of photoinhibition and photodamage.

Light Light exposure Plants allocate nitrogen resources within the canopy to enhance photosynthetic capacity at locations exposed to high incident light levels, thus maximizing whole plant carbon gain (Field and Mooney, 1983; Hollinger, 1996; Carswell et al., 2000). For leaves of a given age and for a given nitrogen supply, leaf N per unit leaf area appears to be strongly related with light exposure (DeJong and Doyle, 1985; Le Roux et al., 1999, 2001; Rosati et al., 1999, 2000). Photosynthetic light acclimation of leaves may result from changes in either leaf nitrogen concentration (Nm) or mass-to-area ratio (Ma) because Na = MaNm. Lynch and González (1993) observed a negative correlation between Nm and light exposure in the tropical fruit tree Borojoa patinoi, but such a behaviour is rare; positive correlations between Nm and light exposure are more commonly observed. In addition, photosynthetic light acclimation of leaves may result from changes in partitioning of total leaf N among the different pools of the photosynthetic machinery (Evans, 1989). In mango, light acclimation of photosynthesis results mainly from changes in Ma, and to a lesser extent from changes in allocation of total leaf N at low irradiance; whereas changes in Nm play only a minor role (Fig. 6.3). Light acclimation of mango leaves thus follows a pattern similar to peach leaves (Le Roux et al., 1999; Walcroft et al., 2002). Light intensity Photosynthesis of ‘Cogshall’ mango trees increases with increasing levels of light intensity to reach a maximum at Q = 1200 Pmol photons/m2/s (L. Urban, unpublished data). Whiley et al. (1999) measured Q at 1284 Pmol photons/m2/s for field-grown ‘Kensington Pride’ trees growing in subtropical Queensland, Australia, which is well below full sunlight (full sunlight ≥ 2000 Pmol photons/m2/s). Such a high threshold is a typical feature of sun plants. Individual leaves are rarely able to utilize full sunlight; whole trees consist of many leaves that shade each other, so that only a small fraction of a tree’s leaves are exposed to full sun at any given time of the day, while the rest of the leaves receive subsaturating photon fluxes in the form of small patches of light that penetrate through gaps of the leaf canopy. Because the photosynthetic response of whole trees is the sum of the photosynthetic activity of all the leaves, only rarely is photosynthesis saturated with light at the wholetree level. While most leaves experience subsaturating light intensities, well-exposed leaves of the upper-crown may receive excessive quantities of light. Those leaves must dissipate the absorbed light energy in excess to prevent damage to the photosynthetic apparatus. Moderate decreases in maximal quantum efficiency (i.e. quantum efficiency of dark-adapted leaves Fv/FmPredawn) are

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Nm (g N/g dry matter)

3.0

2.0

1.0

0.0 0.0

0.2

0.4

0.6

0.8

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Gap fraction

(a) 3.0 2.5

Tree # 1 y = 1.42x + 1.43 R2 = 0.90

Na (g/m2)

2.0

Tree # 2 y = 1.33x + 1.44 R2 = 0.79

1.5 1.0 0.5 0.0 0.0

(b)

0.2

0.4 0.6 Gap fraction

0.8

1.0

Fig. 6.3. Relationship between (a) leaf nitrogen concentration per unit mass (Nm) and (b) leaf nitrogen concentration per unit leaf area (Na) and the gap fraction for mango leaves measured in the crown of two 3-year-old ‘Cogshall’ trees. Gap fractions were measured as an indicator of light exposure. Measurements were performed on leaves < 2 months old (●), 8 months old (■), 12–14 months old (▲) and 17–20 months old (♦) (Source: Urban et al., 2003).

typical features of moderate photoinhibition and should be interpreted in terms of non-photochemical quenching, an adaptative mechanism involving the xanthophyll cycle and allowing excess energy to be dissipated in the form of heat (Adams et al., 2005). Such small decreases in Fv/FmPredawn are commonly observed in mango leaves even from well-irrigated trees (Urban and Alphonsout, 2007). When temperature (30°C) and water vapour pressure deficit (VPD < 1 kPa) are non-limiting, and in the absence of photoinhibition, maximal rates of net leaf photosynthesis (Amax) may reach 12–15 Pmol CO2/m2/s at saturating

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Q, on ‘Cogshall’ trees. Whiley et al. (1999) measured Amax of 15.2 Pmol CO2/ m2/s for ‘Kensington Pride’ trees growing in a subtropical climate in Queensland, Australia. However, values > 16 Pmol CO2/m2/s were observed on field-grown trees of ‘Tommy Atkins’, ‘Haden’ and ‘Irwin’ on sunny days during the wet season in tropical regions of Australia (P. Lu, unpublished data). This is much higher than citrus (< 10 Pmol CO2/m2/s), but substantially lower than plum (approx. 26 Pmol CO2/m2/s). Whiley et al. (1999) estimated the light compensation point to be 29 Pmol photons/m2/s for leaves of non-stressed, field-grown mango trees, which is much higher than that attributed to shade-tolerant species (< 10 Pmol photons/m2/s) (Harvey, 1979). The data show that mango trees are basically sun-adapted plants.

Leaf temperature Effect of temperatures in a normal range on leaf photosynthetic capacity Medlyn et al. (2002) calculated optimal temperatures for Vcmax and Jmax to be 35–41°C and 30–38°C, respectively. Tree species native to cold climates had the lowest temperature optima for both Vcmax and Jmax. For ‘Cogshall’ mango trees, calculated temperature optima for Vcmax and Jmax are 44 and 45.5°C, respectively. They demonstrated that mango photosynthesis increases with temperature well above 40°C (Fig. 6.4). Although there is a clear lack of references for other tropical trees, it is tempting to attribute the temperature response of mango photosynthesis to its tropical origin. Estimates of 'Ha, 'Hd and 'S are 7.0695, 17.0799 and 536 J/mol for Vcmax, and 3.8782, 10.2211 and 317 J/mol for Jmax, respectively. Both 'Hd and 'S are within the range of published values for Vcmax and Jmax (Dreyer et al., 2001). In addition, 'Ha for Vcmax is within the 60–80 kJ/mol range for many species, including crop species as well as deciduous and evergreen trees (Medlyn et al., 2002). For mango, 'Ha for Jmax is consistent with data published for evergreen species (Medlyn et al., 2002), which is consistent with the fact that mango leaves commonly are 2–4 years old before senescence and abscision. However, the Jmax/Vcmax at 25°C for mango is about 1.86, approximately 11% higher than the mean value calculated over the whole range of species studied by Medlyn et al. (2002). Lower activation energies for Jmax than Vcmax result in a temperature-induced decrease in Jmax/Vcmax, confirming previous observations by Walcroft et al. (1997) and Dreyer et al. (2001). The estimate of 'Ha for Rd is 4.5710 J/mol. 'Ha is higher than the range of published values for Rd (Dreyer et al., 2001). Chilling temperatures Fv/FmPredawn decreases in mango leaves with decreasing temperature, while chilling reduces quantum efficiency (Whiley et al., 1999; Sukhvibul et al., 2000; Weng et al., 2006a, b). The decrease in Fv/FmPredawn may be interpreted to reflect sustained engagement of zeaxanthin in photoprotective energy dissipation. Decreases in quantum efficiency correspond to a decrease in the rate of electron flow. It may be argued that sustained zeaxanthin-dependent

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Vcmax /Vcmax at 25°C

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 15

20

25

30

35

40

45

50

35

40

45

50

Tl (°C)

(a) 2.0 1.8

Jmax /Jmax at 25°C

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 15 (b)

20

25

30 Tl (°C)

Fig. 6.4. Temperature response functions adjusted to the (a) maximal rate of carboxylation (Vcmax) and (b) the light-saturated rate of photosynthetic electron flux (Jmax), normalized to the mean value at 25°C in leaves from ‘Cogshall’ mango seedlings. The data scatter represents the real scatter at each temperature. Reference values at 25°C were computed for each of eight leaves, taken from young trees from two origins (● and {), and a unique temperature response was adjusted over the range of normalized data. Tl, the leaf temperature; the dotted lines correspond to Equation 9; the solid lines correspond to Equation 10 (no deactivation energy component).

energy dissipation reduces the risk of formation of singlet oxygen 1O2 in the antennae, while decreases in J lower the risk of electrons reducing O2 to anion superoxide O2− in the photosynthetic electron transport chain (Adams et al., 2005). In other words, decreases in Fv/FmPredawn and quantum efficiency correspond to adaptative mechanisms against the effect of cold, when photosynthesis is low and there is an imbalance between the quantity of light energy absorbed and the quantity of energy used in the photochemical reactions of

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photosynthesis (Adams et al., 2005). Interestingly, Weng et al. (2006b) found that mango leaves transferred from warm and dark to chilling conditions showed only slight down-regulation of PSII efficiency when compared to leaves moved from dim light to chilling conditions. Of course, long-term exposure to cold and very low temperatures (≤ 10°C) may eventually result in true photodamage, not just photoinhibition. Very low values of Fv/ FmPredawn, decreases in chlorophyll content and slow recovery kinetics are all indicators of photodamage. Sukhvibul et al. (2000) observed that susceptibility to cold-induced photodamage was more pronounced in polyembryonic cultivars than in monoembryonic cultivars, possibly reflecting their different eco-evolutionary development.

Elevated atmospheric CO2 concentration The CO2 concentration in the earth’s atmosphere has been increasing rapidly since the early 20th century and is continuing to rise, primarily due to burning of fossil fuels (Houghton, 2005). Earth’s atmospheric CO2 concentration is currently about 370 Pmol CO2/mol (Houghton, 2005) and is projected to reach 600 Pmol CO2/mol by 2050. Elevated ambient CO2 levels will undoubtedly affect cropping systems since atmospheric CO2 concentrations can significantly affect plant growth and productivity (Idso and Kimball, 1991; Houghton, 2005). There is little published information concerning the effects of elevated ambient CO2 levels on physiology, growth and production of tropical fruit trees, including mango. Schaffer et al. (1997) exposed leaves of field- and container-grown ‘Kensington’ (syn. ‘Kensington Pride’) trees to short durations (several minutes) of varying ambient CO2 concentrations. They found that under saturating light levels for photosynthesis, net photosynthesis increased as ambient CO2 concentration increased up to 1200 Pmol CO2/mol. At ambient CO2 concentrations > 1200 Pmol CO2/mol, net photosynthesis stabilized, probably due to leaves reaching their maximum biochemical capacity to fix carbon. Studies with ‘Cogshall’ mango trees indicated that when Ca increases, stomata close swiftly and Ci may become very unpredictable (L. Urban, unpublished data). Therefore, using Ci may be preferable to Ca for quantifying short-term effects of elevated CO2 concentations on Anet of mango. Saturating CO2 levels may often be reached at Ci = 800 Pmol CO2/mol air. Long-term (6–12 months) exposure of ‘Kensington’ mango trees to an atmospheric CO2 concentration of 700 Pmol/mol resulted in higher net CO2 assimilation rates than in leaves of plants grown at atmospheric CO2 concentrations of 350 Pmol/mol when net CO2 assimilation was measured at the same CO2 concentration as the growth environment. However, carboxylation efficiency (the amount of CO2 fixed per mole of ambient CO2) was lower for plants in the CO2-enriched environment compared to plants in the ambient (350 Pmol CO2/mol) environment (Schaffer et al., 1997). Although further studies are needed to determine the effects of long-term exposure to elevated CO2 concentrations on mango growth and productivity, it appears that

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mango will benefit from increases in atmospheric CO2 concentrations. However, the effects of increased atmospheric CO2 concentrations associated with global warming on mango production may be offset by higher respiratory losses and increased assimilate partitioning to shoot growth in highly vegetative cultivars (Schaffer et al., 1999). Therefore, responses of mango cultivars to elevated atmospheric CO2 concentrations need to be evaluated over a range of temperatures to ascertain their likely performance under changing atmospheric conditions.

Humidity Although mango production occurs in the tropics and subtropics in areas of high and low relative humidity (RH) (Campbell, 1984), there are very few published reports on the effects of RH or VPD on physiology and tree growth. In a study with container-grown ‘Kensington’ plants, Pongsomboon et al. (1992) reported that stomatal conductance was inversely correlated with VPD. Differences between cultivar responses to VPD have been observed in field-grown ‘Irwin’ (monoembryonic) and ‘Kensington’ (polyembryonic) mango trees during the wet and dry season in tropical Australia. During the wet season and for well-irrigated trees during the dry season, both ‘Irwin’ and ‘Kensington’ showed decreasing stomatal conductance with increasing leaf-to-air vapour pressure deficit (LAVPD) but ‘Kensington’ showed a more rapid decrease than ‘Irwin’ (Fig. 6.5) (P. Lu, unpublished data). It was also observed that daytime leaf xylem water potential was lower in ‘Irwin’ than in ‘Kensington’ while predawn water potentials were similar for both cultivars (P. Lu, unpublished data). These results indicate that under similar soil water conditions, ‘Kensington’ tends to close stomata much more rapidly than ‘Irwin’ to conserve water under dry atmospheric conditions. This water conservation strategy is probably a reflection of ‘Kensington’s’ adaptive responses to the hot and dry seasonal tropical environment under which it evolved (Wolstenholme and Whiley, 1995). Other studies in tropical Australia revealed that polyembryonic ‘Nam Doc Mai’ behaved like ‘Irwin’ (P. Lu, unpublished data). However, ‘Nam Doc Mai’ in Thailand has comparatively low vigour compared to ‘Kensington’ when grown in the tropics. Further research is required to determine if differences in photosynthetic or stomatal responses of mango to VPD are indeed based on embryonal characteristics. Clarification of the reasons for variation would undoubtedly facilitate breeding and selection of cultivars for dry and humid areas.

Flooding The primary effect of flooding on plants is due to a reduction in soil oxygen concentration. Oxygen levels in the soil can decrease from 20% to < 5% within 1–2 days of flooding (Crane and Davies, 1988) and soils eventually become

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Stomatal conductance (mol/m2/s)

0.6

0.5

0.4

‘Irwin’: R2 = 0.594

0.3

0.2

0.1

‘Kensington’: R2 = 0.635

0.0 1

2

3

4

5

6

7

8

LAVPD (kPa)

Fig. 6.5. Correlation between leaf stomatal conductance and leaf-to-air vapour pressure deficit (LAVPD) during the dry and wet season for ‘Irwin’ (closed circles) and ‘Kensington’ mango trees (open circles). Trees were well irrigated during the dry season and all measurements were taken when the Q > 300 Pmol photons/m2/s (n = 12) (Source: P. Lu, unpublished data).

anoxic (no oxygen). Mango is considered to be a moderately flood-tolerant species (Schaffer et al., 1994, 2006) and waterlogging or flooding of trees periodically occurs in many of the regions where the crop is grown (Plate 41). Mango trees have evolved a mechanism to cope with temporary flooding (see ‘Flooding’ section under Tree Growth and Development, this chapter). Typically, the first easily measurable responses of fruit trees to flooding are reductions in Amax, gs and transpiration, which occur within 2–3 days following flooding (Larson et al., 1991c; Schaffer et al., 1992, 2006). Short-term anoxia results in a decrease in net photosynthesis which cannot be related to a gs-associated decrease in Ci (Zude-Sasse et al., 2001). Removing trees from flooded conditions after 28 days reversed the flooding-induced decrease in leaf gas exchange, resulting in a gradual increase in photosynthesis and transpiration to preflooded rates. Although flooding adversely affects mango trees, short-term flooding of trees in limestone soils can result in increased micronutrient availability with improved plant nutritional status. In calcareous soils of south Florida, in which iron (Fe) was withheld from the fertilizer programme, short-term flooding (10–20 days) of polyembryonic ‘Peach’ mango trees resulted in an increase in net photosynthetic rates to above preflooding levels following the release of trees from flooding (Larson et al., 1992). This increase in photosynthesis has been correlated with improved Fe and manganese (Mn) uptake as

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a result of these elements becoming more soluble when calcareous soils are flooded (Larson et al., 1991b, 1992).

Internal factors Leaf age Leaf characteristics (i.e. photosynthetic capacity and the amount of N per unit area) are generally strongly influenced by leaf age, with maximum values being observed when leaves have just completed full expansion (Constable and Rawson, 1980; Marshall and Biscoe, 1980; Dwyer and Stewart, 1986; Field, 1987; Wilson et al., 2000; Frak et al., 2001). Chlorophyll content is three to four times lower in young than in mature mango leaves (Zude and Ludders, 1997). Similarly, the concentration of Rubisco is lower in young than in mature, green leaves (Nii et al., 1995). In contrast to many other plant species, once mango leaves are mature the relationship between Na and irradiance does not seem to be affected by leaf age (Urban et al., 2003). The Na values may remain high in old leaves experiencing high irradiance. This indicates that changes in Na in mango leaves are influenced by irradiance and not age, at least during the first year. Carbohydrate accumulation and source-sink balance Source-sink imbalances can exert feedback down-regulation or repression of leaf photosynthesis through carbohydrate accumulation in leaves (AzconBieto, 1983; Foyer, 1988; Koch, 1996; Schaffer et al., 1997; Whiley et al., 1999; Paul and Foyer, 2001; Paul and Pellny, 2003). Transient accumulations of carbohydrates in leaves, as they have been observed during the diurnal period, may impair the rate of electron transport (Pammenter et al., 1993). Changes in photosynthetic capacity, not just assimilation rates, are more likely to be observed in association with lasting source-sink imbalances. One hypothetical mechanism is that high levels of carbohydrates repress the expression of genes coding for several photosynthetic enzymes (Krapp and Stitt, 1995; Koch, 1996; Drake et al., 1997). Alternatively, carbohydrates may interact with hormonal signals to control gene expression (Thomas and Rodriguez, 1994). There is also some evidence that photosynthetic capacity is related to leaf carbohydrate status through the effect of the latter on phosphate availability (Riesmeier et al., 1993; Sun et al., 1999). In the long term, carbohydrate accumulation may eventually lead to cell death. High sugar concentration has been associated with senescence in leaves of several species (Noodén et al., 1997; Wingler et al., 1998; Quirino et al., 2001). Reduced energy utilization by CO2 assimilation, like the one resulting from carbohydrate accumulation, in combination with high energy capture is potentially dangerous and can result in over-reduction of the electron transport chain, photoinhibition and oxidative stress caused by photoreduction of oxygen to superoxide O2− in the Mehler-ascorbate peroxidase reaction (Badger, 1985). Moreover, reactive singlet oxygen 1O2 can be formed through reaction of oxygen with triplet chlorophyll released by the breakdown of the chlorophyll-protein complexes in

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thylakoids (Merzlyak and Hendry, 1994). Formation of reactive oxygen species can lead to membrane damage and eventually cell death. Whiley et al. (1999) observed that Amax, which is closely related to photosynthetic capacity, the quantum yield and Fv/FmPredawn are substantially lower in mango trees grown in containers (root-restricted) when compared to field-grown trees. These observations were confirmed by Urban and Alphonsout (2007) who studied the effect of the removal of a 1 cm-wide band of bark on leaf photosynthesis and leaf N content of 3-year-old and 11-yearold ‘Cogshall’ mango trees. Girdling is a common horticultural practice used to manipulate tree growth and development in many fruit species. Its most immediate effect is to stop the basipetal movement of assimilates through the phloem, which results in an accumulation of carbohydrates above the girdle (Roper and Williams, 1989; Schaper and Chacko, 1993; Di Vaio et al., 2001). Girdling can promote floral induction in mango (Chacko, 1991), but it has also been shown to reduce net photosynthesis. The major effect of girdling is a dramatic increase in leaf carbohydrate concentration and a concomitant decrease in photosynthetic electron transport and net photosynthesis (Fig. 6.6) (Gonzalez and Blaikie, 2003; Urban and Alphonsout, 2007). Urban and Alphonsout (2007) observed that Anet was reduced by 77% within 28 days from girdling and remained at about 2 Pmol CO2/m2/s until the beginning of flowering. The decrease in photosynthetic electron transport rate (J) and sustained photoprotection (reflected by the decrease in Fv/FmPredawn) protected leaves of girdled branches effectively from photodamage, as shown by the vigorous recovery of Anet and J observed immediately after the appearance of inflorescences. This increase in Anet and J was associated with no 250

Q = 400 μmol photons/m2/s y = 84.5e–0.0313x R2 = 0.69

J (μmol electrons/m2/s)

A 200 150

Q = 1200 μmol photons/m2/s y = 120.3e–0.0405x R2 = 0.74

100

Q = 2000 μmol photons/m2/s y = 155.4e–0.0401x R2 = 0.74

50 0

0

10

20 Starch (g/m2)

30

40

Fig. 6.6. The relationship between the total photosynthetic electron flux (J) measured at photosynthetic photon flux (Q) = 400 ('), 1200 (●) and 2000 ({) Pmol photons/ m2/s, and the amount of starch per unit leaf area. Best fit lines at each Q were assessed from measurements performed on both girdled and non-girdled mango leaves before flowering. Data were used to establish the following relationship: J = (0.0434Q + 72.8)*e–0.0412[starch]a (Source: Urban and Alphonsout, 2007).

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decrease in leaf carbohydrate content during the first month following the onset of flowering, suggesting that the effect of carbohydrate accumulation on photosynthesis is mediated by sink activity. Apart from its negative effect on the carbon budget of mango trees, girdling appeared to be rather harmless. However, leaf N concentration decreased, which indicates that there may indeed exist long-term negative effects of girdling on photosynthetic capacity. The width of bark (phloem) removed may be critical with respect to the intensity of the effect of girdling on the tree. Whiley et al. (2006) girdled the trunks of ‘B74’ (‘Calypso’™) mango trees in the Northern Territory of Australia in autumn (as soon as they had come out of the wet season). The girdles were no more than the thickness of a pruning saw (about 1 mm) and healed within 6 weeks. In the first and third years after girdling, the trees had significantly higher yields than non-girdled trees on which, coincidentally, fruit matured early, thus giving market advantage. There was no significant difference in yield in the second year of treatment between girdled and nongirdled trees. The first and third years had strong natural induction while the second year gave poor flowering across all varieties in the district. Thus, during years of strong induction, this type of girdling most likely provided extra carbohydrate reserves to drive flowering and support fruit set and retention while in the off-flowering year there was sufficient carbohydrate reserves to support reproductive activity. In contrast to observations with ‘Cogshall’ mango trees (Urban and Alphonsout, 2007), there was no evidence of long-term effects of narrow girdles on leaf N of ‘B74’ mango trees (Whiley et al., 2006). However, when wider girdles are made, tree recovery may take much longer leading to sustained physiological disruption. Proximity of inflorescences While the effects of water stress and high light, temperature and atmospheric CO2 concentration on photosynthesis are increasingly well described, very little is known about the effect of phenology, and especially of flowering on photosynthesis of mango. There is some evidence that flowering may have an effect on photosynthesis. Flowering-associated decreases in Anet and gs were observed in sweet cherry (Roper et al., 1988) and mango (Shivashankara and Mahai, 2000; Urban et al., 2004a). Lack of precise knowledge about the effect of flowering on photosynthesis may impair our ability to adequately simulate photosynthesis, especially for tropical fruit trees for which flowering often extends over a long period of time. Mango flowering can last for > 2 months. Therefore, its effect on photosynthesis should not be overlooked. Urban et al. (2004a) showed that the decrease in Anet in mango leaves close to inflorescences is not attributable to a gs-associated decrease in Ci or to an increase in Rd. Rd was lower in leaves close to inflorescences than in standard leaves. If any, the effect of Rd on Anet was a positive one. This study suggested strongly that the decrease in Anet was due to a decrease in the electron flow in photosystem II, but failed to provide direct evidence for it as well as the elements for interpretation. Using a modelling approach, Urban et al. (2008) confirmed that there is a decrease in the total light-driven photosynthetic electron flux in leaves close to inflorescences and showed that the decrease

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in Anet is also attributable to an increase in photorespiration. The latter appears to be the consequence of a gm-associated decrease in Cc, while the former results from an increase in electron flow towards alternative sinks, a decrease in the amount of leaf N per unit leaf area, and, hypothetically, either a decrease in leaf N allocation to the bioenergetic pool of the photosynthetic machinery, inorganic phosphorus depletion in leaves, or feedback inhibition of photosynthesis. The latter hypothesis is least probable in the absence of carbohydrate accumulation in leaves close to inflorescences. Both of these hypotheses need to be tested to further our understanding of the inhibiting effect of inflorescences on photosynthesis of nearby leaves. Interestingly, net photosynthesis measured on leaves close to panicles bearing set fruits are intermediary between those measured on standard leaves and those measured on leaves close to inflorescences, suggesting that changes in photosynthesis associated with flowering are reversible. Urban et al. (2008) also showed that processes other than temperature or light acclimation, and acclimation to reduced sink activity, may cause leaf N concentration and photosynthetic capacity to vary in mango. Whiley (unpublished data) observed that the mango leaves immediately adjacent to inflorescences lose colour intensity as the inflorescence grows out. Although leaf N over this period was not measured in mango, it has been measured in avocado (Whiley, 1994) which has a similar intense burst of flowering in which a large biomass is produced in a short time. Leaf N declines rapidly in avocado leaves as the inflorescences break from buds and grow and then N stabilizes (at a lower concentration) by mid-bloom. This can be reversed by N applications during flowering and the additional application of a growth retardant (paclobutrazol (PBZ)) giving leaf N and A a significant boost. Similarly to avocado, it is likely that the reduction in A close to mango infloresences is related to reduced leaf N.

Photosynthetic contributions by fruit Fruit of many species have chlorophyll and photosynthetic activity, particularly during the early stages of growth (Jones, 1981; Whiley et al., 1991). However, for most crops, respiratory losses from fruit exceed photosynthetic gains throughout ontogeny (Kriedemann, 1968; Whiley et al., 1991). An exception to this is blueberry (Vaccinium spp.) fruit in which there is a net photosynthetic gain from petal fall through to colour break, with an estimated 15% of the total fruit carbon requirement contributed from fruit photosynthesis (Birkhold et al., 1992). Studies with monoembryonic ‘Dashehari’ mangoes showed that when fruit were approximately 10 mm in diameter, the photosynthetic rate of fruit was 2.7% that of leaves and declined to 1.2% of leaf photosynthesis at fruit maturity (Chauhan and Pandey, 1984). However, even this comparatively small carbon contribution may be important during the critical fruit set period when trees rely on stored carbohydrates and a relatively inefficient canopy to supply current photosynthates. Further studies with mangoes to establish optimum light regimes for fruit photosynthesis at different stages of ontogeny are warranted.

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6.3 Plant Water Relations In this section, theoretical concepts of plant water relations are briefly outlined to help interpret the effects of environmental factors on mango water relations (see also Nobel (1983) and Baker (1984)). An important concept in plant water relations is water potential (Ψ), which is a measure of the free energy of water. For pure water, Ψ = 0. As solutes are added to water, its free energy decreases and < becomes more negative. Water moves along a gradient from higher to lower (more negative) 80% of producers to obtain higher prices. Even when a significant amount of advanced bloom is induced, blooming during the normal flowering period may occur. The intensity of the normal bloom is influenced by the intensity of the fruit set by the advanced bloom. The most common method to advance bloom involves canopy sprays of KNO3 or NH4NO3 (Mosqueda-Vázquez and De los Santos, 1982; Núñez-Elisea, 1986, 1988; Guzmán-Estrada, 1991; Sandoval-Esquivez et al., 1993). The effect of these compounds is influenced by cultivar and environmental conditions (probably temperature). In the Gulf of Mexico region, one to two sprays of 2% KNO3 or 1% NH4NO3 solution are applied to ‘Manila’ trees any time from 15 October to 30 November to stimulate early flowering. ‘Manila’ and ‘Ataulfo’ are sprayed with 2% KNO3 during the same period in the Southern

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Pacific region. In the Central Pacific region, ‘Haden’, ‘Manila’ and ‘Ataulfo’ trees are treated with one or two sprays of 2–4% KNO3 or 1–2% NH4NO3 at any time during the first half of November. Similarly, ‘Haden’ and ‘Manila’ are treated during November with 8% KNO3 or 4% NH4NO3 in the Northern Pacific region. ‘Tommy Atkins’ does not respond to foliar nitrate treatments for promoting early flowering. This is due to delayed floral initiation in this cultivar so that when nitrate treatments are applied the buds are not irreversibly committed to flowering (Pérez-Barraza et al., 2000). Consequently, vegetative growth is produced in response to treatments that stimulate bud break (Pérez-Barraza et al., 2006a). However, application of PBZ promotes early bloom in ‘Tommy Atkins’ (Salazar-García and Vázquez-Valdivia, 1997). Currently, soil applications of Cultar® (25% a.i.) close to the tree trunk is used for most cultivars in dosages that range from 1 ml/m canopy diameter for ‘Manila’ in Veracruz to 2–4 ml for ‘Tommy Atkins’, ‘Haden’ and ‘Ataulfo’ in Michoacán, applied at 1–2 year intervals. The response to PBZ treatment is enhanced by 30–45 days water stress and canopy sprays with nitrates (Chávez-Contreras et al., 2001). In Nayarit and Sinaloa late bloom and harvest are profitable because they are the last two production areas to be harvested in Mexico. Two canopy sprays of 50 mg/l GA3 (15 and 30 November) cause delayed bloom and shift 86% of the harvest to 1 month later (Pérez-Barraza et al., 2006b). In Taiwan, cultivar, latitude, elevation and cultural practices are used for off-season production (Shü et al., 2000). Several strategies are utilized to stimulate flowering and fruit set: 1. After harvest the last one or two vegetative flushes on each shoot are cut back to control tree size. Subsequently, two flushes of healthy shoots are allowed to grow to serve as fruiting shoots for the next year. Weak or crowded shoots are removed to facilitate ventilation and light penetration. 2. In general, flowering is not a problem in subtropical Taiwan; however, poor fruit set due to bad weather and lack of pollinators occurs occasionally. A recent programme to increase the population of pollinators, mainly the greenbottle flies (Chrysomyia megacephala Fabricius) in mango orchards has been very successful. Increased yield has been noted and the practice has been exploited commercially throughout the island. 3. Most of the mango fruit harvest goes to the domestic market within a short time period, causing the price to decline rapidly. Off-season fruit production is thus very important to avoid this sharp drop in price. 4. Physical trunk damage by girdling and ringing and application of ethrel is used to promote early flowering of the early season cultivar ‘Tsar-swain’ (Liu, 1996). Foliar applications of KNO3 can promote early flowering but only if applied to flower-bud-induced shoots; PBZ is not recommended for use on edible crops in Taiwan. 5. Panicle removal has been used to postpone flowering and fruiting (Shü and Sheen, 1987; Shü, 1993). Emerging terminal panicles are removed by hand. Chemical removal of terminal panicles with hydrogen cyanamide (CH2N2) or calcium cyanamide (CaCN2) causes leaf damage and is not as

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effective as pruning (Hwang et al., 2004). Axillary panicle induction has some advantages, because flowering can be timed to avoid frost or cold temperatures or a period of excessive rainfall during the normal flowering period (Singh et al., 1974; Shen and Huang, 1980). Axillary panicle removal also reduces mango malformation and reduces alternate bearing (Majumder et al., 1976; Pal and Chadha, 1982). Control of flowering and tree size in the USA varies with respect to different climatic, edaphic and soil conditions as well as cultural practices (Davenport, 1993). In Florida, cool temperatures during the winter months (December through to February) are usually adequate to arrest vegetative growth and induce flower bud differentiation. In some years, the duration of cool temperatures prohibits floral expression until late winter/early spring (February/ March) and when continuous warm temperatures begin (March), profuse, synchronized flowering occurs. In some years, warm and cool periods may occur for a few days to weeks during the winter and partial flowering may occur 2–4 times during the winter. This prolongs the flowering and harvest season. Flowering and fruiting of trees are not actively manipulated in Florida. For young trees, vegetative growth is encouraged during the first 2–3 years and panicles may be removed by hand or natural pathogens, i.e. powdery mildew or anthracnose are allowed to kill panicles and flowers. Tipping and selective pruning of young trees is recommended to improve tree structure, control tree size and enhance early fruit production (Oosthuyse and Jacobs, 1995; Campbell and Wasielewski, 2000); however, selective pruning and mechanical topping and hedging are used to control mature-tree size. Selective pruning usually involves removal of selected scaffold limbs to open up the tree canopy to light and to remove dead wood. Mature trees may or may not be allowed to grow together in the tree row to form hedgerows. Periodic mechanical topping at 3.5–5 m and hedging to leave a 2.5–3.5 m row middle is common (Crane and Campbell, 1991; J.H. Crane, personal communication). Limiting the between-row spread of the trees to 2.5–3 m improves light penetration into the tree canopy. In some orchards, hedging the inner sides of the canopy of adjacent rows every 2–4 years and/or topping every third or fourth row every 2–4 years is recommended. Trees are mechanically pruned immediately after harvest. Timing the pruning to selected rows each year ensures that most of the planting will always be productive if continuous flushing of pruned parts of the canopy prohibits reproductive growth the following spring. Pruning trees shoots of 2–10 cm diameter immediately after harvest and then tip pruning 3–4 times to force multiple lateral growths has been advocated (Davenport, 2006). This strategy: (i) reduces or controls tree size; (ii) shapes trees to facilitate subsequent tip pruning; (iii) synchronizes the vegetative flushing; and (iv) inhibits continuous vegetative flushing and prolongs the period of vegetative dormancy. After vegetative growth has ceased for 5 or more months, trees will synchronously flower when regrowth occurs. In Puerto Rico, continuous vegetative growth of 1–2-year-old trees is promoted. During this time panicles may be removed by hand to promote vegetative growth, and this encourages rapid development of large trees.

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Temperatures are insufficient to inhibit vegetative growth and induce reliable and consistent bud differentiation, causing erratic or poor flowering and poorly synchronized fruit yields. The most common method for synchronizing and enhancing the time of flowering involves a combination of drought stress and timed application of KNO3. This method depends on cultivar and the desired time of fruit harvest. To slow (or stop) vegetative growth and to stress the trees, irrigation is withheld for 1–3 months prior to flowering. The drought stress is prolonged until leaves become dark green and show slight signs of wilting. A 1–5% solution of KNO3 is applied to the foliage, which induces flowering 3–4 weeks later. Regular irrigation is resumed when c.75% of the panicles have set fruit. The timing of the drought stress and KNO3 spray varies with cultivar and when fruit harvest is desired. PBZ has been used to control vegetative growth after trees flush in response to pruning following harvest. A soil drench of PBZ (7–10 g/tree) is applied and trees are irrigated for 8–12 h. Irrigation is then withheld for 30–90 days until trees show signs of drought stress. A foliar application of 1–2% KNO3 is applied, and flowering occurs 30–45 days later. The amount of tree training depends upon the cultivar and is practised on young trees when they are c.1–1.5 m high. ‘Keitt’ and ‘Palmer’ tend to have long branches of various lengths and benefit from training to create a stronger limb structure and more compact tree. Trees are generally trained to a modified central leader system, and some selective pruning of older trees is practised to open the canopy to more light and air movement. Mechanical topping and hedging are used to shape mature trees. Usually trees are topped to 3–4.5 m immediately after harvest. In Hawaii, seasons with heavy crops are commonly followed by light or no crops for 1–2 years (Nagao and Nishina, 1993). The small variation in warm temperatures and evenly distributed rainfall encourage vegetative growth, which reduces the potential for fruit production. This is less problematic on the drier leeward sides of the islands. Diseases (i.e. anthracnose and powdery mildew) reduce production by infecting panicles and flowers. Preliminary trials with 2 and 4% KNO3 applications during the winter (February) resulted in 66–84% flowering 5 weeks after treatment (Nagao and Nishina, 1993); however, this procedure is not utilized commercially. Young ‘Keitt’ mango trees are extensively trained by hand (usually twice a year) during the first 4–5 years to improve the structural strength of scaffold limbs, increase the number of terminals and to control tree size in California. Panicles are removed by hand during the first 4 years. Training is necessary because non-trained ‘Keitt’ trees tend to have a few very long scaffold limbs, little branching and are structurally weak. Bearing trees are pruned annually to maintain trees at 3.1–4.6 m. In California, cool temperatures during the winter months (November through to February) are adequate to arrest vegetative growth and induce bud differentiation. The duration of cool temperatures may inhibit floral expression until early spring (March and April), when warm temperatures allow profuse, synchronized flowering. Warm periods during winter may stimulate early flowering, which may be damaged by subsequent cold temperatures (Schacht, 1992).

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Early season flowering when cold temperatures and dry windy conditions prevail (December–February) results in poor fruit set and abnormal fruit. Therefore, pruning of mature trees just before April (early spring) delays flowering and induces synchronous axillary flowering after the danger of cold has passed.

13.11 Environmental Stress Management Mango is an adaptable species that withstands a range of subtropical and tropical climates and soils. Physiological responses are related to the evolutionary history of mangoes, with monoembryonic cultivars better adapted to the subtropics and polyembryonic cultivars better adapted to the tropics. In Brazil, the important commercial mango areas are in the tropical semiarid climate of the north-east. Flooding and freezing rarely occur there, but wind and drought stress are very common and negatively affect growth of young mango trees and increase fruit drop. Windbreaks reduce wind stress; compact rows of elephant grass and/or rows of banana trees are utilized (Mouco et al., 2002). In general, 3–4 rows of banana trees are planted around or in perpendicular rows in the orchard against the main wind flow. Drought stress, particularly in north-eastern Brazil, can suppress mango growth and production, and irrigation is used to ameliorate this problem. Drought stress has been used to increase endogenous ethylene concentrations and trigger floral induction 70–90 days after PBZ application. Drought stress should be avoided during fruit development. Coelho et al. (2002) reported the crop coefficient (Kc) for mango increased from 0.39 at flowering to 0.85 during fruit development. In Mexico, the Gulf of Mexico coastal region may experience strong, dry northerly winds (11–28 m/s) from October to April and cause limb breakage and increase flower and fruit drop by desiccation. To ameliorate this problem, growers have planted east-west oriented bamboo (Bambusa vulgaris) and Australian pine (Casuarina equisetifolia) windbreaks. Bamboo is planted outside the Australian pine trees and two rows of pines are planted in a staggered arrangement. All coastal mango-producing regions in Mexico are potential targets of hurricanes during the summer rainy season, even in late October. Broken limbs are pruned, damaged trees are pruned back to sound wood, and some trees are replaced or top-worked. Flooding for 2–3 weeks may occur during the summer rains. This is mainly a problem in low-lying areas of Chiapas and Nayarit that have loamy soils and a high water table. Drainage canals have been constructed in such areas to minimize the problem. Drought stress is common as 67% of Mexico’s mango orchards are not irrigated (SIIAP, 2007). Annual rainfall ranges from 900 to 3700 mm in Mexico and is concentrated in June to October. The dry season begins in October (close to the period of floral initiation) and continues through the harvest period for early and some mid-season cultivars. Drought stress in areas of low rainfall causes intense fruit drop, which reduces yield and fruit size especially in heavily bearing trees. More that 60,000 ha of

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mangoes are irrigated in low rainfall areas. In Veracruz and Chiapas most orchards are adjacent to riverbanks and the deep soils provide root access to the water table. No data are available supporting the benefit of irrigation in medium-high precipitation areas. Most mango-producing regions in Mexico are frost free. The only report of frost damage to 2–4-year-old mango orchards was in Sonora where freezing events may occur every 6–8 years (E. Sánchez, personal communication). Low temperatures (≤10°C) during bloom reduce fruit set, especially in ‘Ataulfo’. Treatment with GA3 to delay the bloom has been suggested as a method to avoid low-temperature damage during flowering but flowering under high-temperature conditions is also detrimental to fruit set and crop yield (Pérez-Barraza et al., 2006b). In Taiwan, damage from typhoons occurs periodically and trees are reset and either pruned to recover or replanted. In general, freezing temperatures are not a problem in the mango-production areas but cool temperatures can reduce fruit set. To avoid cool or cold temperatures during the normal flowering period, shoot tips may be pruned to delay and force flowering from lateral buds. Flooding in production areas is uncommon, and drought stress is not an issue because most producers irrigate during dry periods. The production areas of Hawaii and Puerto Rico are frost free; however, Florida and California may experience temperatures at and below freezing during the winter months (December through to February). In Florida, freezing temperatures (0 to −6°C) may occur for a few hours for 1–4 nights/year, although freezing temperatures for 13–15 h within a 24 h period have been reported (Johnson, 1970; Campbell et al., 1977). In California, temperatures as low as −6.6°C are common and frosts may occur 10–15 times/year during January and February (Aslan et al., 1993). Mango trees do not acclimate to cold temperatures (McKellar et al., 1983), although differences in cold tolerance and recovery from cold damage have been observed (Carmichael, 1958). In Florida, high-volume overhead and under-tree irrigation is used to protect trees during freezing weather. At least 0.6 cm of water/ha is distributed. Overhead systems are designed for complete coverage (overlapping spray patterns) of the trees and under-tree systems are designed to spray 0.9–2.4 m into the tree canopy. Irrigation commences before freezing temperatures are reached (usually c.2–3°C) and continues until ice has melted. These systems are powered by diesel or gas engines as electrical power is unreliable during freezing weather conditions. In California, microsprinklers, wind machines and helicopters are used to raise the air temperature of plantings (Schacht, 1992). Mango trees are relatively tolerant of wind stress (Schaffer et al., 1994; Crane and Balerdi, 2005); however, newly planted trees are commonly staked at planting in the calcareous soils of Florida to prevent damage to the bark and cambium caused by constant movement and rubbing against the rocky soil. Staking also stabilizes the tree against toppling during hurricanes. In contrast, tolerance to mature trees depends on tree size, with larger trees being more vulnerable to wind damage than pruned trees (Crane et al., 1993, 1994, 2001; Crane and Balerdi, 1996; NASS, 2006).

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In the mid-20th century, windbreaks of C. equisetifolia were planted around many mango orchards in Florida. However, intrusion into the orchard, shading and damage to mango trees when trees toppled into orchards during hurricanes has stopped this practice. Some producers have topped remaining pine windbreaks at 4.9–6.7 m to reduce orchard shading and their potential to topple (Crane et al., 1993). In Hawaii, natural windbreaks are recommended for some areas where constant winds are a problem for establishing young trees (C.L. Chia, personal communication). In California, constant winds during spring may damage panicles and young fruit; man-made windscreens are used to protect trees (Scott, 1990; Schacht, 1992). The windscreens can be raised to prevent trapping of cold air within the plantings. Puerto Rico is affected by hurricanes but no specific ameliorating recommendations have been reported (Toro, 1988). Flooding is not common in production areas of Puerto Rico, California and Hawaii; however, periodic flooding (1–21 days) is typical during the summer in Florida. Trees have been planted on beds of crushed limestone rock, 0.6–1.0 m high and 1.0–1.5 m wide, which allows part of the root system to be above water. Planting of orchards at sites at or below 2 m above sea level is not recommended. Mango trees are moderately flood tolerant (Larson et al., 1991c; Schaffer et al., 1994, 2006), although this is affected by floodwater temperature, oxygen content and anatomical adaptations of the rootstock (Larson et al., 1991a, 1993a, b). Periodic flooding of the limestone-based soils in Florida increases the availability of soil Mn and Fe (Larson et al., 1991b, 1991d, 1992), alleviating plant deficiencies of these elements. Furthermore, rhizosphere anoxia increases reduction of Fe3+ to Fe2+ by nicotinamide adenine dinucleotide (NADH) in mango root tissue and Fe uptake by mango roots in oxygen-depleted media (Zude-Sasse and Schaffer, 2000).

13.12 Harvesting Practices Harvesting is done by hand in Brazil, Mexico, Taiwan and the USA (Evans, 2007) and is one of the most expensive operations in mango production because fruit do not mature synchronously, and trees require multiple pickings. The technology to mechanize mango harvest is difficult because of differences in fruit colour, size and weight among cultivars, difficulty in determining fruit maturity, requirement for multiple pickings, lack of tree-size-controlling rootstocks and tree training and moderate to large tree canopies. Prior to harvesting in Brazil, excessive set fruit and injured and diseased fruit are removed, part of the rachis is removed to prevent scarring and bruising of the fruit, and some leaves that shade fruit may be removed to allow for better peel colour development (Alves et al., 2002). Fruit in the lower part of the canopy are harvested from the ground; however, ladders are required for picking fruit high in the tree canopy. Peel damage due to latex exudation at the stem end of the fruit during harvest is a very common problem, and >50% of harvested fruit may be affected. This problem occurs mainly when fruit are picked high in the canopy with a picking pole by severing the fruit

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near the stem end of the pedicel. An improved picking pole that cuts the petiole c.2 cm above the pedicel reduces latex burn to 90% maturity for local markets. Green mature fruits may be triggered to ripen with calcium carbide, ethephon or ethrel at 30–40°C, depending on the cultivar. Mature fruits are stored at at 8–12°C for several days to several weeks. Fruit destined for export are disinfested using the vapour heat method; the fruit core temperature must reach and be held at 46.5°C for 30 min. There are two markets for mango producers in the USA: the ‘green’ market for non-ripe fruit and the ‘tree-ripened’ market. The green and tree-ripened markets are speciality, niche markets where the green fruit are used as a

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component of processed foods (e.g. chutneys, preserved pieces), whereas the tree-ripened fruit target the demand for ready-to-eat mangoes. Green mangoes are picked before the fruit is mature, whereas the tree-ripened mangoes are allowed to develop almost full colour and ripeness before being picked. Florida mangoes are more expensive than imports and the volume of fruit is very limited and cannot supply the demand of the national market. Usually multiple pickings are required to harvest the crop but this is influenced by market demand and prices, the number of blooms producing the crop and weather conditions. Harvesting in the USA is by hand. A long picking pole with a canvas or nylon bag attached to a metal ring with a cutting blade at the distal end is commonly used in Florida (Aponte Morán et al., 1977; Crane and Campbell, 1991). Other picking aids such as ladders and mobile hydraulic lifts are also used. Time of harvesting depends upon cultivar, the intended market and market demand. In Florida, green mangoes may be picked after March, while fruit-picking time for the fresh market depends upon the cultivar reaching the mature stage desired (Crane and Campbell, 1991). In Puerto Rico, mangoes are harvested from March to November, depending upon cultivar, market price and the date when flowering was induced. The mango season in California is restricted to September/November, and in Hawaii the main season is May to August. Approximately 50% of mangoes produced in California are certified organic (Linden, 2006).

13.13 Conclusions Differences in mango culture are due to the climatic and edaphic conditions, available information and technology, and tradition in each production area. The interaction of climate and cultural practices, for example irrigation, fertilizer, pruning, etc., that are essential for optimizing crop yields and quality is not completely understood. None the less, horticultural systems can be developed and tested that can impact fruit production and quality. It is important that area- and, in many cases, site- and cultivar-specific cultural information and practices need to be developed to optimize production and fruit quality. This chapter has addressed the current state of mango culture in four different production areas, and has emphasized improvements that are essential for a prosperous industry.

Ackowledgements The Mexican co-author acknowledges the following INIFAP researchers, based at several Research Stations (CE) and states: Ernesto Sánchez-Sánchez, CE-Valle del Yaqui (Sonora); Camerino Guzmán-Estrada, CE-Sur de Sinaloa (Sinaloa); R. Mosqueda-Vázquez (deceased) and Enrique N. Becerra-Leor, CE-Cotaxtla (Veracruz); Fulgencio M. Tucuch-Cauich, CE-EDZNA (Campeche);

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Rubén Cruzaley-Sarabia, CE-Iguala (Guerrero); Víctor Medina-Urrutia, CE-Tecomán (Colima); Víctor Palacio-Martínez, CE-Rosario Izapa (Chiapas).

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J.H. Crane et al. Núñez-Elisea, R., Ferreira, W., Caldeira, M.L. and Davenport, T.L. (1989) Marcottage of mango: a useful tool for physiological studies of flower induction. (Abstract). In: Proceedings of the 86th Annual Meeting of the American Society for Hortcultural Science, Ames, Iowa, p. 115. Núñez-Elisea, R., Davenport, T.L. and Caldiera, M.L. (1991) An experimental system to study mango flowering using containerized trees propagated by air-layering. Proceedings of the Florida State Horticultural Society 104, 39–41. Núñez-Elisea, R., Ferreira, W., Caldeira, M.L. and Davenport, T.L. (1992) Adventitious rooting of ‘Tommy Atkins’ mango air layers induced with naphthaleneacetic acid. HortScience 27, 926. Oosthuyse, S.A. (1995) Pruning of mango trees: an update. South African Mango Growers’ Association Yearbook 15, 1–15. Oosthuyse, S.A. and Jacobs, G. (1995) Relationship between branching frequency, and growth, cropping and structural strength of 2-year-old mango trees. Scientia Horticulturae 64, 85–93. Pal, R.N. and Chadha, K.L. (1982) Deblossoming mangoes with cycloheximide. Journal of Horticultural Science 57, 331–332. Perez, A. and Pollack, S. (2007) Fruit and Tree Nuts Outlook. FTS-327. United States Department of Agriculture (USDA) Economic Research Service, Washington, DC, pp. 13–14. Pérez-Barraza, M.H., Salazar-García, S. and Vázquez-Valdivia, V. (2000) Delayed inflorescence bud initiation, a clue for the lack of response of the ‘Tommy Atkins’ mango to promoters of flowering. Acta Horticulturae 509, 567–572. Pérez-Barraza, M.H., Vázquez-Valdivia, V. and Salazar-García, S. (2006a) Defoliación de brotes apicales y su efecto sobre la diferenciación floral del mango ‘Tommy Atkins’. Fitotecnia Mexicana 29, 313–319. Pérez-Barraza, M.H., Vázquez-Valdivia, V. and Salazar-García, S. (2006b) Manipulación de la floración y cosecha. In: Vázquez-Valdivia, V. and Pérez-Barraza, M.H. (eds) El Cultivo del Mango: Principios y Tecnología de Producción. Libro Técnico No. 1. Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), Centro de Investigación Regional Pacífico Centro (CIRPAC), Campo Experimental Santiago Ixcuintla, Santiago Ixcuintla, Mexico, pp. 187–209. Pinto, A.C. de Q. (2000) A teorática no Cultivo da Manga: Sinopse. Embrapa Cerrados, Planaltina, Brasilia, Brazil. Pinto, A.C. de Q. (2004) Melhoramento genético da manga (Mangifera indica L.) no Brasil. In: Rozane, D.E., Darezzo, R.J., Aguiar, R.L., Aguilera, G.H.A. and Zambolim, L. (eds) Manga, Produção Integrada, Industrilalização e Comercialização. UFV, Viçosa, Brazil, pp. 17–78. Pinto, A.C. de Q. and Genú, P.J. de C. (1981) Influência do adubo orgânico e de sementes sem endocarpo sobre a germinação e vigor de porta-enxertos de mangueira. Pesquisa Agropecuária Brasileira 16, 111–115. Pinto, A.C. de Q. and Ramos, V.H.V. (1998) Formação do pomar. Guia Técnico do Produtor Rural 18, Embrapa Cerrados, Brasilia, Brazil, p. 2. Pinto, A.C. de Q., Ramos, V.H.V., Junqueira, N.T.V., Lobato, E. and de Souza, D.M. (1994) Relação Ca/N nas folhas e seu efeito na produção e qualidade da manga ‘Tommy Atkins’ sob condições de Cerrados. (Abstract). Congresso Brasileiro de Fruticultura 13, Salvador, Bahia, Brazil, p. 763. Ploetz, R.C. (1994) Mango disease caused by fungi. In: Ploetz, R.C., Zentmyer, G.A., Nishijima, W., Rohrbach, K. and Ohr, H.D. (eds) Compendium of Tropical Fruit Diseases. American Phytopathological Society (APS) Press, St Paul, Minnesota, pp. 34–40.

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Ploetz, R.C. (2003) Diseases of mango. In: Ploetz, R.C. (ed.) Diseases of Tropical Fruit Crops. CAB International, Wallingford, UK, pp. 327–363. Ponce-González, F. and Salazar-García, S. (1992) Etiología del cancro del mango (Mangifera indica L.) cv. Manila en las Varas, Nayarit, México. Revista Mexicana de Fitopatologia 10, 153–155. Quayle, R.G., Cram, R.S. and Burgin, M.G. (1995) Climatic Averages and Extremes for US Cities. Historical Climatology Series 6-3. US Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), Ashville, North Carolina, pp. 76–79. Rajan, S. and Ram, S. (1988) Studies on the root regeneration in mango air-layers. Acta Horticulturae 231, 192–197. Raymond, L., Schaffer, B., Brecht, J.K. and Hanlon, E.A. (1998) Internal breakdown, mineral element concentration, and weight of mango fruit. Journal of Plant Nutrition 21, 871–889. Rossetto, C.J., Ribeiro, I.J.A., Gallo, P.B., Soares, N.B., Bortoletto, N. and Paulo, E.M. (1996) Mango breeding for resistance to diseases and pests. Acta Horticulturae 455, 299–304. Salazar-García, S. and Vázquez-Valdivia, V. (1997) Physiological persistence of paclobutrazol on the ‘Tommy Atkins’ mango (Mangifera indica L.) under rainfed conditions. Journal of Horticultural Science 72, 339–345. Salazar-García, S., Gutiérrez-Camacho, G., Becerra-Bernal, E. and Gómez-Aguilar, R. (1993) Diagnóstico nutricional del mango en San Blas, Nayarit. Revista Fitotecnia Mexicana 16, 190–202. Sandoval-Esquivez, A., Hernández, O.J., Montecillo, T.J.L. and Quilantan, C.J. (1993) Manual de Producción de Mango en la Costa de Chiapas. Publicación especial No. 1. Campo Experimental Rosario Izapa, Centro de Investigación Regional Pacífico Sur (CIRPS), Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), Secretaría de Agricultura y Recursos Hidráulicos (SARH), Tapachula, Chiapas, Mexico. Santos Filho, H.P., Tavares, S.C.C. de H., Matos, A.P., Costa, V.S. de O., Moreira, W.A. and Santos, C.C.F dos (2002) Doenças, monitoramento e controle. In: Genu, P.J.C. and Pinto, A.C. de Q. (eds) A Cultura da Mangueira. Embrapa Informação Tecnológica, Brasília, Brazil, pp. 300–352. Sauls, J.W. and Campbell, C.W. (1980) Mango Propagation. Fact Sheet FC-58. Florida Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences, Gainesville, Florida. Schacht, H. (1992) Desert green. California Farmer 275, 10–11. Schaffer, B., Whiley, A.W. and Crane, J.H. (1994) Mango. In: Schaffer, B. and Andersen, P.C. (eds) Handbook of Environmental Physiology of Fruit Crops, Vol. II, Sub-tropical and Tropical Crops. CRC Press, Boca Raton, Florida, pp. 165–197. Schaffer, B., Davies, F.S. and Crane, J.H. (2006) Responses of subtropical and tropical fruit trees to flooding in calcareous soil. HortScience 41, 549–555. Schnell, R.J. and Knight, R.J., Jr (1991) Are polyembryonic mangos dependable sources of nucellar seedlings for rootstocks? Proceedings of the Florida State Horticultural Society 104, 44–47. Schnell, R.J. and Knight, R.J., Jr (1992) Frequency of zygotic seedlings from five polyembryonic mango rootstocks. HortScience 27, 174–176. Schnell, R.J., Knight, R.J., Jr and Harkins, D.M. (1994) Eliminating zygotic seedlings in ‘Turpentine’ mango rootstock populations by visual roguing. HortScience 29, 319–320. Scott, L. (1990) A Tropical Oasis. The Press-Enterprise, Riverside County, California.

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Young, T.W. and Koo, R.C.J. (1971) Variations in mineral content of Florida mango leaves. Proceedings of the Florida State Horticulture Society 84, 298–303. Young, T.W. and Koo, R.C.J. (1974) Increasing yield of ‘Parvin’ and ‘Kent’ mango on Lakewood sand by increased nitrogen and potassium fertilization. Proceedings of the Florida State Horticulture Society 87, 380–384. Young, T.W. and Miner, J.T. (1960) Response of ‘Kent’ mangos to nitrogen fertilization. Proceedings of the Florida State Horticulture Society 73, 334–336. Young, T.W. and Miner, J.T. (1961) Relationship of nitrogen and calcium to ‘soft-nose’ disorder in mango fruits. Proceedings of the Florida State Horticulture Society 78, 201–208. Young, T.W. and Sauls, J.W. (1989) The Mango Industry of Florida. Bulletin 189. Florida Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences, Gainesville, Florida. Young, T.W., Koo, R.C.J. and Miner, J.T. (1962) Effects of nitrogen, potassium and calcium fertilization on ‘Kent’ mangos on deep, acid, sandy soil. Proceedings of the Florida State Horticulture Society 75, 364–371. Young, T.W., Koo, R.C.J. and Miner, J.T. (1965) Fertilizer trials with ‘Kent’ mangos. Proceedings of the Florida State Horticulture Society 78, 369–375. Zude-Sasse, M. and Schaffer, B. (2000) Influence of soil oxygen depletion on iron uptake and reduction in mango (Mangifera indica L.) root. Proceedings of the Florida State Horticultural Society 113, 1–4.

14

Postharvest Physiology J.K. Brecht1 and E.M. Yahia2 1University

2Universidad

of Florida, Florida, USA Autónoma de Querétaro, Querétaro, Mexico

14.1 Introduction 14.2 Contribution of Mango Fruit to Human Nutrition and Health 14.3 Mango Ripening Physiology Climacteric behaviour Ethylene production and responses 14.4 Compositional Changes during Fruit Maturation and Ripening Organic acids Soluble sugars Structural polysaccharides Pigments and colour Phenolic compounds Flavour (taste, aroma) 14.5 Transpiration and Water Loss 14.6 Physical Damage and Physiological Disorders Chilling injury (CI) Heat injury 14.7 Modified Atmospheres (MA) and Controlled Atmospheres (CA) Injuries associated with MA and CA Modified atmosphere packaging (MAP) Semipermeable coatings Insecticidal CA 14.8 Manipulation of Mango Postharvest Physiology by Molecular Biology 14.9 Conclusions

484 485 491 491 493 494 494 495 496 498 502 504 507 507 507 508 508 510 511 513 514 515 516

14.1 Introduction Successful postharvest handling of mangoes requires knowledge of the postharvest physiology of the fruit and how the fruit physiology determines the best handling practices to maintain and develop high fruit quality. For example, mango, like banana, tomato and avocado, is a climacteric fruit, which means 484

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that it may be picked when mature but before ripening has commenced, and subsequently ripened postharvest. As mango fruit mature on the tree and begin to ripen, eating quality improves, but potential marketable life decreases due to the difficulty of controlling the ripening changes once they have been initiated, increased bruising susceptibility and increased decay. Susceptible mango cultivars tend to develop more internal breakdown (jelly seed, soft nose and stem-end cavity) the longer that harvesting is delayed (Raymond et al., 1998; see Galán Saúco, Chapter 9, this volume). As a tropical species, mangoes are subject to chilling injury (CI), which limits the use of refrigeration to maintain postharvest quality. Mangoes are also subject to other physiological disorders, physical damage and decay, the symptoms of which may make the fruit unmarketable (Yahia et al., 2006a). Mangoes harvested at a mature but unripe stage of development (‘maturegreen’) can be stored in the unripe state as long as the initiation of ethylene production and hence ripening is avoided. The initiation of ripening can be avoided by prompt cooling and storage at a low temperature at which ripening does not occur or, more effectively, by changing the composition of the storage atmosphere so that the oxygen (O2) level is reduced and carbon dioxide (CO2) level is raised. This latter approach is called either modified atmosphere (MA) or controlled atmosphere (CA) storage, depending on the degree of control. These technologies slow fruit metabolism and specifically inhibit the initiation of ethylene production. With MA or CA transport or storage, mangoes can typically be maintained in a firm, green condition for several days longer than can be achieved with normal refrigerated air storage. However, there are limits to the levels of O2 and CO2 that can be tolerated by mangoes and these limits are affected by several factors, including cultivar, maturity or ripeness stage, storage temperature and storage time (Yahia, 1998). Mango postharvest physiology and technology have been described in previous reports, book chapters and reviews (Subramanyam et al., 1975; Lakshminarayana, 1980; Ledger, 1986; Peacock, 1986; Lizada, 1991; Coates and Johnson, 1993; Johnson and Coates, 1993; Lizada, 1993; Heather, 1994; Jacobi et al., 1994; Johnson et al., 1997; Mitra and Baldwin, 1997; Tharanathan et al., 2006).

14.2 Contribution of Mango Fruit to Human Nutrition and Health Consumers are becoming aware of the nutritional and health benefits of fresh fruits and vegetables. Mango fruit are a rich source of vitamin C (Table 14.1), although the content decreases during ripening (Thomas, 1975; Vinci et al., 1995). ‘Raspuri’ mango is rich in vitamin C (300 mg/100 g fresh fruit) during the early stages of development, but the concentration is less (39.1–69.5 mg/100 g) at maturity (Siddappa and Bhatia, 1954). The content of vitamin C was between 13 and 178 mg/100 g in the ripe fruit of 50 cultivars surveyed by Singh (1960). The vitamin C content in fully grown mango fruit of cultivars in Puerto Rico ranged between 6 and 63 mg/100 g (Iguina de George

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Table 14.1. Composition of the edible portion of mango fruit (Source: USDA/ARS, 2007). Nutrient

Unit

Value per 100 g edible portion

Water Energy Energy Protein Total lipid (fat) Ash Carbohydrate, by difference Fibre, total dietary Sugars, total Minerals Calcium Iron Magnesium Phosphorus Potassium Sodium Zinc Copper Manganese Selenium Vitamins Vitamin C (total ascorbic acid) Thiamine Riboflavin Niacin Pantothenic acid Vitamin B6 Folate, total Folic acid Folate, food Vitamin B12 Vitamin A Retinol Vitamin E (D-tocopherol) Vitamin K (phylloquinone) Lipids Fatty acids, total saturated 4:0 6:0 8:0 10:0 12:0 14:0 16:0 18:0 Fatty acids, total monounsaturated

g kcal kJ g g g g g g

81.71 65 272 0.51 0.27 0.50 17.00 1.8 14.80

mg mg mg mg mg mg mg mg mg Pg

10 0.13 9 11 156 2 0.04 0.110 0.027 0.6

mg mg mg mg mg mg Pg Pg Pg Pg IU Pg mg Pg

27.7 0.058 0.057 0.584 0.160 0.134 14 0 14 0.00 765 0 1.12 4.2

g g g g g g g g g g

0.066 0.000 0.000 0.000 0.000 0.001 0.009 0.052 0.003 0.101 (Continued)

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Table 14.1. Continued Nutrient

Unit

16:1 undifferentiated 18:1 undifferentiated 20:1 22:1 undifferentiated Fatty acids, total polyunsaturated 18:2 undifferentiated 18:3 undifferentiated 18:4 20:4 undifferentiated 20:5 n-3 22:5 n-3 22:6 n-3 Cholesterol Amino acids Tryptophan Threonine Isoleucine Leucine Lysine Methionine Phenylalanine Tyrosine Valine Arginine Histidine Alanine Aspartic acid Glutamic acid Glycine Proline Serine Other Ethanol Caffeine Theobromine E-Carotene D-Carotene E-Cryptoxanthin Lycopene Lutein + zeaxanthin

g g g g g g g g g g g g g

0.048 0.054 0.000 0.000 0.051 0.014 0.037 0.000 0.000 0.000 0.000 0.000 0

g g g g g g g g g g g g g g g g g

0.008 0.019 0.018 0.031 0.041 0.005 0.017 0.010 0.026 0.019 0.012 0.051 0.042 0.060 0.021 0.018 0.022

g mg mg Pg Pg Pg Pg Pg

Value per 100 g edible portion

0.0 0 0 445 17 11 0 0

et al., 1969). Vitamin C content was 105.2, 65.7 and 17.3 mg/100 g in ‘Langra’, ‘Ashwini’ and ‘Fazli’ mangoes, respectively (Gofur et al., 1994), and decreased rapidly 5–7 weeks after fruit set, and when ripe fruit were stored at room temperature. Vitamin B1 (thiamine) in two mango cultivars was 35–60 Pg/100 g,

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and vitamin B2 (riboflavin) in three cultivars was 45–55 Pg/100 g (Stahl, 1935). Thiamine content of four Philippine cultivars was 57–600 Pg/100 g, and riboflavin content of three cultivars was 37–730 Pg/100 g (Quinones et al., 1944). Folic acid in green mangoes was 36 mg/100 g (Gosh, 1960). The mango fruit is a rich source of carotenoids, some of which function as provitamin A: E-carotene (all-trans), E-cryptoxthanin (all-trans and cis), zeaxanthin (all-trans), luteoxanthin isomers, violaxanthin (all-trans and cis) and neoxanthin (all-trans and cis) (Mercadante et al., 1997; Yahia et al., 2006b; Ornelas-Paz et al., 2007, 2008). Total carotenoid content rose from 12.3 to 38.0 Pg/g in ‘Keitt’ and from 17.0 to 51.2 Pg/g in ‘Tommy Atkins’ from the maturegreen to the ripe stage (Mercadante and Rodriguez-Amaya, 1998), and ripening alterations occurred principally in the major carotenoids, violaxantin and E-carotene. With ‘Keitt’, all-trans-E-carotene, all-trans-violaxanthin and 9-cis-violaxanthin increased from 1.7, 5.4 and 1.7 Pg/g, respectively, in the mature-green fruit to 6.7, 18.0 and 7.2 Pg/g in the ripe fruit (Mercadante and Rodriguez-Amaya, 1998). In ‘Tommy Atkins’ these carotenoids increased from 2.0, 6.9 and 3.3 Pg/g to 5.8, 22.4 and 14.5 Pg/g, respectively, during ripening. Geographic effects were reported to be substantial (Mercadante and Rodriguez-Amaya, 1998). Some of the cis and trans isomers of provitamin A reported in ‘Haden’ and ‘Tommy Atkins’ mangoes include 13-cis-E-carotene (trace amounts), trans-E-carotene (12.5–15.5 Pg/g) and trans-D-cryptoxanthin (0.3–0.4 Pg/g) (Godoy and Rodriguez-Amaya, 1994). In processed mango juice, violaxanthin was not detected, auroxanthin appeared at an appreciable level, and E-carotene was the principal carotenoid (Mercadante and Rodriguez-Amaya, 1998). The major carotenoid in ‘Bourbon’, ‘Haden’, ‘Extreme’, ‘Golden’ and ‘Tommy Atkins’ mangoes is E-carotene (48–84% of the total), while epoxycarotenoids (violaxanthin, luteoxanthin and mutatoxanthin) constitute 13–49% of the total (Godoy and Rodriguez-Amaya, 1989). Mean vitamin A in these mangoes (retinol equivalents/100 g) ranges from 115.3 (‘Haden’) to 430.5 (‘Extreme’). Children in Senegal with normal cytology had higher serum retinol and E-carotene levels than those with abnormal cytology after massive oral doses of vitamin A and consumption of mangoes (Carlier et al., 1992). Mango retinol is highly bioavailable (82% efficiency) by estimating vitamin A and carotene reserves in the liver and plasma of rats (Yuyama et al., 1991). During mango fruit ripening, vitamin A increases – ripe mangoes are tenfold richer in carotene than partially ripe fruit, while unripe green mangoes contain only trace amounts (Modi and Reddy, 1967). Mevalonic acid, a precursor of carotenoids, increases progressively during mango ripening (Modi and Reddy, 1967). Vitamin A equivalents in 100 g of mango fruit are 1000 to 6000 IU (Singh, 1960). The E-carotene content of the fruit of 30 mango cultivars in Puerto Rico ranged from 400 to 800 IU/100 g fresh fruit (Iguina de George et al., 1969). The development of E-carotene in mangoes held at 16–21°C was lower than that at 20–28°C (Vazquez-Salinas and Lakshminarayana, 1985). Jungalwala and Cama (1963) identified 16 different carotenoids in ‘Alphonso’ mangoes, and E-carotene accounted for 60% of the total. Of the oxycarotenoids, luteoxanthin, violaxanthin and cis-violaxanthin were present in significant amounts.

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All the oxycarotenoids were present as E-carotene derivatives, mostly as epoxides of zeaxanthin. Variation in carotenoid content, as in many other constituents, is due to several factors, including cultivar, geography, climate, storage/processing conditions and analytical procedures employed. Several carotenoids occur in fruit of different mango cultivars (Cano and de Ancos, 1994; Ben-Amotz and Fishler, 1998; Chen et al., 2004), but only a few of them occur in significant concentrations (Ornelas-Paz et al., 2007). Mercadante et al. (1997) quantified several carotenoids in ‘Keitt’ mangoes; the most predominant ones were all-trans-E-carotene, all-trans-violaxanthin and 9-cis-violaxanthin, accounting for 27, 38 and 18% of the total carotenoid content, respectively. Similar findings have been reported for crude extracts from other mango cultivars (Mercadante and Rodríguez-Amaya, 1998; Pott et al., 2003a, b). Carotenoids are responsible for the yellow-orange colour of mango mesocarp (Vázquez-Caicedo et al., 2004). All-trans-E-carotene and the dibutyrates of all-trans-violaxanthin and 9-cis-violaxanthin are the main carotenoids in ‘Ataulfo’ and ‘Manila’ mangoes (Yahia et al., 2006b; Ornelas-Paz et al., 2008; Fig.14.1). The content of these carotenoids during fruit ripening increased exponentially in ‘Ataulfo’ and exponentially or in a second order polynomial manner in ‘Manila’, and the highest correlation coefficients were obtained for the relationships between the internal and external a* and h° colour values and the content of the evaluated carotenoids in both mango 3.5 All-trans-violaxanthin 9-cis-Violaxanthin

Pulp carotenoid content (mg/100 g)

3.0

All-trans-β-carotene 2.5

2.0

1.5

1.0

0.5

0.0 ‘Haden’

‘Ataulfo’ ‘Tommy Atkins’

‘Manila’

‘Criollo’

‘Kent’

‘Paraíso’

Cultivar

Fig. 14.1. Content of selected carotenoids in pulp of several mango cultivars. Data represent the mean of eight individual observations for each cultivar ± standard error (Source: Ornelas-Paz et al., 2007).

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cultivars (R = 0.81–0.94). Equations to predict the content of the most important carotenoids in ‘Manila’ and ‘Ataulfo’ mangoes on the basis of their internal and external colour values were obtained by Ornelas-Paz et al. (2008). The content of D-tocopherol is approx. 0.5 mg/100 g in an unidentified cultivar from Costa Rica (Burns et al., 2003), while the United States Department of Agriculture (USDA) Nutrient Database (USDA/ARS, 2007) indicates an D-tocopherol content of 1.12 mg/100 g. Ornelas-Paz et al. (2007) found that D-tocopherol is the only detectable tocopherol in seven mango cultivars (Fig. 14.2); ‘Haden’ and ‘Tommy Atkins’ mangoes had the highest amounts (380 and 470 Pg/100 g, respectively), with c.200–250 Pg/100 g in the other cultivars. Mango fruit are rich in several types of antioxidant phytochemicals, that is carotenoids and phenolics (Ornelas-Paz et al., 2007; Rocha-Ribeiro et al., 2007). Botting et al. (1999), showed that mango fruit have antimutagens and the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline. Percival et al. (2006) observed that whole mango juice inhibited cell proliferation in the leukaemic cell line HL-60 and also inhibited the neoplastic transformation of BALB/3T3 cells. García-Solís et al. (2008) studied the effect of ‘Ataulfo’ mango consumption on chemically induced mammary carcinogenesis and plasma antioxidant capacity in rats treated with N-methyl-N-nitrosourea (MNU). Mango was administered in the drinking water (0.02–0.06 g/ml) during both short-term and long-term (LT) periods to rats treated or not with

600

α-Tocopherol (μg/100 g)

500

400

300

200

100

0 ‘Haden’ ‘Ataulfo’ ‘Tommy ‘Manila’ ‘Criollo’ Atkins’ Cultivar

‘Kent’

‘Paraíso’

Fig. 14.2. The content of D-tocopherol in the pulp of several mango cultivars. Data represent the mean of eight individual observations for each cultivar ± standard error (Source: Ornelas-Paz et al., 2008).

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MNU. Rats treated with MNU showed no differences in mammary carcinogenesis or in plasma antioxidant capacity measured by both ferric reducing/ antioxidant power (FRAP) and total oxyradical scavenging capacity assays. However, in animals not treated with MNU, but with an LT intake of mango, the plasma antioxidant capacity as measured by the FRAP assay tended to increase in a dose-dependent manner. This suggests that mango consumption by healthy subjects may increase antioxidants in plasma.

14.3 Mango Ripening Physiology Ripening is part of the natural senescence of mango fruit. It is an irreversible process that contributes to organelle disruption and changes in chemical constituents, flavour and texture. While ripening improves the eating quality of mango fruit, the postharvest life of the fruit is reduced. Natural senescence, and thus ripening, is aggravated and promoted by ethylene, mechanical injury and high temperature. This process can be delayed by lower temperature, elimination of mechanical damage and reducing ethylene production (Yahia et al., 2006a). Ripening of mango is inhibited while fruit are attached to the tree, and respiration and ripening are stimulated upon detachment (Lakshminarayana, 1973). Burg and Burg (1962) reported that ethylene levels in the tissues of mature-green, attached mango fruit were relatively high (1.87 Pl/l) and suggested that ethylene was ineffective for promoting ripening due to a ripening inhibitor supplied by the tree. Changes associated with mango fruit ripening include: (i) flesh colour from greenish yellow to yellow to orange in all cultivars (Plate 80a); (ii) skin colour from green to yellow in some cultivars (Plate 80b); (iii) chlorophyll decreases and carotenoid content increases; (iv) flesh firmness decreases and juiciness increases; (v) starch is converted into sugars; (vi) total soluble solids (TSS) content increases; (vii) titratable acidity decreases; (viii) characteristic aroma volatiles increase; (ix) CO2 production rate increases from 40–50 to 160–200 mg/kg/h at 20°C; and (x) ethylene production rate increases from 0.1–0.2 to 1–3 Pl/kg/h at 20°C. Gowda and Huddar (2000) found the changes in eight mango selections during ripening included reductions in fruit weight, volume, length, thickness, firmness, pulp content, pulp:peel ratio, starch and vitamin C, and increases in TSS, pH, total sugars, sugar:acid ratio, pulp carotenoid content and peel colour.

Climacteric behaviour Mango is a climacteric fruit, exhibiting a climacteric pattern of respiration and an increase in ethylene production during ripening (Cua and Lizada, 1990; Reddy and Srivastava, 1999; Lalel et al., 2003; Fig. 14.3). The initiation of ethylene production within the fruit triggers and coordinates the changes that occur during ripening. These changes include colour changes in the peel and flesh, softening of the flesh, and development of sweet flavour and

J.K. Brecht and E.M. Yahia

6

50

5

40

4 3 2 Hard green Half ripe

1

Sprung green Ripe

Ethylene (mmol/kg/h)

CO2 (mmol/kg/h)

492

Hard green Sprung green Half ripe Ripe

30 20 10 0

0 0

1

2

3 4 5 6 7 8 Ripening period (days)

9 10

0

1

2

3 4 5 6 7 8 Ripening period (days)

9 10

Fig. 14.3. The climacteric pattern of respiration and ethylene production during mango fruit ripening (Source: Lalel et al., 2003).

aroma. Mangoes can be ripened after harvest when picked at physiological maturity (mature-green), when they are fully sized, but before ripening has been initiated. Maturity indices are chosen to predict fruit quality potential and postharvest behaviour (Peacock et al., 1986; Medlicott et al., 1988). After harvest, the fruit is then cooled and isolated from possible sources of ethylene (ripening fruit, engine exhaust, smoke, etc.) during storage or shipping. This is the primary strategy used to control ripening and thus extend shelf life. Respiration patterns and ripening behaviour vary among cultivars, with different climatic conditions and growing locations (Krishnamurthy and Subramanyam, 1970). Respiration is very high after fruit set and then declines and is maintained at a low rate until fruit ripening begins. The rise in respiration and ethylene production during the climacteric is related to fruit ripening. The respiratory peak in ‘Alphonso’ mangoes harvested mature-green occurs 5 days after harvest, and the fruit ripens within 7 or 8 days (Karmarkar and Joshi, 1941), while in ‘Kent’ and ‘Haden’ mangoes the peak occurs on days 9 and 11, respectively (Burg and Burg, 1962), and in ‘Pairi’ mangoes on day 9 (Krishnamurthy and Subramanyam, 1970). These differences are normal due to differences in location, climatic conditions, orchard and tree conditions, and postharvest temperature. The rise in the climacteric respiration in ‘Dashehari’, ‘Amrapali’ and ‘Rataul’ mangoes coincides with the highest level of sucrose and polygalacturonase (PG; EC 3.2.1.15) activity in ripening fruit (Kalra and Tandon, 1983). Respiration and ethylene production are excellent maturity indices, but require considerable expense to measure. The expression of alternative oxidase (Aox) and uncoupling proteins (Ucp) has been investigated during mango ripening and compared with the expression of peroxisomal thiolase (EC 2.3.1.16), a ripening marker in mango (Considine et al., 2001). The multigene family for Aox in mango is expressed differentially during mango fruit ripening. Abundance of Aox message and protein peaks at the ripe stage, while expression of the single gene for the Ucp peaks at the turning or half-ripe stage, and the protein abundance peaks at the ripe stage. Proteins of the cytochrome chain peak at the mature-green

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stage, suggesting that increases in cytochrome chain components are important for facilitating the climacteric burst of respiration and that Aox and Ucp are important in postclimacteric senescence processes (Considine et al., 2001). Because both message and protein for the Aox and Ucp increase in a similar pattern, their expression is not controlled in a reciprocal manner but may be active simultaneously. Fruit slicing affects respiration rate (Allong et al., 2001). Slicing of maturegreen ‘Julia’ and ‘Graham’ mangoes increased respiration rate immediately after cutting, but it decreased significantly within the first 12 h of storage at 5 or 10°C, yet still remained at levels above that of the intact fruit throughout the storage period. The effect of slicing on half-ripe and firm-ripe fruit is an initial increase in respiration followed by a decline to levels of the intact fruit.

Ethylene production and responses Mangoes have a moderate ethylene production peak of 1–3 Pl/kg/h during ripening at 20°C. Ethylene, applied directly or as ethrel, induces faster and more uniform fruit softening (Lakshminarayana, 1973; Barmore, 1974; Lakshminarayana et al., 1974; Sornsrivichai and Waru-Aswapti, 1989). Ethylene treatment can be prior to shipping (Barmore and Mitchell, 1975). There is disagreement regarding the effect of ethylene treatment on quality (Chaplin, 1988), and this may be related to maturity when treated. Treatment of immature fruit leads to softening, but the fruit have poor flavour. Mango fruit ripening is accompanied by increased ethylene production, which coordinates the ripening process. Mango expresses an autocatalytic increase in ethylene production during ripening (Mattoo and Modi, 1969b). Ethylene production starts before full ripeness is reached (Burg and Burg, 1962; Cua and Lizada, 1990). Ethylene production in unripe mango fruit is very low (300 volatiles (Pino et al., 2005), but not all of them are odour-active and thus do not contribute significantly to aroma. Studies have identified the volatiles of mango, but not their aromatic activity. The predominant volatiles in some cultivars are monoterpenes and sesquiterpenes (MacLeod and De Troconis, 1982; Engel and Tressl, 1983; Pino et al., 2005), as well as lactones and some fatty acids (MacLeod and Pieris, 1984; MacLeod and Snyder, 1985; Wilson et al., 1990). However, there is no indication of the presence of a single flavour impact component (Engel and Tressl, 1983). Some mango cultivars have a peach-like flavour that may be related to the presence of lactones, which contribute to the flavour of peaches (Prunus persica) (Lakshminarayana, 1980; MacLeod et al., 1988, Wilson et al., 1990). MacLeod et al. (1988) detected four lactones in ‘Kensington Pride’ that are also the major volatiles of peach. Monoterpene hydrocarbons represent about 49% (w/w) of the total volatiles in ‘Kensington Pride’, with D-terpinolene being the most abundant (26%) and 16 esters representing 33% (MacLeod et al., 1988). The esters, together with some of the lactones, contribute to the flavour of ‘Kensington Pride’ mangoes. Indian mangoes have a unique flavour, which has been attributed to (Z)ocimine (Engel and Tressl, 1983; Lizada, 1993). Pino et al. (1989) detected 83 volatiles in ‘Corazon’, ‘Bizcochuelo’ and ‘Super Haden’ mangoes, and total volatiles ranged between 39 mg/kg in ‘Bizcochuelo’ to 70 mg/kg in ‘Corazon’. The identified volatiles include D-cubebene, E-maaliene, ethyl(Z)-9-hexadecanoate, ethyl(Z)-9,12-octadecanoate, ethyl(Z)(Z)(Z)-6,9,12-octadecanoate, cucarvone, 2-methylpropane-2-ol, 3-methylepentan-ol, thymol and carvacrol (Pino et al., 1989). MacLeod and Snyder (1985) listed the volatile components of several mango cultivars, including ‘Willard’ and ‘Parrot’ from Sri Lanka; levels of D-terpinolene were similar to ‘Kensington Pride’. Kostermans and Bompard (1993) considered that lack of fibre was linked to an absence of aroma and flat taste and smell, but some cultivars such as ‘Kensington Pride’ are low in fibre and have a distinctive flavour and aroma profile, and a high level of D-terpinolene (Bartley and Schwede, 1987; MacLeod et al., 1988). Lipid content of the pulp is correlated with the flavour characteristics of some mango cultivars (Bandyopadhyay and Gholap, 1973a; Gholap and Bandyopadhyay, 1975b, 1976). The ripening of ‘Alphonso’ mangoes at ambient temperature is accompanied by a sharp increase in triglyceride content, together with the development of a strong aroma and flavour (Gholap and Bandyopadhyay, 1975a, 1976), but ripening at 10°C results in a bland aroma and flavour (Bandyopadhyay and Gholap, 1973b). ‘Totapuri’ mangoes,

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a bland cultivar, showed no change in the development of aroma or in the pulp lipid content (Gholap and Bandyopadhyay, 1975b). During ripening at ambient temperature, palmitoleic acid content is higher than that of palmitic acid in ‘Alphonso’, whereas ripening at low temperature does not affect the proportions of these two fatty acids (Bandyopadhyay and Gholap, 1973b). The relative proportions of palmitoleic and palmitic acids in ‘Totapuri’ mango pulp are constant irrespective of the ripening conditions (Gholap and Bandyopadhyay, 1975b). Gholap and Bandyopadhyay (1976, 1980) suggested that the relative contents of palmitic and palmitoleic acids determine the flavour quality of mango fruit. The absence of lactones having coconut-like odour notes in ‘Totapuri’ mangoes may be significant for differentiating its aroma characteristics from ‘Alphonso’, together with the presence of certain similar and dissimilar components (Bandyopadhyay, 1983). The aroma of green mangoes has been attributed to cis-ocimine in ‘Alphonso’ and E-myrcene in ‘Batali’ mangoes (Gholap and Bandyopadhyay, 1976; Bandyopadhyay, 1983). Table 14.3 lists characteristic aromas of ‘Alphonso’ and ‘Totapuri’ mangoes and their possible chemical identities. In almost all fruits, aromatic volatiles are produced at later stages of ripening (Yahia, 1994). Tree-ripe ‘Tommy Atkins’ mangoes produce higher levels of all aroma volatiles except hexanal than do mature-green fruit (Bender et al., 2000a). Both mature-green and tree-ripe mangoes stored in 25 kPa CO2 tend to have lower terpene (especially p-cymene) and hexanal concentrations than those stored in 10 kPa CO2 and air-stored fruit. Acetaldehyde and ethanol levels tend to be higher in tree-ripe mangoes held in 25 kPa CO2 than in those from 10 kPa CO2 or air storage, especially at 8°C. Inhibition of volatile production by 25 kPa CO2 is greater in mature-green than in tree-ripe

Table 14.3. Characteristic aromas in ‘Alphonso’ and ‘Totapuri’ mangoes and their possible chemical causes (Source: Bandyopadhyay, 1983). Aroma

‘Alphonso’

‘Totapuri’

Fruit, estery

Acetaldehyde, methyl acetate, ethyl acetate, n-butyl acetate cis-Ocimine Not detected Caryophyllene-pinene Benzaldehyde Benzonitrile Not detected Detected, but not identified D-Caprolactone, D-octalactone, D-undecalactone

Propionaldehyde Methyl acetate E-Myrcene Detected, but not identified Not detected Not detected Not detected D-Terpinene Not detected Not detected

Green-mango-like Camphoraceous Earthy Almond-like Burnt-sugar-like Spicy Sweet, sugar-like Coconut oil-like

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mangoes, and at 8°C compared to 12°C for tree-ripe fruit. However, aroma volatile levels in tree-ripe mangoes from 25 kPa CO2 are equal to or greater than those in mature-green fruit treatments. Atmospheres that prolong mango shelf life by slowing ripening processes can allow tree-ripe mangoes to be stored or shipped without sacrificing their aroma quality. Quality enhancement has been used to determine properties critical to flavour acceptability of mangoes, and focus group interviews have been conducted to determine sensory attributes important to the purchase and consumption of mangoes (Malundo, 1996). Sugars and acids enhance perception of specific flavour notes in mango, including aromatics (Malundo et al., 2001).

14.5 Transpiration and Water Loss Water loss lowers fruit weight, resulting in shrivelling, and may further reduce quality by causing poor colour development and uneven ripening. Water is lost from mango fruit through stomata, lenticels and other openings. Relative humidity (RH) inside the fruit is 100% and water is lost when RH in the environment surrounding the fruit is 10 days, but injury can also occur more rapidly at higher temperatures. The heat disinfestation treatments of mangoes that are required for insect quarantine security may injure fruit that are not fully mature (Jacobi and Giles, 1997; Jacobi et al., 2001a). External symptoms of heat injury include lenticel spotting and skin browning (‘scald’) with secondary disease development, while internal symptoms include mesocarp browning, tissue cavitation and ‘starch spots’ (Jacobi and Wong, 1992; Jacobi and Giles, 1997; Mitcham and McDonald, 1997; Jacobi et al., 2001a, b). Ripening of heat-injured mangoes may also be inhibited (Jacobi et al., 2001a, b).

14.7 Modified Atmospheres (MA) and Controlled Atmospheres (CA) Long-term marine shipping in MA and CA has been used for transit from several countries (Yahia, 1993). Research results are very contradictory due to

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the different cultivars and maturity stages of mangoes used, different atmospheres implemented and lack of experimental controls. Optimum condition for prolonged shipping or storage is reported to be 3–5 kPa O2 plus 5–10 kPa CO2, which can delay ripening, but the benefits are not very significant. Use of CA and MA would most likely be beneficial in delaying fruit ripening during marine transport for 2 weeks or more. Bender et al. (2000b) determined the tolerance of preclimacteric ‘Haden’ and ‘Tommy Atkins’ to reduced O2 levels for storage times in typical marine shipments. They reported that mangoes can tolerate 3 kPa O2 for 2–3 weeks at 12–15°C and that tolerance of low O2 decreases as mangoes ripen. All low O2 treatments reduced mature-green mango respiration; however, elevated ethanol production occurred in 2 and 3 kPa O2 storage, with the levels two to threefold higher in ‘Tommy Atkins’ than in ‘Haden’. ‘Haden’ fruit at the onset of the climacteric accumulated ethanol in 4 kPa O2 and produced 10–20 times more ethanol in 2 and 3 kPa O2 than preclimacteric fruit. There were no visible injury symptoms, but off-flavour developed in mature-green fruit at 2 kPa O2 and in ripening-initiated fruit at 2 and 3 kPa O2. Ethanol production was not affected by storage in 25 kPa CO2. Ethylene production was reduced slightly by low O2; however, ‘Haden’ fruit also showed a residual inhibitory effect on ethylene production at 2 or 3 kPa O2 storage, while ‘Tommy Atkins’ fruit stored in 2 kPa O2 produced a burst of ethylene upon transfer to air at 20°C. Fruit firmness, total sugars and starch levels did not differ among treatments, but 2, 3 or 4 kPa O2 and 25 kPa CO2 maintained significantly higher acidity than 5 kPa O2 or air. The epidermal ground colour responded differently to low O2 and high CO2 in the two cultivars. Only 2 kPa O2 maintained ‘Haden’ colour better than air, while all low O2 levels maintained ‘Tommy Atkins’ colour better than air. High CO2 was more effective than low O2 in maintaining ‘Haden’ colour, but had about the same effect as low O2 on ‘Tommy Atkins’. Properly selected atmospheres, which prolong mango shelf life by slowing ripening processes, can allow tree-ripe mangoes to be stored or shipped without sacrificing their superior aroma. Mature-green and tree-ripe ‘Tommy Atkins’ mangoes were stored for 21 days in air or in a CA (5 kPa O2 + 10 kPa or 25 kPa CO2) at 12°C (mature-green) and at either 8 or 12°C (tree-ripe) (Bender et al., 2000a). Tree-ripe mangoes produced much higher levels of all aroma volatiles except hexanal than mature-green fruit after ripening for 2 days. Both mature-green and tree-ripe mangoes stored in 25 kPa CO2 had lower terpene (especially p-cymene) and hexanal levels than those stored in 10 kPa CO2 and air-stored fruit. Acetaldehyde and ethanol levels were higher in tree-ripe mangoes from 25 kPa CO2 than in those from 10 kPa CO2 or air storage, especially at 8°C. Inhibition of volatile production by 25 kPa CO2 was greater in mature-green than in tree-ripe mangoes, and at 8°C compared to 12°C for tree-ripe fruit. Aroma volatile levels in tree-ripe mangoes from the 25 kPa CO2 treatment equalled or exceeded those in mature-green fruit treatments. Mangoes have high tolerance of short-term elevated CO2 atmospheres (Yahia, 1998). Mangoes can tolerate CO2 atmospheres of up to 25 kPa for

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2 weeks at 12°C (Bender et al., 2000b). High (25 kPa) CO2 inhibits ethylene production, but increases ethanol production. Aroma volatiles are reduced following 25 kPa CO2 treatment, while 10 kPa CO2, low O2 atmospheres and storage temperature did not significantly influence production of terpene hydrocarbons, which are characteristic of Florida-type mangoes. Maturegreen ‘Tommy Atkins’ mangoes can be stored for 21 days in CA (5 kPa O2 + 10 kPa or 25 kPa CO2) at 12°C, while tree-ripe fruit can be stored for 21 days in the same atmospheres at either 8 or 12°C (Bender et al., 2000a). The quality of ‘Keitt’ mangoes was evaluated during storage for 6 days at 20°C in an extremely low O2 (LO) CA (approximately 0.3 kPa) before storage in modified atmosphere packaging (MAP) made from three, low-density polyethylene (LDPE) films with different gas permeability characteristics (González-Aguilar et al., 1997). Both LO and MA treatments delayed the losses of colour, weight and firmness. Fruit maintained good appearance with a significant delay of ripening. Mangoes are very tolerant of LO treatment; however, some MAP fruit developed a fermented taste after 10 and 20 days at 20°C. Short duration (6-day) storage of mangoes in LO did not otherwise have any deleterious effect on fruit quality during subsequent storage under MA or normal atmosphere. Properly selected atmospheres, which prolong mango shelf life by slowing ripening, permit fruit to be shipped without sacrificing superior aroma. Beaulieu and Lea (2003) studied ‘Keitt’ and ‘Palmer’ mangoes without heat treatment to assess volatile and quality changes in stored fresh-cut mangoes prepared from firm-ripe (FR) and soft-ripe (SR) fruit, and to assess what effect MAP may have on cut fruit physiology, overall quality and volatile retention or loss. Subjective appraisals of fresh-cut mangoes based on aroma and cut edge or tissue damage indicated that most SR cubes are unmarketable by day 7 at 4°C. Both cultivars stored in MAP at 4°C had almost identical O2 consumption, which is independent of ripeness. The CO2 and O2 concentrations measured for cubes stored in passive MAP indicated that the system is inadequate to prevent potential anaerobic respiration after 7 days storage.

Injuries associated with MA and CA A 10 kPa CO2 atmosphere alleviates chilling symptoms in ‘Kensington Pride’ fruit, but higher concentrations are injurious; low O2 (5 kPa) has no significant effect (O’Hare and Prasad, 1993). Higher concentrations of CO2 (>10 kPa) are ineffective for alleviating CI at 7°C, and tend to cause tissue injury and high levels of ethanol in the pulp. Injury in ‘Kensington Pride’ caused by higher levels of CO2 appears to be more severe at lower temperatures (O’Hare and Prasad 1993; Bender et al., 1994, 1995), which could be a result of either compounding injury (chilling + CO2) or reduced sensitivity of ripe mango to CO2. ‘Rad’ mangoes develop internal browning and off-flavour in atmospheres containing 6 and 8 kPa CO2 (Noomhorm and Tiasuwan, 1995). The presence of starchy mesocarp in ‘Carabao’ mangoes, which is characteristic

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of internal breakdown, increases during storage in MA (Gautam and Lizada, 1984). Fruit stored for 4–5 days have severe symptoms, including air pockets in the mesocarp resulting in spongy tissue (Nuevo et al., 1984a, b). Parenchyma cells of affected tissues have c.18 starch granules per cell, compared to c.2 starch granules in healthy adjacent cells. However, no difference in starch granule shape was detected between the spongy and healthy tissues. The spongy tissue, which usually occurs in the inner mesocarp near the seed and becomes evident during ripening, has almost ten times the starch content of healthy tissue in the same fruit. External symptoms of internal browning due to MA include failure of the peel to develop colour beyond the half-yellow stage. ‘Carabao’ mangoes stored in polyethylene bags (0.04 mm thickness) for 1 day at 25–31°C had a faint fermented odour that disappeared during subsequent ripening outside the bags (Gautam and Lizada, 1984). The fermented odour increases with time, and persists throughout ripening when the fruit are stored for 2–5 days. The respiratory quotient of this cultivar ranged from 0.59 at 21 kPa O2 to 6.03 at 2.4 kPa O2, which indicates a progressively anaerobic metabolism (Sy and Mendoza, 1984). CO2 production decreases as O2 decreases from 21 to 3 kPa, but increases at 20 kPa while the O2 concentration was 47°C killed all stages of West Indian fruit fly, Anastrepha obliqua (Macquart), in Mexican mangoes, and Sharp (1992) found a centre pulp temperature of >46°C killed all stages of Caribbean fruit fly, Anastrepha alletis (Loew), in Florida-grown mangoes. Hot water Provided that fruit are not damaged, hot water immersion is environmentally safe and efficient for killing mango pests. Use of hot water to kill fruit fly eggs and larvae intensified in the USA when the Environmental Protection Agency (EPA) removed ethylene dibromide from the market as a chemical fumigant because of health concerns (Anonymous, 1983). Sharp and Spalding (1984) showed that mangoes could be disinfested of Caribbean fruit fly using hot water. The work led to more studies in Haiti and a disinfestation method for West Indian fruit fly (Sharp et al., 1988), as well as Mediterranean fruit fly and other Anastrepha spp. in Texas and Mexico (Sharp et al., 1989a, b), Puerto Rico (Segarra-Carmona et al., 1990) and Peru (Sharp and Picho-Martinez, 1990). Nascimento et al. (1992) developed a hot water treatment for fruit flies in mangoes in Brazil. Hot-water-treated mangoes may be imported into the USA from Mexico, Central America, South America and the West Indies (Anonymous, 1994a). Typical treatments include 46.1°C for 65 min for smaller fruit to 90 min for larger fruit (Jacobi et al., 2001b). Large commercial hotwater-treatment facilities have been constructed, certified by the USDAAPHIS PPQ, and used in Mexico, Central and South America, and the West Indies. Generic guidelines for the use of hot water are provided by the USDAAPHIS PPQ manual for hot water treatment. In Australia, Smith (1992) showed that immersing five Australian mango cultivars in 48°C water for 30 min killed eggs and larvae of Bactrocera aquilonis; however, ‘Kensington Pride’ is more sensitive to hot water than to vapour heat, so the latter has been adopted for disinfestation of mangoes in Australia (Jacobi et al., 1994). Grové et al. (1997) found that treatment of several cultivars

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in hot water at 46.1°C for 90 min followed by refrigeration for 24 h did not damage fruit, although some cultivars showed severe lenticel damage. Refrigeration of ‘Tommy Atkins’ fruit immediately after treatment resulted in scald development. Weevils in ‘Alphonso’ mangoes from India were not killed when infested mangoes were immersed in water at 48–52°C for up to 90 min and 54–70°C for up to 5 min (Shukla and Tandon, 1985). Compared with hot air treatments, hot water treatments can damage the skin, partly because of rapid heat transfer from the water to the skin compared with from the skin to the centre of the fruit. Damage includes skin scalding, lenticel damage, cavities, white starchy areas in the flesh and delayed ripening (Jacobi et al., 2001b). Several factors influence damage severity after heat treatment, for example cultivar, temperature and duration (Jacobi et al., 2001b). Immature fruit have low heat tolerance, and small fruit are damaged by heat more readily than large fruit. Conditioning treatments (i.e. 37°C core temperature, for at least 12 h in air) can reduce injury, and preharvest conditions, especially rainfall before harvest, can increase skin damage (Esguerra and Lizada, 1990; Esguerra et al., 1990; Jacobi and Wong, 1992; Jacobi et al., 1994, 1995; Jacobi and Giles 1997). Better understanding of these influences could increase the commercial potential for hot water disinfestation. Hot water dips could pose human health risks. Sivapalasingam et al. (2003) reported that an outbreak of Salmonella enterica that infected 72 patients from 13 USA states may have been due to contamination of hot-water-dipped mangoes from a single farm in Brazil. No outbreaks were reported among consumers in the EU of mangoes from the same farm, and the EU does not require hot water disinfestation. Irradiation Irradiation involves γ rays (at 20 irradiation facilities have been planned, constructed or renovated in ten countries, some of which are mango exporters (Eustice, 2007). Radiation treatments have been developed for fruit flies in mangoes from Florida, Mexico, India and Australia. Von Windeguth (1986) treated mangoes with 76 Gy and disinfested them of Caribbean fruit fly eggs and larvae. Third instar Mediterranean fruit fly larvae in Mexican mangoes irradiated with 250 Gy did not emerge from pupae, and 60 Gy applied to third instar Mexican fruit fly, and West Indian fruit fly in Mexican mangoes prevented adult emergence (Bustos et al., 1992). Bustos et al. (2004) recommended a generic dose of 150 Gy for control of Mexican fruit fly (A. ludens), the West Indian fruit fly (A. obliqua), the sapote fruit fly (Anastrepha serpentina) and the Mediterranean fruit fly (C. capitata) in mango. ‘Kensington Pride’ mangoes infested with eggs and larvae of Queensland fruit fly and Bactrocera jarvisi (Tryon) are disinfested with 74–101 Gy (Heather et al., 1991). International guidelines for the use of irradiation as a phytosanitary measure are available (ISPM, 2003), and recently a fast track process has been proposed as an Annex to ISPM 28 (ISPM, 2008), which endorses irradiation

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at 70 Gy as a generic treatment to control Anastrepha spp. in fruit and vegetables by extrapolating work on mango by Bustos et al. (2004). Heather (2004) provides generic guidelines for the development of irradiation protocols for disinfestation. Fruits are never exposed to radioactive materials (Anonymous, 1986) and most modern treatment units use an electron beam process rather than a radioactive source for irradiation. Irradiation can be used for controlling seed weevil and lepidopterous pests in fruit. Seo et al. (1974) reported that 206 and 329 Gy killed mango weevil in Hawaiian mango. Thomas (1975) showed that 500 Gy killed all mango weevil larvae and pupae and 750 Gy prevented adults from emerging from mangoes in Africa. A dose of 500 Gy, however, did not disinfest ‘Alphonso’ mangoes of seed weevil (Shukla and Tandon, 1985). Indian mangoes from approved packhouses must be irradiated with a minimum of 400 Gy at an approved and certified irradiation treatment facility using Cobalt-60 (APEDA, 2007). A quarantine treatment of 300 Gy has been approved to sterilize mango seed weevil in mangoes exported from Hawaii to USA mainland markets (Follett, 2004). Follett and Lower (2000) demonstrated control of Cryptophlebia illepida (Butler), Cryptophlebia ombrodelta (Lower) and Cryptophlebia illepida (Lepidoptera: Tortricidae), and an irradiation quarantine dose of 250 Gy has been approved for Hawaiian mangoes. The treatment also controls fruit flies (Follett, 2004). USA regulations covering irradation are described in the Code of Federal Regulations GPO Access (2008), revised annually (Wall, 2008), and this summarizes approved treatments for a range of pests (EPA, 2002) (Table 15.5),

Table 15.5. Minimum absorbed dose of gamma irradiation required by USDA for specific pests (Source: adapted from EPA, 2002). Scientific name

Common name

Anastrepha ludens Mexican fruit fly Anastrepha obliqua West Indian fruit fly Anastrepha serpentina Sapote fruit fly Anastrepha suspensa Caribbean fruit fly Bactrocera cucurbitae Melon fruit fly Bactrocera dorsalis Oriental fruit fly Bactrocera jarvisi Jarvis fruit fly Bactrocera tryoni Queensland fruit fly Brevipalpus chilensis False red spider mite Ceratitis capitata Mediterranean fruit fly Cryptophlebia illepida Koa seed worm Grapholita molesta Oriental fruit moth Sternochetus mangiferae Mango seed weevil All other fruit flies of the family Tephritidae which are not listed above Plant pests of the class Insecta not listed above, except pupae and adults of the order Lepidoptera

Minimum absorbed dose (Gy) 70 100 100 70 150 150 100 100 300 150 250 200 300 150 400

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many of which can infest mangoes. The USDA-APHIS PPQ manual on irradiation provides generic guidelines. Irradiation was approved for the USA market as a phytosanitary treatment for all fresh fruits and vegetables from all countries in 2002. Effects of J-irradiation on mango fruit quality and disease control have been reported (Mitchell et al., 1992; Moreno et al., 2006; Reyes and CisnerosZevallos, 2007; Wall, 2008). Only marginal disease control was obtained with ‘Kensington Pride’ at the highest non-deleterious doses for mature-green fruit (300 Gy), with additive effects of disease control treatments and irradiation on disease reduction (Johnson et al., 1990a). Disease control may be more effective in cultivars with greater tolerance of irradiation (van der Linde and Thord-Gray, 1986; Johnson et al., 1990a). Other types of irradiation have been evaluated for mango disinfestation but none has been adequately suitable. Quick freezing Quick freezing of mango, lowering the temperature to –17°C and holding at –6°C or below for 48 h is used to disinfest mangoes for processing (Anonymous, 1994a; PPQ, 2007). The process is not approved for importing mangoes with seeds from most of the West Indies, French Guiana, all countries outside of North, Central and South America, Oceania, Hawaii, South-east Asia, the Philippines and the Republic of South Africa into continental USA because mango weevil could be present (Anonymous, 1994a; PPQ, 2007). Fumigation Fumigation is an ideal methodology for ensuring effective control when the fumigant is effective and safe to use. Until 1994, New Zealand required fumigation of mangoes from Australia, the Cook Islands and the Philippines using 33, 29 or 22 g/m3 ethylene dibromide at 10–15, 15.5–19.5, or 20°C and above, respectively, at normal atmosphere pressure (NAP) to disinfest mangoes of fruit flies before entry. As part of the international phase-out of ozonedepleting substances, the process was banned in 1994 (Anonymous, 1992; N.W. Heather, personal communication, Brisbane, 1994) and most applications as a fruit fumigant have ceased worldwide. Methyl bromide was phased out completely in the USA in 2005, but some emergency uses for quarantine applications may be permitted, e.g. to destroy a serious quarantine pest in an imported consignment or to meet official requirements of an importing country (EPA, 2008). Mangoes imported into Australia from countries where fruit flies occur must be fumigated with 16–35 g/m3 ethylene dibromide for 2 h at 21–26°C or above (Anonymous, 1985, 1988). Phosphine is widely used as a fumigant of durable produce (grains and tobacco). It provides effective control of fruit fly larvae and other pests in temperate fruits under experimental conditions (Horn and Horn, 2004). However, phosphine when mixed with water is highly explosive and the vapour is toxic to humans, so prospects for utilization are not strong. Miscellaneous treatments CHEMICAL TREATMENTS. Postharvest chemical treatments using dimethoate are effective against Queensland fruit fly with ‘Kensington Pride’ (Swaine et al.,

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1984). The treatment is required for Australian-grown mangoes entering all Australian states except Queensland and New South Wales, but is under review. The USA and the EU do not allow the use of chemicals to disinfest mangoes. NATURAL PRODUCTS. The short shelf life of mango and the high level of insect mortality required obviates the use of natural products for disinfestation. Suhaila and Halim (1994) reported the potential of low toxicity, insecticidal compounds from edible plants that may be effective for topical application to harvested fruit. Extracts of black pepper (Piper nigrum) were particularly active in laboratory tests against vinegar fly (Drosophila melanogaster (Meigen)). ATMOSPHERES. CA and MA regimes could have potential for disinfesting mangoes, but there has been less interest in the technology because heat treatments and irradiation are faster (Ke and Kader, 1992; Yahia and Tiznado-Hernandez, 1993; Yahia and Vazquez-Moreno, 1993; Yahia, 1994; León et al., 2000). Treatments are limited to regimes which do not adversely affect ripe fruit quality. León et al. (2000) found that CA of 1% O2 and 30 or 50% CO2 disinfested ‘Manila’ mangoes of A. obliqua, but damage (as spongy tissue) was unacceptably high. Shrink-wrapping has been ineffective as a quarantine treatment to disinfest mangoes of fruit fly immatures. Gould and Sharp (1990) reported that the time needed to disinfest Florida-grown mangoes infested with Caribbean fruit fly eggs and larvae exceeded the shelf life of wrapped mangoes. COMBINATION TREATMENTS. Serial applications of two or more treatments, which alone do not achieve quarantine security, have been used to disinfest mangoes. Seo et al. (1972) reported that eggs and larvae of Mediterranean fruit fly, oriental fruit fly and melon fly were killed in mangoes immersed in water at 46.3°C for 120 min and then fumigated with ethylene dibromide. Lin et al. (1976) reported that all oriental fruit fly and melon fly larvae in Taiwan-grown mangoes were killed when fruit were immersed in 48–50°C water for 120 min, hydrocooled, dried and cooled, and then fumigated with ethylene dibromide. Controlled Atmosphere/Temperature Treatment System (or CATTS) technology applies a short heat treatment in a low O2/high CO2 environment, and controls quarantine insect pests while maintaining commodity quality (Mitcham, 2007; Neven, 2008). Trials using CATTS with mangoes have been conducted in Australia with promising results. Varith et al. (2007) evaluated a microwave-vapour heat treatment (MW-VHT) disinfestation technology for mangoes: the microwave component for pre-heating and the VHT component for the holding process. Temperatures of 46–55°C and holding times of 2–20 min effectively disinfested fruit of oriental fruit fly eggs without effects on physico-chemical parameters, compared to untreated fruit. There was less heat damage compared with conventional VHT only fruit. MW-VHT shortened the process time by 90% compared with the conventional VHT. PACKAGING. Some markets, for example Japan and the USA, require that fruit must be packed into insect-proof packages following disinfestation to preclude

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reinfestation during transportation or storage. The disinfestation facility feeds fruit into an insect-proof area within which waxing (optional), grading and packing occur.

15.7 Preparing Fruit for Market Surface coatings Surface coatings are used to improve fruit appearance and to alter gas permeability to reduce moisture loss or retard ripening. Commercial use of surface coatings on mango fruit needs to be considered carefully because of the fine balance between beneficial and undesirable effects on fruit quality. Negative effects of coatings include reduction in chlorophyll loss (Fonseca et al., 2004a), anaerobic conditions and off-flavours (Amarante and Banks, 2001) and skin damage, possibly due to cytotoxic reactions with other components in the coating formulation (Bower et al., 2003). Generally, coatings have less effect on delaying ripening during cold storage, compared with extending the shelf life at typical ripening temperatures (Amarante and Banks, 2001). Less significant effects are observed in more mature and in ripening fruit. Coatings often delay skin colour change rather than softening, which increases the risk of soft, green fruit with less consumer appeal. Coatings are generally emulsions of synthetic (e.g. polyethylene) or natural (e.g. polysaccharides, carnauba, beeswax, etc.) origin. Surface coatings containing waxes, oils (e.g. carnauba, beeswax, etc.) and resins (e.g. shellac) have a greater effect on limiting water loss then reducing O2 and CO2 permeability, compared with those containing polysaccharides, (e.g. those based on cellulose) (Amarante and Banks, 2001). Formulations based on shellac result in a shinier appearance than those based on carnauba wax and polysaccharidebased waxes (Baldwin et al., 1999; Hoa and Ducamp, 2008). Factors other than coating formulation can affect fruit gas permeability, i.e. cultivar, variations in skin permeability between fruit, inconsistency in coating thickness during application, interference from water during application causing coating cracking and coating thickness and evenness-ofspread over the fruit surface. The effect of coating on fruit quality can vary with holding conditions because of larger temperature effects on respiration rate than on coating permeability. Shorter and Joyce (1994) found commercially formulated Avocado and Passionfruit Wax, a polyethylene and shellac emulsion, and Technimul 9122 Wax, a polyethylene-based emulsion, were acceptable with ‘Kensington Pride’ mango, while Peach Wax, a polyethylene-based emulsion and starch solution was unacceptable. With Peach Wax, deleterious modified atmosphere effects on colour development, softening and flavour were obtained (El Ghaouth et al., 1992b; Shorter and Joyce, 1994). Coating ‘Tommy Atkins’ mango with a carnauba-based coating and BeeCoat (based on beeswax) reduced water loss, shrinkage, chlorophyll breakdown, CI and decay after cold storage, and BeeCoat also reduced red lenticel discoloration (Feygenberg et al., 2005). With

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‘Tommy Atkins’, polysaccharide and carnauba-based coatings modified the atmosphere within the fruit and reduced decay, but only the polysaccharidebased coating delayed ripening (Baldwin et al., 1999). The carnauba-based coating significantly reduced water loss compared with the polysaccharidebased coating treatments; carnauba-based coatings result in lower water permeability and higher O2/CO2 permeability. Coatings may reduce surface defects. Excessive water loss is associated with increased skin CI in avocado and mango, and carnauba-based coatings reduce CI in cold-stored mangoes (Bower et al., 2003). In this study, the carnaubabased coating contained numerous holes, which allowed respiration gas exchange (thereby preventing anaerobic respiration), while still providing efficient control of water loss. Surface coatings may also reduce sapburn, skin browning and lenticel damage (Shorter and Joyce, 1994), but incorporating these potential benefits into commercial systems may be difficult. Waxes should be applied by roller brushes in a specifically designed wax applicator or by very light hand application. Dipping fruit in a wax emulsion is not recommended. A uniform flow of fruit through the wax applicator must be maintained to prevent uneven wax application. Fruit should be dry before entering the wax applicator, otherwise foaming of water-emulsion waxes may occur. Brushes on the wax applicator need to be completely saturated with the wax mixture before any fruit passes over them. Complete coverage of the entire fruit surface is essential. Patchy application can be caused by insufficient wax, too few brushes following application (minimum of six brushes required), poor and/or inadequate drying facilities, and overloading of the unit. Brushes should be kept soft with regular washing with hot water.

Packaging Packaging provides conveniently sized carriage units for product, protects individual fruit from contact rub and compression damage, and excludes dirt, pests and contaminants. McGregor (1987) and Hilton (1994) discussed key aspects of packaging for tropical produce. Packaging is also a marketing tool. Design and colours of symbols and text on carton exteriors portray a marketing image. Manufacturers of consumer products exploit packaging to great advantage (along with advertising) to increase both first-time and repeat sales. Marketing and design professionals may be involved in the development and customer evaluation of product packaging. Cultural preferences need to considered, e.g. use or avoidance of red for some Asian markets. Packaging is the external face of brand loyalty. Consistent product performance and quality is the core. Some constraints to packaging may be specified by market regulations, including carton dimensions and labelling requirements. Country of origin, cultivar, grower, packing shed, market agent, count (number per carton and weight range) and class may be required. The word ‘mangoes’ should be clearly visible (Anonymous, 1993). The information appears on the narrow

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sides of the cartons. Storage and product use information can also be printed on the cartons. Many QA systems require adequate labelling linked to appropriate record keeping for plate-to-farm traceability. Clear labelling facilitates correct delivery, allows immediate buyer recognition of product profile and ensures maintenance of accurate sales records. An exporting country may find it of value to identify individual packers by barcoding or numbers stamped on cartons, so that sources of faulty packaging can be traced. Some countries also use date codes which enable exporters to determine the freshness of the produce at the point of export and evaluate an importers’ capacity to achieve adequate turnover of the fruit without prolonged storage. It also provides invaluable feedback on the efficiency of the total distribution chain. Cartons used for export should be clean, strong, unbroken and new. The water absorption capacity of the material should be evaluated as excess absorption will lead to collapse on the pallet. The cartons’ strength will depend on the starch used by the manufacturer, the outer liner and the direction and numbers of fluting in the carton (Anonymous, 1994b). There is increasing pressure in the EU for recyclable packing material. Cartons that are recyclable should be marked with the appropriate international symbol. Returnable plastic crates are increasingly being used for domestic trade, but the return cost would make this less profitable for international trade.

Inspection In some countries, independent inspectors check the fruit prior to palletizing to ensure that the relevant marketing, residue and phytosanitary standards have been met. Fruit for Japan is disinfested under the supervision of a Japanese inspector. Further inspections are usually made at the port of exit. Some exporting countries require a declaration by the grower to ensure that fruit will comply with the standards specified by importing countries.

Palletizing Handling mangoes on pallets allows convenient movement of large volumes of fruit. McGregor (1987) described critical features and arrangements for loading. The disadvantages of pallets for export are the cost, lower numbers of cartons per sea container and loss. Some domestic markets have pallet share systems. Relevant markets and transporters should be consulted concerning required pallet dimensions and appropriate access for fork-lift systems. The correctly sized pallet, for example as designated by the ISO, which is designed to fit snugly into a standard sea container, should also be used for the local market. Precision stacking with each box fitted exactly on top of the one below minimizes risk of damage. Collapsed or lopsided pallet stacks have usually been due to careless stacking and/or loose placement in the shipping container. Pallet slats should not block ventilation holes in the cartons. Cartons

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should be register-stacked so that ventilation is continuous. Link sheets, which bind the cartons together at intervals, should also be designed to ensure continuous ventilation through the pallet. In the cold room, pallets should not be stacked against a wall or placed directly against each other (Boelema, 1987).

Precooling Precooling removes field heat from the product and lowers the temperature to that required for ripening, transportation or storage. Precooling also reduces the cooling demand on any in-transit cooling system. Precooling concepts and systems are described by Thompson et al. (2002). Forced-air cooling systems efficiently and rapidly remove field heat, and are preferred for bringing fruit to storage temperature. High RH systems are preferred as they reduce fruit water loss. Hydrocooling can increase the risk of infection by wound pathogens (i.e. Rhizopus spp.) and are less effective with large fruit. Kitinoja and Kader (2003) describe low-cost cooling facilities for use in developing countries.

Ethylene and ripening Induction of ripening is routinely employed with mangoes. There are effective low technology methods involving calcium carbide (releases acetylene which mimics ethylene) or the leaves of particular trees (Lizada, 1994). More sophisticated systems include generation of ethylene from ethanol using catalytic conversion, pure ethylene gas, or a mixture of ethylene and an inert gas (CO2 or N2) to reduce the risk of explosion with 3–30% ethylene in air (Reid, 2002). A number of automatic ethylene control systems are available (PDS, 2008) to maintain ethylene concentrations within required limits. Climacteric fruit have differing sensitivities to ethylene. ‘Kensington Pride’ mango is sensitive to concentrations as low as 0.01 Pl/l (O’Hare et al., 1994). Ripening is enhanced with concentrations up to 5–10 Pl/l, with very little benefit at >50–100 Pl/l (Nguyen, 2003). There is more yellow colour on the ripe fruit when ripened at 20°C with 10 Pl/l ethylene for 3 days compared with no ethylene, resulting in a more attractive appearance. Also, diseases are generally less in these fruit (Table 15.6), presumably because fruit ripen more quickly with less time for disease development. Good ethylene treatment can improve presentation appearance and increase saleable life (defined as the days from when the fruit reach at least 60% yellow skin colour to when the fruit had lost saleability because of disease) (Ledger et al., 2002a). Ethylene can also reduce quality if not used appropriately. Ripening ‘Kensington Pride’ fruit at 2000 km to market

System 2 – ripen on farm

To deliver fruit to the market destination ready for retail sale within 1–2 days. Fruit are ripened evenly using ethylene to colour stage 3 (30–50% yellow) before transport and temperature is managed through the chain to avoid high temperatures >22°C. Ripening on farm is not recommended for transport times >4 days

Precool to 18–20°C within 12–15 h of packing Ripen using 10 ppm ethylene for 2–3 days at 18–20°C Hold at 18–20°C until colour stage 3 (30–50% yellow) Transport at 12–16°C for trips of 1–2 days and 12°C for 3–4 day trips Hold at market at 18–20°C until ready for sale Store at 10–12°C to slow ripening for a maximum of 3 days

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The refrigeration equipment must be correctly set on air delivery and must be calibrated for each journey. Equipment needs to function reliably and receive regular servicing. Air should be delivered at the set point and fluctuations should not exceed ±0.5°C from set point. Refrigerated vehicles should be fitted with temperature loggers monitoring the delivery air, and with a digital display on the outside of the box. Refrigerated vehicles are not usually designed for, or capable of, lowering fruit temperatures so the fruit must be at the relevant shipping temperature when loading. Because of the shorter time involved, air-transported fruit may have less stringent temperature requirements than sea-export fruit. Airlines carrying cargo may need to be consulted concerning the normal hold temperatures in their aircraft. Sea-export fruit should be held under refrigeration until loading. Sea transport can be in refrigerated vessels, with entire refrigerated decks filled with pallets, or in sea containers, each of which is linked to a central ducted refrigeration system in refrigerated container vessels. Alternatively, integral containers with their own individual cooling systems or integral CA containers may be used.

Close temperature monitoring on the vessels is essential. By monitoring delivery air temperatures (DAT) and return air temperatures (RAT), it is possible to assess whether fruit is heating up due to respiration or inadequate precooling, and to take necessary steps (Anonymous, 1989; Eksteen, 1990). While most refrigerated container vessels monitor individual container air temperatures, including DAT and RAT, it is sometimes advisable to include additional temperature loggers which can measure air and fruit pulp temperatures for an entire journey. The sea-freight component is generally the most time-consuming part of the whole field-to-supermarket voyage (for example see Table 15.8). Essential activities before and after transport can be significant, for a relatively perishable product like mango. Minimizing time delays in each component of the distribution chain is important. To reduce product deterioration,

Table 15.8. Typical packing and shipping schedules for mangoes consigned by sea to the EU from South Africa. Operation Picking and packing Precooling and accumulation of load Transport to port Port handling and accumulation of load Voyage time Discharge handling Transport and distribution Total

Days required 1 4 2 3 17 1 2 30

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producers and marketers should encourage training in perishable product handling and QA systems for personnel from trucking, sea-freight and airfreight companies who are responsible for loading, unloading and maintaining storage facilities. Co-shipment or storage with fruit or flowers that produce high levels of ethylene can cause unanticipated triggering of mango ripening. Co-shipment with papaya (Carica papaya) increases mango ripening (O’Hare et al., 1994). Conversely, co-shipment of carambolas (Averrhoa carambola) with mangoes caused ripening of the carambolas. The development of specialized packaging materials to eliminate extraneous ethylene may reduce the risk of unwanted ripening, although mixed transport should be avoided.

15.10 Marketing Modern supermarket chains require large quantities of uniform produce that can be purchased on contract for delivery at a particular time to stores across a city or country. This allows the supermarket chain to promote the product at a special price. Mangoes are generally priced per fruit rather than by weight, although this is changing. Barcoding and/or Price Lookup Codes (PLU) on the labels of individual fruit for electronic checkout processing improves monitoring of purchase habits and stock control. The International Federation of Produce Standards (IFPS) (2008) provides a forum for standardization of produce labelling and the PLUs are applicable internationally. Proctor and Cropley (1994) cautioned the need to ensure that label adhesives comply with food additive restrictions in the EU.

Networks and cooperatives Marketing cooperatives or networks can assist individual producers to obtain critical mass in an industry, and fulfil buyer expectations of large supply and seasonal spread of production (Glogoski, 1995; Griffin, 1995; Higginbottom, 1995; M.C. Nguyen et al., 2004).

Promotion and consumer education Mangoes are increasingly popular among affluent consumers in the EU, North America and northern Asia. In the tropics, they are reminders of a non-urban living, which has become less common because of rapid industrialization and migration to the cities. Whether for domestic use or export, mangoes must compete in the fresh market with other equally attractive, nutritious, aromatic and tasty fruit. Mangoes must also increasingly compete with the snack food, beverage and entertainment industries. Consumer education can encourage consumption and sales. Customers can be educated how to select and store mangoes and how to use both the

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fresh and the processed products in a variety of ways, thereby increasing total demand. Production of mango slices in take-away packs can tap domestic and export markets for ready-to-eat, healthy products and circumvent some disinfestation requirements (see Raymundo et al., Chapter 17, this volume). Siriphanich (1994) has reviewed minimal processing of tropical fruit and noted the advantages of gaining market access and reducing transportation costs.

15.11 Conclusions Mango production has been based almost entirely on Mangifera indica, albeit a variable meld of thousands of cultivars which may be derived from interspecific hybrids of a few closely related species (Kostermans and Bompard, 1993). Given its perishable nature, capitalizing more on the diversity of existing germplasm to develop cultivars with superior storage traits linked to customer appeal could deliver major benefits. Future improvements in postharvest technology and quarantine treatment will come from refinement of preharvest management, for example reducing disease inoculum and increasing fruit resistance to disease, reducing harvest costs and fruit damage, improving postharvest treatments and systems, and supply chain approaches to enhance fruit longevity and quality and reduce the risks of product damage. Improvements will also accrue from the provision of user-friendly information for supply chain personnel, but only if the information is utilized and implemented. Increases in throughput via the automation of harvesting and treatment systems for fruit will increase as production and marketing costs escalate. Labour saving and work efficiency will also become more critical. Innovative transport arrangements may become necessary as regional development places greater pressures on transport systems. International, collaborative joint-marketing ventures will ensure year-round supplies of uniform quality fruit, and per capita consumption of mangoes will increase (Johnson, 1995).

Acknowledgements The authors acknowledge the contributions of the co-authors of Johnson et al. (1997), which this book chapter supercedes, and Leanne Taylor and Roberto Marques for assistance with references. The authors also thank the Department of Primary Industries and Fisheries for research programme support.

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16

World Mango Trade and the Economics of Mango Production E.A. Evans and O.J. Mendoza University of Florida, Florida, USA

16.1 Introduction 16.2 Recent Trends in World and USA Mango Production, Trade and Consumption World situation USA mango production, imports and consumption 16.3 Sample Costs and Returns Associated with the Establishment and Production of Mango Orchards General approach to estimating cost of production of orchard crops Main assumptions Discussion of establishment phase budget Discussion of production phase budget Profitability analysis 16.4 Conclusions

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16.1 Introduction Worldwide mango production occurs in over 90 countries. Although only a relatively small proportion of total mango production enters international trade (