Horticultural Reviews 9781119625339, 2132152152, 1119625335, 9781119625353, 1119625351

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HORTICULTURAL REVIEWS Volume 47

Horticultural Reviews is sponsored by: American Society for Horticultural Science International Society for Horticultural Science

Editorial Board, Volume 47 A. Ross Ferguson Robert E. Paull

HORTICULTURAL REVIEWS Volume 47

Edited by

Ian Warrington Massey University New Zealand

This edition first published 2020 © 2020 John Wiley & Sons, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of Ian Warrington to be identified as the author of this editorial material in this work has been asserted in accordance with law. Registered Office(s) John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial Office The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Library of Congress Cataloging‐in‐Publication data applied for ISBN: 9781119625339 (Hardback) Cover Design: Wiley Cover Image: Image courtesy of Jules Janick Set in 10/12pt Melior by SPi Global, Pondicherry, India Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

Contents

Contributors ix Dedication: Theodore DeJong xi Ian Warrington

1. Molecular Physiology of Fruit Growth in Apple

1

Anish Malladi

I. Introduction II. Morphology and Anatomy of the Apple Fruit III. Flower Growth Before Bloom IV. Fruit Set V. Fruit Growth VI. Conclusions Literature Cited

2. Mechanosensing of Plants

2 2 5 7 9 31 33

43

Marc‐André Sparke and Jens‐Norbert Wünsche I. Introduction II. Thigmomorphogenesis III. Natural and Artificial Induction of Thigmo Responses IV. Morphological Plant Responses V. Physiological Plant Responses – Cellular Signaling VI. Molecular Aspects VII. Application Strategies in Horticulture VIII. Conclusions Literature Cited

44 47 48 50 57 69 70 72 73

3. Microgreens: Definitions, Product Types, and Production Practices 85 Sven Verlinden

I. Introduction II. History of Immature Leafy Vegetables

86 92 v

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CONTENTS

III. Seedling Development in Other Crops – Growth and Development of Seedlings 94 IV. Production Strategies 96 V. Nutritional Value 104 VI. Microbiological Safety and Postharvest Biology and Technology 114 VII. Sensory Attributes and Qualities 117 VIII. Health Effects 117 IX. Future of Microgreens 118 Literature Cited 119

4. The Durian: Botany, Horticulture, and Utilization

125

Saichol Ketsa, Apinya Wisutiamonkul, Yossapol Palapol, and Robert E. Paull I. Introduction II. Botany III. Cultural Practices IV. Chemical Composition and Nutritional Value V. Postharvest Physiology VI. Harvesting and Postharvest Handling VII. Utilization VIII. Conclusions Literature Cited

127 140 149 173 177 184 192 195 195

5. The genus Cupressus L.: Mythology to Biotechnology with Emphasis on Mediterranean Cypress (Cupressus sempervirens L.)

213

Homayoun Farahmand

I. Introduction 215 II. Cupressaceae (Geographical Distribution and Horticultural Importance) 215 III. The Genus Cupressus 216 IV. The Role of Mediterranean Cypress in Persian Gardens 249 V. Medicinal Values 252 VI. Breeding and Genetic Improvement 254 VII. Abiotic and Biotic Challenges 256 VIII. Conservation of Genetic Resources 261 IX. Conventional Propagation and Micropropagation 263 X. Biotechnology 265 XI. Conclusions 267 Literature Cited 268

CONTENTS

6. Taxonomy and Botany of the Caricaceae

vii

289

V.M. Badillo and Freddy Leal

I. Introduction II. History of the Papaya and Other Caricaceae III. Taxonomic History IV. New Proposals for the Taxonomy of Caricaceae V. Botany of the Family and the Genera VI. Concluding Comments Literature Cited

290 291 291 295 297 319 320

7. Entomopathogens: Potential to Control Thrips in Avocado, with Special Reference to Beauveria bassiana 325 Gracian T. Bara and Mark D. Laing I. Introduction II. Commercial Production in South Africa III. Requirements for Export and Local Quality IV. Economics of Avocado Production V. Pests and Diseases of Avocado VI. Thrips of Avocado VII. Management of Thrips VIII. Entomopathogens IX. Conclusions Literature Cited

326 328 329 329 330 330 333 336 356 357

Subject Index Cumulative Subject Index Cumulative Contributor Index

369 372 406

Contributors

V.M. Badillo,† Facultad de Agronomía, Universidad Central de Venezuela, Maracay, Aragua, Venezuela Gracian T. Bara, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa Homayoun Farahmand, Department of Horticultural Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran Saichol Ketsa, Department of Horticulture, Faculty of Agriculture, Kasetsart University, Bangkok, and Thailand and Academy of Science, The Royal Society of Thailand, Dusit, Bangkok, Thailand Mark D. Laing, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa Freddy Leal, Facultad de Agronomía, Universidad Central de Venezuela, Maracay, Aragua, Venezuela. Anish Malladi, Department of Horticulture, University of Georgia, Athens, GA, USA Yossapol Palapol, Division of Agricultural Technology, Faculty of Science and Arts, Burapha University, Chanthaburi Campus, Thamai, Chanthaburi, Thailand Robert E. Paull, Department of Tropical Plant and Soil Sciences, University of Hawaii at Manoa, HI, USA Marc‐André Sparke, Department of Crop Science, Institute of Crop Physiology of Specialty Crops, University of Hohenheim, Stuttgart, Germany Sven Verlinden, Department of Plant and Soil Sciences, West Virginia University, Morgantown, West Virginia, USA Apinya Wisutiamonkul, Expert Centre of Innovative Agriculture, Thailand Institute of Scientific and Technological Research (TISTR), Khlong Luang, Pathum Thani, Thailand Jens‐Norbert Wünsche, Department of Crop Science, Institute of Crop Physiology of Specialty Crops, University of Hohenheim, Stuttgart, Germany †

deceased ix

Theodore DeJong

Dedication: Theodore DeJong

Professor Theodore (Ted) DeJong has had a long and distinguished career in the broad area of whole tree physiology, with a particular emphasis on stone fruit species (peach, plum, and nectarine) that are relevant to California but widely grown in many areas of the world. This research has led to an enhanced understanding of tree growth and development, especially in areas relating to carbon balance in the tree, tree architecture, and the growth of the vegetative canopy, fruit, and roots. He has focused considerable effort on modeling these various processes. In addition, he has been a leader in an effective stone fruit breeding program. Ted grew up in Ripon, CA and spent a good deal of time working on peach and almond farms in the area – he had loved farming ever since he was in grammar school. Ted attended Ripon Christian Schools and then Calvin College in Grand Rapids, Michigan. While in college he became interested in ecology and, because of his farming experience, was mainly interested in plant ecology. After college, in 1968, he married his wife Rose, and was scheduled to be drafted into the army and so he volunteered for admission to the Army Officer Candidate School. He graduated from OCS in late 1969, was commissioned, spent most of the next year in Fort Riley, Kansas, and went to Vietnam on September 11, 1970. In September, 1971 he enrolled in an M.S. program at Fullerton State University in Plant Ecology. His mentor there was Dr Ted Haines and he was probably most influential in Ted subsequently choosing an academic career. In Jan, 1974 he enrolled in the Botany Ph.D. program at the University of California, Davis to continue studying Plant Ecology with Prof. Mike Barbour. His research was on the physiological ecology of Californian beach and dune species. In January, 1978 he began a one‐year post‐doctoral fellowship at the Smithsonian Institution and did research on the physiological ecology of tidal marsh species. One year later, Ted returned to UC Davis on a Post‐ Doctoral Fellowship in the Agronomy and Range Science Department xi

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Dedication: Theodore DeJong

with Prof. Don Phillips working on carbon and nitrogen assimilation interactions in legumes. At this time, he realized that he could have a rewarding career working in “applied environmental physiology of crop plants,” otherwise known as “crop physiology.” He was appointed as a Lecturer/Pomologist/Co‐op Extension Specialist at the Kearney Agricultural Experiment Station and Extension Center (KAC) in the Pomology Department in April 1981. Thanks to good field staff support, he remained at Davis but conducted virtually all of his research and extension work at KAC for the first 25 years of his career. He was assigned to teach practical pomology courses at Davis and also co‐taught graduate level courses in plant/crop physiology. He enjoyed teaching and by the end of his career he was the main instructor for the pomology/tree crop physiology courses at UC Davis, even though he had never taken a formal pomology or horticulture course in his life. His teaching had a lot of influence on his research because, early in his career, as he was teaching some of the pomological “dogma” to his students, he realized that some of it made little physiological/ecological sense. Furthermore, many of the current horticultural practices were often not backed up by sound scientific study, so some of these “dogmas” formed ideas for research. Such ideas led to investigating: the importance of leaf photosynthetic capacity in determining crop yield; fruit effects on photosynthesis; causes of the double sigmoid growth of stone fruit; carbohydrate and nitrogen allocation in fruit trees; carbohydrate storage in trees; causes of alternate bearing in fruit trees; physiological mechanisms involved in size‐controlling rootstocks; factors driving shoot growth in fruit trees; and interactions between fruit, shoot, and root growth in fruit trees. Ted’s challenges to much of this “dogma” within the teaching framework have also been widely acknowledged internationally. New Zealand pomologist Dr Stuart Tustin states that “Ted’s incisive consideration of the science presented within the ISHS Fruit Section has always been highly valued by symposia participants, as has the friendly pugilism often arising in such discussions with Ted in such fora. He can always be relied upon to challenge concepts and interpretations and in such ways, contribute greatly to the scientific thinking and advances in fruit crop pomology and physiology.” When he was a graduate student at UCD, he attended Prof. Robert Loomis’s crop ecology lectures for two years in a row and was fascinated with his crop modeling work. When Ted had his first sabbatical opportunity in 1987, he went to Wageningen University in the Netherlands to learn more about developments in that field of research. This was a

Dedication: Theodore DeJong

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watershed experience for his career. While there, he realized that plants can best be viewed as composite organisms made up of semi‐autonomous organs and the key to understanding/modeling whole plants was in understanding what drives the growth of those individual organs. This also led to development of a new model for explaining stone fruit growth patterns. After this sabbatical, much of his conceptually‐based research involved various aspects of crop modeling and the culmination of this work resulted in development of Functional–Structural Plant Models of peach and almond tree growth and physiology. The L‐Peach and L‐Almond models are still the most detailed and advanced virtual computer simulation models of fruit trees in existence today. They permitted the testing of, and/or demonstrated concepts behind, numerous fruit tree management practices that are commonly used in commercial fruit production. Underpinning Ted’s work in crop modeling at the Department of Pomology (later Department of Plant Sciences) at UC Davis, was a range of research that focused on understanding tree physiological and orchard management factors that control the carbon balance/budgets of fruit and nut trees. His initial work focused on understanding the functioning and photosynthetic efficiencies of tree leaves and on understanding factors governing the horticultural efficiencies of orchard canopies. As he gained experience and understanding of factors controlling the “supply side” of the carbon balance equation, later studies focused on the “demand side” of the equation and the integration of both aspects into a functional understanding the how tree carbon budgets work. This “demand side” work focused on characterization and understanding factors governing flowering and fruit set, fruit growth, vegetative (leaf and shoot) growth, and root growth, and eventually involved numerous studies characterizing how rootstocks control shoot growth (see Horticultural Reviews 46:39–97 for this latter topic). Much of his intellectual stimulation for conducting the various aspects of this research came from an overall goal of developing an integrated understanding of fruit tree carbon budgets and growth through crop modeling. As indicated above, this led to the development of very sophisticated and complex functional–structural tree simulation models that are not only carbon budget models but also include integrated understanding of the architectural development of fruit trees. French scientist, Dr Evelyn Costes, notes that: “with an an open‐ minded vision Ted has combined skills in plant physiology, classical horticulture and fruit tree cultivation with new technologies involving computer programming and modelling. He thus has made an exceptional research contribution.”

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Dedication: Theodore DeJong

Italian colleague, Dr Paolo Inglese, states that: “personally I gained a lot of inspiration from his papers on fruit growth and development and carbon partitioning in peach trees. I really learned a lot and, most interesting, it became easy to move from physiology to orchard management, understanding the basic factors of tree behavior. From this point of view, it is clear how strongly Ted DeJong influenced a large number of students, and younger scientists worldwide, with an impressive benefit for horticultural development, in terms of knowledge and, most importantly, field practices and orchard management. Indeed, it is worth noting that Ted’s research was always related to real problems experienced by stone fruit growers, particularly peach and almond growers. He is strongly dedicated to solving real problems through a clear scientific standpoint and this deserves our admiration. I have seen Ted giving lectures several times, but I have also seen him talking to growers in the field ready to learn and to share his knowledge as well as to understand the basic facts behind any particular horticultural technique.” Pomology Farm Advisor, Rachel Elkins, summarizes Ted’s research achievements as follows: “Ted’s successful career reflects his thought process: creativity melded with logic and practicality. His upbringing on an almond farm in the Central Valley provided the necessary ‘grounding’ needed to ensure his research and extension contributions would impact commercial agriculture. His training in basic biology and ecology have provided the unique holistic perspective enabling him to think ‘out of the box’ about fundamental perennial crop physiology concepts. Those of us fortunate enough to take classes from him, study under him, and work with him have benefitted enormously. Indeed, the concept Ted has developed and demonstrated, that tree vigor and bearing at any given time of the year and life stage are fundamentally and primarily related to carbohydrate partitioning and balance has permanently influenced my own thought processes dealing with tree health issues in the field and in developing my own applied research. I am not alone; California tree crop advisors who have studied under, or worked with Ted, are well‐trained and confident in their understanding of fruit and nut crop physiology.” In addition to this physiological research, he has also been the principle investigator on a prune breeding project since 1985. The Californian prune industry is currently dependent on a single cultivar. The goal of this project is the development of new prune/dried plum cultivars for the Californian industry that will increase orchard and processing efficiencies, spread the harvest season, and maintain or increase dried product quality. Ted holds 11 plant patents that cover

Dedication: Theodore DeJong

xv

the cultivars that have been developed in that program as well as collaborative development of size‐controlling rootstocks for peach and nectarine production. In addition to his extensive research activities, Prof. DeJong also held a number of administrative positions at UC Davis, several of which coincided with challenging financial times and consequent organizational restructuring. He served on the College Research Committee and later the College Executive Committee, being the Chair during a College reorganization. In that role he also served on the Campus Senate Executive Council and on the Committee on Academic Planning and Budget Review for eight years, during several budget crises and strategic planning projects. From these experiences, he gained an understanding of the politics involved in campus and university decision making and became somewhat disillusioned in the process given the continuing decline in academic values and principles. He was chair of the Pomology Department for eight years and was also a Vice‐Chair in the Plant Sciences Department for three years. He additionally chaired numerous other committees including the Pomology/Plant Sciences Department’s Field Facilities Committee for nearly 30 years, the College Air Shuttle Committee for 15 years and the Foundation Plant Services (FPS) Strawberry Advisory Committee for 15 years. He also served as a Senate representative on the Athletics Administrative Advisory Committee for more than six years as well as the Administrative Committee for the Transition of UC Davis athletics from Division II to Division I. He regards his main accomplishment in this latter service was to try to maintain the UC Davis vision of “student‐athlete” as the university moved to higher levels of competition. Prof. DeJong’s scientific output has been prodigious over the past four decades. He has published over 200 manuscripts in refereed scientific journals. In addition, he has presented numerous talks at grower meetings and scientific conferences. He has also maintained a regular teaching program and mentored more than 50 Masters, Ph.D., and post‐ doctoral students from the US and several foreign countries. Fellow Pomologist, Prof. Greg Reighard, Clemson University, states: “His publication record is unmatched by his peers, while his research has been productive, relevant, well received and widely implemented by his clientele. In my opinion, he is the foremost authority on stone fruit whole tree physiology in the world. His advice is frequently solicited by his peers for his insight into problems related with fruit production. His prolific publication record and esteemed standing with research journals and professional societies are a testament to his abilities as a scholar and mentor.”

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Dedication: Theodore DeJong

Prof. DeJong has been an active member of professional horticultural science societies for many years, contributing widely and consistently to their scientific programs during that time. In particular, he has supported many ISHS symposia and has, consequently, published in a number of Acta Horticulturae volumes (70 manuscripts in 23 Acta Horticulturae volumes). He has also been the convener of two ISHS symposia and is currently (2014–22) the Chair of the Section Pome and Stone Fruits. His achievements have been recognized by a number of honors and awards, including: Smithsonian Post‐doctoral Fellow, 1979; Netherlands International Agriculture Center Fellowship, January–July, 1987; NATO Senior Guest Fellowship to Italy, July–August 1987; Fellow, American Society for Horticultural Science, Class of 2002; The National Peach Council Outstanding Peach Researcher Award, 2002; UC Davis Distinguished Professor, 2013; ISHS Lifetime Achievement Award for Outstanding Contributions to Research and Education in Fruit Crop Physiology, 2014; and ISHS Fellow, 2018. Prof. DeJong observes that he was extremely fortunate to have had his career in a time that he and many of his colleagues, who were in the Pomology Department during this period, call the “golden age of pomology.” It was a time when there was ample financial and personnel support for research. He started with a department‐paid career staff research associate (SRA) and enough San Joaquin Valley/ industry support to support another young SRA to plant and maintain tree crop research plots and to conduct numerous “exploratory” research projects to gain new perspectives on how fruit trees work. In addition, the university believed in, and supported, field research. Research was valued for the help that it provided growers rather than just how much funding it brought into the university. He observes that too often research is increasingly valued now more for the funding that it generates than the actual societal benefits derived from it. Field stations are run now more as “profit centers” than as research support enterprises. He is deeply concerned that future pomology researchers will not be as successful as he was able to be, not because (he claims) he was especially talented, but because it will be impossible to access the practical, integrated experience that he was able to gain because of the support systems that were in place when he began his career. Because of early experiences, he was able to sustain funding mechanisms with long term horizons. It will be nearly impossible for young researchers to do the same now, when they are obligated to continually develop new projects and garner new funding for projects lasting only two to three years when working on complex, perennial crops.

Dedication: Theodore DeJong

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Prof. DeJong and his wife have a family of three sons and ten grandchildren. Their eldest, Jason, is Professor of Geotechnical Engineering at UCD and the youngest, Matthew, is Professor of Structural Engineering at UC Berkeley. Their middle son, Michael, is a Fire‐fighter/Paramedic, also based in California. Although formally retired, Ted continues to do research and to contribute to the programs at UCD. “I would like to close on a personal note and state that no one currently working in the field of stone fruit pomology is at Ted’s level as to what he has accomplished. There are some outstanding pomologists working throughout the world on stone fruit physiology, but I think Ted stands as tall or taller (no pun intended) than all of them at this stage of his career” – Dr Greg Reighard. Ian Warrington Emeritus Professor Massey University Palmerston North New Zealand

1 Molecular Physiology of Fruit Growth in Apple Anish Malladi Department of Horticulture, University of Georgia, Athens, GA, USA

ABSTRACT Fruit growth and development are processes of primary biological importance and of considerable commercial significance. In apple, the fleshy fruit is derived largely from non‐ovarian tissue. Regulation of fruit growth in apple is therefore likely distinct from that in other model fleshy fruit species. Fruit growth is an integration of multiple processes that are regulated through developmental factors, phytohormones, and availability of metabolic resources. These factors differentially influence growth during diverse stages of development, and across different tissues within the fruit. In recent years, substantial progress has been made in identifying some of the major molecular components and mechanisms involved in the regulation of apple fruit growth. This review presents a comprehensive analysis of our current knowledge of the molecular physiology of fruit growth in apple and identifies gaps where future research is needed to expand our knowledge of the regulation of this trait. KEYWORDS: cell division; cell expansion; fruit development; fruit size; organ growth I. INTRODUCTION II. MORPHOLOGY AND ANATOMY OF THE APPLE FRUIT III. FLOWER GROWTH BEFORE BLOOM IV. FRUIT SET V. FRUIT GROWTH A. Components of Fruit Growth: Cell Production, Expansion, and Void Spaces B. Fruit Growth and its Regulation

Horticultural Reviews, Volume 47, First Edition. Edited by Ian Warrington. © 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc. 1

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Anish Malladi

C. Cell Production Related Genes and Regulation of Fruit Growth D. Organ Size Related Genes and Regulation of Fruit Growth E. Floral Homeotic Genes and Regulation of Fruit Growth F. Cell Wall Modifying Genes and Regulation of Fruit Growth G. Metabolism and Regulation of Fruit Growth H. Phytohormones and the Regulation of Fruit Growth I. A Note on the Measurement of Growth VI. CONCLUSIONS LITERATURE CITED

I. INTRODUCTION Apple (Malus × domestica) is one of the most widely grown temperate fruit crops in the world. Fruit growth and development are not only of botanical significance but are also of vast economic significance in apple production. In this review, growth is defined as the increase in size of the organ, while development is defined as the progression of the organ through various phenological stages. The main emphasis of this review is on the processes and factors mediating fruit growth. However, often, growth of an organ and the processes that mediate it are intimately associated with its development. Hence, where applicable, these inter‐relationships will also be discussed. II.  MORPHOLOGY AND ANATOMY OF THE APPLE FRUIT The apple fruit is botanically a “pome.” Fruits of this class are characterized by the presence of fleshy exocarp and mesocarp tissues and a cartilaginous endocarp. The majority of the fruit tissue is comprised of accessory tissue (Pratt 1988). The central region of an apple fruit is typically constituted by five locules that are derived from five carpels from a syncarpous ovary. Each of these carpels may contain up to four ovules which upon fertilization can yield one to four seeds (Pratt 1988). The seeds are surrounded by the cartilaginous endocarp tissue at maturity. A ring of five sepal and five petal vascular traces occurs towards the periphery of the locules and is often referred to as being the core‐line. Tissue outside of this core‐line develops into the major fleshy and economically significant part of the apple fruit (Figure 1.1). At maturity, this tissue may constitute over 80% of the fruit volume (Tukey and Young 1942; Goffinet et al. 1995). Ontogeny of the fleshy region of the fruit outside of the core‐line and the precise localization of ovarian tissue inside of it have been debated extensively and reviewed previously (Pratt 1988). Briefly, two conflicting hypotheses have been proposed to explain the ontogeny of fruit tissues. According to MacDaniels (1940), the receptacular hypothesis indicates

1.  Molecular Physiology of Fruit Growth in Apple

3

Fleshy pericarp* Dorsal carpellary trace Pith Core-line Locule Sepal vascular trace Petal vascular trace Fruit skin Cortex

Figure 1.1  Transverse section of the apple fruit displaying the primary tissues. *: The fleshy pericarp here is shown to indicate interpretation of the fruit morphology according to the receptacular hypothesis. According to this interpretation, tissue immediately surrounding the locule constitutes the pericarp. The appendicular hypothesis considers tissue inside of the core‐line to be of ovarian origin as described in the text.

that the major fleshy region of the fruit is derived from axial tissues. The central region of the fruit extends from the pedicel into the fruit and the outer fleshy tissue represents an extension of the cortical region peripheral to the vascular tissue within the stem. Hence, this tissue is referred to as the cortex (Figure 1.1). As an extension of this terminology, tissue inside of the core‐line (vascular tissue) is referred to as the pith. The location of the ovarian tissues is within the pith region and restricted to cell layers immediately surrounding the locules ­(Figure 1.1). Further, the true fruit is composed of five drupe‐like structures characterized by a cartilaginous endocarp. As the cell layers constituted by the exocarp and mesocarp tissues are few, most of the pith is comprised of parenchymatous cells of non‐ovarian origin. The alternative appendicular ­hypothesis presents a divergent view. In this context, the tissue peripheral to the core‐line originates from the fusion of the basal tissues of appendages: multiple floral organs including the petals, sepals, and stamens (MacDaniels 1940). Hence, this tissue is often described as a floral tube or a hypanthium derived from fused basal regions of floral appendages. Tissue inside of the core‐line is considered of ovarian origin, such that the innermost layer of this tissue is the endocarp while the rest is constituted by fleshy exocarp and mesocarp tissues. The core‐line is regarded as the line of fusion between the floral tube

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and the ovary. The relative merits of each of these theories have been evaluated with many recent authors preferring the appendicular hypothesis (Pratt 1988), largely owing to interpretations from comparative vascular anatomies across Rosaceae family fruits, as elegantly described by MacDaniels (1940), as well as data from cytochimeras summarized by Pratt (1988). Very few studies since the 1950s have addressed the origin of these tissues, despite its botanical significance. An effective way to determine the origin of these tissues in the apple fruit is through the application of specific tissue‐based markers for development. As the fruit and some of its constituent parts are derived from specific floral organs, identification of markers defining these floral organs in the fruit tissues, especially during early fruit development, can provide clues to the origin of these tissues. The ABC model describes development of floral organ identity (Bowman et  al. 1991; Coen and Meyerowitz 1991) and has been extensively validated across many plant systems (Bowman et  al. 2012; Irish 2017). According to this model, members of the A class of gene products determine sepal identity, and in interaction with those of the B class gene products, the identity of petals. Interaction of the B and C class gene products influences stamen development, while the C class gene products regulate gynoecium development (Irish 2017). Putative homologs of these classes of genes, many of which are MADS box transcription factors, have been identified in apple. The apple APETALA2 (AP2) is a putative A class gene, the transcripts for which were shown to be abundant in sepal tissues (Kotoda et al. 2000) and in the cortex/floral tube region during early fruit development (Yao et al. 1999). This suggested that the fleshy region of the apple fruit was likely derived at least from sepal tissues. Further, facultatively parthenocarpic spontaneous mutants of apple, ‘Rae Ime’ and ‘Spencer Seedless’ were identified to be defective in one type of B class genes, PISTILLATA (PI; Yao et al. 2001). Transcript accumulation of the PI gene was abundant within the petals but could not be observed in the cortex/floral tube region of the developing apple fruit at four weeks after bloom (Yao et al. 2001, 2018). These data suggested that petal and stamen tissues did not likely contribute substantially to development of the cortex/floral tube region of the fruit. The A class gene defining sepal identity, AP2, is regulated post‐­ transcriptionally by microRNA 172 (miR172). In apple, miR172 has been associated recently with regulation of fruit growth and final size (Yao et al. 2015). Higher levels of miR172 were associated with a reduction in fruit growth while the opposite was true under lower levels of miR172. Overexpression of miR172p (one of several active miR172) in transgenic ‘Royal Gala’ plants resulted in a dramatic reduction in fruit size (Yao et al. 2015). The authors proposed

1.  Molecular Physiology of Fruit Growth in Apple

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that the cortex/floral tube was largely derived from the base of the sepals and post‐transcriptional alteration of the A class gene product, AP2, in these transgenic plants leads to altered growth of tissue derived from this floral organ. Together, these data strongly support the appendicular theory of apple fruit development and suggest that the basal regions of the floral organs, particularly the sepals, contribute greatly to development of the major fleshy tissue of the apple fruit. There are, however, a few limitations to the above approaches. Many of the genes described above have been identified and described in apple as floral organ identity genes that have clearly defined roles during flower development, but their roles in post‐flowering fruit development are not as well characterized (Yao et al. 2016). While their transcript and protein accumulation in specific parts of the flower would be clearly indicative of organ identity, the significance of such accumulation at later stages and during fruit growth may need to be interpreted with caution. Further, in case of miR172, substantial growth and development of the fruit cortex/floral tube tissue was still noted as the hypanthium in transgenic lines, where it was overexpressed, was reduced by only about 25% during early fruit development (Yao et al. 2015). Presumably, basal regions of the petals and stamens may still contribute to the growth and development of this tissue. The current availability of additional floral tissue identity genes and newer approaches that aid in isolating specific tissues of the developing flower/fruit, such as laser capture micro‐dissection, need to be applied to clearly identify the origin of this tissue. III.  FLOWER GROWTH BEFORE BLOOM Apple flower buds are induced and initiated in the previous season and display substantial growth and development prior to dormancy (Buban and Faust 1982). Eight stages of progression in apical meristem morphology prior to winter dormancy have been described (Foster et al. 2003). Broadening of the apex of the meristem was identified as a key morphological feature signaling commitment to floral induction. This transition to floral induction peaked around 53 days after full bloom (DAFB) but continued until 127 DAFB. Similarly, broadening of the apex was also considered as a signal committing the meristem to inflorescence initiation (Pratt et al. 1959; Pratt 1988). Doming of the apex was rapid and occurred largely between 96 and 109 DAFB. Lateral floral meristem initiation and terminal floral meristem initiation followed this induction. By winter dormancy (~280 DAFB), floral meristems have clearly discernable initiation of sepals. At least in the terminal flower, further differentiation of floral organs and their development is also evident

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before endo‐dormancy (Pratt 1988). During the period of endo‐dormancy and subsequent eco‐dormancy, little growth and development are observed. Further flower development including microsporogenesis and macrosporogenesis is completed following bud break (Pratt 1988). The period from bud break to anthesis/bloom is associated with substantial growth of the floral tube (Smith 1950; Malladi and ­Johnson 2011): a substantial increase in floral tube diameter from around three weeks before, until full bloom was reported (Smith 1950; Malladi and Johnson 2011). However, growth during this period was not uniform and involved rapid growth during the early part of this period followed by a cessation in growth before bloom (Malladi and Johnson 2011). A similar temporary reduction in growth around bloom was noted previously in several cultivars (Smith 1950), indicating that this may be an important feature of pre‐bloom growth in apple. Reductions in growth prior to pollination and fertilization have also been reported previously in tomato (Vriezen et al. 2008; de Jong et al. 2009). Growth during the period from bud‐break to bloom was largely associated with an increase in cell number, indicating that the majority of this growth was supported by an increase in the extent of cell production, although cell size also increased slightly during this period. The cessation in growth prior to bloom was associated with a quiescence in cell production (Malladi and Johnson 2011). Transcript accumulation of multiple positive regulators of cell production, such as the CYCLIN DEPENDENT KINASE B1;2 (CDKB1;2), was reduced by greater than twofold during this period. Conversely, transcript accumulation of two KIP RELATED PROTEINS (KRP4 and KRP5), which function as negative regulators of cell production by inhibiting progression of the cell cycle, were enhanced by over fourfold. Together, these data suggest coordinated transcriptional regulation to decrease cell production prior to bloom. Such reduction in growth may serve to restrict further nutrient investment in this organ until after successful pollination and fertilization. Alternatively, this reduction in growth may be reflective of extensive competition for limited resources during this period. Early growth, including flower growth after bud‐ break and before bloom, is largely supported by carbohydrate and nutrient resources remobilized from stored reserves (Hansen 1971; Titus and Kang 1982). Flower growth and development likely competes with vegetative growth for these resources, including that of spur leaves during the pre‐bloom period. It may be hypothesized that such competition for resources leads to reduced allocation of these reserves for further growth of the flower before bloom. However, growth cessation during this period is temporary and resumes after successful pollination and fertilization, indicating that internal factors beyond the availability of resources may also temporarily limit growth during the pre‐bloom

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period. There is a general paucity of information regarding the role(s) of such internal factors prior to bloom. It is possible that changes in phytohormone content, transport, or signaling play important roles in regulating growth during this period. In unpollinated ovaries of garden pea, abscisic acid (ABA) concentration was found to be generally higher (Rodrigo and Garcia‐Martinez 1998). Similarly, transcripts of genes associated with ABA and ethylene biosynthesis and signaling were generally upregulated in unpollinated tomato ovaries (Vriezen et al. 2008), suggesting these phytohormones, particularly ABA, may serve as negative regulators of cell production to limit growth during this period. Interestingly, KRPs are known to be positively regulated by ABA (Wang et al. 1998; Vergara et al. 2017). It may be speculated that similar regulation may occur in apple flowers before bloom to alter cell cycle progression and allow for quiescence in cell production. However, this needs to be ­experimentally verified. Measurement of phytohormone concentrations during the pre‐bloom and bloom stages would be insightful in this context. Further, analysis of transcriptome changes during the pre‐bloom period and in relation to cessation of growth is likely to provide further insights into its regulation. IV.  FRUIT SET The term “fruit set” has different implications in apple botany and production. Botanically, fruit set refers to the transition from a flower to fruit upon successful pollination and fertilization. The alternative, and a common use of the term in apple literature, is in reference to the total amount of fruit retained on the tree after bloom (“initial set;” Lakso and Goffinet 2017) or after subsequent events of young fruit abscission (“final set”). In this review, the term is used to refer to the botanical interpretation of fruit formation associated with seed formation. Pollination and fertilization lead to seed set. In other fruits such as tomato, seed set is thought to alter phytohormone synthesis and signaling, such as that of auxin, resulting in the resumption of ovary growth and the initiation of fruit development. Similarly, pollination, fertilization, and/or seed set may result in the generation of signals that trigger the resumption of growth within the fleshy regions of the apple fruit. Malladi and Johnson (2011) studied growth of the floral tube region and associated cell production and expansion in pollinated and unpollinated flowers. Growth of the floral tube region resumed between 3 to 10 DAFB in pollinated flowers but not in unpollinated flowers. This resumption in growth was associated with a rapid increase in cell production. Re‐initiation of growth and cell production following pollination

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was further associated with coordinated changes in accumulation of multiple transcripts associated with the regulation of cell production (Malladi and Johnson 2011). Many of the positive regulators of the cell cycle such as the A and B‐type CYCLINS and several CDKBs displayed a clear increase in transcript abundance during the fruit set period (8–11 DAFB). Further, their abundance was dramatically reduced in ­unpollinated flowers consistent with a reduction in cell production and growth in these flowers. Negative regulators such as the CDK inhibitor, KRP4, displayed severely reduced transcript accumulation during the initial phases of fruit set and enhanced accumulation in unpollinated flowers. Together, these data indicate a coordinated transcriptional regulation of fruit set. Factors that coordinate such a response are not well understood in apple. In other fruits such as tomato, auxins and gibberellins (GAs) are known to regulate fruit set. Exogenous applications of auxin can induce parthenocarpic fruit growth in tomato (­Serrani et al. 2007) and other fruits. Transcriptome analysis of pollinated tomato flowers during fruit set indicated alteration of multiple auxin signaling‐ related components (Vriezen et al. 2008). One set of these are the AUXIN RESPONSE FACTOR genes, ARF7 and ARF9, which are transcription factors that coordinate auxin‐dependent transcriptional responses (de Jong et al. 2009, 2015). ARF7 transcript abundance is reduced during the fruit set period in pollinated tomato flowers. Downregulation of ARF7 in transgenic tomato plants results in parthenocarpic fruit development (de Jong et  al. 2009), indicating that it is involved in downregulating growth until pollination and fertilization occur in tomato flowers. ARF9 overexpression in transgenic tomato lines decreased fruit size through negative regulation of cell production during early fruit development (de Jong et al. 2015). Its downregulation enhanced final fruit size in a complementary way, further implicating it in regulating early fruit growth. These data illustrate the important role of auxin in fruit development. Exogenous applications of GA also induced parthenocarpic fruit development in tomato and multiple other fruits (Bukovac 1963; ­Serrani et al. 2007; Watanabe et al. 2008; Liu et al. 2018). The mode of GA action in inducing fruit set may differ from that of auxins with GAs promoting cell expansion while auxins promote cell division during early fruit development, at least in tomato (Serrani et  al. 2007). In apple, unlike in tomato, auxin applications do not always induce parthenocarpic fruit development (Hayashi et al. 1968; Watanabe et al. 2008), while GA applications have been demonstrated to be effective in inducing parthenocarpy (Bukovac 1963; Bukovac and Nakagawa 1967). Among the various GAs, GA4 and GA7 were likely more effective in initiating parthenocarpic fruit set than GA3 (Bukovac 1963; Bukovac and Nakagawa 1967). An interesting feature of GA applications

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in inducing parthenocarpic fruit set in apple is an associated change in fruit shape. GA treated fruit often tend to display greater growth along the polar diameter and similar or lesser growth along the transverse diameter (Nakagawa et  al. 1967). Increase in growth along the polar diameter is associated with a larger cortex width at the distal end of the fruit through an increase in cell number and size (Nakagawa et al. 1967). Such an inducible system for fruit set and parthenocarpic fruit growth offers an excellent system to investigate molecular components associated with quiescence in fruit growth at bloom, in fruit set, and in early fruit growth. However, this has not yet been explored in apple. In the closely related fruit, pear, similar induction of parthenocarpic fruit growth in response to GAs has been reported and has been used to understand transcriptional processes involved in the regulation of fruit set (Liu et al. 2018). These data indicated an increase in transcript abundance of auxin transport‐related genes in pollinated and parthenocarpic fruit and a corresponding decrease in abundance of transcripts associated with ABA biosynthesis. Further, the abundance of positive regulators of cell production and expansion related transcripts was up‐ regulated in pollinated and GA‐treated fruit. Together, coordinated transcriptional re‐programming of the developing flower/fruit appears to regulate the progression of fruit set. The data in pear are consistent with similar changes in the abundance of cell produ­ction‐related gene products in apple during the fruit set period (Malladi and Johnson 2011). A recent study has investigated changes in the transcriptome, in relation to early flower growth and development, associated with differential chilling accumulation in apple (Kumar et al. 2017). Genes associated with post‐embryonic development were substantially ­enriched in transcript abundance during bud break and subsequent flower development leading to fruit set, suggesting coordinated regulation of this stage of fruit development. Further application of such transcriptomics and proteomics approaches to study fruit set using the inducible/parthenocarpic system is likely to provide important insights into the molecular factors that regulate this key transition in fruit growth and development. V.  FRUIT GROWTH A. Components of Fruit Growth: Cell Production, Expansion, and Void Spaces Organ growth is mediated by three main processes: cell production; cell expansion; and void space development. The relative contribution of these three processes to growth is highly variable depending

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on the organ and the plant species under consideration. However, in many organs including apple fruit, final size is often correlated with cell number rather than cell size (Harada et al. 2005; Johnson et al. 2011). However, it is important to emphasize that both factors contribute greatly to the final size of the fruit and that cell production and expansion are closely inter‐related processes (Harada et  al. 2005; ­Malladi and Hirst 2010). While regulation of cell production and expansion have been studied in detail in many plant systems, including in apple, development of void space remains a poorly understood process in spite of its relatively significant contribution to the final size of the organ. Cell production in this review refers to the generation of new cells through the process of cell division. It is distinguishable from cell division itself owing to the non‐synchronous nature of the population of cells in the organ. Cell division refers to the process of new cell generation at the level of an individual cell. In this context, an existing cell undergoes growth, duplication of the genome, and subsequently mitosis to generate a daughter cell. However, in a population of cells, as in organs such as the fruit or even within a specific tissue of the fruit, not all cells are involved in division. Further, even among those cells that are involved in the division process, not all are at the same stage of the cell division cycle. These factors together influence the rate at which new cells are produced from an existing population of cells. As measurements of cell number within a tissue over time typically do not account for the above factors, it is more appropriate to use the term cell production rather than cell division (Beemster and Baskin 1998; Baskin 2000). The use of these terms is more than just semantics. A change in cell production rate can be achieved due to an increase in the proportion of cells dividing in the population. This would involve acquisition of competency to divide by more cells. Alternatively, cell production rate could increase due to an increase in the cell division rate: the rate at which individual cells within the population complete their cell cycle. These two processes are likely regulated through different mechanisms and their relative contribution to changes in cell production rates may vary depending on the tissue type. One approach to determining the average cell division rate is to divide the relative cell production rate (RCPR) by the proportion of dividing cells, when the latter information is available. During the early period of fruit growth in apple, RCPR peaks around 0.26 cells per cell per day (Dash and ­Malladi 2012). During this period, flow cytometry analysis indicates that around 15% of the cells display nuclear DNA content of 4C, i­ndicating that they are involved in cell division (Malladi and Hirst 2010). Further, a small proportion of cells displays nuclear DNA content between 2C and 4C, likely representing

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nuclei in the process of DNA replication. Hence, around 25% of cells may be estimated to be involved in active cell division through flow cytometry analyses. Together, these data suggest a peak cell division rate of around 1.0 cell per cell per day, indicating a cell doubling time of approximately 24 h. This duration is broadly consistent with previous reports of cell division rates across other types of plant cells (Baskin et al. 1995; Beemster and Baskin 1998). However, it should be noted that flow cytometry provides only a snapshot and likely underestimates the proportion of dividing cells. Hence, the average cell division rate and the cell doubling time may, in fact, be lower and higher, respectively. An important but often underappreciated aspect of cell production is the need for cell growth prior to cell division. The typical plant cell cycle involves four stages: G1: an initial gap phase associated with growth of the new cell; S: a synthesis phase for DNA replication and doubling of nuclear DNA content; G2: a second gap phase associated with more growth and correction of errors in DNA replication; and M: a mitotic phase where cell division occurs. Between the two M phases, the cell at least doubles its volume so that the two daughter cells formed at the end of a division cycle are at least of the same size as the original cell. Measurement of cell size during periods of active cell production generally indicates little change in size, further suggesting that cells are at least doubling in volume prior to their division. This implies that rapid cell growth occurs such that the volume of the cell doubles prior to its division. Under active cell production, as in the example of the apple fruit described above, this may occur within a 24 h period. Increase in cell volume during this short period is associated with synthesis of new organelles, membranes, cytoplasmic content, and cell wall. Hence, cell production requires a large input of carbon (C), nitrogen (N), and other resources to support this rapid growth of the cell (Verbancic et al. 2018). Further, cell growth and associated high metabolic activity during this period are likely to incur substantial energy demands. This aspect of growth and rapid doubling of cell volume associated with cell division is defined here as cell growth. The rate of cell growth associated with the cell production period may, in fact, be substantially higher than the rate of cell expansion observed at later stages of growth. This is an important consideration that explains the high demand for resources during growth phases mediated by cell production. An increase in cell size during later stages of fruit growth following the cell production period is referred to in this review as post‐mitotic cell expansion or simply as cell expansion. The relative cell expansion rate (RCER) is initially high immediately following the cell production period until around 40 DAFB (from Dash and Malladi 2012). Following

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this period, RCER appears to substantially decline before increasing again slightly during the late stages of fruit development (Dash and Malladi 2012; Dash et al. 2013). These data suggest several phases of cell expansion rather than a uniform increase in cell size during fruit development. Post‐mitotic cell expansion immediately following the cell production period may involve an increase in cellular content and organelles, as well as substantial alteration of the cell wall material. Following this period, cell expansion may be driven largely by an increase in vacuolar volume facilitated by uptake of water into the organelle. Such expansion may be metabolically less intensive than that during cell production or in the rapid early cell expansion period. B.   Fruit Growth and its Regulation During fruit set and immediately thereafter, a rapid increase in the size of the organ is observed (Tukey and Young 1942; Smith 1950; ­Malladi and Johnson 2011). This pattern continues for several weeks, after which growth occurs at a more linear rate throughout the rest of fruit development. The increase in fruit size may continue until later stages of fruit development, sometimes into maturity and ripening, and may depend on environmental factors (Lakso and Goffinet 2017). Fruit growth in apple has been typically described as displaying a sigmoid growth pattern (Pratt 1988; Ryugo 1988). Increase in size is initially low around bloom, is rapid during fruit set and immediately thereafter, proceeds at a linear rate until later stages of fruit development, and tapers off at late stages. However, studies where growth was monitored on individual fruit suggested a double‐sigmoid fruit growth pattern similar to that observed in some other Rosaceae members such as peach (Magein 1989). This has been questioned due to the relatively short lag period in apple which could potentially be attributed to adverse environmental conditions (Lakso et al. 1995). Schechter et al. (1993) suggested two linear phases of fruit growth in apple coincident with the cell production and expansion phases. However, while growth during later stages does often suggest a more linear pattern, initial growth deviates substantially from this. Hence, Lakso et al. (1995) proposed an expolinear model to describe apple fruit growth. Such a model appears to fit measured fruit growth, especially under non‐limiting conditions such as when seed set is optimal, crop load on the tree is non‐limiting, and when environmental conditions are favorable: a set of conditions that allow for inherent growth characteristics to manifest. In the expolinear model, the early period of fruit growth is considered exponential and associated primarily with the cell production period. The rest of fruit development

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displays a linear growth and is largely associated with cell expansion. This suggests a nearly constant rate of cell expansion throughout most of fruit development and an associated constant demand for C and other resources during this period (Lakso et al. 1995). Using the model parameter, a nearly constant rate of cell expansion was estimated across different crop load reduction treatments (Lakso et al. 1995). Early fruit growth in apple is largely associated with intensive cell production. A review of previous studies across multiple genotypes suggests that this duration typically lasts until 3–4 weeks after full bloom (WAFB; Blanpied and Wilde 1968; Malladi and Hirst 2010; Dash and Malladi 2012), but may continue until around 7 WAFB (Denne 1960). This duration may vary depending on several factors. Genotypic differences in the duration of the cell production period have been reported (Blanpied and Wilde 1968; Hirst and Malladi 2008). Duration of the cell production phase may be affected by environmental factors such as temperature. Warrington et al. (1999) conducted a series of experiments subjecting potted apple trees to various temperature regimes during different stages of early‐ to mid‐fruit development. They indirectly assessed the duration of cell production and reported an inverse relationship between this factor and mean temperature. Additionally, the duration of cell production may potentially be affected by availability of resources (Dash and Malladi 2012; Dash et al. 2013). Together, these results suggest some plasticity in the duration of the cell production period in apple. Such plasticity may allow for fine‐tuning fruit growth responses to external environmental factors and availability of resources. C.   Cell Production Related Genes and Regulation of Fruit Growth Progression of cell production during early fruit growth involves several cycles of cell division. The plant cell cycle involves progression of the cell through multiple phases leading up to the division of the cell and generation of daughter cells. As discussed above, the plant cell cycle consists of four phases: 1. G1 phase – a gap phase immediately following the generation of a new cell, and associated with intensive cell growth; 2. S phase – a synthesis phase involving DNA replication and doubling of the nuclear genome; 3. G2 phase – another gap phase involving cell growth and DNA repair; and 4. M phase – a phase involving mitosis and generation of daughter cells (Inze and De Veylder 2006; Francis 2007). Key transitions in progression of the cell cycle are from G1 to the S phase and another from G2 to the M phase (Inze and De ­Veylder 2006; Francis 2007). Multiple gene products are associated with the regulation of the cell cycle. In the model plant Arabidopsis thaliana,

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around 70–80 genes are reported to be closely associated with cell cycle regulation and are considered to constitute the core cell cycle machinery (Menges et  al. 2005). Although there are multiple components to this machinery, the key units are the CYCLINS (CYC) and CYCLIN DEPENDENT KINASES (CDKs). CYCs accumulate and are degraded during specific phases of the cell cycle. They associate with CDKs to regulate downstream targets through phosphorylation. Multiple CYCs have been identified in plants, generally more than those identified in other eukaryotes (Inze and De Veylder 2006). Similarly, multiple types of CDKs have been identified in plants, some of which – such as the B‐type CDKs (CDKBs) – are considered plant specific. Specific interactions of CYCs with CDKs control progression of the cell cycle through its phases and through the key transitions. For example, an association of D‐type CYCs (CYCDs) with A‐type CDKs (CDKAs) regulates G1–S phase transition while CYCA and CDKA interactions regulate progression through the S phase and transition to the M phase (Scofield et al. 2014). CYCB associations with CDKAs and CDKBs regulate progression through G2, transition from G2–M, and progression through the M phase during the cell cycle (Inze and De Veylder 2006). Knowledge of the downstream targets of the core cell cycle machinery is rather poorly developed in plants. Some estimates suggest that over a thousand gene products display cell cycle modulated changes in transcript accumulation (Breyne et al. 2002; Menges et al. 2002). It is likely that many of these are downstream targets of the core cell cycle machinery. For example, phosphorylation of two downstream targets (mitotic kinesin‐like protein and a MAP kinase kinase kinase) by CDKA regulates transition to cytokinesis in plants (Sasabe et al. 2011). Several regulators of the cell cycle are included within the core cell cycle machinery. Plant CDKs are negatively regulated by KINASE INHIBITOR PROTEIN (KIP) RELATED PROTEINS (KRPs). KRPs can bind to and negatively regulate the activity of CDK/CYCLIN complexes (Verkest et  al. 2005; Inze and De Veylder 2006; Van Leene et al. 2010). In Arabidopsis, KRP2 inhibited CDKA;1 activity and was itself regulated through phosphorylation by CDKB1;1 and subsequent proteasome mediated degradation (Verkest et al. 2005). Such regulation allows for fine‐tuning of the cell cycle. The core cell cycle regulators can alter competency for cell division of individual cells. Further, the rate of progression through the cell cycle can also be affected by the activities of the cell cycle machinery. Together, these two processes can have a strong impact on the extent of cell production and can thereby influence growth rates of organs. However, multiple studies involving direct manipulation of the cell cycle  machinery components have indicated that growth may not be

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directly altered by their mis‐expression in part due to “compensation” mechanisms (Hemerly et al. 1995; De Veylder et al. 2001; Dewitte et al. 2003; Verkest et  al. 2005). Compensation refers to an active process where alteration in the extent of cell production is countered at least in part by a complementary change in the extent of cell expansion (­Horiguchi and Tsukaya 2011). Nevertheless, as cell cycle regulators are key components controlling progression through the cell division process, it is likely that they are the key downstream effectors facilitating organ growth. In apple, multiple members of the cell cycle machinery were ­identified and their transcript accumulation patterns during different stages of fruit growth and development were characterized (Malladi and Johnson 2011). Based on pre‐bloom, fruit set, and fruit developmental patterns of transcript abundance, 14 genes were identified as being positively associated with cell production. Transcripts of these genes accumulated in response to fruit set and during early stages of fruit growth (3–4 WAFB). Several CDKBs and multiple A‐ and B‐type CYCLINS were included within this group, suggesting that availability of these G2/M phase‐related factors may be limiting for cell production during apple fruit growth. Similar results were reported in one of the earliest microarray‐based transcriptome studies of fruit development in apple which evaluated eight stages of fruit growth and development (­Janssen et al. 2008), and in another study describing impaired fruit growth responses to elevated temperature (Flaishman et  al. 2015). Further, proteomics studies of fruit development also indicate similar changes in cell production regulator abundance (Li et al. 2016). Transcript abundance of several of these genes (CYCAs) was altered by severe shading during early fruit development, a treatment which reduces the extent of cell production (Dash et al. 2012). Conversely, many of the CDKBs and CYCAs displayed higher transcript abundance in response to a reduction in fruit load, a treatment that enhances growth through cell production (Dash et  al. 2013). Duan et  al. (2017) suggested a potential role for several CYC genes in evolution of fruit size during domestication as they were co‐localized to regions associated with selective sweeps. Five genes were also identified as potential negative regulators of cell production by Malladi and Johnson (2011), two of which were KRPs (KRP4 and KRP5). These KRPs displayed transcript accumulation patterns complementary to those of the positive regulators; generally declining during early fruit development and increasing in abundance during transition from cell production to expansion (Malladi and ­Johnson 2011). Further, both these KRPs displayed increased transcript abundance in unpollinated fruit and in response to severe shading,

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instances associated with reduced cell production (Malladi and Johnson 2011; Dash et  al. 2012). Together, these data suggest important roles for these genes in regulating cell production and growth during early stages of fruit development. D.  Organ Size Related Genes and Regulation of Fruit Growth While the core cell cycle machinery facilitates cell production, additional factors may also be involved in regulating this process. Many organ growth‐related genes have been identified in other plant systems such as Arabidopsis and tomato. Some of these genes affect cell production and their orthologs in apple are likely to perform similar functions. For example, the FRUIT WEIGHT 2.2 (FW2.2)/ CELL NUMBER R ­ EGULATOR (CNR) gene was initially identified in tomato as being associated with fruit weight (Frary et al. 2000). Differential temporal transcript accumulation of this gene during fruit development is thought to negatively regulate cell production and thereby influence fruit size across tomato genotypes (Nesbitt and Tanksley 2001; Cong et  al. 2002). Multiple putative CNR homologs were identified in peach and cherry (Franceschi et  al. 2013). The genomic position of two of these co‐localized with that of two quantitative trait loci (QTLs) associated with fruit size in cherry (Franceschi et al. 2013). Hence, these genes may play similar roles in Rosaceae family members as well. No reports on the roles of these genes in regulating apple fruit growth are yet available. Transcription factors that can modulate the transcript abundance of downstream targets associated with cell division are potential candidates associated with the regulation of fruit growth. One such transcription factor belonging to the plant specific APETALA2 (AP2) domain family is AINTEGUMENTA (ANT). In Arabidopsis, ANTs positively regulate cell production and thereby influence organ growth (Mizukami and Fisher 2000), although in a different Arabidopsis ecotype, they were reported to affect cell size (Krizek 1999). Loss of its function reduces overall organ size while its overexpression enhances shoot organ size in Arabidopsis (Krizek 1999; Mizukami and Fisher 2000). ANTs are thought to regulate the duration of cell production and its overexpression can affect cell cycle progression by enhancing CYCD3 transcript abundance (Mizukami and Fisher 2000). However, such a direct relationship to CYCD3 expression and the cell cycle has recently been questioned (Randall et al. 2015), and it may be likely that alternative mechanisms are involved. Putative homologs of ANT, ANT1 and ANT2, and ANT‐like (AIL) genes were identified and characterized in apple (Dash and Malladi 2012). The two genes, ANT1 and ANT2,

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share high sequence similarity and are likely duplicated forms of the apple ANT gene. Expression of ANT1 and ANT2 in apple is coincident with transcript accumulation of many positive regulators of cell production (Dash and Malladi 2012). Transcript abundance of both these genes increases during early fruit growth during the period of cell production and dramatically declines during exit from this phase (Dash and Malladi 2012). Reduction in fruit load enhances cell production in apple and this is associated with an increase in transcript abundance of at least ANT1. Further, comparison of two genotypes differing in final fruit size potential through differences in cell number, indicated substantial differences in transcript abundance profiles of these ANT genes. These data are consistent with a role for the apple ANT genes in regulating cell production during early fruit growth. Further analysis of their function and their downstream targets is necessary to clearly determine their specific roles in promoting cell production during early fruit growth. Daccord et al. (2017) performed re‐sequencing of the apple genome and genome‐wide DNA methylation analysis in apple. In their study of fruit development, they utilized a double haploid ‘Golden Delicious’ apple genotype (GDDH13) and compared it to an isogenic line (GDDH18) derived from the same haploid. While these two genotypes were phenotypically largely similar, they differed primarily in their fruit size, with GDDH18 displaying smaller fruit owing to reduced cortex cell number. Multiple single nucleotide polymorphisms (SNPs), with a few resulting in potential amino acid changes, were identified through the comparison of these genotypes. Further, comparison of DNA methylation across these two genotypes over different developmental stages identified 22 differentially methylated genes including several transcription factors, and a gene associated with ethylene biosynthesis (Daccord et al. 2017). Several of these genes are homologous to genes with potential organ‐growth regulating roles in other plants. Functional characterization of these genes may provide useful insights into regulation of cell production during early fruit growth in apple. This study also implicates DNA methylation as a potential fruit growth regulatory mechanism in apple (Daccord et al., 2017). E.  Floral Homeotic Genes and Regulation of Fruit Growth Multiple floral organ identity genes have been defined in studies on apple and many of these genes appear to have functions beyond regulation of flower development, such as in fruit growth and ripening. In fact, several of these studies are examples of the clearest genetic case studies

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for regulation of apple fruit growth. Potential changes in tissue and cell layer specifications during flower development can have profound effects on organ growth at later stages and may explain some of these effects on growth. The microRNA, miR172, was recently described as being associated with regulation of fruit size in apple (Yao et al. 2015). Overexpression of miR172p in apple resulted in multiple phenotypic changes in floral and fruit morphology, some of which were associated with the intensity of its overexpression. A transgenic apple line overexpressing miR172p by 15‐fold displayed a dramatic reduction in fruit size, reducing ‘Royal Gala’ fruit size to that of a crabapple fruit. This was associated with a reduction in the size of the hypanthium at bloom and during early fruit development. During this period, cell size was similar in wild‐type and transgenic lines indicating that a reduction in cell production capacity during early fruit growth may contribute partially to the reduced fruit size phenotype in these plants (Yao et al. 2015). An allele of miR172 displaying a transposon insertion and potentially reduced expression was associated with larger fruit size across multiple Malus accessions and a segregating population. The wild type allele was named as the CRAB APPLE FRUIT SIZE (CAFS) locus (Yao et  al. 2015). The miR172 may regulate expression or translation of AP2 genes which are floral homeotic genes regulating floral organ identity. This work in apple is somewhat contrary to a fruit growth promoting role proposed for miR172 in Arabidopsis (Ripoll et  al. 2015). However, this apparent discrepancy has been attributed to the fundamentally different origins of the fruit tissue in these two species with Arabidopsis forming a silique derived primarily from the ovary (Yao et al. 2015; 2016). In the proposed model, AP2 may function to promote sepal identity and growth and its downregulated activity in genotypes with higher miRNA172p expression results in reduced fruit size as this cortex tissue is largely derived from the fused basal regions of floral appendages including sepals. In addition to miRNA172p, Duan et al. (2017) identified two other miR172 genes that may also be associated with fruit size evolution in apple. Another floral homeotic gene belonging to the class B of organ identity genes, PI, has also been associated with regulation of localized fruit growth in apple (Yao et al. 2018). Alteration of PI expression was previously reported to be associated with parthenocarpic apple fruit development (Yao et  al. 2001). Over and ectopic expression of PI in ‘Bolero’ apple resulted in the conversion of sepals to petals and altered fruit morphology by altering fruit shape (Yao et  al. 2018). Beginning from early stages of fruit growth (eight days after pollination), transgenic lines overexpressing the PI gene displayed characteristic longitudinal

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grooves on the fruit and a temporary transverse groove. By maturity, the fruit displayed a reduced height to width ratio and a flattened fruit shape. While cell size was reduced within the groove regions, cell production may also have been potentially altered in this region resulting in the observed changes in fruit morphology. The authors hypothesized that PI may heterodimerize with another homeotic gene product AP3 to suppress growth in the fruit and that the localized accumulation of AP3 may contribute to such spatial growth regulation. However, the localized accumulation of AP3 transcripts or the protein remains to be characterized. A potentially conserved role for PI in regulating fleshy fruit growth is supported by work in grape where a fleshless berry (flb) mutant was found to contain a transposon insertion within the promoter region of PI resulting in its ectopic expression during early fruit development and an associated loss of fleshy tissue growth due to reduced cell division and expansion (Fernandez et al. 2006, 2007, 2013). A MADS box gene belonging to the class E floral homeotic gene family (SEPALLATA1/2; SEP1/2), a class of gene products that function along with other floral homeotic gene products to determine floral organ identity, has also been associated with regulation of fruit growth and development in apple (Ireland et al. 2013). Antisense suppression of one of these genes (MADS8) in apple also affected transcript accumulation of several closely related genes: MADS9 and MADS7. Transgenic apple lines displaying reduced expression of these genes displayed floral, fruit growth, and ripening related phenotypes. Floral morphology was altered through the development of sepalloid petals and reduced post‐ bloom petal abscission. Histological analysis revealed that in these transgenic lines, the outer hypanthium tissue development was already affected at bloom. Further, fruit from these transgenic lines displayed reduced growth primarily due to a reduction in growth within the cortex tissue. Cells within the cortex were substantially reduced at maturity, indicating that cortex cell expansion was altered in these lines resulting in a dramatically reduced fruit size phenotype. Interestingly, reduced expression of a closely related MADS9 genes appears to similarly alter fleshy fruit growth in strawberry, at least in some severe phenotype lines (Seymour et al. 2011), suggesting a more general role for these genes in the growth of fleshy fruits. F.  Cell Wall Modifying Genes and Regulation of Fruit Growth Multiple cell wall modifying genes have been investigated in apple in relation to their potential roles in regulating fruit growth. Cell expansion is primarily driven by turgor within cells (Cosgrove 2018). Increase in

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volume of cells, either in relation to cell growth or in relation to post‐ mitotic cell expansion, is associated with loosening of the cell wall and the associated relaxation of wall stress resulting in an irreversible increase in the surface area (Cosgrove 2016, 2018). Multiple enzymes such as expansins, endoglucanases, endotransglucosylases, and pectin‐modifying enzymes such as pectinmethylesterases and polygalacturonases, have been associated with cell wall loosening in relation to growth and other responses (Cosgrove 2016). Only a few of these have been systematically evaluated in apple in relation to cell expansion during fruit growth. An initial study evaluated the transcript abundance of six EXPA (α‐EXPANSIN) genes in apple and identified at least one for which the expression pattern coincided with the cell expansion period of fruit growth (Wakasa et al. 2003). Dash et al. (2013) also evaluated the transcript accumulation patterns of several EXPA genes during fruit development and in relation to reduction in fruit load. These E­XPAs displayed varying transcript abundance during fruit development but at least two of them displayed an increase in abundance during mid‐ fruit development coincident with the post‐mitotic cell expansion phase of fruit growth. One of these, EXPA10;1, displayed a reduction in transcript abundance in response to severe shading, a treatment associated with a reduction in cell expansion (Dash et al. 2012). A systematic genome‐wide analysis of EXPANSINs in apple identified 41 such genes that could be classified into four sub‐groups (Zhang et al. 2014). While the transcripts of many of these genes were identified within the fruit, a detailed analysis of abundance was performed primarily in relation to ripening (Zhang et al. 2014). While many putative endoglucanase, endotransglucosylase, and pectin modification‐associated genes have been identified in transcriptome studies and other studies in apple (Atkinson et al. 2012; S. Jing and others, unpubl.), analysis of their expression profiles and their responses to factors that alter growth is still lacking, although they have been studied in relation to fruit ripening (e.g., Atkinson et  al. 2012). A proteomic study indicated higher expression of several endotransglucosylase and pectin modification‐associated gene products during mid‐ fruit development coincident with the period of cell expansion (Li et al. 2016). Additionally, two beta‐galactosidase genes were co‐­localized to a locus associated with fruit size evolution during domestication (Duan et al. 2017). The potential roles of these genes in regulating apple fruit growth is unclear. In strawberry, downregulation of the expression of these genes reduced fruit weight likely due to impaired pollen tube growth, fertilization, and reduced achene numbers, but not by altering fruit growth processes directly (Paniagua et al. 2016).

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An additional set of cell wall modifying factors are the gene products of the COBRA (COB) and COBRA‐LIKE gene families. COB was identified in Arabidopsis as a gene associated with oriented cell expansion (Schindelman et al. 2001). Further analysis suggested crystalline cellulose and microfibril orientation were significantly impacted in the cob mutant. These data indicated a role for COB in regulating the deposition of cellulose microfibrils during cell elongation (Roudier et  al. 2005). A putative COB homolog, COB1, was identified in apple and its transcript accumulation during fruit development was characterized (Dash et al. 2012, 2013). COB1 transcript abundance was relatively constant during the cell production period but rapidly increased by over fourfold following exit from this phase and remained high and stable during the rest of fruit development. Interestingly, the period of rapid increase in COB1 transcript abundance in apple coincides with the period of highest RCER during fruit growth (Dash et al. 2013). Further, its transcript abundance was slightly but significantly reduced in response to severe shading which induced a reduction in cell production and expansion (Dash et al. 2012). Together, these data suggest a potential role for the COB1 gene product in facilitating rapid cell expansion during fruit development. In tomato, a putative homolog of COB was identified and functionally characterized (Cao et  al. 2012). The tomato COB displays higher transcript abundance during early fruit development coincident with the period of rapid cell expansion and declines towards ripening, a period where no additional cell expansion occurs in tomato. Fruit‐specific downregulation of the tomato COB due to co‐suppression leads to reduced crystalline cellulose content and fruit cracking. Further, pericarp cell walls appeared to be compromised in these lines, leading to the collapse of some cells. Its overexpression resulted in increased cellulose content, fruit firmness, and shelf‐life (Cao et al. 2012). Together, these data suggest an important role for COB in regulating cell wall remodeling during cell expansion mediated fruit growth. In apple, much of the information on regulation of cell expansion remains to be functionally analyzed. A systematic functional analysis of some of the above described genes in relation to cell expansion during fruit growth is necessary to determine the key components associated with cell wall loosening in relation to fruit growth. G.  Metabolism and Regulation of Fruit Growth Fruit metabolism is an integral component of fruit development and plays primary roles in determining the rate of growth and final fruit quality. Integration of molecular regulation of fruit metabolism with

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regulation of growth in the organ is only recently being achieved in model fruit systems. In apple, further work is necessary to achieve a better understanding of the role of fruit metabolism in the molecular physiology of fruit growth. A brief discussion of apple fruit metabolism in presented below to allow for an appreciation of the inter‐dependence of these processes. The apple fruit possesses significant photosynthetic ability (­Blanke and Lenz 1989), but it also functions as a heterotrophic organ. ­Blanke and Lenz (1989) proposed that apple fruit photosynthesis was intermediate between that of C3 and C4/CAM. Such photosynthetic activity allows for the fruit to partially meet (5–20%) its carbohydrate demands for growth, at least during early fruit development (Blanke and Lenz 1989; Lakso and Goffinet 2017). Hence, the apple fruit still functions as a major sink and is greatly dependent on resource import to meet its metabolic demands. Much of the carbohydrate and other nutritional requirements before bloom are supported by remobilized reserves from the previous season in roots and stems (Hansen 1971; Titus and Kang 1982). Around bloom or slightly after, there appears to be a transition such that current photosynthesis from newly emerged and photosynthetically established leaves begins to support the majority of growth of the fruit (Hansen 1967, 1971; Quinlan, 1969; Oliviera and Priestley 1988; Forshey and Elfving 1989). The cell production phase of growth creates intensive demands for carbohydrates and other nutrients. Cell growth requires additional cytoplasmic material, cell wall components, membranes, and organelles. Subsequently, there is also an increased energy demand to facilitate the high metabolic activity during this period. In fact, the rate of respiration during fruit development is highest during this growth period (Blanke and Lenz 1989; Beshir et al. 2017). Post‐mitotic cell expansion involves multiple metabolic changes which allow for some cytoplasmic growth of the cell but also allow for a large increase in vacuolar volume through the intake of water, a process mediated by the accumulation of osmoticum within these organelles. Further, this period of growth also involves transitory accumulation of carbohydrate in the form of starch (Berüter 1985). This is subsequently metabolized during later stages to support accumulation of other sugars and to meet the respiratory demands of ripening. These aspects of carbohydrate and nutrient requirement clearly demonstrate the dependence of the fruit cells on resource import to sustain growth. Further, a reduction of fruit load often leads to enhanced fruit growth, especially if performed early in the season (Auchter 1920; Denne 1960; Westwood et  al. 1967; Dennis 2000). This increase in fruit growth is mediated by an increase in cell production but can also involve an

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23

increase in cell expansion (Denne 1960; Westwood et al. 1967; Goffinet et al. 1995; Dash et al. 2013). Such an increase in growth is one of the main reasons for application of extensive crop load management practices in apple (Wunsche and Ferguson 2005; Kon and Schupp 2019). Carbon may enter apple fruit primarily in the form of sorbitol (Sor) or sucrose (Suc), with the extent of carbon in the form of Sor being ­several‐fold higher than that in the form of Suc (Webb and Burley 1962; Berüter and Droz 1991). Phloem unloading in apple occurs apoplastically during early fruit development (Zhang et al. 2004), requiring the function of transporters to allow for its intake into fruit cells. Several putative sugar transporters have been identified and their transcript abundance characterized in apple, some of which may be involved in the entry of Sor and Suc into fruit cells (Gao et al. 2005; Li et al. 2012; Wei et al. 2014). Although Sor serves as one of the main forms of carbon entry into the fruit, it does not typically accumulate during fruit development (Berüter 1985; Yamaki and Ishikawa 1986; Zhang et  al. 2010). Instead, Sor is rapidly converted to fructose (Fru) by sorbitol dehydrogenase (SDH) (Yamaki and Ishikawa 1986; Archbold 1999). Multiple genes coding for SDH have been identified in apple and the expression patterns of some of them are consistent with changes in Sor concentration, especially during early fruit development, indicating that SDH activity can affect sink strength of apple fruit (Nosarszewski et al. 2004). Sucrose concentration increases during most of fruit development (Berüter 1985; Yamaki and Ishikawa, 1986), mediated by the entry of Suc into the fruit cells, and extensive interconversions during Suc metabolism. Sucrose metabolism in apple fruit may occur through the activity of multiple enzymes. Invertases convert Suc into Fru and glucose (Glc). Cell wall invertases may metabolize Suc following its apoplastic ­unloading, but such invertase content was found to be low in the fruit cortex (Li et al. 2016). In tomato, a cell wall invertase gene (LIN5) was identified as the underlying gene for a major QTL for fruit sugar content and yield, and its downregulation resulted in reduced fruit size (Fridman et al. 2004; Zanor et al. 2009), supporting a substantial role for these genes in regulating fruit growth. Neutral invertases (NINV) function in the cytoplasm and one of the genes coding for an NINV, NINV5, was postulated to be associated with Suc unloading in apple (Li et al. 2012, 2016). Vacuolar invertases (VINV) may also metabolize Suc leading to the production and potential accumulation of Fru and Glc in the vacuole. Acid invertase activity is generally higher during early fruit growth (Berüter 1985) and may therefore serve as an important mechanism for Suc metabolism during this period. Sucrose may also be metabolized

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by sucrose synthase (Susy), yielding Fru and UDP‐Glc. Potentially, such Susy activity can feed into cellulose synthesis to support the new cell wall growth requirements associated with rapid early fruit growth (Verbancic et al. 2018). In fact, Susy activity was generally higher during early fruit development and s­ ubsequently declined at later stages (Li et al. 2012). Further, Suc metabolism in the apple fruit also involves a Suc–Suc cycle contributing to the accumulation of Suc during fruit development through the activity of sucrose phosphate synthase (SPS; Li et  al. 2012). Starch breakdown during late fruit development may also contribute to Suc accumulation (Berüter and Feusi 1997). Fructose and Glc generated from the metabolism of carbon imported into the fruit can have multiple metabolic fates. Fru and Glc can enter glycolysis following their phosphorylation by fructokinase and hexokinase, respectively. Fructokinase protein content and activity are higher during early fruit growth (Li et al. 2012, 2016). Similarly, hexokinase activity and transcript abundance of hexokinase genes was greater during early fruit growth (Li et al. 2012; S. Jing and A. Malladi, unpubl.). Such flux into glycolysis and subsequent respiration is critical to meet energy and carbon skeleton demands of early fruit growth. Glycolytic flux was in fact reported to be high during early fruit development (Beshir et  al. 2017) and to decline at later stages (Li et  al. 2016). In tomato, overexpression of an Arabidopsis hexokinase gene reduced fruit growth underlining the important role of these genes in supporting organ growth (Menu et  al. 2004). Hexose phosphates can also be converted to nucleotide‐sugars which then serve as precursors for the synthesis of non‐cellulosic cell wall material (Verbancic et  al. 2018). Another metabolic fate for these sugars is their accumulation in the vacuoles during early fruit development (Berüter 1985; Zhang et  al. 2010; S. Jing and A. Malladi, unpubl.). This may serve multiple purposes, including that of increasing osmoticum to allow for cell expansion at later stages. Fructose, in fact, continues to accumulate during mid and late stages of fruit development at levels higher than that of Glc such that it is typically the most abundant simple sugar at maturity (Berüter 1985; Zhang et al. 2010). These sugars may also contribute to transitory starch biosynthesis and accumulation that occurs during mid stages of fruit development, coincident with the period of cell expansion. This metabolic transition away from glycolysis during mid fruit development may reflect lower demands for carbon skeletons and energy to facilitate cell expansion‐mediated growth. Malic acid (malate) accumulates during fruit development in apple and is the most abundant organic acid in apple fruit (Ulrich 1970; Berüter 2004; Walker and Famiani 2018). Fixation of CO2 (HCO3−) by

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25

phosphoenolpyruvate carboxylase (PEPC) with PEP serving as the other substrate to generate oxaloacetic acid (OAA) has been reported in apple (Blanke and Lenz 1989). Malate dehydrogenase (MDH) activity may subsequently convert OAA to malate (Blanke and Lenz 1989). In fact, such a pathway for malate synthesis appears to be common across multiple fruits and may serve as the major route for its synthesis (Etienne et al. 2013; Walker and Famiani 2018). Malate concentration increases gradually during early fruit development reaching a peak towards the end of the cell production period of fruit growth (Zhang et al. 2010; S. Jing and A. Malladi, unpubl.). Putative PEPC genes and MDH genes have been isolated from apple and partially characterized (Yao et  al. 2009, 2011). Transcript abundance of some PEPC genes increases during early fruit growth and development, while that of some MDH genes is also high during this period, consistent with a role for PEPC and MDH in generating malate during early fruit development (Yao et  al. 2009, 2011; S. Jing and A. Malladi, unpubl.). Malate generated through such metabolism or through the tricarboxylic acid (TCA) cycle may be transported into vacuoles for storage allowing for its accumulation. The capacity for storage may determine the ability of a given apple cultivar to accumulate malate (Berüter 2004). Further, a potential gene responsible for a low fruit acidity phenotype was found to be an aluminum activated malate transporter (Bai et  al. 2012). The physiological significance for such accumulation of malate is not entirely clear. One ­hypothesis is that malate accumulation in the vacuole during early fruit growth may serve as an osmoticum that allows for cell expansion at later stages, as has been proposed for tomato (Guillet et al. 2002), indicating direct implications for cell expansion‐mediated fruit growth. Alternatively, malate may serve as a storage form of carbon that can re‐enter respiration (TCA cycle) at later stages such as during the respiratory climacteric. Overall, malate accumulation influences fruit growth and development, and contributes to final fruit quality. An area that has had relatively little study is N metabolism during fruit growth. Much of the N required to support pre‐bloom growth until full bloom is likely to be supported by remobilization of N reserves (Titus and Kang 1982; Malaguti et al. 2001; Guak et al. 2003). Remobilization of N continues to support early fruit growth, although current N acquisition also contributes to growth during this period (Titus and Kang 1982; Malaguti et al. 2001; Guak et al. 2003). The entry of N into the fruit is likely in the form of amino acids during this period, predominantly in the form of asparagine (Asn), aspartate (Asp), glutamine (Gln), and arginine (Tromp and Ovaa 1971; Malaguti et al. 2001). In fact, within the fruit tissue, Asn is the most abundant amino acid during

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early fruit development (Zhang et  al. 2010; Beshir et  al. 2017). How these forms of N imported into the fruit are metabolized to support N demands during early fruit growth remains unclear. It is likely that Asn is metabolized by asparaginase to yield Asp and ammonium (NH4+; Gaufichon et  al. 2016). Aspartate may have several metabolic fates including conversion to OAA, and as the N source for the biosynthesis of other amino acids. The NH4+ released may be re‐assimilated through the glutamine synthetase–glutamine 2‐oxo‐glutarate aminotransferase (GS–GOGAT) pathway leading to the synthesis of glutamate. Owing to higher N demand during cell production, it may be speculated that such N metabolism is substantially higher during early fruit growth. Nitrogen availability does in fact limit fruit growth and increased N availability increases cell production and fruit size (Xia et  al. 2009). Future studies should evaluate the contribution of N metabolism and its molecular regulation to fruit growth and development as this represents a major gap in knowledge. H.  Phytohormones and the Regulation of Fruit Growth Phytohormones are key factors that coordinate cell production and expansion and may therefore have profound effects on fruit growth in apple. Multiple phytohormones are thought to regulate apple fruit growth. Auxins have been implicated in the regulation of various aspects of fruit growth and development including cell production, expansion, and ripening (Srivastava and Handa 2005). In apple, synthetic auxins such as naphthalene acetic acid (NAA) are regularly used for crop load management and can therefore influence fruit growth indirectly (Dennis 2000; Zhu et al. 2011). It is likely that endogenous auxins play significant roles in regulating fruit growth as well. Consequently, detailed genomic analysis of the potential role of auxins, their metabolism, transport, and signaling, has been reported in apple (Devoghalaere et al. 2012). Free auxin (indole‐3‐acetic acid; IAA) concentration increased in the fruit cortex during mid‐fruit growth coincident with the period of post‐mitotic cell expansion. Interestingly, IAA concentration in the seeds was substantially higher and continued to increase during fruit development. Injection of IAA into the fruit at 30 DAFB enhanced growth, resulting in larger fruit. This was primarily achieved through an increase in cell size indicating a role for IAA in promoting cell wall loosening and facilitating cell expansion (Devoghalaere et  al. 2012). Transcript abundance of six classes of auxin‐related genes – ­including those coding for putative receptors, signaling proteins, and transport proteins  –  were evaluated during fruit  development and found to be

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27

dynamically altered. One such class evaluated included auxin metabolism‐related genes (GH3) involved in its conjugation. Transcript abundance of several of these genes declined during cell expansion, suggesting a decrease in IAA conjugation during this period allowing for a larger pool of free and active auxin (­Devoghalaere et  al. 2012). A key aspect of that study was the identification of several fruit size‐ related QTLs using two mapping populations. One of the auxin signaling‐related genes, ARF106, was co‐localized to a QTL associated with fruit size. ARFs are transcription factors involved in mediating auxin responses through binding to auxin response elements within promoters of auxin‐inducible genes. Modulation of gene expression by ARFs is repressed by their interaction with AUX/IAA proteins. Once auxin binds to the TIR1–AUX/IAA co‐receptor complex, AUX/ IAA is degraded and its repression of ARF activity is released. Subsequently, the ARFs dimerize and, by binding to promoter regions of auxin‐inducible genes, regulate downstream transcription of those genes (Leyser 2018). ARF106 transcript abundance was higher during cell production and expansion phases, consistent with a potential role in promoting growth through both processes (Devoghalaere et al. 2012; Dash et  al. 2013). These data implicate endogenous auxins in regulating fruit growth, but further studies are clearly needed to determine ­mechanisms mediating this response. For example, identification of ARF targets may provide mechanistic explanations for the roles of auxins in regulating apple fruit growth. Cytokinins are known to promote cell production in a range of plant systems by potentially altering cell cycle progression (Schaller et  al. 2014). CYCD3 transcript abundance has in fact been demonstrated to be affected by cytokinin availability (Riou‐Khamlichi et al. 2000). Hence, cytokinins may also regulate cell production during early fruit growth (Srivastava and Handa 2005). The plant growth regulators (PGRs), 6‐­ benzyl adenine (6‐BA) and N‐(2‐chloro‐4‐pyridyl); N’‐phenylurea (CPPU) have been studied in reference to crop load management and enhancement of fruit size in apple (Greene 2001; Stern et  al. 2003, 2006). Applications of 6‐BA can result in a reduction in fruit load which can indirectly allow for enhanced fruit growth of remaining fruit (Greene et al. 2016). However, a more direct effect of 6‐BA on cell division within apple fruit has also been suggested (Wismer and Procter 1995). Stern et  al. (2003, 2006) reported an increase in fruit size by early applications of 6‐BA and CPPU at lower rates than those used for crop load reduction. The molecular components facilitating such an increase in cell production in relation to these PGR applications remain to be identified. Analysis of changes in cell production, and

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changes in the transcript abundance of genes associated with regulating cell production, would be an initial step in this direction. Owing to its importance in regulating cell production, it is essential to characterize spatial and temporal changes in cytokinin metabolism and changes in associated transcript abundance during the cell production phase of fruit growth. A related study in tomato indicated high cytokinin metabolism during the cell production phase of fruit growth and high cytokinin biosynthesis and signaling‐related transcript accumulation during this period (Matsuo et al. 2012). Endogenous abscisic acid (ABA) concentration in the fruit cortex appears to decline during fruit development, although this was studied during only a short period spanning four days (Giulia et al. 2013). Transcriptomics analysis of shaded, 6‐BA treated, and NAA treated fruit in relation to fruit abscission revealed substantial alteration in ABA biosynthesis and signaling suggesting a role for this phytohormone in mediating this response (Botton et  al. 2011; Zhu et  al. 2011). In fact, exogenous ABA applications are able increase fruit drop (Giulia et al. 2013). However, whether endogenous ABA contributes to fruit abscission by altering growth characteristics directly remains to be evaluated. Ethylene is a gaseous phytohormone with well‐defined roles in fruit ripening and mature fruit drop in apple (Li et al. 2015). Ethylene concentration and emission are often affected by PGRs and other chemical agents functioning as chemical thinners in apple (Zhu et al. 2011), but the role of ethylene in regulating apple fruit growth remains unexplored. Endogenous ethylene emission decreases during the first few weeks of fruit development following petal fall (Walsh and ­Solomos 1987). Large variability in ethylene emission characteristics during this period were noted, but this was not necessarily correlated with abscission potential. Whether this is related to the growth potential of the fruit remains to be established. This is a potentially important aspect considering that emerging evidence in model plant systems suggests that ethylene signaling can regulate organ growth by altering cell production (via the cell cycle) and expansion (via cell wall l­oosening agents) in a context‐specific manner (Dubois et al. 2018). For example, while ethylene inhibits young leaf growth in ­Arabidopsis, it can p ­ romote cell expansion in grape berries (Chervin et al. 2008; Dubois et al. 2018). Jasmonates are another class of phytohormones with potential roles in regulating apple fruit growth and development. The concentrations of jasmonates, jasmonic acid (JA), and methyl‐jasmonate (MeJA) were high during early fruit development coincident with the period of cell production, declined at later stages, and increased during ripening

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29

(Kondo et al. 2000). A clear role for jasmonates in regulating fruit ripening in apple by alteration of ethylene biosynthesis has recently been demonstrated (Li et al. 2017). However, the role of jasmonates during early fruit growth and development remains unclear. Jasmonates are generally associated with negative regulation of cell cycle progression (Pauwels et al. 2008; Noir et al. 2013). The spatial and temporal context of elevated concentrations of jasmonates during early fruit growth needs to be better characterized to understand their roles in regulating fruit growth. Further, the molecular mechanisms associated with jasmonate metabolism and signaling need to be explored to better understand their roles in fruit growth and development. I.  A Note on the Measurement of Growth Future research on understanding molecular regulation of fruit growth should aim to integrate spatial and temporal characteristics of growth with molecular mechanisms of their regulation. Hence, it is important that fruit growth and its contributing components are measured accurately and with high spatiotemporal resolution. Diverse methods of growth measurement have been used in apple and other fruits. One of the most effective methods to monitor growth is through measurement of increase in dry weight over time. However, this method is not widely used owing to the destructive nature of sampling. Growth is most frequently measured by monitoring changes in fruit diameter over time, a relatively simple and non‐destructive method that can allow for repeated measurements of individual fruit. However, fruit diameter is a one‐dimensional measure of a three‐dimensional organ and is therefore limited in the information it provides, especially if growth is monitored over the entire fruit developmental period as this can involve substantial changes in fruit shape. An approach often used by multiple authors is to establish a relationship between fruit diameter and weight for the genotype under consideration (e.g., Warrington et al. 1999). Estimations of fruit weight from these data can be used to monitor growth. An alternative is the estimation of fruit volume using fruit diameter data. However, this can also be complicated by changes in fruit shape over development and the fact that the typical apple fruit often deviates from a simple sphere. In this context, measurement of fruit diameter and length can provide better estimates of volume, which can then be related to fruit weight. Advances in the application of imaging tools are necessary to non‐destructively measure fruit growth parameters. One such approach is the use of three‐dimensional imaging methods such as light detection and ranging (LiDAR) to obtain dense‐point clouds

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from which fruit morphology metrics can be extracted. A recent study demonstrated such an application of multiview stereovision to obtain fruit height, width, volume, and other metrics from mature strawberry fruit (He et  al. 2017). Similar tools are also being employed in other types of fruit such as peach (D. Chavez, pers. commun.). Some limitations of current technology are low spatial resolution and issues with interference from alternative light sources making their application more challenging on younger fruit and under field conditions. However, further improvements in these imaging technologies and their decreasing costs should allow for their application to non‐destructively monitor individual fruit growth under field conditions. Such developments are essential to improve high throughput fruit growth phenotypic characterization, an essential metric in studies of molecular regulation of fruit growth. An inherent issue with all of the above methods of growth measurement is that they limit monitoring to growth across the entire organ. However, the apple fruit is not homogenous and is constituted by multiple tissue types. It is likely that growth across all of these tissues is not uniform (Tukey and Young 1942; Herremans et al. 2015; S. Jing and A. Malladi, unpubl.). Better characterization of fruit growth, therefore, requires spatial resolution in measurement and integration with overall organ growth. Emerging imaging technologies need to be employed to make progress in this area. Such tools have recently been employed in some initial efforts to obtain information on void space and vascular tissue development within the fruit. Three‐dimensional imaging analysis through X‐ray micro‐tomography was used to determine and compare void spaces in apple and pear fruits and was effective in providing micro‐meter resolution of some internal features of the fruit (Mendoza et al. 2007; Verboven et al. 2008). These studies indicated a higher void fraction within the cortex of mature apple fruit (~23%) than in pear fruit (~5%; Verboven et al. 2008). The estimate for apple is consistent with previous studies that used light microscopy‐based estimates of void space (Goffinet et  al. 1995). These tools were further employed to determine temporal and spatial growth and development of void fractions within the fruit (Herremans et al. 2015). Two key aspects of growth in void space emerged from these analyses. Firstly, there was a progressive increase in porosity within the fruit cortex from around 5 to around 22 WAFB (from about 10% to around 25% of the fruit volume). Secondly, spatial differences in the development of these voids were identified. The pith of the fruit displayed clearly lower porosity at maturity (21 d after germination Kale was grown to five defined developmental stages, fully expanded cotyledon (microgreen 1 or MG1), seedlings with two true leaves (microgreen 2 or MG2), seedlings with four true leaves (baby green 1 or BL1), seedlings with six true leaves (baby green 2or BL2), and mature plants with more than eight true leaves (adult). Microgreens have been defined as salad crop shoots harvested for consumption within 10 to 20 days of seedling emergence. Generally, microgreens have two fully developed cotyledon leaves, with the first pair of true leaves emerged or partially expanded, and during harvest they are cut above the soil line, whereas sprouts are mainly soaked in the water and younger, with the cotyledon not opened or just opened. Microgreens are cotyledonary‐leafed seedlings harvested within 10–20 d after vegetable seed germination. Microgreens are harvested at the first true leaf stage of growth and belong to the group of “functional foods,” and have higher levels of bioactive compounds. Microgreens are a new class of specialty vegetables that are often harvested at the cotyledonary leaf stage without roots and seed coats. Microgreens, an emerging category of edible greens, are tender seedlings produced from the seeds of different species of vegetables, aromatic herbs and herbaceous plants, including wild edible species. Microgreens are generally harvested 7–21 days after germination, when cotyledonary leaves are fully developed, with or without the emergence of a small pair of true leaves. Harvested at the first true leaf stage and sold with the stem, cotyledons (seed leaves), and first true leaves attached, they are among a variety of novel salad greens available on the market that are typically distinguished categorically by their size and age. Sprouts, microgreens, and baby greens are simply those greens harvested and consumed in an immature state. Based on size or age of salad crop categories, sprouts are the youngest and smallest, microgreens are slightly larger and older (usually 2 in. tall), and baby greens are the oldest and largest (usually 3–4 in. tall).

Kopsell and Sams 2013

Gerovac et al. 2016

Waterland et al. 2017

Lee et al. 2004; Wang and Kniel 2016

Kou et al. 2015 Samuoliene et al. 2017

Xiao et al. 2014a

Di Gioia et al. 2016

Treadwell et al. 2012

Table 3.1  (Continued) Definition

Reference

Microgreens have been defined as salad crop shoots harvested for consumption within 10 to 20 days of seedling emergence, and they are developmentally classified between “sprouts” and “baby salads.” They are young seedlings of vegetables, herbs, or other plants, with cotyledons fully developed and the first pair of true leaves emerged or partially expanded. They are young seedlings of vegetables herbs, harvested when cotyledons are fully developed and the first pair of true leaves are emerging or partially expanded. Microgreens, frequently called “vegetable confetti,” are a new class of specialty crop, defined as tender immature greens produced from the seeds of vegetables, herbs, or grains, including wild species. Depending on species and growing conditions, microgreens are generally harvested at the soil level, i.e. at the base of hypocotyls, upon appearance of the first pair of true leaves, when cotyledons are fully expanded and still turgid, usually within 7–21 days from seed germination depending on the species. Microgreens are tender immature plants produced from the seeds of vegetables (such as red cabbage) and herbs having two fully developed cotyledon leaves with or without the emergence of a rudimentary pair of first true leaves. Microgreens are young edible greens produced from vegetables, herbs, or other plants, ranging in size from 5 to 10 cm long including stem and cotyledons (seed‐leaves). Greenhouse production of salad crop shoots for harvest and consumption within 10 to 20 d of seedling emergence (i.e., microgreens) is becoming increasingly popular. Microgreens, the plantlet stage of various species …. Microgreens are harvested just above the roots when the cotyledons are fully formed or the first true leaves have emerged. They can be grown in soil or soil substitutes or hydroponically and require high‐light conditions for efficient growth. Microgreens are halfway in size between sprouts and their older counterparts, such as baby spinach, but deliver the most in terms of flavor and nutritional values compared to the other two types of crops. Microgreens are edible seedlings that are usually harvested 7–14 days after germination when they have two fully developed cotyledon leaves. Microgreens have a central stem with two fully developed cotyledon leaves and mostly one pair of small true leaves. Microgreens are young and tender cotyledonary leafy greens that are found in a pleasing palette of colors, textures and flavors. Microgreens are seedlings of vegetables and herbs that are grown to the fully opened cotyledon or first true leaf stages. Microgreens are a new class of edible vegetables harvested when seed leaves have fully expanded and before true leaves have emerged.

Murphy et al. 2010

Xiao et al. 2015a

Xiao et al. 2016

Kyriacou et al. 2016

Huang et al. 2016

Sun et al. 2013

Lee et al. 2004

Lobiuc et al. 2017a Reed et al. 2018

Weber 2017

Vaštakaitė and Virsile 2015 Kou et al. 2012

Brazaitytė et al. 2015a Pinto et al. 2014

(continued)

Table 3.1  (Continued) Definition

Reference

They are tender cotyledonary‐leaf plants having vivid colors, intense flavors and tender textures … … a type of specialty leafy greens harvested shortly after the first true leaves have emerged. Microgreens are a new class of specialty vegetables that are often harvested at the cotyledonary leaf stage without roots and seed coats. Microgreens are young and tender cotyledon greens harvested within 7–14 d of vegetable seedling emergence. Microgreens are a type of specialty leafy greens harvested shortly after the first true leaves have emerged. They are cut just above the roots and consumed fresh as salad greens. Microgreens are seedlings of vegetable and herbs that are grown to fully opened cotyledons or first true leaf stage. Microgreens are a type of specialty leafy green harvested shortly after the first true leaves have emerged. They are harvested just above the roots and consumed fresh as salad greens. Plants raised from seed that are larger than sprouts and smaller than “baby” salad greens. Microgreens are defined as salad crop shoots harvested for consumption within 10–20 days of seedling emergence. Microgreens are the young, tender shoots of vegetables and herbs harvested just after the true leaves have emerged. … edible plantlets, also 34 microgreens … A microgreen has a single central stem, which has been cut just above the soil during harvesting…. The seedlings are well suited for local growers because microgreens are harvested just 7 to 14 days after germination when the cotyledons (seed leaves) have fully developed and before the true leaves have expanded. Microgreens are a new class of edible vegetables, a very specific type which includes seedlings of edible vegetables, herbs or other plants, ranging in size from 5 to 10 centimeters long (including stem and cotyledons). … salad crop shoots for harvest and consumption within 10 to 20 days of seedling emergence (“microgreens”) … … vegetables, grains and herbs grown to the phenological phase of cotyledons, or to the development of the first pair of true leaves. Microgreens can be described as young and tender edible seedlings produced using the seeds of different species of vegetables, herbaceous plants, aromatic herbs, and wild edible plants. Depending on the species that has been used, they can be harvested 7–21 days after germination, when the cotyledon leaves have fully developed and the first true leaves have emerged. Microgreens are salad crop shoots harvested for consumption within 10 – 20 d of seedling emergence.

Xiao et al. 2014a Vaštakaitė et al. 2015a Xiao et al. 2014a

Kou et al. 2014 Virsile and Sitautas 2013

Brazaitytė et al. 2013 Kopsell et al. 2012

Hill 2010 Pill et al. 2011 Anon. 2016 Lobiuc et al. 2017a Bliss 2014

Delian et al. 2015

Lee and Pill 2005 Andrejiova et al. 2017

Renna et al. 2017

Murphy et al. 2010

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Figure 3.1  Arugula (Eruca sativa) (front) and red cabbage (Brassica oleracea var. ­capitata) (back) microgreens eight days after sowing and ready to harvest.

(a)

(b)

(c)

(d)

Figure 3.2  Arugula (Eruca sativa) microgreens at stage 1 of development, ­cotyledons fully expanded, first leaf emerging (a); thirteen‐day‐old carrot (Daucus carota) ­microgreens at stage 1, ready to harvest (b); 20 day‐old lemon balm (Melissa officinalis) microgreens at stage 3 (c); 13 day‐old marigold (Tagetes spp.) microgreens at stage 3, second leaf or set of leaves emerging (d).

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overlap with conditions ideal for pathogen development (Reed et  al. 2018). Although poor sanitation and unhygienic conditions can contribute to contamination of sprouts, most investigations have identified seeds as the major source of contamination. Even so, proper production and postharvest practices have been shown to limit pathogenic microbial exposure (Baenas et al. 2017; Reed et al. 2018). Since microgreens are mostly harvested without the seed, seed coat, or roots, microbial contamination is less of an issue, although voluntary recalls have been instituted. The fact that there are fewer recalls of microgreens than baby greens may simply be the result of the difference in the amount of baby greens produced and consumed. II.  HISTORY OF IMMATURE LEAFY VEGETABLES The history of immature vegetables, such as microgreens, started as a food fashion that was tied to high‐end restaurants and their demand for heirloom, locally sourced, and unique offerings (Bliss et al. 2014). Although immature vegetables have long been part of our diet, the meteoric rise of fresh microproduce shipped over long distances is a more recent trend. One of the most recognized suppliers of microproduce in the US is A Chef’s Garden, a farm that in its current form has its origins in the 1980s (Lubow 2006). However, microgreens are now produced by small and large greenhouses throughout the world. Since the 2000s, microgreens have been propelled into the mainstream as the interest in functional foods that support health and longevity has become significant (Kyriacou et al. 2016). They are now widely promoted for production in small scale and diversified agricultural operations (Treadwell 2013; Alexander 2016), sometimes grouped together with other specialty items such as edible flowers and sprouts (Eber 2012). Many species have been tested and are commercially used for microgreen production (Table 3.2). The Brassicaceae and Amaranthaceae families contribute the majority of species and varieties used in current microgreen production (Kyriacou et al. 2016; Xiao et al. 2016). Some of the more popular species, subspecies, and varieties include: beet, chard, and amaranth in the Amaranthaceae family; and radish, broccoli, kale, cabbage, tatsoi, pak choi, mizuna, arugula, and mustard in the Brassicaceae family (Figure 3.3). Grain crops such as buckwheat, wheat, and rye have also been grown as microgreens. In addition, a number of herbs, both medicinal and culinary, have been used for microgreen production. These include herbs such as borage (or starflower), parsley, basil, and fenugreek, among many others.

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Table 3.2  Plant families, species and common names of some plants used in ­microgreen production and discussed in this review. Family

Species

Common Name

Apiaceae       Amaranthaceae      

Cilantro, Coriander Carrot Parsley   Table Beet, Bull’s Blood Beet Chard Amaranth  

Amaryllidaceae  

Coriandrum sativum Daucus carota Petroselinum crispum   Beta vulgaris subsp. vulgaris Beta vulgaris subsp. vulgaris – cicla group Amaranthus spp.   Allium schoenoprasum  

Asteracaea     Boraginaceae   Brassicaceae                          

Lactuca sativa Tagetes spp.   Borago officinalis   Brassica juncea Brassica oleracea var. alboglabra Brassica oleacea var. italic Brassica oleracea var. capitata Brassica oleracea var. gongylodes, Brassica rapa var. rapa Brassica rapa var. rosularis Brassica rapa var. chinensis Brassica rapa var. niposinica Eruca sativa Lepidium bonariense Raphanus raphanistrum var. sativus Raphanus sativus var. longipinnatus  

Fabaceae     Lamiaceae       Poacaea       Polygonaceae

Pisum sativum Trigonella foenum‐graecum   Ocimum basilicum Melissa officinalis Perilla frutescens   Triciticum aestivum Secale cereal Zea mays   Fagopyrum esculentum Rumex acetosa

Chives   Lettuce Marigold   Starflower, Borage   Mustard, Dijon Mustard Chinese Kale Broccoli Cabbage, Red Cabbage, Green Cabbage Kohlrabi Rapini Tatsoi Pak Choi, Red Pak Choi Mizuna Arugula Peppercress Radish, China Rose Radish Daikon Radish   Pea Fenugreek   Basil, Red Basil, Green Basil Lemon Balm Perilla   Wheat (Wheat Grass) Rye Popcorn, Corn   Buckwheat Sorrel

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Figure 3.3  Microgreens can be sold as blends. This blend consists of arugula (Eruca sativa), chard (Beta vulgaris subsp. vulgaris), red cabbage (Brassica oleracea var. ­capitate), and sorrel (Rumex acetosa). Both 4 oz (approx. 110 g) and 8 oz (approx. 220 g) clam shell packages are used. Some microgreens are marketed as live plants in ­containers with a growing substrate allowing for chefs to harvest microgreens as needed.

III. SEEDLING DEVELOPMENT IN OTHER CROPS – GROWTH AND DEVELOPMENT OF SEEDLINGS Seedling development and stages in the early growth of a number of crops have been studied extensively. Most major crops have well‐ defined stages of seedling development, but the system of seedling classification that is most useful when discussing microgreens, is the classification that has been developed in the production of ornamental and vegetable plugs (Nau 2011). Plugs are those seedlings that will be transplanted into larger containers upon reaching a predetermined stage of development. Plug development is classified by four stages, defined as: 1) germination to radicle emergence; 2) emergence of the cotyledons to emergence of the first true leaves; 3) development of the  first true leaves; and 4) development of additional leaves and is ­terminated by transplanting into larger containers (Figure 3.4). Although this system of seedling classification has not been applied to microgreens, work by Waterland et al. (2017) and Verlinden et al. (­unpubl.) suggests that ­microgreen seedlings can be classified into two or three stages. The two‐stage system includes fully developed cotyledons being microgreen stage 1 of development and the emergence of two true leaves

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(a)

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(b)

Figure 3.4  Two types of germination chambers for microgreen production. ­Commercially available germination chamber (a) compared to self‐fabricated germination chamber (b). Microgreens can also be germinated directly in the greenhouse with overhead mist. Using growth chambers saves greenhouse space and creates optimum conditions for ­germination. Most microgreens spend one to five days in these germination chambers before being moved to the greenhouse.

being microgreen stage 2 of development (Waterland 2017). These stages roughly correspond to stages 1 and 2, and 3 and 4, respectively, in plug production (Nau 2011). In this review, it is suggested that microgreens could be classified into three stages of development: 1) fully expanded cotyledons up to the emergence of the first true leaf (comparable to stages 1 and 2 in plug production); 2) emergence of the first true leaf or set of leaves until the emergence of the second true leaf or set of leaves (similar to stage 3 in plug production); and 3) a second true leaf or set of leaves is (are) developing (similar but often short of the full development desired in plug production). Slightly different stages most likely would have to be developed for monocotyledous versus dicotyledonous microgreens (Bliss 2014). Morphological quality indicators for microgreens have been suggested in a number of publications, and especially hypocotyl length which has been reported as a feature that could be useful in determining quality (Vaštakaitė and Virsile 2015; Vaštakaitė et al. 2015a; Andrei et al. 2017). Antioxidants have also featured as a determinant of quality (Sun et al. 2013; Eber et al. 2014). However, to date no visual, physical, physiological, or biochemical quality indices have been developed for microgreens.

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IV.  PRODUCTION STRATEGIES Most microgreen production facilities are small or are part of larger diversified greenhouses or farms. A 400  m2 facility, when optimally managed, can produce approximately 90 kg of microgreens per week assuming 75% space use efficiency, or a yield of 300  g wk−1 m−2 of growing space. Such a facility would employ 3–4 people. However, yields can range from 300 g m−2 to 3 kg m−2 of actual growing space with a 10–14 days harvest depending on species. Production temperature can greatly affect production efficiency. Days to harvest decreases linearly by 35–40% as temperatures increase from 14 °C to 22 °C (Allred and ­Mattson, 2018). Planting density of microgreens depends on species and the stage of development at which the microgreen will be harvested and can range from 1 seed per cm2 for pea shoots (Pisum sativum) and sunflower (Helianthus annuus) to 10 seeds per cm2 for small‐seeded ­microgreen species and varieties. Increasing seed density 1 seed per cm2 to 3 seeds per cm2 in arugula, mizuna, and mustard microgreens saw a significant increase in harvested fresh weight. However, individual plant weights decreased at the same time (Allred and Mattson, 2018). Seeds can be sown on a variety of substrates and can be germinated in the greenhouse on benches with overhead or sub‐irrigation or in germination chambers (Figures 3.4 and 3.5). Depth of substrate affects yield. Increasing substrate depth from approximately 1.75 cm to 6 cm had a positive effect on harvestable fresh weight, an observation most likely related to moisture balance in the media (Allred and Mattson 2018). Although microgreen production can be carried out in growth chambers under artificial light, most production still takes place in greenhouses. Supplemental light provided by high intensity discharge lights such as high‐pressure sodium (HPS) lights or light‐emitting diode (LED) arrays are essential in any climate where natural light falls below 10–12 mol day−1 m−2 (Gerovac et al. 2016; Craver et al. 2017) (Figure 3.5). Fertilization is used sparingly and often depends on the nutrient charge present in many commercially available peat‐lite substrates. If produced hydroponically or production time is longer than 2 weeks in a regular greenhouse media, 50–100 mg L−1 nitrogen from a complete greenhouse fertilizer is often applied. Higher concentration of fertilizer did not show significant increases in fresh weights in mizuna, arugula, or mustard microgreens (Allred and Mattson 2018). Sanitation is key to microgreen production, not only to minimize microbiological contamination with human pathogens, but also to exclude insects and diseases. The short production cycle (6 to 20 days) (Xiao et al. 2016), precludes the use of most but not all pesticides in microgreen production. Humidity

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Figure 3.5  Supplemental light application in microgreen production with LED arrays. Two different methods of irrigation: capillary mats (front) and trough culture (back) are in use.

control and insect exclusion are important to successful microgreen production. Harvesting is often done by hand (Figure 3.6), but equipment is being developed to facilitate harvesting (Figure 3.7) A.  Sowing Methods – Seed Treatments Although most microgreens are established as single seeds, seed balls or multigerm seeds (Bailey 1976) are a common way to sow and establish some crops in the Amaranthaceae (formerly Chenopodiaceae) (Lee et al. 2004). Fruits of some species in the Amaranthaceae develop from aggregates of two or more flowers, cohering at the base and forming very irregular dry structures with multiple seeds. This terminology is not to be confused with seed balls made of clay to include multiple seeds. Sowing seed balls of table beet at below commercially recommended seeding rates resulted in higher individual shoots but lower yields (weight m−2) (Murphy et  al. 2010). Highest yields of table beet microgreens were obtained by pre‐germination in vermiculite and sowing at commercially recommended rates (201 g of seed balls m−2). High seeding rates in the production of arugula microgreens (55 g m−2) also resulted in higher yields but lower individual plantlet weights.

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Figure 3.6  Hand harvesting of arugula (Eruca sativa) into a holding tray followed by packaging in plastic bags for wholesale market.

(a)

(b)

Figure 3.7  A prototype (patent pending) of a microgreen harvester (a). A reciprocating serrated knife cuts the microgreens from a tray positioned on a moveable platform (b).

Priming of seeds before sowing is a decades‐old method that is used to improve germination percentages and uniformity in a number of crops. While germination percentages of table beet and chard were little affected by matric priming of various soaks in sodium hypochlorite or hydrogen peroxide, shoot dry weights were significantly higher, mostly the result of germination advancement by the respective treatment

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(Lee et al. 2004). However, the same study concluded that germinating seeds in vermiculite, regardless of seed treatment, resulted in higher shoot dry weight than sowing untreated seeds and that additional seed treatments did not significantly add fresh weight to this germination and sowing technique (Lee et al. 2004). Similar results were obtained with radish, kale, and amaranth (Lee and Pill 2005). While g­ ermination percentage was little affected, the study showed that there was significantly faster germination and that this resulted in increased shoot dry weights, especially in primed‐germinated seed treatments (Lee and Pill 2005). Work by Murphy et  al. (2010) corroborated these results and showed that greatest shoot fresh weight of table beet microgreens and of arugula was obtained by pre‐germination in vermiculite and production in a hydroponic nutrient film technique system. Incubating seeds with Trichoderma fungi in vermiculite had the additional advantage of controlling Pythium in beet seed balls and of enhancing subsequent germination (Pill et al. 2011). Work with arugula microgreens sown in a peat‐lite mix showed similar results and pre‐germination resulted in significantly higher yields when compared to sowing seed directly (Murphy and Pill 2010). In conclusion, most seed treatments have minimal effects on germination percentages or on harvestable fresh weight (Murphy and Pill 2010). However, priming and pre‐germinating seed does reduce cropping time and can, therefore, lead to higher yields within a shorter production period (Lee et al. 2004). B.  Seedling Pathogens The high seed and plant densities, the seedling stage of development, and the environmental conditions used during production can make microgreens highly susceptible to a number of plant pathogens that thrive in these very specific conditions. Seed, root, and seedling rot can be caused by a number of plant pathogens, including Pythium (Pill et al. 2011). The edible nature of the products and the very short production times limit traditional fungicide use in microgreen production. Alternative methods of pathogen control have been studied, including the application of Trichoderma species (Pill et al. 2011). These methods have shown some success but are only effective at high application rates and relatively low disease pressures (Pill et al. 2011). However, the authors did conclude that high Trichoderma application lead to increased yields due to increased survival of seedlings. Application of bacteria as a seed treatment has also been shown to be beneficial to buckwheat microgreen growth. In a study by Briatia

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et  al. (2018) buckwheat was shown to harbor endophytic bacteria in the genus Herbaspirillum. Upon isolation and subsequent application of this endophytic bacteria as a seed and media treatment, the authors showed increased fresh and dry weight in microgreen production and they suggested that the treatment would be a feasible way to increase yields in buckwheat microgreen production (Briatia et al. 2018). Minimal work has been carried out on seed treatments to promote growth in microgreens or effective ways to combat seedling and root rots that undoubtedly can become a problem in the high moisture and dense planting associated with microgreen production. Additional work on organic or non‐chemical ways to combat this issue would be very useful to microgreen producers. C.  Growing Media Microgreens can be grown in a number of media. Some growers prefer perlite (Johnson 2012) while others grow in vermiculite (Lee et al. 2004), or in commercially available soil‐less greenhouse mixes (Di Gioia et al. 2016). Most growers prefer peat‐based mixes or synthetic mats (Di Gioia et al. 2016) and germination and early growth on filter paper have been used in experimental settings to study additions to the germination ­media such spent brewer’s yeast (Lobiuc et al. 2017a). Composts mixed with sand and vermiculite have also been evaluated (Anon. 2016), as well as sand, peat, coconut coir dust, sugarcane filter cake, and vermicompost in several ratios. All were found to be effective in producing microgreens (Muchjijab et al. 2015). Recycled textile fiber, and jute‐kenaf fiber, peat, and polyethylene‐ terephthalate mats all produced comparable fresh weights with slightly lower yields observed in polyethylene‐terephthalate mats and higher yields on peat substrate (Di Gioia et  al. 2016). Differences in nitrate, sulfate, and potassium levels in microgreens have been observed for microgreens grown in these substrates. Peat‐based substrates not only showed higher nitrate, sulfate, and potassium levels but also higher enterobacteriaceae populations and yeast mold counts. No differences, however, in aerobic microbial populations were detected and no E. coli was observed in any of the tested substrates besides peat (Di Gioia et al. 2016). Interestingly, in a study of radish microgreens grown hydroponically on polyethylene‐terephthalate mats compared to a peat‐based ­media, E. coli was more likely to proliferate in a hydroponic system than in the soil‐less peat‐based substrate. However, this may have been due to differences in irrigation regimes and not directly to the substrates being tested (Xiao et al. 2015a). The addition of ascorbic acid and spent

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brewer’s yeast in the germination media (at least at 10% of the original volume) have also been shown to improve germination percentages in rye microgreens (Lobiuc et al. 2017a). Microgreens can, therefore, be satisfactorily grown in a number of inert and organic media. The ease of procurement and cost, in addition to an ability to suppress human and plant pathogens, should be key factors that determine the choice of a suitable growing medium. D. Fertilizers The relative short production cycle of microgreens requires minimal fertilization. Nutrients can be provided from conventional sources of fertilizer or from less conventional sources such as spent brewer’s yeast (Andrei et al. 2017). Both biomass and length of the hypocotyl in rye microgreens were higher in treatments that included 50% by volume of spent brewer’s yeast (Andrei et  al. 2017). Treatment with ascorbic acid at 100 mg L−1 also showed higher fresh weights in the same study. A more conventional treatment comprising a pre‐plant calcium nitrate fertilizer application followed by a liquid fertilizer treatment post‐ planting increased fresh weight by approximately 20% despite the very short cropping time of 15 days (Murphy et al. 2010). Work with arugula microgreens also showed the benefit of a pre‐plant fertilizer followed by 75 to 150 mg L−1 nitrogen fertilization during production (Murphy and Pill 2010). In Chinese kale microgreen production, half‐strength Hoagland’s solution was judged adequate for commercial production. However, the plants in that study were grown beyond the normal time‐span for ­microgreen production (30 days) (Kopsell et  al. 2017). The authors noted that responses of Chinese kale to the light regimes used were quite different from the responses observed in previous studies with 21 day‐old brassica microgreens. E.  Light Conditions Many microgreen crops are grown in controlled environment enclosures with the full exclusion of daylight. One of the most studied aspects of microgreen production, therefore, is the effect of light quantity and quality on biomass accumulation, the concentrations of bioactive compounds, and on the concentrations of carotenoids and other pigments (Kopsell et al. 2012; Virsile and Sirtautus 2013; Brazaitytė et al. 2015a; Kopsell et al. 2015; Craver et al. 2017; Lobiuc et al. 2017b). The vast number of species that have been studied, and the light quantity and

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quality treatments combinations that have been investigated, make it difficult to draw generalized conclusions. Furthermore, the literature often has conflicting results and even slightly different treatments can result in statistically different outcomes (Craver et al. 2017). However, a few general statements can be made about optimum light conditions and the effect of light quality on biomass, pigment concentrations, and the presence of bioactive compounds. Studies with borage (or starflower) show that when a combination of red, blue, and far‐red LEDs are used to produce borage microgreens, the optimum photosynthetic photon flux (PPF) was 440 μmol m−2 s−1. Both lower and higher PPF resulted in decreased biomass as well as reduced antioxidant concentrations (Virsile and Sirtautas 2013; Samuoliene et al. 2013). Optimum PPF levels for brassica microgreens grown under LEDs were also determined to be in this same range (330–440 μmol m−2 s−1) (Samuoliene et al. 2013). Both lower and higher PPFs negatively affected growth and/or the accumulation of some antioxidants. A low PPF of 110 μmol m−2 s−1 suppressed normal growth and the nutritional value of the microgreens, while levels of 545  μmol  m−2  s−1 induced a mild photostress. When LED illumination was compared to a combination of fluorescent and incandescent lights – at the same PPF – LEDs resulted in higher shoot fresh mass. When microgreens were exposed from 105 to 315 μmol m−2 s−1 for a DLI ranging from 6 to 18 mol m−2 d−1, the highest percent dry weight was observed at the highest light intensities, while fresh weights remained relatively unchanged (Craver et al. 2017). This is in contrast with data from a subsequent but longer experiment with Chinese kale in which higher fresh weights and dry weights were observed under incandescent and fluorescent lights (Kopsell et  al. 2017). Fluorescent light supplementation – in addition to natural light – resulted in higher vitamin C and chlorophyll concentrations in a number of microgreens (Andrejiova et al. 2017). In experiments where LEDs were compared with high pressure sodium (HPS) lights, no differences in leaf area were observed but hypocotyl length and plant height were significantly lower in LED illumination at the same total photon flux (Vaštakaitė and Virsile 2015). Results suggested 150 μmol m−2 s−1 as optimal for microgreen production, much lower than that in other reports. Adding UVA LED exposure to HPS illumination resulted in reduced plant height, hypocotyl length, and leaf area (Vaštakaitė et al. 2015a). These features were seen as positive outcomes as there was more compact growth. However, the same experiment showed that UVA generally showed fewer positive effects in terms of antioxidant properties (the concentrations of anthocyanins and total phenols, and ABTS radical activity) in purple compared with green basils.

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Zeaxanthin concentrations can be increased by inducing high light stress upon emergence of the first true leaf in mustard. However, this treatment is at the expense of chlorophyll content and it is unclear if this reduction negatively affects the marketability of the microgreens (Kopsell et al. 2012). Nonetheless, carotenoid levels can be increased under yellow LED illumination in tatsoi and under multiple wavelengths in red pak choi, indicating that in specific species and supplemental light conditions, carotenoid levels can be positively affected (Brazaitytė et al. 2015a). In mizuna and mustard microgreens, increasing PPFs from 105 to 315  μmol  m−2  s−1, however, showed decreasing carotenoid concentrations, while kohlrabi showed increases in anthocyanin concentration (Craver et  al. 2017). Increasing light levels also increased chlorophyll concentration (Gerovac et  al. 2016). Blue light provided at the end of the production of microgreens led to an increase in carotenoids, glucosinolates, micronutrients, and macronutrients (Kopsell and Sams 2013). This was further confirmed by additional work from the same group where increasing ratios of blue to red light showed the same results (Kopsell et al. 2014, 2015). When blue and red LED illumination in differing ratios was compared to fluorescent and incandescent lighting, in Chinese kale grown beyond the microgreen stage of development, LED treatment clearly resulted in higher chlorophyll and carotenoid concentrations (Kopsell et al. 2017). The effect of light levels and light quality differs by species and sometimes by variety. For example, green light can enhance carotenoid accumulation in mustard microgreens, but red pak choi and tatsoi accumulate carotenoids under blue, red, and far‐red illumination (Brazaitytė et al. 2015a). Interestingly, high blue light (445 nm) to red and far‐red light ratios (638, 660, and 731  nm) have been shown to increase photosynthetic and carotenoid pigments in parsley, beet, and mustard microgreens in other work (Samuoliene et  al. 2017). In the same study, blue light also increased tocopherol levels (Samuoliene et al. 2017). When blue light (447 nm) was evaluated at five different levels in red pak choi, tatsoi, and basil microgreen production, it was shown that 16–33% blue light led to significantly shorter hypocotyls and plant height (Vaštakaitė et  al. 2015b). In general, high blue light exposure also led to higher total phenol concentrations while both the absence of blue light and the highest blue light levels led to the highest DPPH radical scavenging ability. Red light (638 nm) at the end of a production cycle in Perilla frutescens showed that total anthocyanins and ascorbic acid can be increased, but this increase is at the expense of tocopherol content (Brazaitytė et al. 2013). Mixed results were obtained with short‐term supplementary red

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LED illumination. Ascorbic acid concentrations increased in amaranth, pea, kale, broccoli, and mustard but were lower in basil and borage (Samuoliene et al. 2012). However, total phenols were increased in all microgreens tested except amaranth (Samuoliene et  al. 2012). When green basil and red basil were grown under differing ratios of blue and red light compared to white light, growth was mostly stimulated under higher blue light conditions. Overall, the authors concluded that red and green basil varieties responded differently to the varying ratios of blue and red light. For example, phenolic content and free radical scavenging activity were stimulated by red light in the green cultivar and by blue light in the red cultivar of basil (Lobiuc et al. 2017b). In other work, purple leaf basils were shown to be more sensitive to UVA exposure from LEDs than green leaf basils, resulting in lower antioxidant properties (Vaštakaitė et  al. 2015a). Brazaitytė et  al. (2015b), showed that 366 nm and 390 nm were most effective at eliciting antioxidants in microgreen production, especially at photon flux densities of 12.4 μmol m−2 s−1. Supplemental UVA lighting was suggested as an effective method to increase leaf area, yield, radical scavenging activity, total phenols, anthocyanins, ascorbic acid, and α‐tocopherol, especially in pak choi microgreens (Brazaitytė et al. 2015b). In conclusion, illumination from LED lighting compares favorably with other forms of supplemental lighting and photon flux densities between 150 and 440 μmol m−2 s−1 are optimal for most microgreen production. The effect of light quality on microgreen production is less clear as many different responses have been observed across different species and varieties, depending on the parameter measured and on the light quality combinations tested. However, high blue light exposure seems to have positive effects on both growth and antioxidant concentrations. High light and UVA exposure treatments appear to trigger antioxidant accumulation. V.  NUTRITIONAL VALUE A. Micronutrients Microgreens are often promoted as being more healthful than mature leafy greens such as head lettuces (Xiao et  al. 2016). A study of 10 species and a total of 30 varieties of microgreens showed that microgreens are a good source of microelements such as Fe and Zn, as well as K and Ca (Xiao et al. 2016). As expected, significant differences were noted in mineral content between and among species and varieties. For example, rapini showed significantly higher concentrations of Fe, Zn,

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and Cu than most of the other tested microgreens and Fe was approximately 50% higher in Tuscan versus red kale. Waterland et al. (2017) also showed different levels for a number of nutrients when they compared three kale varieties. In that study, comparisons were also made between the kale varieties at different stages of development from microgreen to mature leaves. They concluded that, on a dry weight basis, microgreens contained higher concentrations of many nutrients than adult leaves. However, on a fresh weight basis, it was shown that microgreens contained lower concentrations of K, Ca, Mg, Fe, and Zn when compared to immature leaves. Additionally, it was shown that mature, fully‐expanded leaves of kale showed higher concentrations of Ca and Mg and lower concentrations of Na (Waterland et al. 2017). Sprouts of different cultivars of amaranth, in contrast, were shown to have higher concentrations of zinc and iron than occurred in microgreens of the same cultivars (Eber et al. 2014). When mature lettuce was compared to lettuce microgreens of the same variety, significantly higher concentrations of Ca, Mg, Fe, Mn, Zn, Se, and Mo were observed in microgreens (Pinto et al. 2015). Increasing light levels in microgreen production of kohlrabi, mizuna, and mustard showed decreasing concentrations of B, Cu, Fe, Mn, and Zn. However, changes in light quality in the same study showed mixed effects in different species and with different lighting regimes (Gerovac et al. 2016). Light treatments (41 μmol m−2 s−1 of 470 nm light for five days) at the end of microgreen production were shown to positively affect a number of micronutrients (Kopsell and Sams 2013). Vaštakaitė and Virsile (2015) concluded that LED lighting had a positive effect on micronutrient concentrations when compared to HPS lighting. In conclusion, significant differences in a number of micronutrients can be observed in species and cultivars of many microgreens. Relative concentrations of nutrients also change with stage of development with some species and cultivars showing higher levels of micronutrients and/or macronutrients at an early stage of development and others at later or at adult stages of development. A comprehensive study, that includes a range of microgreens at several stages of development, may be more conclusive in attempts to confirm the nutritional importance of microgreens. B. Macronutrients Very few studies have investigated the concentrations of macronutrients in microgreens. Where they have been analyzed, higher N, P, and K concentrations have been observed in mature leafy vegetables than

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in microgreens (Pinto et  al. 2015; Waterland et  al. 2017). Low light levels during the production of microgreens resulted in higher N, P, K, S, Ca, and Mg in kohlrabi, mizuna, and mustard (Gerovac et al. 2016). Varying light qualities in the same study showed some effect on macronutrient content but these effects were specific to some crop and light treatments. Blue light treatment of microgreens at the end of the production cycle resulted in increased Ca, P, Mg, and S concentrations in broccoli microgreens (Kopsell and Sams 2013). When increasing blue to red light ratios were used in a subsequent study, Kopsell et al. (2014) reported similar results. Nitrate levels  –  considered a health risk for infants and other vulnerable segments of the population – were shown to be much lower in microgreens, suggesting that microgreens could be a healthy addition to a balanced diet (Pinto et al. 2015). Low irradiance has been associated with increased nitrate concentrations, a potential health problem, in borage microgreens and as irradiance levels increased, nitrate levels decreased (Virsile and Sirtautas 2013). High irradiance during production also showed a significant decrease in nitrate levels in several brassica microgreens (Samuoliene et al. 2013). However, in an experiment that compared HPS to LED lighting in tatsoi, red pak choi, and mustard microgreens, nitrate concentration was lower in the LED treatment at the same irradiance level. When the same LED irradiance was compared to a higher LED photon flux, the results were reversed and the high LED levels led to significantly higher nitrate concentrations. Nitrate concentrations in perilla microgreens subjected to red light at the end of the production cycle decreased, suggesting that a brief period of high light at the end of the production cycle may also lower nitrate levels (Brazaitytė et al. 2013). As in many leafy crops, nitrate levels should be monitored and maintained as low as possible and short‐term red light exposure may achieve that objective (Brazaitytė et al. 2013). Additionally, the effects of different treatments, ranging from light quality and quantity to media comparisons, on these compounds have been tested and many examples of both positive and negative effects on the concentrations of vitamins, antioxidants and bioactive compounds can be found in the literature (Table  3.3). Samuoliene et  al. (2013) concluded that a PPF of 330–440  μmol  m−2  s−1 is, in general, optimal for brassica microgreen production and results in some of the largest surface area, lowest nitrate content, and highest concentrations of total anthocyanins and total phenols, and highest free radical scavenging capacity. However, in an effort to increase zeaxanthin, a pigment produced by plants to alleviate high light stress and an important antioxidant in the human diet, microgreens have been exposed

Table 3.3  Effect of light treatments on growth and development, bioactive principles, pigments, and phytonutrients in microgreens. Species and Cultivar

Treatments

Measured responses

References

Chinese kale ‘Green Lance’ (30 day‐old plants)

Comparison of fluorescent/incandescent, 10% blue (447 nm)/90% red (627 nm), 20% blue/80% red, and 40% blue/90% red at 250 μmol m−2 s−1 16 h photoperiod resulting in a daily light integral of 6, 12, 18 mol m−2 d−1 from LED arrays with light ratio of R87:B13, R84:FR7:B9, and R74:G18:B8

• Blue light increases total chlorophyll and the concentration of most carotenoids compared at standard fluorescent/ incandescent light. • Total carotenoids were lower under 12 and 18 mol m−2 d−1 than 6 mol m−2 d−1 for mizuna and mustard. • Higher chlorophyll concentrations were detected in the R87:B13 treatment with kohlrabi and mustard. • Anthocyanin concentrations were greater in higher light intensities for kohlrabi, especially under the R87:B13 and R84:FR7:B9 treatments. • Phenolics were affected minimally with kohlrabi grown under R84:FR7:B9 at the lowest light levels showing higher concentrations than R74:G18:B8. • Hypocotyl length decreased and dry weight increased as light intensity increased for kohlrabi, mizuna, and mustard. • Chlorophyll concentration was not affected by the treatments. • The effect of light quality on macronutrients and micronutrients was species dependent and so was the interaction of light intensity and quality.

Kopsell et al. 2017

Kohlrabi, mustard (‘Garnet Giant’), and mizuna

Purple kohlrabi, mizuna and mustard (‘Garnet Giant’)

16 h photoperiod resulting in a daily light integral of 6, 12, 18 mol m−2 d−1 from LED arrays with light ratio of R87:B13, R84:FR7:B9, and R74:G18:B8

Craver et al. 2017

Gerovac et al. 2016

(continued)

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Table 3.3  (Continued) Species and Cultivar

Treatments

Measured responses

References

Broccoli

16 h photoperiod with treatments of fluorescent/incandescent light compared to LED treatments with light ratios of B5:R95, B5:R85:G10, B20:R80,abd B20:R70:G10 at 350 μmol m−2 s−1 for 20 d

Kopsell et al. 2014

Broccoli

24 h photoperiod using red (627 nm) and blue (470 nm) LEDs at 350 μmol m−2 s−1 for 13 days followed by a blue LED light treatment at 41 μmol m−2 s−1 for 5 d 14 h photoperiod of 275 μmol m−2 s−1 of fluorescent and incandescent light followed by 463 μmol m−2 s−1 (36 h before harvest)

• Leaf shoot fresh weight was significantly lower under fluorescent/incandescent light than all LED treatments except the B20:R70:G10 treatment. • Highest concentrations of carotenoids, glucosinolates, macronutrients and macronutrients were found in the B20:R80 treatment. • Low levels of blue light before harvest increased carotenoids, glucosinolates, micronutrients (Cu, Fe, B, Mn, Mo, Na, Zn) and macronutrients (P, K, Mg, S). • Decrease in chlorophyll a and b, β‐ carotene, neoxanthin levels. • Increases in zeaxanthin, antheraxathin levels. • No change in lutein levels. • Light exposure increased ascorbic acid but had no effect on α‐tocopherol, total phenolic concentrations, and DPPH radical scavenging activity. • Dark storage resulted in higher hydroxyl scavenging activity and maintained carotenoid levels better than light storage and was found to be the best approach for microgreen storage. • Packaging in propylene maintained quality better than polyethylene bags.

Kopsell et al. 2012

Mustard ‘Florida Broadleaf’

Daikon radish

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Packaging in laser micro‐perforated oriented polypropylene film and polyethylene with oxygen transmission rate of 29.5 pmol s−1 m−2 Pa−1 stored in light (30 μmol m−2 s−1) and dark for 16 d

Kopsell and Sams 2013

Xiao et al. 2014a

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Mustard (‘Red Lion’), beet and parsley

Exposure to 638, 660, and 731 nm standard illumination (approx. 300 μmol m−2 s−1) with the addition of 0, 8, 16, 25 and 33% 445 nm blue light during production

Basil and parsley

Microgreens were exposed to 210 μmol m−2 s−1 from a mix of blue (447 nm), red (638 nm), red (665 nm and far red (731 nm) LEDs during production followed by a 3‐day treatment that contained higher levels and/ or different ratios of red (665 nm) versus red (638 nm). These treatments were also compared to high pressure sodium (HPS) light with and without the addition of red light (638 nm) from LEDs

Tatsoi, mustard (‘Red Lion’), and red pak choi (‘Rubi F1’)

Exposure to 520, 595, and 622 nm LEDs supplemental to standard irradiation with 447, 638, 665, and 731 nm LED at PPFDs of 545, 440, 330, 220, and 110 μmol m−2 s−1

• In general, high blue light exposure (16–33%) resulted in higher concentrations of chlorophyll and carotenoids. • Tocopherol concentrations were higher in 16% blue light exposure. • Species affects response to blue light supplementation. • Exposure to supplemental or increased red light (638 nm) resulted in higher amounts of antioxidants in basil and also increased phenolics, radical scavenging activity, ascorbic acid, and α‐tocopherol. These treatments, however, suppressed concentration of lutein and β‐carotene. • Exposure to sole red light during the 3‐day treatment (665 nm or 638 nm) resulted in higher amounts antioxidants in parsley. • Increased red light amounts or supplemental red light increases β‐carotene and radical scavenging activity in parsley. • Carotenoid concentrations were highest for tatsoi and red pak choi under 330– 440 μmol m−2 s−1 and 110–220 μmol m−2 s−1 for mustard. • All supplemental wavelengths increased total carotenoid levels in mustard, yellow light increased carotenoid levels in mustard, and carotenoids decreased under all supplemental light in red pak choi.

Samuoliene et al. 2017

Samuoliene et al. 2016

Brazaitytė et al. 2015a

(continued)

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Table 3.3  (Continued) Species and Cultivar

Treatments

Measured responses

References

Red pak choi (‘Rubi F1’), tatsoi, and mustard (‘Red Lion’)

Comparison of HPS (150 μmol m−2 s−1) to a mix of violet (420–430 nm), blue (460–470 nm), orange (610–615 nm), red (620–630 nm and 660–670 nm) and white LEDs (with blue and green and red spectra) at 150 and 250 μmol m−2 s−1 irradiance

Vaštakaitė and Virsile 2015

Basil (‘Dark Opal’ and ‘Sweet Genovese’)

Exposure to 13 μmol m−2 s−1 UV‐A (390 nm) for 1, 7, or 14 days before harvest in addition to 125 μmol m−2 s−1 natural day length and HPS supplemental light

Red pak choi (‘Rubi’ F1), Tatsoi, and basil (‘Sweet Genovese’)

Exposure to 520, 595, and 622 nm LEDs supplemental to standard irradiation with 447, 638, 660, and 731 nm LED at PPFDs of 545, 440, 330, 220, and 110 μmol m−2 s−1

• Microgreens grown under LED light did not exhibit undesirable elongation, and in general showed higher concentrations of phenolics, anthocyanins, flavonols, acorbic acid, and number of mineral elements compared to HPS lights. • Nitrate content was elevated under the 250 μmol m−2 s−1 LED treatment in tatsoi and red pak choi but not mustard microgreens when compared to both the HPS and 150 μmol m−2 s−1 LED treatment. • A decrease in hypocotyl and plant height was observed, especially when basil was exposed to UV for 7 to 14 days. • A trend towards an increased leaf flavonol index as well as increased ascorbic acid concentrations were observed under UV exposure. • Response to UV light treatment was different in green versus red basil in terms of ABTS radical scavenging activity, total phenols, and anthocyanin concentration. • Blue light dosages of 16 and 33% resulted in shorter hypocotyls and lower plant height in all three microgreens and highest total phenols, flavonol index, and anthocyanin concentration for tatsoi and basil. • The highest ascorbic acid concentrations were observed under 8% blue light in tatsoi and 16% in pak choi and basil. • The control (0% blue light) and 33% blue light resulted in the highest DPPH radical scavenging activity in tatsoi and basil. • Species affects response to blue light supplementation.

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Vaštakaitė et al. 2015a

Vaštakaitė et al. 2015b

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Perilla frutescens

Kohlrabi (‘Delicacy Purple’), mustard (‘Red Lion’), red pak choi (‘Rubi F1’), and tatsoi

Microgreens were expose to natural day light supplemented with HPS for a PPFD of 90 μmol m−2 s−1 during production followed by 3‐day supplementation of 210 μmol m−2 s−1 of red light from a 638 nm LED or HPS lighting Illumination with 447, 638, 665, and 731 nm LED at PPFDs of 545, 440, 330, 220, and 110 μmol m−2 s−1

• Red light reduced nitrate content and increased antioxidants content (anthocyanins and ascorbic acid). • Red light addition resulted in lower α‐tocopherol concentrations and did not influence DPPH free‐radical scavenging activity or flavonol index. • Low light (110 μmol m−2 s−1) suppressed growth as measured by increased hypocotyl length, and decreased leaf area and dry weight. • Nitrates increased as light levels decreased, whereas sucrose levels and chlorophyll showed a trend towards higher concentrations in higher light conditions. • DPPH free radical scavenging activity and total phenols generally increased as light intensity increased. • The highest levels of anthocyanins were observed in red pak choi and tasoi under 330 μmol m−2 s−1. • High ascorbic acid levels were found in the low light environment in red pak choi and tasoi but not with kohlrabi and mustard.

Brazaitytė et al. 2013

Samuoliene et al. 2013

(continued)

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Table 3.3  (Continued) Species and Cultivar

Treatments

Measured responses

References

Borage

Illumination with 445, 638, 665, and 735 nm LEDs at PPFDs of 545, 440, 330, 220, and 110 μmol m−2 s−1

Virsile and Sirtautus 2013

Basil (‘Sweet Genovese’ and ‘Red Rubin’)

Exposure of red and green basil to white light, and red and blue light in differing ratios of 2R:1B, 1R:1B and 1R:2B (red light approx. 660 nm and blue light approx. 450 nm). Light supplied by LEDs at 120 μmol m−2 s−1

• Increased biomass, decreased hypocotyl length as illumination increased from 110–440 μmol m−2 s−1. • 545 μmol m−2 s−1 illumination resulted in decreased biomass, inhibited hypocotyl elongation, and suppressed antioxidants levels. • 440 μmol m−2 s−1 irradiance was determined optimal in terms of biomass accumulation, hypocotyl, leaf area, nitrate concentrations, and the accumulation of antioxidant phytochemicals. • A high ratio of blue to red light resulted in high fresh and dry mass in green basil when compared to other light treatments. • No differences in chlorophyll or carotenoid levels between light treatments or cultivars. • Response to light treatment was different in green versus red basil in terms of phenolic and flavonoid content, and free radical scavenging activity. • In green basil, the highest concentration of phenolics and flavonoids, and free radical scavenging capacity was observed in high red to blue light ratio treatment. • In red basil, the highest concentration of phenolics and flavonoids, and free radical scavenging capacity was observed in the 1R:1B ratio treatment.

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Lobiuc et al. 2017b

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to higher light levels than those shown to be optimal for these other compounds (Kopsell et al. 2012). Results indicate that it is indeed possible to significantly increase certain carotenoids in microgreens but at the expense of chlorophyll content (Kopsell et al. 2012). In contrast, higher light intensities used in the production of mizuna and mustard microgreens decreased carotenoid production (Craver et al. 2017). The same treatments resulted in higher anthocyanin accumulation in kohlrabi but not in mizuna and mustard microgreens. Other studies have shown that high blue to red and far‐red light ratios also show positive effects on carotenoid accumulation (Samuoliene et al. 2017). However, these same light ratios had no effect on tocopherol content. When basil was exposed to different wavelengths of red light (638 and 665  nm) in addition to other wavelengths, Samuoliene et  al. (2016) showed that tocopherol content could be increased, in addition to increases in phenolics, ascorbic acid, and free radical scavenging ability. However, these same treatments resulted in lower lutein and beta‐carotene concentrations (Samuoliene et  al. 2016). The authors suggested that significant trade‐offs among the different antioxidants can exist with decreases in some antioxidants resulting in increases in others (Samuoliene et al. 2016). UVA LED exposure showed positive effects in terms of leaf flavonol index, ABTS radical scavenging activity, and ascorbic acid accumulation. However, more positive effects were observed in green than purple basil (Vaštakaitė et al. 2015a). When broccoli microgreens were exposed to five days of blue light before harvesting, Kopsell and Sams (2013) showed a significant increase in the concentrations of carotenoids at harvest. Increasing blue to red light ratios saw increases similar to results with blue light only exposure (Kopsell et al. 2014, 2015). Blue light exposure of 8 and 16% of total illumination of red pak choi, tatsoi, and basil in general showed the highest levels of ascorbic acid, whereas accumulation of total phenols was observed in high blue light exposure (16–33%) in basil and tatsoi and low blue light exposure (8%) in red pak choi. Both a lack of blue light and the highest blue light exposure resulted in high DPPH radical scavenging activity in tatsoi and basil but not in pak choi (Vaštakaitė et al. 2015b) Glucosinolates, a phytonutrient in broccoli, were found to be significantly higher in broccoli microgreens than broccoli florets (Lu et  al. 2018). Preharvest exposure to blue light of broccoli microgreen not only increased glucoraphanin and epiprogoitrin, but also other glucosinolates (Kopsell and Sams 2013; Kopsell et  al. 2015). Postharvest UVB exposure of the microgreens resulted in even higher levels of glucosinolates (Lu et al. 2018).

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Tocopherol levels can be enhanced with blue light exposure in some microgreens (Samuoliene et al. 2017), while red light, in comparison, can show decreases in tocopherol, at least in Perilla frutescens. Red light supplementation has shown positive effects on the concentrations of ascorbic acid, total phenols, and anthocyanins in many but not all of the microgreens studied by Samuoliene et al. (2012). Other treatments besides light such as the inclusion of spent brewer’s yeast and ascorbic acid in the germination media may increase total phenolic content (Lobiuc et al. 2017a). However, the limited statistical analysis of data in that study make those conclusions less than certain. In conclusion, microgreens in some cases have higher levels of bioactive compounds than those that occur at other developmental stages or in other plant parts of the same species or variety. Significant differences in bioactive principles have been observed among different species. Exposure of microgreens to various quantities and qualities of light and media treatments can positively affect bioactive compound levels in microgreens. However, the myriad of treatments, species, and cultivars make blanket statements about phytonutrient content problematic. Including more species and cultivars in studies that try to increase phytonutrient content may lead to more conclusive results and may tease apart the genetic components that influence phytonutrient levels. VI. MICROBIOLOGICAL SAFETY AND POSTHARVEST BIOLOGY AND TECHNOLOGY Microgreens are typically harvested by hand (Figure  3.6), although mechanical harvesting methods are under development (Figure  3.7). Packaging is normally into clamshells or into plastic bags for larger ­volumes (Figures 3.3 and 3.6). Despite the fact that the US FDA considers microgreens safer than sprouts and that microgreen production is not covered by the same ­legislation as sprouts in Europe and the US (Xiao et al. 2014c; FDA 2017; Wright and Holden 2018), studies do suggest that some of the similarities in production and overlap in growth and development between the later stages of development in sprouts and early stages of harvesting in microgreens could pose health risks (Xiao et  al. 2014c; Wright and Holden 2018; Riggio et al. 2019). However, the same studies suggest that colonization with E. coli is lower in true leaves than in cotyledons and decreases over time, indicating that there may be an overall reduced level of risk of foodborne illness in microgreens compared to sprouts

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(Xiao et al. 2014c). Reed et al. (2018) also suggest lower risk associated with microgreen versus sprout production. However, recommendations limiting the introduction of pathogens through seed or irrigation water contamination should be similar to those for sprout production (Xiao et al. 2014c; Reed et al. 2018; Wright and Holden 2018). Although both routes of contamination can lead to increased levels of E. coli, irrigation water contamination showed much higher levels of E. coli than when seeds were inoculated with the bacterium (Wright and Holden 2018). Interestingly, spatial distribution of E. coli O157:H7 clearly indicates that contaminated seeds of radish can easily lead to the contamination of whole plants and that seed coat remains are the highest source of contamination throughout production (Xiao et al. 2015a). Furthermore, proliferation during production was observed and was higher in hydroponic than in production in a peat moss‐based substrate. Work with ­Salmonella showed that hydroponic systems can be more problematic than soil‐less media when it comes to microbial safety (Reed et al. 2018). Di Gioia et al. (2016) also suggested that growing media selection can influence the microbial safety of microgreens. Especially jute‐kenaf and peat treatments which showed elevated levels of enterobacteriaceae in harvested microgreens, while E. coli was detected in microgreens in the peat treatment. The authors suggested caution in selecting media for microgreen production without specifically identifying peat as a problem (Di Gioia et al. 2016). Washing of buckwheat microgreens with chlorinated water reduces microbial populations initially, but growth of those populations accelerates after 1 week of storage compared to that in unwashed microgreens (Kou et  al. 2013). Similar observations were made for daikon radish ­microgreens (Xiao et al. 2014b). Washing, spinning, and drying of microgreens has been shown to negatively affect shelf life and some authors have suggested growing microgreens under controlled e­ nvironments to avoid washing altogether (Kou et  al. 2015). Artificial contamination in a hydroponic production system with norovirus showed that ­recirculated water maintained high level of infectious viruses and that previously contaminated systems maintained infectious viruses from crop cycle to crop cycle (Wang and Kniel 2016). All studies recommend vigilance and proper sanitation both in the production and in the postharvest environment (Wang and Kniel 2016; Wright and Holden 2018; Riggio et al. 2019). Storage conditions for harvested microgreens need to consider the perishable and delicate nature of the product in addition to species specific parameters. Temperature, light, and gas composition are key environmental factors in maintaining fresh produce quality after

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harvest. Low temperatures, light, and modified atmosphere packaging have been shown to be effective and is some cases to be beneficial to the storage of microgreens (Kou et al. 2013; Xiao et al. 2014a,b; Baenas et al. 2017). A study of buckwheat microgreens suggested that chilling sensitivity can occur in microgreens and that both the lowest possible temperature without adverse physiological effects  –  in this case 5 °C – and modified atmosphere can be beneficial in the storage of microgreens (Kou et  al. 2013). Work with radish microgreens corroborated the usefulness of modified atmosphere on microgreen shelf life (Xiao et  al. 2014b). However, washing of microgreens and light exposure during storage did not improve shelf life, although higher levels of ascorbic acid have been observed due to light exposure in radish microgreens (Kou et  al. 2013; Xiao et  al. 2014a). Despite this one improved characteristic, daikon radish microgreens stored in the dark had a higher radical scavenging activity and carotenoid retention and were judged superior in quality over light stored produce (Xiao et al. 2014a). Similarly, Kou et al. (2013) found that light exposure of radish microgreens accelerated deterioration and they concluded that dark storage was better than light exposure in maintaining microgreen quality. Optimum storage temperature for daikon radish was reported at 1 °C as no chilling injury was observed at this storage temperature (Xiao et al. 2014b). Interestingly, while modified packaging has shown positive effects in buckwheat storage, those same benefits have not been observed for daikon radish, and overall quality decreased at the same rate in different modified atmospheres, despite significant changes in oxygen and carbon dioxide concentrations (Xiao et al. 2014b). Washing with chlorinated water can initially decrease bacterial contamination but seemed to negatively affect shelf life as measured by final microbial counts and electrolyte leakage of the stored tissues (Lee et al. 2009; Kou et al. 2013; Xiao et al. 2014b). In other work with preharvest and postharvest calcium sprays and dips, the authors suggested that postharvest technologies need to be developed that are less destructive than the current washing methods that are used with leafy greens (Kou et al. 2015). Preharvest treatments can also positively affect microgreens in storage. Preharvest calcium chloride applications result in higher biomass, higher calcium concentrations in broccoli microgreens, lower electrolyte leakage, better visual quality, reduced microbial growth, higher superoxide dismutase and peroxidase activities, lower microbial growth, and reduced expression of senescence associated genes (Kou et al. 2014). In a subsequent study, Kou et al. (2015) showed that calcium lactate and calcium amino acid chelate were also effective at

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improving microgreen quality and inhibiting microbial populations, but less so than calcium chloride. Calcium chloride sprays also increased glucosinolate levels in broccoli microgreens and extended the shelf life of those microgreens, possibly through the elevated levels of glucosinolate induced by the calcium treatment (Lu et al. 2018), among the many other parameters positively affected by calcium applications (Kou et  al. 2014). UVB treatment in the postharvest environment increased glucosinolate levels and shelf life even further (Lu et al. 2018). VII.  SENSORY ATTRIBUTES AND QUALITIES Relatively little attention has been given to sensory attributes (­flavor, texture, visual appearance) and some of the associated chemical composition of microgreens. When Dijon mustard, opal basil, ‘bull’s blood’ beet, red amaranth, peppercress, and ‘China rose’ radish were evaluated for their sensory qualities and associated chemical compositions such as titratable acids, pH, total sugars, and phenolic content, the authors concluded that all six microgreens received a good or excellent overall consumer acceptance score (Xiao et  al. 2015b). Overall eating quality was highly correlated with flavor attributes, much more so than visual and textural quality. ‘Bull’s blood’ beet showed the highest acceptance, whereas peppercress showed the lowest acceptance by a consumer panel. Interestingly, the high flavor acceptance of ‘bull’s blood’ beet was, in turn, highly correlated with a higher pH and an average total phenolic content, giving microgreen growers useful and relatively objective predictors of consumer acceptance (Xiao et al. 2015b). VIII.  HEALTH EFFECTS Although microgreens are advocated as being a healthy addition to the diet, very little work has been carried out to substantiate such claims. Many microgreens have significant levels of antioxidants, glucosinolates, and vitamins and, as such, can be considered a healthy addition to any diet (see above). However, no studies have been carried on the health effects of including microgreens in the human diet (Sun et al. 2013). Animal studies are encouraging and showed that the addition of red cabbage microgreens lowered low density lipoprotein (LDL) and reduced inflammatory cytokines in the liver of mice fed a high fat diet (Huang et al. 2016). Fenugreek and mint microgreen leaf extracts showed

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high levels phenolics, flavonoids, and antioxidants, compounds which were thought to lead to the anti‐diabetic activity observed in cell lines and in vitro assays used to study diabetes (Wadhawan et al. 2018). The authors concluded that the extracts not only inhibited amylase and glucosidase activity and non‐enzymatic glycation of proteins but also led to enhanced glucose uptake. Additional work on inclusion of microgreens in the human diet may be useful. In lieu of such work, having clear evidence of the efficacy of a number of phytonutrients found in microgreen on animal or human health may help in the continued promotion of microgreens as healthful additions to the human diet. IX.  FUTURE OF MICROGREENS Microgreens have been promoted as a healthful addition to the diet and there is some evidence to support this (Sun et al. 2013; Eber et al. 2014; Xiao et al. 2016; Waterland et al. 2017). However, the limited total amount of microgreens consumed, because of their current use as a garnish, make claims of any large impacts on human diet and health doubtful. Only if and when microgreens are p ­ romoted as a substitute for salad greens will their full potential be realized. However, their addition to dishes to enhance flavor, texture, and visual appeal make them a crop type that will endure. These high value crops, requiring minimal production space and having a high  ­ turnover, make them ideal for entering into or for diversifying horticultural operations. To date, much attention has been primarily focused on microgreens in the Brassicaceace family (Kyriacou et  al. 2016; Xiao et  al. 2016), while species in other families and herbs have only been occasionally researched (Wadhawan et al. 2018). Future work in microgreens could, therefore, include greater attention to other plant families, species, or groups of plants such as medicinal and culinary herbs, weeds, native plants, and so on. The medicinal value and the often smaller dosages associated with this use of plants may well provide people with an alternative to dried herbal supplements. Since many microgreens are grown for aroma, texture, and visual appeal, a range of culinary herbs could also be easily adopted to microgreen production. Besides finding new species to include in the microgreen producers’ repertoire, research should be focused on several issues. First, additional seed and media treatments to alleviate seed and seedling rots should be developed as growers have very few options beyond

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good sanitation practices to curb a number of fungal pathogens that can destroy a crop. Second, although it is well established that LEDs can grow quality microgreens, it is unclear how the numerous different light levels and combinations of wavelengths can be used in a practical sense to optimize production and to enhance the concentrations of desirable constituents. The wide variety of treatments and of responses to those treatments in terms of growth, development, and phytonutrients makes their application difficult. Research treatments that only vary one parameter at a time combined with application to a range of microgreens in different plant groups and families may lead to better recommendations to microgreen growers. Third, proper postharvest procedures should be investigated further. Although, it is quite clear that washing does not necessarily improve the microbial safety and storability of microgreens (Kou et al. 2013; Xiao et al. 2014b), additional work should be carried out on alternative ways to improve product quality, microbial safety, and storage life in the postharvest environment. Investigations into the lowest possible storage temperatures for microgreens and alternative ways to slow microbial activity, such as ozonation or other treatments, could be very beneficial to microgreen producers. Microgreens have been described as “confetti” and as the “lingerie of the culinary” world and they undoubtedly add to the variety and excitement in human diets. Their health benefits are very much dependent on the quantity of microgreens consumed and on the specific species and varieties that consumers demand as part of their health regimen. Safeguarding and protecting the consumer has to be paramount if microgreens want to maintain their current level of success. Their compact form, rapid production, appeal, and a relative safety make them an exciting crop for the foreseeable future. LITERATURE CITED Alexander, L. 2016. How to tap into the latest trends. Am. Veg. Grower 64(2):38. Allred, J. and N. Mattson. 2018. Growing better greenhouse microgreens in under control: tips for controlled environment growing. Greenhouse Product News, Vegetable Growers News. October 2018:10–13 Andrei, L., D. Cristina, C. Naela, and L. Ana. 2017. Morphological and biochemical parameters in chemically elicited rye sprouts. Studia Universitatis “Vasile Goldis”, Seria Stiintele Vietii 27(3):157–162. Andrejiova, A., A. Hegedusova, E. Konova, and I. Mezeyova. 2017. Content of selected bioactive substance in dependence on lighting in microgreens. Acta Hortic. Regiotecturae 20(1):6–10. Anon. 2016. Restaurant compost into microgreens. Biocycle 57(6):9.

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Baenas, N., I. Gomez‐Jodar, D.A. Moreno, C. Garcia‐Viguera, and P.M. Periago. 2017. Brocolli and radish sprouts are safe and rich in bioactive phytochemicals. Postharvest Biol. Technol. 127:60–67. Bliss, R.M. 2014. Specialty greens pack a nutritional punch. Agric. Res. Jan.:10–11. Brazaitytė, A., J. Jankauskiene, and A. Novickovas. 2013. The effects of supplementary short‐term red LED lighting on nutritional quality of Perilla frutescens L. microgreens. Proc. Intl. Sci. Conf.: Rural Devel. 2013:272–275. Brazaitytė, A., S. Sakalauskiene, G. Samuoliene, J. Jankauskiene, A. Virsile, A. Novickovas, R. Sirtautas, J. Miliauskiene, V. Vaštakaitė, L. Dabasinskas, and P. Duchovskis. 2015a. The effects of LED illumination spectra and intensity on carotenoid content in Brassicaceae microgreens. Food Chem. 173:600–606. Brazaitytė, A., A. Viršilė, J. Jankauskienė, S. Sakalauskienė, G. Samuolienė, R. Sirtautas, A. Novicˇkovas, L. Dabašinskas, J. Miliauskienė, V. Vaštakaitė, A. Bagdonavicˇienė, and P. Duchovski. 2015b. Effect of supplemental UV‐A irradiation in solid‐state lighting on the growth and phytochemical content of microgreens. Intl. Agrophysics 29(1):13–22. Briatia, X., S. Jomduang, C.H. Park, S. Lumyong, A. Kanpiengjai, and C. Khanongnuch. 2018. Enhancing growth of buckwheat sprouts and microgreens by endophytic bacterium inoculation. Int. J. Agric. Biol. 19:374–380. Chappell, M.M. 2016. Spring green. Vegetarian Times, March 2016:88. Active Interest Media. Craver, J.K., J.R. Gerovac, R.G. Lopez, and D.A. Kopsell. 2017. Light intensity and light quality from sole‐source light‐emitting diodes impact phytochemical concentrations within brassica microgreens. J. Am. Soc. Hortic. Sci. 142(1):3–12 Delian, E., A. Chira, L. Badulescu, and L. Chira. 2015. Insights into microgreen p ­ hysiology. p. 447–454. In: Scientific papers ‐ Series B, Horticulture (59), Bucharest: University of Agronomic Sciences and Veterinary Medicine of Bucharest. Di Gioia, F., and P. Santamaria. (Eds). 2015. Microgreens. Novel Fresh and Functional Food to Explore all the Value of Biodiversity. http://www.gustailbiodiverso.com/en/ microgreens‐ebook/. Di Gioia, F., P. De Bellis, C. Mininni, P. Santamaria, and F. Serio. 2016. Physiochemical, agronomical and microbiological evaluation of alternative media for the production of rapini (Brassica rapa L.) microgreens. J. Sci. Food Agric. 97:1212–1219. Eber, A. 2012. Sprouts, microgreens, and edible flowers: the potential high value specialty produce. SEAVEG2012 Reg. Symp., 24–26 January 2012: AVRDC – The World Vegetable Center, Publication No. 12‐758:216–227. Eber, A., T.H. Wu, and R.Y. Yang. 2014. Amaranth sprouts and microgreens – a homestead vegetable production option to enhance food and nutrition security in the rural‐urban continuum. p. 233–244. In: Proc. Reg. Symp. Sustaining Small‐scale Veg. Production. Marketing Systems for Food and Nutrition Security (SEAVEG2014), 25–27 February 2014, Bangkok, Thailand; Tainan: AVRDC – The World Vegetable Center. Food and Drug Administration (FDA). 2017. Compliance with and recommendations for implementation of the standards for the growing, harvesting, packing, and holding of produce for human consumption for sprout operations: guidance for industry (draft guidance). January 2017. Gerovac, J.R., J.K. Craver, J.K. Boldt, and R.G. Lopez. 2016. Light intensity and quality from sole‐source light‐emitting diodes impact growth, morphology, and nutrient content of brassica microgreens. HortScience 51(5):497–503. Hill, F. 2010. Microgreens: How to Grow Nature’s Own Superfood. Firefly Books, Richmond Hill, Ontario, Canada.

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Huang, H., X. Jiang, Z. Xiao, L. Yu, Q. Pham, J. Sun, P. Chen, W. Yokoyama, L. Yu, S. Luo, and T.T.Y. Wang. 2016. Red cabbage microgreens lower circulating low‐density lipoprotein (LDL), liver cholesterol, and inflammatory cytokines in mice fed a high fat diet. J. Agric. Food Chem. 64:9161–9171. Johnson, C. 2012. Small product, big market: Marvin Wilhite finds niche with tasty microgreens. Grove and Vegetable October:4–5. Kadey, M. 2013. Little green giants. The Environmental Magazine, May/June:36–37. Kadey, M. 2016. Make your diet more nutrient‐dense. Environmental Nutrition 39(10):1. Kopsell, D.A. and C.E. Sams. 2013. Increases in shoot tissue pigments, glucosinolates, and mineral elements in sprouting broccoli after exposure to short‐duration blue light from light emitting diodes. J. Am. Soc. Hortic. Sci. 138(1):31–37. Kopsell, D.A., C.E. Sams, and R.C. Morrow. 2015. Blue wavelengths from LED lighting increase nutritionally important metabolites in specialty crops. HortScience 50(9):1285–1288. Kopsell, D.A., C.E. Sams, and R.C. Morrow. 2017. Interaction of light quality and fertility on biomass, shoot pigmentation and xanthophyll cycle flux in Chinese kale. J. Sci. Food Agric. 97:911–917. Kopsell, D.A., N.I. Pantanizopoulos, C.E. Sams, and D.E. Kopsell. 2012. Shoot tissue pigment levels increase in ‘Florida Broadleaf’ mustard (Brassica juncea L.) microgreens following high light treatment. Scientia Hortic. 140:96–99. Kopsell, D.A., C.E. Sams, T.C. Barickman, and R.C. Morrow. 2014. Sprouting broccoli accumulate concentrations of nutritionally important metabolites under narrow‐band light‐emitting diode lighting. J. Am. Soc. Hortic. Sci. 139(4):469–477. Kou, L., Y. Luo, T. Yang, Z. Xiao, E.R. Turner, G.E. Lester, Q. Wang, and M.J. Camp. 2013. Postharvest biology, quality, and shelf life of buckwheat microgreens. Food Sci. Technol. 51:73–78. Kou, L., T. Yang, X. Liu, and Y. Luo. 2015. Effects of pre‐ and postharvest calcium treatments on shelf life and postharvest quality of broccoli microgreens. HortScience 50(12):1801–1808. Kou, L., T. Yang, Y. Luo, X. Liu, L. Huang, and E. Codling. 2014. Pre‐harvest calcium application increases biomass and delays senescence of broccoli microgreens. Postharvest Biol. Technol. 87:70–78. Kyriacou, M.C., Y. Rouphael, F. Di Gioa, A. Kyratzis, F. Serio, M. Renna, S. De Pascale, and P. Santamaria. 2016. Micro‐scale vegetable production and the rise of microgreens. Trends Food Sci. Technol. 57:103–115. Lee, J., J. Kim, and S. Park. 2009. Effects of chlorine wash on quality and microbial population of ‘Tah Tasai’ Chinese cabbage (Brassica campestris var. narinosa) microgreen. Kor. J. Hortic. Sci. Technol. 27(4):625–630. Lee, J.S. and W.G. Pill. 2005. Advancing greenhouse establishment of radish, kale, and amaranth microgreens through seed treatments. J. Kor. Soc. Hortic. Sci. 46(6):363–368. Lee, J.S., W.G. Pill, B.B. Cobb, and M. Olszewski. 2004. Seed treatments to advance greenhouse establishment of beet and chard microgreens. J. Hortic. Sci. Biotechnol. 79(4):565–570. Lobiuc, A., C. Damian, N. Costica, and A. Leahu. 2017a. Morphological and biochemical parameters in chemically elicited rye sprouts. Studia Universitatis ‘Vasile Goldis’. Seria Stiintele Vietii 27(3):157–162. Lobiuc, A., V. Vasilache, O. Pintilie, T. Stoleru, M. Burducea, M. Oroian, and M.  ­Zamfirache. 2017b. Blue and red LED illumination improves growth and bioactive compounds contents in acyanic and cyanic Ocimum basilicum L. microgreens. ­Molecules 22(12):2111.

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Lu, Y., W. Dong, J. Alcazar, T. Yang, Y. Luo, Q. Wang, and P. Chen. 2018. Effects of preharvest CaCl2 spray and postharvest UV‐B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates. J. Food Comp. Anal. 67:55–62. Lubow, A. 2006. The squash blossom solution. Inc. Magazine, October 2006, p.108–115. Mir, S. 2017. Microgreens: production, shelf life, and bioactive components. Critical Rev. Food Sci. Nutrit. 57(12):2730–2736 Muchjajib, U., S. Muchjajib, S. Suknikom, and J. Butsai. 2015. Evaluation of organic media alternatives for the production of microgreens in Thailand. Acta Hortic. 1102:157–162. Murphy, C.J. and W.G. Pill. 2010. Cultural practices to speed the growth of m ­ icrogreen arugula (roquette; Eruca vesicaria subsp. sativa). J. Hortic. Sci. Biotechnol. 85(3) 171–176. Murphy, C.J., K.F. Llort, and W.G. Pill. 2010. Factors affecting the growth of microgreen table beet. Int. J. Veg. Sci. 16:253–266. Nau, J. (Ed.) 2011. Ball Red Book. Ball Publishing, Chicago, USA. Palmer, S. 2010. Microgreens become a macro trend to follow. Environ. Nutrit. (June):8. Pill, W.G, T.A. Evans, N. Gregory, and C.M. Collins. 2011. Application method and rate of Trichoderma species as a biological control against Pythium aphanidermatum (Edson) Fitzp. in the production of microgreen table beets (Beta vulgaris L.). Scientia Hortic. 129(4):914–918. Pinto, E., A.A. Almeida, A.A. Aguiar, and I.M.P.L.V.O. Ferreira. 2015. Comparison between the mineral profile and nitrate content of microgreens and mature lettuces. J. Food Comp. Anal. 37:38–43. Reed E., C.M. Ferreira, R. Bell, E.W. Brown, and J. Zheng. 2018. Plant‐microbe and abiotic factors influencing Salmonella survival and growth on alfalfa sprouts and Swiss chard microgreens. Appl. Environ. Microbiol. 84(9): e02814–17. https://doi.org/10.1128/ AEM.02814‐17. Reinfeld, M. 2013. Earth Day delights. Vegetarian Times (April/May):48–51, Active Interest Media. Renna, M., F. Di Gioia, B. Leonia, C. Mininnib, and P. Santamaria. 2017. Culinary assessment of self‐produced microgreens as basic ingredients in sweet and savory dishes. J. Culinary Sci. Technol. 15(2)126–142. Riggio, G.M., Q. Wang, K.E. Kniel, and K.E. Gibson. 2019. Microgreens – A review of food safety considerations along the farm to fork continuum. Int. J. Food Microbiol. 290:76–85. Ruch, P. 2015. A crop for all seasons; microgreens: nearly instant gratification from your greenhouse. Hortic. Mag., p. 8, F&W Media Inc. Samuoliene, G., A. Brazaitytė, J. Jankauskiene, A. Virsile, R. Sirtautas, A. Novickovas, S. Sakalauskiene, J. Sakalauskaite, and P. Duchovskis. 2013. LED irradiance level affects growth and nutritional quality of brassica microgreens. Central Eur. J. Biol. 8(12):1241–1249. Samuoliene, G., A. Brazaitytė, J. Jankauskiene, A. Virsile, J. Jankauskiene, S. ­Sakalauskiene, and P. Duchovskis. 2016. Red light‐dose or wavelength‐dependent photoresponse of antioxidants in herb microgreens. PLoS ONE 11(9):e0163405. doi:10.1371/journal. pone.0163405. Samuoliene, G., J. Jankauskien, P. Duchovskis, A. Novikovas, A. Brazaitytė, R. Sirtautas, and S. Sakalauskiene. 2012. The impact of supplementary short‐term red led lighting on the antioxidant properties of microgreens. Acta Hortic. 956:649–656. Samuoliene, G., A. Virsile, A. Brazaitytė, J. Jankauskiene, S. Sakalauskiene, V. Vaštakaitė, A. Novickovas, A. Viskeliene, A. Sasnauskas, and P. Duchovskis. 2017.

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Blue light dosage affects carotenoid and tocopherols in microgreens. Food Chem. 228:50–56. Sun, J., Z. Xiao, L. Lin, G.E. Lester, Q. Wang, J.M. Harnly, and P. Chen. 2013. Profiling polyphenols in five brassica species microgreens buy UHPLC‐PDA‐ESI/RMS. J. Agric. Food Chem. 61:10960–10970. Treadwell, D.D., R. Hochmuth, L. Landrum, and W. Laughlin. 2013. Microgreens: a new specialty crop. HS1164. Horticultural Sciences Department, UF/IFAS Extension, p. 1–3. Vaštakaitė, V. and A. Virsile. 2015. Light‐emitting diodes (LEDs) for higher nutritional quality of Brassicaceae microgreens. Research for Rural Development, Latvia University for Rural Development 1:111–117. Vaštakaitė, V., A. Virsile, A. Brazaitytė, G. Samuoliene, J. Jankauskiene, R. Sirtautas, and P. Duchovskis. 2015a. The effect of UV‐A supplemental light on antioxidant properties of Ocimum basilicum L. microgreens in greenhouse. Proc. 7th Intl. Sci. Conf. Rural ­Devel. doi.org/10.15544/RD.2015.001 Vaštakaitė, V., A. Viršilė, A. Brazaitytė, G. Samuoliene, J. Jankauskienė, R. Sirtautas, A. Novičkovas, L. Dabašinskas, S. Salauskienė, J. Miliauskienė, and P. Duchovskis. 2015b. The effect of blue light dosage on growth and antioxidant properties of microgreens. Scientific Works of the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry and Aleksandra Stulginskis University, Sodininkyste Ir Darzininkyst 34(1–2):1–35. Virsile, A. and R. Sirtautus. 2013. Light irradiance level for optimum growth and nutrient contents in borage microgreens. Proc. Intl. Sci. Conf.: Rural Devel. 2013:272–275. Wadhawan, S., J. Tripathi, and S. Gautum. 2018. In vitro regulation of enzymatic release of glucose and its uptake by fenugreek microgreen and mint leaf extract. Int. J. Food Sci. Technol. 53(2):320–326. Wang Q. and K.E. Kniel. 2016. Survival and transfer of Murine norovirus within a hydroponic system during kale and mustard microgreen harvesting. Appl. Environ. Microbiol. 82(2):705–713. Waterland, N.L., Y. Moon, J.C. Tou, M.J. Kim, E.M. Pena‐Yewtukhiw, and S. Park. 2017. Mineral content differs among microgreen, baby leaf, and adult stages in three cultivars of kale. HortScience 52(4):566–571. Weber, C.F. 2017. Microgreen farming and nutrition: a discovery‐based laboratory module to cultivate biological and information literacy in undergraduates. Am. Biol. Teacher 79(5):375–386. Wright, K.M. and N.J. Holden. 2018. Quantification and colonization dynamics of Escherichia coli O157:H7 inoculation of microgreens species and plant growth substances.Int. J. Food Microbiology 273:1–10. Xiao, Z., G.E. Lester, Y. Luo, Z. Xie, L. You, and Q. Wang. 2014a. Effect of light exposure on sensorial quality, concentrations of bioactive compounds and antioxidant capacity of radish microgreens during low temperature storage. Food Chem. 151:472–479. Xiao, Z., Y. Luo, G.E. Lester, L. Kou, T. Yang, and Q. Wang. 2014b. Postharvest quality and shelf life of radish microgreens as impacted by storage temperature, packaging film, and chlorine wash treatment. Food Sci. Technol. 55:551–558. Xiao, Z., X. Nou, Y. Luo, and W. Qin. 2014c. Comparison of the growth of Escherichia coli O157: H7 and O104: H4 during sprouting and microgreen production from contaminated radish seeds. Food Microbiol. 44:60–63. Xiao, Z., G. Bauchan, L. Nichols‐Russell, Y. Luo, Q. Wang, and X. Nou. 2015a. Proliferation of Escherichia coli O157:H7 in soil‐substitute and hydroponic microgreen production systems. J. Food Protect. 78(10):1785–1790.

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Xiao, Z., G.E. Lester, E. Park, R.A. Saftner, Y. Luo, and Q. Wang. 2015b. Evaluation and correlation of sensory attributes and chemical composition of emerging fresh produce: microgreens. Postharvest Biol. Technol. 110:140–148. Xiao, Z., E.E. Codling E, Y. Luo, X. Nou, G.E. Lester, and Q. Wang. 2016. Microgreens of Brassicaceae: mineral composition and content of 30 varieties. J. Food Comp. Anal. 49:87–93.

4 The Durian: Botany, Horticulture, and Utilization Saichol Ketsa Department of Horticulture, Faculty of Agriculture, Kasetsart University, Bangkok, and Thailand and Academy of Science, The Royal Society of Thailand, Dusit, Bangkok, Thailand Apinya Wisutiamonkul, Expert Centre of Innovative Agriculture, Thailand Institute of Scientific and Technological Research (TISTR), Khlong Luang, Pathum Thani, Thailand Yossapol Palapol Division of Agricultural Technology, Faculty of Science and Arts, Burapha University, Chanthaburi Campus, Thamai, Chanthaburi, Thailand Robert E. Paull Department of Tropical Plant and Soil Sciences, University of Hawaii at Manoa, HI, USA ABSTRACT Durian is native to Southeast Asia where it is grown commercially. It is also a common feature of home gardens in rural areas. The durian has been introduced to other tropical countries where limited commercial production occurs, although it is commonly found in arboretums. It is known for its unique intense aroma and its sweet custard-like aril flesh, which have led to its title of “King of Fruit.” It has ardent afficionados who strongly advocate the appeal and benefits of the fruit. The aril flesh contains a number of different bioactive compounds, many of which are beneficial to human health. Processed durian products are Horticultural Reviews, Volume 47, First Edition. Edited by Ian Warrington. © 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc. 125

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available worldwide and are in demand by consumers. A short period of water stress induces flowering and, though there are some differences amongst cultivars, this stress requirement leads to periods when there is an excess fruit available in markets. This climacteric fruit has a short postharvest life at ambient temperatures that has posed problems in extending the marketing period, and this is compounded by its strong and particular smell that makes it difficult to export to distant markets. Research is needed to develop improved cultivars that have both disease and insect resistance, to develop production practices that control flowering and enhance yield and fruit quality, and to extend knowledge of postharvest physiology and technology to improve handling and to extend the fresh market period within the postharvest chain. KEYWORDS: durian; botany; cultivation; nutrition; morphology; physiology; postharvest physiology; postharvest handling; processed products

I.  INTRODUCTION A. Climate B. Cultivar Origin II.  BOTANY A. Morphology 1. Fruit 2. Flowers 3. Leaves 4. Roots 5. Stems B. Physiology 1. Flowering 2. Pollination 3. Tree Growth 4. Fruit Growth III.  CULTURAL PRACTICES A. Propagation B. Planting C. Hand Pollination D. Flower and Fruit Thinning E. Pruning F. Irrigation G. Fertilizer Application H. Diseases and Their Control I. Insect Pests and Their Control J. Physiological Disorders 1. Wet or Water Core (Sai Suem) 2. Aril Tip Burn (Tao Pao) 3. Uneven Fruit Ripening IV.  CHEMICAL COMPOSITION AND NUTRITIONAL VALUE A. Vitamins and Minerals B. Antioxidants

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C. Carotenoids D. Carbohydrates E. Aroma V.  POSTHARVEST PHYSIOLOGY A. Respiration B. Ethylene Production C. Fruit Softening D. Color Development E. Weight Loss F. Dehiscence VI.  HARVESTING AND POSTHARVEST HANDLING A. Harvest Season B. Maturity Indices 1. Day Count 2. Husk Color 3. Abscission Layer 4. Spines 5. Fruit Stalk 6. Grooves 7. Suture 8. Sap 9. Tapping 10. Dry Matter 11. Non‐destructive Methods 12. Other Methods C. Harvesting D. Ripening E. 1‐Methylcyclopropene (1-MCP) F. Waxing G. Packing H. Storage VII.  UTILIZATION A. Fresh Fruit B. Durian Products C. Durian Husk and Seed VIII.  CONCLUSIONS LITERATURE CITED

I. INTRODUCTION Durian (Durio zibethinus L.) is an important economic crop of Southeast Asian countries including Thailand, Malaysia, and Indonesia. Durian fruit is known by admirers as the “King of Fruit” (Subhadrabandhu and Ketsa 2001), and by others as “Heaven and Hell Fruit” (tastes like heaven, smells like hell). Wherever you personally stand on the merit or aversion of durian, one thing is clear: there are some who really love this fruit. The common name durian is derived from the Malay word

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duri meaning thorn while the species name zibethinus is derived from the Italian word zibetto for the civet, a cat‐like animal with a strong musky smell (Reksodihardjo 1962). Durian fruit is characterized by its large size, strong odor, and hard thorn‐covered husk. Ripe durian has a unique taste with a strong aroma. The aril is widely believed to act as an aphrodisiac. Eating durian fruit is simply “mind over matter” for Westerners who are unfamiliar with the smell. A. Climate This strictly tropical plant grows best between 27 and 30°C, with humidity of 75 to 80%. Durian can be grown in latitudes up to 18° north and south of the equator in the northern areas of Myanmar, ­Thailand, Vietnam, and India. Commercial production is more common and more successful within 12° of the equator (Subhadrabandhu and Ketsa 2001). It does not tolerate cold temperatures or low humidity. If minimum temperature falls below 8°C, the tree suffers from chilling injury that leads to leaf abscission and sometimes death. Annual rainfall exceeding 2000 mm is ideal for durian production, and mean yearly total rainfall should exceed 3000  mm. The rainfall should be well distributed throughout the year with a short period of dry weather. A prolonged period of drought of up to three months is harmful to durian, which may suffer irreversible damage. Hence, irrigation is essential during long periods of drought in the dry season (Subhadrabandhu and Ketsa 2001). Hariyono et al. (2013) reported that precipitation intensity in a year does not significantly correlate with flower bud formation or the harvest time of local durian. However, the number of dry months at each altitude correlated significantly with flower bud formation. The average temperature, temperature difference (maximum and minimum), and the minimum temperature are negatively correlated with intensity of flower bud formation and the length of the harvest period of durian at different altitudes. This suggests that there is a close relationship between latitude, altitude, and flower bud formation. An increase in the altitude of production will lengthen the flower bud formation period. Studies at different agroclimatic zones indicate that durian flower emergence coincides with the onset of the dry season. For mature trees, durian requires a dry period of about one to two months for flowers to initiate and develop fully. Four weeks after flowers have bloomed, the tree must receive just enough water for proper fruit development. Too much water will cause the tree to bear new leaves at the expense of the fruit (Suaybaguio and Odtojan 1992; Masri 1999; Hariyono et al. 2013). Nevertheless, in Australia, low night temperature seemed to induce

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flowering (Lim and Luders 1998). In general, durian trees come into flower about one month after the onset of a dry period. Continued dry weather is also required for subsequent good fruit set and development. Excessive rainfall during these phases of flower bud development is detrimental to pollination and fruit set. B.  Cultivar Origin Durian is a native fruit of Southeast Asia. Its center of diversity appears to be the Malay Peninsula, Indonesia, and the island of B ­ orneo, but it has been introduced into many countries in tropical Asia (­Subhadrabandhu et al. 1991). The durian is a tropical fruit tree in the order Malvales, family Malvaceae. Some taxonomist originally placed Durio in the fam­ ily ­Bombacaceae, but recent molecular data has led to it being placed in the expanded Malvaceae that includes the former members of the Bombacaceae. The genus Durio has approximately 28 species, 19 of which are native to the island of Borneo – which is thought to be the original center of diversity. From this group of 19, 14 species are found in S ­ abah (­Reksodihardjo 1962) and 16 in Sarawak (Abang Mohd Mokhtar 1991). In Malaysia there are 23 species, of which 13 are found in the lowland forests of Peninsular Malaysia (Cockburn 1976). Among the species found in Peninsular Malaysia, five are endemic. Seven species are known on the island of S ­ umatra but none of them are endemic (Kostermans 1958). Four species are reported in the Philippines (Coronel 1983), and six species are known in Thailand (Smitinand 1980). Apart from Durio zibethinus, seven species are notable for producing edible fruit: Durio testudinarius Becc., Durio graveolens Becc., Durio grandiflorus Kosterm. & Soegeng, Durio dulcis Becc., Durio ­oxleyanus Griff., Durio kutejensis Hassk. & Becc., and Durio lowianus Scort. ex King. The small country of Brunei, on the island of Borneo, has perhaps the largest concentration of these Durio species. Each of these species has many variants for fruit size, fruit and aril color, and leaf area. These edible species are relatively rare and are more often found wild in various locations of Southeast Asia, rather than being ­cultivated. They are found for sale in local markets. The most domesticated species of durian is D.  zibethinus which is ­ cultivated commercially in large orchards thoughout Southeast Asia (Yaacob and Subhadrabandhu 1995). It is endemic to the Malay ­Peninsula, southern Thailand, Indonesia, the island of Borneo, and New Guinea. The species has also been introduced to India, Sri Lanka, Myanmar, Vietnam, and Jamaica (Subhadrabandhu and Ketsa 2001). A few trees are grown in small orchards in Hawaii while, in tropical

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SAICHOL KETSA ET AL.

northern Australia, significant plantings have been made in orchards similar to those in Thailand with some use of trellises. Natural interspecific cross‐pollination has occurred with a hybrid of D. zibethinus and D. graveolens being found in northeastern I­ ndonesia and Borneo, and some trees of normally white‐flowered D. malaccensis Planch. ex Mast. have been discovered in Johore State with reddish flowers, perhaps from cross‐pollination by the pink or red‐flowered D. lowianus and D. pinangianus (Becc.) Ridl. (Anon. 2018). Most small‐scale farmers use seedlings from seeds harvested from their farms or use clonal material from hybridization and selection programs. The strategy adopted in durian breeding, where selections are then clonally propagated, is dependent upon existing variation from natural populations or from hybridization. The first step is to identify and select promising maternal trees and to test them over time and at different locations to establish their adaptability. Selection has been based on characteristics such as fruit shape, size, smell, color, texture, taste, and tree growth habit (Chan 1992; Belgis et al. 2016). As with all fruit tree breeding, the major challenges are a long juvenile period, perennial growth cycles and a large growth form, sterility, self‐­incompatibility, polyploidy, and inherent heterozygosity. Self‐incompatibility between durian clones may require the use of complementary clones. The Malay clone D10 is highly compatible, with the current recommended D24 giving better fruit development – larger fruit that are more rounded and have fewer empty locules (Shaari et al. 1985). Durian breeding programs have relied on outcrossing and selection to generate new cultivars in Malaysia, Thailand, the Philippines and ­Indonesia (Chan 1992; Nanthachai 1994; Somsri et al. 2008; Bansir et al. 2010; Somsri 2014; Bais 2016). This strategy has led to numerous cultivars, often from chance seedlings (Table 4.1). The Malayan registered clones D2, D10, D24, and D145 were all selected from farmers plots, while others are hybrids (D188, D189, and D190) derived from crosses using D10 and D24 – with D188 being mild and milky and D190 being sticky‐bitter‐caramel in flavor (Sani et al. 2015). In Thailand, ‘Monthong’ and ‘Chanee’ are the most popular clones. New cultivars have been developed in Thailand numbered from #1 to #9: Chanthaburi #1 to #3 have an early maturity; #4 to #6 have an intermediate maturity; and #7 to #9 a late maturity. The first six recommended hybrid cultivars of durian, Chanthaburi #1 to #6, were released officially between late 2006 and late 2013. Chanthaburi #7 to #9 were recently released and recommended for cultivation in 2016 (Somsri 2017, 2018). A breeding program in Indonesia focused on crosses between D.  zibethinus and D. kutejensis that have progeny with golden yellow fruit arils without smell (Hariyati et al. 2013).

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131

Table 4.1  Characteristics of main durian cultivars grown in some ASEAN countries. Location/ Cultivars Indonesia Ajimah

Aspar

Bokor

Bubur

Gandaria

Kamun

Characteristics

References

Bears globose, greyish‐green fruit with large, sharp, widely spaced spines. The husk  is thin. The aril is large, thick, pale yellow, dry, slightly fibrous, sweet and somewhat bitter. the seeds are small. Each fruit weighs 1.5–3 kg and exhibits uniform ripening. The fruit is ellipsoid, light brown with short, conical widely‐spaced spines. Each fruit weighs 6–8 kg and the fruit can easily be opened. The husk is 1–1.5 cm thick. Each fruit has 5 locules each with 18–22 arils. The aril weight is 2.5–3.75 kg, golden yellow, fine textured, dry, sweet, delicious and aromatic. There are 14–22 seeds per fruit. The seed is ellipsoid and weighs 25 g. Large fruit weigh up to 4 kg, are oblong, yellowish‐green, with medium thick husk (3–5 mm) and large, conical, widely spaced spines. The aril is pale yellow, fine textured, smooth, medium thickness, sweet and odorous. There are 15–20 arils per locule and 10–20 seeds. Old trees yield 150–200 fruit per tree per year and the cultivar is tolerant to Phytophthora but susceptible to fruit borer. The fruit is large, 4–5 kg, oblong to cylindrical, greenish‐yellow, distinctly lobed with pointed closely‐spaced spines and has small seeds. It yields 300–400 fruit per tree per year. The fruit is large weighing 4–7 kg, elongated, brownish‐green with short, widely‐spaced spines. The husk is thin and can be easily opened. There are 4–5 arils per locule. The aril is cream-colored, slightly fibrous, sweet with an alcoholic taste. The seeds are shrunken and flat. It yields 400 fruit per tree per year. The tree is about 30 m high and 20 m wide. It bears 1–4 fruit per cluster from the 8–12 flowers in each cluster. The fruit is elongated ellipsoid, yellowish‐green, with sparse, conical spines and a husk of 1–1.3 cm which can be opened with ease. Each fruit weighs 2–3.5 kg. There are 5 locules producing 15– 18 arils each. Aril weight is 0.6–1.0 kg, i.e., 30% of total fruit weight. The aril is golden yellow, thick 1.5–2.5 cm, fine‐textured, dry, delicious, sweet and aromatic. All seeds are shrunken, and flat, each weighing 5–8 g.

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

(continued)

Table 4.1  (Continued) Location/ Cultivars Mansau

Perwira

Petruk*

Si Dodol

Si Hijau

Si Japang

Characteristics

References

The fruit are ellipsoid, yellow with small sharp, conical, dense spines. Each fruit weighs 0.9–1.5 kg. The husk is thin 0.9 cm and easily opened. There are 5 locules with 14–17 arils each. Aril weight is 277–460 g, dark red, 0.5–1.0 cm thick, fine‐textured, dry, sweet and odorless. The seed number is 14–16, small and ellipsoid. The tree is resistant to fruit borer and root rot. The fruit is round with a thin green husk and large, conical, dense spines. The thick, yellow aril is dry, sweet and strongly odorous. There are 15–20 arils/fruit with the same number of ovoid seeds. Each fruit weighs 2–3 kg. It produces 200–300 fruit per tree per year. The cultivar is resistant to Phytophthora and fruit borer. Tree height and canopy spread are 18 and 10 m, respectively. Branching habit is close. The fruit is shaped like an egg with yellowish green skin and small spines which are close together. Fruit are not easily opened. Each fruit weighs about 1.0–1.5 kg, has 5 locules containing 5–10 yellow aril units. Each tree produces 50– 150 fruit per year. The cultivar is resistant to Phytophthora and fruit borer. The fruit is round, five‐lobed, yellowish‐ green with blunt, conical, dense spines. The fruit is easy to open. The aril is thick, golden‐yellow, soft, fine‐textured, sweet and delicious. It has 20–25 arils per fruit with 15–20 small, elongated seeds. Each fruit weighs 1.5–2.5 kg. The cultivar is resistant to Phytophthora and fruit borer. The fruit is round, green, five‐lobed with sharp, conical, dense spines. The fruit is easy to open. The golden‐yellow aril is soft, fine‐textured, sweet, delicious and aromatic. Each fruit weighs 2–2.5 kg and each tree can bear 300–400 fruit per tree per year. The cultivar is resistant to Phytophthora and fruit borer. The fruit is elongated oblong, five‐lobed, greenish‐yellow with widely spaced, conical spines. The aril is yellow‐ivory, dry, smooth, creamy and has a coconut taste. It is sweet and high in alcohol content and strongly odorous. Many of the small seeds are shrunken and flat. Each fruit weighs 1.5–2.5 kg. It yields 300–600 fruit per tree per year and is resistant to Phytophthora and fruit borer.

Lim and Luders (1997)

Lim and Luders (1997)

Nanthachai (1994); Yaacob and Subhadrabandhu (1995)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Table 4.1  (Continued) Location/ Cultivars Si Mas*

Sitokong*

Sukun*

Sunan*

Characteristics

References

Tree height and canopy spread are 15 and 6 m, respectively. Branching habit is close. Fruit is oblong in shape with reddish yellow skin and spines which are close together. The husk is intermediate in thickness and not easily opened. Each fruit weighs 1.5–2.0 kg, has 5–7 locules with 20–30 bright yellow arils. Each tree produces 50–200 fruit per year and is resistant to Phytophthora but susceptible to fruit borer. Tree height and canopy spread and 20 and 8 m, respectively. Branching habit is sparce. The fruit is long not round with yellowish green skin and small spines which are close together. The husk is intermediate in thickness and difficult to open. Each fruit weighs 2.0–2.5 kg, has 5–7 locules with 20–30 arils which are bright yellow. Each tree produces 50–200 fruit per year. The cultivar is resistant to Phytophthora but not to fruit borer. Fruit is long and round with yellowish skin and small spines which are close together. The fruit has quite a thick husk, is easily opened and weighs 2.5–3.0 kg. Each fruit has 5 locules with 5–15 yellowish white arils with flattened seeds. Each tree produces 100–300 fruit per year and is resistant to Phytophthora and fruit borer. Tree height and canopy spread are 10 and 10 m, respectively. Branching habit is close. The fruit is reverse egg‐shaped, brownish‐green skin and small spines which are widely separated. The fruit weighs 1.5–2.5 kg and has a thin husk which can be easily opened. Each fruit has 5 locules, with 20–35 cream-colored aril units with flattened seeds. Each tree produces 200–800 fruit per year and is resistant to Phytophthora and fruit borer. The appearance of fruit is very attractive compared to other cultivars.

Nanthachai (1994); Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

Nanthachai (1994); Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

Nanthachai (1994); Lim and Luders (1997)

Nanthachai (1994); Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

(continued)

134

SAICHOL KETSA ET AL.

Table 4.1  (Continued) Location/ Cultivars Malaysia D2*

D10*

D24*

Characteristics

References

The tree is medium large and erect in form. It flowers regularly but is comparative low yielding. The plants show good tolerance to Phytophthora stem canker. The fruit are generally borne on smaller secondary/ tertiary branches. The fruit are medium to large weighing 1.3–1.8 kg and are lop‐sided (kidney) in shape. The fruit is difficult to open though the valves are thin with small sharp spines. The aril is thick, copper yellow in color and firm. Each locule possesses only a few aril units, often variable in size. The aril quality is excellent. The tree is medium in size with a broad canopy. It flowers regularly and is medium to high yielding. This clone is sensitive to Phytophthora stem canker. Fruit are borne uniformly over the tree. The fruit is round to oval weighing 1.0–1.7 kg each. The fruit has poor keeping quality and tends to split easily. The husk is medium‐thick and yellowish‐green in color. The aril is thick, bright yellow in color and is sweet and nutty. Each locule is completely filled with aril units arranged in single rows. The aril quality is considered very good. This is the leading commercial clone in Malaysia. The tree is large (19 m height, 20 m canopy width) with a broad, pyramid canopy. The trees flower regularly and are very high yielding. Single trees may bear 100–150 fruit per tree per season at 10–15 years of age. Fruit are borne all over the tree. The large lower branches are, however, more productive. The fruit are medium‐large, weigh 1.0–1.8 kg each and have a round to oval shape. The husk is thick and light green in color. Each locule contains 1–4 large aril units arranged in single rows. The aril is thick, light yellow in color and is firm and fine in texture. It is sweet and nutty with a slightly bitter taste. The main disadvantage of D24 is that it is extremely susceptible to Phytophthora stem canker. Fruit of D24 also exhibit some degree of the physiological disorder called “uneven fruit ripening”.

Nanthachai (1994)

Nanthachai (1994)

Yaacob and Subhadrabandhu (1995); Lim and Luders (1997);

4.  THE DURIAN: BOTANY, HORTICULTURE, AND UTILIZATION

135

Table 4.1  (Continued) Location/ Cultivars D105

D145

D146

D148

D150

D158

D160

D162

D163

Characteristics

References

The fruit is ellipsoid ‐ tapering slightly towards the polar ends, 2–2.5 kg in weight, brownish‐yellow when mature ripe with straight, short spines widely spaced apart. The peduncle is moderately long and the husk is thick. Usually there are 3 arils per locule which are creamy, firm and yellow. It ripens green and produces moderately large, 1.3–1.5 kg, round to oval fruit. It bears less frequently but yields a good crop. The husk is moderately thick and encloses 1–4 arils per locule in a single row. The aril is thick, bright yellow, fine‐textured, sweet and nutty with a good aroma. The fruit weighs 1–3 kg, ellipsoid in shape and dark green. The aril is large, yellowish, sweet and delicious. The fruit is moderately large, round with delicate spines. The sweet, yellow aril is of moderate quality. The fruit is elongated, tapering at the apical end and brownish green, with a moderately long, 9 cm peduncle. The aril is thick, large, fine‐textured and yellow. It produces round or globose, brownish‐ yellow fruit with a moderately thick husk and sharp, straight, dense spines. There are 3 large arils per locule. The aril is thick, creamy, firm, sweet, golden‐yellow with a pleasant aroma which is not strong. The fruit is large, 3 kg, oval to ellipsoid, green and rough, with short, widely spaced spines. The thin husk can be easily opened. The large aril is thick, firm, brownish‐yellow, creamy sweet and of excellent quality. The fruit is medium large, elongated, and yellowish‐green. The aril is medium large, firm, yellow‐white and of excellent bitter but creamy sweet taste. The fruit is oval, cylindrical, medium size with a thick husk and a short peduncle. The spines are closely spaced and of medium length. There are 2–3 arils per locule. The arils are moderately thick, yellow-colored, smooth, creamy sweet and of excellent quality.

Lim and Luders (1997)

Nanthachai (1994)

Lim and Luders (1997) Lim and Luders (1997) Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

(continued)

136

SAICHOL KETSA ET AL.

Table 4.1  (Continued) Location/ Cultivars D164

D165

D166

D168

D175

D176

D182

MDUR78* (D188)

Characteristics

References

It bears medium sized, elongated to ellipsoid fruit with medium length, sharp, conical, densely spaced spines; medium thick husk and short peduncle. The aril is moderately thick, orange yellow, fine textured, creamy sweet and of excellent quality. It produces medium-sized fruit, ellipsoid to round with large, long, densely spaced spines. The large aril is cream-colored, medium thick and smooth, with creamy, excellent quality. The fruit is medium large, oval, green with large, short, sharp and widely spaced spines. The aril is moderately thick, yellow, sweet and of good quality. The tree yields well. The tree is moderately large and bears frequently with high yields. The fruit is round, weighs 1.4–1.6 kg, brownish green with a short peduncle. The fruit is easily opened exposing 3–4 moderately large arils per locule. The aril is orange yellow, firm, sweet and creamy. Some of the seeds are small and shrunken. The fruit is fairly large (1.5–3.0 kg) elongate‐ ellipsoidal with brown‐green skin and small spines. The aril is creamy, sweet, thick, soft, fine, and yellow. The fruit is round, copper‐green with a short stalk and is easy to open. The aril is sweet, soft, fibrous, slightly thick, and creamy‐ yellow. The fruit weighs 1.4 kg and is heart‐shaped with fine, sharp spines and a thin, green rind which opens easily. The aril is moderately thick, firm, dry creamy, sweet, and soft. Tree height and canopy spread are 20 and 22 m, respectively. Branching habit is close. The plant is comparatively small, shady, and often high yielding. Each fruit weighs 1.5–1.8 kg and is round oval in shape. Skin color is yellowish light green. The aril is thick and each aril unit is big. The aril is orangish‐yellow, with fine texture, and is sweet and nutty. It has good keeping quality with a natural shelf‐ life of about 70 h. It is resistant towards Phytophthora stem canker and fruit borer.

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Lim and Luders (1997)

Nanthachai (1994); Yaacob and Subhadrabandhu (1995)

4.  THE DURIAN: BOTANY, HORTICULTURE, AND UTILIZATION

137

Table 4.1  (Continued) Location/ Cultivars MDUR79* (D189)

MDUR88* (D190)

The Philippines DES 806*

DES 916*

CA3266*

Umali*

Singapore H.C. Tan No.2*

Characteristics

References

Tree height and canopy spread are 18 and 20 m, respectively. Branching habit is sparse. The plant fruits regularly and has average yields. The fruit is roundish oval and each fruit weighs 1.0–1.6 kg. The husk color is dark green. The aril is thick and each aril unit is big, colored orangish‐yellow with a fine texture and is sweet and nutty. The fruit is easily split open but has a relatively short shelf‐life, only 27 h. It is resistant towards Phytophthora stem canker and fruit borer. Tree height and canopy spread 18 and 10 m, respectively. Branching habit is close. The plant is vigorous, high yielding and a consistent bearer. Fruit weighs 1.5–2.0 kg each and is round to oval in shape with a yellowish‐green skin. The aril is very thick and each aril unit is big, colored golden yellow, is slightly dry, with a fine texture, and is sweet and nutty. The fruit has a relatively long storage life, between 78–86 h. The cultivar is resistant to Phytophthora and fruit borer.

Nanthachai (1994); Yaacob and Subhadrabandhu (1995)

The fruit is ellipsoid, weighs 2–4 kg, yellowish‐green with a thick husk, medium length densely spaced spines and a short stalk. The aril is yellow, sweet, and very glutinous with a slightly bitter taste. The fruit has a 25% recoverable edible portion. The fruit is ellipsoidal, 2–4 kg, greenish‐ brown with long, sharp, dense spines. The yellow aril is sweet and glutinous and makes up about 25% edible portion. The fruit is globose, 1.5–2.5 kg, greenish‐ yellow with a pale yellow and sweet aril. The recovery ratio is about 25% edible portion. The fruit is globose to elongated, 2–3 kg, yellowish‐brown with golden yellow aril. The recovery ratio is about 32% edible portion.

Nanthachai (1994)

The fruit bears 1–2 kg, light green, pear‐shaped fruit with medium length spines. The aril is thin but creamy, sweet with some bitterness. The seeds are shrunken and flat.

Nanthachai (1994)

Nanthachai (1994); Yaacob and Subhadrabandhu (1995)

Nanthachai (1994)

Nanthachai (1994)

Nanthachai (1994)

(continued)

Table 4.1  (Continued) Location/ Cultivars H.C. Lim*

Lim Keng Meng* Thailand Chanee*

Kob

Kampan

Characteristics

References

The fruit is 1–2 kg, elongated oval, brownish with medium length spines. The aril is pink, thin, sweet, not fibrous, and has small seeds. The fruit is round, 1–2 kg, brownish with medium length spines. The aril is yellow, medium thick, creamy and bitter‐sweet.

Nanthachai (1994)

Tree height and canopy spread are 10–15 and 8–10 m, respectively. Branching habit is sparse. This is an early cultivar which bears fruit 4–6 years after planting. The fruit is 2.0–4.5 kg, oval to broad cylindrical, lobed and greyish brown. The peduncle is thick and moderately long, and the husk is brownish yellow, thin with blunt, large, widely spaced spines. Each locule has 3–4 arils. The bright yellow aril is thick, fine textured, firm, creamy smooth, sweet and of excellent taste. The aril exhibits uniform ripening. The inferior qualities include high aril fiber, frequent occurrence of a physiological disorder, watery at the full ripening stage, poor fruit setting, and it is susceptible to Phytophthora and fruit borer. The fruit is usually globose, slightly compressed at the polar ends with a slight depression in the apical end, or lychee shaped. The peduncle is relatively short and thick, the husk is thin with long, recurved, sharp, densely packed spines. Each locule has 2–3 arils which are pale yellow to yellow, thick, sweet, and creamy. Generally, the fruit is small, 1–2 kg and yellowish‐green brown. It bears fruit 6–8 years after planting. The fruit is round, medium to large, 27 cm long by 18 cm wide. Fruit shoulder is enlarged tapering toward apex. Fruit apex is round. The fruit has 5 lobes and the skin is greenish‐brown with reddish‐brown depressions. The spine is thick, short straight and angled, greenish‐brown in color. The fruit has 5 locules, with 1–2 seeds each. The aril is thick, pale yellow to white in color, very fine textured, with a strong aroma, and is very sweet.

Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

Nanthachai (1994)

Lim and Luders (1997)

Somsri (2007)

Table 4.1  (Continued) Location/ Cultivars Kan Yao

Kradum (Kradumthong)

Luang

Monthong*

Characteristics

References

Tree height and canopy spread are 10–15 m and 9–12 m, respectively. Branching habit is sparse. The fruit is characterized by a long, thick peduncle of 10–14 cm. The fruit is lychee‐shaped to globose, greyish‐brown, rough with a moderately thick husk bearing short, sharp, straight, moderately dense spines. There are 3–4 large, thick arils per locule. The aril is golden‐yellow, smooth, creamy, sweet with a pleasant aroma. Each fruit weighs 2.0–4.5 kg. Inferior fruit characters include the large seed and the high number of seeds per fruit, high incidence of wet core, branch dieback, low Phytophthora resistance and poor processing properties. This cultivar bears fruit 4–6 years after planting and is also an early season cultivar in Thailand, fruiting around March. The fruit is large, 2–4 kg, oval and symmetrically or uniformly distinctly lobed. The husk is brownish‐green, thin and bears short, sharp densely packed spines. The fruit peduncle is moderately long. There are 3–4 large, thick, yellow arils/locule. The fruit is medium‐sized, oval in shape 20–30 cm long by 16–30 cm wide, yellowish‐green in color at maturity, 4–5 lobes with slight depressions. The medium‐ spaced spines are thick, yellow in color. Coarse texture and sweet. The fruit has 5 locules, each contains 1–6 aril units. Tree height and canopy spread are 10–12 m and 8–10 m, respectively. Branching habit is sparse. It produces large, elongated, oval‐cylindrical fruit tapering at the stylar end. The large fruit has a pronounced beak, lobed, yellowish‐brown, each weighing about 2–6 kg. The peduncle is thick and moderately long and the husk is thick and covered with sharp, pointed, small, conical, densely packed spines. Each fruit has 10–15 arils and many small, shrunken (aborted) seeds. Each locule has usually 3 large, thick, creamy, smooth, pale yellow arils. The aril has mild odor and is of excellent quality, constituting more than 30% edible portion. The cultivar has few physiological disorders. This cultivar is extremely amenable for processing of preserved frozen aril. It bears fruit after 8 years. It is susceptible to Phytophthora and fruit borer.

Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

Lim and Luders (1997)

Somsri (2007)

Yaacob and Subhadrabandhu (1995); Lim and Luders (1997)

(continued)

140

SAICHOL KETSA ET AL.

Table 4.1  (Continued) Location/ Cultivars Tongyoi

Vietnam Com Vang, Sua Hat Lep*

Hat Lep, Dong Nai*

Kho Qua Xanh*

Characteristics

References

This cultivar is common but not as popular or as good as the ones described above. The fruit is heart‐shaped or lychee‐shaped, small 2–3 kg, brownish‐grey‐green with a very short, thick peduncle. The husk is thin and bears small, sharp, dense spines. The arils usually number three per locule and are pale yellow and thick. It bears fruit 6–8 years after planting.

Lim and Luders (1997)

Tree has vigorous growth. Fruit is round, average weight 2.5–2.7 kg; aril yellow, soft, fine, and non‐fibrous; high edible portion (26–30%), taste is sweet, creamy with attractive aroma; small seed. Tree has vigorous growth. Fruit is elliptical, average weight 1.5–1.8 kg; aril yellow, firm, fine, dry and non‐fibrous, high edible portion (29.6%), taste is sweet, creamy with attractive aroma. It has vigorous growth. Fruit is elliptical, average weight 1.5–1.8 kg; aril light yellow, soft and fibrous; medium edible portion (15–17%), taste is sweet, fat, and bitter with attractive aroma; high yield.

Durian information (2018)

Durian information (2018)

Durian information (2018)

 Recommended for individual countries by Nanthachai (1994).

*

II. BOTANY A. Morphology 1. Fruit.  Durian fruit is characteristic for its large size, strong odor, and hard thorn‐covered husk that takes 95 to 130 days to develop. The fruit occurs on a stout peduncle from the underside of branches with the peduncle having an abscission zone just above the fruit. The pendulous, round to oblong, commonly 13 to 16 cm wide and 15 to 25 cm long, fruit may be up to 35 cm long (Wisutiamonkul et al. 2017a). The fruit may exceed 3 kg in weight and is typically olive‐green to yellow in color, and is covered with broadly pyramidal, coarse, hard, and sharp spines. The fleshy aril (pulp) is the edible portion of the fruit and is an outgrowth from the funiculus – the point of attachment of the seed to the carpel. The development of the aril starts about four weeks after successful ­pollination. The aril varies in color, texture, and thickness between different seedlings or cultivars (Subhadrabandhu and Ketsa 2001).

4.  THE DURIAN: BOTANY, HORTICULTURE, AND UTILIZATION

(a)

141

(b)

Figure 4.1  Fruit of durian cultivars ‘Chanee’ (a) and ‘Monthong’ (b). (Photo credit: ©Yossapol Palapol.)

The mature fruit is a loculicidal dehiscent capsule (Ketsa and ­Pangkool 1994). Locules with abortive seeds occur infrequently and have a larger percentage of edible aril compared to those with normal seeds. One of the five locules will always contain seeds, whether the seeds are big or small in size. The seeds are usually large and vary in number with one to four per locule. Each seed is fully covered by the edible fleshy aril, which has a custard‐like consistency when ripe. The thickness of the aril and its contents are variable from very tasty, sweet, and pleasant to bland. Fruit of cultivated varieties have very thick, fleshy, juicy, and tasty arils when compared to wild varieties (Kothagoda and Rao 2011). Different cultivars can be distinguished to some extent by variations in fruit morphology (Figure 4.1). For example, the shape of the spines has been described for several Thai cultivars (Hiranpradit et al. 1992a). The overall gross morphology of the fruit is useful in grading them for market (Hiranpradit et  al. 1992b). Hiranpradit et  al. (1987) reported that fruit shape and spine morphology are useful for characterizing durians into distinct groups, and both are highly heritable characters. The shape of durian fruit is affected by the presence of seeds. If a locule contains an unfertilized ovule, that locule tends not to develop and the fruit becomes uneven in shape. Fruit shape greatly affects marketability and thus an understanding of pollination and its effect on durian fruit development is important for the improvement of durian. The color of its husk is green to brown and the aril ranges from white to yellow and red, depending on the cultivar and species (Voon et al. 2007).

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Figure 4.2  Complete or perfect flowers of durian. (Photo credit: © Yossapol Palapol.)

2. Flowers.  Flowers are large and normally possess five staminal groups that bear varying numbers of filaments. Inflorescences on older branches form fascicles of corymbs of 3–50 flowers, up to 15 cm long. The five petals are white, light yellow, or cream in color, and longer than the calyx (Subhadrabandhu and Ketsa 2001). Durian flowers are complete or perfect (Figure  4.2) in that each flower has both stamens and a pistil (Polprasid 1960). The flowers, when open, produce ­copious nectar containing sucrose, fructose and glucose. The stigma, which first appears at the apex of the petals before opening, is receptive in the early afternoon (13.00–14.00 h) before pollen is released. All flower parts except the pistil are shed by the following morning. The stigma varies in color and shape (Lye 1980) and subtends a single superior, normally five to seven locule ovary, but with a range of three to seven (Brown 1997). 3. Leaves.  The alternate leaves are simple lanceolate in shape (4 to 7.5 cm wide and 10 to 20 cm long) with an acuminate tip. The ­adaxial (upper) surface of durian leaves is smooth and apparently hairless while the abaxial (lower) surface is shiny bronze. The color ranges from glossy olive to dull green (Figure 4.3). The round petiole is about 2.5 cm long. The leaves of D. zibethinus are hypostomatic, with stomata only on the underside (Shanmukha Rao and Ramayya 1981). Depending on the location, there can be two to five vegetative flushes per year with the old leaves being shed at the end of fruit abscission. Salma (1991) ­recorded five different types of trichome morphology on the leaves of Durio, which can be useful in the identification of species; unfortunately, no key was given.

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(a)

(b)

Figure 4.3  Leaves of durian cultivars ‘Monthong’ (a: upper and lower surface) and ­‘Chanee’ (b: upper and lower surface). (Photo credit: ©Yossapol Palapol.)

4. Roots.  Durian root distribution varies depending on whether they were grown from seeds or from grafted plants. Differences in root development between marcotted, inarched, and seed grown trees have been noted (Polprasid 1961). Original anchor roots are observed only in trees grown from seed or produced by inarching but are not found in trees produced by marcots. Further, the roots of marcotted trees, although well distributed, did not extend as deeply into the soil as those of the other two types (Polprasid 1961). Generally, 72–87% of the root length density is found in the top 45 cm of the soil. ­Furthermore, 85% of the root length density is contained within the canopy radius of the tree (Masri 1991). These results are used in developing ideal ­fertilizer and irrigation application strategies to enhance fertilizer use efficiency and to minimize runoff. It has been reported that durian roots lack root hairs and form vesicular‐arbuscular mycorrhizal associations (Nanthachai 1994; Smith et al. 1998). 5. Stems.  Durian is a large forest tree that can reach heights of 37 m (Foxworthy 1927), with the first branch as much as 18–21  m off the ground (Brown 1997). Under optimum conditions, a durian tree can eventually grow to be very tall, large and majestic (another of its many aspects through which it deserves the title “King of Fruit”). Adult trees started from seeds can eventually reach up to 40 to 50  m in height,

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with a trunk diameter of 120 cm, although lesser dimensions are more common. Seedlings usually have a tall branchless trunk with an irregular, dense, or open crown of rough branches. The trunks of most species are normally buttressed in mature specimens. Out of over 300 trees measured, an average trunk diameter of 56 cm and a maximum diameter of 107 cm were recorded (Brown 1997). This growth habit means that early tree training and regular pruning are necessary in orchard cultivation. Young grafted clonal trees are easily identified, having a distinctive shape similar to a large Christmas tree with the branches growing out from the main trunk in every direction. Unless pruned, older clonal trees will eventually grow into the same tall form as seedling trees though only to 40–70% of the height at 12 m. B. Physiology 1. Flowering.  Durian flowers are borne in clusters on main trunk (Figure  4.4a), which is not common, and on lateral branches (­Figure 4.4b). Each inflorescence or flower cluster contains 8 to 20 or more individual flowers, but only 1–2 fruit are set and harvested from each cluster. Individual flowers from the same flush do not develop at the same rate; hence, fruit in the same cluster can be found to d ­ iffer in size.

(a)

(b)

Figure 4.4  Flowers of durian on the main trunk (a) and lateral branch (b). (Photo credit: © Saichol Ketsa.)

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Flowering is first observed as a small “pimple” protuberance on the branches. These buds enlarge, develop, and, over one month, differentiate into the inflorescence through to an open blossom stage (­Figure 4.5) (Salakpetch 2006). The most rapid floral bud growth occurs just one to two weeks before flower opening, with a dramatic increase in flower bud size the night before anthesis (Honsho et al. 2004b). The large receptive stigma, that is covered with stigmatic fluid, protrudes from the petals at about 13.00 h, about 2 h before flower petal opening in the late afternoon. Anther dehiscence does not occur until about 18.00 to 19.00 h or later depending on cultivar. By 24.00 h, all flower parts including stamens, except for the pistil, abscise naturally and fall to the ground. Soil moisture plays a significant role in flower induction. Studies ­indicate that a period of dry weather (three to four weeks) is needed to trigger flowering. Durian flowers are seen to emerge in the latter part of the driest month or immediately after a prolonged dry period (­Suaybaguio and Odtojan 1992; Masri 1999; Hariyono et al. 2013; Hoe and Palaniappan 2013). However, a continuous long period of drought does not stimulate trees to produce more flowers and wet humid conditions lead to a reduction in flower numbers. These results suggest a biphasic response with flower bud development requiring a level of drought, with subsequent bud growth and development requiring a moderate level of irrigation (Chandraparnik et  al. 1992a; Masri 1999).

(a)

(b)

(c)

Figure 4.5  Flower bud (a), flower bud with calyx splitting (b), and full bloom (c) stage of durian on the branch. (Photo credits: ©Saichol Ketsa and Yossapol Palapol.)

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It has been observed that raking the leaf litter away from under the canopy and exposing the soil leads to earlier flowering. Floral induction has been reported f­ ollowing water stress in other fruit crops including apple (­Elfving 1994), carambola (Masri 1995), citrus (Southwick and ­Davenport 1986, 1987; Phadung et al. 2011), lychee (Menzell and S ­ impson 1992), mango (Núñez‐Elisea and Davenport 1994; Lu and Chacko 2000), mangosteen (Salakpetch et  al. 2006), and peach (Johnson et  al. 1992). In the Australian tropical Northern Territory, flowering is associated with alternating cycles of cool, dry nights below 25°C and above 15°C. These temperature fluctuations give rise to an extended flowering period of two to three months (Lim and Luders 1996; Hariyono 2017). Chandraparnik et  al. (1992b) studied the impact of rain on very young flower bud dormancy. The branches, when the first sign of bud development was observed, were first pretreated with 1000 ppm ethephon and then sprayed with 0, 500, 1000, or 1500 ppm thiourea. Thiourea concentration was positively related to flower density (expressed as the number of inflorescences per meter of branch). Application of paclobutrazol (PBZ) either as a foliar spray or as a soil drench significantly enhanced flowering time and flower anthesis of mature trees in some orchard trials (Chandraparnik et al. 1992b; Subhadrabandhu and ­Kaiviparkbunyay 1998; Jantee et  al. 2017). However, harvested fruit per tree and mean fruit weight of PBZ treated trees were lower than those from untreated trees (Chandraparnik et  al. 1992a). Fruit maturity time, mean fruit weight, and incidence of uneven fruit ­ripening were not significantly affected by the time of application (Rushidah and Razak 2001). Tri et  al. (2011) found that PBZ application to two durian cultivars in Vietnam at the fully expanded stage of the second flushing, stimulated flower bud formation to happen 21–22 days earlier and for harvest to be 2–3 weeks earlier than with untreated control trees. Paclobutrazol application also increased the number the fruit per tree and yield (kg per tree), whereas the treatment had no effect on the total soluble solids concentration  of the aril or the proportion of aril to fruit (Subhadrabandhu and Kaiviparkbunyay 1998; Tri et al. 2011). The application of PBZ followed by a dormancy‐breaking substance to mango, citrus, and mangosteen trees does induce earlier and off‐season flower production (Poerwanto et  al. 2008), but this response has not been reported for durian. Paclobutrazol applied to lychee (Chaitrakulsub et al. 1992) and mango (Tongumpai et al. 1991) had no effects on fruit quality. Another anti‐gibberellic compound, uniconazole (UCZ), sprayed on mature durian leaves after the second leaf flush, did induce earlier flowering along with a significant reduction in inflorescence length, shortening of the fruit peduncle, and reduced fruit size and number of normal seeds (Jutamanee et al. 2014). These differences in

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the responses reported can possibly be ascribed to differences in cultivars and environmental conditions. Both PBZ and UCZ have generally similar effects in shortening the peduncle and reducing fruit size. A short peduncle can limit fruit growth in the same cluster and lead to misshapen fruit. Reduced fruit size is welcomed by growers who produce fruit for export. International markets, as well as most local markets, desire medium‐sized fruit (2.0–3.0 kg depending on the cultivar). This small to medium fruit size is more in demand than large fruit as the smaller fruit can be consumed all at once. The price of durian fruit in the market is determined by weight, thus small and medium‐sized fruit can be purchased by consumers with a wider range of incomes (Subhadrabandhu and Kaiviparkbunyay 1998). New leaf flushes that occur three to eight weeks after pollination can reduce fruit number and increase the number of deformed fruit. The application of potassium nitrate and high concentrations of foliar fertilizer (0‐52‐34) can damage bud scales and delay new leaf flushes by up to two weeks. Similarly, the growth retardants, daminozide and mepiquat chloride, can retard leaf development for up to three weeks (­ Punnachit et  al. 1992). Foliar application of foliar fertilizer ­without nitrogen (0‐52‐34) in combination with glucose, humic acid, and PBZ (Cultar®) applied weekly three to twelve weeks after a­ nthesis ­suppressed new leaf flushes and increased both the total n ­ umber of harvestable fruit per tree and the marketable yield. Foliar application of PBZ alone gave the same result. These growth retardants, by inhibiting new leaf development, potentially act by reducing competition of assimilates between new leaves and the developing fruit (Salakpetch et  al. 1992b). Leaf flushing 10–12 weeks after anthesis can lead to a reduction in the quality of ripe fruit and to the formation of hard flesh disorder (Punachit et al. 1992). 2. Pollination.  Most durian cultivars show self‐incompatibility (Shaari et al. 1985; George et al. 1994; Lim and Luders 1998; Lo et al. 2007; Bumrungsri et  al. 2009; Jutamanee and Sirisuntornlak 2017). Cross‐pollination of the Malay D24 cultivar had a fruit set rate of 54– 60%, while self‐pollination produced 1000 mm p.a.), and warm temperatures favor the spread of the disease. This disease is effectively controlled through phosphorous acid trunk injections integrated with practices that promote root health, such as the addition of compost and mulches. The majority of plantings since the early 1980s have been on phytophthora‐tolerant rootstocks, such as Duke 7, and, in recent years, a growing number of trees on the rootstock Merensky II (Dusa®) have been planted. Approximately 60% of current nursery trees are on Merensky II. Other commonly used rootstocks include Bounty and Velvick seedlings (Donkin 2007). Several other pests and diseases provide major challenges to the South African avocado industry. Among those insect pests are stink bugs, fruit flies, thrips, false codling moths (Erichsen and Schoeman 1992), and the heart shaped scale (Protopulvinaria pyriformis (Cockerell)) (Du Toit et al. 1991). Diseases other than phytophthora root rot (P. cinnamomi) (Zentmyer 1979), include stem canker (Phytophthora cinnamomi) (Lonsdale et al. 1988), anthracnose (Colletotrichum gloeosporioides (Penz.)), and cercospora spot (Pseudocercospora purpurea (Cooke)) (Darvas and Kotze 1987). VI.  THRIPS OF AVOCADO Thrips are fringe winged insects in the order Thysanoptera. A study by Johansen et al. (1999) revealed 38 thrips species on avocado, only six of them being primary pests of this crop. Worldwide some of the species recorded on avocados include Liothrips persea (Watson), Scirtothrips aceri (Moulton), Frankiniella cephalica (Crawford), ­Heliothrips haemorrhoidalis (Bouche) (FAO, 2004), and Selenothrips rubrocinctus (Giard) (Steyn et al. 1993). These cosmopolitan, polyphagous species survive on

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foliage by scraping and sucking the superficial cells, in the process leaving silver‐white discolored spots, which later turn dark. The damage is mostly observed on leaves and fruits; however, they can also be found on tender shoots, buds, and flowers. Species of thrips occupy widely disparate niches resulting in the manifestation of a diverse array of life styles. Phytophagous thripids, such as Scirtothrips spp., can exploit immature foliage, mature leaves support H. haemorrhoidalis, and senescing leaves can be utilized by S. rubrocinctus (Morse and Hoddle 2006). Thrips cause malformation of fruit, induce premature fruit drop, and also create lesions that become entry points for microorganisms such as Sphaceloma perseae (Jenkins) (González‐Hernández et  al. 1999). While minor thrips damage can be tolerated, any damage covering an area of more than about 2 cm2 will result in the fruit being unacceptable for premium export grade (Stevens et al. 1999). According to Steyn et al. (1993), the red‐banded thrips, S. rubrocinctus, and the greenhouse thrips, H. haemorrhoidalis, are the most common thrips species in South Africa. A recent study by Bara and Laing (2019) revealed Scirtothrips aurantii (Faure), the South African citrus thrips, to also be an economic pest of avocado fruit in South Africa. A. Classification Thrips are insects in the Kingdom: Animalia, Phylum: Arthropoda, and Class: Insecta (CABI 2018). The order Thysanoptera includes over 8800 species (Kumar et  al. 2013) and is sub‐divided into two sub‐orders: ­Terebrantia and Tubulifera. Tubulifera has a single family (Phlaeothripidae) while Terebrantia has four families (Aleolothripidae, Merothripidae, Thripidae, and Heterothripidae) (Lewis 1973). The most damaging thrips (>90%), belong to the family Thripidae (sub‐order Terebrantia). In this family belong the damaging Frankliniella occidentalis (Pergande), Thrips tabaci (Lind), Heliothrips haemorrhoidalis (Bouche), Thrips simplex (Morison), Taeniothrips dianthi (Priesner), Thrips fuscipennis (Haliday), Parthenothrips dracaenae (Heeger), Thrips palmi (Karny), and Hercinothrips femoralis (Reuter). In the family Phlaeothripidae the common pests include Haplothrips cottei (Vuillet) and Liothrips vaneeckei (Priesner) (Tommasini 2003). B.  Biology of Thrips H. haemorrhoidalis, S. rubrocinctus, and S. aurantii are all members of the sub‐order Terebrantia and have similar life cycles (Figure 7.1). The development of thrips includes six stages: egg, two larval stages, two

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Typical Thrips Life Cycle Egg (2.5–4 days)

Adult

(Longevity 30–45 days 150–300 eggs)

1st Instar Larva (1–2 days)

(Immature stages = max. 15 days)

2nd Instar Larva (2–4 days)

Tree

Pupa and propupa beneath leaf litter and soil

Pupa (1–3 days)

Soil Propupa (1–2 days)

Figure 7.1  Typical (generalized) thrips life cycle. (Adapted from https://www. discoverlife.org/nh/tx/Insecta/Thysanoptera/images/thrips10‐300x261.gif.html, © Mark S. Hoddle, all rights reserved.)

pronymph stages, and an adult stage. Thrips lay extremely small eggs, about 0.2 mm long, by cutting slits in plant tissue with their ovipositors, and inserting their eggs, one per slit (Gullan and Cranston 2010). The eggs take up to four days to hatch. Sex determination is through haplodiploidy. The haploid males are produced from unfertilized eggs whereas the diploid females are produced from fertilized eggs (Moritz 1997). Terry and Kelly (1993) argued that mated females do not allocate the sex of their progeny; rather the adult sex ratios resulted from their dispersal and distribution in response to host quality and longevity. Members of the Thripidae exhibit high female fecundity. After an initial pre‐oviposition period, a female can oviposit throughout her lifetime (Reitz 2009) and, under optimum conditions of temperature and food, produce up to seven progeny per day (Robb and Parrella 1991). Robb and Parrella (1991) reported an average total lifetime fecundity exceeding 200 per female. This high level of fecundity can lead to high intrinsic rates of population increase which can result in the rapid development of outbreaks of this pest (Hulshof et al. 2003). The Terebrantia pupate in soil or on leaves (Mound and Walker 1982) and the resting stages can last three to five days before adults emerge (Chin and Brown 2008). During this pupal stage, the insect’s body organs are reshaped, wing‐buds develop, and genitalia are formed (Gullan and

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Cranston 2010). In warm weather, the adult stage can be attained in three weeks (Mound and Walker 1982) and last 45 days with several generations in a single year being possible (Chin and Brown 2008). Development is temperature and host dependent. At 25–30°C, egg to adult development time can be as brief as 9–13 days. Eggs hatch in two to four days under optimum temperatures followed by two nymphal stages (Reitz 2008), after which feeding stops and the thrips drop to the ground to pupate. Buitenhuis and Shipp (2008) reported that while pupation in the ground does occur, there are also significant numbers that remain on the host plants. The first pupal stage (propupa) is non‐ feeding and is followed another non‐feeding pupal stage known as the pupa. Winged adults usually appear one to three days later (Reitz 2009). VII.  MANAGEMENT OF THRIPS A.  Thrips Monitoring Early detection of thrips infestation is crucial for successful control. Newly flushed leaves can be examined to get an indication of whether thrips are abundant enough to be a likely problem later when young fruit are present. Visual inspection methods by tapping plants on a tray or checking flowers at regular time intervals are often used (Pearsall and Myers 2000). Thrips are highly attracted to blue and yellow colored sticky cards (Blumthal et  al. 2005; Muvea et  al. 2014) and the use of these is currently the best monitoring tool for assessing thrips populations (Koschier et al. 2000). B.  Cultural Control Sanitary practices such as removing weeds, old plant material, and debris from the orchard are essential elements for controlling thrips infestation (Northfield et al. 2008). Adding coarse organic mulch beneath trees and maintaining a mulch layer 15 cm thick may reduce survival of avocado thrips that drop from trees to pupate (Jensen et al. 2002). C.  Silicon Fertilization In some agricultural systems, silicon is applied as a crop protection treatment. A number of studies have shown enhanced resistance to insect herbivores of plants that have been treated (using soil and/or foliar application) with silicon (Korndorfer et al. 2004; Redmond and Potter 2006; Massey et al. 2007). Silicon deposition contributes to increased rigidity and abrasiveness of plant tissues, creating a mechanical barrier and reducing their

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palatability and digestibility to invertebrate herbivores (Goussain et al. 2005; Massey and Hartley 2009). Stanley et al. (2014), however, ­disputed this claim suggesting that other mechanisms may be involved in silicon‐ mediated plant resistance. It has been suggested that priming of plant defense responses, alterations in phytohormone homeostasis, and interaction with defense signaling components are all potential mechanisms involved in regulating silicon‐triggered resistance responses (Van Bockhaven et  al. 2012). Gatarayiha et  al. (2010) hypothesized that silicon application primed biochemical defenses in plants which can make insect pests more susceptible to entomopathogens. In addition, silicon‐ treated, arthropod‐attacked plants have been demonstrated to display increased attractiveness to natural enemies, as reflected by elevated biological control in the field (Reynolds et al. 2016). D.  Chemical control Currently, several insecticides are available for the control of avocado thrips (Scirtothrips perseae) in avocado such as Sabadilla (e.g., Veratran®), Spinosad (e.g., Success®), and abamectin (e.g., Agri‐Mek®) (Morse et al. 2006). Stevens et al. (2001) also noted that Carbaryl 80 W and Diazinon 50% WP are effective against greenhouse thrips, H. haemorrhoidalis, but are not recommended under the current AvoGreen IPM program in New Zealand as they have moderate toxicity to beneficial insects (AvoGreen 2010). Chemical control is complicated by the fact that most of the developmental stages in thrips are shielded from chemicals (the eggs are laid within tissue, pupae in the soil/leaf litter, larval and adult stages hidden in buds or between leaves and flower structures). In addition, due to their rapid reproductive cycle, with several generations in the same year or season, thrips continuously develop resistance to pesticides (Jensen 2000). Only a few crop protection products are registered for avocados and this, coupled with the need to meet food quality and safety standards, creates an urgent need to seek out alternative control products and associated new management techniques. E.  Biological control Larvae of thrips are easy prey for a wide range of general arthropod predators but those more specific to thrips include members of the Aeolothripidae (e.g., Franklinothrips vespiformis), the anthocorid genera Orius and Montandoniola, the Cecidomyiid genus Thripsobremia and the Sphecidae genus Microstigmus (Mills 1991). Some of these are commercially available and are currently used as biological control agents in a variety of crops (Loomans and van Lenteren 1995; Loomans 2003).

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Table 7.1  Overview of entomopathogens (after Gwynn (2014) and Yashaswini and Kumar (2016)). Classification /species Bacteria Bacillus thuringiensis subsp. aizawai Bacillus thuringiensis subsp. israelensis (serotype H‐14) Bacillus thuringiensis subsp. kurstaki Bacillus firmus Werner Fungi Purpureocillium lilacinus (Thom) Samson (formerly Paecilomyces lilacinus) Isaria fumosorosea Wize (formerly Paecilomyces fumosoroseus Wize) Metarhizium spp. Lecanicillium lecanii Beauveria bassiana Nomuraea rileyi Hirsutella thompsonii Viruses Helicoverpa armigera nuclear polyhedrosis virus Spodoptera exigua nuclear polyhedrosis virus Spodoptera littoralis nuclear polyhedrosis virus Nematodes Steinernema spp. Heterorhabditis spp.

Target pests Lepidoptera Fungus gnats Lepidoptera Nematodes Root‐knot nematodes Whiteflies, thrips and aphids Beetles, locusts and grasshoppers, hemiptera, spiders Whiteflies, thrips, and aphids Whiteflies, thrips, weevils, and aphids Foliage feeding caterpillars Citrus rust mite Helicoverpa armigera Spodoptera exigua Spodoptera littoralis Thrips, fungus gnat larvae, various orders of soil‐borne insects Thrips, fungus gnat larvae, various orders of soil‐borne insects

Thrips parasitoids all belong to the superfamily Chalcidoidea. Most of them are solitary endoparasitoids of larvae (Eulophidae) or eggs (Mymaridae, Trichogrammatidae) (Loomans and van Lenteren 1995). The Eulophid larval parasitoids Thripobius semiluteus and Ceranisus menes have been recorded in avocado orchards parasitizing thrips larvae and Thripobius is known to significantly reduce fruit scarring by greenhouse thrips in South Africa (Steyn et al. 1993). Biological control, utilizing entomopathogens, provides an approach where resistance to the control agent is less likely to develop. Entomopathogens are microorganisms that are pathogenic to arthropods such as insects, mites, and ticks (Table  7.1). Several species of naturally‐­ occurring bacteria, fungi, nematodes, and viruses infect a variety of arthropod pests and can play an important role in their management (Chandler et  al. 2011). Some entomopathogens are mass‐produced

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in vitro (bacteria, fungi, and nematodes) or in vivo (nematodes and viruses) and are sold commercially (Glare et  al. 2012). Research has been conducted on the use of entomopathogens of thrips in greenhouse crops but very little on perennial crops (as in the case with avocados). Studies conducted in South Africa have revealed that S. aurantii is a recently established economic pest in avocado (Bara and Laing 2019), but no biocontrol studies have been conducted on this pest to date. VIII. ENTOMOPATHOGENS A. Bacteria A number of spore‐forming bacteria, such as Bacillus spp., Paenibacillus spp., and Clostridium spp., and non‐spore‐forming ones that belong to the genera Photorhabdus, Pseudomonas, Serratia, Xenorhabdus, and Yersinia have been shown to be entomopathogens. Bacillus and Paenibacillus are pathogenic mainly to coleopteran, dipteran, and lepidopteran insects. When Bacillus thuringiensis is ingested, alkaline conditions in the insect gut (pH 8–11) activate the toxic protein (delta‐ endotoxin) that attaches to the receptor sites in the midgut and creates pores in midgut cells (Gill et al. 1992). This leads to the loss of osmoregulation, midgut paralysis, and cell lysis. Contents of the gut leak into the insect’s body cavity (haemocoel) and the blood (haemolymph) leaks into the gut disrupting the pH balance, resulting in septicemia and eventual death of the host insect (Vachon et al. 2012). The most successful microbial pesticide to date is Bacillus thuringiensis (Bt), which has dominated the microbial pesticide market worldwide in its use as a biological pesticide (Glare et al. 2017). B. thuringiensis crops are plants genetically engineered (modified) to contain the endospore (or crystal) toxins of the bacterium to be resistant to specific insect pests (Abbas 2018). Genetic transformation is achieved by ­insertion of the target gene, its promoter and termination sequences, and a marker gene into the crop genome using the microprojectile ­ bombardment method (“gene gun”) or Agrobacterium tumefaciens (­ Peterson et  al. 2013). When Bt spores are ingested by susceptible insects, Cry toxins are activated by proteoletic enzymes in the alkaline gut (Bravo et al. 2007). The activated toxin passes through the peritrophic membrane and binds to specific receptors on apical microvillar brush border membranes of the epithelial cells of the midgut, making pores through which the toxin penetrates the cells. Eventually, the cells lyse and separate from the basement membrane of the midgut epithelium. The alkaline gut juices then leak into the haemocoel causing a rise in haemolymph pH resulting in paralysis and death of the insect (Soberón et al. 2010).

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Bt cotton produces toxins that target specific caterpillar pests such as beet armyworm (Spodoptera exigua (Hübner)), cotton bollworm (­Helicoverpa armigera (Hübner)), and tobacco budworm (Heliothis ­virescens (Fabricius)) (Abbas 2018) whereas Bt corn is modified to resist the European corn borer (Ostrinia nubilalis (Hübner)), the corn earworm (Helicoverpa zea (Boddie)), southwestern corn borer (Diatraea grandiosella (Dyar)), fall armyworm (Spodoptera frugiperda (Smith)), and the corn rootworm (Diabrotica virgifera (LeConte)) (Peterson et al. 2013). Commercially registered Bt products include YieldGard® (Monsanto) and Agrisure® (Syngenta) in maize, and Bollgard® (Monsanto) for cotton (Koch et al. 2015). Bt toxins are also effective against s­ everal other lepidopteran, dipteran, and coleopteran pests (Schnepf et  al. 1998) as well as members of Hymenoptera, Homoptera, Orthoptera, and Mallophaga (Crickmore et al. 1998). Other commercially available entomopathogenic bacteria include Lysinibacillus sphaericus for mosquito control (Charles et al. 2000), Paenibacillus popilliae for Japanese beetle control, and gram‐negative bacteria in the genus Serratia for the control of beetle larvae (Glare et al. 2017). Toxins ­produced by Photorhabdus temperate strains were found to be effective against Frankliniella occidentalis (western flower thrips) and Thrips tabaci (onion thrips) with fecundity in F. occidentalis being significantly reduced (Gerritsen et al. 2004). F. occidentalis and T. tabaci are both terebrantian species and, in addition to having similar biologies, cause damage consistent with that caused by thrips in avocado. It is, therefore, likely to be worthwhile to look at entomopathogenic bacteria currently registered for other insect pests (Table 7.2) for efficacy for controlling thrips on avocados. B. Nematodes Entomopathogenic nematodes (EPNs) are microscopic, soil‐dwelling, worm‐like organisms that are parasitic to insects. Several species of Heterorhabditis and Steinernema are available in multiple commercial formulations (Ruiu 2018), primarily for managing soil insect pests. Towards the end of the larval stages, mature terebrantian thrips larvae drop to the ground to pupate (Gilbert and Samways 2018). The below‐ ground stages, therefore, present an opportunity for control by EPNs. If the thrips life cycle could be disrupted, subsequent population growth would be curtailed and fruit damage would be minimized. Infective juveniles of EPNs actively seek out their hosts and enter through natural openings such as the mouth, spiracles, and anus or the intersegmental membrane. Once inside the host body, the nematodes release symbiotic bacteria that kill the host through bacterial septicemia. Heterorhabditis spp. carry Photorhabdus spp. bacteria and Steinernema

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Table 7.2  Examples of registered bioinsecticides based on entomopathogenic bacteria (Copping 1998; Sparks et al. 2012; Ruiu 2018). Active substances

Trade names*

Main targets

Crops

Bacillus thuringiensis aizawai Bacillus thuringiensis kurstaki

Able‐WG, Agree‐WP, Florbac, XenTari Biobit, Cordalene, Costar‐WG, Crymax‐WDG, Deliver, Dipel, Foray, Javelin‐ WG, Lepinox Plus, Lipel, Rapax Teknar, VectoBac, Vectobar

Armyworms, diamondback moth Lepidoptera

Maize, cotton, potato, eggplant

Mosquitoes and Black flies

Novodor, Trident

Colorado potato beetle

Mosquito, black fly, fungus gnat larvae Potato, eggplant, tomato

VectoLex, VectoMax

Mosquitoes

Mosquitoes

Majestene, Venerate

Chewing and sucking insects and mites; nematodes Lepidoptera, Thysanoptera, Diptera, Coleoptera, and Hymenoptera Chewing and sucking insects and mites

Maize, wheat, rice, grass, oat, lupine, and coffee Rape seed, wheat, cotton, avocado, tomato, pepper, eggplant, potato, sweet potato Alfalfa, asparagus, banana, brassica leaf vegetables, bulb vegetables, cereal grains, citrus, cucurbits Tuff grass, tomato

Bacillus thuringiensis israelensis Bacillus thuringiensis tenebrionis Bacillus thuringiensis sphaericus Burkholderia spp.

Saccharopolyspora spinosa

Tracer120, Conserve, Spinosad

Chromobacterium subtsugae

Grandevo

Bacillus firmus

Bionemagon, Votivo

Nematodes

Tomato, leafy vegetables

* Strains may be registered under different trade names.

spp. carry Xenorhabdus spp. bacteria (Dara 2017). EPN members of Heterorhabditidae and Steinernematidae families were ­reported to be effective against both adult and nymph stages of onion thrips, T. tabaci, under field conditions (Azazy et al. 2018). Under glasshouse conditions, Steinernema feltiae and S. carpocapsae were found to be efficacious against adults and nymphs of the western flower thrips, F. occidentalis (Tomalak et al. 2005). In semi‐field experiments, two EPNs, S. ­feltiae and S. ­carpocapsae, showed that the highest T. tabaci mortality was ­recorded

Table 7.3  Commercially available nematicides based on entomopathogenic nematodes (Rechcigil and Rechcigil 2000; Ruiu 2018). Active substances

Trade names*

Main targets

Crops

Steinernema carpocapsae

Capsanem, Carpocapsae‐System, Exhibitline SC, Optinem‐C, NemaGard, Nemastar, NemaTrident‐T, NemaRed, Nemasys C, Palma‐Life, Ecomask, Hortscan Entonem, NemaShield, NemaTrident‐F, Nemapom, Nemaplus, Nemaflor, NemaFly, Nemafrut, Nemasys F, Nematrip, Nematech‐S SP, NemaTrident‐S, Nemax‐F, Nemycel, Steinernema‐System, Optinem‐F, Sciarid, Nemasys Larvanem, Nemaplant, NemaShield‐ HB, Nematop, Nematech‐H NemaTrident‐H, NemaTrident‐C, Nema‐green, Optinem‐H

Borer beetles, caterpillars, cranefly, moth larvae, Rhynchophorus ferrugineus, Tipulidae, fleas, fungus gnats, termites Bradysia spp., Chromatomyia syngenesiae, Phytomyza vitalbae, soil dwelling pests, codling moth larvae, sciarids, thrips

Artichoke, banana, tuff grass, cranberries, leafy vegetables, sweet potato, pome fruit

Otiorhynchus spp., chestnut moths, black vine weevil and soil‐dwelling beetle larvae, Melolontha melolontha, caterpillars, cutworms, leaf miners Black vine weevil Otiorhynchus sulcatus Molluscs

Cranberry, tree nurseries, and soft fruits

Berries and ornamentals

Hetromask, Cruiser, Nematop

Soil insects, primarily Otiorhynchus sulcatus Root knot nematodes

Nemaslug

Slugs

Steinernema feltiae

Steinernema kraussei

Heterorhabditis downesi Phasmarhabditis hermaphrodita Heterorhabditis megidis Heterorhabditis bacteriophora Phasmarhabditis hermaphrodita

NemaTrident‐CT Slugtech‐SP Dickmaulrusser‐nematoden

Sweet potato, leafy vegetables, pome fruit, other fruit trees, banana

Forest plantings, berries, ornamentals Molluscs

Tuff grass, sweet potato, citrus, grapes Snails and slugs

* Strains may be registered under different trade names.

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for prepupae (92%) and pupae (92.6%), respectively (Khajehali and Poorjavad 2014). However, in another study, S. feltiae, H. bacleriophora, and S. carpocapsae were ineffective against whitefly, Bemisia tabaci, under controlled conditions in peppers (Ruiz‐Platt and Cabello 2009). Research is required to augment what has been established to further understand how EPNs can be effectively used to control thrips in IPM programs. Typically, infective juveniles can be applied at a spray volume of 750 L to 1890 L ha−1 using ground‐spraying equipment such as mist blowers, pressurized blowers, and electrostatic blowers, as well as being applied aerially (Georgis 1992). Furthermore, EPNs can also be applied using drip systems, making application convenient as this method is simple, quick, and provides good coverage. Drip systems are the main irrigation systems used in South African avocados. However, no EPNs are currently registered specifically for thrips control. Commercial formulations for other problem pests are available (Table 7.3) from which further research can be undertaken. C. Viruses The Baculoviridae family includes DNA viruses that form pathogenic relationships with invertebrates, showing potential in biological control (Haase et al. 2015). Baculoviruses are ingested orally in insects, with the first infection normally taking place after ingestion of contaminated food (Ruiu 2018). As entomopathogenic viruses need to be ingested by the insect host to be effective, they are therefore ideal for controlling pests that have chewing mouthparts, such as lepidopteran caterpillars (Ruiu 2018), with some strains having been commercialized (Table 7.4). All commercial strains, with the exception of the forest control product for sawfly (Hymenoptera: Diprionidae), target Lepidoptera (Rechcigil and Rechcigil 2000). Several lepidopteran pests are important hosts of baculoviruses including nucleopolyhedroviruses (NPV) and granuloviruses (GV). These related viruses have different types of inclusion bodies in which the virus particles (virions) are embedded. Virus particles invade the nucleus of the midgut, fat body, or other tissue cells, compromising the integrity of the tissues and liquefying the cadavers (Williams et al. 2017). Before death, infected larvae climb higher in the plant canopy, which aids in the dissemination of virus particles from the cadavers to the lower parts of the canopy, thus aiding in the spread of the virus to healthy larvae (Dara 2017). Viruses are very host specific and can cause significant reduction of host populations (Chen et al. 2011). However, the widespread use of baculovirus formulations is limited owing to their low stability in the environment and high production costs (Sun 2015). Examples of some commercially‐available

Table 7.4  Commercially available microbials with their target pest based on entomopathogenic viruses (Copping 1998; Ruiu 2018). Active substances

Trade names*

Main targets

Crop

Helicoverpa zea nucleopolyhedrovirus

Heligen

Helicoverpa spp. and Heliothis virescens

Spodoptera litura nucleopolyhedrovirus Adoxophyes orana granulovirus (AoGV) Cryptophlebia leucotreta granulovirus Helicoverpa armigera nucleopolyhedrovirus (HearNPV)

Biovirus–S, Somstar‐SL

Spodoptera litura

Tomato, cotton, tobacco, beans, soybeans, maize, lettuce Cotton

Capex

Apple, pear, plum, rose

Helicoverpa zea Nuclear Polyhedrosis virus Plutella xylostella granulovirus Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) Cydia pomonella granulovirus (CpGV)

Gemstar

Summer fruit tortrix moth (Adoxophyes orana) False codling moth (Thaumatotibia leucotreta) African cotton bollworm (Helicoverpa armigera), corn earworm (Helicoverpa zea), and other Helicoverpa species (Helicoverpa virescens, Helicoverpa punctigera) Heliothis and Helicoverpa spp

Plutellavex

Plutella xylostella

Littovir

African cotton leaf worm (Spodoptera littoralis)

Cruciferous vegetable crops Vegetables, fruits

Gypchek

Lymantria dispar

Apple, poplar, maple

CYD‐X, Madex, Carpovirusine, Carposin, Granupom, Madex 3

Cydia pomonella

Apple, pear

Cryptex Biovirus–H, Helicovex, Helitec, Somstar‐Ha

Citrus, avocado, tea, cotton Vegetables, fruit

Maize, cotton

(continued)

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Table 7.4  (Continued) Active substances

Trade names*

Main targets

Crop

Neodiprion abietis nucleopolyhedrovirus (NeabNPV) Spodoptera exigua nucleopolyhedrovirus (SeNPV) Autographa californica MNPV Anticarsia gemmatalis Mamestra brassicae MNPV

Neodiprion abietis NPV

Neodiprion abietis

Balsam fir

Spexit, Spod‐X

Spodoptera exigua

Vegetables, fruits

VPN‐80

Lepidoptera larvae

Tomato, tobacco

Polygen Virin‐ EKS

Velvet bean caterpillar, sugarcane borer Lepidoptera larvae

Soybean Cabbage, tomato, potato

* Strains may be registered under different trade names.

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viruses include Helicoverpa zea single‐enveloped nucleopolyhedrovirus (HzSNVP), Spodoptera exigua multi‐enveloped nucleopolyhedrovirus (SeMNPV), and Cydia pomonella granulovirus (CpGV) (Dara 2017). Viral pathogens of thrips do exist but, presently, no commercial formulations have been developed (Hauxwell 2008). D. Fungi Entomopathogenic fungi play an important role in the regulation of a number of different insect populations (Goettel et al. 2010). An entomopathogenic fungus (EPF) is a fungus that can act as a parasite of insects and kills or seriously disables them. The majority of EPFs are found within two groups: the order Hypocreales within the phylum Ascomycota, and the phylum Entomophthoromycota (Humber 2012). Ansari et al. (2007) showed that in horticultural growing media, Metarhizium brunneum (a member of the Ascomycota) was more effective than chemical insecticides (imidacloprid, fipronil) in killing pupae of the western flower thrips (70–90% compared to 20–50% when using the chemical insecticides). EPFs cause lethal infections and regulate insect and mite populations in nature by epizootics (McCoy et al. 1988). B. bassina was found to cause 96% mortality in the western flower thrips, F. occidentalis (Gao et al. 2012), while in another study M. brunneum strains V275 and ERL700 caused 85–96% mortality of F. ­occidentalis larvae and pupae (Ansari et al. 2008). Several pathogenic fungi based bio‐insecticides have been formulated and commercially manufactured (Gul et al. 2014) (Table 7.5). Ramanujam et al. (2014) reported that of the 171 EPF products developed, B. bassiana‐ based products accounted for 34%, while Metarhizium anisopliae (more recently named M. brunneum), Isaria fumosorosea, and Beauveria brongniartii products accounted for 34, 6, and 4% of total products, respectively. For the control of various insect pests, several commercial entomopathogenic products are available and include: BIO 1020®, ­Biogreen®, Green Guard®, Green Muscle®, and Metarhizium 50® (based on Metarhizium spp.) and Bb plus® (based on B. bassiana) (Bidochka and Small 2005). Research on Jalapeño peppers under greenhouse conditions revealed that foliar applied B.  bassiana (­BotaniGard®) reduced chilli thrips (Scirtothrips dorsalis) larvae by about 50%, five days after treatment (Seal and Kumar 2010). A list of commercially available mycoinsecticides, their target pests and related crops is presented in Table 7.5. Entomopathogenic fungi infect insects of almost all orders; most commonly Hemiptera, Diptera, Coleoptera, Lepidoptera, Orthoptera, and Hymenoptera (Ramanujam et al. 2014). Unlike bacterial, viral, and protozoan pathogens that need to be ingested to be active, EPFs work

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Table 7.5  Commercially available mycoinsectides with their target pest (Milner 2000; Ramanujam et al. 2014; Ruiu 2018). Active substances

Trade names*

Main targets

Crops

Beauveria bassiana

Bio‐Power, Biorin/ Kargar, Botanigard, Daman, Naturalis, Nagestra, Beauvitech‐WP, Bb‐Protec, Conidia, Naturalis L, Ago Bio, Bassiana Bas‐Eco, Betel

Wide range of insects and mites (e.g., whitefly, thrips, aphids, mealybugs)

Berries, maize, fruit, ornamentals, banana, leafy vegetables, pastures, and tuff grass

Helicoverpa armigera, berry borer, root grubs, scarab beetle larvae Citrus rust mite

Sugarcane

Biomet/Ankush, Bio‐ Magic, Devastra, Kalichakra, Novacrid, Met52/ BIO1020 granular, Pacer, Bioblast, Metaquino, DeepGreen, Metarhizium 50 Attracap

Beetles and caterpillar pests, grasshoppers, termites, spittle bugs

Grapes, berries, cabbage, banana, maize, leafy vegetables, bulbous plants

Agriotes spp.

Biogreen, Green muscle

Scarab larvae, locusts, grasshoppers Whitefly

Potatoes, leafy vegetables Wheat, oilseed rape

Beauveria brongniartii

Hirsutella thompsonii Metarhizium anisopliae

Metarhizium brunneum Metarhizium flavoviride

No‐Mite

Isaria fumosoroseus Paecilomyces lilacinus

PFR‐97, Pae‐Sin Bio‐Nematon, MeloCon, Mytech‐ WP, Paecilo

Plant pathogenic nematodes

Paecilomyces fumosoroseus

Bioact WG, No‐Fly‐ WP, Paecilomite, PFR‐97 Bio‐Catch, Mealikil, Bioline/Verti‐Star, Vertalec Lecatech‐WP, Varunastra

Insects, mites, nematodes, thrips Mealy bugs and aphids and sucking insects Aphids, leaf miners, mealybugs, scale insects, thrips, whiteflies

Verticillium lecanii Lecanicillium lecanii

Citrus

Citrus, sugarcane Banana, capsicum, tomato, brinjal, onion, chilli, okra, papaya Ornamentals, cut flowers, lettuce Cabbage, cucumber Cabbage, cucumber

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Table 7.5  (Continued) Active substances

Trade names*

Main targets

Crops

Lecanicillium muscarium

Mycotal

Whiteflies, thrips

Myrothecium verrucaria

DiTera

Nematodes

Lagenidium giganteum Nomuraea rileyi

Laginex

Mosquitoes

Cucumber, strawberries, sweet pepper, tomato, and ornamentals Food, fiber, ornamental crops Mosquitoes

Numoraea 50

Lepidoptera

Hirsutella thompsonii Conidiobolus thromboides Beauveria bassiana + Metarhizium anisopliae + Isaria fumosoroseus

Mycohit

Acari

Soybean, tomato, cotton Citrus

Vektor 25SL

Aphids, thrips, whiteflies Psyllid

Potato, soybean, cotton Tomato, potato

Tri‐Sin

* Strains may be registered under different trade names.

by penetrating the insect host’s cuticle through contact. Therefore, entomopathogenic fungi have the potential to be active against non‐ feeding stages such as pupae. Thrips have a critical non‐feeding soil dwelling pupal stage (Gilbert and Samways 2018), that can be targeted in control regimes. Keller and Zimmermann (1989) reported that the order Hyphomycetes typically induce epizootics in populations of soil dwelling insects. Hyphomycetes, such as Metarhizium and Beauveria, can infect both adult and larval stages and this ability to attack ­multiple life stages is important in disease transmission, as winged individuals can assist in the spread of disease (Goettel et al. 2010). Commercially developed B. bassiana formulations registered for thrips control in orchards include Mycotrol®, Naturalis®, and BotaniGard® (Maina et al. 2018). The commercially available BotaniGard® was reported to be effective against the citrus thrips, Scirtothrip citri, and the avocado thrips, S. perseae Nakahara, under laboratory conditions (Zahn and Morse 2013). Both these thrips species are taxonomically related to the South African citrus thrips, S. aurantia, and their potential to be controlled by a commercial GHA strain of B. bassiana supports efforts to control S. aurantii using entomopathogens.

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Four steps are usually necessary for infection: adhesion, germination, differentiation, and penetration. A range of integrated intrinsic and extrinsic factors, such as water, ions, fatty acids, and nutrients on the cuticle surface, as well as the physiological state of the host, influence spore adhesion and germination (Hassan et al. 1989). S ­ uccessful germination requires the assimilation of utilizable nutrients and a tolerance to any toxic compounds present on the surface of the insect or mite (Latgé et al. 1987). Adhesion is achieved when spores successfully attach or adhere to the external body surface of the insect. Under the right conditions of temperature and (usually high) humidity, these spores germinate, grow as hyphae, and colonize the insect’s cuticle. Penetration of the cuticle is accomplished by the germ tube itself or by the formation of an appressorium that attaches to the cuticle and gives rise to a narrow penetration peg (Wraight et al. 1998). Penetration is both a mechanical and an enzymatic process, the exact mechanism for entry being species specific (McCoy et al. 1988). Most terrestrial pathogens are known to penetrate directly, rarely via wounds, sense organs, or spiracles. Inside the host body cavity, the fungal cells proliferate, usually as walled hyphae or in the form of wall‐less protoplasts (depending on the fungus involved). After some time, the insect succumbs to the infection (sometimes by fungal toxins) and new propagules (spores) are formed in or on the cadaver if environmental conditions are conducive. Conditions such as high humidity are known to provide a conducive environment for sporulation (Shahid et al. 2012). In addition to being stable, the development of resistance to entomopathogenic fungi in insect populations has rarely been documented (Goettel et  al. 2010) and is thus proposed as a sustainable alternative to the use of synthetic insecticides for the control of thrips. 1.  Beauveria bassiana.  In the early 1800s, a white muscardine disease that periodically decimated the European silk industry plagued the silkworm farms of Italy and France. Steinhaus (1956) asserted that the probable causal organism had been reported as early as 2700 BC in China but had never been identified. In 1835, an Italian scientist, Agostino Bassi, demonstrated that the disease was caused by a microbial infection and that it could be controlled by altering the living ­conditions of the silkworms (Bombyx mori L.) to decrease the spread of the disease (Lord 2005). Later the microbe, a filamentous fungus, responsible for the disease was named B. bassiana in honour of Bassi’s discovery (Alexopoulos et al. 1996). In addition to being an entomopathogen, B. bassiana (formerly Tritirachium shiotae) commonly occurs as a saprophyte in soil and as a plant

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endophyte (Bruck and Lewis 2002). It is a naturally occurring soil‐borne fungus that parasitizes various arthropod species, causing white muscardine disease. It is cosmopolitan and is pathogenic to a wide spectrum of arthropods spanning most orders of class Insecta (Zimmermann 2007) and is reported to have a host range of up to 700 insect species (Goettel et al. 2000). Rehner and Buckley (2005) described B. bassiana as a species complex of morphologically similar and closely related isolates. Just before entering the second molt, larvae of many thrips species drop to the soil litter beneath the plant or move to some protected place on the plant (crevices, such as bark scales, hollow twigs, bases of leaf stalks, leaf sheaths, and leaf spaces) to pupate (Gilbert and Samways 2018). This stage is generally protected as the pupae are shielded from predators and do not feed, only exhibiting slight mobility when disturbed. With full coverage of B. bassiana on the soil and leaf litter (pupation sites), high infection rates and high mortality can be attained. For example, Ansari et  al. (2007) noted that the application of entomopathogenic fungi through soil drenches or pre‐mixing with potting ­compost is an effective control strategy against F. occidentalis. ­Similarly, Zhang et al. (2019) reported that granules impregnated with B bassiana were 70% effective against F. occidentalis on eggplants when applied as a soil treatment against soil‐dwelling pupal phases. After pupation, the adults may escape predation by jumping or flying to refuge. Adult and larval thrips feed by sucking plant cell contents of epidermal cells in host plants. Deposition of infective B. bassiana spores on the plant surfaces can increase the likelihood of spores being picked‐up during feeding and spread during dispersal (Hajek 1997). Alexopoulos et al. (1996) described endophytes as being non‐pathogenic fungi that live inside healthy plants and (Bacon 1993) suggested that the mutualistic association provides nutrients and moisture for the fungus, and imparts stress tolerances to the plant. B. bassiana has been shown to be an endophyte (Moonjely et  al. 2016) in maize (Poaceae) (Lewis and Bing 1991), cassava (Euphorbiaceae) (Greenfield et al. 2016), and potatoes (Solanaceae) (Jones 1994). Lewis and Bing (1991) reported that once established in the plant, B. bassiana reduced tunneling by larval European corn borer, Ostrinia nubilalis (Hubner), in maize. Injection of conidial suspensions was also an effective means for inoculation of maize plants (Leckie 2002). Studies conducted by Wagner and Lewis (2000) in maize revealed that when B. bassiana conidia were applied as a foliar application, the spores germinated and penetrated the plant through natural openings (such as stomata) and through small holes (facilitated by enzymatic activity and mechanical pressure produced by the fungus). Once inside the plant, the mycelium branched and grew throughout the epidermal regions and into the palisade parenchyma

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but did not exhibit any adverse effects on the plants. Interestingly, saprophytic EPFs (such as B. bassiana and M. anisopliae) can establish ­colonies in plant roots even in the absence of insect hosts (Barelli et al. 2016). In the plant, B. bassiana produces toxins as metabolites such as beauvericin, bassianolide, and the red pigmented toxin oosporein which may build up in the plant and deter insect herbivory (Leckie 2002). Avocado thrips (S. perseae) and citrus thrips (S. citri) were found to be very susceptible to the commercial B. bassiana strain GHA (Zahn and Morse 2013). Granules impregnated with B. bassiana were also reported to be 70% effective against F. occidentalis on eggplants when  applied as a soil treatment against soil‐dwelling, pupal phases (Zhang et  al. 2019). These terebrantian thrips exhibit the same life histories as the thrips spectrum in South Africa. While no biocontrol tests have been conducted on thrips on South African avocados, there is good reason to support such studies. Commercially developed formulations registered for general thrips control include (M. anisopliae) Met52®, (Isaria fumosorosea) NoFly™ (Kivett et al. 2016), (B. bassiana) Mycotrol® and BotaniGard® (Maina et  al. 2018), and (Lecanicillium longisporum) Vertalec® (Rechcigil and Rechcigil 2000). Classification of Beauveria bassiana.  B. bassiana  is in the Kingdom: Fungi, Phylum: Ascomycota, Class: Sordariomycetes, Order: Hypocreales and Family: Cordycipitaceae (CABI 2018). Several genera are included in the family including entomopathogenic Cordyceps, Isaria, Lecanicillium, and Beauveria. Species within the genus Beauveria are typically differentiated from other fungi by specific morphological characteristics. B. bassiana is a filamentous fungi that produces colorless (hyaline) aerial conidia from conidiogenous cells freely on the mycelia (CABI 2018). Morphology of Beauveria bassiana.  B. bassiana is characterized morphologically by its sympodial to whorled clusters of short‐globose to flask‐ shaped conidiogenous cells, which give rise to a succession of one‐celled, hyaline, holoblastic conidia that are borne on a progressively ­elongating sympodial rachis (Saranraj and Jayaprakash 2017). Conidia are the principal morphological feature used for species identification in ­Beauveria. Conidia may be globose, ellipsoidal, cylindrical, or comma shaped and range in size from 1.7 to 5.5 mm. Petch (2006) highlighted the complexity of species identification owing to the proliferation of new species described between the late nineteenth to mid‐twentieth centuries, few of which are morphologically distinct from previously described species. In all, 49 species have been placed in Beauveria and 22 epithets are currently valid. Presently,

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most environmental isolates of Beauveria are classified in either B. bassiana or B. brongniartii (Tanada and Kaya 2013). In culture, B. bassiana grows as a white mold. The conidiogenous cells of B. bassiana are short, ovoid, and terminate in a narrow apical extension called a rachis. The rachis elongates after each conidium is produced, resulting in a long zig‐zag extension (Humber 2007). The conidia are single‐celled, haploid and hydrophobic (Saranraj and Jayaprakash 2017). Physiology and  Life Cycle.  B. bassiana is considered to be the anamorph of Cordyceps bassiana, an ascomycete in the order Clavicipitales, and both are considered to be endoparasitic pathogens of insects and other arthropods (Nikoh and Fukatsu 2000). All life stages of the fungus appear to be infectious, including hyphae, aerial conidia, single‐ cell blastospores, and submerged conidia (specialized cells produced in minimal liquid media). However, the asexually produced (aerial) conidia are considered to be the main dispersal and infectious structures, capable of resisting, to a greater extent than hyphae and blastospores, various abiotic stresses (Holder et al. 2007). Disease development is strongly influenced by a pathogen’s ability to disperse (Anderson and May 1981). Infective propagules of entomopathogenic fungi in the Hypocreales are passively dispersed, by wind and rain (Shah and Pell 2003), as well as by the migration and subsequent death of infected hosts (Hajek 1997). B. bassiana is a polymorphic fungus whose life cycle includes both single and multicellular stages. In soil or decaying plant material, it grows as multicellular mycelia (St. Germain and Summerbell 2006), whereas it reproduces and disperses as asexual conidia. Akbar et  al. (2004) reported that B. bassiana conidia are smaller than most other fungal spores, measuring only 2–4 μm wide, and, when released into the environment, remain dormant or in a non‐vegetative state until appropriate conditions activate germination. Under optimum temperature and high humidity, these spores germinate, grow as hyphae, and colonize the insect’s cuticle (Figure 7.2) (Boucias et al. 2008). B. bassiana conidia require a temperature range of between 0 and 40°C with an optimum temperature of 20–30°C (Benz 2015) and a relative humidity above 97% for germination (Saranraj and Jayaprakash 2017). At 25°C, germination takes between 10 and 20 hours and usually takes place on thinner, non‐sclerotized areas of the cuticle, like joints, between segments or the mouthparts (Zimmermann 2007). The interactions between the penetrating fungus and the insect immune system are complex and comprise many molecular and

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Epicuticle

Progressive hyphal invasion Procuticle

Epidermis Haemocoel Hyphal bodies Figure 7.2 Infection by Beauveria bassiana (Sandhu et al. 2012).

c­ ellular reactions (Vilcinskas and Götz 1999). During the infection process, Beauveria spp. produce proteolytic enzymes and toxins, while the host insects respond with cellular and humoral defense reactions. These reactions consist of the production of antifungal compounds, inducible protease inhibitors, and proteins, which detoxify fungal toxins in the insect. The fungi proliferate inside the haemocoel, producing hyphal bodies that are distributed passively in the haemolymph, depleting nutrients and producing biologically active metabolites such as beauvericin (Wang and Xu 2012), 2‐pyridone tenellin, bassianolide, beauverolides, bassianin, dibenzoquinone oosporein (Vey et al. 2001), and bassiacridin (Quesada‐Moraga and Alain 2004) which account for its toxicity to insects. Beauvericin is thought to be the most important toxin, exhibiting insecticidal, antimicrobial, cytotoxic, and apoptotic activity (Klarić and Pepeljnjak 2005). Zimmermann (2007) noted that the incubation period is dependent on the host, host stage, temperature, and virulence of the fungal strain. During incubation, the fungus induces behavioral and feeding changes in the insect resulting in reduced feeding and reduced fecundity (Ouedraogo et al. 2003). Eventually, the insect succumbs to the infection (sometimes by fungal toxins) and new propagules (spores) are formed in or on the cadaver. Under humid conditions, the fungus grows saprophytically,

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emerging out of the host body, producing conidia on the exterior surface of the cadaver and setting the stage for future infections. Under very dry conditions, the fungus may also persist in the hyphal stage inside the cadaver. Zimmermann (2007) noted this phenomenon in locusts in Africa, where the fungus produced conidia inside the locust body. Villamizar et  al. (2018) further showed that B. bassiana produced resilient overwintering propagules called microsclerotia that enable the fungi to survive unfavorable environmental conditions and the  absence of hosts. Microsclerotia are tolerant to desiccation and able to produce infective conidia under nutritionally poor conditions. This makes these structures promising stages to develop as formulated propagules for use as mycoinsecticides for soil or aquatic applications. The microsclerotia propagules form either microsclerotia or mycelial pellets which are harvested by liquid culture fermentation (Jackson and Payne 2016; Song et al. 2016). Further, Huarte‐Bonnet et al. (2019) demonstrated that the microsclerotial structures produced viable conidia upon rehydration. These features make the fungus attractive as a crop protection tool under variable environmental conditions, especially for soil dwelling stages such as S. aurantii pupae. Beauveria bassiana in Insect Vectored Technology. Insects may function as a mechanical carrier or vector for B. bassiana, aiding in the transportation of the fungal spores. They have been used in the auto‐dissemination of the fungus to pest populations (Zimmermann 2007). Dowd and Vega (2003) noted that sap beetles (Coleoptera: Nitidulidae), contaminated with B. bassiana by means of an autoinoculative device, successfully transferred the fungus to the beetles’ overwintering sites. Bumble bees have been used to deliver Beauveria conidia to target western flower thrips (F. occidentalis), greenhouse whitefly (Trialeurodes vaporariorum), and green peach aphid (Myzus persicae) in greenhouse crops (Shipp et al. 2006). Bee‐vectored B. bassiana were reported to cause substantial mortality of lygus, whiteflies, thrips, and aphids (up to 80% mortality) in greenhouse cage trials on tomato and sweet pepper. The main advantage of using bees is that they deliver the fungal spores directly to the flowers and leaves where the thrips are feeding (Mascarin and Jaronski 2016). Effects of Beauvaria bassiana on Non‐Target Organisms. Several interactions of Beauveria spp. with hyperparasitic, antagonistic, and, especially, phytopathogenic fungi have been reported (Zimmermann 2007). The ascomycete Syspastospora parasitica, formerly known as Melanospora parasitica, is a known hyperparasitic fungus that attacks

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B. bassiana (Posada et al. 2004), while Krauss et al. (2004) noted that Clonostachys spp. and Trichoderma spp. may suppress or overgrow B. bassiana in vitro. This interaction has been exploited in crop protection, as Beauveria spp. have been shown to be antagonistic to various plant pathogenic fungi. Vesely and Koubova (1994) reported that under greenhouse conditions, B. bassiana was antagonistic to Pythium ultimum, Pythium debaryanum, and Septoria (Leptosphaeria) nodorum. However, Pythium irregulare, Phoma betae, Phoma exigua var. foveate, and Rhizoctonia solani showed resistance to B. bassiana. The effect of B. bassiana on plants has also been investigated and ­Zimmermann (2007) concluded that no known side‐effects or phytopathogenic activity had been reported. The plant may affect the infectivity and persistence of B. bassiana, but no phytopathogenic reactions have been recorded. Poprawski et al. (2000) observed that nymphs of the greenhouse whitefly, T. vaporariorum, were highly susceptible to B. bassiana on cucumber plants, while insects reared on tomato plants were significantly less susceptible. This was thought to be as a result of the inhibitory effect that tomatine (a glycoalkaloid found in the stems and leaves of tomato plants) has on B. bassiana. B. bassiana is a soil‐borne fungus and findings by Zimmermann (2007) suggest that there were no or very low detrimental effects on the soil‐dwelling collembolans and mites that were tested. Vestergaard et al. (2003) noted that data from field investigations did not reveal any indication of possible adverse effects on honeybees (Vandenberg 1990) (Copping 2004), non‐target arthropods (Brinkman and Fuller 1999), earthworms (Hozzank et al. 2003), fish (Copping 2004), birds (Althouse et al. 1997), or vertebrates and plants (Zimmermann 2007). In humans, conidia of Beauveria species have been identified to have allergenic potential (Westwood et al. 2005). Beauveria bassiana in Integrated Pest Management  Fungal biopesticides, such as B. bassiana, are suitable for incorporating into IPM programs and can play a key role in resistance mitigation, evolution to synthetic pesticides, and reduction in chemical reliance. B. bassiana has been successfully incorporated in IPM of coffee berry borer (Hypothenemus hampei Ferrari) in monocropping systems. Coffee bean borer (CBB) is a serious pest of coffee worldwide (Velmourougane et al. 2010). Biological control is achieved when formulations are applied as a foliar spray targeting CBB female founders as they migrate from refuges or parchment coffee areas during the peak flight activity, and as a ground treatment targeting fallen infested berries on the ground. Aristizábal et al. (2016) reported that these treatments resulted in a decrease in CBB infestation of up to 75% in Colombia. Other control techniques,

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such as sanitization of the fallen berries and use of mass capturing with methanol‐ethanol traps, also reduced coffee berry losses. The same technique holds promise in avocado against thrips. The above‐ground and below‐ground stages could be successfully targeted using B. bassiana, with other control techniques such as mulching being integrated into an IPM program to aid thrips suppression and reduce fruit quality losses. The strategy requires the substitution of chemical pesticides by microbial control agents, but complemented with cultural control and habitat management. The cultural practices may include mulching and provision of a suitable environment that enhances the reproduction, survival, and efficacy of natural enemies (conservation biological control), combined with silicon fertilization to increase attractiveness of the avocados to natural enemies (Reynolds et al. 2016) and to enhance fungal efficacy (Gatarayiha et al. 2010). Limitations to the Use of  Beauveria bassiana as a Biocontrol Agent. The effectiveness of B. bassiana as a biocontrol agent is moderated by a range of abiotic (Fernandes et al. 2015) and biotic factors (Mascarin and Jaronski 2016). Fargues and Luz (2000) noted that when environmental conditions are unsuitable, the conidia are easily inactivated, reducing their capacity to regulate pest populations. Foliar application of fungal conidia may be inactivated by sunlight and ultraviolet light or conidia may simply die due to rapid drying (Skinner et al. 2012). Moisture is an important factor affecting spore germination, mycelial growth, and the pathogenicity of B. bassiana (Richter and Fuxa 2004). While soil moisture may be higher and more constant than on the plants, spore movement is, however, more restricted resulting in reduced infection levels (Goettel et al. 2010). The level of organic matter and pH can be important in the eventual infection levels, as well as in the survival of propagules. In soil, other microbes such as the hyperparasitic fungus S. parasitica (Posada et al. 2004) and small invertebrates such as springtails (Broza et al. 2001), have been shown to consume the fungi or to be directly or indirectly antagonistic to entomopathogens. In addition, microbes such as bacteria resident within insect hosts can compete within infected cadavers and, if the fungus does not have mechanisms to exclude these microbes, the fungus will be unable to colonize the cadaver and sufficiently sporulate. These limitations can possibly explain why B. ­bassiana and Cladosporium oxysporum were ineffective in field trials against the citrus pests citrus psylla (Trioza erytreae), the black citrus aphid (Toxoptera citricida (T. citricidus)), and the false codling moth (FCM; Cryptophlebia leucotreta), yet they were promising under laboratory assays (Moore 2002). Effective IPM requires that B. bassiana be compatible with several pesticides. To date, the efficacy of B. bassiana has been tested under

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various formulations and some agrochemicals are known to modify conidial survival (Benz 2015). For example, under laboratory conditions, chlorpyriphos was relatively less toxic, spinosad, econeem (azadirachtin), quinalphos, acetamprid, endosulfan, and thiodicarb were found to be relatively slightly toxic, two insecticides (imidacloprid and triazophos) were moderately toxic, and three insecticides (profenofos, indoxacarb, and methyldemeton) were highly toxic to the fungus (Amutha et  al. 2010). Kahn et  al. (2012) reported that the popular fungicides mancozeb and copper oxychloride were not compatible ­ with B. bassiana and caused complete or strong inhibition of vegetative growth as well as sporulation. Commercial production and use of B. bassiana are limited by cost effectiveness as considerable material is required to achieve an acceptable level of control (typically 2–3 kg ha−1 of dried mycelia or conidia (1013)). This application rate goes up tenfold for cryptic insects such as beetle larvae in soil. In addition, formulations are bulky and preservation of fungal viability beyond a few months is low due to the fragile nature of the conidia (Federici 1999). Large‐scale production of entomopathogenic fungi concentrates mainly on three types of propagules: vegetative cells (blastospores); vegetative, multicellular mycelium (Andersch 1992); and conidia (­Jenkins and Prior 1993; Jenkins and Lomer 1994). While blastospores and conidia can infect the host directly, the mycelium needs to first grow and form infectious propagules. Conidia can be produced easily and are more stable in challenging environmental conditions than blastospores. It has been noted that spore germination on artificial media can differ greatly to germination on an insect cuticle. The insect cuticle is covered by a waxy layer containing fatty acids, lipids, and sterols (Hackman 1987), some of which contain fungistatic compounds that retard spore germination (Latgé et al. 1987). To overcome the myriad of field application challenges, strategies have been devised to overcome or ameliorate fungal performance under such stresses. Commercial mycoinsecticides are formulated to ease field application, enhance shelf‐life, and to increase environmental persistence after application (Feng et  al. 1994). Formulated microbials are typically prepared as technical concentrates, wettable powders, or oil dispersions (de Faria and Wraight 2007) and usually have a combination of an active ingredient (typically conidia), a thinner and/ or disperser, a wetting agent, and an adherent (Latgé and Moletta 1988). Conidia can also be suspended in aqueous liquid or mixed with a powder carrier and sprayed as a mist or a dust with conventional equipment used for the application of synthetic chemical insecticides. Dry

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formulations (in which the active ingredient is formulated and stored until used (Soper and Ward 1981)) are the forms which have been used to date commercially for B. bassiana conidia, although oil and water‐ based formulations are also used (Feng et al. 1994). Under field conditions, suboptimum temperature, humidity, and exposure to UV light can render the conidia ineffective. Some adjuvants and other ingredients can improve the persistence of microbials in the environment by protecting them from inactivation (Reddy et al. 2008; Shapiro 1992). Rangel et al. (2015) suggested that more environmentally robust strains can also be attained through the selection of more tolerant and virulent phenotypes (isolates). Leger and Wang (2010) outlined the efforts that have been made to create superior Beauveria strains by direct genetic manipulation. The approach has been to use protoplast fusion combined with selection for improved virulence aimed at a faster speed of kill and a reduction in the lethal dose required for effective control. Beauveria has also been enhanced by genetically modifying the fungus to express the Bacillus thuringiensis Vip3Aa insecticidal protein (Ren et  al. 2011). The ­characterization of the complete genome of B. bassiana has opened new insights into the complex mechanisms involved in its different life‐histories and enabled the manipulation of its genes for various industrial purposes, including biocontrol (Xiao et al. 2012). Careful selection of substrates can also enhance fungal viability, virulence, disease transmission, and field persistence. Most common substrates for fungal entomopathogens include primary products from agriculture (Alves and Pereira 1989; Moore and Prior 1993; ­Zimmermann 1993). For example, work done by Ummid and Vadlamani (2014) revealed that vegetable oil can be used as a substrate as it promotes adherence of spores to the insect cuticle facilitating spore germination and infection. Simple and low‐cost substrates have been developed using agricultural waste products such as cracked maize, maize bran, and rice grains (Jenkins and Goettel 1997). Essentially, a substrate that supports high conidia yield, is cheap and readily available, easy to culture, and is persistent in the environment can be used.  Novel techniques for increasing field efficacy are being developed. For example, one such technique is encapsulation of the bioactive ingredient. Encapsulation of microorganisms by enveloping spores, mycelia, or blastospores in a matrix with adjuvants and phagostimulants, can increase virulence and prolong the viability of the microorganism over an extended period (Rodrigues et al. 2017). Hanafi et al. (2000) also reported that encapsulated bioinsecticides can minimize the effects of environmental factors, such as inactivation due to light

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and heat. Potential biocontrol agents can be encapsulated in polymeric matrices or in hybrid materials such as alginate and carrageen to preserve the intrinsic properties of the fungus and increase its effectiveness. Some of the inoculum carriers that are being used in encapsulation technology include cellulose and cassava starch, cyclodextrins, sodium alginate, aliphatic polyesters, such as homo and copolymers of lactate and glycolate (including poly lactic acid, PLA; poly‐gamma‐ glutamic acid, PGA; and poly lactic‐co‐glycolic acid, PLGA), poly and caprolactone (PCL), and the polyhydroxyalkanoates, known as PHAs (Kumari et al. 2010). In biological systems, these polymers are biodegraded through the relaxation of the polymer chain, the breaking of the monomeric unit located at the end of the chain (erosion), or even by the random split of a link at any point along the polymer chain (Ré and Rodrigues 2006). When hydrated or degraded, the polymer relaxation process releases the infective conidia. Degradation processes occur when the polymers react with oxygen, light, or ambient temperature, and when acted upon by microorganisms present in the environment (Mohan 2011). Microencapsulation has great potential for use in EPF formulations as it has been used successfully to protect bioactive ingredients that are sensitive to temperature, photodegradation, oxidization, moisture, and other undesirable reactions (Gonsalves et al. 2009). IX. CONCLUSIONS The need to adhere to MRLs for export avocado production, coupled with the need for insecticide‐resistance management, suggest that evaluation of entomopathogenic fungi for control of thrips in avocado could be worthwhile. Fungal biopesticides such as B. bassiana are suitable for incorporating into IPM programs, as they play a key role in resistance mitigation, evolution to synthetic pesticides, and reduction of chemical reliance. Several mycoinsecticides have been developed, registered, and are in use worldwide against many insect pests of economic importance. However, little work has been done on the biological control of thrips in avocado using entomopathogens. While acknowledging the limitations of using B. bassiana as a potential c­ ontrol agent, this review supports its evaluation for the sustainable control of thrips in integrated pest management strategies. Indeed, other entomopathogens may also have potential to control thrips on avocado as indicated in this review. However, research will likely be required in order to increase their performance under the challenging environmental conditions in commercial orchards.

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Subject Index

Abscisic acid (ABA) apple fruit growth, 28 Apple flower growth, 5–7 fruit cell production and expansion, 9–12 fruit growth, 9–31 fruit morphology and anatomy, 2–5 fruit set, 7–9 Auxin apple fruit growth, 26–27 role in thigmomorphogenesis, 66–67 Avocado diseases, 330 entomopathogens for pest control, 336–356 global production, 326–329 thrips, 330–336 Calcium role in thigmomorphogenesis, 57–58, 64 Caricaceae Carica species, 310–311 Cylicomorpha species, 298–299 distribution, 291 evolution, 316–319 genera and species descriptions, 297–316 Horovitzia species, 311–315 Jacaratia species, 299–301 Jarilla species, 315–316 taxonomic classification, 295–297 taxonomic history, 291–295 Vasconcellea species, 301–310

Cell membranes ion channels, 61–65 Classification Caricaceae, 295–297 Cupressus, 217–227 Cupressus canker, 259–261 classification, 217–227 diseases, 259–261 genetics and breeding, 254–256 geographic distribution, 215–223 insects and mites, 261 in vitro, 264–265 medicinal uses, 252–254 molecular biology, 265–267 monumental accessions, 227–232 ornamental uses, 245–249 propagation, 263–265 species conservation, 256–263 traditional, cultural and religious values, 232–245 use in Persian gardens, 249–252 Cyprus, see Cupressus Cytokinins apple fruit growth, 27–28 Dedication T.M. DeJong, xi–xvii Disease avocado, 330 Cupressus, 259–261 durian, 163–168 Durian centre of origin, 129–130 climatic requirements, 128–129

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370

Subject Index

Durian (cont’d) cultivars, 131–140 diseases, 163–168 fertilizer practices, 159–163 flower and fruit thinning, 156–157 flowering habit, 147 flower morphology, 142 fresh fruit consumption, 192–193 fruit morphology and growth, 140–141, 149 harvesting and postharvest practices, 184–192 insect pests, 168–170 irrigation, 158–159 nutritional composition, 173–177 physiological disorders, 170–172 pollination, 147–148, 154–156 postharvest physiology, 177–183 processed products, 193–195 propagation, 149–152 pruning, 157–158 vegetative morphology and growth, 142–144, 148–149

Fruit growth measurement, 29–31

Electrical signals role in thigmomorphogenesis, 60–61 Entomopathogens bacteria, 336–338 Beauvaria bassiana, 346–356 fungi, 343–356 nematodes, 337–340 viruses, 340–343 Ethylene apple fruit growth, 28 role in thigmomorphogenesis, 65–66

Light quality impact on microgreen quality, 101–114

Fertilization and fertilizer, durian, 159–163 Flower and flowering, durian, 142, 147, 156–157 Food safety microgreens, 114–117 Fruit apple fruit growth, 9–31 durian fruit morphology and growth, 140–141, 149 Fruit crops apple fruit growth, 9–31 durian, 125–211

Genetic control apple fruit growth, 13–21 thigmomorphogenesis, 69–70 Genetics and breeding, Cupressus, 254–256 Growth substances apple fruit growth, 26–29 Harvest, durian, 184–192 Insects and mites Cupressus, 261 durian, 168–170 entomopathogens, 336–356 thrips, avocado, 330–336 In vitro, Cupressus, 264–265 Jasmonate apple fruit growth, 28 role in thigmomorphogenesis, 67–68

Mechanosensing, 43–83 Medicinal uses, Cupressus, 252–254 Metabolism apple fruit growth, 21–26 Microgreens definitions, 87–92 food safety, 114–117 growth stages, 94–95 production strategies, 96–104 quality, impact of light conditions, 101–114 species produced, 91–94 Molecular biology, Cupressus, 265–267 Nutrition (human), durian, 173–177 Ornamental uses, Cupressus, 245–249, 249–252 Papaya, see Caricaceae Pollination, durian, 147–148, 154–156 Postharvest physiology, durian, 170–172, 177–183

Subject Index Processing, durian, 193–195 Propagation Cupressus, 263–265 durian, 149–152 Pruning, durian, 157–158 Reactive oxygen species(ROS) role in thigmomorphogenesis, 59–60 Species conservation, Cupressus, 256–263 Taxonomy, Caricaceae, 289–323 Temperature apple fruit growth, 13 Thigmomorphogenesis cell wall and membrane responses, 55–57

371 definition, 47–48 horticultural applications, 70–72 induction, natural, 4849 induction, artificial, 49–50 leaf responses, 50–51 reproductive organ responses, 54–55 role of calcium, 57–58 role of electrical signals, 60–61 role of phytohormones, 65–68 role of protein complexes, 61–65 role of reactive oxygen species, 59–60 root responses, 53–54 stem responses, 51–53 Vegetative morphology and growth, durian, 142–144, 148–149

Cumulative Subject Index

(Volumes 1–47) Abscisic acid: apple fruit growth, 47:28 chilling injury, 15:78–79 cold hardiness, 11:65 dormancy, 7:275–277 genetic regulation, 16:9–14, 20–21 lychee, 28:437–443 mango fruit drop, 31:124–125 mechanical stress, 17:20 role in fruit thinning, 46:206–211 rootstocks, 46:67–73 rose senescence, 9:66 stress, 4:249–250 Abscission: anatomy & histochemistry, 1:172–203 citrus, 15:145–182, 163–166 flower & petals, 3:104–107 mango fruit drop, 31:113–155 regulation, 7:415–416; 46:206–211 rose, 9:63–64 Acclimatization: foliage plants, 6:119–154 herbaceous plants, 6:379–395 micropropagation, 9:278–281, 316–317 Actinidia, see Kiwifruit Adzuki bean, genetics, 2:373 Agapanthus, 25:56–57 Agaricus, 6:85–118 Agrobacterium tumefaciens, 3:34 Air pollution, 8:1–42 Alkaloids, steroidal, 25:171–196 Alkekenge, history & iconography, 34:36–40

Allium: development, 32:329–378 phytonutrients, 28:156–159 Almond: bloom delay, 15:100–101 breeding, 34:197–238 in vitro culture, 9:313 origin and dissemination, 38:23–81 postharvest technology & utilization, 20:267–311 rootstock, 46:39–97 wild of Kazakhstan, 29:262–265 Alocasia, 8:46, 57. See also Aroids Alternate bearing: chemical thinning, 1:285–289; 46:186–191, 257–258 fruit crops, 4:128–173 pistachio, 3:387–388 Aluminum: deficiency & toxicity symptoms in fruits & nuts, 2:154 Ericaceae, 10:195–196 Amarcrinum, 25:57 Amaryllidaceae, growth, development, flowering, 25:1–70 Amaryllis, 25:4–15 Amorphophallus, 8:46, 57. See also Aroids Anatomy & morphology: Allium development, 32:329–378 apple flowers & fruit, 10:273–308; 45:319 apple tree, 12:265–305 asparagus, 12:71 cassava, 13:106–112

Horticultural Reviews, Volume 47, First Edition. Edited by Ian Warrington. © 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc. 372

Cumulative Subject Index citron, 45:160–169, 173–179, 181–190 citrus, abscission, 15:147–156 daylily, 35:196–203 embryogenesis, 1:4–21, 35–40 fig, 12:420–424; 34:127–137 fruit abscission, 1:172–203 fruit storage, 1:314 garlic, 46:7–26 ginseng, 9:198–201 grape flowers, 13:315–337; 45:317–319 grape seedlessness, 11:160–164 heliconia, 14:5–13 kiwifruit, 6:13–50 magnetic resonance imaging, 20:78–86, 225–266 navel orange, 8:132–133 orchid, 5:281–283 pecan flower, 8:217–255 plant architecture, 32:1–61 pollution injury, 8:15 red bayberry, 20:92–96 rootstocks, 46:54–65 sapota fruit, 45:105–142 strawberry flowers, 45:1–32 turmeric, 46:106–108 waxes, 23:1–68 Ancient spices, 39:1–76 Androgenesis, woody species, 10:171–173 Angiosperms, embryogenesis, 1:1–78 Annatto, 39:389–419 Anthocyanin: accumulation in apple, 38:357–391 foliar, 42:209–251 Anthurium, fertilization, 5:334–335. See also Aroids, ornamental Antitranspirants, 7:334 cold hardiness, 11:65 Apical meristem, cryopreservation, 6:357–372 Apple: alternate bearing, 4:136–137 anatomy & morphology of flower & fruit, 10:273–309 anthocyanin accumulation, 38:357–391 bioregulation, 10:309–401 bitter pit, 11:289–355 bloom delay, 15:102–104 budbreak, 45:322–324 CA storage, 1:303–306

373 carbohydrate partitioning, 45:339–340 chemical thinning, 1:270–300 cider, 34:365–415 climate change, 41:57–66; 45:356–357 crop load, 31:233–292 deficit irrigation, 38:166–177; 45:350–351 fertilization, 1:105 fire blight control, 1:423–474; 44:361–389 flavor, 16:197–234 flower growth, 47:5–7 flower induction, 4:174–203 fruit cracking & splitting, 19:217–262 fruit growth, 45:264–266, 345–338; 47:9–31 fruit morphology and anatomy, 47:2–5 fruit set, 47:7–9 fruit thinning, 46:196–199, 255–298 fruiting, 11:229–287 functional phytonutrients, 27:304 germplasm acquisition & resources, 29:1–61 in vitro, 5:241–243; 9:319–321 light, 2:240–248 maturity indices, 13:407–432 mealiness, 20:200 nitrogen metabolism, 4:204–246 phenology, 45:317, 356–357 photosynthesis, 45:345–349 pollination, 34:267–268 replant disease, 2:3 rootstocks, 45:197–312; 46:39–97 root distribution, 2:453–456 rootstocks, 46:39–97 scab, 44:361–389 scald, 27:227–267 stock–scion relationships, 3:315–375; 45:197–312 summer pruning, 9:351–375 temperature responses, 45: 225–232, 313–369 tree morphology & anatomy, 12:265–305 vegetative growth, 11:229–287; 45:204–224, 320–324, 328–329, 331–332 watercore, 6:189–251 weight loss, 25:197–234 wild of Kazakhstan, 29:63–303, 305–315

374 Apple: (cont’d) winter chilling, 45:322–324 winter injury, 45:225–230 yield, 1:397–424 Apricot: bloom delay, 15:101–102 CA storage, 1:309 deficit irrigation, 38:160–163 origin & dissemination, 22:225–266 wild of Kazakhstan, 29:325–326 Arabidopsis: circadian clock, 41:3–8 molecular biology of flowering, 27:1–39, 41–77 Architecture, plant, 32:1–61 Aroids: edible, 8:43–99; 12:166–170 ornamental, 10:1–33 Arsenic, deficiency & toxicity symptoms in fruits & nuts, 2:154 Artemisia, 19:319–371 Artemisinin, 19:346–359 Artichoke, CA storage, 1:349–350 Ascorbic acid: metabolism, functions and contents, 45:385–389 Asexual embryogenesis, 1:1–78; 2:268–310; 3:214–314; 7:163–168, 171–173, 176–177, 184–189; 10:153–181; 14:258–259, 337–339; 24:6–7; 26:105–110 Asparagus: CA storage, 1:350–351 fluid drilling of seed, 3:21 postharvest biology, 12:69–155 Aubergine, see Eggplant Auxin: abscission, citrus, 15:161, 168–176 apple fruit growth, 47:26–27 apple rootstock, dwarfing mechanism, 45:217–221 bloom delay, 15:114–115 citrus abscission, 15:161, 168–176 dormancy, 7:273–274 flowering, 15:290–291, 315 genetic regulation, 16:5–6, 14, 21–22 geotropism, 15:246–267 mango fruit drop, 31:118–120 mechanical stress, 17:18–19 petal senescence, 11:31

Cumulative Subject Index role in fruit thinning, 46:206–211 role in thigmomorphogenesis, 47:66–67 rootstocks, dwarfing mechanism, 46:67–73 Avocado: CA & MA, 22:135–141 diseases, 47:330 entomopathogens for pest control, 47:336–356 flowering, 8:257–289 fruit development, 10:230–238 fruit ripening, 10:238–259 global production, 47:326–329 rootstocks, 17:381–429 thrips, 47:330–336 Azalea, fertilization, 5:335–337 Babaco, in vitro culture, 7:178 Bacteria: diseases of fig, 12:447–451 ice nucleating, 7:210–212; 11:69–71 pathogens of bean, 3:28–58 tree short life, 2:46–47 wilt of bean, 3:46–47 Bacteriocides, fire blight, 1:450–459 Bacteriophage, fire blight control, 1:449–450 Balm of Gilead, 39:47–66 Banana: botany, dispersal, evolution, 36:117–164 CA & MA, 22:141–146 CA storage, 1:311–312 climate change, 41:55–79 diseases & pests, 43:321–341 fertilization, 1:105 in vitro culture, 7:178–180 production future, 43:311–350 Banksia, 22:1–25 Barberry, wild of Kazakhstan, 29: 332–336 Bean: CA storage, 1:352–353 fluid drilling of seed, 3:21 resistance to bacterial pathogens, 3:28–58 rust, 37:1–99 Bedding plants, fertilization, 1:99–100; 5:337–341

Cumulative Subject Index Beet: CA storage, 1:353 fluid drilling of seed, 3:18–19 Begonia (Rieger), fertilization, 1:104 Belladonna, history & iconography, 34:14–19 Ber, postharvest biology, 41:201–240 Biennial bearing, see Alternate bearing Bilberry, wild of Kazakhstan, 29:347–348 Biochemistry: fruit acids, 45:371–430 petal senescence, 11:15–43 Bioreactor technology, 24:1–30; 44:173–228 Bioregulation, apple & pear, 10:309–401. See also Growth substances Biotechnology, orchid, 44:173–228 Bird damage, 6:277–278 Bitter gourd, 37:101–141 Bitter pit in apple, 11:289–355 Bixa orellana, see Annatto Black currant, bloom delay, 15:104 Black pepper, 33:173–266 Blackberry: harvesting, 16:282–298 wild of Kazakhstan, 29:345 Bloom delay, deciduous fruits, 15:97 Blueberry: developmental physiology, 13:339–405 harvesting, 16:257–282 nutrition, 10:183–227 Boron: deficiency & toxicity symptoms in fruits & nuts, 2:151–152 foliar application, 6:328 nutrition, 5:327–328 pine bark media, 9:119–122 Boswellia, see Frankincense Botanic gardens: history, 43:269–310 North American, 15:1–62 Bramble, harvesting, 16:282–298 Branching, lateral: apple, 10:328–330 pear, 10:328–330 Brassica classification, 28:27–28 Brassicaceae, in vitro, 5:232–235 Breadfruit: classification, 46:303–306 cultivation, 46:311–317, 336–343 diseases and pests, 46:351–363

375 distribution, 46:306–311, 320–323 growth and development, 46:330–335 morphology, 46:326–328 physiology, 46:325 propagation, 46:343–351 reproductive biology, 46:328–330 Breeding, see Genetics & breeding Broccoli, CA storage, 1:354–355 Brussels sprouts, CA storage, 1:355 Bulb crops, see Tulip development, 25:1–70 flowering, 25:1–70 genetics & breeding, 18:119–123 growth, 25:1–70 industry, 36:1–115 in vitro, 18:87–169; 34:427–445 micropropagation, 18:89–113 root physiology, 14:57–88 virus elimination, 18:113–123 Bunch stem necrosis of grape, 35:355–395 CA storage, see Controlled‐atmosphere storage Cabbage: CA storage, 1:355–359 fertilization, 1:117–118 Cacao & climate change, 41:84–87 Cactus: crops, 18:291–320 grafting, 28:106–109 reproductive biology, 18:321–346 Caladium, see Aroids, ornamental Calcifuge, nutrition, 10:183–227 Calciole, nutrition, 10:183–227 Calcium: bitter pit, 11:289–355 cell wall, 5:203–205 container growing, 9:84–85 deficiency & toxicity symptoms in fruits & nuts, 2:148–149 Ericaceae nutrition, 10:196–197 foliar application, 6:328–329 fruit deficiency disorders, 40:107–146 fruit softening, 10:107–152 nutrition, 5:322–323 pine bark media, 9:116–117 role in thigmomorphogenesis, 47:57–58, 64 tipburn, disorder, 4:50–57

376 Calmodulin, 10:132–134, 137–138 Caparis, see Caper bush Caper bush, 27:125–188 Capsicum pepper, history & iconography, 34:62–74. See also Pepper Carbohydrate: fig, 12:436–437 grapevine, 37:143–211 kiwifruit, 46:397–401 kiwifruit partitioning, 12:318–324 metabolism, 7:69–108 partitioning, 7:69–108; 45:339–340 petal senescence, 11:19–20 reserves, impacts of rootstocks, 46:73–77 reserves in deciduous fruit trees, 10:403–430; 45:348–349 Carbon dioxide, enrichment, 7:345–398, 544–545 Carnation, fertilization, 1:100; 5:341–345 Carrot: CA storage, 1:362–366 fluid drilling of seed, 3:13–14 postharvest physiology, 30:284–288 Caryophyllaceae, in vitro, 5:237–239 Caricaceae: Carica species, 47:310–311 Cylicomorpha species, 47:298–299 distribution, 47:291 evolution, 47:316–319 genera and species descriptions, 47:297–316 Horovitzia species, 47:311–315 Jacaratia species, 47:299–301 Jarilla species, 47:315–316 taxonomic classification, 47:295–297 taxonomic history, 47:291–295 Vasconcellea species, 47:301–310 Cassava: crop physiology, 13:105–129 molecular biology, 26:85–159 multiple cropping, 30:355–50 postharvest physiology, 30:288–295 root crop, 12:158–166 Cauliflower, CA storage, 1:359–362 Celeriac, CA storage, 1:366–367 Celery: CA storage, 1:366–367 fluid drilling of seed, 3:14

Cumulative Subject Index Cell culture, 3:214–314 woody legumes, 14:265–332 Cell membrane: calcium, 10:126–140 ion channels, 47:61–65 petal senescence, 11:20–26 role in thigmomorphogenesis, 47:55–57 Cell wall: calcium, 10:109–122 hydrolases, 5:169–219 ice spread, 13:245–246 role in thigmomorphogenesis, 47:55–57 tomato, 13:70–71 Cellular mechanisms, salt tolerance, 16:33–69 Ceratonia siliqua, see Carob Chayote, origins and dispersal, 43:89–140 Chelates, 9:169–171 Chemical thinning, 46:195–200, 212–213, 263–279, 283 Cherimoya: CA & MA, 22:146–147 pollination, 34:266–267 Cherry: bloom delay, 15:105 CA storage, 1:308 deficit irrigation, 38:163–164 origin, 19:263–317 wild of Kazakhstan, 29:326–330 rootstock, 46:39–97 Chestnut: blight, 8:281–336 botany & horticulture, 31:293–349 in vitro culture, 9:311–312 Chicory, CA storage, 1:379 Chilling: injury, 4:260–261; 15:63–95; 45:121 injury, chlorophyll fluorescence, 23:79–84 pistachio, 3:388–389 China: apple rootstocks, 45:276 citron, 45:143–196 protected cultivation, 30:37–82 Chlorine: deficiency & toxicity symptoms in fruits & nuts, 2:153 nutrition, 5:239 Chlorophyll fluorescence, 23:69–107 Chlorosis, iron deficiency induced, 9:133–186

Cumulative Subject Index Chrysanthemum fertilization, 1:100–101; 5:345–352 Cider, 34:365–415 Circadian regulation, 41:1–46 Citric acid: metabolism, functions and contents, 45:399–412 Citron: cultivars, 45:158–190 distribution in China, 45:148–151 nomenclature, 45:147–148 Citrus: abscission, 15:145–182 alternate bearing, 4:141–144 asexual embryogenesis, 7:163–168 CA storage, 1:312–313 chlorosis, 9:166–168 citron, 45:143–196 climate change, 41:79–84 cold hardiness, 7:201–238 fertilization, 1:105 flowering, 12:349–408 fruit splitting, 41:177–240 functional phytochemicals, fruit, 27:269–315 honey bee pollination, 9:247–248 in vitro culture, 7:161–170 irrigation, 30:37–82 juice loss, 20:200–201 navel orange, 8:129–179 nitrogen metabolism, 8:181 practices for young trees, 24:319–372 rind disorders, 41:131–175 rootstock, 1:237–269; 46:39–97 viroid dwarfing, 24:277–317 Classification: Brassica, 28:27–28 breadfruit, 46:303–306 Caricaceae, 47:295–297 Cupressus, 47:217–227 lettuce, 28:25–27 potato, 28:23–26 tomato, 28:21–23 Climate change: apple, 45:356–357 crop phenology, 46:214–216 grape, 45:355–356 Clivia, 25:57 Cloche (tunnel), 7:356–357 Coconut palm: asexual embryogenesis, 7:184

377 in vitro culture, 7:183–185 Coffee & climate change, 41:87–91 Cold hardiness, 2:33–34 apple & pear bioregulation, 10:374–375 apple rootstocks, 45:225–230 citrus, 7:201–238 factors affecting, 11:55–56 herbaceous plants, 6:373–417 injury, 2:26–27 nutrition, 3:144–171 pruning, 8:356–357 Colocasia, 8:45, 55–56. See also Aroids Commiphora, see Balm of Gilead, Myrrh Common blight of bean, 3:45–46 Compositae, in vitro, 5:235–237 Container production, nursery crops, 9:75–101 Controlled‐atmosphere (CA) storage: asparagus, 12:76–77, 127–130 chilling injury, 15:74–77 flowers, 3:98; 10:52–55 fruit quality, 8:101–127 fruits, 1:301–336; 4:259–260 pathogens, 3:412–461 sapota, 45:125–126 seeds, 2:134–135 tropical fruit, 22:123–183 tulip, 5:105 vegetable quality, 8:101–127 vegetables, 1:337–394; 4:259–260 Controlled environment agriculture, 7:534–545. See also Greenhouse & greenhouse crops; Hydroponic culture; Protected culture Copper: deficiency & toxicity symptoms in fruits & nuts, 2:153 foliar application, 6:329–330 nutrition, 5:326–327 pine bark media, 9:122–123 Corynebacterium flaccumfaciens, 3:33, 46 Cotoneaster, wild of Kazakhstan, 29:316–317 Cowpea: genetics, 2:317–348 U.S. production, 12:197–222 Cranberry: botany & horticulture, 21:215–249 fertilization, 1:106 harvesting, 16:298–311 wild of Kazakhstan, 29:349

378 Crinum, 25:58 Crop load: chemical thinning, 46:195–200, 212–213, 263–279, 283 decision support models, 46:202–205, 284–286 hand thinning, 46:193–195 mechanical thinning, 46:201, 279–282 pruning, 46:259–263 Crucifers, phytochemicals, 28:150–156 Cryopreservation: apical meristems, 6:357–372 cold hardiness, 11:65–66 Cryphonectria parasitica, see Endothia parasitica Crytosperma, 8:47, 58. See also Aroids Cucumber: CA storage, 1:367–368 grafting, 28:91–96 Cucumis melo, see Melon Cucurbita pepo, cultivar groups history, 25:71–170 Cucurbitaceae, renaissance history, 40:215–257 Cucurbits: oomycete diseases, 44:279–314 renaissance history, 40:215–257 Cupressus canker, 47:259–261 classification, 47:217–227 diseases, 47:259–261 genetics and breeding, 47:254–256 geographic distribution, 47:215–223 insects and mites, 47:261 in vitro, 47:264–265 medicinal uses, 47:252–254 molecular biology, 47:265–267 monumental accessions, 47:227–232 ornamental uses, 47:245–249 propagation, 47:263–265 species conservation, 47:256–263 traditional, cultural and religious values, 47:232–245 use in Persian gardens, 47:249–252 Curcuma longa see turmeric Currant: harvesting, 16:311–327 wild of Kazakhstan, 29:341 Custard apple, CA & MA, 22:164 Cut flowers:

Cumulative Subject Index postharvest, 40:1–55 water relations, 40:14–17, 55–106 Cyprus, see Cupressus Cyrtanthus, 25:15–19 Cytokinin: apple fruit growth, 47:27–28 apple rootstocks, dwarfing mechanism, 45:217–221; 46:67–73 cold hardiness, 11:65 dormancy, 7:272–273 floral promoter, 4:112–113 flowering, 15:294–295, 318 genetic regulation, 16:4–5, 14, 22–23 grape root, 5:150, 153–156 lettuce tipburn, 4:57–58 mango fruit drop, 31:118–120 petal senescence, 11:30–31 rose senescence, 9:66 Date palm: asexual embryogenesis, 7:185–187 history, 40:183–213 in vitro culture, 7:185–187 Datura, history & iconography, 34:44–51 Daylength, see Photoperiod Daylily, 35:193–220 Dedication: Bailey, L.H., 1:v–viii Beach, S.A., 1:v–viii Bukovac, M.J., 6:x–xii Campbell, C.W., 19:xiii–xiv Cantliffe, D.J., 33:xi–xiii Clark, J.R., 40:xiii–xx Costa, G., 46:vi–x Cummins, J.N., 15:xii–xv De Hertogh, A.A., 26:xi–xiii DeJong, T.M., 47: xi–xvii Dennis, F.G., 22:xi–xii Faust, M., 5:vi–xvi Finn, C.E., 43:xiii–xvii Ferguson, A.R., 35:xiii Goldman, I.L., 37:xiii–xxi Hackett, W.P., 12:x–xiii Halevy, A.H., 8:x–xii Hess, C.E., 13:x–xii Hummer, K, 39:xiii–xiv Janick, J., 45:xii–xvi Kader, A.A., 16:xii–xv Kamemoto, H., 24:x–xiii Kester, D.E., 30:xiii–xvii

Cumulative Subject Index Looney, N.E., 18:xii–xv Magness, J.R., 2:vi–viii Maynard, D.N., 36:xiii–xv Mitchell, C.A., 44:xiii–xxii Mizrahi, Y., 34:xi–xv Moore, J.N., 14:xii–xv Possingham, J.V., 27:xi–xiii Pratt, C., 20:ix–xi Proebsting, Jr., E. L., 9:x–xiv Rick, Jr., C.M., 4:vi–ix Ryugo, K., 25:x–xii Sansavini, S., 17:xii–xiv Sedgely, M., 32:x–xii Sherman, W.B., 21:xi–xiii Simon, P.W., 41:xiii–xx Smock, R.M., 7:x–xiii Sperling, C.E., 29:ix–x Spiegel‐Roy, P., 42:xi–xv Stevens, M.A., 28:xi–xiii Thompson, M.M., 38:xiii–xv Warrington, I.J., 31:xi–xii Weiser, C.J., 11:x–xiii Whitaker, T.W., 3:vi–x Wittwer, S.H., 10:x–xiii Yang, S.F., 23:xi–xiv Deficiency symptoms, fruit & nut crops, 2:145–154 Deficit irrigation, 21:105–131; 32: 111–165; 38:149–189; 45:350–351 Defoliation, apple & pear bioregulation, 10:326–328 ‘Delicious’ apple, 1:397–424 Desiccation tolerance, 18:171–213 Dieffenbachia, see Aroids, ornamental Dioscorea, see Yam Disease: air pollution, 8:25 apple rootstocks, 45:242–258 aroids, 8:67–69; 10:18; 12:168–169 avocado, 47:330 bacterial, of bean, 3:28–58 banana, 43:321–341 bean rust, 37:1–99 breadfruit, 46:351–360 cassava, 12:163–164 control by virus, 3:399–403 controlled‐atmosphere storage, 3:412–461 cowpea, 12:210–213 Cupressus, 47:259–261

379 detection, remote sensing, 45:56–57 durian, 47:163–168 fig, 12:447–479 flooding, 13:288–299 fusarium wilt, watermelon, 42:349–442 hot water treatment, 38:191–212 huanglongbing, citrus, 44:315–361 hydroponic crops, 7:530–534 lettuce, 2:187–197 melon, 36:185–190 mycorrhizal fungi, 3:182–185 oomycete, cucurbits, 44:279–314 ornamental aroids, 10:18 resistance, acquired, 18:247–289 root, 5:29–31 rust, bean, 37:1–99 sapota, 45:122–123 scab, apple, 44:363–389 stress, 4:261–262 sweet potato, 12:173–175 tulip, 5:63, 92 turnip moasic virus, 14:199–238 vine decline or wilt of melon, 39:77–120 waxes, 23:1–68 yam (Dioscorea), 12:181–183 Disorder, see Postharvest physiology bitterpit, 11:289–355 fig, 12:477–479 grape physiological, 35:355–395 kiwifruit, 46:408–410 leaf blackening, 17:173–201; 45:71–104 pear fruit, 11:357–411 watercore, 6:189–251; 11:385–387 Dogrose, botany, breeding, horticulture, 36:199–255 Dormancy, 2:27–30 apple, 45:317–324 blueberry, 13:362–370 fruit trees, 7:239–300 garlic, 46:9 grape, 45:317–322 tulip, 5:93 Drip irrigation, 4:1–48 Drought resistance, 4:250–251 cassava, 13:114–115 Durian: CA & MA, 22:147–148 centre of origin, 47:129–130 climatic requirements, 47:128–129 cultivars, 47:131–140

380 Durian: (cont’d) diseases, 47:163–168 fertilizer practices, 47:159–163 flower morphology, 47:142 flowering habit, 47:147 flower and fruit thinning, 47:156–157 fresh fruit consumption, 47:192–193 fruit morphology and growth, 47: 140–141, 149 harvesting and postharvest practices, 47:184–192 insect pests, 47:168–170 irrigation, 47:158–159 nutritional composition, 47:173–177 physiological disorders, 47:170–172 pollination, 147–148, 47:154–156 postharvest physiology, 47:177–183 processed products, 47:193–195 propagation, 47:149–152 pruning, 47:157–158 vegetative morphology and growth, 47:142–144, 148–149 Dwarfing: apple, 3:315–375 apple rootstocks, 45:197–312 apple mutants, 12:297–298 by virus, 3:404–405 rootstocks, 46:39–97 Dye plant, annatto, 39:389–419 Early bunch stem necrosis of grape, 35:355–395 Easter lily, fertilization, 5:352–355 Eastern Hemlock: conservation, 46:243–246 ecology, 46:232–235 genetic variation, 46:237–239 propagation, 46:239–242 woolly adelgid, 46:235–237 Ecology, Eastern Hemlock, 46:232–235 Eggplant: grafting, 28:103–104 history & iconography, 34:25–35 phytochemicals, 28:162–163 Elderberry, 37:213–280 botany, 37:215–226 horticulture, 37:226–224 wild of Kazakhstan, 29:349–350 Electrical signals, role in thigmomorphogenesis, 47:60–61

Cumulative Subject Index Embryogenesis, see Asexual embryogenesis Endothia parasitica, 8:291–336 Energy efficiency, in greenhouses, 1:141–171; 9:1–52 Entomopathogens: bacteria, 47:336–338 Beauvaria bassiana, 47:346–356 fungi, 47:343–356 nematodes, 47:337–340 viruses, 47:340–343 Environment: air pollution, 8:20–22 controlled for agriculture, 7:534–545 controlled for energy efficiency, 1:141–171; 9:1–52 embryogenesis, 1:22, 43–44 fruit set, 1:411–412 garlic flowering, 46:9–16 ginseng, 9:211–226 greenhouse management, 9:32–38 navel orange, 8:138–140 nutrient film technique, 5:13–26 turmeric, 46:133–134 Epipremnum, see Aroids, ornamental Eriobotrya japonica, see Loquat Erwinia: amylovora, 1:423–474; 45:268–269 lathyri, 3:34 Essential elements: foliar nutrition, 6:287–355 pine bark media, 9:103–131 plant nutrition, 5:318–330 soil testing, 7:1–68 Ethylene: abscission, citrus, 15:158–161, 168–176 apple bioregulation, 10:366–369 apple fruit growth, 47:28 avocado, 10:239–241 bloom delay, 15:107–111 CA storage, 1:317–319, 348 chilling injury, 15:80 citrus abscission, 15:158–161, 168–176 cut flower storage, 10:44–46 dormancy, 7:277–279 flower longevity, 3:66–75 flowering, 15:295–296, 319 fruit thinning, 46:206–211 genetic regulation, 16:6–7, 14–15, 19–20 kiwifruit ripening, 46:393–394

Cumulative Subject Index kiwifruit respiration, 6:47–48 mango fruit crop, 31:120–122 mechanical stress, 17:16–17 1‐methylcyclopropene, 35:263–313 petal senescence, 11:16–19, 27–30 role in thigmomorphogenesis, 47:65–66 rose senescence, 9:65–66 sapota storage, 45:126–127 Eucharis, 25:19–22 Eucrosia, 25:58 Feed crops, cactus, 18:298–300 Feijoa, CA & MA, 22:148 Fertilization & fertilizer: anthurium, 5:334–335 azalea, 5:335–337 bedding plants, 5:337–341 blueberry, 10:183–227 carnation, 5:341–345 chrysanthemum, 5:345–352 controlled release, 1:79–139; 5:347–348 durian, 47:159–163 Easter lily, 5:352–355 Ericaceae, 10:183–227 foliage plants, 5:367–380 foliar, 6:287–355 geranium, 5:355–357 greenhouse crops, 5:317–403 lettuce, 2:175 monitoring, remote sensing, 45:52–54 nitrogen, 2:401–404 orchid, 5:357–358 poinsettia, 5:358–360 rose, 5:361–363 snapdragon, 5:363–364 soil testing, 7:1–68 trickle irrigation, 4:28–31 tulip, 5:364–366 turmeric, 46:141–149 Vaccinium, 10:183–227 zinc nutrition, 23:109–128 Fig: botany, horticulture, breeding, 34:113–195 industry, 12:409–490 ripening, 4:258–259 Filbert, in vitro culture, 9:313–314 Fire blight, 1:423–474; 44:361–389; 45:268–269

381 Flooding, fruit crops, 13:257–313 Floral scents, 24:31–53 Floricultural crops, see individual crops Amaryllidaceae, 25:1–70 Banksia, 22:1–25 China, protected culture, 30:141–148 cutting industry, 44:121–172 daylily, 35:193–220 dogrose, 36:199–255 fertilization, 1:98–104 flower bulb industry, 36:1–115 growth regulation, 7:399–481 heliconia, 14:1–55 Leucospermum, 22:27–90 orchid biotechnology, 44:173–228 postharvest physiology & senescence, 1:204–236; 3:59–143; 10:35–62; 11:15–43 Protea, 26:1–48 Florigen, 4:94–98 Flower & flowering: Amaryllidaceae, 25:1–70 apple anatomy & morphology, 10:277–283 apple bioregulation, 10:344–348 Arabidopsis, 27:1–39, 41–77 aroids, ornamental, 10:19–24 avocado, 8:257–289 Banksia, 22:1–25 blueberry development, 13:354–378 bulb industry, 36:199–255 cactus, 18:325–335 citrus, 12:349–408 control, 4:159–160; 15:279–334 daylily, 35:193–220 development (postpollination), 19:1–58 durian, 47:142, 147, 156–157 fig, 12:424–429 garlic, 46:1–38 girdling, 20:1–26 grape anatomy & morphology, 13:354–378 homeotic gene regulation, 27:41–77 honey bee pollination, 9:239–243 induction, 4:174–203, 254–256; 45:5–13 initiation, 4:152–153 in vitro, 4:106–127 kiwifruit, 6:21–35; 12:316–318 Leucospermum, 22:27–90 lychee, 28:397–421

382 Flower & flowering: (cont’d) morphology (strawberry), 45:3–5 orchid, 5:297–300 pear bioregulation, 10:344–348 pecan, 8:217–255 perennial fruit crops, 12:223–264 phase change, 7:109–155 photoperiod, 4:66–105 pistachio, 3:378–387 postharvest physiology, 1:204–236; 3:59–143; 10:35–62; 11:15–43 postpollination development, 19:1–58 protea leaf blackening, 17:173–201; 45:73–104 pruning, 8:359–362 raspberry, 11:187–188 regulation in floriculture, 7:416–424 rhododendron, 12:1–42 rootstocks, 46:77–80 rose, 9:60–66 scents, 24:31–53 senescence, 1:204–236; 3:59–143; 10:35–62; 11:15–43; 18:1–85 strawberry, 28:325–349; 45:1–32 sugars, 4:114 thin cell layer morphogenesis, 14:239–256 tulip, 5:57–59 turmeric, 46:106–108 water relations, 18:1–85 Fluid drilling, 3:1–58 Foliage plants: acclimatization, 6:119–154 fertilization, 1:102–103; 5:367–380 industry, 31:47–112 Foliar nutrition, 6:287–355 Food safety, microgreens, 47:114–117 Frankincense, 39:27–39 Freeze protection, see Frost protection Frost: apple fruit set, 1:407–408 citrus, 7:201–238 protection, 11:45–109 Fruit: abscission, 1:172–203 abscission, citrus, 15:145–182 acids, 45:371–430 apple anatomy & morphology, 10:283–297 apple bioregulation, 10:348–374

Cumulative Subject Index apple bitter pit, 11:289–355 apple crop load, 31:233–292 apple flavor, 16:197–234 apple fruit growth, 47:9–31 apple growth, 45:335–338 apple maturity indices, 13:407–432 apple ripening & quality, 10:361–374 apple scald, 27:227–267 apple weight loss, 25:197–234 avocado development & ripening, 10:229–271 banana, 36:117–164; 43:311–350 bloom delay, 15:97–144 blueberry development, 13:378–390 calcium, 40:107–140 calcium disorders, 40:127–135 carbohydrate partitioning, 45:338–340 CA storage & quality, 8:101–127 cactus physiology, 18:335–341 chilling injury, 15:63–95 citron, 45:143–196 citrus fruit splitting, 41:177–240 citrus rind disorders, 41:131–175 coating physiology, 26:161–238 cracking, 19:217–262; 30:163–184 development, kiwifruit, 46:391–394 diseases in CA storage, 3:412–461 drop, apple & pear, 10:359–361; 46:186–191 durian fruit morphology and growth, 47:140–141, 149 elderberry, 37:213–280 fig, 4:258–259; 12:409–490; 34:113–195 fresh cut, 30:185–251 functional phytochemicals, 27:269–315 grape, 35:355–395 grape berry growth, 45:332–335 growth, kiwifruit, 46:394–396 growth measurement, 24:373–431 jujube, 32:229–298 kiwifruit, 6:35–48; 12:316–318 loquat, 23:233–276 lychee, 28:433–444 mango fruit drop, 31:113–155 maturation, kiwifruit, 46:385–421 maturity indices, 13:407–432 melon, 36:165–198 navel orange, 8:129–179 nectarine, postharvest, 11:413–452

Cumulative Subject Index nondestructive postharvest quality evaluation, 20:1–119 olive oil composition, 38:83–147 olive physiology, 31:157–231 olive processing, 25:235–260 organic research, 43:183–267 pigmentation, 39:239–271 pawpaw, 31:351–384 peach, postharvest, 11:413–452 peach texture, 41:241–301 pear, bioregulation, 10:348–374 pear, fruit disorders, 11:357–411 pear maturity indices, 13:407–432 pear ripening & quality, 10:361–374 pear scald, 27:227–267 pear volatiles, 28:237–324 pistachio, 3:382–391 phytochemicals, 28:125–185 plum, 23:179–231 pollination, 34:239–275 pomegranate, 35:127–191 quality, impact of rootstock, 45:262–266 quality & pruning, 8:365–367 red bayberry, 30:83–113 ripening, 5:190–205 rose, wild of Kazakhstan, 29:353–360 sapota, 45:105–142 set, 1:397–424; 4:153–154 set in navel oranges, 8:140–142 size & thinning, 1:293–294; 4:161 softening, 5:109–219; 10:107–152; 46:396–397 splitting, 19:217–262 strawberry growth & ripening, 17:267–297 texture, 20:121–224 thinning, apple & pear, 10:353–359; 46:185–226, 255–298 tomato chilling, 44:229–278 tomato cracking, 30:163–184 tomato parthenocarpy, 6:65–84 tomato ripening, 13:67–103 volatiles, pear, 28:237–324 Fruit crops, see Individual crop almond origin and dissemination, 38:23–81 alternate bearing, 4:128–173 anthocyanins, foliar, 42:209–251 apple, wild of Kazakhstan, 29:63–303, 305–315

383 apple anthocyanin accumulation, 38:357–391 apple bitter pit, 11:289–355 apple, climate change, 45:356–357 apple crop load, 31:233–292 apple deficit irrigation, 38: 166–177; 45:350–351 apple fireblight, 44:361–389 apple flavor, 16:197–234 apple fruit growth, 47:9–31 apple fruit splitting & cracking, 19:217–262 apple germplasm, 29:1–61, 63–303 apple growth, 11:229–287 apple maturity indices, 13:407–432 apple photosynthesis, 45:345–349 apple rootstocks, 45:197–312; 46:39–97 apple scab, 44:361–389 apple scald, 27:227–267 apricot, origin & dissemination, 22:225–266 apricot, wild of Kazakhstan, 29:325–326 apricot deficit irrigation, 38:160–163 architecture, 32:1–61 avocado flowering, 8:257–289 avocado rootstocks, 17:381–429 banana, 36:117–164 banana & climate change, 41:55–79 barberry, wild of Kazakhstan, 29:332–336 ber, posthavest biology, 41:201–240 berry crop harvesting, 16:255–382 bilberry, wild of Kazakhstan, 29:347–348 blackberry, wild of Kazakhstan, 29:345 bloom delay, 15:97–144 blueberry developmental physiology, 13:339–405 blueberry harvesting, 16:257–282 blueberry nutrition, 10:183–227 bramble harvesting, 16:282–298 breadfruit, 46:299–384 CA & MA for tropicals, 22:123–183 CA storage, 1:301–336 CA storage diseases, 3:412–461 cacao & climate change, 41:84–87 cactus, 18:302–309 carbohydrate reserves, 10:403–430 carob, 41:385–456

384 Fruit: (cont’d) cherry, wild of Kazakhstan, 29:326–330 cherry deficit irrigation, 38:163–164 cherry rootstocks, 46:39–97 cherry origin, 19:263–317 chilling injury, 15:145–182 chlorosis, 9:161–165 cider, 34:365–414 citron, 45:143–196 citrus, culture of young trees, 24:319–372 citrus, huanglongbing, 44:315–361 citrus abscission, 15:145–182 citrus & climate change, 41:84–87 citrus cold hardiness, 7:201–238 citrus dwarfing by viroids, 24:277–317 citrus flowering, 12:349–408 citrus irrigation, 30:37–82 citrus nutrition diagnostics, 34:277–364 citrus rootstocks, 46:39–97 coffee and climate change, 41:87–91 cotoneaster, wild of Kazakhstan, 29:316–317 cranberry, 21:215–249 cranberry, wild of Kazakhstan, 29:349 cranberry harvesting, 16:298–311 currant, wild of Kazakhstan, 29:341 currant harvesting, 16:311–327 date palm, 40:183–213 deficit irrigation, 21:105–131; 38:149–189 dormancy release, 7:239–300; 45:317–324 durian, 47:125–211 elderberry, 37:213–280 elderberry, wild of Kazakhstan, 29:349–350 Ericaceae nutrition, 10:183–227 fertilization, 1:104–106 fig, industry, 12:409–490; 34:113–195 fireblight, 11:423–474 flowering, 12:223–264 foliar anthocyanins, 42:209–251 foliar nutrition, 6:287–355 frost control, 11:45–109 gooseberry, wild of Kazakhstan, 29:341–342 grape, wild of Kazakhstan, 29:342–343 grape & climate change, 41:66–73; 45:355–356

Cumulative Subject Index grape flower anatomy & morphology, 13:315–337 grape harvesting, 16:327–348 grape irrigation, 27:189–225 grape nitrogen metabolism, 14:407–452 grape photosynthesis, 45:340–345 grape physiological disorder, 35:355–395 grape root, 5:127–168 grape seedlessness, 11:164–176 grapevine carbohydrates, 37:143–211 grapevine pruning, 16:235–254, 336–340 greenhouse, China, 30:149–158 honey bee pollination, 9:244–250, 254–256 hot water treatment, 38:191–212 jojoba, 17:233–266 jujube, 32:229–298 in vitro culture, 7:157–200; 9:273–349 irrigation, deficit, 21:105–131 kiwifruit, 6:1–64; 12:307–347; 33:1–121 kiwifruit rootstocks, 46:50–51, 55, 64–65 lingonberry, 27:79–123 lingonberry, wild of Kazakhstan, 29:348–349 longan, 16:143–196 loquat, 23:233–276 lychee, 16:143–196; 28:393–453 melon, 36:165–198 mango fruit drop, 31:113–155 mango physiological disorders, 42:313–347 mountain ash, wild of Kazakhstan, 29:322–324 mulberry, wild of Kazakhstan, 29:350–351 muscadine grape breeding, 14:357–405 navel orange, 8:129–179 nectarine postharvest, 11:413–452 nondestructive postharvest quality evaluation, 20:1–119 nutritional ranges, 2:143–164 oleaster, wild of Kazakhstan, 29:351–353 olive, high density, 41:303–383 olive oil composition, 38:83–147 olive physiology, 31:157–231 olive salinity tolerance, 21:177–214

Cumulative Subject Index orange, navel, 8:129–179 orchard floor management, 9:377–430 packaging, modified humidity, 37:281–329 pawpaw, 31:351–384 peach deficit irrigation, 38:151–160 peach orchard systems, 32:63–109 peach origin, 17:331–379 peach postharvest, 11:413–452 peach rootstocks, 46:39–97 peach thinning, 28:351–392 peach & nectarine soluble solids, 42:253–311 pear, wild of Kazakhstan, 29:315–316 pear deficit irrigation, 38:177–180 pear fruit disorders, 11:357–411; 27:227–267 pear maturity indices, 13:407–432 pear scald, 27:227–267 pear volatiles, 28:237–324 pecan flowering, 8:217–255 phenology, 45:316–317 photosynthesis, 11:111–157; 45:340–349 Phytophthora control, 17:299–330 plum, wild of Kazakhstan, 29:330–332 plum deficit irrigation, 38:165–166 plum origin, 23:179–231 pollination, 34:239–275 pomegranate, 35:127–191 prune deficit irrigation, 38:165–166 pruning, 8:339–380 rambutan, 16:143–196 raspberry, 11:185–228 raspberry, wild of Kazakhstan, 29:343–345 red bayberry, 30:83–113 roots, 2:453–457 rootstocks, apple, 45:197–312 sapota, 45:105–142 sapindaceous fruits, 16:143–196 sea buckthorn, wild of Kazakhstan, 29:361 short life & replant problem, 2:1–116 strawberry, wild of Kazakhstan, 29:347 strawberry flowering, 45:1–32 strawberry fruit growth, 17:267–297 strawberry harvesting, 16:348–365 summer pruning, 9:351–375 Vaccinium nutrition, 10:183–227 vacciniums, wild of Kazakhstan, 29:347–349

385 viburnam, wild of Kazakhstan, 29:361–362 virus elimination, 28:187–236 water status, 7:301–344 water stress, 32:111–165 Fruit growth, measurement, 47:29–31 Functional phytochemicals, fruit, 27:269–315 Fungi: bean rust, 37:1–99 fig, 12:451–474 mushroom, 6:85–118 mycorrhiza, 3:172–213; 10:211–212 pathogens in postharvest storage, 3:412–461 rust, bean, 37:1–99 truffle cultivation, 16:71–107 Fungicide, & apple fruit set, 1:416 Fusarium wilt, watermelon, 42:349–441 Galanthus, 25:22–25 Garlic: annual life cycle, 46:6–9 botany and horticulture, 33:123–172 breeding, 46:1–38 CA storage, 1:375 centre of origin, 46:5–6 environmental control of flowering, 46:9–16, 27 flower anatomy, 46:16–20 genetic regulation, 46:11–16, 20–24 genome, 46:3 male sterility, 46:20–24 molecular markers, 46:27–29 sexual reproduction, 46:1–38 types, 46:3–5, 24–27 Gboma eggplant, history & iconography, 34:25 Genetic resources, see Germplasm Genetic control: apple fruit growth, 47:13–21 thigmomorphogenesis, 47:69–70 Genetic variation: alternate bearing, 4:146–150 banana, 36:117–164 dogrose, 36:225–244 flower bulb crops, 36:16–36 kiwifruit, 33:1–121 melon, 36:165–198 photoperiodic response, 4:82 pollution injury, 8:16–19

386 Genetic variation: (cont’d) temperature‐photoperiod interaction, 17:73–123 wild apple, 29:63–303 Genetics & breeding: almond, 34:197–238 anthocyanin in apple, 38:363–370 apple rootstocks, 45:266–277 aroids (edible), 8:72–75; 12:169 aroids (ornamental), 10:18–25 bean, bacterial resistance, 3:28–58 bitter gourd, 37:120–131 bloom delay in fruits, 15:98–107 bulbs, flowering, 18:119–123 cassava, 12:164 chestnut blight resistance, 8:313–321 citron, 45:190–192 citrus cold hardiness, 7:221–223 cranberry, 21:236–239 Cupressus, 47:254–256 date palm, 40:203–209 daylily, 35:207–214 dogrose, 25:225–244 embryogenesis, 1:23 fig, 12:432–433; 34:165–170 fire blight resistance, 1:435–436 flower bulb crops, 36:16–36 flower longevity, 1:208–209 flower postharvest life, 40:36–42 flowering, 15:287–290, 303–309, 314–315; 27:1–39, 41–77 garlic, 46:1–38 ginseng, 9:197–198 gladiolus, 36:20–23 grafting use, 28:109–115 horseradish, 35:247–255 in vitro techniques, 9:318–324; 18:119–123 iris (bulbous), 36:23–25 kiwifruit, 33:1–121 lettuce, 2:185–187 lily, 36:25–29 lingonberry, 27:108–111 loquat, 23:252–257 macadamia, 35:1–125 melon, 36:165–198 muscadine grapes, 14:357–405 mushroom, 6:100–111 narcissus, 36:29–30 navel orange, 8:150–156 nitrogen nutrition, 2:410–411

Cumulative Subject Index pineapple, 21:138–164 plant regeneration, 3:278–283 pointed gourd, 39:328–330 pollution insensitivity, 8:18–19 pomegranate, 35:172–175 potato tuberization, 14:121–124 rhododendron, 12:54–59 strawberry, 45:16–26 sweet potato, 12:175 sweet sorghum, 21:87–90 tomato parthenocarpy, 6:69–70 tomato ripening, 13:77–98 tree short life, 2:66–70 tulip, 36:30–33 turmeric, 46:109–110, 120–122 vegetable, 38:324–344 Vigna, 2:311–394 waxes, 23:50–53 woody legume tissue & cell culture, 14:311–314 yam (Dioscorea), 12:183 Genetic variation: citron, 45:158–192 Eastern Hemlock, 46:237–239 garlic, 46:3–6 strawberry, 45:5–13 turmeric, 46:116–120 Geophyte, see Bulb, tuber Geranium, fertilization, 5:355–357 Gerard, J., 40:215–257 Germination, seed, 2:117–141, 173–174; 24:229–275 Germplasm: acquisition, apple, 29:1–61 apple, 29:1–61 carob, 41:419–434 characterization, apple, 29:45–56 citron, 45:158–192 cryopreservation, 6:357–372 garlic, 46:3–6 in vitro, 5:261–264; 9:324–325 macadamia, 35:1–125 pineapple, 21:133–175 pomegranate, 35:134–141 rhubarb, 40:147–182 turmeric, 46:116–120 Gibberellin: abscission, citrus, 15:166–167 apple rootstocks, dwarfing mechanism, 45:217–221; 46:67–73 bloom delay, 15:111–114

Cumulative Subject Index citrus, abscission, 15:166–167 cold hardiness, 11:63 dormancy, 7:270–271 floral promoter, 4:114 flowering, 15:219–293, 315–318 genetic regulation, 16:15 grape root, 5:150–151 mango fruit drop, 31:113–155 mechanical stress, 17:19–20 sapota storage, 45:125–126 Ginger: botany & horticulture, 39:273–399 postharvest physiology, 30:297–299 Ginseng, 9:187–236 Girdling, 1:416–417; 4:251–252; 30:1–26 Glucosinolates, 19:99–215 Gooseberry, wild of Kazakhstan, 29:341–342 Gourd, history, 25:71–171 Graft & grafting: citron, 45:151 durian, 47:149–152 herbaceous, 28:61–124 history, 35:437–493 incompatibility, 15:183–232; 46:52–53 phase change, 7:136–137, 141–142 rose, 9:56–57 Grape: berry growth, 45:332–335 budbreak, 45:320–322 CA storage, 1:308 carbohydrates, 37:143–211; 45:338–340 chlorosis, 9:165–166 climate change, 41:66–73; 45:355–356 flower anatomy & morphology, 13:315–337 functional phytochemicals, 27:291–298 harvesting, 16:327–348 irrigation, 27:189–225; 45:349–350 muscadine breeding, 14:357–405 nitrogen metabolism, 14:407–452 photosynthesis, 45:340–345 physiological disorder, 35:355–395 pollen morphology, 13:331–332 pruning, 16:235–254, 336–340 root, 5:127–168 seedlessness, 11:159–187 sex determination, 13:329–331 wild of Kazakhstan, 29:342–343 Gravitropism, 15:233–278 Greenhouse & greenhouse crops: carbon dioxide, 7:357–360, 544–545

387 China protected cultivation, 30:115–162 covers, 40:259–395 design, 40:267–286 energy efficiency, 1:141–171; 9:1–52 growth substances, 7:399–481 nutrition & fertilization, 5:317–403 pest management, 13:1–66 vegetables, 21:1–39 Growth regulators, see Growth substances Growth substances, 2:60–66; 24:55–138. See also Abscisic acid; Auxin; Cytokinins; Ethylene; Gibberellins abscission, citrus, 15:157–176 apple bioregulation, 10:309–401 apple dwarfing, 3:315–375; 45:197–312 apple fruit growth, 47:26–29 apple fruit set, 1:417 apple thinning, 1:270–300 aroids, ornamental, 10:14–18 avocado fruit development, 10:229–243 bloom delay, 15:107–119 CA storage in vegetables, 1:346–348 cell cultures, 3:214–314 chilling injury, 15:77–83 citrus abscission, 15:157–176 cold hardiness, 7:223–225; 11:58–66 dormancy, 7:270–279 embryogenesis, 1:41–43; 2:277–281 floral life, 40:18–25 floriculture, 7:399–481 flower induction, 4:190–195 flower storage, 10:46–51 flowering, 15:290–296 fruit calcium disorders, 40:127–135 genetic regulation, 16:1–32 ginseng, 9:226 girdling, 20:1–26 grape seedlessness, 11:177–180 hormone reception, 26:49–84 impacts of rootstocks, 46:67–73 in vitro flowering, 4:112–115 mango fruit drop, 31:113–155 mechanical stress, 17:16–21 meristem & shoot–tip culture, 5:221–227 1‐methylcyclopropene, 35:355–395 navel oranges, 8:146–147 pear bioregulation, 10:309–401

388 Growth substances (cont’d) petal senescence, 3:76–78 phase change, 7:137–138, 142–143 raspberry, 11:196–197 regulation, 11:1–14 rose, 9:53–73 seedlessness in grape, 11:177–180 triazole, 10:63–105 Haemanthus, 25:25–28 Halo blight of beans, 3:44–45 Hand thinning, 46:193–195 Hardiness, 4:250–251 Harvest: durian, 47:184–192 flower stage, 1:211–212 index, 7:72–74; 46:389–391 lettuce, 2:176–181 mechanical of berry crops, 16:255–382 Hawthorne, wild of Kazakhstan, 29:317–322 Hazelnut, wild of Kazakhstan, 29: 365–366. See also Filbert Health phytochemicals: citron, 45:152–155 durian, 47:173–177 fruit, 27:269–315 horseradish, 35:243–244 pomegranate, 35:175–177 sapota, 45:111–113 turmeric, 46:110–116 vegetables, 28:125–185 Heat treatment (postharvest), 22:91–121 Heliconia, 14:1–55 Hemlock woolly adelgid, 46:235–237 Henbane, history & iconography, 34:10–14 Herbaceous plants, subzero stress, 6:373–417 Hippeastrum, 25:29–34 Histochemistry: flower induction, 4:177–179 fruit abscission, 1:172–203 Histology, flower induction, 4:179–184. See also Anatomy & morphology History & iconography: alkekenge, 34:36–40 apple rootstocks, 45:199–204 aubergine, see Eggplant Balm of Gilead, 39:47–66 belladonna, 34:14–19

Cumulative Subject Index botanical gardens, 15:11–62; 43:269–310 breadfruit, 46:301–323 capsicum pepper, 34:62–74 citron, 45:145–147 Cucurbitaceae, 40:215–247 cucurbits, 40:215–257 Cupressus, monumental accessions, 47:227–232 Cupressus, traditional, cultural and religious values, 47:232–245 date palm, 40:183–213 datura, 34:44–51 eggplant, 34:25–35 frankincense, 39:27–39 gboma eggplant, 34:25 grafting, 35:437–493 henbane, 34:10–14 husk tomato, 34:40–44 Lycium spp., 34:23 mandrake, 34:4–10 myrrh, 39:39–47 nightshades, 40:215–257 potato, 34:85–89 scarlet eggplant, 34:25 Scopolia spp., 34:20–23 Solanaceae, 34:1–111; 40: 215–257 Solanum dulcamara, 34:25 Solanum nigrum, 34:23–24 tobacco, 34:51–62 tomato, 34:75–85 turmeric, 46:102–103 Voynich codex, 44:1–64 Withania spp., 34:19–20 Honey bee, 9:237–272 Honeysuckle, wild of Kazakhstan, 29:350 Horseradish: botany, horticulture, breeding, 35:221–265 CA storage, 1:368 Huanglongbing: citron, 45:152 Husk tomato, history & iconography, 34:40–44 Hybridization: garlic, 46:1–38 Hydrolases, 5:169–219 Hydroponic culture, 5:1–44; 7:483–558 Hymenocallis, 25:59 Hypovirulence, in Endothia parasitica, 8:299–310

Cumulative Subject Index Ice, formation & spread in tissues, 13:215–255 Ice‐nucleating bacteria, 7:210–212; 13:230–235 Iconography, see History Incompatibility: rootstocks, 46:52–53 Industrial crops, cactus, 18: 309–312 Insects & mites: aroids, 8:65–66 avocado pollination, 8:275–277 banana, 43:321–341 Cupressus, 47:261 durian, 47:168–170 entomopathogens, 47:336–356 fig, 12:442–447 hydroponic crops, 7:530–534 integrated pest management, 13:1–66 lettuce, 2:197–198 ornamental aroids, 10:18 particle film control, 31:1–45 thrips, avocado, 47:330–336 tree short life, 2:52 tulip, 5:63, 92 waxes, 23:1–68 Integrated pest management: apple, 44:363–389 greenhouse crops, 13:1–66 Interstems: apple, 45:259–262 Invasive plants, 32:379–437 In vitro: abscission, 15:156–157 apple propagation, 10:325–326 aroids, ornamental, 10:13–14 artemisia, 19:342–345 bioreactor technology, 24:1–30 bulbs, flowering, 18:87–169; 34:417–445 cassava propagation, 13:121–123; 26:99–119 cellular salinity tolerance, 16:33–69 cold acclimation, 6:382 cryopreservation, 6:357–372 Cupressus, 47:264–265 embryogenesis, 1:1–78; 2:268–310; 7:157–200; 10:153–181 environmental control, 17:123–170 flowering, 4:106–127 flowering bulbs, 18:87–169; 34:417–445 geophytes, 34:417–445

389 orchid, propagation, 44:173–228 pear propagation, 10:325–326 phase change, 7:144–145 propagation, 3:214–314; 5: 221–277; 7:157–200; 9:57–58, 273–349; 17:125–172 thin cell layer morphogenesis, 14:239–264 turmeric, 46:122–130 woody legume culture, 14:265–332 Iron: deficiency chlorosis, 9:133–186 deficiency & toxicity symptoms in fruits & nuts, 2:150 Ericaceae nutrition, 10:193–195 foliar application, 6:330 nutrition, 5:324–325 pine bark media, 9:123 Irrigation: apple, 45:350–351 citrus, 30:37–82 deficit, deciduous orchards, 21: 105–131; 32:111–165; 38:149–189 drip or trickle, 4:1–48 frost control, 11:76–82 fruit trees, 7:331–332 grape, 27:189–225; 45:349–350 grape root growth, 5:140–141 lettuce industry, 2:175 navel orange, 8:161–162 root growth, 2:464–465 scheduling, 32:111–165 Ismene, 25:59 Jacobaea vulgaris, see Ragwort Jasmonate: apple fruit growth, 47:28 role in thigmomorphogenesis, 47:67–68 Jojoba, 17:233–266 Jujube, 32:229–298 Juvenility, 4:111–112 pecan, 8:245–247 rooting, 38:225–226 tulip, 5:62–63 woody plants, 7:109–155 Kale, fluid drilling of seed, 3:21 Kazakhstan, see Wild fruits & nuts Kiwifruit: botany, 6:1–64 fruit maturation, 46:385–421

390 Kiwifruit: (cont’d) genetic resources and breeding, 33:1–121 nutrition and vine growth, 12:307–347 photosynthesis, 45:340 rootstocks, 46:50–51, 55, 64–65 shoot growth, 45:326 Lamps, for plant growth, 2:514–531 Lanzon, CA & MA, 22:149 Leaf area development: temperature, 45:329–332 Leaf blackening, Proteaceous species, 17:173–201; 45:73–104 Leaves: apple morphology, 12:283–288 flower induction, 4:188–189 Leek: CA storage, 1:375 fertilization, 1:118 Leguminosae, in vitro, 5:227–229; 14:265–332 Lemon, rootstock, 1:244–246. See also Citrus Lettuce: CA storage, 1:369–371 classification, 28:25–27 fertilization, 1:118 fluid drilling of seed, 3:14–17 industry, 2:164–207 seed germination, 24:229–275 tipburn, 4:49–65 Leucadendron, 32:167–228 Leucojum, 25:34–39 Leucospermum, 22:27–90 Light: fertilization, greenhouse crops, 5:330–331 flowering, 15:282–287, 310–312 fruit set, 1:412–413 impact on microgreen quality, 47:101–114 lamps, 2:514–531 LED, 43:1–87 light‐emitting diodes, 43:1–87 nitrogen nutrition, 2:406–407 orchards, 2:208–267 ornamental aroids, 10:4–6 photoperiod, 4:66–105 photosynthesis, 11:117–121

Cumulative Subject Index plant growth, 2:491–537 tolerance, 18:215–246 Lingonberry, 27:79–123 wild of Kazakhstan, 29:348–349 Longan, CA & MA, 22:150. See also Sapindaceous fruits Loquat: botany & horticulture, 23:233–276 CA & MA, 22:149–150 Lychee, see Sapindaceous fruits CA & MA, 22:150 flowering, 28:397–421 fruit abscission, 28:437–443 fruit development, 28:433–436 pollination, 28:422–428 reproductive biology, 28:393–453 Lycium spp., history & iconography, 34:23 Lycoris, 25:39–43 Macadamia, genetic resources & development, 35:1–125 Magnesium: container growing, 9:84–85 deficiency & toxicity symptoms in fruits & nuts, 2:148 Ericaceae nutrition, 10:196–198 foliar application, 6:331 nutrition, 5:323 pine bark media, 9:117–119 Magnetic resonance imaging, 20:78–86, 225–266 Male sterility: garlic, 46:20–24 temperature‐photoperiod induction, 17:103–106 Malic acid: metabolism, functions and contents, 45:399–412 Mandarin, rootstock, 1:250–252 Mandrake, history & iconography, 34:4–10 Manganese: deficiency & toxicity symptoms in fruits & nuts, 2:150–151 Ericaceae nutrition, 10:189–193 foliar application, 6:331 nutrition, 5:235–326 pine bark media, 9:123–124 Mango: alternate bearing, 4:145–146

Cumulative Subject Index asexual embryogenesis, 7:171–173 CA & MA, 22:151–157 CA storage, 1:313 fruit drop, 31:113–155 in vitro culture, 7:171–173 physiological disorders, 42:313–347 Mangosteen, CA & MA, 22:157 Master Gardener program, 33:393–420 Mechanical harvest, berry crops, 16:255–382 Mechanical stress regulation, 17:1–42 Mechanical thinning, 46:201, 279–282 Mechanosensing, 47:43–83 Media: fertilization, greenhouse crops, 5:333 pine bark, 9:103–131 Medicinal crops: Artemisia, 19:319–371 citron, 45:152–155 Cupressus, 47:252–254 poppy, 19:373–408 ragwort, 43:145–183 sapota, 45:111–113 Taxus, 32:299–327 turmeric, 46:114–116 Voynich codex, 44:1–64 Melon: diversity, 36:176–198 grafting, 28:96–98 vine or wilt decline, 39:77–120 Meristem culture, 5:221–277 Metabolism: apple fruit growth, 47:21–26 flower, 1:219–223 fruit acids, 45:371–430 nitrogen in citrus, 8:181–215 seed, 2:117–141 1‐Methylcyclopropene, 35:263–313 Microgreens: definitions, 47:87–92 food safety, 47:114–117 growth stages, 47:94–95 production strategies, 47:96–104 quality, impact of light conditions, 47:101–114 species produced, 47:91–94 Micronutrients: container growing, 9:85–87 pine bark media, 9:119–124 Micropropagation, see In vitro; Propagation

391 bulbs, flowering, 18:89–113 environmental control, 17: 125–172 nuts, 9:273–349 rose, 9:57–58 temperate fruits, 9:273–349 tropical fruits & palms, 7:157–200 Microtu, see Vole Modified atmosphere (MA) for tropical fruits, 22:123–183 Modified humidity packaging, 37:281–329 Moisture & seed storage, 2:125–132 Molecular biology: cassava, 26:85–159 Cupressus, 47:265–267 disease resistance, 45:268–270 dwarfing mechanism, 45:266–268 floral induction, 27:3–20 flowering, 27:1–39, 41–77 garlic flowering, 46:11–16, 20–24, 27–29 hormone reception, 26:49–84 turmeric, 46:131–132 Molybdenum nutrition, 5:328–329 Momordica charantia, see Bitter gourd Monocot, in vitro, 5:253–257 Monosporascus melon vine decline, 39:77–120 Monstera, see Aroids, ornamental Morphology: garlic, 46:4, 24–27 navel orange, 8:132–133 orchid, 5:283–286 pecan flowering, 8:217–243 red bayberry, 30:92–96 strawberry, 45:2–3 turmeric, 46:106–108 Moth bean, genetics, 2:373–374 Mountain ash, wild of Kazakhstan, 29:322–324 Mulberry, wild of Kazakhstan, 29:350–351 Multiple cropping, 30:355–500 Mung bean, genetics, 2:348–364 Musa, see Banana Mushroom: CA storage, 1:371–372 cultivation, 19:59–97 spawn, 6:85–118

392 Muskmelon, fertilization, 1:118–119 Mycoplasma‐like organisms, tree short life, 2:50–51 Mycorrhizae: apple rootstocks, 45:250–258 biochemistry & biology, 36:257–287 container growing, 9:93 Ericaceae, 10:211–212 fungi, 3:172–213 grape root, 5:145–146 Myrica, see Red bayberry Myrrh, 39:39–47 Narcissus, 25:43–48 Navel orange, 8:129–179 Nectarine: bloom delay, 15:105–106 CA storage, 1:309–310 postharvest physiology, 11:413–452 soluble solids, 42:253–311 Nematodes: aroids, 8:66 fig, 12:475–477 lettuce, 2:197–198 tree short life, 2:49–50 Nerine, 25:48–56 NFT (nutrient film technique), 5:1–44 Nightshades, renaissance history, 40:215–257 Nitric oxide, 42:121–155 Nitrogen: CA storage, 8:116–117 container growing, 9:80–82 deficiency & toxicity symptoms in fruits & nuts, 2:146 Ericaceae nutrition, 10:198–202 fixation in woody legumes, 14: 322–323 foliar application, 6:332 in embryogenesis, 2:273–275 metabolism in apple, 4:204–246 metabolism in citrus, 8:181–215 metabolism in grapevine, 14:407–452 nutrition, 2:395, 423; 5:319–320 pine bark media, 9:108–112 trickle irrigation, 4:29–30 vegetable crops, 22:185–223 Nomenclature, 28:1–60 Nondestructive quality evaluation of fruits & vegetables, 20:1–119

Cumulative Subject Index Nursery crops: fertilization, 1:106–112 nutrition, 9:75–101 Nut crops, see individual crop almond, wild of Kazakhstan, 29:262–265 almond breeding, 34:197–238 almond postharvest technology & utilization, 20:267–311 chestnut, botany & horticulture, 31:293–349 chestnut blight, 8:291–336 fertilization, 1:106 hazelnut, wild of Kazakhstan, 29:365–366 honey bee pollination, 9:250–251 in vitro culture, 9:273–349 macadamia, 35:1–125 nutritional ranges, 2:143–164 pine, wild of Kazakhstan, 29:368–369 pistachio, wild of Kazakhstan, 29:366–368 pistachio culture, 3:376–396 stone pine, 39:153–201 walnut, wild of Kazakhstan, 29:369–370 Nutrient: citrus diagnosis, 34:277–364 concentration in fruit & nut crops, 2:154–162 film technique, 5:1–44 foliar‐applied, 6:287–355 impact of rootstocks, 45:214–217 media, for asexual embryogenesis, 2:273–281 media, for organogenesis, 3:214–314 monitoring, remote sensing, 45:53–54 plant & tissue analysis, 7:30–56 solutions, 7:524–530 uptake, in trickle irrigation, 4:30–31 Nutrition (human): aroids, 8:79–84 CA storage, 8:101–127 durian, 47:173–177 organic horticulture, 43:207–214 phytochemicals in fruit, 27:269–315 phytochemicals in vegetables, 28:125–185 steroidal alkaloids, 25:171–196 Nutrition (plant): air pollution, 8:22–23, 26

Cumulative Subject Index blueberry, 10:183–227 calcifuge, 10:183–227 citrus diagnostics, 34:277–364 cold hardiness, 3:144–171 container nursery crops, 9:75–101 cranberry, 21:234–235 ecologically based, 24:156–172 embryogenesis, 1:40–41 Ericaceae, 10:183–227 fire blight, 1:438–441 foliar, 6:287–355 fruit & nut crops, 2:143–164 ginseng, 9:209–211 greenhouse crops, 5:317–403 kiwifruit, 12:325–332 mycorrhizal fungi, 3:185–191 navel orange, 8:162–166 nitrogen in apple, 4:204–246 nitrogen in vegetable crops, 22:185–223 nutrient film techniques, 5:18–21, 31–53 ornamental aroids, 10:7–14 ornamentals in containers, 38: 253–297 pine bark media, 9:103–131 raspberry, 11:194–195 rootstock effects, 46:65–67 slow‐release fertilizers, 1:79–139 turmeric, 46:141–149 Oil palm: asexual embryogenesis, 7:187–188 in vitro culture, 7:187–188 Okra: botany & horticulture, 21:41–72 CA storage, 1:372–373 Oleaster, wild of Kazakhstan, 29:351–353 Olive: alternate bearing, 4:140–141 high density orchards, 41:303–383 oil composition, 38:83–147 physiology, 31:147–231 pollination, 34:265–266 processing technology, 25:235–260 rootstock, 46:63–64 salinity tolerance, 21:177–214 Onion: CA storage, 1:373–375 fluid drilling of seed, 3:17–18

393 Oomycete diseases, cucurbits, 44:231–314 Opium poppy, 19:373–408 Orange, see Citrus alternate bearing, 4:143–144 sour, rootstock, 1:242–244 sweet, rootstock, 1:252–253 trifoliate, rootstock, 1:247–250 Orchard & orchard systems: floor management, 9:377–430 light, 2:208–267 olive high density, 41:303–383 rootstocks, apple, 45:197–312 root growth, 2:469–470 water, 7:301–344 Orchid: biotechnology, 44:173–228 fertilization, 5:357–358 physiology, 5:279–315 pollination regulation of flower development, 19:28–38 Organic acids: kiwifruit, 46:401–402 Organic horticulture, sustainability, 36:257–287; 37:331–362 Organogenesis, 3:214–314. See also In vitro; Tissue culture Ornamental plants, see individual plant Amaryllidaceae, 25:1–70 Banksia, 22:1–25 cactus grafting, 28:106–109 chlorosis, 9:168–169 cotoneaster, wild of Kazakhstan, 29:316–317 Cupressus, 47:245–249, 249–252 cut flower postharvest, 40:1–106 dogrose, 36:199–255 Eastern Hemlock, 46:227–253 fertilization, 1:98–104, 106–116 flowering bulb roots, 14:57–88 flowering bulbs in vitro, 18:87–169 foliage acclimatization, 6:119–154 foliage industry, 31:47–112 geophytes, in vitro, 34:417–445 grasses, 39:121–152 heliconia, 14:1–55 honeysuckle, wild of Kazakhstan, 29:350 Leucadendron, 32:167–228 Leucospermum, 22:27–90

394 Ornamental plants, see individual plant (cont’d) nutrient management in containers, 38:253–297 oleaster, wild of Kazakhstan, 29:351–353 orchid pollination regulation, 19:28–38 palms, 42:1–120 poppy, 19:373–408 potted plant postharvest, 40:1–54 protea leaf blackening, 17:173–201; 45:73–104 rhododendron, 12:1–42 rose, wild of Kazakhstan, 29:353–360 Salix, 34:447–489 viburnam, wild of Kazakhstan, 29:361–362 water management in containers, 38:253–297 water relations, cut flowers, 40:14–18, 55–106 Osier, see Salix Oxalic acid: metabolism, functions and contents, 45:395–397 Paclobutrazol, see Triazole Palms, ornamental, 42:1–120 Papaya, see also Caricaceae: asexual embryogenesis, 7:176–177 CA & MA, 22:157–160 CA storage, 1:314 in vitro culture, 7:175–178 Parasitic weeds, 33:267–349 Parsley: CA storage, 1:375 drilling of seed, 3:13–14 Parsnip, fluid drilling of seed, 3:13–14 Parthenocarpy, tomato, 6:65–84 Particle films, 31:1–45 Passion fruit: CA & MA, 22:160–161 in vitro culture, 7:180–181 Pathogen elimination, in vitro, 5:257–261 Pawpaw, 31:351–384 Peach (and nectarine): bloom delay, 15:105–106 CA storage, 1:309–310 deficit irrigation, 38:151–160 orchard systems, 32:63–109

Cumulative Subject Index origin, 17:333–379 postharvest physiology, 11:413–452 short life, 2:4 soluble solids, 42:253–311 summer pruning, 9:351–375 texture, 41:241–301 thinning, 28:351–392 wooliness, 20:198–199 Peach palm (Pejibaye): in vitro culture, 7:187–188 Pear: bioregulation, 10:309–401 bloom delay, 15:106–107 CA storage, 1:306–308 deficit irrigation, 38:177–180 decline, 2:11 fire blight control, 1:423–474 fruit disorders, 11:357–411; 27:227–267 fruit thinning, 46:199–200 fruit volatiles, 28:237–324 in vitro, 9:321 maturity indices, 13:407–432 root distribution, 2:456 rootstocks, 46:39–97 scald, 27:227–267 short life, 2:6 wild of Kazakhstan, 29:315–316 Pecan: alternate bearing, 4:139–140 fertilization, 1:106 flowering, 8:217–255 in vitro culture, 9:314–315 Pejibaye, in vitro culture, 7:189 Pepper (Capsicum): CA storage, 1:375–376 fertilization, 1:119 fluid drilling in seed, 3:20 grafting, 28:104–105 phytochemicals, 28:161–162 Pepper (Piper), 33:173–266 Persimmon: CA storage, 1:314 quality, 4:259 Pest control: aroids (edible), 12:168–169 aroids (ornamental), 10:18 avocado, thrips, 47:330–356 banana, 43:321–341 breadfruit, 46:360–363

Cumulative Subject Index cassava, 12:163–164 cowpea, 12:210–213 ecologically based, 24:172–201 fig, 12:442–477 fire blight, 1:423–474 ginseng, 9:227–229 greenhouse management, 13: 1–66 hydroponics, 7:530–534 parasitic weeds, 33:267–349 particle films, 31:1–45 sweet potato, 12:173–175 vertebrate, 6:253–285 yam (Dioscorea), 12:181–183 Petal senescence, 11:15–43 pH: container growing, 9:87–88 fertilization greenhouse crops, 5:332–333 pine bark media, 9:114–117 soil testing, 7:8–12, 19–23 Phase change, 7:109–155 Phenolic acids: metabolism, functions and contents, 45:382–385 Phenology: apple, 11:231–237; 45:317 grape, 45:316–317 raspberry, 11:186–190 Philodendron, see Aroids, ornamental Phoenix dactyfera, see Date palm Phosphonates, Phytophthora control, 17:299–330 Phosphorus: container growing, 9:82–84 deficiency & toxicity symptoms in fruits & nuts, 2:146–147 nutrition, 5:320–321 pine bark media, 9:112–113 trickle irrigation, 4:30 Photoautotrophic micropropagation, 17:125–172 Photoperiod, 4:66–105, 116–117; 17:73–123 flowering, 15:282–284, 310–312; 45:5–13; 46:9–16, 27 Photosynthesis: apple, 45:345–349 cassava, 13:112–114 efficiency, 7:71–72; 10:378 fruit crops, 11:111–157

395 ginseng, 9:223–226 grape, 45:340–345 water stress, 45:349–351 light, 2:237–238 Physiology, see Postharvest physiology abuscular mycorrhizae, 36:257–290 adventitious rooting, 38:213–225 Allium development, 32:329–378 anthocyanin accumulation, apple, 38:357–391 anthocyanins, foliar, 42:208–241 bitter pit, 11:289–355 blueberry development, 13:339–405 budbreak, 45:320–324 cactus reproductive biology, 18:321–346 calcium, 10:107–152; 40:107–146 carbohydrate metabolism, 7:69–108 carbohydrate partitioning, 45:338–340 cassava, 13:105–129 circadian regulation, 41:1–46 citrus cold hardiness, 7:201–238 citrus irrigation, 30:55–67 conditioning, 13:131–181 cut flower, 1:204–236; 3:59–143; 10:35–62 desiccation tolerance, 18:171–213 disease resistance, 18:247–289 dormancy, 7:239–300; 45:317–320 dwarfing mechanisms, apple, 45:209–224 embryogenesis, 1:21–23; 2:268–310 floral scents, 24:31–53 flower bulb crops, 36:36–49 flower development, 19:1–58 flowering, 4:106–127 fruit acids, 45:371–430 fruit calcium, 40:107–146 fruit growth, 45:332–338 fruit pigments, 39:239–271 fruit ripening, 13:67–103 fruit softening, 10:107–152 garlic, 46:1–38 ginseng, 9:211–213 girdling, 30:1–26 glucosinolates, 19:99–215 grafting, 28:78–84 grapevine carbohydrates, 37:143–211 heliconia, 14:5–13 high temperature stress, 45:351–354

396 Physiology, see Postharvest physiology (cont’d) hormone reception, 26:49–84 juvenility, 7:109–155 lettuce seed germination, 24:229–275 light tolerance, 18:215–246 loquat, 23:242–252 lychee reproduction, 28:393–453 male sterility, 17:103–106 mango fruit drop, 31:113–155 mechanical stress, 17:1–42 1‐methylcyclopropene, 35:253–313 mycorrhizae, 36:257–289 nitric oxide, 42:121–155 nitrogen metabolism in grapevine, 14:407–452 nutritional quality & CA storage, 8:118–120 olive, 31:157–231 olive salinity tolerance, 21: 177–214 orchid, 5:279–315 particle films, 31:1–45 petal senescence, 11:15–43 photoperiodism, 17:73–123 photosynthesis, 45:340–354 pollution injury, 8:12–16 polyamines, 14:333–356 potato tuberization, 14:89–188 pruning, 8:339–380 raspberry, 11:190–199 red bayberry, 30:96–99 regulation, 11:1–14 roots of flowering bulbs, 14:57–88 root pruning, 6:158–171 rootstock, dwarfing mechanism, 46:39–97 rose, 9:3–53 salinity hormone action, 16:1–32 salinity tolerance, 16:33–69 seed, 2:117–141 seed priming, 16:109–141 shoot growth, 45:324–329 soluble solids, peach & nectarine, 42:157–208 strawberry flowering, 28:325–349; 45:1–32 subzero stress, 6:373–417 summer pruning, 9:351–375 sweet potato, 23:277–338; 42:157–208 thin cell layer morphogenesis, 14:239–264

Cumulative Subject Index tomato fruit ripening, 13:67–103 tomato parthenocarpy, 6:71–74 triazoles, 10:63–105; 24:55–138 tulip, 5:45–125 vernalization, 17:73–123 vines, 38:1–21 volatiles, 17:43–72 water relations cut flowers, 18:1–85; 40:14–18, 55–106 watercore, 6:189–251 waxes, 23:1–68 Phytochemicals, functional: fruits, 27:269–315 vegetables, 28:125–185 Phytohormones, see Growth substances Phytophthora control, 17:299–330 Phytotoxins, 2:53–56 Pigmentation: flower, 1:216–219 rose, 9:64–65 Pinching, by chemicals, 7:453–461 Pine, wild of Kazakhstan, 29:368–369 Pine bark, potting media, 9:103–131 Pineapple: CA & MA, 22:161–162 CA storage, 1:314 genetic resources, 21:138–141 in vitro culture, 7:181–182 Pinus pinea, see Stone pine Piper, see Black pepper Pistachio: alternate bearing, 4:137–139 culture, 3:376–393 in vitro culture, 9:315 pollination, 34:264 wild of Kazakhstan, 29:366–368 Plant: architecture, 32:1–63 breeding, see Genetics & breeding classification, 28:1–60 protection, short life, 2:79–84 systematics, 28:1–60 Plantain, see Banana CA & MA, 22:141–146 in vitro culture, 7:178–180 Plastic cover, sod production, 27:317–351 Plug transplant technology, 35:397–436 Plum: CA storage, 1:309 deficit irrigation, 38:165–166

Cumulative Subject Index origin, 23:179–231 wild of Kazakhstan, 29:330–332 Poinsettia, fertilization, 1:103–104; 5:358–360 Pointed gourd, 39:203–238; 41:457–495 Pollen, desiccation tolerance, 18:195 Pollination: apple, 1:402–404 artificial, 34:239–276 avocado, 8:272–283 cactus, 18:331–335 durian, 47:147–148, 154–156 embryogenesis, 1:21–22 fig, 12:426–429 floral scents, 24:31–53 flower regulation, 19:1–58 fruit crops, 12:223–264 fruit set, 4:153–154 ginseng, 9:201–202 grape, 13:331–332 heliconia, 14:13–15 honey bee, 9:237–272 kiwifruit, 6:32–35 lychee, 28:422–428 navel orange, 8:145–146 orchid, 5:300–302 petal senescence, 11:33–35 protection, 7:463–464 rhododendron, 12:1–67 Pollution, 8:1–42 Polyamines: chilling injury, 15:80 in horticulture, 14:333–356 mango fruit drop, 31:125–127 Polygalacturonase, 13:67–103 Pomegranate, 35:127–191 Poppy, opium, 19:373–408 Postharvest physiology: almond, 20:267–311 apple bitter pit, 11:289–355 apple maturity indices, 13:407–432 apple scald, 27:227–257 apple weight loss, 25:197–234 aroids, 8:84–86 asparagus, 12:69–155 bitter melon, 35:343–344 CA storage diseases, 3:412–461 CA storage & quality, 1:301–336; 8:101–127 CA tropical fruit, 22:123–183

397 carrot storage, 30:284–288 cassava storage, 30:288–295 chilling injury, 4:260–261; 15:63–95; 44:229–278s chlorophyll fluorescence, 23:69–107 coated fruits & vegetables, 26:161–238 cucumber, 35:325–330 cucurbits, 35:315–354 cut flower, 1:204–236; 3:59–143; 10:35–62; 40:1–106 cuttings, 44:121–172 durian, 22:147–148; 47:170–172, 177–183 fig, 34:146–164 foliage plants, 6:119–154 fresh‐cut fruits & vegetables, 30:85–255 fruit, 1:301–336 fruit softening, 10:107–152 ginger storage, 30:297–299 heat treatment, 22:91–121 hot water treatment, 38:191–212 Jerusalem artichoke storage, 30:271–276 kiwifruit, 46:405–413 leaf blackening, 17:173–201; 45:73–104 lettuce, 2:181–185 low‐temperature sweetening, 17: 203–231; 30:317–355 luffa, 35:344–345 MA for tropical fruit, 22:123–183 Mango disorders, 42:313–347 melon, 35:330–337 modified humidity packaging, 37:281–329 navel orange, 8:166–172 nectarine, 11:413–452 nitric oxide, 42:121–155 nondestructive quality evaluation, 20:1–119 pathogens, 3:412–461 peach, 11:413–452 pear disorders, 11:357–411; 27:227–267 pear maturity indices, 13:407–432 pear scald, 27:227–257 petal senescence, 11:15–43 potato low temperature sweetening, 30:317–355 potato storage, 30:259–271 potted plants, 40:1–54

398 Postharvest physiology: (cont’d) protea leaf blackening, 17:173–201; 45:73–104 pumpkin & squash, 35:337–341 quality evaluation, 20:1–119 sapota storage, 45:122–132 scald, 27:227–267 seed, 2:117–141 senescence of cut flowers, 40:29–36 sweet potato storage, 30:276–284 taro storage, 30:295–297 texture in fresh fruit, 20:121–244 tomato chilling, 44:229–278 tomato fruit ripening, 13:67–103 tomato posthavest losses, 33:351–391 vegetables, 1:337–394 water relations of cut flowers, 40:14–18, 55–106 watercore, 6:189–251; 11:385–387 watermelon, 35:319–325 wax gourd, 35:342 Potassium: container growing, 9:84 deficiency & toxicity symptoms in fruits & nuts, 2:147–148 foliar application, 6:331–332 nutrition, 5:321–322 pine bark media, 9:113–114 trickle irrigation, 4:29 Potato: CA storage, 1:376–378 classification, 28:23–26 fertilization, 1:120–121 history & iconography, 34:85–89 low temperature sweetening, 17:203– 231; 30:317–353 phytochemicals, 28:160–161 postharvest physiology & storage, 30:259–271 tuberization, 14:89–198 Potted plants, postharvest, 40:1–54 Processing: durian, 47:193–195 table olives, 25:235–260 Propagation, see In vitro adventitious rooting in trees, 38:213–225 apple, 10:324–326; 12:288–295 aroids, ornamental, 10:12–13 bioreactor technology, 24:1–30 breadfruit, 46:343–351

Cumulative Subject Index cassava, 13:120–123 Cupressus, 47:263–265 cutting industry, 44:121–172 durian, 47:149–152 Eastern Hemlock, 46:239–242 floricultural crops, 7:461–462 foliage plants, 31:47–112 ginseng, 9:206–209 grafting, 46:40–42 macadamia, 35:92–95 orchid, 5:291–297; 44:173–228 pear, 10:324–326 rose, 9:54–58 tropical fruit, palms, 7:157–200 turmeric, 46:134–135 woody legumes in vitro, 14:265–332 Protea: floricultural crop, 26:1–48 leaf blackening, 17:173–201; 45:73–104 Proteaceous flower crop: Banksia, 22:1–25 Leucospermum, 22:27–90 Leucadendron, 32:167–228 Protea, 17:173–201; 26:1–48; 45:73–104 Protected crops, carbon dioxide, 7:345–398 Protoplast culture, woody species, 10:173–201 Prune deficit irrigation, 38:165–166 Pruning: alternate bearing, 4:161 apple, 9:351–375 apple training, 1:414 chemical, 7:453–461 cold hardiness, 11:56 durian, 47:157–158 fire blight, 1:441–442 grapevines, 16:235–254 light interception, 2:250–251 peach, 9:351–375 phase change, 7:143–144 physiology, 8:339–380 plant architecture, 32:1–63 root, 6:155–188 Prunus, see Almond; Cherry; Nectarine; Peach; Plum in vitro, 5:243–244; 9:322 root distribution, 2:456 Pseudomonas: Phaseolicola, 3:32–33, 39, 44–45

Cumulative Subject Index Solanacearum, 3:33 Syringae, 3:33, 40; 7:210–212 Pumpkin, history, 25:71–170 Quality evaluation: fruits & vegetables, 20:1–119, 121–224 nondestructive, 20:1–119 texture in fresh fruit, 20:121–224 Quinic acid: metabolism, functions and content, 45:377–382 Rabbit, 6:275–276 Radish, fertilization, 1:121 Ragwort, 43:145–183 Rambutan, CA & MA, 22:163. See also Sapindaceous fruits Raspberry: harvesting, 16:282–298 productivity, 11:185–228 wild of Kazakhstan, 29:343–345 Reactive oxygen species, role in thigmomorphogenesis, 47:59–60 Red bayberry, 30:83–113 Rejuvenation: rose, 9:59–60 woody plants, 7:109–155 Remote sensing, using unmanned aircraft: aircraft systems, 45:36–42 applications, 45:52–61 disease monitoring, 45:56–57 nutrient status, 45:53–54 sensors, 45:42–51 water stress detection, 45:54–56 weed infestation, 45:57–58 Replant problem, deciduous fruit trees, 2:1–116; 45:250–258 Respiration: asparagus postharvest, 12:72–77 fruit in CA storage, 1:315–316 kiwifruit, 6:47–48 sapota fruit, 45:114–125 vegetables in CA storage, 1:341–346 Rheum, see Rhubarb Rhizobium, 3:34, 41 Rhododendron, 12:1–67 Rhubarb, botany & horticulture, 40:147–182 Rice bean, genetics, 2:375–376 Root: adventitious, 38:213–225 apple, 12:269–272

399 cactus, 18:297–298 diseases, 5:29–31 environment, nutrient film technique, 5:13–26 Ericaceae, 10:202–209 grape, 5:127–168 kiwifruit, 12:310–313 physiology of bulbs, 14:57–88 pruning, 6:155–188 raspberry, 11:190 rose, 9:57 sweet potato, 42:157–207 tree crops, 2:424–490 Root & tuber crops: Amaryllidaceae, 25:1–79 aroids, 8:43–99; 12:166–170 carrot postharvest physiology, 30:284–288 cassava crop physiology, 13:105–129 cassava molecular biology, 26:85–159 cassava multiple cropping, 30:355–50 cassava postharvest physiology, 30:288–295 cassava root crop, 12:158–166 garlic, 46:1–38 ginger, 39:273–388 horseradish, 35:221–265 low–temperature sweetening, 17: 203–231; 30:317–355 minor crops, 12:184–188 potato low temperature sweetening, 30:317–355 potato tuberization, 14:89–188 sweet potato, 12:170–176; 42:157–208 sweet potato physiology, 23: 277–338 sweet potato postharvest physiology, 30:276–284 taro postharvest physiology, 30:295–297 turmeric, 46:99–183 yam (Dioscorea), 12:177–184 Root–shoot interaction, impact of rootstocks, 46:52–80 Rootstocks: alternate bearing, 4:148 apple, 1:405–407; 12:295–297; 45:197–312 avocado, 17:381–429 citron, 45:151 citrus, 1:237–269 clonal history, 35:475–478

400 Rootstocks: (cont’d) cold hardiness, 11:57–58 dwarfing mechanisms, 46:52–81 fire blight, 1:432–435 growth effects, 46:39–51 impacts on carbohydrate reserves, 46:73–77 impacts on flowering, 46:77–80 impacts on hormones, 46:67–73 impacts on nutrient status, 46:65–67 impacts on water relations, 46:54–65 light interception, 2:249–250 macadamia, 35:92–95 navel orange, 8:156–161 root‐shoot interactions, 46:52–80 root systems, 2:471–474 source‐sink responses, 46: 73–80 stress, 4:253–254 tree short life, 2:70–75 Rosa, see Dogrose; Rose Rosaceae, in vitro, 5:239–248 Rose: dogrose, 36:199–255 fertilization, 1:104; 5:361–363 growth substances, 9:3–53 in vitro, 5:244–248 wild of Kazakhstan, 29:353–360 Salinity: air pollution, 8:25–26 apple rootstocks, 45:241–242 citrus irrigation, 30:37–83 olive, 21:177–214 soils, 4:22–27 tolerance, 16:33–69 Salix, botany & horticulture, 34:447–489 Sambucus, see Elderberry Sapindaceous fruits, 16:143–196 Sapota (Sapodilla): CA & MA, 22:164; 45:125–126 fruit quality, 45:114–132 fruit storage, 45:125–126 fruit processing, 45:132–134 Scab in apple, 44:361–389 Scadoxus, 25:25–28 Scald, apple & pear, 27:227–265 Scarlet eggplant, history & iconography, 34:25 Scopolia spp., history & iconography, 34:20–23 Scoring & fruit set, 1:416–417

Cumulative Subject Index Sea buckthorn, wild of Kazakhstan, 29:361 Secondary metabolites, woody legumes, 14:314–322 Seed: abortion, 1:293–294 annatto, 39:389–419 apple anatomy & morphology, 10:285–286 conditioning, 13:131–181 desiccation tolerance, 18: 196–203 environmental influences on size & composition, 13:183–213 flower induction, 4:190–195 fluid drilling, 3:1–58 garlic, 46:6 germination, ancient date, 40:205–207 grape seedlessness, 11:159–184 kiwifruit, 6:48–50 lettuce, 2:166–174 lettuce germination, 24:229–275 priming, 16:109–141 rose propagation, 9:54–55 vegetable, 3:1–58 viability & storage, 2:117–141 Senecio jacobaea, see Ragwort Senescence: chlorophyll senescence, 23:88–93 cut flower, 1:204–236; 3:59–143; 10:35–62; 18:1–85; 40:29–36 petal, 11:15–43 pollination‐induced, 19:4–25 rose, 9:65–66 whole plant, 15:335–370 Sensory quality, CA storage, 8:101–127 Shakespeare, W., 40:215–257 Shikimic acid: metabolism, functions and content, 45:377–382 Shoot‐tip culture, 5:221–277. See also Micropropagation Shoot growth: temperature, 45:324–329 Short life problem, fruit crops, 2:1–116 Sicyos edulis, see Chayote Signal transduction, 26:49–84 Small fruit, CA storage, 1:308 Small unmanned aircraft systems: applications, 45:52–61 nutrient monitoring, 45:53–54 sensors, 45:42–51

Cumulative Subject Index stress detection, 45:54–56 weed infestation, 45:57–58 Snake gourd, 41:475–495 Snapdragon fertilization, 5:363–364 Sod production, 27:317–351 Sodium, deficiency & toxicity symptoms in fruits & nuts, 2:153–154 Soil: grape root growth, 5:141–144 management & root growth, 2:465–469 orchard floor management, 9:377–430 plant relations, trickle irrigation, 4:18–21 replant problem, 45:250–258 stress, 4:151–152 testing, 7:1–68; 9:88–90 zinc, 23:109–178 Soilless culture, 5:1–44 Solanaceae: history and iconography, 34:1–111; 40:215–247 in vitro, 5:229–232 steroidal alkaloids, 25:171–196 Solanum dulcamara, history & iconography, 34:25 Solanum nigrum, history & iconography, 34:23–24 Somatic embryogenesis, see Asexual embryogenesis Sorghum, sweet, 21:73–104 Spathiphyllum, see Aroids, ornamental Species conservation, Cupressus, 47:256–263 Spices: ancient trade, 39:3–27 balm of Gilead, 39:47–66 black pepper, 33:173–266 frankincense, 39:27–39 ginger, 39:273–388 myrrh, 39:40–47 Spur extinction, 46:259–263 Squash, history, 25:71–170 Stem, apple morphology, 12:272–283 Sternbergia, 25:59 Steroidal alkaloids, solanaceous, 25:171–196 Stone pine, 29:153–201 Storage, see Controlled–atmosphere (CA) storage; Postharvest physiology carrot postharvest physiology, 30:284–288

401 cassava postharvest physiology, 30:288–295 cut flower, 3:96–100; 10:35–62 ginger postharvest physiology, 30:297–299 Jerusalem artichoke postharvest physiology, 30:259–271 low temperature sweetening, 17:203– 231; 30:317–353 potato low temperature sweetening, 30:317–353 potato postharvest physiology, 30:259–271 root & tuber crops, 30:253–316 rose plants, 9:58–59 sapota, 45:125–126 seed, 2:117–141 sweet potato postharvest physiology, 30:295–297 taro postharvest physiology, 30:295–297 Strawberry: breeding, 45:16–26 fertilization, 1:106 flowering, 28:325–349; 45:1–32 fruit growth & ripening, 17:267–297 functional phytonutrients, 27:303–304 harvesting, 16:348–365 in vitro, 5:239–241 wild of Kazakhstan, 29:347 Stress: benefits of, 4:247–271 chlorophyll fluorescence, 23:69–107 climatic, 4:150–151 flooding, 13:257–313 high temperature, 45:351–354 irrigation scheduling, 32:11–165; 45:349–350 mechanical, 17:1–42 olive, 31:205–217 petal, 11:32–33 plant, 2:34–37 protectants (triazoles), 24: 55–138 protection, 7:463–466 salinity tolerance in olive, 21:177–214 subzero temperature, 6:373–417 waxes, 23:1–68 Sugar, see Carbohydrate allocation, 7:74–94 flowering, 4:114 Sugar apple, CA & MA, 22:164

402 Sugar beet, fluid drilling of seed, 3:18–19 Sulfur: deficiency & toxicity symptoms in fruits & nuts, 2:154 nutrition, 5:323–324 Sustainable horticulture, 36: 289–333; 37:331–362 Sweet potato: culture, 12:170–176 fertilization, 1:121 physiology, 23:277–338 postharvest physiology & storage, 30:276–284 Sweet sop, CA & MA, 22:164 Symptoms, deficiency & toxicity symptoms in fruits & nuts, 2:145–154 Syngonium, see Aroids, ornamental Systematics, 28:1–60 Taro, postharvest physiology & storage, 30:276–284. See also Aroids, edible Tartaric acid: metabolism, functions and contents, 45:389–392 Taxonomy, 28:1–60 Taxus, 32:299–327 Tea, botany & horticulture, 22:267–295 Temperature: apple fruit growth, 47:13 apple fruit set, 1:408–411 bloom delay, 15:119–128 CA storage of vegetables, 1:340–341 carbohydrate partitioning, 45:338–340 chilling injury, 15:67–74 climate change impacts, 45:355–357 cryopreservation, 6:357–372 cut flower storage, 10:40–43 dormancy and budbreak, 45:317–324 fertilization, greenhouse crops, 5:331–332 fire blight forecasting, 1:456–459 flowering, 15:284–287, 312–313; 46:9–16, 27 interaction with photoperiod, 4:80–81 leaf area development, 45:329–332 low temperature sweetening, 17:203–231 navel orange, 8:142 nutrient film technique, 5:21–24 photoperiod interaction, 17:73–123

Cumulative Subject Index photosynthesis, 11:121–124; 45:340–349 plant growth, 2:36–37; 45: 324–329, 351–354 seed storage, 2:132–133 subzero stress, 6:373–417 Texture: fresh fruit, 20:121–224 peach, 41:241–301 Thigmomorphogenesis: cell wall and membrane responses, 47:55–57 definition, 47:47–48 horticultural applications, 47:70–72 induction, natural, 47:48–49 induction, artificial, 47:49–50 leaf responses, 47:50–51 reproductive organ responses, 47:54–55 role of calcium, 47:57–58 role of electrical signals, 47:60–61 role of phytohormones, 47:65–68 role of protein complexes, 47:61–65 role of reactive oxygen species, 47:59–60 root responses, 47:53–54 stem responses, 47:51–53 Thinning: apple, 1:270–300 chemical thinning, 46:195–200, 212–213, 263–279, 283 decision support models, 46:202–205, 284–286 hand thinning, 46:193–195 mechanical thinning, 46:201, 279–282 peach & Prunus, 28:351–392 Tipburn, in lettuce, 4:49–65 Tissue culture, 1:1–78; 2:268–310; 3:214–314; 4:106–127; 5: 221–277; 6:357–372; 7:1 57–200; 8:75–78; 9:273–349; 10:153–181; 24:1–30. See also In vitro culture bulb organ formation, 34:417–444 cassava, 26:85–159 dwarfing, 3:347–348 geophyte organ formation, 34:417–444 nutrient analysis, 7:52–56; 9:90 turmeric, 46:122–130 Tobacco, history & iconography, 34:51–62 Tomato: CA storage, 1:380–386

Cumulative Subject Index chilling injury, 20:199–200; 44:229–278 classification, 28:21–23 fertilization, 1:121–123 fluid drilling of seed, 3:19–20 fruit cracking, 30:163–184 fruit ripening, 13:67–103 galacturonase, 13:67–103 grafting, 28:98–103 greenhouse quality, 26:239 history & iconography, 34: 75–85 parthenocarpy, 6:65–84 phytochemicals, 28:160 postharvest losses, 33:351–391 Toxicity symptoms in fruit & nut crops, 2:145–154 Transport, cut flowers, 3:100–104 Tree: adventitious rooting, 38:213–225 decline, 2:1–116 Triazoles, 10:63–105; 24:55–138 chilling injury, 15:79–80 Trichosanthes cucumerina, see Snake gourd Trichosanthes dioica, see Pointed gourd Trickle irrigation, 4:1–48 Truffle cultivation, 16:71–107 Tsuga canadensis, 46:227–253 Tuber, potato, 14:89–188 Tuber & root crops, see Root & tuber crops Tulip, see Bulb fertilization, 5:364–366 in vitro, 18:144–145 physiology, 5:45–125 Tunnel (cloche), 7:356–357 Turf grass, fertilization, 1:112–117 Turmeric: biochemistry, 46:110–113 biotechnology, 46:122–132 botany, 46:105–110 breeding, 46:120–122 center of origin, 46:102–105 genetic resources, 46:116–120 medicinal uses, 46:114–116 fertilization, 5:364–366 processing, 46:154–156 production, 46:133–154 Turnip, fertilization, 1:123–124 Turnip Mosaic Virus, 14:199–238

403 Urban agriculture, 44:65–120 Urban horticulture, 44:65–120 Urd bean, genetics, 2:364–373 Urea, foliar application, 6:332 Vaccinium, 10:185–187. See also Blueberry; Cranberry; Lingonberry functional phytonutrients, 27:303 wild of Kazakhstan, 29:347–349 Vase solutions, 3:82–95; 10:46–51 Vegetable crops, see Specific crop Allium development, 32:329–378 Allium phytochemicals, 28:156–159 aroids, 8:43–99; 12:166–170 asparagus postharvest, 12:69–155 bean rust, 37:1–99 bitter gourd, 37:101–141 breeding, 38:324–444 CA storage, 1:337–394 CA storage diseases, 3:412–461 CA storage & quality, 8:101–127 cactus, 18:300–302 caper bush, 27:125–188 carrot postharvest physiology & storage, 30:284–288 cassava crop physiology, 13:105–129 cassava molecular biology, 26:85–159 cassava multiple cropping, 30:355–50 cassava postharvest physiology & storage, 30:288–295 cassava root crop, 12:158–166 chayote, 43:89–143 chilling injury, 15:63–95; 44:229–278 coating physiology, 26:161–238 crucifer phytochemicals, 28:150–156 cucumber grafting, 28:91–96 cucurbit postharvest, 35:315–354 cucurbits, oomycetes, 44:229–278 cucurbits renaissance history, 40:215–257 ecologically based, 24:139–228 eggplant grafting, 28:103–104 eggplant phytochemicals, 28:162–163 fertilization, 1:117–124 fluid drilling of seeds, 3:1–58 fresh cut, 30:185–255 garlic, 46:1–38 ginger, 30:297–299; 39:273–388 gourd history, 25:71–170 grafting, 28:61–124

404 Vegetable crops, see Specific crop: (cont’d) greenhouse management, 21:1–39 greenhouse pest management, 13:1–66 greenhouses in China, 30:126–141 honey bee pollination, 9:251–254 horseradish, 35:221–265 hot water treatment, 38:191–212 hydroponics, 7:483–558 Jerusalem artichoke postharvest physiology & storage, 30:271–276 lettuce seed germination, 24:229–275 low‐temperature sweetening, 17:203–231 melon, 36:165–198 melon grafting, 28:96–98 melon vine decline, 39:77–120 minor root & tubers, 12:184–188 mushroom cultivation, 19:59–97 mushroom spawn, 6:85–118 nightshades, renaissance history, 40:147–182 nondestructive postharvest quality evaluation, 20:1–119 nutrition, 22:185–223 okra, 21:41–72 oomycete, cucurbits, 44:229–278 organic research, 43:185–267 packaging, modified humidity, 37:281–329 pepper phytochemicals, 28:161–162 phytochemicals, 28:125–185 plug industry & technology, 35:387–436 pointed gourd, 39:203–238; 41:475–484 potato low temperature sweetening, 30:317–353 potato phytochemicals, 28:160–161 potato postharvest physiology & storage, 30:271–276 potato tuberization, 14:89–188 pumpkin history, 25:71–170 rhubarb, 40:147–182 root & tuber postharvest & storage, 30:295–297 seed conditioning, 13:131–181 seed priming, 16:109–141 snake gourd, 41:457–475 squash history, 25:71–170 steroidal alkaloids, Solanaceae, 25:171–196

Cumulative Subject Index sweet potato, 12:170–176 sweet potato physiology, 23: 277–338; 42:157–208 tomato chilling injury, 44:229–278 tomato fruit ripening, 13:67–103 tomato (greenhouse) fruit cracking, 30:163–184 tomato (greenhouse) quality, 26:239–319 tomato parthenocarpy, 6:65–84 tomato phytochemicals, 28:160 tropical production, 24:139–228 truffle cultivation, 16:71–107 watermelon, fusarium wilt, 42:349–441 watermelon grafting, 28:86–91 world industry, 38:299–356 yam (Dioscorea), 12:177–184 Vegetative growth, impacts of rootstocks, 46:47–51 Vegetative morphology and growth, durian, 47:142–144, 148–149 Vegetative tissue, desiccation tolerance, 18:176–195 Vernalization, 4:117; 15:284–287; 17:73–123; 46:9 Vertebrate pests, 6:253–285 Viburnam, wild of Kazakhstan, 29:361–362 Vigna, see cowpea genetics, 2:311–394 U.S. production, 12:197–222 Vine decline of melon, 39:77–120 Vines, biology and physiology, 38:1–21 Viroid, dwarfing for citrus, 24:277–317 Virus: apple rootstocks, 45:244–250 benefits in horticulture, 3: 394–411 dwarfing for citrus, 24:277–317 elimination, 7:157–200; 9:318; 18:113–123; 28:187–236 fig, 12:474–475 tree short life, 2:50–51 turnip mosaic, 14:199–238 Volatiles, 17:43–72; 24:31–53; 28:237–324 Vole, 6:254–274 Voynich codex, 44:1–64 Walnut: in vitro culture, 9:312 wild of Kazakhstan, 29:369–370

Cumulative Subject Index Water relations: apple, 45:350–351 citrus, 30:37–83 container‐grown ornamentals, 38:253–297 cut flower, 3:61–66; 18:1–85; 40:14–18, 55–106 deciduous orchards, 21:105–131; 32:111–165; 38:149–189 deficit irrigation, 21:105–131; 32: 111–165; 38:149–189; 45:350–351 desiccation tolerance, 18:171–213 fertilization, greenhouse crops, 1:117–124 grape & grapevine, 27:189–225; 45:349–350 kiwifruit, 12:332–339 light in orchards, 2:248–249 packaging, modified humidity, 37:281–329 photosynthesis, 11:124–131; 45:349–351 stress monitoring, 45:54–56 trickle irrigation, 4:1–48 Watercore, 6:189–251 apple, 6:189–251 pear, 11:385–387 Watermelon: fertilization, 1:124 fusarium wilt, 42:349–441 grafting, 28:86–91 Water relations, rootstocks, 46: 54–65 Wax apple, CA & MA, 22:164 Waxes, 23:1–68 Weed control, ginseng, 9:228–229 Weeds: invasive, 32:379–437 lettuce research, 2:198 parasitic, 33:267–349 ragwort, 43:145–183 virus, 3:403 Wild fruit & nuts of Kazakhstan, 29:305–371 almond, 29:262–265 apple, 29:63–303, 305–315 apricot, 29:325–326 barberry, 29:332–336 bilberry, 29:347–348 blackberry, 29:345 cherry, 29:326–330

405 cotoneaster, 29:316–317 cranberry, 29:349 currant, 29:341 elderberry, 29:349–350 gooseberry, 29:341–342 grape, 29:342–343 hazelnut, 29:365–366 lingonberry, 29:348–349 mountain ash, 29:322–324 mulberry, 29:350–351 oleaster, 29:351–353 pear, 29:315–316 pine, 29:368–369 pistachio, 29:366–368 plum, 29:330–332 raspberry, 29:343–345 rose, 29:353–360 sea buckthorn, 29:361 strawberry, 29:347 vacciniums, 29:347–349 viburnam, 29:361–362 walnut, 29:369–370 Willow, see Salix Withania spp., history & iconography, 34:19–20 Woodchuck, 6:276–277 Woody species, somatic embryogenesis, 10:153–181 Xanthomonas phaseoli, 3:29–32, 41, 45–46 Xanthophyll cycle, 18:226–239 Xanthosoma, 8:45–46, 56–57. See also Aroids Yam (Dioscorea), 12:177–184 Yield: determinants, 7:70–74, 97–99 limiting factors, 15:413–452 Zantedeschia, see Aroids, ornamental Zephyranthes, 25:60–61 Zinc: deficiency & toxicity symptoms in fruits & nuts, 2:151 foliar application, 6: 332, 336 nutrition, 5:326; 23:109–178 pine bark media, 9:124 Zingiber officinale, see Ginger Ziziphus jujuba, see Jujube Ziziphus mauritiana, see Ber

Cumulative Contributor Index

(Volumes 1–47) Aarthi, S., 46:99 Abbott, J.A., 20:1 Adams III, W.W., 18:215 Afek, U., 30:253 Aharoni, N., 37:281 Albrigo, L.G., 34:277 Aldwinckle, H.S., 1:423; 15:xiii; 29:1 Allen, A.C., 38:357 Alonso, J.M., 34:197 Alsanius, B., 43:185 Aly, R., 33:267 Amarante, C., 28:161 Anderson, I.C., 21:73 Anderson, J.L., 15:97 Anderson, P.C., 13:257 Andrews, P.K., 15:183 Ascough, G.D., 34:417 Ashworth, E.N., 13:215; 23:1 Asokan, M.P., 8:43 Atkinson, D., 2:424 Aung, L.H., 5:45 Babadoost, M., 35:221; 44:279 Badillo, V.M., 47:289 Bailey, W.G., 9:187 Baird, L.A.M., 1:172 Baldwin, E., 44:315 Banks, N.H., 19:217; 25:197; 26:161 Bara, G.T., 47:325 Barden, J.A., 9:351 Barker, A.V., 2:41; 36:xiii Barney, D.L., 40:147 Barranco, D., 41:303

Bartz, J.A., 30:185; 33:351 Bar‐Ya’akov, I., 35:127 Basile, B., 46:39 Bass, L.N., 2:117 Bassett, C.L., 26:49 Batlle, I., 41:385 Becker, J.S., 18:247 Beckerman, J.L., 44:363 Beer, S.V., 1:423 Behboudian, M.H., 21:105; 27:189; 38:149 Behera, S., 37:101 Behera, T.K., 37:101; 41:457 Ben‐Jaacov, J., 32:167 Bennett, A.B., 13:67 Benschop, M., 5:45; 36:1 Ben‐Ya’acov, A., 17:381 Ben‐Yehoshua, L.J., 40:183 Ben‐Yehoshua, S., 37:281; 39:1; 40:183 Benzioni, A., 17:233 Bevington, K.B., 24:277 Bewley, J.D., 18:171 Bharathi, L.K., 37:101; 41:457 Bieleski, R.L., 35:xiii Binder, B.M., 35:263 Binzel, M.L., 16:33 Biswas, P., 44:229 Blanpied, G.D., 7:xi Blenkinsop, R.W., 30:317 Bliss, F.A., 16:xiii; 28:xi Boardman, K., 27:xi Bolt, J.K., 42:209 Bono, D., 39:153 Borochov, A., 11:15 Borowitz, C., 39:2

Horticultural Reviews, Volume 47, First Edition. Edited by Ian Warrington. © 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc. 406

CUMULATIVE CONTRIBUTOR INDEX Both, A.J., 43:1 Botton, A., 46:185 Bounous, G., 31:293 Bourget, C.M., 43:1 Bower, J.P., 10:229 Bowling, A.J., 38:1 Bradeen, J.M., 38:357; 46:227 Bradley, G.A., 14:xiii Brandenburg, W., 28:1 Brecht, J.K., 30:185 Brennan, R., 16:255 Broadbent, P., 24:277 Broschat, T.K., 14:1; 42:1 Brown, S., 15:xiii Buban, T., 4:174 Bukovac, M.J., 11:1 Burdon, J.N., 46:385 Burger, Y., 36:165 Burke, M.J., 11:xiii Burr, J.F., 43:1 Buwalda, J.G., 12:307 Byers, P.L., 37:213 Byers, R.E., 6:253; 28:351 Calama, R., 39:153 Caldas, L.S., 2:568 Campbell, L.E., 2:524 Cantliffe, D.J., 16:109; 17:43; 24:229; 28:325; 35:397 Carter, G., 20:121 Carter, J., 35:193 Carter, J.V., 3:144 Castro‐Garcia, S., 41:303 Cathey, H.M., 2:524 Chakrabarti, S.K., 42:157 Chambers, R.J., 13:1 Chandler, C.K., 28:325 Charlebois, D., 37:213 Charles, J., 34:447 Charron, C.S., 17:43 Chen, J., 31:47 Chen, K., 30:83 Chen, Z., 25:171 Chin, C.K., 5:221 Clark, J.R., 41:241; 43:xiii Clarke, N.D., 21:1 Coetzee, J.H., 26:1 Cohen, M., 3:394 Cohen, R., 36:165; 39:77 Cohen, S., 37:281

407 Collier, G.F., 4:49 Collins, G., 25:235 Collins, W.L., 7:483 Colmagro, S., 25:235 Compton, M.E., 14:239 Connor, D.J., 31:157; 41:303 Conover, C.A., 5:317; 6:119 Coombs, B., 32:xi Coppens d’Eeckenbrugge, G., 21:133 Corelli‐Grappadelli, L., 32:63 Costa, G., 28:351; 46:185 Costes, E., 32:1 Coyne, D.P., 3:28 Crane, J.C., 3:376 Criley, R.A., 14:1; 22:27; 24:x Cronjé, P.J.R., 41:131, 177 Crosby, K.M., 39:77 Crowley, W., 15:1 Cuevas, J., 34:239 Curry, C.J., 43:1 Cutting, J.G., 10:229 Daie, J., 7:69 Dale, A., 11:185; 16:255 Darnell, R.L., 13:339; 28:325 Daunay, M.‐C., 34:1; 40:215 Davenport, T.L., 8:257; 12:349; 31:113 Davies, F.S., 8:129; 24:319 Davies, P.J., 15:335 Davis, T.D., 10:63; 24:55 Decker, H.F., 27:317 DeEll, J.R., 23:69 DeGrandi‐Hoffman, G., 9:237 De Hertogh, A.A., 5:45; 14:57; 18:87; 25:1; 36:1 Deikman, J., 16:1 DeJong, T.M., 46:39 DellaPenna, D., 13:67 DeLong, J.M., 32:299 Demers, D.‐A., 30:163 Demmig‐Adams, B., 18:215 Dennis, F.G., Jr., 1:395 Dickson, E.E., 29:1 Dole, J.M., 44:121 Dorais, M., 26:239; 30:163; 43:185 Doud, S.L., 2:1 Dudareva, N., 24:31 Duke, S.O., 15:371 Dunavent, M.G., 9:103

408 Duval, M.‐F., 21:133 Düzyaman, E., 21:41 Dyer, W.E., 15:371 Dzakovich, M.P., 43:1 Dzhangaliev, A.D., 29:63, 305 Early, J.D., 13:339 East, A.R., 44:229 Eastman, K., 28:125 Egea‐Cortines, M., 41:1 Eizenberg, H., 33:267 Ejeta, G., 33:267 Elfving, D.C., 4:1; 11:229 El‐Goorani, M.A., 3:412 Elliott, M.L., 42:1 Ellingson, E.K., 46:227 Erwin, J.E., 34:417; 42:209 Esan, E.B., 1:1 Esposto, S., 38:83 Evans, D.A., 3:214 Evans, E.A., 43:311 Ewing, E.E., 14:89 Fallik, E., 39:191 Famiani, F., 38:83; 45:371 Farahmand, H., 47:213 Faust, J.E., 44:121 Faust, M., 2:vii, 142; 4:174; 6:287; 14:333; 17:331; 19:263; 22:225; 23:179 Fazio, G., 45:197 Felkey, K., 30:185 Fenner, M., 13:183 Fenwick, G.R., 19:99 Fereres, E., 31:157 Ferguson, A.R., 6:1; 33:1; 46:vi Ferguson, I.B., 11:289; 30:83; 31:233 Ferguson, J.J., 24:277 Ferguson, L., 12:409 Ferree, D.C., 6:155; 31:xi Ferreira, J.F.S., 19:319 Fery, R.L., 2:311; 12:157 Field, S.K., 37:143 Finn, C.E., 37:213; 40:xiii Fischer, R.L., 13:67 Flaishman, M.A., 34:113 Fletcher, R.A., 24:53 Flick, C.E., 3:214 Flore, J.A., 11:111 Forshey, C.G., 11:229 Forsline, P.L., 29:ix; 1

CUMULATIVE CONTRIBUTOR INDEX Franks, R.G., 27:41 Fujiwara, K., 17:125 Gadkar, V., 36:257 Galvano, F., 38:83 Gazit, S., 28:393 Geisler, D., 6:155 Geneve, R.L., 14:265 George, K.J., 33:173 George, W.L., Jr., 6:25 Gerrath, J.M., 13:315 Gil, L., 39:153 Gilley, A., 24:55 Giovannetti, G., 16:71 Giovannoni, J.J., 13:67 Girona, J., 38:149 Glenn, D.M., 31:1; 41:47 Glenn, G.M., 10:107 Goffinet, M.C., 20:ix Golding, J., 42:253; 45:105 Goldman, I.L., 41:xiii Goldschmidt, E.E., 4:128; 30:1; 35:437; 42:xi Goldy, R.G., 14:357 Gómez, C., 43:1 Gomez del Campo, M., 41:303 González‐Martínez, S.C., 39:153 Goodwin, I., 42:253 Gordo, F.J., 39:153 Goren, R., 15:145; 30:1 Gosselin, A., 26:239 Goszczynska, D.M., 10:35 Grace, S.C., 18:215 Gradziel, T.M., 30:xiii; 34:197; 38:23 Graves, C.J., 5:1 Gray, D., 3:1 Greer, D.H., 45:313 Grierson, W., 4:247 Griesbach, R.J., 35:193 Griffen, G.J., 8:291 Grodzinski, G.J., 7:345 Gucci, R., 21:177 Guest, D.I., 17:299 Guiltinan, M.J., 16:1 Gulia, S.K., 35:193 Gupta, K.J., 42:121 Hackett, W.P., 7:109 Halevy, A.H., 1:204; 3:59 Hallett, I.C., 20:121 Hallett, S., 44:65

CUMULATIVE CONTRIBUTOR INDEX Hammerschmidt, R., 18:247 Hanson, E.J., 16:255 Hanuš, L.O., 39:2 Hardie, W.J., 37:143 Hardner, C.M., 35:1 Harker, F.R., 20:121 Hatib, K., 35:127 Heaney, R.K., 19:99 Heath, R.R., 17:43 Helzer, N.L., 13:1 Hendrix, J.W., 3:172 Henny, R.J., 10:1; 31:47 Hergert, G.B., 16:255 Hernández, R., 43:1 Hershenhorn, J., 33:267 Hess, F.D., 15:371 Hetterscheid, W.L.A., 28:1 Hewett, E.W., 44:229 Heyes, J.A., 44:229 Heywood, V., 15:1 Hjalmarsson, I., 27:79–123 Hoagland, L., 44:65 Hodel, D.H., 42:1 Hofmann, T., 40:259 Hoffman, E.W., 45:73 Hogue, E.J., 9:377 Hokanson, S.C., 29:1; 46:227 Holland, D., 35:127 Holford, P., 42:253 Holt, J.S., 15:371 Holzapfel, B.P., 37:143 Hoover, E.E., 38:357; 45:1 Hu, X., 45:143 Huang, H., 33:1 Huber, D.J., 5:169 Huberman, M., 30:1 Hummer, K.E., 38:xiii; 40:147 Hunter, E.L., 21:73 Hurst, S., 34:447 Hutchinson, J.F., 9:273 Hutton, R.J., 24:277 Indira, P., 23:277 Ingle, M., 27:227 Inglese, P., 38:83 Isenberg, F.M.R., 1:337 Iwakiri, B.T., 3:376 Jackson, J.E., 2:208 Jacobs, G., 45:73

409 Jahn, M., 37:v Janick, J., 1:ix; 8:xi; 17:xiii; 19:319; 21:xi; 23:233; 34:1; 35:437; 40:215; 44:1 Jarvis, W.R., 21:1 Jenks, M.A., 23:1 Jensen, M.H., 7:483 Jeong, B.R., 17:125 Jewett, T.J., 21:1 Jiang, C.‐Z., 40:1 Jiang, W., 30:115 Joel, D.M., 33:267 Joiner, J.N., 5:317 Joly, R., 44:xiii Jones, A.M.P., 46:299 Jones, H.G., 7:301 Jones, J.B., Jr., 7:1 Jones, R.B., 17:173 Joseph, J.K., 37:101; 41:452 Kagan‐Zur, V., 16:71 Kalt, W., 27:269; 28:125 Kamenetsky, R., 32:329; 33:123; 36:1; 46:1 Kandiannan, K., 46:99 Kang, S.‐M., 4:204 Kapulnik, Y., 36:257 Karp, A., 34:447 Karp, D., 45:143 Kato, T., 8:181 Katzir, N., 36:165 Kawa, L., 14:57 Kawada, K., 4:247 Kays, S.J., 30:253 Kelly, J.F., 10:ix; 22:xi Kester, D.E., 25:xii Ketsa, S., 47:125 Khan, A.A., 13:131 Khoddamzadeh, A.A., 44:173 Kierman, J., 3:172 Kim, K.‐W., 18:87 Kim, S.‐H., 41:47 Kinet, J.‐M., 15:279 King, G.A., 11:413 Kingston, C.M., 13:407–432 Kirschbaum, D.S., 28:325 Kliewer, W.M., 14:407 Knight, R.J., 19:xiii Knox, R.B., 12:1 Kodad, O., 34:197 Kofranek, A.M., 8:xi

410 Koltai, H., 36:257 Kon, T.M., 46:255 Korcak, R.F., 9:133; 10:183 Kozai, T., 17:125 Krezdorn, A.H., 1:vii Kubota, C., 43:1 Kumar, A., 39:273 Kumar, S., 39:203 Kushad, M.M., 28:125 Kuzovkina, Y.A., 34:447 Labrecque, M., 34:447 Läderach, P., 41:47 Laimer, M., 28:187 Laing, M.D., 47:325 Lakso, A.N., 7:301; 11:111 Lamb, R.C., 15:xiii Lang, G.A., 13:339 Larsen, R.P., 9:xi Larson, R.A., 7:399 Laterrot, H., 34:1 Lauri, P.E., 32:1 Layne, D.R., 31:351 Lea‐Cox, J.D., 38:253 Leal, F., 21:133; 39:389; 47:289 Ledbetter, C.A., 11:159 Lee, J.‐M., 28:61 Lee, S.A., 43:269 Leela, N.K., 46:99 Le Nard, M., 36:1 Levy, Y., 30:37 Lewinsohn, E., 36:165 Li, P.H., 6:373 Liebenberg, M.M., 37:1 Lill, R.E., 11:413 Lin, S., 23:233 Lincoln, N.K., 46:299 Lipton, W.J., 12:69 Littlejohn, G.M., 26:1 Litz, R.E., 7:157 Liu, M., 32:229 Liu, Z., 27:41 Lockard, R.G., 3:315 Loescher, W.H., 6:198 Lokesh, V., 42:121 Lopez, G., 38:149 Lopez, R., 43:1; 44:121 Lopresti, J., 42:253 Lorenz, O.A., 1:79 Lowe, A.J., 35:1

CUMULATIVE CONTRIBUTOR INDEX Lu, R., 20:1 Luby, J.J., 29:1; 38:358 Lurie, S., 22:91–121 Lyrene, P., 21:xi Madani, B., 45:105 Maguire, K.M., 25:197 Magwaza, L.S., 41:131 Mahovic, M.J., 33:351 Majsztrik, J.C., 38:253 Makeshkumar, T., 42:157 Maladi, A., 47:1 Malik, A.U., 31:113 Manivel, L., 22:267 Manjunatha, G., 42:121 Maraffa, S.B., 2:268 Marangoni, A.G., 17:203; 30:317 Marini, R.P., 9:351; 32:63; 45:197 Marinoni, D.T., 31:293 Marlow, G.C., 6:189 Maronek, D.M., 3:172 Marsal, J., 38:149 Martin, G.G., 13:339 Martyn, R.D., 39:77; 42:349 Masiunas, J., 28:125 Mattoo, A.K., 37:331 Max, J.F.J., 40:259 Mayak, S., 1:204; 3:59 Maynard, D.N., 1:79; 35:31 McCollum, G., 44:315 McConchie, R., 17:173 McConnell, D.B., 31:47 McGlasson, B., 42:253 McIvor, I., 34:447 McKeon‐Bennett, M., 43:145 McNicol, R.J., 16:255 Meng, Q., 43:1 Merkle, S.A., 14:265 Merlin, M., 46:299 Merwin, I.A., 34:365 Meyer, M.H., 33:393; 39:121; 42:209 Michailides, T.J., 12:409 Michelangeli de Clavijo, C., 39:389 Michelson, E., 17:381 Michler, C.H., 38:213 Mika, A., 8:339 Miller, A.R., 25:171 Miller, S.S., 10:309 Mills, H.A., 2:411; 9:103 Mills, T.M., 21:105

CUMULATIVE CONTRIBUTOR INDEX Mirshekari, A., 45:105 Mitcham, E.J., 40:107 Mitchell, C.A., 17:1; 43:1 Mizrahi, Y., 18:291, 321 Mohankumar, C.R., 30:355 Molnar, J.M., 9:1 Monk, G.J., 9:1 Monselise, S.P., 4:128 Moore, G.A., 7:157 Mor, Y., 9:53 Morreira, F.A., 43:89 Morris, J.R., 16:255 Morrow, R.C., 43:1 Mu, D., 30:115 Mudge, K., 35:437 Mulwa, R.M.S., 35:221 Murashige, T., 1:1 Mureinik, I., 34:xi Murr, D.P., 23:69 Murray, S.H., 20:121 Mutke, S., 39:153 Myers, P.N., 17:1 Nadeau, J.A., 19:1 Nair, R.R., 33:173; 39:273 Naor, A., 32:111 Nascimento, W.M., 24:229 Nayar, N.W., 36:117 Neal, J., 35:1 Neelwarne, B., 42:121 Neilsen, G.H., 9:377 Nelson, P.V., 26:xi Nerd, A., 18:291, 321 Nicolaï, B.M., 41:131 Niemiera, A.X., 9:75; 32:379 Nirmal Babu, K., 46:99 Nobel, P.S., 18:291 Norman, D.J., 31:47 Norton, M.A., 35:221 Nybom, H., 36:199 Nyujtò, F., 22:225 Oda, M., 28:61 O’Donoghue, E.M., 11:413 Ogden, R.J., 9:103 O’Hair, S.K., 8:43; 12:157 O’Keeffe, C.M., 43:145 Okubo, H., 36:1 Oliveira, C.M., 10:403 Oliver, M.J., 18:171

411 O’Neill, S.D., 19:1 Opara, L.U., 19:217; 24:373; 25:197; 41:131 Ormrod, D.P., 8:1 Ortiz, R., 27:79 Padilla‐Zakour, O.I., 34:365 Palapol, Y., 47:125 Palser, B.F., 12:1 Papadopoulos, A.P., 21:1; 26:239; 30:163 Pararajasingham, S., 21:1 Pareek, S., 41:201 Parera, C.A., 16:109 Paris, H.S., 25:71; 36:165; 40:215 Parthasarathy, V.A., 33:173; 39:273 Paull, R.E., 47:125 Peace, C., 35:1; 41:241 Pegg, K.G., 17:299 Pellett, H.M., 3:144 Perkins‐Veazil, P., 17:267 Petran, A., 45:1 Phillips, G., 32:379 Pichersky, E., 24:31 Pickering, A.H., 35:355 Piechulla, B., 24:31 Pijut, P.M., 389:213 Pisanu, P., 35:1 Ploetz, R.C., 13:257; 43:311 Pokorny, F.A., 9:103 Pomper, K.W., 31:351 Poole, R.T., 5:317; 6:119 Poovaiah, B.W., 10:107 Portas, C.A.M., 19:99 Porter, M.A., 7:345 Possingham, J.V., 16:235 Postman, J., 39:viii Prange, R.K., 23:69; 32:299; 35:263 Prasath, D., 39:273; 46:99 Pratt, C., 10:273; 12:265 Predieri, S., 28:237 Preece, J.E., 14:265 Pretorius, Z.A., 37:1 Priestley, C.A., 10:403 Proctor, J.T.A., 9:187 Puonti‐Kaerlas, J., 26:85 Puterka, G.J., 31:1 Qu, D., 30:115 Quamme, H., 18:xiii

412 Rabinowitch, H.D., 32:329 Raese, J.T., 11:357 Ragone, D., 46:299 Rakow, D.A., 43:269 Rallo, L., 41:303 Rallo, P., 41:303 Ramirez‐Villegas, J., 41:47 Ramming, D.W., 11:159 Ransom, J.K., 33:267 Rapparini, F., 28:237 Ravi, V., 23:277; 30:355; 42:157 Raviv, M., 36:289 Reddy, A.S.N., 10:107 Redgwell, R.J., 20:121 Regnard, J.L., 32:1 Reid, M., 12:xiii; 17:123; 40:1 Reuveni, M., 16:33 Rich, P.J., 33:267 Richards, D., 5:127 Rieger, M., 11:45 Ristvey, A.G., 38:253 Robbins, J.A., 45:33 Roberts‐Nkrumah, L.B., 46:299 Rodov, V., 34:113; 37:281 Romero, A., 41:385 Romero, M.A., 34:447 Roper, T.R., 21:215 Rosa, E.A.S., 19:99 Roth‐Bejerano, N., 16:71 Roubelakis‐Angelakis, K.A., 14:407 Rouse, J.L., 12:1 Royse, D.J., 19:59 Rubiales, D., 33:267 Rudnicki, R.M., 10:35 Ruiz‐Ramon, F., 41:1 Runkle, E.S., 43:1 Ryder, E.J., 2:164; 3:vii; 38:299 Sachs, R., 12:xiii Sakai, A., 6:357 Salisbury, F.B., 4:66; 15:233 Salova, T.H., 29:305 Saltveit, M.E., 23:x; 30:185 San Antonio, J.P., 6:85 Sanderfur, P., 41:241 Sankhla, N., 10:63; 24:5 Saravanan, R., 42:157 Sargent, S.A., 35:315 Sasikumar, B., 33:173; 46:99 Sauerborn, J., 33:267

CUMULATIVE CONTRIBUTOR INDEX Saure, M.C., 7:239 Schaffer, A.A., 36:165 Schaffer, B., 13:257 Schenk, M.K., 22:185 Schneider, G.W., 3:315 Schneider, K.R., 30:185; 33:351 Schotsmans, W.C., 35:263 Schupp, J.R., 46:255 Schurr, U., 40:259 Schuster, M.L., 3:28 Scofield, A., 35:437 Scorza, R., 4:106 Scott, J.W., 6:25 Sedgley, M., 12:223; 22:1; 25:235 Seeley, S.S., 15:97 Serrano Marquez, C., 15:183 Servili, M., 38:83 Sharp, W.R., 2:268; 3:214 Sharpe, R. H., 23:233 Shattuck, V.I., 14:199 Shear, C.B., 2:142 Sheehan, T.J., 5:279 Shehata, A., 35:221 Shemesh‐Mayer, E., 46:1 Shipp, J.L., 21:1 Shirra, M., 20:267 Shivashankar, S., 42:313 Shorey, H.H., 12:409 Silber, A., 32:167 Silva Dias, J., 38:299 Simon, J.E., 19:319 Simon, P.W., 37:101 Singh, B.D., 39:203 Singh, B.P., 35:193 Singh, N.B., 34:447 Singh, S.H., 34:277 Singh, Z., 27:189; 31:113; 42:121 Skirvin, R., 35:221 Sklensky, D.E., 15:335 Smart, L.B., 34:447 Smith, A.H., Jr., 28:351 Smith, G.S., 12:307 Smith, J.P., 37:143 Smith, M.A.L., 28:125 Smock, R.M., 1:301 Socias i Company, R., 34:197 Sommer, N.F., 3:412 Sondahl, M.R., 2:268 Sopp, P.I., 13:1 Soule, J., 4:247

CUMULATIVE CONTRIBUTOR INDEX Sozzi, G.O., 27:125 Sparke, M.A., 47:43 Sparks, D., 8:217 Splittstoesser, W.E., 6:25; 13:105 Spooner, D.M., 28:1 Srinivasan, C., 7:157 Srinivasan, V., 39:273 Srivastava, A.K., 34:277 Stander, O.P.J., 41:177 Stang, E.J., 16:255 Staub, J.E., 37:101 Steffens, G.L., 10:63 Stern, R.A., 28:393 Stevens, M.A., 4:vii Steyn, W.J., 39:239 Stoffella, P.J., 33:xi Stover, E., 34:113 Stroshine, R.L., 20:1 Struik, P.C., 14:89 Studman, C.J., 19:217 Stundin, G.W., 44:361 Stutte, G.W., 13:339; 43:145 Styer, D.J., 5:221 Sunderland, K.D., 13:1 Sung, Y., 24:229 Surányi, D., 19:263; 22:225; 23:179 Sureja, A.K., 41:457 Swanson, B., 12:xiii Swietlik, D., 6:287; 23:109 Syvertsen, J.P., 7:301; 30:37 Tadmor, Y., 36:165 Talcott, S.T., 30:185 Tantau, H.‐J., 40:259 Tattini, M., 21:177 Teasdale, J.R., 37:331 Tellias, A., 38:357 Teodorescu, T.L., 34:447 Terry, L.A., 41:131 Tétényi, P., 19:373 Theron, K.I., 25:l; 41:177 Thomas, A.L., 37:213 Tibbitts, T.W., 4:49 Timon, B., 17:331 Tindall, H.D., 16:143 Tisserat, B., 1:1 Titus, J.S., 4:204 Toner, E., 44:65 Tonetto de Freitas, S., 40:107 Tous, J., 41:385

413 Trigiano, R.N., 14:265 Trybush, S., 34:447 Tucker, A.o., 44:1 Tunya, G.o., 13:105 Turekhanova, P.M., 29:305 Uchanski, M., 35:221 Ulbrich, A., 40:259 Upchurch, B.L., 20:1 Urbani, S., 38:83 Valenzuela, H.R., 24:139 Valois, S., 34:365 van den Berg, W.L.A., 28:1 van Doorn, W.G., 17:173; 18:1; 40:55 Van Iepersen, W., 30:163 van Kooten, o., 23:69 van Nocker, S., 27:1 van Staden, J., 34:417 Vardien, W., 45:73 Vaughn, K.C., 38:1 Veilleux, R.E., 14:239 Vendrame, W.A., 44:173 Verlinden, S., 47:85 Vizzotto, G., 28:351; 46:185 Volk, T.A., 34:447 Vorsa, N., 21:215 Walker, R.P., 45:371 Wallace, A., 15:413 Wallace, D.H., 17:73 Wallace, G.A., 15:413 Walters, S.A., 35:221 Wang, C.Y., 15:63 Wang, L., 30:115 Wang, S.Y., 14:333 Wann, S.R., 10:153 Warrington, I.J., 35:355; 45:xii; 47:xi Watkins, C.B., 11:289 Watson, G.W., 15:1 Webster, B.D., 1:172; 13:xi Wehner, T.C., 41:457 Weichmann, J., 8:101 Weih, M., 34:447 Weiss, J., 41:1 Werlemark, G., 36:199 Wetzstein, H.Y., 8:217 Whiley, A.W., 17:299 Whitaker, T.W., 2:164

414 White, J.W., 1:141 Williams, E.G., 12:1 Williams, M.W., 1:270 Windell, N.E., 45:73 Wismer, W.V., 17:203 Wisutiamonkul, A., 47:125 Wittwer, S.H., 6:xi Woeste, K.E., 38:213 Woodson, W.R., 11:15 Woolley, D.J., 35:355 Wright, R.D., 9:75 Wünsche, J.N., 31:23; 47:43 Wutscher, H.K., 1:237 Xu, C., 30:83

CUMULATIVE CONTRIBUTOR INDEX Yada, R.Y., 17:203; 30:317 Yadava, U.L., 2:1 Yahia, E.M., 16:197; 22:123; 41:201; 45:105 Yan, W., 17:73 Yarborough, D.E., 16:255 Yelenosky, G., 7:201 Zachariah, T.J., 39:273 Zanini, E., 16:71 Zerega, N., 46:299 Zhang, B., 30:83 Zieslin, N., 9:53 Zimmerman, R.H., 5:vii; 9:273 Ziv, M., 24:1 Zucconi, F., 11:1

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