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Table of contents :
Volume VI: Is a supplementary volume and includes chapters on plants not included in volumes I to IV, listed in alphabetical order.
CRC Handbook of Flowering Volume VI Editor
Abraham H. Halevy
Professor Department of Ornamental Horticulture The Hebrew University of Jerusalem Rehovot Israel
Boca Raton London New York
CRC Press is an imprint of the Taylor & Francis Group, an informa business
First published 1989 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 Reissued 2018 by CRC Press © 1989 by CRC Press, Inc. CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright. com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data (Revised for vol. 6) CRC handbook of flowering (Includes bibliographies and indexes. 1. Plants, Flowering of—Handbooks, manuals, etc. 2. Plants, Cultivated—handbooks, manuals, etc. I. Halevy, Abraham H., 1927II. Handbook of flowering. SB126.8.C73 1985 635.9 83-21061 ISBN 0-8493-3910-3 (set) ISBN 0-8493-3911-1 (v. 1) Publisher’s Note The publisher has gone to great lengths to ensure the quality of this reprint but points out that some imperfections in the original copies may be apparent. Disclaimer The publisher has made every effort to trace copyright holders and welcomes correspondence from those they have been unable to contact. ISBN 13: 978-1-315-89348-8 (hbk) ISBN 13: 978-1-351-07258-8 (ebk) Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com
FOREWORD Life would be awfully dull without flowers. The love of flowers is common to all people all over the world, no matter how different their cultural patterns may be. Artistically, flowers play an important role in poetry and in decorative arts for their attractive structure, color and odor in endless variation: for their eternal beauty. Agriculturally, and perhaps still more so horticulturally, flowers play an essential part in the production of all crops. This is, of course, most evident in floriculture, where the flower is the final product. In all fruit crops, whether deciduous or evergreen, and in crops like grains and the fruit-vegetables, the fruit is the final product, but flowers are the indispensable introductory step to fruit formation. For the many crops which are grown for their seeds, including all breeding projects, flowers and fruits cannot be missed for seed formation. On the other hand, there are crops where flowers and fruits are undesirable — for instance, those which are grown for their roots, stems, or leaves. However, in seed growing and breeding of these crops, flowers again are indispensable. The above implies that control of flowering, whether positively promoting or negatively preventing flowering, is a cultural measure which has to be applied in the growing of most, if not all, crops. No wonder that in several cases more or less sophisticated methods for controlling flowering are rather well known. Quite generally, such empirically developed methods are genetical and ecological, but an endless variation occurs in the requirements for flowering among different species and even among the cultivars of one species. The human mind is not satisfied by answering the question as to which factors influence flowering — as approached empirically — it also wants to know the physiological background of the actions of these factors. This is a much more difficult problem, and disciplines like biophysics, biochemistry, and molecular biology enter the picture. It is self-evident that this approach has made much less progress than the empirical one. However, it has become clear that also in this respect an endless variation occurs among different species and that a general mechanism of action — if it exists — has not been found yet. Be that as it may, the study of flowering, whether empirical or — on a higher level — physiological, contributes to the development of the human mind by the attempt to understand some of the mysteries of Life. In the foregoing I used "endless variation" no less than three times, and students of flowering, who concentrate on their own plant(s), run the risk of becoming one-sided. It is, therefore, highly important to provide them with a catalogue of the flowering behavior of as many other plants as possible. The present Handbook fills the existing gap by bringing together our knowledge of the individual cases. The "Table of Contents" illustrates that it was no simple effort to compose this edition. A. H. Halevy, "Abe" to his friends, has had the courage and the energy to undertake this task. All those who are interested in flowering in some or other way owe him their gratitude. S. J. Wellensiek
PREFACE Rise up, my love, my fair one, and come away. For, lo, the winter is past, The rain is over and gone; The flowers appear on the earth; The time of singing is come, And the voice of the turtledove is heard in our land; The fig tree puts forth her green f i g s , And the vines in blossom give forth their fragrance.
(Song of Songs 2:10—13) From antiquity, poets have expressed humanity's association of flowering with spring, renewal, singing, beauty, fragrance, and love. This book deals with the more prosaic aspects of flowering: flower formation and development and the environmental and physiological factors which regulate them. Several excellent reviews and books on flowering have been published in the last 25 years. These include Lang's 6 and SchwabeV chapters in general encyclopedias of plant physiology, Evans' opening and concluding chapters in his book,4 the books by Salisbury,8 Vince-Prue," and Bernier et al. 1 - 13 and the several review articles in the Annual Reviews of Plant Physiology.2-*^-1 • 1 ( U 2 With the exception of Evans, 4 these authors have presented a general review of the flowering process and attempted to integrate the data into a unifying theory. Such unifying theories have generally suffered from the disadvantages noted by Evans in the preface to his book;4 they deal primarily with the earliest events of the flowering process, and they are based on data obtained from a small number of "model" plants. Evans' book, which contains flowering "case histories" of the majority of these species, includes chapters on only 20 plants, of which only one is a woody plant, two are monocotyledons, and none is a gymnosperm. A great wealth of data on the regulation of flower formation and development can be found in the practical literature of agriculture, horticulture, and forestry. Much of this has been often ignored by flowering physiologists. The flowering process is indeed much more diverse than that revealed in the 20 "model" plants presented in Evans' book. It was my aim in planning this book to make a more comprehensive view of the flowering process possible by presenting relevant data from as many plants as possible. This includes the majority of the cultivated plants on which such information is available: field crops, fruits, vegetables, ornamentals, industrial plants, and forest trees, not only of the temperate regions, but also of subtropical and tropical climates. To accomplish this goal I have invited scientists from all over the world to contribute chapters on specific plants or groups of plants. Many of the authors have not only reviewed the available literature, but have also included previously unpublished data. Many of the chapters present the first general review of the flowering process in their specific subject area. The book deals with all aspects of flowering, including juvenility and maturation, flower morphology, flower induction, and morphogenesis to anthesis. Flower morphogenesis has been taken to include also development of individual flower parts, sex expression, and flower malformations. When possible, the authors have attempted to present information on all stages of the flowering process. In many cases, however, this has not been feasible, since little or nothing is known about some of the stages. In most cases the "flowering story" is terminated at anthesis. In some plants, however, flower structure and anthesis are directly
related to pollination, and in these cases pollination is also included. In some commercial food crops the description is also extended somewhat beyond anthesis to include important factors in crop production. In many cultivated plants, mostly ornamentals, practical methods for manipulation of flowering are included. The length of the individual chapters and the emphasis on specific aspects depends in most cases on the availability of experimental information and not on the importance of the plant as a crop or the significance of the physiological stage described. Some important economic plants are absent from this book since little or no information is available on their flowering. In some cases most of the chapter is devoted to a single aspect of flowering, such as juvenility, flower induction, flower development, sex expression, cleistogamy, development of certain flower parts, or flower opening. Some chapters concentrate on physiological aspects, others on ecological, morphological or genetic ones. Other aspects are covered only briefly or even absent, not because they are not important but because they have not been studied in detail. I am well aware that this book is far from being a comprehensive encyclopedia of flowering, I would greatly appreciate comments from readers on errors found in articles, missing information, and plants not included in the book, whose flowering process have been documented. The handbook consists of six volumes: • • • • • •
Volume I — contains general chapters on groups of plants, and individual chapters on plants beginning with the letter A Volume II — contains plants of letters B to E Volume III — contains plants of letters F to O Volume IV — contains plants of letters P to Z Volume V — is a supplementary volume and includes chapters on plants not included in Volumes I to IV, listed in alphabetical order. Volume VI — a second supplementary volume
The merit of the book rests upon the work of the individual authors. I am grateful to them for their efforts, cooperation, and forbearance. I would like to thank my colleagues in the Editorial Board who helped me to select the authors and to review the chapters, and the many other colleagues who helped in reviewing (and sometimes rewriting) specific chapters. I hope that this handbook will serve as a reference and source book for scientists interested in the flowering process of particular plants, and will draw their attention to the lack of information on important aspects of the flowering process in many important plant species. I also hope that the wealth of information accumulated here will be useful in future attempts to synthesize general theories of the physiology of flowering.
REFERENCES 1. Bernier, G., Kinet, J. M., and Sachs, R. M., The Physiology of Flowering, CRC Press, Boca Raton, Fla., 1981, Vol. 1, 149; Vol. 2, 231. 2. Chouard, P., Vernalization and its relation to dormancy, Annu. Rev. Plant Physiol., 11, 191—238, 1960. 3. Doorenbos, J. and Wellensiek, S. J., Photoperiodic control of floral induction, Annu. Rev. Plant Physiol., 10, 147—184, 1959. 4. Evans, L. T., Ed., The Induction of Flowering. Some Case Histories, Macmillan, Melbourne, 1969, 328. 5. Evans, L. T., Flower induction and the flowering process, Annu. Rev. Plant Physiol., 22, 365—394, 1971.
6. Lang, A., The physiology of flower initiation, in Encyclopedia of Plant Physiology, Vol. 15 (Part I), Ruhland, W., Ed., Springer-Verlag, Berlin, 1965, 1380—1563. 7. Salisbury, F. B., The Flowering Process, Pergamon Press, Oxford, 1963, 234. 8. Salisbury, F. B., Photoperiodism and the flowering process, Anna. Rev. Plant Physiol., 12, 293—326, 1961. 9. Schwabe, W. W., Physiology of vegetative reproduction and flowering, in Plant Physiology, A Treatise, Steward, F. C., Ed., Vol. VI-A, Academic Press, New York, 1971, 233^11. 10. Searle, N. E., Physiology of Flowering, Anna. Rev. Plant Physiol., 16, 97—118, 1965. 11. Vince-Prue, D., Photoperiodism in Plants, McGraw Hill, London, 1975, 444. 12. Zeevaart, J. A. D., Physiology of flower formation, Annu. Rev. Plant Physiol., 27, 321—348, 1976. 13. Kinet, J. M., Sachs, R. M., and Bernier, G., The Physiology of Flowering, Vol. 3, CRC Press, Boca Raton, Fla., 1985, 274.
Abraham H. Halevy
PREFACE Volume VI This final second supplementary volume of the Handbbook of Flowering is the largest of this treatise, containing 84 chapters by 80 authors. As with Volume V, some of the included chapters were planned for earlier volumes and some were commissioned specifically for this volume. In a few cases, I invited colleagues to contribute new chapters on plants already previously described (Anigozanthus, Trifolium, Zantedeschia), when I realized that important information had not been included in earlier chapters. This volume includes a major contribution by Anton Lang on Nicotiana and four major chapters on coniferous forest trees, as well as others on important crops and model plants of flowering physiology. The six volumes of this encyclopedia include 380 chapters on specific plants or groups of plants, written by more than 250 authors. Since these plants were arranged three times in alphabetical order in Volumes I to IV, V, and VI, and many plants were described in general chapters according to categories (e.g., Forage Plants), we have included a comprehensive taxonomic index of all the plants mentioned in Volumes I through VI. Although this Handbook is the most comprehensive book on flowering published to date, I am well aware that it does not contain all the relevant available information on the subject. Almost 20 years have passed since the publication of Evans' book and this final volume of the present Handbook. I sincerely hope that a second, better, and more comprehensive edition of the Handbook of Flowering will be published in less time. I have worked on this book for more than 8 years. Many colleagues have helped me carry out this undertaking, for which I am very grateful. I would especially like to thank Mr. and Mrs. Carl Pearlstein and their family of San Francisco, who so generously supported the research on flowering in my laboratory during the last 10 years. Without their continuous help and interest, it would have been impossible for me to continue my research activities while working on the book.
Abraham H. Halevy
THE EDITOR Abraham H. Halevy, Ph.D., is Professor of Horticulture and Plant Physiology at the Hebrew University of Jerusalem, Rehovot, Israel. Dr. Halevy obtained his M.Sc. and Ph.D. degrees from the Hebrew University in 1953 and 1958, respectively. Dr. Halevy was a Research Fellow at the U.S. Department of Agriculture Research Center at Beltsville, Md. (1958 to 1959) and has been a Visiting Professor at Michigan State University (1964 to 1965) and the University of California, Davis (1970 to 1971, 1982 to 1984, and 1986). He has twice received the Alex Laurie award of the American Scoiety of Horticultural Science, and was recently (1983) nominated as a fellow of the society. Dr. Halevy is the Editor-in-Chief of the Israel Journal of Botany and the Flowering Newsletter. He has published over 200 scientific papers in international journals, and has been a guest invited lecturer in numerous symposia around the world. His current research interests are the regulation of flowering and of flower senescence.
CONTRIBUTORS Aage S. Andersen, Ph.D. Department of Horticulture Agricultural University Copenhagen Denmark Vera M. Andrade, Dr. in Sciences Department of Applied Biology UNESP Jaboticabal, Sao Paulo Brazil Allan M. Armitage, Ph.D. Department of Horticulture University of Georgia Athens, Georgia Yolande Arnaud Laboratoire du Physiologie du Developpement des Plantes Universite Pierre et Marie Curie (Paris VI) Paris France Tova Arzee, Ph.D. Department of Botany Tel Aviv University Tel Aviv Israel Amos Blumenfeld, Ph.D. Department of Subtropical Horticulture Volcani Center Agricultural Research Organization Bet Dagan Israel Bertrand Boeken, Ph.D. Department of Biology and Jacob Blaustein Institute for Desert Research Sede Boqer Campus Israel J. Br0ndum-Pedersen Research Centre for Horticulture Institute of Glasshouse Crops Arslev Denmark
Osvaldo H. Caso, Dr. in Natural Sciences Centre de Ecofisiologia Vegetal CONICET Buenos Aires Argentina Michael St. John Clowes, D.Phil. Tea Research Foundation Mulanje Malawi Lila Cohen, Ph.D. Department of Botany Tel Aviv University Tel Aviv Israel Anthony J. Davy, Ph.D. School of Biological Sciences University of East Anglia Norwich England August A. De Hertogh, Ph.D. Department of Horticultural Science North Carolina State University Raleigh, North Carolina Tom J. de Jong, Ph.D. Department of Population Biology University of Leiden Leiden Netherlands Nativ Dudai Experiment Station, Newe Ya'ar Agricultural Research Organization Haifa Israel Rivka Dulberger, Ph.D. Department of Botany G.S. Wise Center for Life Sciences Tel Aviv University Ramat Aviv Israel
L. T. Evans, Ph.D.
Division of Plant Industry Commonwealth Scientific and Industrial Research Organization Canberra, Australian Capital Territory, Australia
John David Faragher, Ph.D. Department of Agriculture and Rural Affairs Horticultural Research Institute Ferntree Gully, Victoria Australia D. Carl Freeman, Ph.D. Department of Biological Sciences Wayne State University Detroit, Michigan Jacob Galil, Ph.D. Department of Botany George S. Wise Faculty of Life Sciences Tel Aviv University Ramat Aviv Israel Kristin L. Groom Botany Department University of Tasmania Hobart, Tasmania Australia Yitzchak Gutterman, Ph.D. Department of Biology and Jacob Blaustein Institute for Desert Research Ben Gurion University of the Negev Sede Boqer Campus Israel Abraham H. Halevy, Ph.D. Department of Ornamental Horticulture Hebrew University of Jerusalem Rehovot Israel Ola M. Heide, Dr. Agric. Department of Botany Agricultural University of Norway
Richard J. Henny, Ph.D. Agricultural Research and Education Center-Apopka University of Florida Apopka, Florida Niels Holmenlund, Ph.D. Horticultural School Vilvorde Tollose Denmark Roger F. Horton, D. Phil. Department of Botany College of Biological Science University of Guelph Guelph, Ontario Canada Hideo Imanishi, Dr. Agric. Department of Horticultural Science and Agronomy University of Osaka Prefecture Sakai, Osaka Japan Reuven Jacobsohn, Ph.D. Department of Vegetable Crops Agriculture Research Organization Volcani Center Bet Dagan Israel Monique Jacques, Dr. es Sc. Laboratoire du Phytotron Centre National de la Recherche Scientifique Gif-sur-Yvette France Roger Jacques, Dr. es Sc. Laboratoire du Phytotron Centre National de la Recherche Scientifique Gif-sur-Yvette France Ichiro Kajiura, Ph.D. National Institute of Agrobiological Resources Tsukuba, Ibaraki Japan
Jawahir L. Karihaloo, Ph.D. Division of Ornamental Crops Indian Institute of Horticultural Research Hessaraghatta Lake, Bangalore India
E. Durant McArthur, Ph.D. Shrub Sciences Laboratory Forest Service U.S. Department of Agriculture Provo, Utah
H. J. Ketellapper, Ph.D. Department of Botany University of California Davis, California
Bastiaan J. D. Meeuse, Dr. Tech. Sci. Botany Department University of Washington Seattle, Washington
Peter G. L. Klinkhamer, Ph.D. Department of Population Biology University of Leiden Leiden, Netherlands
James D. Metzger, Ph.D. Biosciences Research Laboratory Agricultural Research Service U.S. Department of Agriculture State University Station Fargo, North Dakota
Roger M. Knutson, Ph.D. Department of Biology Luther College Decorah, Iowa Gregory P. Lamont NSW Agriculture and Fisheries Horticulture Research and Advisory Station Gosford, New South Wales Australia Anton Lang, Dr. Nat. Sci. MSU-DOE Plant Research Laboratory Michigan State University East Lansing, Michigan Christian Lavigne, Ph.D. IRFA Ste. Marie Confestre Guadeloupe Mexico David B. Layzell, Ph.D. Department of Biology Queen's University Kingston, Ontario Canada K. Allan Longman, Ph.D. ONAREF Yaunde Cameroon
Emile Miginiac, Dr. es Sc. Department of Developemental Plant Physiology Pierre and Marie Curie University Paris France Roar Moe, Dr. Scient. Department of Horticulture Agricultural University of Norway As Norway H. Y. Mohan Ram, Ph.D. Department of Botany University of Delhi Delhi India Glenda S. Motum Horticultural Research and Advisory Station Gosford, N.S.W. Australia Amitabha Mukhopadyay, Ph.D. (deceased) Division of Ornamental Crops Indian Institute of Horticultural Research Hessaraghatta Lake, Bangalore India
Ian C. Murfet, Ph.D. Botany Department University of Tasmania Hobart, Tasmania, Australia
Richard P. Pharis, D.For. Department of Biological Sciences University of Calgary Calgary, Alberta Canada
Akinori Nagao, Dr. Forestry and Forest Products Research Institute Tsukuba Norin Kenkyu Danchi Ibaraki Japan
Usher Posluszny, Ph.D. Department of Botany University of Guelph Guelph, Ontario Canada
Ian B. Norris, Ph.D. Crop Improvement Department Institute for Cropland and Animal Production Welsh Plant Breeding Station Aberystwyth Wales Colin R. Norton, Ph.D. Department of Plant Science University of British Columbia Vancouver, British Columbia, Canada Arlette Nougarede, Dr.es Sc. Department of Experimental Cytology and Plant Morphogenesis Pierre and Marie Curie University Paris France Kiyoshi Ohkawa, Dr.Sci. Department of Horticulture University of Shizuoka Shizuoka-City Japan Robert Ornduff, Ph.D. Department of Botany University of California Berkeley, California J. J. Brondum Pedersen, Ph.D. Research Centre for Horticulture Institute of Glasshouse Crops Arslev Denmark
Robert Poulhe, Ph.D. Department of Physiology of Reproduction University of Paris VI Paris France Eli Putievski, Ph.D. Department of Aromatic Plants Agricultural Research Organization Haifa Israel Yong Qu, Ph.D. Department of Horticulture Oregon State University Corvallis, Oregon Uzi Ravid, Ph.D. Department of Aromatic Plants Experiment Station, Newe Ya'ar Agricultural Research Organization Haifa Israel Mark S. Roh, Ph.D. Florist and Nursery Crops Laboratory Agricultural Research Service U.S. Department of Agriculture Beltsville, Maryland Carlos Ruggiero, Dr.Sci. Fitotecnia Department UNESP Jaboticabal, Sao Paulo Brazil
Satohiko Sasaki, Ph.D. Department of Forestry University of Tokyo Tokyo Japan
Hideyuki Takahashi, Ph.D. Institute of Genetic Ecology Tohoku University Sendai Japan
Amnon Schwartz, Ph.D. Agricultural Botany Department Hebrew University Rehovot Israel
Susan Taylor, Ph.D. (deceased) Department of Horticulture Wye College London University Ashford, Kent England
Walter W. Schwabe, Ph.D., D.Sc. Department of Horticulture Wye College London University Ashford, Kent England Robin Scribailo, Ph.D. Department of Botany University of Toronto Toronto, Ontario Canada Margaret Sedgley, Ph.D. Department of Plant Physiology Waite Agricultural Research Institute University of Adelaide Glen Osmond, South Australia Australia Ruth Shillo, Ph.D. Department of Horticulture Hebrew University of Jerusalem Rehovot Israel Ian A. Staff, Ph.D. Department of Botany La Trobe University Bundoora, Victoria Australia
Benny O. Tjia, Ph.D. Department of Ornamental Horticulture University of Florida Gainesville, Florida Israela Wallerstein, Ph.D. Department of Floriculture and Ornamental Horticulture Volcani Center Agricultural Research Organization Bet Dagan Israel S. J. Wellensiek, Dr. Hort. Sci. Department of Horticulture Agricultural University Wageningen Netherlands Harold F. Wilkins, Ph.D. Department of Horticulture Science University of St. Paul St. Paul, Minnesota Pieter Wolswinkel, Ph.D. Botanical Laboratory State University of Utrecht Utrecht Netherlands
Edward C. Yeung, Ph.D. Department of Biological Sciences University of Calgary Calgary, Alberta Canada Jan A. D. Zeevaart, Ph.D. MSU-DOE Plant Research Laboratory Michigan State University East Lansing, Michigan
Karl Zimmer, Dr.rer.hort. Institute of Ornamental Horticulture University of Hannover Hannover West Germany
TABLE OF CONTENTS
Acacia Aglaonema Agrostemma githago Allium — Ornamental Species Alopecurus pratensis Anigozanthos Arisarum Arum Atriplex canescens Banksia ashbyi Bellevalia desertorum and B. eigii Bidens radiata Blepharis Boronia Bouteloua Bromus inermis Calamintha nepetoides Camellia sinensis Campanula poscharskyana Carlssa Carrichtera annua Caryopteris Chamaecyparis Chondrilla juncea Chrysanthemum segetum Cirsium vulgare Colchicum tunicatum Coreopsis Cryptomeria japonica Cuscuta Cyanella Cynoglossum Deschampsia Diospyros kaki Epilobium adenocaulon Epilobium hirsutum and E. parviflorum Eustoma grandiflorum Exacum Ficus Gentiana Gymnarrhena micrantha Hieracium Hydrocharis Iris ensata Ixora Jasminum auriculatum and J. sambac
1 12 15 22 34 37 47 52 75 87 93 103 108 117 122 128 131 139 146 151 157 162 170 189 196 228 234 243 257 270 275 281 287 298 307 317 322 328 331 351 356 361 365 375 379 387
Jasminum grandiflorum Kleinia articulata and K. repens Lagenaria siceraria Luffa Lychnis X arkwrightii Lysichiton Meconopsis Nicotiana Nopalxochia Oreganum syriacum var. syriacum Orobanche Passiflora Passiflora caerulea Pentas lanceolata Phleum pratense Picea Poa Rottboellia cochinchinensis Salsola inermis and S. volkensii Salvia riparia Schismus arabicus Schizanthus x wisetonensis Sicyos angulatus Sternbergia clusiana Symplocarpos Telopea Themeda australis Thlaspi arvense Thuja Trachelium caeruleum Trifolium repens Trifolium subterraneum Trigonella arabica and T. stellata Tulipa systola Utricularia inflexa var. stellaris Vicia saliva Aggregate Viscaria alba Xanthorrhoea Zantedeschia
395 399 409 412 417 420 423 427 484 487 490 495 507 515 520 522 538 547 553 558 564 569 573 580 589 593 598 601 610 625 630 636 641 648 655 661 669 681 697
Abbreviations and Alternative Names of Chemicals
Taxonomic Index (Volumes I through VI)
ACACIA En. Acacia, Wattle; Fr. Acacia, Mimosa; Ge. Akazie, Schotendorn; Sp. Acacia Margaret Sedgley INTRODUCTION The genus Acacia (Mimosaceae) contains over 1200 species65 with world-wide distribution between the latitudes 35° N and 45° S. 18 The greatest species diversity occurs in Australia where over 800 species are known, with many more as yet. undescribed.46 Acacia is essentially a pantropical genus with relatively few species from the humid tropics or cold climates. Tolerance of arid conditions is considered to be fundamental to the success of the genus in Australia where acacias are a major component of the vegetation.3 The genus is important for timber production, tanning, animal feed, fuel wood, agroforestry, ornamental horticulture, and essential oil production. A particularly important feature of acacias is their nitrogenfixing ability via Rhizobium bacteria in root nodules. 3 Acacia is a woody genus consisting of short- and long-lived perennials varying between small shrubs, climbing lianes, and tall forest trees. Most species are evergreen and there is great diversity in leaf form. Seedlings of all acacia species produce pinnate or bipinnate leaves. In many Australian species, heteroblastic development results in the formation of entire flattened structures termed phyllodes, which generally appear between nodes one and five. 11 - 32 In most other species the pinnate or bipinnate condition persists throughout the life of the plant. Phyllodes were formerly considered to be expanded petioles that developed leaf-like characteristics, but recent work has shown that the phyllode blade is the positional homologue of the lamina region of the dissected leaf. 32 The phyllode is considered to be an adaptation to arid conditions. Extrafloral nectaries or glands occur on the leaf base or lamina of both phyllodinous and pinnate species.9-43-45 They may secrete all year round and appear to have the dual function of attracting ants, which defend the plant against destructive insect herbivores, 4>29 - 31 and of attracting foraging fauna, which may pollinate the flowers during the period of an thesis.22-39-42 Spines and prickles are a common feature, particularly in the species from Africa and South America. The stipular spines may grow up to 18 cm in length in A. karroo and are important taxonomically.55 In some cases their repellent function is augmented by providing accommodation and a food source for ants,30'61 which readily protect their host plant from predators. Acacia flowers are grouped into inflorescences that are either spherical or cylindrical, axillary or terminal, and may themselves be grouped into spikes or racemes. The term "flowering system" is frequently used to describe the branch system on which inflorescences are produced.62 The color of the flowers, generally shades of cream or yellow, although very rarely pink or purple, is mainly due to the colored filaments of the stamens. The plants are particularly conspicuous during flowering and their attractive appearance has contributed to the importance of acacias in ornamental horticulture. Many Australian species of Acacia flower during winter and early spring8'56'65'7" and most species from southern Africa flower during spring and summer.47-55 The seeds often have a thick seed coat which requires scarification before germination will occur. They are produced in pods which are lignified at maturity and usually dehisce longitudinally along both margins. Seed, pod, and funicle structure may be important in species identification. TAXONOMY The genus Acacia consists of three major subgenera, Aculeiferum, Heterophyllum, and
CRC Handbook of Flowering
Acacia.25*9 Species belonging to Aculeiferum are woody vines or small trees with spines or prickles of nonstipular origin. The subgenus Heterophyllum is the largest group and consists mainly of phyllodinous species usually with no thorns or prickles. Most Australian species belong to Heterophyllum, whereas subgenus Acacia consists largely of African and South American species with bipinnate leaves and stipular spines. Pedley has recently elevated the subgenera to generic status.57 The subgenera Aculeiferum, Heterophyllum, and Acacia are now known as the genera Senegalia, Racosperma, and Acacia, respectively. In this chapter the previous classification of Vassal69 is used because all species have not yet been formally transferred to the new genera. FLORAL DEVELOPMENT Acacia is a woody genus and shows the period of juvenility characteristic of this group of plants. The juvenile phase, during which the plant will not flower, generally varies between 1 and 10 years, depending on species and environment. In Acacia pycnantha there is variability for the character within the species which may be under genetic control. There have been relatively few reports on the sequence of floral development throughout the year. In well-watered plants of Acacia pycnantha floral buds are produced during every month of the year in South Australia,10 but flowering occurs only once a year in late winter. Most of the buds which initiate during the period of pod set and development abort, and are shed from the plant. This is suggested to be due to competition between the developing pods and flower buds for reserves or for products of photosynthesis. Buds which initiate immediately after pod maturity develop more slowly than those which initiate later in the growth cycle, so that all buds flower during the same month (Figure 1). In Acacia bailey ana, however, flower buds are produced only once a year in summer.8
FLORAL MORPHOLOGY Acacia inflorescences consist of numerous small flowers, generally between 3 and 100, depending on the species. The flowers are regular and usually hermaphrodite with 4 to 7 (usually 5) sepals, and petals which may be free or united, numerous stamens with filaments which may be free or connate at the base, and a single ovary with many ovules, up to 20 in Australian species.37 The flowers of most Australian species do not have nectaries, but a cup-like disc is present around the base of the ovary of members of the subgenus Aculeiferum, and many African species have stalked glands on the tips of the anthers. In A. terminalis the individual buds in an inflorescence open synchronously although the inflorescences in the center of the raceme may be ahead of those above and below.39 Male flowers with sterile ovaries, or which lack ovaries completely are also produced in many species, and both male and hermaphrodite flowers may occur in the same inflorescence.25-51-53'66'71 This andromonoecious condition may be influenced by environmental factors during floral development. Descriptions of various aspects of floral morphology have been published for a number of species of Acac/a.10'18-31-35-49"53-65 The sequence of floral development is similar in all species studied to date. In well-watered A. pycnantha plants, inflorescence buds are produced all year round on new extension growth. Flower buds are rarely produced on old wood or following a cessation of growth as is the case in many other woody perennial species,28 although in some African species the flowers grow on specialized short shoots or brachyblasts which are at least 6 months old.26 The apex of an axillary shoot either produces phyllode primordia with relatively flat, vegetative axillary buds or floral bracts with dome-shaped axillaries.63 These latter meristems are inflorescence buds and individual flower buds differentiate acropetally (Figure 2A). Each individual flower bud meristem is subtended by a bract, and the floral parts are
i j /Flowering
A 1 -
1 I< D O
0 2 •
/* / I J
FIGURE 1. Increase in equatorial diameter of early and late initiated Acacia pycnantha inflorescences through the year until flowering. Vertical bars represent standard errors for the monthly inflorescence equatorial diameter. Letters refer to the developmental stages listed in Table 1. (From Buttrose, M. S., Grant, W. J. R., and Sedgley, M., Aust. J. Bot., 29, 385—395, 1981. With permission.)
differentiated centripetally, in the order sepals, petals, stamens, and pistil. In A. pycnantha, there are 5 sepal primordia, 5 petal primorida, numerous stamen primordia, and a single pistil primordium (Figure 2B).10 Pollen grains of acacias are unusual in that they are aggregated into composite structures called polyads.2'15-19-21-23-67-68 These consist of 4, 8, 12, 16, 32, or 64 pollen grains, with 16 the most common number in the genus.2-19'20'34-37 A polyad is the product of a single primary sporogenous cell.51'53 In A. auriculaeformis,19 A. baileyana,51-53 A. pycnantha,10 A. conferta, A. iteaphylla, and A. subulata,34 each primary sporogenous cell undergoes two mitotic divisions followed by meiosis to form the 16-celled polyad. As one primary sporogenous cell forms in each of the four locules in each of the two anther lobes, this results in 128 pollen cells per anther with one 16-celled polyad per locule (Figure 2C). The 16-cell polyad forms a biconvex disc with 8 cells in the center arranged in 2 tiers of 4 cells with 8 cells arranged in a single layer around the periphery (Figure 2D). Cytoplasmic connections link the inner faces of the microspores during polyad development.34 These cytoplasmic bridges may determine the sites of the pollen wall bridges which are found in mature polyads and serve to hold the grains together.24 Further adhesion between the grains is provided by "Kittsubstanz" or cement between the inner faces.2 The developing anther wall consists of four layers, an outer epidermis, a middle layer, an endothecium, and the tapetum. The endothecium develops conspicuous radial thickenings except in the area of dehiscence, and the anther lobes split longitudinally. The pistil primordium develops into a curved structure. Differential growth of the inner
CRC Handbook of Flowering
' jf**'* t v
b V«^ 4 8
FIGURE 2. A. Longitudinal section of axillary shoot of Acacia pycnantha showing inflorescence bud (i) with developing flower primordia (arrows). B. Transverse section of Acacia pycnantha flower bud showing sepals (se), petals (pe), stamens (st), and ovary (o). C. Longitudinal section of developing Acacia pycnantha anther lobe showing a polyad (p) in each of the four locules. D. Surface view of mature 16-grain Acacia pycnantha polyad showing individual pollen grains (pg). E. Scanning electron micrograph of pollinated stigma of Acacia subulata showing 16-grain polyad (p) in stigmatic cup(s). Arrow indicates style. (A—C, Bar represents 100 |j.m; D—E, bar represents 10 u,m.) (A and B, From Sedgley, M., Aust. J. Plant Physio!., 12, 109—118, 1985; C and D, from Buttrose, M. S., Grant, W. ). R., and Sedgley, M., Aust. J. Bot.. 29, 385—395, 1981; E, from Kenrick, J. and Knox, R. B.,Ann. Bot., 50, 721—727, 1982. With permission.)
Table 1 SEQUENCE OF FLORAL DEVELOPMENT IN ACACIA PYCNANTHA AS REFERRED TO IN FIGURE 1 Developmental stage Female A B C D E F G H I J
Differentiation of sepals and petals Early pistil primordium Pistil primordium Enlarged pistil primordium Pistil primoridum enfolding Enclosed ovary with ovule primordia Developing style, ovule primordia Megaspore mother cell Megaspore tetrad, stigma and style developed Mature embryo sac
Early staminal primordium Staminal primordium Separate stamen primordia Stamens with filaments and differentiating anthers Two separate anther lobes Primary sporogenous cells Microspore mother cell Polyads with uninucleate cells, endothecial thickenings in anther wall Polyads with binucleate cells Anthesis
From Buttrose, M. S., Grant, W. J. R., and Sedgley, M., Aust. J. Bot., 29, 385-395, 1981. With permission.
and outer surfaces forms a cavity and ovules are initiated at the junction of the two edges of the primordium.10-54-66 Following meiosis in the megaspore mother cell, one of the resulting megaspores develops into a seven-celled embryo sac containing eight nuclei. Starch is often present in the embryo sac.10-''1 Integument development is limited prior to anthesis and the micropyle does not develop until after fertilization.10-52-66 Following the formation of the ovary cavity, rapid development at the apex of the pistil results in the formation of the relatively long style which becomes folded and contorted within the unopened flower bud.l0-36-66 The simple blunt stigma is nonpapillate and forms a cup-shaped depression at the tip of the style. An exudate is present on the stigma at anthesis and consists of protein, carbohydrate, lipid, and enzymes.3'' In the species of Acacia that have been studied in detail, the pollen develops more rapidly than the pistil. l0 - 51 - 66 In A. pycnantha poly ads are developed in the anther when the ovules are at the tetrad stage, despite the occurrence of megaspore and microspore mother cells at the same stage of flower development (Table 1).
BREEDING SYSTEMS Despite the more rapid development of pollen than pistil, many species of Acacia are reported to show protogynous dichogamy, with the stigma receptive to pollen before the flower's pollen is released from the anther."6-52 The female stage lasts for between 6 and 48 hr in A. terminalis.*9 In A. nilotica, on the other hand, the flowers are reported to be protandrous.66 The dichogamous condition promotes cross-pollination and is one of three outcrossing mechanisms recorded in the genus. The other two mechanisms are andromonoecy, the presence of male and hermaphrodite flowers on the same plant,51 •53-66-72 and self-incompatibility, the inability of the pollen to produce successful seed set.33-38-71 High rates of outcrossing, up to 100% in some cases, have been reported in a number of specie^ 13.33.38,41,48,58,65 -phe pOuen may be transferred from flower to flower by insects5 7J4 - 41 - 64 ' 72 or birds,22-39-41 depending on the species. Bees appear to be the major pollinator group associated with the genus.5"7'64 The acacia stigma is very small in diameter, only 60 |xm in diameter in A. subulata,37 and the polyad is often of comparable diameter, generally between 30 and 70 fjim. Thus a
CRC Handbook of Flowering
single polyad fits neatly into the stigmatic cup (Figure 2E). A relationship exists between poly ad grain number and maximum pod seed number indicating, that most flowers are pollinated by a single polyad. Observations on Acacia retinodes in Victoria, Australia showed that over 80% of pollinated flowers had only one polyad on the stigma.41 The composite grain is suggested to be a mechanism which ensures seed set following a single pollination event.37 The success of this event appears to be further assisted by the postpollination secretion of stigma exudate.35-44 This increased volume of secretion, produced by the stigma in response to the presence of pollen, has been recorded in a number of species and completely submerges the polyad on the stigma. It may be a means of providing sufficient germination medium for all pollen grains of the polyad, including those which are not in direct contact with the stigma.44
ENVIRONMENTAL EFFECTS ON FLOWERING Water Water availability is considered to be a major factor in determining whether or not aridzone species flower.49 Well-watered acacias under cultivated conditions may initiate flower buds10 or flower55 all year round, indicating that water availability is an important factor in the flowering of acacias. In the extremely arid climate of central Australia, rainfall is highly variable in both amount and time of precipitation. A. aneura, one of the major species of the Australian arid zone, has the ability to flower in any month after rain has fallen,16 although the main flowering periods are summer and winter.18 When additional water is supplied to A. aneura trees under natural conditions, flowering occurs several times, but the main flowering periods are still late summer and winter.59 These results suggest that factors other than water availability are influencing the flowering process. In the arid zone of Western Australia, there is a correlation between flowering and winter rainfall in only one of 11 species of Acacia native to the region.16 The strict seasonal flowering periods of most species, despite variability in rainfall, suggest that flowering is more related to the less variable temperature or photoperiodic conditions. This is also indicated in experiments with A. pycnantha, where well-watered plants initiate flower buds in all months of the year but flower only once a year in late winter.10 Acacias growing in north Africa and parts of Asia are generally subjected to a more regular rainfall pattern than those growing in Australia. There is a summer wet season extending from May to October and a winter dry season from November to April. In general, the acacias growing in this environment drop some or all of their leaves during or following the dry season. New leaves are produced during the wet season and are accompanied by floral development. Flowering peaks at the end of the wet season and extends into the dry season, during which the pods develop.12-26'40'60'71 Flowering of A. albida in Sudan appears to be controlled by water supply, as out of season rains can result in out of season flowering.71 Flowering can be induced in this species by lopping of branches. Peak flowering of A. nilotica in Sudan follows the 2 wettest months, which receive over 70% of the total annual rainfall.40 However, the wettest months are also relatively cool, and temperature is considered to be the major factor affecting flowering in A. nilotica. The north African species A. raddiana, A. tortilis, and A. gerrardii ssp. negevensis also occur in Israel.26 Irrespective of climate, however, these species flower at the same time in Israel as in Sudan, and A. raddiana also undergoes partial defoliation in July even when given supplementary irrigation. Similar behavior is shown by 13 Australian Acacia species which have naturalized in South Africa. All flower at the same time of year as in Australia irrespective of climate or location.47 Water availability appears to be a factor in determining whether acacias will flower, but the effects probably interact with other variables such as temperature and photoperiod.
Table 2 FLOWERING OF ACACIA PYCNANTHA PLANTS TRANSFERRED BETWEEN TWO DIFFERENT ENVIRONMENTS
Treatment Outside throughout experiment Outside until June, then transferred to greenhouse Greenhouse throughout experiment Greenhouse until June then transferred outside L.S.D. (/> = 0.05)
Mean no. of developing racemes per plant in June
No. of plants which flowered (of five)
Mean no. of racemes which flowered
Period of anthesis (1984)
Aug. 20 to Oct. 29
Sept. 7 to Oct. 19
From Sedgley, ML, Aust. J. Plant Physio/., 12, 109—118, 1985. With permission.
Temperature The effect of temperature on flowering of A. pycnantha has been studied by comparing development under ambient southern Australian conditions and in a controlled-environment greenhouse.63 Floral development in the two environments is similar until the beginning of winter, when the inflorescence buds on the plants in the greenhouse cease to grow. Anthesis occurs during late winter in the outside plants, whereas the greenhouse plants do not flower and the inflorescence buds are shed from the plant. Microscopical examination of the inhibited inflorescence buds shows that floral development has proceeded up to the stage of anther and ovule development but that microsporogenesis and megasporogenesis have not occurred. The major difference between the two environments in winter is in the temperature. Both maximum and minimum temperatures are 8 to 9°C higher in the greenhouse (mean max. 28°C, mean min. 16°C) than outside (mean max. 19°C, mean min. 8°C). The results suggest that flowering is controlled by the temperature during development, and that meiosis will occur only at a temperature below 16 to 19°C. This would explain why flowering of A. pycnantha occurs only once a year following the low temperatures of winter, despite the fact that floral buds are initiated all year round. Those initiated during the heat of summer (mean max. 32°C, mean min. 16°C) do not undergo meiosis and are shed from the plant without reaching anthesis. Further evidence for this theory has been obtained by transferring plants between the two environments. Those plants which are transferred in early winter from outside to the greenhouse do not flower. Most of the plants transferred from the greenhouse to outside flower but have fewer floral racemes which open later and for a shorter period than in the plants kept outside throughout the experiment (Table 2). Thus floral development under the greenhouse conditions is physiologically normal until early winter. However, the fact that on the transferred plants fewer inflorescences flower later and for a shorter period suggests that irreversible inhibition of development can occur under high temperatures. Phenological observations support the experimental results. In Victoria, Australia, A. terminalis normally flowers during summer or autumn. Plants from cool, montane areas flower earlier than lower altitude plants. In warm years, when no cold periods occur in February, flowering is late and the flowering period is extended, suggesting that cool temperatures are important for flowering of A. terminalis.32" Temperature is considered to be the major factor affecting flowering in A. nilotica.40 In the Sudan, A. nilotica flowers from
CRC Handbook of Flowering
July to January with the peak in September and October. Flowering coincides with the relatively cool times of year and no flowers at all are produced during the hot season. High temperature and humidity are used commercially in Europe to force early and uniform flowering of acacias. Australian acacias, particularly the species A. dealbata, A. retinodes, and A. podalyriaefolia, are cultivated in southern Europe for the cut flower trade.'7 A number of horticultural cultivars have been developed and are propagated by grafting. The trees flower in winter, as in Australia, and so are a popular source of cut flowers at a time when little else is available. The trees are carefully managed to promote maximum flowering. They are heavily pruned to promote numerous lateral shoots which produce floral buds. Branches are harvested at the yellow bud stage, just prior to anthesis, and placed in forcing rooms. The branches are maintained in a warm humid atmosphere, with a temperature of 22 to 25°C and a relative humidity of 85 to 90%, for between 48 and 72 hr. This treatment forces simultaneous flowering of all the buds, producing an attractive and showy display of flowers. Megasporogenesis and microsporogenesis have already occurred at the yellow bud stage and postmeiotic development of acacia flowers is accelerated by this relatively high temperature and humidity. Vase life of A. dealbata can be prolonged by keeping the flowers in a solution containing 1 to 10% sucrose, 200 ppm 8-hydroxyquinoline citrate, 50 ppm silver nitrate, and 50 ppm aluminum sulfate. 1 The results suggest that temperature has a major effect on flowering of some species of Acacia. Meiosis appears to be a very sensitive stage which is inhibited by temperatures over 19°C in Acacia pycnantha. Light Variation in daylength on flowering in acacias has not been investigated, although the strictly seasonal flowering of some Australian species has been suggested to be under photoperiodic control.16'54 The effect of light intensity, on the other hand, has been studied in A. pycnantha by comparing development under ambient southern Australian conditions with that under shadecloth.63 The temperatures and daylength are the same for the two sets of plants, but the shaded plants experience a 70% reduction in photon irradiance. Microscopical investigation of axillary shoot tips shows that floral initiation occurs in both sets of plants. Further floral development is inhibited in the shaded plants, however. Macroscopically visible inflorescence buds are observed only rarely and are soon shed from the plant. The shaded plants are never observed to reach anthesis, indicating that a 70% reduction in sunlight inhibits floral development at an early stage. It is suggested that the inhibition of floral development under low light intensity may be a mechanism for preventing flowering on shaded parts of the plant. Shaded flowers would have a reduced chance of attracting pollinating fauna and thus may set less seed. The shaded plant would also be less efficient photosynthetically than one in full sunlight and so assimilates available to the developing flowers and fruits would be reduced. Although the effect of photoperiod on flowering in acacias has not been investigated, low light intensity has been found to inhibit flowering drastically. Floral initiation occurs under low light intensity, but differentiation of the floral parts is prevented under 30% sunlight.
CONCLUSIONS In a genus containing over 1200 species classified into three major subgenera and native to a range of climates in all continents except Europe and Antarctica, it is likely that the flowering response is highly variable. Very few species of Acacia have been studied, and the sample cannot be considered to be representative of the genus. Despite the relatively small amount of work that has been conducted on flowering in Acacia, recent research has
greatly improved our understanding of both the flowering process and the breeding systems. There is a need to understand and control the reproductive stage of acacias for further exploitation of the genus. Breeding of improved cvs or provenances with the desired characteristics for tanning, agroforestry, essential oil production, ornamental horticulture, and timber production is one goal. A further possibility is to manipulate the plant for continuous flowering for purposes of essential oil production and ornamental horticulture. Recent work has shown that A. pycnantha will not flower during spring, summer, and autumn in southern Australia because the temperature is too high. This may also be the reason why flowering of acacias is often poorer in the more northerly, and thus warmer, parts of Australia compared with the south. By artificially providing low temperatures during times of the year other than winter it may be possible to induce out-of-season flowering by exploiting the yearround production of inflorescence buds. As with many other species it appears that flowering of acacias involves a number of sequential processes and that different steps are sensitive to varying environmental conditions. A greater understanding of these controls and sensitive stages will aid further manipulation of this useful and important genus.
ACKNOWLEDGMENTS Appreciation is expressed to Professor R. B. Knox and Ms. J. Kenrick for critical reading of the manuscript, for providing Figure 2E, and for making available unpublished data.
REFERENCES 1. Accati, E, and Sulis, S., Preparazkme del ramifioriti di mimosa e toro conservazione, Annali Istituto Sperimentale per la Floricoltura, 11, 1—12, 1980. 2. Barth, O. M., Feinstruktur des Sporoderms einiger brasilianischer Mimosoiden-Polyaden, Pollen Spores, 1, 429—441, 1965. 3. Beadle, N. C. W., The Vegetation of Australia, Cambridge University Press, Cambridge, 1981. 4. Bentley, B. L., Extrafloral nectaries and protection by pugnacious bodyguards, Annu. Rev. Ecol. Syst., 8, 407—427, 1977. 5. Bernhardt, P., Kenrick, J., and Knox, R. B., Pollination biology and the breeding system of Acacia retinodes (Leguminosae: Mimosoideae), Ann. Mo. Hot. Card., 71, 17—29, 1984. 6. Bernhardt, P. and Walker, K., Bee foraging on three sympatric species of Australian Acacia, Int. J. Entomology, 26, 322—330, 1984. 7. Bernhardt, P. and Walker, K., Insect foraging on Acacia retinodes var. retinodes in Victoria, Australia, Int. J. Entomology, 27, 97—101, 1985. 8. Boden, R. W., Variation and inheritance of flowering in Acaci'a baileyana F. Muell., Australian Plants, 5, 230—237, 1969. 9. Boughton, V. H., Extrafloral nectaries of some Australian phyllodineous acacias, Aust. J. Bot., 29, 653—664, 1981. 10. Buttrose, M. S., Grant, W. J. R., and Sedgley, M., Floral development in Acacia pycnantha Benth. in Hook., Aust. J. Bot., 29, 385—395, 1981. 11. Carr, D. J. and Burden, J. J., Temperature and leaf shape in seedlings of Acacia aneura, Biochem. Physiol. Pflanzen, 168, 307—318, 1975. 12. Cheema, M. S. Z. A. and Qadir, S. A., Autecology of Acacia Senegal (L.) Willd., Vegetatio, 27, 131—162, 1973. 13. Coaldrake, J. E., Variation in some floral, seed and growth characteristics of Acacia harpophylla (Brigalow), Aust. J. Bot., 19, 335—352, 1971. 14. Coetzee, J. A., The morphology of Acacj'a pollen, 5. Afr. J. Sci., 52, 23—27, 1955. 15. Cookson, I. C., The Cainozoic occurrence of Acacia in Australia, Aust. J. Bot., 2, 52—59, 1953. 16. Davies, J. J. F., Studies on the flowering season and fruit production of some arid zone shrubs and trees in Western Australia, J. Ecol., 64, 665—687, 1976.
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17. De Ravel d'Esclapon, G., Les mimosas sur le littoral mediterranean, Rev. Hortic., 134, 332—339, 1962. 18. Doran, J. C., Turnbull, J. W., Boland, D. J., and Gunn, B. V., Handbook on Seeds of Dry-Zone Acacias, Food and Agricultural Organization, Rome, 1983. 19. Dnyansagar, V. R., Embryological studies in the Leguminosae. VIII. Acacia auriculaeformis A. Cunn., Adenanthera pavonina Linn., Calliandra hematocephala Hassk., and Ca/liandra grandiflora Benth., Lloydia, 21, 1—25, 1958. 20. Engler, A., Beitrage zue Kenntis der Antherenbildung der Metaspermen, Prings, Jahrb, Wiss. Bar., 10, 275—316, 1876. 21. Erdtman, G., Pollen Morphology and Plant Taxonomy, Vol. 1, Angiosperms, Almqvist and Wiksell, Stockholm, 1971. 22. Ford, H. A. and Forde, N., Birds as possible pollinators of Acacia pycnantha, Aust. J. Hot., 24, 793—795, 1976. 23. Guinet, P., Les Mimosacees, etude de palynologie fondamentale, correlations, evolution, Trav. Sect. Set. Tech. Fr. Pondichery, 9, 1—293, 1969. 24. Guinet, P. and Lugardon, B., Diversite des structures de 1'exine dans le genre Acacia (Mimosaceae), Pollen Spores, 18,483—511, 1976. 25. Guinet, P. and Vassal, J., Hypotheses on the differentiation of the major groups in the genus Acacia (Leguminosae), Kew Bulletin, 32, 509—527, 1978. 26. Halevy, G. and Orshan, G., Ecological studies on Acacia species in the Negev and Sinai. II. Phenology of Acacia raddiana, Acacia tortilis and Acacia gerrardii ssp. negevensis. Israel J. Bot., 22, 120—138, 1973. 27. Heithaus, E. R., Opler, P. A., and Baker, H. G., Bat activity and pollination of Bauhinia pauletia: plant-pollinator coevoluation, Ecology, 55, 412—419, 1974. 28. Jackson, D. I. and Sweet, G. B., Flower initiation in temperate woody plants, Hortic. Abstr., 42, 9—24, 1972. 29. Janzen, D. H., Coevolution of mutualism between ants and acacias in Central America, Evolution, 20, 249—275, 1966. 30. Janzen, D. H., Birds and the ant x acacia interaction in Central America; with notes on birds and other myrmecophytes, Condor, 71, 240—256, 1969. 31. Janzen, D. H., Swollen-thorn Acacias of Central America, Smithsonian Contributions to Botany, 31, 1—131, 1974. 32. Kaplan, D. R., Heteroblastic leaf development in Acacia, La Cellule, 12, 135—203, 1980. 32a. Kenrick, J., personal communication, 1986. 33. Kenrick, J., Kaul, V., and Knox, R. B., Self incompatibility and the site of pollen tube arrest in Australian species of Acacia, Incompatibility Newsl., 16, 3—4, 1984. 34. Kenrick, J. and Knox, R. B., Pollen development and cytochemistry in some Australian species of Acacia, Aust. J. Bot., 27, 413—427, 1979. 35. Kenrick, J. and Knox, R. B., Post-pollination exudate from stigmas of Acacia (Mimosaceae), Ann. Bot., 48, 103—106, 1981. 36. Kenrick, J. and Knox, R. B., Structure and histochemistry of the stigma and style of some Australian species of Acacia, Aust. J. Bot., 29, 733—745, 1981. 37. Kenrick, J. and Knox, R. B., Function of the polyad in reproduction of Acacia, Ann. Bot., 50, 721—727, 1982. 38. Kenrick, J. and Knox, R. B., Self-incompatibility in the nitrogen-fixing tree, Acacia retinodes: quantitative cytology of pollen tube growth, Theor. Appl. Genet., 69, 481—488, 1985. 39. Kenrick, J., Marginson, R., Beresford, G., and Knox, R. B., Birds and pollination in Acacia terminalis, in Pollination '82, Williams, E. G., Knox, R. B., Gilbert, J. H., and Bernhardt, P., Eds., University of Melbourne, Australia, 1982, 102—108. 40. Khan, M. A. W., Phenology of Acacia ni/otica and Eucalyptus microtheca at Wad Medani (Sudan), Indian For., 96, 226—248, 1970. 41. Knox, R. B. and Kenrick, J., Polyad function in relation to the breeding system of Acacia, in Pollen: Biology and Implications for Plant Breeding, Mulcahy, D. C. and Ottaviano, E., Eds., Elsevier, 1983, 411^17. 42. Knox, R. B., Kenrick, J., Bernhardt, P., Marginson, R., Beresford, G., Baker, I., and Baker, H. G., Extrafloral nectaries as adaptations for bird pollination in Acacia terminalis. Am. J. Bot., 72, 1185— 1196, 1985. 43. Marginson, R., Sedgley, M., and Knox, R. B., Structure and histochemistry of the extrafloral nectary of Acacia terminalis (Salisb.) MacBride (Leguminosae, Mimosoideae), Protoplasma, 127, 21—30, 1985. 44. Marginson, R. B., Sedgley, M., and Knox, R. B., Physiology of post-pollination exudate production in Acacia, J. Exp. Bot., 36, 1660—1668, 1985. 45. Marginson, R., Sedgley, M., Douglas, T. J., and Knox, R. B., Structure and secretion of the extrafloral nectaries of Australian acacias, Israel J. Bot., 34, 91—100, 1985.
46. Maslin, B. R., Acacia, in Flora of Central Australia, Jessop, J., Ed., A. H. & A. W. Reed, Sydney, 1981, 115—124. 47. Milton, S. J. and Moll, E.J., Phenology of Australian acacias in the S. W. Cape, South Africa, and its implications for management, Bot. J. Linn. Soc., 84, 295—327, 1982. 48. Moffett, A. A., Genetical studies in acacias. I. The estimation of natural crossing in black wattle, Heredity, 10, 57—67, 1956. 49. Mott, J. J., Flowering, seed formation and dispersal, in Arid-land Ecosystems: Structure, Functioning and Management, Vol. 1, Cambridge University Press, Cambridge, 1979, 627—644. 50. Narasimhachar, S. G., A contribution to the embryology of Acacia farnesiana L. (Willd.), Proc. Indian Acad. Sci. Sect. B, 28, 144—149, 1948. 51. Newman, I. V., Studies in the Australian acacias. II. The life history of Acacia baileyana F.v.M. I. Some ecological and vegetative features, spore production, and chromosome number, J. Linn. Soc. London, Bot., 49, 145—171, 1933. 52. Newman, I. V., Studies in the Australian acacias. III. Supplementary observations on the habit, carpel, spore production and chromosomes of Acacia baileyana, Proc. Linn. Soc. N.S.W., 59, 237—251, 1934. 53. Newman, I. V., Studies in the Australian acacias. IV. The life history of Acacia baileyana F.v.M. II. Gametophytes, fertilization, seed production and germination, and general conclusions, Proc. Linn. Soc. N.S.W., 59, 277—313, 1934. 54. Newman, I. V., Studies in the Australian acacias. VI. The meristematic activity of the floral apex of Acacia longifolia and Acacia suaveolens as a histogenetic study of the ontogeny of the carpel, Proc. Linn. Soc. N.S.W., 61, 56—88, 1936. 55. Palmer, E. and Pitman, N., Trees of Southern Africa, A. A. Balkema, Cape Town, 1972. 56. Pedley, L., A revision of Acacia Mill, in Queensland, Austrobaileya, 1, 75—234, 1978. 57. Pedley, L., Derivation and dispersal of Acacia (Leguminosae), with particular reference to Australia, and the recognition of Senegalia and Racosperma, Bot. J. Linn. Soc., 92, 219—254, 1986. 58. Philp, J. and Sherry, S. P., The degree of natural outcrossing in green wattle, Acacia decurrens Willd. and its bearing on wattle breeding, J. S. Afr. For. Assn., 14, 1—28, 1946. 59. Preece, P. B., Contributions to the biology of mulga. I. Flowering, Aust. J. Bot., 19, 21—38, 1971. 60. Radwanski, S. A. and Wickens, G. E., The ecology of Acacia albida on mantle soils in Zalingei, Jebel Marra, Sudan, J. Appl. Ecol, 5, 569—579, 1967. 61. Ross, J. H., An analysis of the African Acacia species: their distribution, possible origins and relationships, Bothalia, 13, 389—413, 1981. 62. Robbertse, P. J., The genus Acacia in South Africa. 11. With special reference to the morphology of the flower and inflorescence, Phytomorphology, 24, 1—15, 1974. 63. Sedgley, M., Some effects of temperature and lighten floral initiation and development in Acacia pycnantha, Aust. J. Plant Physiol, 12, 109—118, 1985. 64. Sherry, S. P., The Black Wattle (Acacia mearnsii De Wild.), University of Natal Press, Natal, 1971. 65. Simmons, M., Acacias of Australia, Thomas Nelson, Melbourne, 1981. 66. Sinha, S. C., Floral morphology of acacias, Caribbean J. Sci., 11, 137—153, 1971. 67. Sorsa P., Pollen morphological studies in the Mimosaceae, Ann. Bot. Fenn., 6, 1—34, 1969. 68. Van Campo, M., and Guinet, P., Les pollens composes: 1'exemple des Mimosacees, Pollen Spores, 3, 201—218, 1961. 69. Vassal, J., Apport des recherches ontogeniques et seminologiques a 1'etude morphologique, taxonomique et phylogenique du genre Acacia, Bull. Soc. Histoire Nat. Toulouse, 108, 125—247, 1972. 70. Whibley, D. J. E., Acacias of South Australia, Government Printer, Adelaide, 1980. 71. Wickens, G. E., A study of Acacia albida Del. (Mimosoideae), Kew Bull., 23, 181—202, 1969. 72. Zapata, T. R. and Arroyo, M. T. K., Plant reproductive ecology of a secondary deciduous tropical forest in Venezuela, Biotropica, 10, 221—230, 1978.
CRC Handbook of Flowering AGLAONEMA R. J. Henny
Aglaonema, a member of the Araceae family and comprised of 21 species, is native to southeast Asia, northeast India, and southern China southward through Malaysia, New Guinea, and the Philippines.They are popular ornamental tropical foliage plants because of their ability to tolerate low light and humidity levels often encountered under interior conditions. Aglaonemas are also valued for their variegated foliage and compact growth habit. Foliar variegation in Aglaonema usually consists of grey, silvery-grey, or silver markings contrasted against a green background and is normally limited to the upper leaf surface. However, one species, (Aglaonema rotundum N. E. Br.) has wine-red coloration in its leaves while another (Aglaonema pictum (Roxb.) Kunth 'Tricolor') has lime-green coloration as part of its overall variegation pattern. In addition, Aglaonema petioles may be green, green mottled with ivory, pure ivory, russet, or pink. All of these characteristics make Aglaonema a desirable genus for breeding studies.2 The Aglaonema inflorescence consists of a central spadix subtended by a spathe. Pistillate flowers are attached to the base of the spadix and staminate flowers cover the distal portion (Figure 1). A narrow region of sterile staminoids often separates the staminate and pistillate flowers. Aglaonema inflorescences have no ornamental value; they are green and relatively inconspicuous, but tend to disfigure a plant once they have opened and begin to deteriorate and decay (Figure 1). Most commercial growers of Aglaonema regard inflorescences as a nuisance which must be removed. There is no information in the literature regarding the natural flowering habits of Aglaonema. Our breeding stock is maintained in heated greenhouses with a day/night temperature regime of 36/18°C at 20 to 30 klx light intensity and a natural photoperiod (at 29°N latitude). Under these conditions, many Aglaonema species and cultivars flower in the spring (April to June). Some may be found in bloom at other times of the year, while one species, (Aglaonema pictum 'Tricolor'), flowers more or less continuously. Our research has not involved attempts to control flowering of Aglaonema using environmental manipulation. Instead, previous successful attempts at stimulating flowering of Dieffenbachia4 and Spathiphyllum5 using foliar sprays of GA3 encouraged us to try a similar approach with Aglaonema. Aglaonema commutatum Schott 'Treubii' was selected as the initial test plant. Uniform-sized mature plants growing in 15-cm pots were given a single foliar spray until runoff with 0, 100, 200, or 400 ppm GA3 in December.1 All 27 plants treated with GA3 produced open inflorescences within an average of 143 days after treatment (Table 1). One of 9 control plants produced 3 blooms during the same period, while none of the others showed any sign of flowering at 165 days after treatment when the experiment was terminated. Plants treated with 400 ppm GA3 produced significantly more inflorescences than those treated with 100 or 200 ppm (Table 1). Flowers were normal in appearance and produced pollen. These results have led to routine use of a 250 ppm GA3-spray to promote flowering Aglaonema for breeding purposes. Subsequently, many different species and cultivars flowered simultaneously for the first time after treatment. This technique has greatly aided in the production of many interspecific Aglaonema hybrids. In one instance, different stock plants were treated with GA3 in November to ensure flowering for the following spring.3 Treated plants not only produced open inflorescences by mid-April, but also many continued to flower into July (Figure 2) allowing pollination for a period of over 3 months. Plants which would normally produce 3 to 5 inflorescences per stem (if flowering naturally) produced 12 to 15 per stem, and seed production per plant
FIGURE 1. Typical inflorescences of Aglaonema modestum Schott ex Engl. (A) Bud stage; (B) at anthesis, with unfurled spathe allowing observation of basal pistillate and upper staminate flowers visible; (C) with spathe removed.
Table 1 EFFECT OF A SINGLE GA3 TREATMENT ON NUMBER OF DAYS TO FLOWER AND NUMBER OF INFLORESCENCES PER PLANT OF AGLAONEMA COMMUTATUM 'TREUBII' GA3 cone (ppm)
Mean days to first bloom"
0 100 200 400
— 144 ac 143 a 142 a
Mean number of inflorescences 0.3 4.7 5.3 6.7
a" b b c
Days after treatment until first inflorescence opened Mean separations within columns by Duncan's multiple range test, 5% level One of 9 control plants flowered after 143 days with 3 blooms
From Henny, R. L, HonScience, 18, 374, 1983. With permission.
CRC Handbook of Flowering
FIGURE 2. Aglaonema stock plant 8 months after a single foliar spray with 250 ppm GA3. Note seeds in various stages of development, plus newly opened bloom ready for pollination (—>). The plant was treated in November and pollinations started in April (photograph taken in July). (From Henny, R. J., Aroideana, 6, 135—136, 1983. With permission.)
increased accordingly. These results have allowed us to make maximum use of a limited number of stock plants and greenhouse space.
REFERENCES 1. Henny, R. J., Flowering of Aglaonema commutatum Treubii' following treatment with gibberellic acid, HortScience, 18, 374, 1983. 2. Henny, R. J., Aglaonema breeding: Past, present and future, Proc. Fla. State Hortic. Soc., 96, 140—141, 1983. 3. Henny, R. J. and Fooshee, W. C., Flowering of Aglaonema with gibberellic acid (GA3) — A follow-up report, Aroideana, 6, 135—136, 1983. 4. Henny, R. J., Dieffenbachia, in CRC Handbook of flowering, Vol. 2, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 443^45. 5. Henny, R. J., Spathiphyllum, in CRC Handbook of flowering, Vol. 4, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 382—383.
En. Corn cockle; Fr. Nielle des bles; Ge. Kornrade; Sp. Neguillon Jan A. D. Zeevaart
INTRODUCTION Agrostemma githago L., a member of the Caryophyllaceae, is a weed adapted to the cultivation of cereals. Two varieties of Agrostemma have been distinguished, namely, the var. linicolum (Terech.) Hammer with small, smooth seeds which is adapted to flax, and the large-seeded var. macrospermum (Levina) Hammer which grows mainly in wheat fields.5 Agrostemma is native to Europe and was introduced into the U.S. and Canada. The center of origin of Agrostemma is thought to be the eastern Mediterranean region.18 The seeds of Agrostemma are much larger than those of any other species of the Silenoideae and are difficult to separate from cereal seeds by traditional processes, such as winnowing. 18 As a result, the species was distributed as a contaminant of grain and resown with the seed grain in autumn or spring. Thus, Agrostemma became established in the temperate regions as a weed in grain fields. Since the early 1900s, it is much less common, due to improvements in seed-cleaning techniques5-14-16-18 and more recently to the use of herbicides.5'16 Because of the changes in agricultural practices, Agrostemma is now threatened with extinction,5-'6 or as dramatized by Franks,4 " . . . who knows, or cares about the disappearance of the corn cockle, murdered by the agrochemical revolution, . . . . " A collection of about 100 strains of Agrostemma is maintained in a gene bank in Gatersleben, G.D.R. for preservation of the species and for studying its evolution.5 The seeds of Agrostemma are poisonous, due to the presence of a saponin of which the aglycone has been identified as the triterpene gypsogenin, formerly called githagenin. 6 - 14 - 17 This compound amounts to 5 to 7% of the dry weight of the seeds.14 Studies with Agrostemma, other than flowering, include extensive work on seed dormancy by Borriss and associates1-7 in Greifswald, G.D.R., and by Thompson18 at Kew Gardens, U.K. Protein synthesis in Agrostemma seeds was studied by De Klerk2 at the University of Nijmegen, the Netherlands. Kende and associates3-13 in East Lansing, Mich., investigated induction of nitrate reductase by cytokinins in Agrostemma embryos. The local strain of Agrostemma used in this work was subsequently used by Jones and Zeevaart9"12-20"22 in their studies on photoperiodic control of stem growth. GROWTH HABIT AND PROPAGATION Agrostemma has an erect growth habit and reaches a height of 0.5 to 1 m at maturity (Figure 1). The leaves are opposite, nearly linear. The stems and leaves are white-hairy. The flowers are solitary and are borne on long pedicels. The calyx is leaf-like; the petals are magenta-purple and shorter than the calyx. The capsule contains many seeds on a central placenta. The developing seeds are white and covered with a slimy liquid, but during desiccation the testa turns black. Uniform batches of plants can be readily grown from seed. In the soil, seeds of Agrostemma show a fast and uniform germination.16 However, when stored dry at 0°C, the seeds remain viable for 20 to 25 years.5 Freshly harvested Agrostemma seeds germinate only at relatively low temperatures (from 0°C to approximately 15°C), but when afterripened at room temperature, the seeds will also germinate at higher temperatures.1>18 To ensure uniform germination, the following procedure
CRC Handbook of Flowering
FIGURE 1. Plants of Agrostemma githago L. in continuous SD growing as rosette (left), and flowering 43 days after transfer to LD (right). Plants 100 days old. LD consisted of 8-hr periods of light from fluorescent and incandescent lamps, followed by 16 hr of lowintensity supplementary illumination from incandescent lamps.
may be used. The seeds are sterilized in 1% NaOCl solution for 20 min, washed several times with distilled water, and placed in Petri dishes on wet filter paper at 4°C for 1 week before planting." The plants are suitable for experimentation when 7 to 9 weeks old. Several axillary shoots are formed and these are removed periodically, so that flower formation and stem growth are only observed on the main axis.9
60 ro c V
E a> 40 (0
FIGURE 2. Stem growth of different groups of Agrostemma plants that were returned to SD after exposure to various numbers of LD. Only the plants with 24 and 45 LD had open flowers when the experiment was discontinued after 45 days.
PHOTOPERIODIC CONTROL OF DEVELOPMENT Agrostemma is a LD rosette plant. Under SD conditions, the plants remain vegetative and the stems are very short. Upon transfer to LD, the stem starts to elongate rapidly after 10 days (Figure 2), differentiation of flower primordia occurs at about the same time, and anthesis takes place after approximately 40 days (Figure 1). Stem elongation caused by LD is solely the result of internode elongation.9 Supplementary light from incandescent lamps (Figure 1) is more effective in causing rapid stem elongation than light from fluorescent tubes. The critical daylength of Agrostemma has not been determined, but it is of interest to note that the distribution of Agrostemma in Europe is north of the 40th parallel,18 where the longest days consist of at least 15 hr light. Agrostemma requires a minimum of 5 to 6 LD for flower formation (Table 1). Although the terminal flower primordia develop into macroscopically visible flower buds under subsequent SD, most of them never reach the stage of anthesis, and the stems remain short (Table 1). Thus, Agrostemma requires LD not only for flower initiation, but also for further development of the primordia into open flowers. The effect of LD in Agrostemma is therefore predominantly direct, i.e., for maximal stem growth continuous exposure to LD is necessary. However, as illustrated in Figure 2, there is definitely some photoperiodic after-effect on stem growth when plants are transferred back from LD to SD. The immediate effect is a
CRC Handbook of Flowering Table 1 EFFECT OF DURATION OF LD TREATMENT ON FLOWER FORMATION AND STEM GROWTH IN AGROSTEMMA GITHAGO
Number of LD"
0 2 4 6 8 10 12 46
0/6 0/6 1/6 5/6 6/6 6/6 6/6 6/6
Stem length1 1.4 1.3 1.5 3.3 6.3 10.6 25.7 100.2
All LD treatments started on the same day; after-treatments in SD. Both SD and LD consisted of 8 h of highintensity light provided by fluorescent and incandescent lamps (4.5 rnW-cm" 2 ) which in the case of LD was supplemented by 16 hr low-intensity light from incandescent lamps (0.7 mW-cm" 2 ). Number of plants with flower buds/number of plants per treatment. Measured 46 days after beginning of LD treatment.
decrease in the growth rate of the stem,9 but the stems continue to elongate at this new rate for a long time (Figure 2). Thus, with respect to photoperiodic after-effect, Agrostemma is intermediate between the LDP Spinacia oleracea in which stem elongation is completely halted when the plants are returned to SD,15 and the LDP Silene armeria in which normal development continues in SD after exposure to a minimum number of SD.19 GIBBERELLINS AND STEM GROWTH Agrostemma exhibits rapid stem elongation in response to exposure to LD (Figures 1 and 2), and is therefore a suitable plant for studying the role of endogenous GAs in this process. When Agrostemma plants were transferred from SD to LD and treated with the growth retardants AMO-1618 or 5-(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo-5,4,l,02-6,08'"dodeca-3,9-diene (tetcyclacis), both of which block GA biosynthesis, stem elongation was inhibited. This inhibition was overcome by simultaneous application of GA20,9 orGA 1 (Figure 3).20 Both growth retardants caused a drastic reduction in the levels of endogenous GA-like substances, as measured in the d-5 corn (Zea mays L.) bioassay,9'20 and by gas chromatography-selected ion monitoring,10-20 thus demonstrating that endogenous GAs play a role in the photoperiodic control of stem elongation in Agrostemma. When the GA-like activity was measured in plants exposed to various numbers of LD, a large, but transient, increase was observed after 8 to 10 LD which coincided with the onset of stem elongation. After 16 LD, the GA activity had returned to that in plants under SD, even though the stems were elongating rapidly at that time. When AMO-1618 was applied to plants after 11 LD, there was a rapid reduction in the rate of stem growth, indicating that continued GA biosynthesis was necessary for sustained stem elongation under LD.9 In further work, the following GAs were identified in Agrostemma shoots and leaves by combined gas chromatography-mass spectrometry: GA53, GA^, GA I9 , GA17, GA20, GA,,
FIGURE 3. Inhibition of stem growth of Agrostemma in LD by tetcyclacis, and its reversal by applied GA.20 From left to right, plant treated with tetcyclacis (Tcy), treated with both tetcyclacis and GA, (Tcy + GA), and untreated control plant (C). Photograph 19 days after beginning of LD treatment.
and 3-epi-GAl (Figure 4).10 The same GAs were also identified in immature seeds of Agrostemma.12 In addition, a novel trihydroxylated GA has been found in Agrostemma seeds.8 Changes in the levels of the endogenous GAs during photoperiodic treatment were measured by gas chromatography-selected ion monitoring. The levels of GA44, GA19, GA17, and GA20 all increased up to 8 LD, and then declined, whereas GA t and 3-epi-GAl peaked after 12 LD.10 All the GAs found in Agrostemma have a hydroxyl group at the C-13 position (Figure 4). The GA biosynthesis pathway in Agrostemma must therefore involve an early C-13 hydroxylation step. On the basis of the structural relationships, the following metabolic sequence has been proposed: GA53 —> GA^ —> GA]9 —> GA20 —> GA t and 3-epi-GA, (GA17 with C-20 as a carboxyl group is a dead-end product, presumably derived from GAi9).10 When four different GAs were applied to Agrostemma under SD, GAt was more active than GA20 in causing stem growth, whereas 3-epi-GA.,^ had little activity, and GA17 was inactive.10 These data are in agreement with the proposed GA biosynthetic pathway, and suggest that in Agrostemma, GAl is the physiologically active GA, while other GAs would be active only because they are converted to GA!. Further evidence in support of the proposed GA biosynthetic pathway (see above) was obtained by feeding [2H]GA53 to Agrostemma plants under SD and LD conditions. In both groups of plants [2H]GA53 was converted to pHJGA^, [2H]GA19, [2H]GA,, and [2H]3-epiGA,. 22 No [2H]GA20 was detected, but this may be due to the fact that in Agrostemma the level of GA20 is always very low. Also, when [3H]GA20 was fed to Agrostemma, [3H]3-epi-
CRC Handbook of Flowering
'O^Nr 20 "r\\I3
I I / 2^\j^2\
numbering system of ent-gibberellane /—\ s*^.\J. VOH
o—CH2/—\ >\!J/ VOH
one /-—\ /\!7 VOH
Ctvv^ CS^c^ Ctvv^ ^H COOH COOH GA53
A H COOH COOH GA19
C XvS/^" L^^Ii/^/^ X^l-V^v7^ AUUUH H COOH GA|7
FIGURE 4. Numbering system of the c«r-gibberellane skeleton (Top), and the structures of six GAs identified by combined gas chromatography-mass spectrometry in extracts from Agrostemma shoots (Bottom). An additional GA, 3-epi-GA, (in which the C-3 hydroxyl group is in the a- rather than the pi-configuration as in GA,) has also been identified.
GA,, but no [3H]GA, was produced.11 It is possible, however, that due to the presence of 3 H at the 2,3-positions of GA20, the label was lost during oxidation at the 3 position. When this problem was reinvestigated with [14C]GA20, both radioactive GA, and 3-epi-GA., were formed.21 Thus, as a whole, the metabolic studies with labeled GAs have provided evidence in support of the GA biosynthetic pathway as outlined above. In conclusion, in Agrostemma the photoperiod does not appear to regulate any late step (after GA53) in the GA biosynthetic pathway, as it does in spinach.15 Rather, LD conditions increase the turnover rate of several GAs. 9 " In addition, the sensitivity of Agrostemma plants to GAs is greater under LD than under SD conditions.9 However, the nature of this increased sensitivity under LD remains unknown.
ACKNOWLEDGMENTS My research discussed in this review was supported by AEC/ERDA/DOE. The preparation of this chapter was supported by Contract DE-ACO2-76ERO-1338.
REFERENCES 1. Borriss, H., Uber die inneren Vorgange bei der Samenkeimung und ihre Beeinflussung durch Auszenfaktoren, Jahrb. Wiss. Bot., 89, 254—339, 1940. 2. De Klerk, G. J., Protein synthesis in ripening, dormant and after-ripened Agrostemma githago L. seeds, Ph.D. thesis, University of Nijmegen, Krips Repro, Meppel, 1983, 175 pp. 3. Dilworth, M. F. and Kendo, H., Comparative studies on nitrate reductase in Agrostemma induced by nitrate and benzyladenine, Plant Physiol, 54, 821—825, 1974. 4. Franks, F., Cryopreservation — time to turn to plants, Trends Biochem. Sci., 6(5), I—II, 1981. 5. Hammer, K., Hanelt, P., and Kniipffer, H., Vorarbeiten zur monographischen Darstellung von Wildpflanzensortimenten: Agrostemma L., Kulturpflanze, 30, 45—96, 1982. 6. Hegenauer, R., Chemotaxonomie der Pflanzen, Vol. 3, Birkhauser Verlag, Basel, 1964, 382—383. 7. Htibel, M., Untersuchungen tiber die Beeinflussung der Nachreifung von Agrostemma-Szmen durch Temperatur und Wassergehalt, Flora, 157, 109—130, 1966. 8. Jones, M. G., Endogenous gibberellins and stem extension, in Biochemical Aspects of Synthetic and Naturally Occurring Plant Growth Regulators, Brit. Plant Growth Regul. Group, Monogr. 11, Menhenett, R. and Lawrence, D. K., Eds., Wantage, 1984, 33—42. 9. Jones, M. G. and Zeevaart, J. A. D., Gibberellins and the photoperiodic control of stem elongation in the long-day plant Agrostemma githago L., Planta, 149, 269—273, 1980. 10. Jones, M. G. and Zeevaart, J. A. D., The effect of photoperiod on the levels of seven endogenous gibberellins in the long-day plant Agrostemma githago L., Planta, 149, 274—279, 1980. 11. Jones, M. G. and Zeevaart, J. A. D., Effect of photoperiod on metabolism of [3H]gibberellins A,, 3e/H-A,, and A20 in Agrostemma githago L., Plant Physiol., 69, 660—662, 1982. 12. Jones, M. G. and Zeevaart, J. A. D., unpublished results, 1982. 13. Kende, H., Hahn, H., and Kays, S. E., Enhancement of nitrate reductase activity by benzyladenine in Agrostemma githago, Plant Physiol., 48, 702—706, 1971. 14. Kingsbury, J. A., Poisonous Plants of the United States and Canada, Prentice Hall, Englewood Cliffs, N.J., 1964, 245—246. 15. Metzger, J. D. and Zeevaart, J. A. D., Spinacia oleracea, in CRC Handbook of Flowering, Vol. 4, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 384—392. 16. Svensson, R. and Wigren, M., Klattens historia och biologi i Sverige, Sven. Bot. Tidskr., 77, 165—190, 1983. 17. Merck Index, 9th ed., Merck & Co., Rahway, N.J., 1976, 597. 18. Thompson, P. A., Effects of cultivation on the germination character of the corn cockle (Agrostemma githago L.), Ann. Bot. London, 37, 133—154, 1973. 19. Wellensiek, S. J., Silene armeria, in CRC Handbook of Flowering, Vol. 4, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 320—330. 20. Zeevaart, J. A. D., Inhibition of stem growth and gibberellin production in Agrostemma githago L. by the growth retardant tetcyclacis, Planta, 166, 276—279, 1985. 21. Zeevaart, J. A. D., unpublished results, 1985/86. 22. Zeevaart, J. A. D. and Lusk, W. J., Metabolism of [2H]GA53 in Agrostemma githago, in Plant Research '82, Annu. Rep. MSU-DOE Plant Res. Lab. Michigan State University, East Lansing, Mich., 1983,92—93.
CRC Handbook of Flowering
ALLIUM — ORNAMENTAL SPECIES A. A. De Hertogh and Karl Zimmer INTRODUCTION The genus Allium is comprised of approximately 500 species.4'12-21'28-29-32 Their indigenous range covers almost the entire northern hemisphere and it extends from western Europe and northern Africa across Asia to the Pacific and Atlantic coasts of North America. Very few species originate in the Southern Hemisphere. With few exceptions, they are found in temperate regions that have distinct seasons. This accounts for the periodicity in their growth and development cycles. At present, alliums are classified in the Liliaceae family ,9-18'21 but they have been placed in the Amaryllidaceae family.4 The alliums include not only edible species but also many ornamentals.18'23-25 The 1975 "Classified List and International Register of Hyacinths and other Bulbous and TuberousRooted Plants" describes 22 ornamental species and numerous cultivars or interspecific hybrids of the ornamental species.9 The Netherlands is the leading producer of these species, and over 20 species are in commercial production.24 The characteristics and uses of the principal species are provided in Table 1.
STRUCTURE AND MORPHOLOGY All of the ornamental Allium species are geophytes possessing true bulbs as their geophytic organ.4'21 All of them are tunicated. Scale numbers for the species have not been studied extensively, but some, e.g., A. aflatunense,34-35 have only 2 scales. The minimum circumference bulb sizes that are commercially marketed range from 3 cm for A. neapolitanum 'Grandiflorum' to 20 cm for A. giganteum (Table 1). The root systems have not been studied extensively. Thus, the extent or existence of root hairs and contractile roots is not definitively known. Bijl has indicated that the roots are nonbranching.8 Alliums are scapose plants with mostly only radical or subbasal narrow leaves that range in number from 2 to 3 for A. karataviense to 7 to 8 for A. christophii.4-21 The leaves and scapes can be hollow, square, or triangular. With the exception of A. christophii (Figure 1), which has large (3 to 4 cm) diameter florets, most florets are small (Figure 2). Florets range in number from a few (A. moly) to hundreds (A. giganteum). They are borne in a terminal umbel emerging from a scarious 1- to 3-leafed cap or spathe. They have 6 perianth parts, 6 anthers, and a pistil with 3-celled superior ovary, slender style, and entire or 3parted stigma. Seeds are black and flat, angled, or rounded. Ornamental onions are available in several flower colors (Table 1). Some of them have scents, e.g., A. karataviense (sweet) and A. moly (astringent). PERIODICITY The normal Dutch production systems involve either bulbs or bulblets (asexual) or seed (Table I). 7 - 17 - 20 Depending on the species, they are planted in October or November. Wilson and Peterson,33 using a rhizotron in Ontario, Canada observed that after planting, A. moly exhibited root growth until the soil temperature dropped to 3°C. When the temperature subsequently rose to 4°C or higher, root growth resumed. As will be discussed later, Zimmer et al.34-35 found that preplanting storage temperatures had a marked effect on root dry matter content.
Table 1 PLANT CHARACTERISTICS, PRODUCTION IN HECTARES, SYSTEMS USED, AND PRINCIPAL USES OF ORNAMENTAL ALLIUM SPP. IN PRODUCTION IN THE NETHERLANDS 817202431 1985/86 Hectares24
Production system(s) used
Minimum commercial size (cm)
Bulblets and seed
caeruleum (azureum) christophii (albo-pilosum) elatum giganteum
Bulbs and bulblets
karataviense moly (luteum) neapolitanum 'Grandiflorum' cowanii oreophilum (ostrowskianum) roseum sphaerocephalon stipitatum
.in i ue iieiLJ1CI liiliua
r iiuiijjic uaca
Dried Potted plants
End Mayearly June June
Seed Bulbs and bulblets
End May End Junebegin July End May June
Bulbs and bulblets
Bulbs and bulblets Bulblets
0.29 4.68 0.94
Bulbs and bulblets Bulbs and bulblets Bulbs and seed
3.5 5 16
Flower color Lilac-purple
95—105 Hardy 125—140 Semihardy
Light rose Reddish-purple Lilac-purple
June End July May
X X X
X X X
— X X
35—45 Semihardy 75—85 Hardy 100—120 Hardy
— — —
3 (^ 5 tj oj
CRC Handbook of Flowering
Close up of A. christophii umbel.
The effects of temperature on seed germination of several alliums have been reported.2-27 Depending on their origin, the species can be divided into four types: (1) those that germinate over a wide temperature range (5 to 25°C), (2) those whose germination occurs only at warm temperatures (15 to 25°C), (3) those whose gennination occurs only at cool temperatures (5 to 13°C), and (4) those whose germination only occurs at cold temperatures (2 to 7°C). Rohde27 found that A. caeruleum had two optima (1 to 5°C and 17°C). Time required for germination ranged from 30 to 40 days to 150 to 180 days. Alkema reported that A. giganteum and A. christophii can be increased by scale cuttings.' Presently, however, this system is not commercially practiced. Also, tissue culture has not been highly successful with ornamental onions. 5 Zimmer and co-workers investigated the effects of low temperature storage on subsequent bulb growth of four Allium species.34"36 The two main ones were A. aflatunense (Figure 2) and A. christophii (Figure 1). They found that A. aflatunense developed 1 or 2 new buds at the base of the scape. This occurred simultaneously with differentiation of the inflorescence and before the beginning of the low temperature requirement. By mid-November, the new buds had grown to 2 mm and growth was inhibited during the low temperature treatments. After satisfying the low temperature requirement, i.e., after at least 12 weeks at 5°C or 8°C, the bulb initials started to grow. The grand growth period of the new bulb (usually only one) occurred from the time of emergence of the leaves until senescence. With A. christophii, the optimum storage temperature before elongation of the leaves was about 8°C. Plants stored for 24 weeks at 8°C and then transferred to greenhouse conditions
A. aflatunense plants.
produced the highest fresh weight of bulbs within 16 weeks after planting (Table 2). They concluded that elongation of scape and growth of the daughter bulbs occurred at the expense of the mother bulb and that bulbing required a prolonged cold temperature treatment. This is in agreement with Aoba who found that Allium seedlings would not form a bulb without exposure to a prolonged low temperature treatment. 3 As with most fall-planted bulbs, the leaves of ornamental onions are the first aerial organs to emerge. With some species, they persist until flowering, while for others, e.g., A. stipitatum, they are almost totally senesced at flowering.8 The normal flowering periods for The Netherlands are provided in Table 1. In studies conducted in North America,10 most of the ornamental species tested were found to flower 4 to 6 weeks earlier in climatic zones (minimum winter temperatures are given) 7 ( — 1 8 to - 12°C) and 8 (- 12 to -7°C), 1 to 3 weeks earlier in zones 5 (-29 to -24°C) and 6 ( — 24 to — 18°C), and approximately the same as The Netherlands in zone 4 ( — 34 to — 29°C). These variations in time of flowering are generally a response to the length of the winter and the spring temperatures. As indicated in Table 1, certain species are more hardy than others and, thus, are more adaptable for naturalization for a given climatic zone than others.10
CRC Handbook of Flowering Table 2 EFFECT OF PREPLANTING STORAGE TEMPERATURES OVER TIME ON GROWTH OF NEW DAUGHTER BULB OF A. CHRISTOPH1P6 Preplanting storage temperatures °C
5 8 11 14 17
12.1 14.4 4.5 1.2 0.1
12.0 13.2 10.0 3.0 0.2
12.6 16.0 11.5 8.3 2.8
Weeks of storage'
Fresh weight (g) 16 weeks after planting.
When naturalized, ornamental onions have an apparent rest period from summer until spring when the leaves again emerge. Flower formation, as discussed in the subsequent section, is initiated in late summer.34"36 The normal harvest period for the bulbs in The Netherlands is mid-June to mid-August.7-20-31 After harvest, both planting stock and commercial bulbs of most species are stored dry with ventilation at 20 to 23°C.17-20-31 A. cowanii should be held at a constant 23°C, A. oreophilum at 23 to 25°C, and A. giganteum at 25 to 28°C.17-31
FACTORS INFLUENCING FLOWERING Bulb Size All bulbous plants must reach a minimum bulb size before they can flower.16'26 The precise minimum flowering sizes for the alliums has not been reported. However, minimum sizes for several commercial species, all of which will flower, are given in Table 1. Bulbs that are produced from seed require 4 to 6 years to produce a commercial sized bulb.8 Flowering for most species should be reached in 4 years. Juvenility in ornamental onion species clearly needs further investigation. Temperature The process of floral development from induction to anthesis has been intensively studied in only two species.They are A. aflatunense*4-*5 and A. christophii.36 A. aflatunense bulbs harvested at the end of June had a fresh weight of 30 to 40 g, a circumference of 12 to 14 cm, and they were vegetative.34-35 The bulbs consisted of 2 fleshy bulb scales. The outer scale had a thickness of 12 to 17 mm and the inner scale, surrounding the bud, had a thickness of 2 to 4 mm. The vegetative bud had 5 leaf primordia. Bulbs from this harvest that were stored in peat moss at 11, 17, or 23°C from the beginning of July until the beginning of September developed buds that were 6 mm (23°C), 10 mm (17°C), and 12 mm (11°C) long, respectively (Figure 3). During the storage period, some additional leaves were initiated. Also, bulbs at all temperatures developed an inflorescence; however, growth of the inflorescence depended on the storage temperature. At 11°C, the inflorescence was about 4 mm in diameter after 10 weeks of storage (Figure 4). The number of leaves, including the leaf sheath, was 6 to 10. Inside the bulb, root primordia started to grow. Thus, by mid-September, the developmental stages of bulbs were as follows: (1) all leaves were initiated and formed a bud of about 10 to 12 mm in length, (2) interior to the leaves, the inflorescence was 3 to 6 mm high, and (3) the basal plate showed advanced root development (Figure 5).
mm bud length
11 ° 17°
ol I . . . 1 5.7.
I . . . . I
Weeks dry storage
FIGURE 3. Bud length (mm) of A. aflatunense after 5 or 10 weeks of dry storage at 11, 17, or 23°C. (From Zimmer, K., Walingen, M., and Renken, M., Dtsch. Gartenbau, 39, 594—596, 1985. With permission.) °/o bulbs with flower buds ^prtorl
I Vf i '
/ 0 I
."^Length of ' inflorescence
FIGURE 4. Percent of bulbs with flower buds and length of inflorescence of A. aflatunense after 5 or 10 weeks of dry storage at 11, 17, or 23°C. (From Zimmer, K., Walingen, M., and Renken, M., Dtsch. Gartenbau, 39, 594—596, 1985. With permission.)
When these bulbs were planted in mid-September, the storage temperature initially affected rooting. The lower the storage temperature (17 to 5°C), the higher was the yield of root dry matter. The greatest root dry matter was obtained at 8 to 11°C. During subsequent cooling, there was very little development. Thus, a low temperature requirement for elongation of leaves and scape was clearly demonstrated (Table 3). They also found that after 16 weeks of storage at 5°C, the length of buds had increased up to nearly 5 cm; after 20 weeks the buds were 12 cm; and after 24 weeks, they were 30 cm. With an exposure to constant 8°C, elongation of leaves started after 20 weeks. An 11°C treatment was not effective.
CRC Handbook of Flowering
FIGURE 5. Basal plate of A. aflatunense showing root initials and inflorescence development in mid-September.
Thus, these researchers concluded that A. aflatunense has an optimum temperature for flower formation near 11°C and that the low temperature requirement for leaf growth was 16 weeks at 5°C and, for inflorescence elongation, 20 weeks at 5°C. Without satisfying the low temperature requirement, growth of the new bulb (Figure 6) was inhibited. When A. christophii bulbs were harvested at the end of July, they were vegetative and had 7 to 11 leaf primordia.36 During 12 weeks of subsequent storage in moist peat at 11, 17, or 23°C, the average number of leaf primordia increased, but there was no marked effect of the storage temperature. During the same storage period, the inflorescences were formed; however, temperature did affect this process. After 12 weeks at 17°C, all bulbs had produced an inflorescence, and elongation was accelerated (Figure 7). This was a different response from that observed with A. aflatunense. The optimum storage temperature for root formation was 11 to 14°C. At 17°C, rooting did not occur 8 weeks after the bulbs were planted. Elongation of A. christophii leaves (Figure 8) was significantly affected by the storage temperature. For the initial 8 and 16 week storage periods, elongation was uniform. However,
Table 3 EFFECT OF DURATION OF THREE LOW TEMPERATURE STORAGE TREATMENTS ON LEAF AND FLOWER SCAPE ELONGATION OF A. AFLATUNENSE Pregreenhouse storage treatment Weeks
„, . . ,„„„ Weeks at 18 C in greenhouse
5 8 11 5 8 11 5 8 H 5 8 H
10 11 11 6 8 9 4 5 5 3 3 3
16 20 24
,, . . , Maximum leaf length (cm) 36 22 5 43 2 9 5 40 3 4 7 42 3 8 9
,, . Maximum scape length (cm) 36 Aborted Aborted 47 Aborted Aborted 57 3 3 Aborted 56 5 6 Aborted
Note: Bulbs were initially planted in moist soil, stored, and subsequently grown under greenhouse conditions at 18"CM
Cross-section of scape (lower organ) and developing daughter bulb (upper organ) (A. aflatunense).
CRC Handbook of Flowering No of bulbs
11° 17° 23° after 12 weeks FIGURE 7. The length (mm) of the leaves of 13 A. christophii bulbs after 12 weeks of moist storage at 11, 17, or 23°C. (From Zimmer, K., Walingen, M., and Gebauer, B., Dtsch. Gartenbau, 39, 2206—2209, 1985. With permission.)
mm 300 y
200 - -
12 16 20 24 12 16 20 24
22.7 21.3 29.2 35.4 75.0 51.4 33.6 22.4
24.8 24.3 28.6 41.8 83.6 50.4 35.8 23.2
22.4 24.6 25.3 30.6 107.4 86.1 58.4 36.5
18.0 19.4 22.8 24.7 107.9 95.4 79.1 52.9
12.8 15.8 17.0 21.7 109.6 109.2 100.4 79.8
Tukey (5%) Temp 5.5 Weeks 6. 1 Temp 10.1 Weeks 11.1
rapid elongation occurred with bulbs stored for 24 weeks at 8°C or 11°C. The inflorescence did not show a similar increase in length. When plants exposed to various storage temperature treatments were transferred to the greenhouse, it was clear that 8 weeks of storage at 5, 8, and 11 °C did not satisfy the low temperature requirement for rapid elongation of leaves (Table 4). After 24 weeks of storage at 5°C, however, leaf length reached 35 cm within 22 days after transfer to the greenhouse and nearly 42 cm within 23 days after 24 weeks storage at 8°C. Higher storage temperatures decreased leaf lengths and increased the time required for elongation, e.g., 24 weeks at 17°C resulted in 22 cm leaf length within 80 days after transfer to the greenhouse. As with A. aflatunense, the scape elongated later than the leaves, but the effect of temperature was bascially the same. The longer the cool storage period, the faster the development in the greenhouse; the higher the storage temperature, the slower their development (Figure 8). Thus, for A. christophii, the optimum temperature for flower formation was concluded to be 14 to 17°C; for rooting 14°C; and for satisfying the low temperature requirement and new bulb growth, 5 to 8°C. In contrast to A. aflatunense, an 11 to 17°C storage treatment did not inhibit elongation of leaves and scape, but those temperatures retarded development of the plant. In outdoor flowering trials, de Winter found that growth of A. aflatunense and A. sphaerocephalon could be accelerated by about 2 weeks with 16 weeks of 2°C dry bulb storage before late planting in the fall.13 In greenhouse forcing trials, Dosser14 found that A. karatavlense could be used as a potted plant for mid-April to mid-May flowering. Her studies indicated that this species required a minimum of 19 cold-weeks for optimal flowering. It has also been reported that A. cowanii, A. neapolitanum 'Grandiflorum', and A. unifolium can be forced as cut flowers.3' Other factors The effects of light on flowering of ornamental onions has not been extensively studied. A. ampeloprasum is native to Israel; it is violet-purple and about 100-cm tall.22 It was found16 that photoperiodic long days (4 hr NB of 200 Ix with incandescent lights) advanced flowering of this species by about 50 days (164 days vs. 220 days under natural winter days). This treatment reduced the number of leaves from 18 to 14. Bulb size (4 to 30 grams) had little effect on flowering percentage and quality. Van Meeteren has found that LD in combination with an extended cold treatment accelerated the flowering of A. sphaerocephalon,™ but flower quality was significantly reduced.
CRC Handbook of Flowering
The effects of plant growth regulators or moisture levels has not been reported for ornamental onions. As with any other plant, serious disease infestations will affect flowering. Major diseases are Penicillium spp., Sclerotium cepivorum, tobacco ratel virus, and nematodes.6-17'20-31 Physiological disorders have been reported in some species A. aflatunense, A. datum, and A. giganteum.h-"-20-3> Rough handling during mechanical harvesting and sorting can cause bulbs to become seriously impaired. Thus, normal rooting and subsequently flowering are affected. POSTHARVEST HANDLING OF FLOWERS When alliums are used as cut flowers (Table 1), they should be cut when the florets are approximately 50% open." Most of them can be held for up to 1 week at 0 to 2°C in dry conditions,7 or up to 2 weeks when held in water.22 As with most cut flowers, little or no storage of alliums is recommended.19 No studies on the storage of forced A. karataviense have been reported, but De Hertogh suggested that this plant could be stored for a short period at 0 to 2°C.12 This was inferred by the cut flower studies that have been conducted. ACKNOWLEDGMENTS The authors wish to express their appreciation to Mr. J. Bijl (Breezand) and Ir. M. Benschop (Lisse) of The Netherlands and Dr. W. E. Ballinger of North Carolina State University for their review of this manuscript.
REFERENCES 1 . Alkema, H. Y., Vegetatieve vermeerdering van Allium species, Bloembollencultuur, 86(48), 981—982, 1976. 2. Aoba, T., Effects of different temperatures on seed germination of garden ornamentals in Allium, J . Jpn. Soc. Home. Sci., 36, 333—338, 1967. 3. Aoba, T., Effect of low temperature on the bulb or corm formation in some ornamental plants, J. Jpn. Soc. Hortic. Sci., 39, 369—374, 1970. 4. Bailey, L. H., Manual of Cultivated Plants, Macmillan Company, New York, 1949, 245. 5. Benschop, M., personal communication, 1986. 6. Bergman, B. H. H., Allium, in Ziekten en Afivijkingen bij Bolgewassen, Part I, Liliaceae, 2nd ed., Laboratorium voor Bloembollenonderzoek, Lisse, The Netherlands, 1983, 13—18. 7. Bijl, J., Diverse alliums zijn uitstekende snijbloemen, zeer houdbaar op water en dikwijls goed bestand tegen het "cellen", Bloembollencultuur, 87(48), 1025—1028, 1977. 8. Bijl, J., personal communication, 1986. 9. Classified list and international register of hyacinths and other bulbous and tuberous-rooted plants, Koninklijke Algemeene Vereeniging voor Bloembollencultuur, Hillegom, The Netherlands, 1975, 12—15. 10. De Hertogh, A. A., Ho/land Bulb Garden Guide, International Flower-Bulb Centre, Hillegom, The Netherlands, 1982, IV-A-1—22. 1 1 . De Hertogh, A. A., Hoi/and Bulb Forcers Guide, 4th ed., International Flower-Bulb Centre, Hillegom, The Netherlands, 1989. 12. De Janka, V., Key to the alliums of Europe, Herbertia, 11, 219—226, 1944. 13. De Winter, J. A. T., Bloeispreiding bij Allium door temperatuurbehandeling, Vakbl. Bloemisterij, 39(29), 28—29, 1984. 14. Dosser, A., Allium karataviense — A lonely little onion in a petunia patch, N.C. Flower Growers Bull., 24, 11 — 12, 1980. 15. Halevy, A. H., personal communication, 1986.
16. Hartsema, A. M., Influence of temperatures on flower formation and flowering of bulbous and tuberous plants, Handbuch der Pflanzenphysiologie, Vol. 16, Ruhland, W., Ed., Springer Verlag, Berlin, 1961, 123—167. 17. Hoog, Th., Allium, in Tips voor de Bloembollenkwekers, Part 1, Teelt van Bijgoedgewassen: Acidanthcra tot Gladiolus, Vereniging Proeftuin Bloembollencultuur, Lisse, The Netherlands, 1969, 12—21. 18. Jones, H. A. and Mann, L. K., Onions and their Allies, Leonard Hill, London, 1963. 19. Kalkman, E. Ch., Bewaring negatieve invloed op houdbaarheid Allium en Eremurus, Vakbl. Bloemislerij, 39(26), 33, 1984. 20. Krabbendam, P., Allium, in Bloembollenteelt, Bijgoed, Part VII, W. E. J. Tjeenk Willink, Zwolle, The Netherlands, 1967, 15—20. 21. Bailey, L. H., Staff of the Hortorium, Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada, 3rd ed., Macmillan, New York, 1976, 47. 22. Mevel, A., Deux bulbeuses en vue: Allium et Liatris, Hortic. Fr., 150, 21—24, 1983. 23. Nakamura, E., Allium — minor vegetables, CRC Handbook >f Flowering, Vol. 1, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 410—418. 24. Produktschap voor Siergewassen and Bloembollenkeuringsdienst, Bloembollen (voorjaarsbloeiers), Beplante Oppervlakten 1982/83 Tot en met 1985/85, Den Haag and Lisse, The Netherlands, 1985, 30. 25. Rabinowitch, H. D., Onion and other edible onions, CRC Handbook of Flowering, Vol. 1, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 398—409. 26. Rees, A. R., Ornamental bulbous plants, CRC Handbook of Flowering, Vol. 1, Halevy, A. H., Ed., CRC Press, Boca Raton, Fla., 1985, 259—261. 27. Rohde, J., Abhangigkeit der Keimung von der Temperatur bei Allium- und Friti/laria-Arten, Gartenbauwissenschaft, 35, 329—345, 1975. 28. Stearn, W. T., Notes on the genus Allium in the Old World. Its distribution, names, literature, classification and garden-worthy species, Herbertia, 11, 11—34, 1944. 29. Stearn, W. T., 2. Description, classification and phylogeny. The floristic regions of the U.S.S.R. with reference to the genus A/lium, Herbertia, 11, 45—63, 1944. 30. Van Meeteren, U., personal communication, 1986. 31. Van Nes, C. R. and Schoorl, C. E., Ed., Teelt en gebruiks moglijkheden van bigoedgewassen, Consulentschap in Algemene Dienst voor de Bloembollenteelt, Lisse, The Netherlands, 1988. 32. Vvedensky, A. I., The genus Allium in the U.S.S.R., Herbertia, 11, 65—218, 1944. 33. Wilson, C. and Peterson, C. A., Root growth of bulbous species during winter, Ann. Bot. London, 50(5), 615—619, 1982. 34. Zimmer. K. and Renken, M., Untersuchungen an A/lium af/atunense. Dtsch. Gartenbau, 38, 2004— 2008, 1984. 35. Zimmer, K., Walingen, M., and Renken, M., Untersuchungen zur periodischen Entwicklung von Allium aflatunense, Dtsch. Gartenbau, 39, 594—596, 1985. 36. Zimmer, K., Walingen, M., and Gebauer, B., Untersuchungen an Allium christophii, Dtsch. Gartenbau, 39, 2206—2209, 1985.
CRC Handbook of Flowering
ALOPECURUS PRATENSIS En. Meadow foxtail; Fr. Vulpin de pres; Ge. Wiesenfuchsschwanz Ola M. Heide
INTRODUCTION The genus Alopecurus L. (Gramineae) comprises about 50 species native to the temperate regions, some in both hemispheres.1-3 They are annuals or perennials and some are valuable forage grasses. A. pratensis L. is a 50- to 110-cm tall perennial which is commonly cultivated as a forage and pasture grass. It occurs in meadows and pastures throughout Europe and Asia and has become naturalized in other regions.1-3 The plant is vigorously growing, somewhat cespitose, with 4- to 8-mm wide leaves; the flag leaf sheath is usually inflated. The inflorescence is a 5- to 11-cm long, cylindrical, spike-like panicle with laterally compressed spikelets, each with only 1 floret. The glumes have silky hairs, giving the inflorescence a soft and silky touch. The palea is absent.3 A. pratensis is easily grown from seeds. Under SD conditions it produces a rosette with short leaves and abundant tillering. Stem elongation is associated with flowering. FLOWERING RESPONSE TO PHOTOPERIOD AND TEMPERATURE A. pratensis is one of the earliest grasses to head and flower in the spring, and inflorescence primordia are already formed in late September under field conditions in central Europe.2 Studies in controlled environments also revealed that flower initiation occurs over a wide range of temperatures in both SD and LD4 (Figure 1). With a 6-week induction period, a high proportion of the plants of two Norwegian ecotypes initiated inflorescences at temperatures up to 15°C in SD and 9°C in LD. Marginal induction was obtained even at 21°C in SD and 18°C in LD. With decreasing temperature the difference in efficiency between SD and LD decreases so that at 6°C there is little effect of daylength.4 These results are in good agreement with reports of FI during the long days and cool temperatures of the subarctic summer.6 Since SD and low temperatures also strongly reduce leaf elongation in this and other temperate grasses,5 a strong negative correlation was established between the length of basal leaves and the number of panicles initiated.4 Heading and flower development are promoted by LD and relatively high temperature while the combination of SD and low temperature effectively suppresses flower development4 (Figure 2). Given the early initiation of flower primordia in the autumn, this seems an important control mechanism to prevent precocious stem elongation and heading which would lead to winter damage of the developing inflorescences. Latitudinal ecotype differentiation in flowering requirements seems not to be very pronounced in A. pratensis. The time of inflorescence initiation was about the same in plants of Finnish and German origin,2 and ecotypes from 60 and 69°N latitude in Norway also responded very similarly to photoperiod and temperature treatments.4
Temperature (°C) FIGURE 1. Heading in two Norwegian ecotypes of A. pratensis after 6 weeks primary induction in SD (8 hr) and LD (24 hr) and various temperatures as indicated. Flower development at 21°C and 24 hr photoperiod. (From Heide, O. M., Physiol. Plant., 66, 252, 1986. With permission.)
FIGURE 2. Effects of various photoperiods at 12°C on heading and flower development in A. pratensis, ecotype from south Norway. Photoperiods left to right: 8, 13, 19, and 24 hr. At 18 and 24°C a high proportion of plants headed also in 8-hr photoperiod. The plants had previously received 50 days primary induction at 9°C and 12 hr photoperiod. (From Heide, O. M., Physiol. Plant., 66, 255, 1986. With permission.)
CRC Handbook of Flowering REFERENCES 1 . Bews, J. W., The World's Grasses, Longmans, Green, London, 1929, 408 pp. 2. Bommer, D., Uber Zeitpunkt und Verlauf der Bliitendifferenzierung bei perennierenden Grasern, Z. AckerPflanzenbau, 109, 95—118, 1959. 3. Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M., and Webb, D. A., Flora Europaea, Vol. 5, Cambridge University Press, Cambridge, vol 5, 1980, 241—243. 4. Heide, O. M., Primary and secondary induction requirements for flowering inAlopecuruspratensis, Physiol. Plant., 66, 251—256, 1986. 5. Heide, O. M., Bush, M, G., and Evans, L. T., Interaction of photoperiod and gibberellin on growth and photosynthesis of high-latitude Poa pratensis, Physiol. Plant., 65, 135—145, 1985. 6. Vasiliskov, V. F., (On the state of perennial herbs before overwintering in Khibiny), Prinkl. Bot. Genet. Sel. Ser. 01, 43, 267—274, 1970 (transl.).
ANIGOZANTHOS* En. Kangaroo Paw Mark S. Roh and Glenda J. Motum INTRODUCTION Kangaroo paws are a group of Australian native plants from the genera Anigozanthos (11 species) and Macropidia (1 species). Kangaroo paws are monocots in the Haemodoraceae, a family closely related to the lily (Liliaceae) and iris (Iridaceae) families. The plants are herbaceous perennials with creeping and clumping rhizomes and basal strap-shaped or swordshaped leaves. Flowers with bright red, purple, green, or yellowish colors are borne in a single row along a narrow woolly spike or raceme that stands tall above the foliage. As the flowers open, the spike is bent and resembles a kangaroo's paw; thus, the common name.
NATURAL HABITAT Species of Anigozanthos and Macropidia occur as part of the scrub vegetation along the coast and up to 160 km inland in southwestern Australia. They grow in full sun among the shrubs and herbs common in open heath and woodland areas, where the soils are highly leached and mineral deficient, and in deep sands of the coastal plain.7 Kangaroo paw species experience a warm temperate Mediteranean climate with summer drought and dominant winter rainfall with a range of 380 to 1200 mm according to species.7 In the north, summer temperatures average 26°C or more with relatively frequent temperatures in excess of 38°C. Humidity is relatively low throughout the year. All species are inactive from midsummer, with some species showing a full dormancy, surviving solely as subsurface rhizomes. Active vegetative growth resumes with lower temperatures and the onset of rains in autumn or early winter. Each species has a more-orless distinctive flowering period within the range late winter to early summer. DESCRIPTION OF THE SPECIES Twelve species of kangaroo paws are recognized and fall into two sections of the genus Anigozanthos, together with the monotype Macropidia fuliginosa. Descriptions are based on various Australian publications.L4-7-10-17 A. manglesii — The red and green kangaroo paw produces grey-green, broad, swordshaped leaves, 15 to 150 cm long with stiff hairs scattered on both leaf edges. The flowering stem emerges from the center of the leaf fans and grows up to 1 m in height. The simple or occasionally forked flower stalk is covered with scarlet red woolly hairs that continue onto the swollen red base (ovary) of the flowers. The remainder of the 8-cm flower perianth is green and covered with dense greenish hairs. This species flowers from July to December, with peak flowering in September and October. A. manglesii is the official floral emblem of the state of Western Australia. A. bicolor — The red and green kangaroo paw grows 30 to 45 cm tall with narrow leaves and resembles a dwarf A. manglesii. It produces flowers with a red and green corolla from August to November and becomes dormant in summer. A. gabrielae — This is another red and green kangaroo paw, closely related to A. bicolor *
Supplement to the chapter in Volume 1, pp. 468—470.
CRC Handbook of Flowering
but of even more dwarf habit. Leaves rarely exceed 10 cm and flower stems 20 cm. Flowering period is similar to A. bicolor. A. rufus — The red kangaroo paw grows on the southern coast from the Stirling Range to Cape Arid. Leaves are dull green in color; flowers with a deep red corolla are produced on an inflorescence 60 to 90 cm tall from October to January. A. pulcherrimus — This species, known as golden kangaroo paw, is found in a restricted area on the west coast north of Perth. Leaves are grey-brown and the compound inflorescence is 60 to 90 cm tall. Flower color ranges from rich yellow to full gold and rarely apricot when flowers appear from November to February. A. viridis — The green kangaroo paw is found in wet to swampy areas on the west coast from Augusta to Watheroo. The simple or forked flower stalk is almost 60 cm tall and is produced from September to November. The flowers are nearly 8 cm long and have a yellowgreen base and bright emerald green corolla. A. flavidus — The Albany kangaroo paw has evergreen leaves; it grows in the cool and cloudy region from Albany to Cape Naturaliste, where rainfall is nearly 1500 mm annually. The branched inflorescences are 180 to 210 cm tall and are produced from October to December. Flowers are over 2.5 cm long and range from green to predominantly deep red due to the dense branched hairs on the exterior which contrast strongly to the grey throat. A pink variant of this species is also found. A. humilis — The cat's paw is widespread, ranging from the south coast near Albany to the Murchison River. Leaves are 15 cm long, green with stiff hairs. The simple or forked spike is 15 to 45 cm tall and bears yellow to orange-red flowers from June to November. This species has not grown well in cultivation. Macropidia fuliginosa — The black kangaroo paw grows near the west coast, from Muchea to Geraldton. It grows in large clumps; the yellow-green leaves have a yellow marking with dark tip. The compound inflorescence grows up to 90 cm tall and is covered with black branched hairs. Flower buds are also clothed in black hairs but open to show greenish to whitish petals. The flowering season is from September to November. Three other species are all very localized in occurrence. A. preissii typically grows as single plants rather than clumps. The leaves are shiny green, narrow, and fleshy and grow approximately 46 cm long. The flowers have a redish-orange base and a yellow corolla. A. onycis and A. kalbarriensis are small plants with foliage 10 to 20 cm long and flower stems 15 to 30 cm tall. Flowers of A. onycis are red and yellow and flowers of A. kalbarriensis are yellow and green.
BREEDING Kangaroo paws have proven to be amenable to interspecific hybridization.9>'9'20 Early breeders, such as Oliver and Hopper, of kangaroo paws aimed to transfer the vigor, hardiness, and disease resistance of A. flavidus to species with more spectacular flowers but which were less reliable in cultivation. The color and vigor of the foliage of A. flavidus was dominantly inherited in all hybrids. Three cultivars with horticultural merit have been introduced to the industry from Hopper's breeding program. They are 'Dwarf Delight', 'Regal Claw', and 'Red Cross' from crosses with A. onycis, A. preissii, and A. rufus as seed parents and with A. flavidus as the pollen parent, respectively. More recently, a large number of hybrids of Turner's breeding program have been released commercially and are known collectively as 'Bush Gems' hybrids. Current breeding has aimed at producing plants for cut-flower or container plant production, with improved range and quality of flower color, resistance to fungal infection, and reduced seasonality of flowering.19-20
PROPAGATION Kangaroo paws can be propagated from seed, division of the rhizome, or by in vitro tissue culture. Seed matures about a month after the flowers have dried off and must be collected as soon as it is ripe and before it is shed. Most species of kangaroo paw show a low percentage of germination.23 Seeds germinate in 21 to 35 days in A. manglesii, A. flavidus, A. viridis, and A. bicolor, and germination can be longer than 45 to 50 days in A. preissii. Macropidia, on the other hand, is very hard to germinate, possibly due to the imposed dormancy by the seed coat. Germination could be improved by soaking seeds in 50 to 60°C water for 2 hr Germination of A rufus seeds could be improved by a 24-hr soak in 1000 ppm GA3. Germination of A. viridis is increased by a 4-min dip in concentrated sulfuric acid, while A. manglesii seeds germinate after a combination of 1-min dip in sulfuric acid followed by a 24-hr soak in GA3.2 From one mature plant, 10 to 20 small fans can be propagated by division. The divided fans will root in 2 to 4 weeks under mist or in a greenhouse with regular watering. Tissue culture is now a well established technique for propagation and research with kangaroo paws. Shoot induction and continued proliferation from lateral bud explants was achieved using a combination of 0.5 mg/€ IBA and 0.5 mg/€ NAA supplemented to Murashige and Skoog medium. Continued proliferation was possible by subculturing in a medium containing 0.25 mg/€ of BA and NAA each. Rooting of plantlets occurs within 4 weeks in a medium containing 0.2 mg/€ NAA. 5 SOIL TYPE AND NUTRITION Most kangaroo paws, with a possible exception of A. flavidus, require well-drained soils. In heavy clay soil, A. manglesii, A. rufus, and A. pulcherrimus fail to grow, since in western Australia, kangaroo paws are cultivated on acid soils and heaths.1 Kangaroo paws respond to fertilizer and grow well with relatively high levels of applied nutrients. A. flavidus x A. onycis and A. flavidus grew well at a rate of 4.6 g/€ of 14 N—1.8 P—5 K or of 7.3 g/€ of 14 N—3.4 P—5 K fertilizer, respectively. The species appeared to be tolerant to phosphorus. A. mangelsii has been grown very successfully with 93 kg N, 50 kg P, and 140 kg K per hectare in seven monthly applications.21 Leaf tip blackening is thought to be caused by calcium deficiency rather than disease. Increased growth rate, less leaf tip burn, and increased frost resistance resulted from supplemental calcium fertilization.24 WATER REQUIREMENTS Under natural conditions kangaroo paws become dormant during dry summers and grow again after winter rains. However, if plants are watered during the summer, all species continue to grow throughout the summer.22 A. manglesii flowered 1 month earlier and a greater number of flowers were produced in irrigated plants compared to nonirrigated plants. Trickle irrigation methods are most suitable for kangaroo paw cultivation to prevent foliar fungal diseases caused by constant wetting of foliage by overhead irrigation.21'22
PLANT DENSITY Flower production in kangaroo paw is influenced by plant spacing. A. manglesii plants spaced 50 cm apart produced many more flowers than those spaced at 25 cm apart, particularly in irrigated plots.22
CRC Handbook of Flowering
-^ 60" LU ,* '
SD ^ x^ .X^
2 T 2 ^ ? (weeks in daylength)
FIGURE 1. Percentage of A. flavidus plants in flower over time in long (16 hr) and short (8 hr) daylength. (From Motum, G. J. and Goodwin, P. B., Sci. Horde., 32, 123—133, 1987. With permission.)
In commercial plantings, it was suggested that plants should be set out in double rows 1 to 1.5 m apart with 50 to 75 cm between individual rows and plants. The wider spacings are for A. pulcherrimus, A. rufus, and Macropidia fuliginosa.22
DISEASES, PESTS, AND PHYSIOLOGICAL DISORDERS Ink disease is recognized by small black spots first occurring on the older leaves. Inking of leaves is a generalized response to stress which can be caused by a multiplicity of factors alone or in combination. In extreme cases, the disease attacks the rhizome leading to the death of the plant.3-6 Alternaria alternata is established as the casual organism of ink disease in Western Australia. 18 Ink disease could be partially prevented by growing under full sun to allow leaves to dry off quickly and by avoiding excessive use of water and fertilizer application that causes lush vegetative growth which is more susceptible to infection. A. humilis, A. kalbarriensis, A. manglesii, and A. gabrielae are susceptible to ink disease, although A. flavidus and A. viridus were resistant.4 Blackening and withering of leaf tips appears to be caused by calcium deficiency rather than pathogenic disease. Kangaroo paws benefit from the addition of calcium in low-calciumcontent soil. Due to improved growth, flowering was accelerated and the flower stems were longer.24 FLOWERING OF KANGAROO PAWS To be able to flower under field conditions, rhizomes need to be of a certain size. The minimum sizes when leaves are trimmed to 5 cm above the apex are A. flavidus 175 g; A. manglesii 75 g; and A. viridis 25 g. 16 The flowering of kangaroo paws with respect to daylength response are species specific; A. flavidus is a quantitative LDP (Figure 1), A. manglesii is a quantitative SDP (Figure 2), and A. rufus, A. pulcherrimus, and hybrid of A. flavidus X A. manglesii are DNP.16
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A. mangles ii