Reevaluation of Systematic Relationships in Triticum L. and Aegilops L
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AN ABSTRACT OF THE THESIS OF Laura A. Morrison for the degree of Doctor of Philosophy in Botany and Plant Pathology presented on October 21, 1994. Title: Reevaluation of Systematic Relationships in Triticum L. and Aegilops L. Based on Comparative Morphological and Anatomical Investigations of Dispersal Mechanisms Redacted for Privacy Abstract approved: Kenton L. Chambers Comparative morphological and anatomical studies of the dispersal mechanisms characterizing the wheat complex (Triticum L. and Aegilops L.) have documented patterns of adaptive radiation which may have significance for evolutionary relationships. These patterns, which form an array of diverse types of diaspores among the diploid taxa, appear conceptually to have a starting point in the dimorphic inflorescence of Ae. speltoides. Separate dispersal trends, centered primarily in features of rachis disarticulation, lead in the direction of novel diaspore types for Aegilops and in the direction of domestication for Triticum. With respect to the taxonomy, this structural evidence supports the traditional Linnaean generic circumscriptions and suggests a need for a monographic revision of Triticum. In documenting the dispersal mechanisms, these studies have clarified conventional interpretations and have offered new insights on the developmental relationships linking the wild and domesticated taxa of the wheat complex. Although genetic studies were not encompassed within this research, a consideration of the genetic explanations for rachis disarticulation and glume closure suggests that the phenotypic traits typically used in genetic studies are not well understood. Given that the reticulate nature of genomic relationships in the wheats is coupled with intergrading variation and polymorphic species, a proposal is made for a broader evolutionary view than is found in the strict cladistic concept. This proposal emphasizes the need of an improved understanding of fundamental structural traits and an inclusion of these traits in evolutionary analyses. °Copyright by Laura A. Morrison October 21, 1994 All Rights Reserved Reevaluation of Systematic Relationships in Triticum L. and Aegilops L. Based on Comparative Morphological and Anatomical Investigations of Dispersal Mechanisms by Laura A. Morrison A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed October 21, 1994 Commencement June 1995 Doctor of Philosophy thesis of Laura A. Morrison presented on October 21, 1994 APPROVED: Redacted for Privacy Major Professor, representing Botany and Plant Pathology Redacted for Privacy LIVHead of Department of Botany & P1 t o ogy Redacted for Privacy Dean of Graduate Sc I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Redacted for Privacy thor ACKNOWLEDGEMENTS The research reported in this thesis would not have been possible without the assistance, guidance, and encouragement of faculty and staff members associated with Oregon State University and members of the international wheat research community. I am particularly grateful to those individuals who provided germplasm material, answered the many questions I posed in correspondence or in meetings at international conferences, and encouraged my alternative approach to modern systematic studies in the wheat complex. I offer a special note of appreciation to the following people who were instrumental in guiding my work: to Kenton L. Chambers, my major professor, for the freedom which he provided in my pursuit of the mysteries of wheat evolution; to Robert J. Metzger (Oregon State University), for his sharing of an encyclopedic knowledge of the wheats; to Dr. J. Giles Waines (University of California, Riverside), for his support from afar; to Dr. Joachim Kummerow (Oregon State University), for the many hours of his time devoted to translating an obscure, but important German literature; to the organizers of the 1992 ICARDA International Workshop on Evaluation and Utilization of Biodiversity in Wild Relatives and Primitive Forms for Wheat Improvement and the 8th International Wheat Genetics Symposium (1993) for arranging my attendance at these two international conferences; and to Lynda M. Ciuffetti and Donald J. Armstrong (Department of Botany and Plant Pathology) for their wise advice and counsel, particularly on matters of teaching. I am also grateful to the administrative staff of the Department. A sincere expression of appreciation to Diane Simpson and Blaine Baker for all the significant ways in which they helped with my journey through a PhD program; to Lewis Tate and his assistants for their cooperation and accommodation of my unusual agronomic needs for the research field at the Botany and Plant Pathology Field Lab; and to Kevin Currans and Galen Krokum of the College of Science Biocomputing Consortium for their patient assistance with computer matters. Funding for this research was obtained from the Tyson Fellowship Fund of the Woman's National Farm and Garden Association, Inc., the Northwest Scientific Association, and the Bonnie Templeton Fund (Department of Botany and Plant Pathology). Trips to the International Triticeae Symposia (1991, 1993), the ICARDA International Workshop (1992), and the 8th International Wheat Genetics Symposium (1993) were funded with donations from private and public sources. I appreciate the efforts of all those who assisted in large and small ways with the financial arrangements for these trips. In this regard, I am deeply grateful to Kenton L. Chambers, Stella M. Coakley (Head, Department of Botany and Plant Pathology), J. Giles Waines, Warren E. Kronstad and the Oregon Wheat Commission, Ardeshir Damania (formerly of ICARDA), and my parents, Robert L. and Marion W. Morrison. The botanical illustrations contained in Chapters 4 and 5 proved an essential part of this thesis. For her daring entry into the pictorial world of wheat, I am indebted to Christine Roberts to whom I wish a prosperous career as an illustrator should graduate school no longer offer an option. I also appreciate the supplementary support offered by Pablo Rosso who contributed three illustrations while emersed in the last stages of his masters degree in Plant Pathology. To a warm and caring community of friends--Tina Dreisbach, Frank Gecina, Catharina Coenen, Chris Lundberg, Kyoung-Hee Kim, Jolene and Steven Broich, Hillary Egna, Marty Fitzpatrick, Robin Wagers, Carolyn Wright, David Gross, and Barbara Wilson--my sincere gratitude. And to Raan Young, a multitude of thanks for midnight assistance at the scanner. TABLE OF CONTENTS Page I. INTRODUCTION 1 II. TAXONOMY OF THE WHEATS: A COMMENTARY 4 Abstract 4 Introduction 5 The Taxonomy 7 Taxonomic Deficiencies and Evolutionary Considerations 13 Triticum urartu Thumanjan ex Gandilian 14 Aegilops speltoides Tausch 16 Anomalous Wheat Taxa 18 Conclusion 20 Acknowledgements 21 References 22 III. A MONOGRAPHIC PROJECT TO REVISE THE TAXONOMY OF TRITICUM L. 26 References 33 IV. DISPERSAL MECHANISMS IN THE WHEAT COMPLEX (TRITICUM L. AND AEGILOPS L.): ADAPTIVE RADIATION 35 Abstract 35 Introduction 36 Materials and Methods 42 Clarification of Terminology 43 Inflorescence Structure 63 Page Historical Perspective 63 Deficiencies in Current Interpretations of Dispersal Mechanisms 70 Developmental Relationships of Diaspore Types 73 A Reinterpretation of the Adaptive Radiation 75 Wedge Diaspore Class 75 Synaptospermic Diaspore Class 89 Anomalous Dispersal Strategies 101 Spike let Dispersal 101 Floret Dispersal 104 Seed Dispersal 105 Dispersal and Seedling Establishment 109 Passive Dispersal 109 Penetration in the Soil 112 Seedling Establishment 113 Developmental Relationships Within the Tribe Triticeae 118 Conclusion 121 References 122 V. DISPERSAL MECHANISMS IN THE WHEAT COMPLEX (TRITICUM L. AND AEGILOPS L.): RACHIS DISARTICULATION AND GLUME CLOSURE 130 Abstract 130 Introduction 131 Materials and Methods 134 Rachis Disarticulation 135 Page Morphology of the Fracture Zone 138 Anatomy of the Fracture Zone 142 Development of the Tough Rachis 157 Glume Closure 159 The Glume Base 164 A Glume Pulvinus 166 The Wu 1st 168 Glume Texture 170 Implications for Genetic Studies 171 Genetics of Rachis Disarticulation and Glume Closure 171 Misinterpretation of Phenotypic Characters 178 Conclusions 182 References 184 VI. REINTERPRETATION OF DISPERSAL STRATEGIES IN TRIT7CUM L. AND AEGILOPS L 192 Abstract 192 Introduction 193 Adaptive Radiation 193 Significance of Aegilops Speltoides 196 An Alternative Interpretation 198 References 200 VII. CHARACTER ANALYSES IN THE WHEAT COMPLEX 203 Genetic Connections and Within-Species Variability 208 An Alternative Evolutionary Concept 213 Page Conclusion 218 References 218 BIBLIOGRAPHY 225 APPENDICES 243 Appendix A Workshop on Triticum Systematics: Need for a Monographic Revision of Triticum 244 Appendix B Accessions of Wheat and Non-Wheat Species Used in Comparative Morphological Investigations 246 Appendix C Attribution for Translations 266 Appendix D Zhukovsky Classification of Aegilops (1928) 267 Appendix E Eig Classification of Aegilops (1929) 268 Appendix F Kihara Genomic Classification of Aegilops (1954) 269 Appendix G Letter to Dr. Stephen Jury 270 LIST OF FIGURES Page Figure 4.1. Wedge diaspores of Ae. speltoides ssp. ligustica showing their sequential position of disarticulation 45 Figure 4.2. Barrel diaspores of Ae. tauschii showing their