Role of the Ascigerous State in the Epidemiology Of
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ROLE OF THE ASCIGEROUS STATE IN THE EPIDEMIOLOGY OF EYESPOT IN WHEAT By DANILO ISAAC VERA COELLO A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Plant Pathology MAY 2015 © Copyright by DANILO ISAAC VERA COELLO, 2015 All Rights Reserved © Copyright by DANILO ISAAC VERA COELLO, 2015 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of DANILO ISAAC VERA COELLO find it satisfactory and recommend that it be accepted. ____________________________________ Timothy D. Murray, Ph.D., Chair ____________________________________ Dennis A. Johnson, Ph.D. ____________________________________ Gary G. Grove, Ph.D. ____________________________________ Weidong Chen, Ph.D. ii ACKNOWLEDGEMENT I would like to express my warmest gratitude to my supervisor, Professor Timothy D. Murray for having confidence in me from the start, for his invaluable guidance and encouragement throughout this project. I would also like to thank Dr. Murray for his patience and time invested in giving me pieces of advice and preparing me for future challenges. I thank my other committee members, Professors Dennis A. Johnson, Gary G. Grove and Weidong Chen, for their input, guidance during my graduate work and critical review of my dissertation. I would like to thank the Plant Pathology Department at Washington State University, especially the faculty, staff and graduate students who provided encouragement and friendship during my time as graduate student. I would like a special thank Dr. Scot Hulbert, Dr. Hanu Pappu, Cheryl Hagelganz, Debra Marsh, Mary Stormo, and Mike Adams. I would like to acknowledge all the members of the Dr. Murray research group, especially to Dr. Henry Wetzel and Dr. Hongyan Sheng for their help and support in setting up experiments in field and lab and to the graduate students in Dr. Murray lab for their friendship. I also would like to thank the National Institute of Agricultural Research (INIAP) in Ecuador for offer me a scholarship to obtain my Ph.D., and the Washington Grain Commission for financial support of part of my research. My special appreciation goes to Dr. Carmen Suarez, for transmitting me her spirit of adventure and excitement in regard to research. Her guidance during my initial formation encourages me to continue my preparation as a researcher. Also, I am particularly grateful to Dr. Devra Jarvis and Bioversity International for initial support of my research. iii A very special thanks to my beloved parents Hipolito and Isabel, and to my brother and sisters for their patience; for always being there for me, for their teaching and guidance which made me become as to what I am now. Finally, and most importantly, I would like to thanks my wife and kids for being the reason behind my smiles, my inspiration and motivation to always do my best in everything I do -without them this effort would have been worth nothing. iv ROLE OF THE ASCIGEROUS STATE IN THE EPIDEMIOLOGY OF EYESPOT IN WHEAT Abstract by Danilo Isaac Vera Coello Washington State University May 2015 Chair: Timothy D. Murray Eyespot is a chronic disease of winter wheat, caused by Oculimacula yallundae (OY) and O. acuformis (OA) that results in premature ripening of grain, lodging, and reduced grain yield. Discovery of the Oculimacula spp. teleomorph in the Pacific Northwest region of the United States (PNW) is relatively recent and the role of apothecia or ascospores in the epidemiology of eyespot is unclear. Our goals were to determine the occurrence of OY and OA apothecia in commercial and inoculated field plots, to investigate when apothecia are produced and ascospores released, to determine persistence of apothecia to over summer and over winter, and to investigate factors influencing production of OY apothecia in vitro. Apothecia of OY and OA were found in spring and fall in commercial wheat fields, demonstrating that sexual reproduction occurs regularly in the PNW and may play a role as primary inoculum in the eyespot disease cycle. Apothecia survived over summer but not over winter in inoculated field plots. Occurrence of ascospores was monitored with Burkard spore traps in inoculated field plots. Ascospores of OY and OA were trapped during spring and fall, and there were no v differences in the number of ascospores trapped from fields with a wheat crop or stubble. Number of ascospores m-3 wk -1 was positively correlated with relative humidity and weekly accumulated precipitation. Regression models based on environmental variables accounted for 27 to 36% of the variation in number of ascospores trapped. The effect of media, host substrate, inoculation method, temperature, light and stress-shock preconditions on development of primordial and mature apothecia of OY were studied. Inoculation of winter wheat and spring barley straw segments with a suspension of conidia or mycelial plugs favored apothecia development; however, mature apothecia did not developed in treatments without host substrate. This research provides a base-line offering new insights into the role of the sexual stage of Oculimacula spp. in the epidemiology of eyespot. Understanding the incidence, seasonality and occurrence of apothecia and ascospores provides a better understanding of the role of ascospores as an inoculum source. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ................................................................................................... iii-iv ABSTRACT ............................................................................................................................ v-vi LIST OF TABLES .................................................................................................................. ix-x LIST OF FIGURES .............................................................................................................. xi-xii PREFACE ................................................................................................................................ xiii DEDICATION ......................................................................................................................... xiv CHAPTER 1. INTRODUCTION AND LITERATURE REVIEW ...................................... 1 Wheat .................................................................................................................. 1 Eyespot disease ................................................................................................... 2 Causal organisms .................................................................................... 5 The sexual stage .................................................................................... 11 Epidemiology ........................................................................................ 15 Management .......................................................................................... 23 Objectives ......................................................................................................... 28 Literature cited .................................................................................................. 30 2. OCCURRENCE AND SURVIVAL OF APOTHECIA OF OCULIMACULA ACUFORMIS AND O. YALLUNDAE ON WHEAT STUBBLE IN THE U.S. PACIFIC NORTHWEST ............................................................................... 49 Introduction ....................................................................................................... 50 Materials and Methods ...................................................................................... 52 vii Results ............................................................................................................... 55 Discussion ......................................................................................................... 57 Literature cited .................................................................................................. 62 3. SEASONAL AND TEMPORAL VARIATION OF ASCOSPORE RELEASE BY OCULIMACULA YALLUNDAE AND O. ACUFORMIS IN THE U.S. PACIFIC NORTHWEST ............................................................................... 73 Introduction ....................................................................................................... 74 Materials and Methods ...................................................................................... 75 Results ............................................................................................................... 80 Discussion ......................................................................................................... 82 Literature cited .................................................................................................. 87 4. PRODUCTION OF APOTHECIA BY OCULIMACULA YALLUNDAE IN VITRO ............................................................................................................ 100 Introduction ..................................................................................................... 101 Materials and Methods .................................................................................... 103 Results ............................................................................................................. 106 Discussion ....................................................................................................... 108 Literature cited ...............................................................................................