Epidemiological Studies of Soybean Vein Necrosis Virus and Potential Resistance Mechanisms to its Vector Neohydatothrips variabilis (Beach)

Soybean (Glycine max (L.) Merrill) is one the most important crops in global agriculture with annual production of over 260 million metric tons. As the dependence of a growing global population to soybean has increased, so does the importance of soybean diseases and pests. Over 200 pathogens attack soybean; among them, viruses pose a major threat to the soybean industries accounting for approximately 10% of the annual yield reduction caused by diseases in the past two decades. Soybean vein necrosis virus (SVNV) is a relatively newly discovered virus causing the homonymous disease. The widespread occurrence of the disease in major soybean producing regions in North America and its negative impact on seed quality led to the work presented here; research that aims to better understand virus epidemiology so as to develop effective virus control and disease management tools. In order to further understand the potential roles of weeds in SVNV cycle, surveys were conducted to determine the presence of SVNV among 32 weed species collected from soybean fields in Arkansas. Kudzu (Pueraria montana), a common weed present in millions of acres in Southeastern United States, can sustain SVNV replication in a systemic manner without developing virus-like symptoms. SVNV – a localized virus in soybean, could move systemically with the assistance of bean pod mottle virus, one of the most economically important soybean viruses. The ineffectiveness of pesticides in thrips management highlights the need to identify potential resistance mechanisms to the primary and highly efficient vector of SVNV – Neohydatothrips variabilis (Beach). The comparison of transmission efficiency of thrips fed with polypeptides containing RGD motif and N-linked glycosylation sites of SVNV glycoproteins indicated that blocking putative cellular receptors prior to virus acquisition could significantly reduce the virus transmission efficiency. Due to the lack of resistance to SVNV, efforts were made to identify genotypes with resistance to the vector, which could modify vector behavior and reduce the incidence of transmission and disease. Screening of soybean accessions with differential leaf pubescence levels revealed that feeding damage caused by thrips differs among accessions and is weakly correlated to their pubescence levels. ACKNOWLEDGEMENTS I am deeply grateful to my major advisor Dr. Ioannis Tzanetakis for his guidance and continuous support through my PhD program. His sharp vision and timeless pursue of highquality science deeply influenced me. The tremendous freedom he provided in his laboratory and his criticism combined with genuine concern through each critical step of my graduate study play a pivotal role in making me an independent researcher. With a special mention to my committee member Dr. Donn Johnson, who provided valuable suggestions regarding the research and dissertation, I am sincerely thankful to him and all other committee members Dr. Pengyin Chen, Dr. John Rupe and Dr. Garry McDonald for their great effort in helping me growing as a better scientist along the way. The complexity of my PhD projects called for intellectual input from experts beyond my committee members, it is impossible to accomplish the work I presented here without their help. I would like to give special thanks to Dr. Mariusz Lewandowski at Warsaw University of Life Sciences, Dr. Suresh Thallapuranam and Dr. Roger Koeppe at University of Arkansas, Dr. Anna Whitfield at North Carolina State University and Dr. Seed Sabanadzovic at Mississippi State University for their heartwarming support. I also greatly appreciate Dr. Ken Korth, Mr. Scott Winters, Ms. Jessica Kivett and Mr. Bob Holland for their generous assistance which made the challenging projects went smoothly. Last but not the least, I would like to thank all current and past members of the plant virology laboratory as well as faculties, staffs and students of the Department of Plant Pathology during my stay at the University of Arkansas. I greatly appreciate everyone’s support, help and encouragement which motivated me to be a better person. DEDICATION This dissertation is dedicated to my dear father for his unfailing love and unconditional support. His love is my inspiration which motivates me in all aspects of my life. Without his guidance and patience, I could not reach where I am today. TABLE OF CONTENTS Chapter I .