BIOLOGICAL AND MOLECULAR CHARACTERIZATION OF DAHLIA MOSAIC CAULIMOVIRUS By

I would like to express my sincere gratitude to my major advisor, Dr. Hanu Pappu, for the tremendous support, guidance, encouragement and most of all the numerous opportunities that he made available to me during the time I spent working with him. Dr. Pappu has been an exceptional mentor who has been a constant source of inspiration to me. I would also like to thank Dr. Patricia Okubara, Dr. Ken Eastwell and Dr. Gary Chastagner for their advice, guidance and helpful discussions throughout my tenure. I wish to extend my gratitude to Keri Druffel, who taught me numerous techniques in the laboratory and for all the work she did that made my work so much easier. A special thanks to Robert Brueggeman for technical assistance. I am also grateful to the faculty and staff of the Department of Plant Pathology for all the help and support during my graduate studies at Washington State University. A special thank you to Dr. Tim Murray, for arranging departmental financial support and for giving me the opportunity to serve as a teaching assistant. I would also like to thank the Samuel and Patricia Smith Endowment for Dahlia Virus Research, created by the American Dahlia Society for the financial support for this study. Thank you to all my friends in Pullman for their friendship and support. I am very much indebted to my parents for their constant support, love and encouragement. This achievement would not have been possible without their assistance, especially after the birth of my son. Last but not least a heartfelt thank you to my husband Shantanu for his love, encouragement and patience, throughout my graduate program. Finally, to my son Adheesh for putting a smile on my face even on the toughest day

Inheritance and Molecular Mapping of Barley Genes Conferring Resistance to Wheat Stripe Rust

Most barley cultivars are resistant to stripe rust of wheat that is caused by Puccinia striiformis f. sp. tritici. The barley cv. Steptoe is susceptible to all identified races of P. striiformis f. sp. hordei (PSH), the barley stripe rust pathogen, but is resistant to most P. striiformis f. sp. tritici races. To determine inheritance of the Steptoe resistance to P. striiformis f. sp. tritici, a cross was made between Steptoe and Russell, a barley cultivar susceptible to some P. striiformis f. sp. tritici races and all tested P. striiformis f. sp. hordei races. Seedlings of parents and F1, BC1, F2, and F3 progeny from the barley cross were tested with P. striiformis f. sp. tritici races PST-41 and PST-45 under controlled greenhouse conditions. Genetic analyses of infection type data showed that Steptoe had one dominant gene and one recessive gene (provisionally designated as RpstS1 and rpstS2, respectively) for resistance to races PST-41 and PST-45. Genomic DNA was extracted from the parents and 150 F2 plants that were tested for rust reaction and grown for seed of F3 lines. The infection type data and polymorphic markers identified using the resistance gene analog polymorphism (RGAP) technique were analyzed with the Mapmaker computer program to map the resistance genes. The dominant resistance gene in Steptoe for resistance to P. striiformis f. sp. tritici races was mapped on barley chromosome 4H using a linked microsatellite marker, HVM68. A linkage group for the dominant gene was constructed with 12 RGAP markers and the microsatellite marker. The results show that resistance in barley to the wheat stripe rust pathogen is qualitatively inherited. These genes might provide useful resistance against wheat stripe rust when introgressed into wheat from barley

A new and distinct species in the genus Caulimovirus exists as an endogenous plant pararetroviral sequence in its host, Dahlia variabilis

Viruses in certain genera in family Caulimoviridae were shown to integrate their genomic sequences into their host genomes and exist as endogenous pararetroviral sequences (EPRV). However, members of the genus Caulimovirus remained to be the exception and are known to exist only as episomal elements in the infected cell. We present evidence that the DNA genome of a new and distinct Caulimovirus species, associated with dahlia mosaic, is integrated into its host genome, dahlia ( Dahlia variabilis). Using cloned viral genes as probes, Southern blot hybridization of total plant DNA from dahlia seedlings showed the presence of viral DNA in the host DNA. Fluorescent in situ hybridization using labeled DNA probes from the D10 genome localized the viral sequences in dahlia chromosomes. The natural integration of a Caulimovirus genome into its host and its existence as an EPRV suggests the co-evolution of this plant–virus pathosystem