Population Structure, Aggressiveness, and Molecular Genetic Variability of Sclerotinia Sclerotiorum

94 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002.Population structure, isolate aggressiveness, and molecular genetic variability of Sclerotinia sclerotiorum (Lib) de Bary was investigated. Population structure was determined by mycelial compatibility grouping (MCG). MCG and aggressiveness of S. sclerotiorum isolates from diverse hosts and geographic locations, from soybean fields in Argentina, and DeKalb and Watseka, Illinois were assessed. Among 301 isolates tested, 42 MCGs were identified, and 61% were represented by single isolates observed at a single location. Within the Diverse Set, 17 MCGs were identified. Each Illinois field consisted of a mosaic of MCGs, but MCG profiles differed between the two fields. Nine MCGs were identified within the Argentine field. MCGs were shared among the Diverse, DeKalb, and Watseka Sets, but MCGs within the Argentine Set were not shared with other sets. MCGs within the DeKalb and Watseka Sets were spatially aggregated. MCG 8 was the most frequently sampled and widely distributed MCG and occurred at a frequency of 29, 36, and 62% in the Diverse, DeKalb, and Watseka Sets, respectively. Isolate aggressiveness varied within the Diverse, DeKalb, Watseka, and Argentine Sets and varied within MCGs composed of isolates from different locations, but did not vary within MCGs composed of isolates from a single field. Additionally, MCGs within the DeKalb and Watseka Sets differed in aggressiveness. Molecular genetic variability among 48 S. sclerotiorum isolates was assessed by amplified fragment length polymorphism (AFLP). A dendrogram was calculated utilizing the neighbor joining method within the NTSYS-pc system. Each isolate produced a unique AFLP genotype, and the range in genetic similarity was 0.1022 to 0.3387. AFLP analysis revealed that S. sclerotiorum populations are genotypically variable and did not support a close correlation between location of isolates and MCG. Distant isolates were genetically similar suggesting that recent movement of the pathogen among these agricultural regions has occurred. Within MCGs, AFLP analysis clearly showed genoyic differences. The genotypic variability seen among S. sclerotiorum isolates within MCGs does not support MCGs being defined as clones or clonality groups. Although isolates within MCGs may have a common origin, propagate mitotically, and retain respective MCG designations, MCG genets may not be conserved.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD