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Oral: Pathogen Diversity


Genetic diversity of Colletotrichum isolates from Sorghum bicolor and S. halepense in the Southeastern United States
K. XAVIER (1), C. Schardl (1), E. Buiate (1), M. Torres (2), M. Queiroz (3), S. Chopra (4), L. Vaillancourt (5) (1) Department of Plant Pathology, University of Kentucky, U.S.A.; (2) Functional Genomics Laboratory, Cornell University/Qatar Foundation, Qat

Anthracnose caused by Colletotrichum sublineola is the most important disease of grain sorghum worldwide, and it is emerging as a significant production constraint for sweet sorghum grown in the Southeastern U.S. Anthracnose is also common on the wild sorghum relative johnsongrass (S. halapense). Marker analysis using repetitive fingerprinting probes revealed that isolates from cultivated sorghum were generally distinct from isolates from S. halpense. RFLP analysis based on probes against individual sequences presumed to encode effectors and secondary metabolism enzymes showed that most isolates from johnsongrass grouped separately from most isolates from cultivated sorghum. Isolates from cultivated sorghum were generally aggressive to sweet sorghum variety Sugar Drip, while isolates from S. halapense generally caused little or no disease. Phylogenetic trees were inferred based on isolates from both host species using portions of the DNA lyase gene, the manganese superoxide dismutase gene, and a region between the APN1 and the MAT2 genes (MATAPN) genes. These trees were found to be congruent, and to identify two distinct species, the first one associated with the cultivated S. bicolor, and a second, new species associated with S. halepense. Strong evidence was found that cross-infection of these two species does occur, and this could be expected to complicate efforts to develop and deploy resistant sweet sorghum varieties in areas where johnsongrass is common.