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Poster: Biology & Disease Mgmt: Mycology


Identifying Diversity Within Corynespora cassiicola, Cause of Target Spot of Cotton, Tomato, and Soybean in the Southeastern U.S.
L. SUMABAT (1), M. Brewer (1), R. Kemerait (2) (1) University of Georgia, U.S.A.; (2) University of Georgia, U.S.A.

Target spot, caused by the fungus Corynespora cassiicola, is a disease that is emerging on crops in the southeastern U.S., including cotton. Previous studies suggest that populations from cotton, tomato, and soybean in the U.S. are host specific and genetically differentiated based on host of origin. Although variation in aggressiveness to cotton was observed, no genetic variation was detected within populations sampled from cotton. The aim of this study was to develop markers to detect genetic variation in C. cassiicola. Variable microsatellite motifs with conserved flanking regions were identified in draft genomes of two isolates from cotton, an isolate from tomato, and an isolate from soybean. Thirty-one sets of primers were designed, and then tested for amplification of these four isolates. The nineteen loci that amplified well were evaluated on a panel of 15 isolates from diverse hosts of origin and geographic regions. Fourteen of the markers were robust and informative. Preliminary results showed diverse genotypes among C. cassiicola populations from different hosts, yet there was no genotypic variation detected within tomato or cotton isolates sampled from different cultivars, states, and years, suggesting that populations from these hosts represent distinct clonal genotypes. Determining levels of variation among isolates of C. cassiicola from cotton is critical for screening for cultivar resistance and identifying fungicides for management of target spot.