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Poster: Biology & Disease Mgmt: Chemical Control


Screening for QoI resistance among Colletotrichum species associated with ripe rot of grape in Virginia vineyards
M. NITA (1), A. Bly (1) (1) Virginia Tech, U.S.A.

Ripe rot of grape is a fungal disease caused by two Colletotrichum species complexes, C. acutatum and C. gloeosporioides. This disease can result in significant crop loss and off-flavors in wine. Among recommended fungicides against ripe rot are the QoI group, or strobilurins. We examined the prevalence of QoI insensitivity among Colletotrichum isolates collected throughout Virginia during 2013. For the fungicide-amended medium assay, petri dishes containing potato dextrose agar amended with 100 ppm azoxystrobin (Abound, 22.9% a.i. azoxystrobin, Syngenta Crop Protection) and 1,000 ppm SHAM (salicylhydroxamic acid) were inoculated with a mycelial plug of each of the isolates and then incubated at 25oC. The presence or absence of growth on azoxystrobin-amended medium was examined after 6 days. PCR-RFLP was utilized to detect a point mutation (G143A) of the cytochrome b gene. Primers GCCBF1 and RSCBR2 were used to amplify a 120-bp fragment, which was digested with restriction enzyme Fnu4HI to detect the G143A mutation. The results showed that among 283 isolates tested, 28% of isolates was insensitive to azoxystrobin in vitro, and 16% of the isolates had the G143A mutation. The higher percentage with the fungicide-amended medium assay was expected, since there are multiple mutations that can lead to insensitivity. High prevalence of QoI-insensitive isolates in Virginia vineyards warrants the modification of our management recommendations.