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Poster: Biology & Disease Mgmt: Chemical Control


Detection of quinone outside inhibitor resistant isolates of Erysiphe necator in Oregon vineyards
B. WARNEKE (1), J. Yamagata (2), T. Neill (3), T. Miles (2), W. Mahaffee (3) (1) Oregon State University, U.S.A.; (2) California State University Monterey Bay, U.S.A.; (3) USDA-ARS, U.S.A.

Grape Powdery Mildew (GPM, caused by Erysiphe necator (En)) is the most persistent disease in the west coast grape industry due to a long and dry growing season which favors its fecundity and inoculum dispersal via airborne conidia. GPM control failures in 2015 led to the exploration of the possibility of quinone outside inhibitor (QoI) fungicide resistance present in Oregon En populations. A survey of spatially distinct vineyards in Oregon was performed in which leaf and fruit samples infected with En were collected. Isolation and DNA extraction of En samples and subsequent quantitative PCR analysis using competitive TaqMan probes detected the presence of the G143A mutation. Isolates with the G143A mutation were considered resistant to QoIs. Conidia germination bioassays using Trifloxystrobin and Kresoxim-Methyl in 1.5% water agar confirmed genetic results of 28 isolates examined. Of the 28 isolates examined, 22 were resistant to both QoIs (EC50>100µg/ml), while 6 were sensitive (EC50 from 0.004 to 0.06µg/ml). Using a discriminatory dose of 0.1ug/ml, 19 of 19 more isolates were resistant to QoIs and agreed with results from the qPCR assay.