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Poster: Biology & Disease Mgmt: Chemical Control


Evaluating fungicide sensitivity of regional populations of Blumeria graminis f.sp. tritici in the United States
E. MEYERS (1), C. Cowger (2) (1) North Carolina State University, U.S.A.; (2) USDA-ARS Plant Science Research Unit & North Carolina State University, U.S.A.

Blumeria graminis f.sp. tritici (Bgt), the causal agent of wheat powdery mildew, is primarily controlled by resistant wheat varieties and foliar fungicides. However, both control strategies risk being defeated by the large, rapidly adapting pathogen population. In 2013 and 2014, over 350 Bgt isolates were sampled from 27 fields in 15 states. The fungicide sensitivity of these single-spored isolates was evaluated using a detached leaf assay of fungicide-treated susceptible wheat leaf pieces. Five different fungicides, representing three major fungicide classes, were evaluated using 11 concentrations per fungicide. Detached leaves were inoculated with individual isolates and after 10 days leaf pieces were rated for sporulation. Bgt isolates from Mid-Atlantic states (NC, VA), Great Lakes states (MI, NY, OH, PA), and Deep South states (AL, FL, GA, MS) exhibited decreased sensitivity to the Demethylation Inhibitor (DMI) fungicides tebuconazole and prothioconazole compared to isolates from MO, AR, and the Plains states (KS, NE, OK). Plains isolates exhibited decreased sensitivity to the succinate dehydrogenase inhibitor (SDHI) fungicide fluxapyroxad compared to Deep South isolates. Sensitivity to the Quinone outside Inhibitor (QoI) fungicides pyraclostrobin and picoxystrobin did not differ by region. Genotypic evaluation of phenotypically insensitive isolates will further clarify the extent and nature of potentially fungicide-resistant isolates in this collection.