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POSTERS: Fungicide and antibiotic resistance

Fungicide Sensitivity of 395 Sclerotinia sclerotiorum Isolates from Dry Bean and Soybean
Thomas Jose Justo Miorini - North Dakota State University - Carrington Res Ext Center. Sydney Everhart- Oregon State University, Edgar Nieto-Lopez- University of Nebraska

Fungicide applications are integral to reduce yield loss from Sclerotinia sclerotiorumon dry bean and soybean. Increasing use in production may lead to resistance and few studies have investigated this. We sought to determine if there is a difference in fungicide sensitivity betweenisolates from dry bean and soybean and those exposed to intensive, moderate, and no fungicide, in fungicide field trials (FFT), farmer fields (FF), and white mold nurseries (WMN), respectively. We also sought to determine if reduced sensitivity is linked to use of fungicides with a single active ingredient. Initially, fungicide sensitivity was assessed to thiophanate methyl (MBC), tetraconazole (DMI), boscalid (SDHI), and picoxystrobin (QoI) using serial dilution for 42 isolates and a dose-response curve was fit to estimate the EC50.Linear regression of % mycelial growth at each concentration vs. logEC50 was used to identify the best predictor of EC50, used as the discriminatory concentration (DC). Thiophanate methyl had a qualitative DC of 10 ppm thatclassified as sensitive or resistant. Others were 2.0 ppm for tetraconazole, 0.2 ppm for boscalid, and 0.01 ppm for picoxystrobin. These concentrations will be used to assess sensitivity to all four fungicides for an additional 165 isolates (1-3 per field) to compare isolates grouped by source (FF, FFT, WMN) and also by host (dry bean and soybean). An additional 188 isolates (5-10 per field) from fields with applications of single-site fungicides will be used to assess ifthere is reduced sensitivity to fungicide used in each field.