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American Phytopathological Society, Plant Disease, 2023

DOI: 10.1094/pdis-07-22-1707-re

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Fungicide sensitivity of Sclerotinia sclerotiorum from U.S. soybean and dry bean, compared to different regions and climates

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Fungicide use is integral to reduce yield loss from Sclerotinia sclerotiorum on dry bean and soybean. Increasing fungicide use against this fungus may lead to resistance to the most common fungicides. Resistance has been reported in Brazil (Glycine max) and China (Brassica napus subsp. napus), however, few studies have investigated fungicide sensitivity of S. sclerotiorum in the U.S. The work presented here was conducted to determine if there was a difference in fungicide sensitivity of S. sclerotiorum isolates in the U.S. from: (i) dry bean versus soybean and (ii) fields with different frequencies of fungicide application. We further hypothesized that isolates with fungicide applications of a single active ingredient from tropical Brazil and sub-tropical Mexico were less sensitive compared to temperate U.S. isolates due to different management practices and climates. The EC50(D) fungicide sensitivity of 512 S. sclerotiorum isolates from the U.S. (443), Brazil (36), and Mexico (33) was determined using a discriminatory concentration (DC) previously identified for tetraconazole (2.0 ppm; EC50(D) ranged of 0.197 to 2.27 ppm), boscalid (0.2; 0.042 to 0.222), picoxystrobin (0.01; 0.006 to 0.027), and thiophanate-methyl, which had a qualitative DC of 10 ppm. Among the 10 least sensitive isolates to boscalid and picoxystrobin, two presented mutations known to confer resistance in the SdhB (qualitative) and SdhC (quantitative) genes; however no strong resistance was found. This study established novel DCs that can be used for further resistance monitoring and baseline sensitivity of S. sclerotiorum to tetraconazole throughout the world plus baseline sensitivity to boscalid in the U.S.