Fungicide resistance of Botrytis cinerea: first results from Switzerland
Abstract: Resistance of Botrytis cinerea, causal agent of gray mold, to fungicides is an increasing problem in the strawberry production in Switzerland. In 2017 and 2018, a monitoring survey to assess the actual situation in four major strawberry growing cantons was conducted by the concerned cantonal extension services. Samples from fruits with typical gray mold sporulation were sent to the laboratories of Agroscope (microbial analysis) and of the Zurich University of Applied Sciences, ZHAW (molecular analysis). Samples were taken in fields of ten growers who assumed to have a resistance problem. Six-seven strains per grower were isolated and analyzed. Resistance to nine following active ingredients was assessed: boscalid, cyprodinil, fenhexamid, fenpyrazamine, fludioxonil, fluopyram, iprodione, mepanipyrim and pyrimethanil. The microbial analysis revealed that the median number of fungicide resistances per strain were 5 and 4 in 2017 and 2018, respectively. The molecular analysis showed that Multidrug resistance MDR1 and MDR1h were present in both years. The results of the survey have to be considered with care as i) only 136 strains were analyzed in total, and ii) the strains originated from fields suspected to have a fungicide resistance problem.