Prevalence of isolates of Botrytis cinerea resistant to multiple fungicides in Chilean vineyards

Gray mold (Botrytis cinerea) is an important disease of grapevines (Vitis vinifera) and requires several fungicide treatments to achieve a satisfactory control in Chile. Furthermore, a high resistance risk has developed because of the extensive use of specific fungicides with a single-site mode of action. The aim of this study was to determine the presence of resistance to the multiple fungicides currently used against B. cinerea in Chile. During 2007–2009 and 2011, 214 isolates of B. cinerea from 36 commercial vineyards were examined for sensitivity to anilinopyrimidines (cyprodinil or pyrimethanil), demethylation inhibitors (DMIs) (tebuconazole), hydroxyanilides (fenhexamid) and phenylpyrroles (fludioxonil). Of all of the isolates, 62.7% were resistant to anilinopyrimidines, 7.2% to DMIs, 27.1% to hydoxyanilides and 44.8% to phenylpyrrole derivates. Overall, 16 (12.3%) of the isolates were sensitive; although none was resistant to all four of the fungicide classes, and 50 (38.5%), 51 (39.2%), and 13 (10.0%) isolates were resistant to one, two and three fungicides, respectively. In vitro, resistant isolates were capable of causing fruit rot on wounded apples pretreated with any one of the five fungicides at label concentrations. To the best of our knowledge, this is the first report of isolates having simultaneous resistance to anilinopyrimidines, DMIs, phenylpyrroles and hydroxyanilides in B. cinerea populations from grapevines in Chile. Therefore, fungicide resistance is a serious problem that questions the sustainability of the current gray mold control strategy, which relies almost exclusively on fungicides with single-site modes of action. ► Resistance of Botrytis cinerea to single-site mode of action fungicides was studied. ► Isolates exhibiting simultaneously double or triple resistance were found. ► These results question the gray mold control that relies on single-site fungicides.