LAUSR

BACKGROUND Oxathiapiprolin is a novel fungicide and the first of the piperidinyl-thiazole-isoxazoline class to be discovered. This fungicide has been reported to have high activity against Plasmopara viticola, the grapevine downy mildew agent, and other plant-pathogenic oomycetes. In this study, the baseline sensitivity of Italian P. viticola populations towards oxathiapiprolin was established on 29 samples collected in ten different viticultural areas. Two insensitive strains were characterized for their mechanism of resistance. RESULTS Oxathiapiprolin exhibited substantial inhibitory activity against 27 of the 29 populations tested, with EC50 values ranging from a minimum of under 4x10-5 mgL-1 to over 4x10-1 mgL-1 , with an average value of 3.2x10-2 mgL-1 . Two stable suspected oxathiapiprolin-resistant mutants were isolated from population exhibiting reduced sensitivity, and sequenced for the oxathiapiprolin target gene PvORP1. The comparison with wild-type isolates revealed that the resistant isolates possessed a heterozygous mutation causing the amino acid substitution N837I, recently reported in the literature. CONCLUSION The results obtained indicate a risk for Italian P. viticola populations to develop resistance to oxathiapiprolin in association with the N837I mutation at PvORP1. Anti-resistance strategies should be carefully implemented and the sensitivity levels to this molecule should be monitored accurately in future to preserve its effectiveness. This article is protected by copyright. All rights reserved.