Monitoring of a Single Point Mutation in the PvCesA3 Allele Conferring Resistance to Carboxylic Acid Amide Fungicides in Plasmopara viticola Populations In Yamanashi Prefecture, Japan

Aoki, Y., Kawagoe, Y., Fujimori, N., Tanaka, S., and Suzuki, S. 2015. Monitoring of a single point mutation in the PvCesA3 allele conferring resistance to carboxylic acid amide fungicides in Plasmopara viticola populations in Yamanashi prefecture, Japan. Plant Health Progress doi:10.1094/PHP-RS-140041. The use of the carboxylic acid amide (CAA) fungicide mandipropamid to manage grapevine downy mildew in vineyards in Japan has been increasing since 2010, because of widespread quinone outside inhibitor fungicide resistance in the Plasmopara viticola population. However, CAA fungicide resistance in P. viticola is becoming a serious problem worldwide. In 2013, we monitored for the presence of a single point mutation at codon 1105 of the cellulose synthase gene PvCesA3, which confers resistance to mandipropamid in P. viticola samples collected from four vineyards in Yamanashi prefecture in Japan. Five out of 157 samples were found to be heterozygotes, carrying both the mutated and nonmutated PvCesA3 alleles. Although CAA fungicide-resistant P. viticola isolates have not been reported yet in Japan, the emergence of heterozygous P. viticola populations indicates the potential risk of emergence of resistant homozygotes.