Identification of Host-Resistant and Susceptible Varieties of Korean Grapes to Plasmopara viticola, a Pathogen Causing Grapevine Downy Mildew

다국어 초록 (Multilingual Abstract)

Grapevine downy mildew, caused by Plasmopara viticola, significantly damages vineyardsand is one of the most devastating diseases affecting cultivated grapes worldwide. In thisstudy, we characterized the phenotypic and molecular traits of 11 P. viticola isolates fromfour grape-growing regions in South Korea. Additionally, we investigated the diversity ofpathogenicity among these isolates and conducted an assay to evaluate the responseof grape cultivars to P. viticola infection. Lemon-shaped sporangia were identified in thecollected isolates, which released zoospores into the suspension at room temperature. Withina few hours of inoculation, the zoospores developed germ tubes. We tested 11 P. viticolaisolates for pathogenicity in 845 grape cultivars to screen for grape host resistance to downymildew infection. Among the tested isolates, JN-9 showed the highest virulence. Grapecultivars displayed varying phenotypic reactions to P. viticola infection: approximately 7%were highly susceptible, 41% were susceptible, 20% were moderately susceptible, 8% wereresistant, and 24% exhibited extreme resistance. Phylogenetic analysis based on four genomicregions (internal transcribed spacer 1 [ITS1], actin, beta-tubulin, and cytochrome c oxidaseII) revealed a close evolutionary relationship among all the Korean isolates, forming a singlemonophyletic lineage. Notably, these isolates showed greater similarity to European isolatesthan to American isolates. This comprehensive study contributes to a deeper understandingof the identity and behavior of P. viticola, which is crucial for developing effective resistancestrategies against this pathogen in grape cultivars cultivated in South Korea.