Downy mildew caused by the oomycete Plasmopara viticola is one of the most important diseases affecting grapevine. Resistant varieties are an environmentally-friendly tool to control grapevine downy mildew. Efficient breeding for durable resistance requires knowledge of the underlying mechanisms. Here we aimed at identifying the molecular basis of Rpv2 , a gene for extreme resistance to downy mildew derived from Vitis rotundifolia , and at characterizing its effect on pathogen development. Individuals from two populations segregating for Rpv2 were evaluated for resistance to downy mildew and genotyped. Following genetic mapping, markers flanking Rpv2 were used to screen new populations and identify recombinant individuals. Sequencing of recombinants and in silico chromosome painting was used to reduce the interval containing Rpv2 . Comparative genomics inside the Vitaceae , involving de novo assembly of the V. rotundifolia Regale genome, allowed narrowing-down the list of candidate genes. We restrict Rpv2 to a 250 kb genomic region that contains two resistance genes of the NLR type. Comparative genomics analyses could not find orthologs of both NLRs in the other Vitis species studied. We also show that Rpv2 -mediated resistance leads to pathogen arrest early in the infection cycle. Our results show that Rpv2 belongs to the NLR family of resistance genes, contributing thus to understand the potential and risks of its use in breeding programs and suggesting that combining NLR-type genes may lead to durable resistance
KEY MESSAGE
The Rpv2 locus for extreme resistance to grapevine downy mildew is mapped to a 250 kb genomic region containing two NLR-type genes specific to V. rotundifolia .