<i>Rpv10.2</i>: A Haplotype Variant of Locus <i>Rpv10</i> Enables New Combinations for Pyramiding Downy Mildew Resistance Traits in Grapevine

In viticulture, pathogens like the oomycete <i>Plasmopara viticola</i>, the causal agent of downy mildew, can cause severe yield loss and require extensive application of plant protection chemicals. Breeders are generating pathogen-resistant varieties exploiting American and Asian wild <i>Vitis</i> germplasm as sources of resistance. Several loci mediating resistance to <i>P. viticola</i> have been identified in the past but may be overcome by specifically adapted strains of the pathogen. Aiming to find and characterize novel loci, a cross population with <i>Vitis amurensis</i> ancestry was investigated searching for resistance-correlated quantitative trait loci (QTL). As a prerequisite, a genetic map was generated by analyzing the 244 F₁ individuals derived from a cross of the downy mildew susceptible <i>Vitis vinifera</i> cultivar ‘Tigvoasa’ and the resistant <i>V. amurensis</i> pBC1 breeding line We 90-06-12. This genetic map is based on the information from 627 molecular markers including 56 simple sequence repeats and 571 rhAmpSeq markers. A phenotypic characterization of the progeny showed a clear segregation of the resistance traits in the F₁ population after an experimental inoculation of leaf discs with downy mildew. Combining genetic and phenotypic data, an analysis for QTL revealed a major locus on linkage Group 9 that correlates strongly with the resistance to downy mildew. The locus was mapped to a region of about 80 kb on the PN40024 (12x.V2) grapevine reference genome. This genomic region co-localizes with the formerly identified locus <i>Rpv10</i> from the grapevine cultivar ‘Solaris’. As we found different allele sizes of the locus-linked SSR markers than those characterizing the known <i>Rpv10</i> locus and differences in the sequence of a candidate gene, it was regarded as a haplotype variant and named <i>Rpv10.2</i>.