: A Haplotype Variant of Locus Enables New Combinations for Pyramiding Downy Mildew Resistance Traits in Grapevine.

In viticulture, pathogens like the oomycete , 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 germplasm as sources of resistance. Several loci mediating resistance to 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 ancestry was investigated searching for resistance-correlated quantitative trait loci (QTL). As a prerequisite, a genetic map was generated by analyzing the 244 F individuals derived from a cross of the downy mildew susceptible cultivar 'Tigvoasa' and the resistant 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 F 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 from the grapevine cultivar 'Solaris'. As we found different allele sizes of the locus-linked SSR markers than those characterizing the known locus and differences in the sequence of a candidate gene, it was regarded as a haplotype variant and named .