Plasmopara viticola, causing downy mildew in grapevine, is responsible for considerable yield loss in viticulture. The reason why large amounts of fungicides are needed to prevent infestation. To reduce this environmental and financial burden, the identification of resistance-mediating genomic sequences, which enable the targeted breeding of resistant species, is essential. To date, more than twenty resistance loci have been identified against P. viticola, but their detailed function and the associated resistance-mediating gene have rarely been elucidated. We documented P. viticola infection in Rpv12-carrying genotypes in detail by microscopic imaging. For this purpose, the genotypes `Afus Ali´ and `Italia´ were used as susceptible reference cultivars, `Kunbarat´ (Rpv12, Rcg1) and `Kunleany´ (Rpv12) as original backcrosses of Rpv12-carrying Vitis amurensis, were analysed in comparison to genotypes homozygous in the Rpv12 locus. We included supplemental genotypes 65-153-18 (Rpv12, Rcg1), 2004-043-0021 (Rpv1/Run1, Rpv3.1, Ren3, Ren9), and 2014-099-0003 (Rpv12, Rcg1, Ren3, Ren9). We verified the lineage of these genotypes by SSR-Marker analysis. `Kunbarat´ was previously listed as a cross product of `Italia´ and 28/19. However, our analysis showed that it actually is a cross product of `Afus Ali´ and 28/19 and is therefore a full sibling of `Kunleany´. Another misconception in the progeny of `Kunbarat´ could be clarified: `Petra´ is a descendant of `Savagnin blanc´ and not `Pinot Noir´. Using different staining methods for microscopy, we showed that the Rpv12-mediated resistance is a post-penetration resistance. Primarily, this is based on a rapid hypersensitive response upon release of H2O2. This was confirmed by excessive expression of haustoria of P. viticola in resistant genotypes but also by almost complete inhibition of mycelial growth in genotypes homozygous in the Rpv12 locus. No callose or other cell wall enhancement could be documented as Rpv12-related at the microscopic level. We documented an enhancement of resistance by homozygosity in the Rpv12 locus. Furthermore, we demonstrated an additive effect in the homozygous genotypes Hozy01 (Rpv12 homozygous), Hozy10 (Rpv3.1 and Rpv12 homozygous). As part of a collaboration with the Commonwealth Scientific and Industrial Research Organisation, we tested various CAPS markers for over two hundred Rpv12-carrying genotypes, of which one can be evaluated as putative resistance-associated. In another collaboration with the Center for Biotechnology (CeBiTec) of Bielefeld University and the Max Planck Institute for Plant Breeding Research, Genome Center Cologne of the Max Planck Society, a de novo assembly of genotype 2014-099-0003 (Rpv12, Rcg1, Ren3, Ren9) differentiated by haplotype could be performed using trio binning. This reduced the Rpv12 locus identified by Venuti et al. (2013) between SSR markers UDV-350 and UDV-370 by approximately 366 kb. As well as the number of potential resistance genes based on NLR motifs was reduced from twelve (PN40024) to four. RNA-Seq of a non-inoculated leaf identified two transcripts each with separate partial function of NLRs on two of the four candidate genes, which lead to the hypothesis of differential splicing. Based on this sequences, new SSR markers were developed to identify the Rpv12 locus. An additional aspect of this work was the discovery of a new potential resistance locus carrier. A crossbreed between V. riparia and V. rupestris proved to be highly resistant to P. viticola. Initial microscopic and molecular biological studies to exclude possible known resistance loci showed no matches with the corresponding locus-associated reference cultivars.weiterlesen