Sustainability and environmental protection are objectives that become increasingly important in viticulture. As traditional European grapevine cultivars are very susceptible to various fungal pathogens introduced from North America, such as powdery mildew, downy mildew and black rot, they have to be protected with several fungicide sprays each year. One way to reduce the use of fungicides in viticulture is to breed for genetically resistant grape cultivars that carry defence genes against fungal pathogens. Consequently, grapevine breeding aims at combining the wine quality characteristics of traditional European Vitis vinifera cultivars with genetic resistance loci against the fungal pathogens occurring in North American and Asian wild Vitis species.
Thus, in this work, genetic resistance to black rot was studied in three different F1 cross populations (V3125 x ‘Börner’, ‘Calardis Musqué’ x ‘Villard Blanc’ and ‘Morio Muskat’ x ‘Calardis Blanc’) through genetic mapping and QTL analysis. In all three cross populations a known resistance locus on chromosome 14 (Rgb1) was verified and several new QTL were identified. This highlights the Rgb1 locus as the most important one for mediation of black rot resistance. Therefore, the resistance locus was studied in the reference genome of the susceptible grapevine genotype PN40024, a ‘Helfensteiner’ (‘Pinot Precoce Noir’ x ‘Schiava Grossa’) descendent, and in the two resistance donors ‘Börner’ and ‘Calardis Musqué’. In the candidate gene region of the Rgb1 locus spanning from SSR marker GF14-35 to VMC6e1, a resistance gene cluster consisting of receptor-like proteins, belonging to the class of ethylene-inducing xylanases (EIX), was found in addition to several other genes associated with pathogen defence. The EIX genes are described in Solanum lycopersicum (tomato) and bind the fungal elicitor EIX (ethylene inducing xylanase). These genes encode for leucine-rich repeat cell-surface glycoproteins which contain a signal for receptor-mediated endocytosis.
SSR marker analysis confirmed the allelic status of the Rgb1 loci originating from V. rupestris (Rgb1.1) and V. riparia (Rgb1.2). The SSR marker UDV-095 allows the tracing of both allelic versions of the resistance locus in breeding lines and cultivars. Additional allele specific SSR markers were also established. For the first time, reliable markers for the marker assisted selection of black rot resistance can be proposed.