Identification of Vitis riparia as Donor of Black Rot Resistance in the Mapping Population V3125 x ‘Börner’ and Additive Effect of Rgb1 and Rgb2

Viticulture is facing challenges, like the impact of climate change and various pests and pathogens. Alongside powdery and downy mildew, black rot is one of the most prevalent fungal diseases in European wine-growing regions. The focus of grapevine breeding research has so far been mainly on resistance to mildew diseases, and marker-assisted selection (MAS) in breeding material is possible for the most important resistance loci. However, only a few loci have been described for black rot resistance and these cannot yet be used for MAS. Thus, the characterization of genetic resistance to black rot and the establishment of closely linked genetic markers is important for the breeding of cultivars with multifungal resistances. In this study, an improved SSR marker-based genetic map of the biparental mapping population V3125 (‘Schiava Grossa’ x ‘Riesling’) x ‘Börner‘ (Vitis riparia x Vitis cinerea) was used to perform QTL analysis for black rot resistance. A total of 195 F1 individuals were analyzed at 347 SSR marker positions distributed on all 19 chromosomes. QTL analysis detected two QTLs conferring resistance to black rot on linkage groups 14 (Rgb1) and 16 (Rgb2). Our results revealed for the first time that Rgb1 and Rgb2 are derived from the wild species V. riparia. The presence of both loci in F1 individuals showed a clear additive effect for black rot resistance, supporting the breeding strategy of pyramiding two or more resistance factors to achieve a stronger overall resistance.