Investigating the black rot resistance locus Rgb7 in the cultivar ‘Villard blanc’ and its progeny

Abstract

Grapevine is grown under extensive fungicide use, mainly due to two diseases native to North America that were introduced to Europe in the nineteenth century, downy mildew and powdery mildew. Breeding programs aim to combine desirable properties for wine production from the European Vitis vinifera with resistance loci from North American or Asian wild Vitis species in new cultivars. The cultivation of these new disease-resistant varieties, so called “PIWIs”, allow the winegrowers to reduce the utilised amounts of fungicides as well as the number of applications needed. These changes in plant protection measures lead to an increasing number of infections with black rot (Guignardia bidwellii, synonym: Phyllosticta ampelicida), as the fungicides applied also controlled black rot. This fungus infects all green tissues in the plant including young berries in multiple infection cycles, resulting in reduced or complete loss of harvest.

In previous work, a cross-population of two cultivars resistant to black rot (‘Calardis Musqué’ x ‘Villard Blanc’) was investigated to further understand black rot resistance in grapevine. Quantitative Trait Locus (QTL) analysis revealed the resistance loci Rgb1, Rgb5 and Rgb6 in ‘Calardis Musqué’ as well as the resistance locus Rgb7 in ‘Villard Blanc’. ‘Villard Blanc’ is a resistant French cultivar that was frequently used for breeding in the twentieth century and gave rise to several pathogen-resistant varieties such as ‘Bianca’ and ‘Felicia’.

The current project aims to further analyse Rgb7 in ‘Villard Blanc’ and its progeny, as well as to potentially find additional resistance loci in ‘Villard Blanc’. Therefore, a cross-population of ‘Villard Blanc’ x V. vinifera is analysed. F1 plants were phenotyped for the degree of resistance after artificial infection. Genotyping of the plants was carried out with rhAmpSeq-markers, enabling the generation of a dense genetic map and QTL analysis. F1 individuals of the cross-population carrying the Rgb7 locus will be further analysed to better understand this specific resistance locus and develop Rgb7-associated markers for marker-assisted selection in breeding programs. The overall goal is to make this novel locus accessible for breeding of new cultivars with stacked black rot resistances.