Genetic Characterization and Pedigree Validation of Grapevine Hybrids, Donors of Resistance to Downy and Powdery Mildews

Viticulture has often been plagued by encounters with new parasites that still represent a major constraint. Even though some inter-specific varieties (hybrids) between V. vinifera and Vitis spp. are widely present, the majority of cultivated grapevines are highly susceptible V. vinifera varieties. Fungal diseases, such as downy (DM) and powdery (PM) mildew, represent some of the most severe plagues and growers are obliged to a large of use pesticides to prevent serious yield loss. Research applied to breeding for resistance and the deployment of new resistant grapevine varieties are therefore strongly encouraged. Nowadays, grapevine genetics and genomics are rapidly developing but, despite these advances, traditional breeding approaches are still dominant, while Marker-Assisted Breeding (MAB) implementation has been minimal both at the national and international level. In this study we focus on the genetic characterization of numerous Vitis hybrids, donors of resistance to DM and/or PM, in order to identify breeding signatures. In particular, 110 hybrids of European origin and of 120 American hybrids, along with 38 related V. vinifera varieties, have been genotyped at 70 SSR loci well-scattered along each of the 7 chromosomes that carry Resistance Gene Analog (RGA) clusters. Based on the SSR profiles, the historical pedigree information has been checked and, following the true-to-typeness validation for most of the studied hybrids, the Identity By Descent (IBD) analysis has been performed, tracing the allelic flow through the successive generations, also on the other 12 chromosomes (additional 120 SSRs). Molecular markers valuable for grapevine MAB will then be released.