Innovative strategies towards marker-assisted pre-breeding for Downy and Powdery mildew resistance in grapevine

Grapevine (Vitis vinifera L.) is one of the most valuable crops worldwide, mainly studied for quality and disease resistance traits. Viticulture has often been affected by encounters with new parasites that still represent a major constraint. This is a particularly important issue because, even though some inter-specific varieties (hybrids) between V. vinifera and Vitis spp. are widely present, the majority of cultivated grapevines are pure V. vinifera varieties, which are highly susceptible to pathogen attack. Fungal diseases represent some of the most severe plagues and growers are obliged to use pesticides to prevent serious yield loss. Within the FEM grapevine breeding program, re-established in the middle ’80s, the selection process has been based on the major need for innovation raised by grapevine growers. During the past years, this request has been addressed to increase the complexity and the originality of wines, while in the last decade the need for new varieties resistant/tolerant to abiotic and biotic stresses has emerged. In order to reach this goal, the FEM pre-breeding activity targets the introgression of grapevine downy (GDM) and powdery (GPM) mildew resistance/tolerance into vinifera background, to be coupled with grape quality characteristics in the next future. In a woody species - as grapevine - the achievements of this long-term objective can be anticipated by means of continuous-flowering genotypes or ad hoc agronomical practices, such as fruiting cuttings. The main objective is to create introgression lines in which the dilution of the Vitis spp. in the V. vinifera genome occurs with a selective and focused method based on the molecular detection of specific chromosome arms. With this aim, we focused on the genetic (190 SSRs) and phenotypic (GDM and/or GPM resistance) characterization of about 300 Vitis hybrids in order to identify selection signatures. Based on SSR profiles, the historical pedigree information has been checked and the trueness-to-type validated for several of the studied hybrids. This allowed to perform the Identity By Descent analysis, tracing the allelic flow through the successive generations. In particular, we exploited the information derived from the genome sequencing related to the presence of resistance gene analogue clusters along the chromosomes 5, 7, 9, 12, 13, 15 and 18. The final result of this study will be the release of molecular markers valuable for grapevine Marker-Assisted Breeding, upon their validation in ad hoc segregating populations.