An optimization of the marker-assisted breeding process for downy and powdery mildew resistance in grapevine

Today the reduction in pesticide use is imperative and the implementation of sustainable viticulture is an urgent necessity. With this awareness and vision, the genetic improvement program for biotic stress resistances began at the Fondazione Edmund Mach (FEM) in 2010. Initially a genotypic characterization of grapevine materials acquired from other European and extra-European breeding programs, as well as wild material collected in 2011 in northeastern America, was conducted. In parallel, investments were addressed to the development and optimization of phenotyping protocols for the evaluation of the symptoms of downy (DM) and powdery (PM) mildew both in laboratory conditions on detached organs and in greenhouses on seedlings and potted plants. A series of parents has therefore been identified suitable for different objectives and used over the years in the process of introgression and pyramiding of resistance (R) loci (genomic regions). In 2017, through a Marker-Assisted Parental Selection (MAPS) procedure, a high number of stacked (or pyramided) genotypes was reached in the open field, 48.4% against DM and 59.5% against PM; in particular, 30.3% of genotypes resulted pyramided for R-loci against both mildews. Having achieved this result, it is timely to make the process of Marker-Assisted Seedling Selection (MASS) more efficient: investment in low-cost genotyping and in a phenotyping workflow capable of guaranteeing the scouting of PM as well as the maintenance of DM resistance. After the phenotyping tests, approximately 1,200 progeny individuals were sampled in the 2018 season, which were then characterized at nine R-loci. Updated and detailed results will be presented regarding the level of pyramiding now reached and the correlation between genetic makeup and levels of resistance to downy and powdery mildews in greenhouse conditions. Thanks to this application study, starting from the 2019 season we have been able to adopt a pure MAS process ̶ that is without upstream phenotyping screening ̶ especially for those parental lines by now well established and with a known behavior in the breeding program.