Forward marker-assisted selection for mildew resistance in grapevine: an optimized applied process

Nowadays the transition to sustainable agriculture is of primary importance for the international community. A promising strategy for reducing the use of chemicals is to cross quality varieties with resistant ones. However, traditional breeding of woody plants is extremely challenging due to some limitations: long reproductive cycle and large plant size make the evaluation period very long and costly. Fortunately, in the last decade the employment of marker-assisted selection (MAS) has changed the paradigm, improving the efficiency of the early stage screening steps and reducing the number of plantlets reaching the open field. With these awareness and vision, the genetic improvement program for biotic stress resistance in grapevine began at the Fondazione Edmund Mach in 2010. After an initial phase of scouting a various and complex genetic pool of resistance (R) traits/loci to downy and powdery mildews (DM and PM), a group of accessions were selected as R-donors. Then, through Marker-Assisted Parental Selection (MAPS), various genotypes with stacked loci reached the open field and were than used for breeding purposes. Subsequently, the optimization of phenotyping and genotyping protocols was conducted for a highly efficient Marker-Assisted Seedling Selection (MASS). Two phenotyping workflows were developed to ensure preferential selection of DM or PM resistance, possibly in combination with the additional resistance trait. Eventually, genotyping costs were reduced of more than one fourth (4.73€; five loci screened on average per individual). In 2018, approximately 650 progeny individuals were tested and characterized at nine R-loci, revealing a maximum of seven stacked loci and up to three loci in homozygous state. The optimized applied process in more than 20 segregating populations and the several detected R-loci arrangements allowed to unveil both inter- and intra- population effects: the first is the effect of a diverse genetic background on the same R-loci asset, while the second one represents the impact of different R-loci arrangements within the same population. Thanks to these findings, starting from the 2019 a forward MAS process ̶ without phenotypic screening ̶ was established on the progenies derived from those parental lines with a known behavior within the FEM breeding program.