Prospecting for resistance of interspecific hybrids of Vitis spp. to Plasmopara viticola

Abstract

In partnership with the University of California—UCDavis, this study intends to develop downy mildew-resistant grape cultivars with good agronomic traits. Hence, the goals of this research were to estimate the genetic parameters, via REML/BLUP, of variables related to downy mildew resistance in a population composed of 63 interspecific hybrids and to select promising clones on the basis of genotypic values for the breeding program of the grapevine. The experiment was conducted in randomized blocks with three replicates and one plant per plot. The evaluations were carried out in two different seasons and focused on determining disease severity. The severity data provided the basis for calculating the area under the disease progress curve (AUDPC) and the maximum severity (Smax). Differences in the severity of downy mildew symptoms were reported among the 63 genotypes of Vitis spp., such as immune individuals (score 0) and highly susceptible to the AUDPC (3146.67) and Smax (80.56) variables in the two seasons analyzed. The high genotype correlation seen for AUDPC (80.95%) and Smax (89.68%) suggests that the majority of genotypes had a similar response in terms of symptom severity in the two seasons evaluated. The greatest proportion of genetic variance was resulting from the effects of dominance, which corresponds to 244,165.9580 and 179.83, for AUDPC and Smax, respectively, suggesting that hybridizations are viable in the introgression of the resistance. Consequently, the values for individual heritability of the effects of dominance were greater (50.34 and 52.83%) for the AUDPC and Smax variables, respectively. It is thus recommended that the 20 most resistant genotypes, with lower genetic values for the two variables analyzed, be selected and crossed with Vitis vinifera genotypes to obtain resistant hybrids.