Rpv3 locus and stilbenoid induction mediate downy mildew resistance in the Merzling x Teroldego segregating population

All grapevine cultivars (Vitis vinifera L.) traditionally grown in Europe are susceptible to downy mildew (DM) caused by Plasmopara viticola, an oomycete which is able to attack any grapevine green tissue. DM control mainly relies on the use of synthetic fungicides which are costly and have negative environmental impact. The exploitation of DM-resistant Vitis genetic resources for the development of new resistant varieties is a promising alternative. Recent studies conducted at FEM, taking advantage of a segregating population derived from Merzling (a tolerant hybrid) and Teroldego (a susceptible landrace), pointed to the importance of stilbenoids in conferring DM resistance. However, the genetic bases of DM resistance as well as stilbenoid biosynthesis upon DM infection in this population have not been elucidated yet. With this aim, in the present study 136 F1 individuals of this cross were characterized at genotypic level by means of 190 microsatellite markers used to build the Merzling × Teroldego linkage map. The F1 individuals were also screened for degree of disease resistance and production of 42 phenolics (including 18 different stilbenoids). Our results indicated a normal distribution of several disease resistance parameters, and a significant induction of stilbenoids upon infection. The integration of genotypic and phenotypic data by QTL analysis showed that DM resistance in this segregating population is mainly mediated by the Rpv3 locus and defined a number of novel regions associated to the traits under investigation. The validation of some candidate genes positioned within these genomic regions will identify those possibly involved in DM resistance and in the biosynthesis of phenolics related to the plant response to DM.