Resistance components to Plasmopara viticola in grapevine genotypes

The use of resistant varieties against downy mildew (DM, Plasmopara viticola) is increasingly gaining ground in Europe to reduce fungicide applications. A research was conducted to characterize the resistance components to DM in 16 grapevine genotypes bringing one or more of the following resistance genes from Muscadinia and American Vitis spp.: Rpv3, Rpv4, Rpv10, Rpv11, and Rpv12. The following resistance components were assessed in monocyclic experiments with artificial inoculation on leaf discs: i) infection efficiency of sporangia (percentage of the inoculation sites showing DM symptoms); ii) AUDPC (area under the disease progress curve); iii) incubation length; iv) latency period (in degree-days); v) sporangia produced per unit of DM lesion (number of sporangia per mm2 of lesion area); v) infectivity of the produced sporangia (by re-inoculation on susceptible variety); and vi) infectiousness (time a DM lesion produces sporangia, evaluated through repeated washings). Leaf discs were excised from fully developed young leaves collected in 2014 and 2015 at shoot growing, flowering and fruit set. Resistance components were expressed at different degrees in the different genotypes and at the different growth stages, with significant differences in comparison to the susceptible Vitis vinifera variety used as reference (Merlot). Data from monocyclic experiments were used for calibrating a DM epidemiological model able to predict disease progress in resistant genotypes. The research was funded by the FP7 European collaborative project “Innovine” (grant agreement n° 311775). Federica Bove carried out this work within the Doctoral School Agrisystem of the Università Cattolica del Sacro Cuore (Italy).