Resistance components to Plasmopara viticola in grapevine genotypes

The use of resistant varieties against downy mildew (DM, Plasmopara viticola) is\r\nincreasingly gaining ground in Europe to reduce fungicide applications. A research was\r\nconducted to characterize the resistance components to DM in 16 grapevine genotypes\r\nbringing one or more of the following resistance genes from Muscadinia and American Vitis\r\nspp.: Rpv3, Rpv4, Rpv10, Rpv11, and Rpv12. The following resistance components were\r\nassessed in monocyclic experiments with artificial inoculation on leaf discs: i) infection\r\nefficiency of sporangia (percentage of the inoculation sites showing DM symptoms); ii)\r\nAUDPC (area under the disease progress curve); iii) incubation length; iv) latency period (in\r\ndegree-days); v) sporangia produced per unit of DM lesion (number of sporangia per mm2 of\r\nlesion area); v) infectivity of the produced sporangia (by re-inoculation on susceptible\r\nvariety); and vi) infectiousness (time a DM lesion produces sporangia, evaluated through\r\nrepeated washings). Leaf discs were excised from fully developed young leaves collected in\r\n2014 and 2015 at shoot growing, flowering and fruit set. Resistance components were\r\nexpressed at different degrees in the different genotypes and at the different growth stages,\r\nwith significant differences in comparison to the susceptible Vitis vinifera variety used as\r\nreference (Merlot). Data from monocyclic experiments were used for calibrating a DM\r\nepidemiological model able to predict disease progress in resistant genotypes. The research\r\nwas funded by the FP7 European collaborative project “Innovine” (grant agreement n°\r\n311775). Federica Bove carried out this work within the Doctoral School Agrisystem of the\r\nUniversità Cattolica del Sacro Cuore (Italy).