Breakdown of resistance to grapevine downy mildew upon limited deployment of a resistant variety

Our results are the first description of a resistance-breaking isolate in the grapevine/P. viticola interaction, and show that, despite the reduced genetic variability of P. viticola in Europe compared to its basin of origin and the restricted use of natural resistance in European viticulture, resistance-breaking isolates overcoming monogenic resistances may arise even in cases where deployment of the resistant varieties is limited to small acreages. Our findings represent a warning call for the use of resistant varieties and an incentive to design breeding programmes aiming to optimize durability of the resistances.