A new in vitro method for the assessment of Plasmopara viticola resistance on grapevine inflorescences

Grapevine downy mildew (DM), caused by the pathogen Plasmopara viticola, is one of the most important plagues affecting viticulture, especially in humid climates. This pathogen is able to differentially attack leaves and grapes and is currently controlled with a massive use of fungicides; the numerous treatments have considerable economic costs as well as a relevant negative impact on environment, human health and public perception. The use of resistant grapevine cultivars, obtained through breeding programs, is a cost-efficient way to control grapevine DM. Nevertheless, most of the in vitro tests developed so far for DM resistance assessment are focused on leaf disc bioassays. These tests might not always represent a proper evaluation and prediction of the disease impact on grape inflorescences/bunches and in turn on final production and quality