Europe as a bridgehead in the worldwide invasion history of grapevine downy mildew,Plasmopara viticola

Europe is the historical cradle of viticulture, but grapevines have been increasingly threatened by pathogens of American origin. The invasive oomycete Plasmopara viticola causes downy mildew, one of the most devastating grapevine diseases worldwide. Despite major economic consequences, its invasion history remains poorly understood. Comprehensive population genetic analyses of ~2000 samples from the most important wine-producing countries revealed very low genetic diversity in invasive downy mildew populations worldwide. All the populations originated from one of five native North American lineages, the one parasitizing wild summer grape. After an initial introduction into Europe, invasive European populations served as a secondary source of introduction into vineyards worldwide, including China, South Africa and, twice independently, Australia. Invasion of Argentina probably represents a tertiary introduction from Australia. Our findings provide a striking example of a global pathogen invasion resulting from secondary dispersal of a successful invasive population. It will help designing quarantine regulations and efficient breeding for resistance against grapevine downy mildew.