Genetic variability and population structure of Plasmopara viticola in Italy

Plasmopara viticola (Berk. et Curt.) Berl. and De Toni is an obligate biotrophic Oomycete which causes grapevine downy mildew, one of the most important grapevine disease, affecting particularly the European grapevine, Vitis vinifera L. The pathogen originated in Northern America and was for the first time reported in Europe in 1878 undergoing a bottleneck resulting in reduced genetic diversity across Europe. The genetic variability of P. viticola in Italy was investigated by genotyping, at 32 microsatellite markers, 106 P. viticola strains collected from 13 different regions. Each strains analysed presented a different multilocus genotype, suggesting that sexual reproduction is important. The lack of significant deviation from Hardy–Weinberg equilibrium indicates that P. viticola populations are panmictic. The study also revealed low genetic diversity and a lack of genetic structure according to geographic origin, V. vinifera cvs nor disease management (organic vs IPM). The mixed reproductive system of P. viticola results in a great evolutionary potential and adaptability that could have a negative impact on the durability of resistance over a long term period. Therefore, all the disease control methods available should be integrated in order to reduce the selection pressure towards pathogen strains able to overcome the plant’s defense system.