The effectiveness of QoI fungicides against grape downy mildews in European vineyards has decreased significantly in the last years. A single nucleotide polymorphism, G143A in the cytochrome b gene of Plasmopara viticola was detected to confer QoI resistance. Polymorphism analyses of the mitochondrial genome showed that 4 major haplotypes (IR, IS, IIR, IIS) coexisted in French vinyards. By contrast, mitochondrial and RNA 28s analyses showed that 3 sub-species coexisted in vineyards of the USA. In Bordeaux vineyards, the most frequent haplotype (IR, IS) in P. viticola population reached 74%. The resistant allele frequencies ranged from 0 to 75 % with an average of 29 %. Therefore, at least two independent events led to the emergence of QoI resistance. By combining (non-coding) microsatellite and selective markers, a temporal genetic structure was obtained for P. viticola populations in which genetic variability was low and genotypic richness was high. To manage QoI resistance, it is important to understand how resistant populations appear, spread and survive.