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Microsatellite loci were isolated from Plasmopara viticola (Oomycetes), the causal agent of downy mildew of grape, one of the most damaging fungal diseases of grapevine worldwide. Seven polymorphic loci were obtained from an enriched partial genomic library. A low genetic diversity was observed at all loci, with a mean observed allele number of 3.75 and an observed heterozygosity ranging from 0.074 to 0.547. Cross‐amplification tests on three closely related taxa indicated that two loci could be used in other Oomycetes species. These microsatellite loci were proved to be useful for population genetic analysis.

Abstract• Powdery mildew is a major fungal disease of oaks in Europe. Recent studies using internal transcribed spacer (ITS) sequences suggested the presence of four different lineages (putative species). The objective of the study was to investigate the spatial distribution of these lineages/species and, in particular, to test the hypothesis of a spatial differentiation, at various scales: regional (France), altitudinal (a Pyrenean transect) and local (within a forest plot).• Detection methods for the four ITS types were developed: (1) single strand conformation polymorphism analysis (SSCP); (2) PCR amplifications, for which specific primers were designed. SSCP proved to be efficient for the detection of Erysiphe alphitoides and E. quercicola types. In contrast, the rarer ITS types corresponding to E. hypophylla and Phyllactinia guttata (sensu lato) were only detected by specific amplification.• The study confirmed the strong predominance of the ITS sequence associated with E. alphitoides at all spatial scales (with a frequency higher than 80%). Isolates presumably belonging to E. quercicola (i.e. with same ITS type), a recently described species not yet recorded in Europe, were also found in all French regions at a significant frequency (15% at national level).• No pattern of spatial differentiation between the putative species could be demonstrated: E. alphitoides was often found in association with different ITS types in the same region, the same tree, and even in the same lesion. Mots-clés :Erysiphe alphitoides / Erysiphe quercicola / espèces sryptiques / Erysiphales / ITS / invasion biologique Résumé -Distribution spatiale de lignées d'oïdium des chênes en France analysée à l'aide d'outils rapides de caractérisation moléculaire.• L'oïdium est l'une des maladies fongiques les plus importantes sur chênes en Europe. Des études récentes basées sur l'internal transcribed spacer (ITS) ont suggéré l'implication de quatre lignées (espèces putatives) différentes. L'objectif de l'étude était de caractériser la distribution spatiale de ces lignées/espèces et en particulier de tester l'hypothèse d'une différenciation spatiale à plusieurs échelles : régionale (France), altitudinale (transect pyrénéen) et locale (au sein d'une parcelle forestière).• Des méthodes de détection des quatre types d'ITS ont été développées : (1) analyse SCCP ; (2) amplification par PCR de l'ITS par des amorces spécifiques. La SSCP a permis de détecter facilement les ITS correspondant à E. alphitoides et E. quercicola. Par contre, les ITS plus rares correspondant à E. hypophylla et Phyllactinia guttata (sensu lato) n'ont été détectés que par amplification spécifique.• L'étude a confirmé la forte prédominance (avec une fréquence supérieure à 80 %) de la séquence d'ITS associée à E. alphitoides. Les isolats présentant la même séquence d'ITS qu'E. quercicola, espèce récemment décrite et encore non mentionnée en Europe, ont également été retrouvés dans toutes les régions françaises à une fréquence importante (15 % en moyenne pour l'échantillonnage...

Scaphoideus titanus, a leafhopper native to North America and invasive in Europe, is the vector of the Flavescence dorée phytoplasma, the causal agent of the most important form of grapevine yellows in European vineyards. We studied 10 polymorphic microsatellite loci and a 623 bp fragment of the mitochondrial cytochrome oxidase II gene in native S. titanus from north-eastern America and introduced European populations, to elucidate the colonization scenario. Consistent with their recent history, invasive European populations were less genetically diverse than American populations for both types of markers, suggesting a recent bottleneck. Significant isolation by distance was detected between American populations but not between European populations. None of the European mitochondrial haplotypes was found in the American vineyards, from which they are assumed to have originated. The precise source of the invasive S. titanus populations therefore remains unclear. Nevertheless, the high heterozygosity of North-East American populations (which contained 92% of the observed alleles) suggests that this region is part of the native range of S. titanus. Clustering population genetics analyses with microsatellite and mitochondrial data suggested that European populations originated from a single introduction event. Most of the introduced populations clustered with populations from Long Island, the Atlantic Coast winegrowing region in which Vitis aestivalis occurs.

Twelve expressed sequence tags-derived markers were isolated from Plasmopara halstedii (Oomycetes), the causal agent of sunflower downy mildew. A total of 25 single nucleotide polymorphisms and five indels were detected by single-strand conformation polymorphism analysis and developed for high-throughput genotyping of 32 isolates. There was a high level of genetic diversity (HE = 0.484). Observed heterozygosity ranged from 0 to 0.143 indicating that P. halstedii is probably a selfing species. These markers were also useful in detecting significant genetic variations among French populations (FST = 0.193) and between French and Russian populations (FST = 0.23). Cross-amplification tests on three closely related species indicated that no loci amplified in other Oomycete species

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Here, we describe the development of an oomycetespecific primer pair for amplification of the cytochrome b region in plant pathogenic species that span the order Peronosporales (Phytophthora spp., downy mildews). Because of the high number of variable sites at both inter-and intra-specific levels this marker provides a powerful tool for population genetics and phylogenetic studies in this taxa. We also demonstrate its potential compared with other oomycete-specific mitochondrial markers currently available.

We report 34 new nuclear single-nucleotide-polymorphism (SNP) markers that have been developed from an expressed sequence tag library of Plasmopara viticola, the causal agent of grapevine downy mildew. This newly developed battery of markers will provide useful additional genetic tools for population genetic studies of this important agronomic species.