Distribution spatiale de lignées d’oïdium des chênes en France analysée à l’aide d’outils rapides de caractérisation moléculaire

Abstract

Keywords: Erysiphe alphitoides / Erysiphe quercicola / cryptic species / Erysiphales / ITS / biological invasion Abstract • Powdery mildew is a major fungal disease of oaks in Europe. Recent studies using internal tran- scribed 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 poly- morphism 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. alphi- toides was often found in association with different ITS types in the same region, the same tree, and even in the same lesion.