High genetic diversity in a population of the ectomycorrhizal basidiomycete Laccaria amethystina in a 150-year-old beech forest

The genetic structure of a population of the ectomycorrhizal basidiomycete Laccaria amethystina (Bolt. ex Hooker) Murr. was assessed in a closed 150-y ear-old beech (Fagus sylvatica L.) forest in the Vosges Mountains in northe astern France. During the autumn of 1994 and 1997, sporophores were collect ed from three 100-m(2) sampling plots located along a 120-m transect crossi ng the beech stand. The genetic variation of 676 sporophores was initially estimated using heteroduplex analysis of the ribosomal DNA intergenic space r (IGS1). Ten unique IGS1 heteroduplex/homoduplex patterns were identified, although three types represented most of the sporophores analysed. Each gr oup of IGS1 type was then analysed using random amplified microsatellite an alysis (RAMS). RAMS resolved 388 different genotypes amongst the 634 sporop hores analysed from the three plots during the autumn of 1994 and 1997. Den sity as high as 130 genets per 100 m(2) was observed during the autumn of 1 994. The largest clone covered approximate to 1 m(2), but most genets cover ed a few cm(2) and produced only one to three sporophores. Only eight genot ypes identified in 1994 were found in 1997. Although L. amethystina has the capacity for vegetative persistence, the present study indicates that its populations maintain a genetic structure more consistent with a high freque ncy of sexual reproduction. This suggests that beech trees could be recolon ized by new genotypes each year. Alternatively, this spatial distribution m ay also arise from erratic fruiting of underground persistent genets. These features (i.e. numerous genets of small size), typical of ruderal species, contrast with studies carried out on other ectomycorrhizal basidiomycetes occurring in mature closed forests.