Founder effect in a young Leccinum duriusculum (Schultzer) Singer population.

The genetic diversity of a Leccinum duriusculum population growing under <20-year-old Populus alba on former farming soil was analysed from 1998 to 2001 and compared in 2000 to the two nearest populations found under >70-year-old P. alba. Genets were recognized using RAPD amplifications with three different primers, while their conspecificity was assessed by sequencing the nuclear ITS and mitochondrial large ribosomal subunit. The young population was colonized by a large genet that persisted from 1998 to 2001 (most distal sporophores were 10.4 m apart in 2001) and a second genetically related genet appeared in 2001. Five and six genets, respectively, of smaller size were found in the two other populations, while the investigated area was slightly smaller (72.25 m2) and the three populations were strongly divergent genetically (>33%). The genetic uniformity, as well as the high speed of radial growth of the lasting genet under <20-year-old P. alba (radial growth: 1 m/year), are interpreted in the framework of a founder effect. The slow recruitment of genets is proposed to lower the intraspecific competition and to entail large, fast-growing genets. The differences from ectomycorrhizal populations due to secondary colonization, which have been investigated often, are also emphasized.