Fine‐scale structure of populations of the ectomycorrhizal fungus Hebeloma cylindrosporum in coastal sand dune forest ecosystems

Abstract

The basidiomycete mushroom Hebeloma cylindrosporum is a frequently found pioneer ectomycorrhizal species naturally associated with Pinus pinaster trees growing in coastal sand dune ecosystems along the Atlantic south‐west coast of France. The genotypic diversity and spatial structure of three populations of this fungal species have been studied. At each site the basidiocarps were mapped, sampled and propagated as pure mycelial cultures. For each of the isolates, we have studied polymorphisms in the mitochondrial genome, polymorphisms at two different nuclear loci and also fingerprints produced with a multicopy DNA probe. The comparison of the different polymorphisms obtained, with each of the four molecular methods used, allowed the identification of several of the different genets present in each site. In two of the studied sites most of the basidiocarps, which often occurred as dense patches of 10–30 in 1 m2 or less, were of a unique genotype, suggesting the below‐ground mycelia to be of a small size (from 50 cm2 to approx. 7 m2 for the larger mycelia) and that the root system of a single Pinus tree can host several genets of the same symbiotic fungus. In the two sites, which were studied again after a 3‐year interval, none of the genotypes identified in the first year of sampling was re‐identified 3 years later. These results contrast with those reported for other species of soilborne homobasidiomycete species, either ectomycorrhizal, parasitic or saprophytic, showing mostly large clones resulting from the vegetative growth and from persistence of below‐ground mycelia. Sexual reproduction through meiospore dispersal seems to play a key role in the structuring of the populations of H. cylindrosporum. Mycelia associated with the root systems seem to be replaced after 1 or a few years, during which basidiocarp differentiation takes place. As opposed to the few other studied ectomycorrhizal species, H. cylindrosporum has the characteristics of ruderal species, with a short life‐span adapted to pioneer situations, e.g. to nutrient‐poor and unstable sandy soils of coastal sand dunes.

Survival of an introduced ectomycorrhizal Laccaria bicolor strain in a European forest plantation monitored by mitochondrial ribosomal DNA analysis

“…Such a pattern could result from the use of a conserved marker that underestimates the total number of cytotypes. However, a similar situation has been described in natural populations of the ectomycorrhizal fungus Hebeloma cylindrosporum (Gryta et al, 1997) and other basidiomycetes (Saville et al, 1996) using multilocus mitochondrial markers. A striking feature of our population is the persistence of the mitochondrial haplotype of the introduced strain S238N (haplotype II) over 10 yr in forest conditions.…”

“…In natural fungal populations, mitochondrial and nuclear markers might thus be expected to show independent transmission. Although poorly investigated in the field, the distribution of mitochondrial haplotypes seems to differ from the distribution of nuclear genotypes, with clonal transmission of mitochondria between genets (Saville, Yoell & Anderson, 1996 ;Gryta et al, 1997). At the func-tional level, the diversity of cytoplasmic genomes might contribute to the structure of the population by influencing several abilities of the fungus, such as competitiveness and growth rate (de la Bastide et al, 1997), adaptation to abiotic factors or symbiotic properties.…”

Recent advances in population genetics of ectomycorrhizal mushroomsRussulaspp.

“…The high replacement rate of genotypes suggested frequent sexual reproductions and short genet persistence. Similar contradictory results were observed in Hebeloma cylindrosporum (Gryta et al 1997, 2000; Guidot et al 2002). At present, the mechanisms for such conflicting results are not known.…”

Soil eukaryotic functional diversity, a metatranscriptomic approach

“…The sampling site was a monospecific Pinus pinaster forest planted on a stabilized coastal sand dune in SouthWest France (Truc Vert site, 441 43 0 N, 11 15 0 W; Gryta et al, 1997;Guidot et al, 2001). Understorey vegetation was composed of dispersed Arbutus unedo shrubs and seedlings of unidentified grasses on a bare floor devoid of litter.…”