TEMPORAL PERSISTENCE AND SPATIAL-DISTRIBUTION OF AN AMERICAN INOCULANT STRAIN OF THE ECTOMYCORRHIZAL BASIDIOMYCETE LACCARIA BICOLOR IN A FRENCH FOREST PLANTATION

Selected strains of ectomycorrhizal fungi, such as the basidiomycete L accaria bicolor, are currently being used as inoculants in nurseries t o improve growth of forest trees after outplanting. Information is nee ded on the survival of these introduced strains in forests and their i mpact on indigenous biodiversity. Dissemination and persistence of an American strain, L. bicolor S238N, were studied 10 years after outplan ting in a Douglas fir plantation located at Saint-Brisson (Morvan, Fra nce). About 430 Laccaria spp. sporophores were collected over 3 years. Inheritance of nuclear ribosomal DNA, as well as RAPD markers, was ch aracterized in L. bicolor S238N, using a haploid progeny set of 91 mon okaryons. More than 50 markers were identified (19 heterozygous and 33 homozygous or cytoplasmic markers), which unambiguously confirmed tha t the introduced strain was still present in the inoculated plots. Nei ther selfing (P < 0.0008) nor introgression with indigenous strains wa s detected although in vitro interfertility between the American strai n and indigenous L. bicolor was identified. No ingress of the introduc ed genet into adjacent uninoculated plots colonized by various local L accaria genets was detected. It is proposed that the spatial distribut ions identified have developed through mycelial propagation of the int roduced strain and intraspecific competition with native genets. Altho ugh longer-term data is still lacking, the stability of the inoculant strain and the limited disturbance to indigenous populations described support large-scale nursery production of this host-fungal combinatio n.