Population genetics and spatial structure of the fairy ring fungus Marasmius oreades in a Norwegian sand dune ecosystem.

The population genetics and spatial structure of the fairy ring fungus Marasmius oreades (Bolt. : Fr.) Fr. was studied by DNA amplification fingerprinting (DAF). Basidiocarp samples were collected from fairy rings from two separate sand dune systems of about 560 m(2) and 1750 m(2), respectively, on the Lista Peninsula in southwestern Norway in 1996. Samples were collected after a careful mapping of fairy rings and a vegetation survey of the composition and spatial structure of vascular plants, bryophytes and lichens. DAF with standard arbitrary oligonucleotide primers was used to examine the genetic relationship between basidiocarp samples. The study showed that the fungal population contained a high number of genotypes and that about 90% of the fairy rings represented a separate genet. Both cluster and phylogenetic analyses of DAF amplification products established relationships between fairy rings and showed that genetically similar basidiocarps were found close to each other. Overall results showed a weak correspondence between genotype and spatial distribution and no correspondence between genotype and composition of the surrounding vegetation. Furthermore, the occurrence of the four dominant sand dune grass species was randomly distributed among the localities housing the various fungal genotypes, indicating that the fungus did not exhibit genotypic specialization to the various grass species that could host it as a pathogen. Results show that establishment of new individuals generally was mediated by basidiospore dispersal and not by fragmenting dikaryotic, vegetative mycelium, as previously proposed.