Molecular markers reveal genetic isolation and phylogeography of the S and F intersterility groups of the wood-decay fungus Heterobasidion annosum

The root-rot fungus Heterobasidion annosum (Fr.) Bref. species complex consists of three intersterility groups (S, F, and P), separated by their host affinity. The phylogenetic relationship of the species complex was studied, with the focus on the S and F groups, by comparing DNA sequences of four nuclear gene fragments: calmodulin, glyceraldehyde 3-phosphate dehydrogenase, heat stress protein 80-1, and elongation factor 1-alpha, and one anonymous locus, from 29 fungal isolates originating from Europe, Asia, and North America. The phylogeny of each separate gene locus as well as the combined dataset consisted of three main clades: European F group isolates, Euroasian S group isolates, and North American S group isolates, suggesting them to be separated into phylogenetic species. The results also support the hypothesis of an early separation between the S and F groups, indicating that their distribution have followed their host tree species for a considerable time period.