Sexual compatibility and taxonomy of a new species of <i>Epichloë</i> symbiotic with fine fescue grasses

Mating tests among stroma-forming and nonstroma-forming strains of Epichloë from several fine fescue species, including Festuca rubra subsp. rubra and F. rubra subsp. commutata, indicated a distinct mating population of Epichloë from the Festuca hosts. Reciprocal matings of these strains with E. typhina from Dactylis glomerata, Lolium perenne and Anthoxanthum odoratum, and with a third mating population from Elymus spp. indicated complete sexual incompatibility between members of different mating populations. Two mating types, mat-1 and mat-2, were identified and shown to be segregating in exclusion in ascospore progeny, consistent with a heterothallic mating system. Based on criteria of intersterility with other known species, and the morphology of fruiting structures (size and disarticulation of ejected ascospores) a new species of Epichloë was described for which the name E. festucae is proposed. Allozyme profiles of isolates of E. festucae and of three other recognized species, E. typhina, E. baconii, and E. clarkii, emphasized genetic distinctness of the new species. Average genetic identity values between E. festucae and the other three Epichloë species ranged from 0.138 to 0.331 but was 0.872 among E. festucae isolates. All isolates of the same species were grouped in distinct, clearly separated clusters of a dendrogram.