SEXUAL COMPATIBILITY AND TAXONOMY OF A NEW SPECIES OF EPICHLOE SYMBIOTIC WITH FINE FESCUE GRASSES

Mating tests among stroma-forming and nonstroma-forming strains of Epi chloe from several fine fescue species, including Festuca rubra subsp. rubra and F. rubra subsp. commutata, indicated a distinct mating popu lation of Epichloe from the Festuca hosts. Reciprocal matings of these strains with E. typhina from Dactylis glomerata, Lolium perenne and A nthoxanthum odoratum, and with a third mating population from Elymus s pp. indicated complete sexual incompatibility between members of diffe rent mating populations. Two mating types, mat-1 and mat-2, were ident ified and shown to be segregating in exclusion in ascospore progeny, c onsistent with a heterothallic mating system. Based on criteria of int ersterility with other known species, and the morphology of fruiting s tructures (size and disarticulation of ejected ascospores) a new speci es of Epichloe was described for which the name E. festucae is propose d. Allozyme profiles of isolates of E. festucae and of three other rec ognized species, E. typhina, E. baconii, and E. clarkii, emphasized ge netic distinctness of the new species. Average genetic identity values between E. festucae and the other three Epichloe 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 cluste rs of a dendrogram.