Three new species of Epichloe symbiotic with North American grasses

The genus Epichloe sensu stricto includes several mating populations (biological species) of endophytic fungal symbionts of cool season grasses. To date, six Eurasian and one North American morphospecies have been described, and these approximately correspond to six distinct mating populations. Here we describe three additional Epichloe species found in natural symbioses with grasses native to North America. In mating tests three species were not interfertile with each other or any previously described Epichloe species. Sequences of β-tubulin gene introns, which have been useful for Epichloe phylogenetics, clearly distinguished the three species, isolates of each constituting a well supported clade. The three new species were host specific: E. brachyelytri was naturally associated only with Brachyelytrum erectum, E. elymi only with Elymus species, and E. glyceriae only with Glyceria striata. While most morphological characteristics of E. elymi and E. glyceriae were typical of the genus, the ascus structure of E. brachyelytri was unique among described Epichloe species. Vertical transmission by systemic infection of host seeds was common for E. brachyelytri and E. elymi but never occurred for E. glyceriae. Conversely, E. glyceriae developed stromata on every infected host inflorescence (preventing its maturation), E. elymi produced stromata on some but not all inflorescences, and E. brachyelytri very rarely produced stromata. Thus, symbioses of the three new Epichloe species with host grasses span the continuum from antagonistic to commensal or mutualistic.