Three new species of Epichloë symbiotic with North American grasses

Abstract

The genus Epichloë 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 Epichloë species found in natural symbioses with grasses native to North America. In mating tests the three species were not interfertile with each other or any previously described Epichloë species. Sequences of β-tubulin gene introns, which have been useful for Epichloë 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 Epichloé 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 Epichloë species with host grasses span the continuum from antagonistic to commensal or mutualistic.