Genetic Diversity and Host Specificity of Fungal Endophyte Taxa in Fescue Pasture Grasses

A number of pasture and turf grass species form mutually beneficial symbiotic associations with endophytic fungal species. Within the fescue grasses, diploid meadow fescue (Festuca pratensis Huds.) interacts with Neotyphodium uncinatum while allohexaploid tall fescue (Festuca arundinacea Schreb.) has been reported to associate with Neotyphodium coenophialum and two other morphologically distinct taxa (Festuca arundinacea taxonomic groups 2 and 3 [FaTG-2 and FaTG-3]). The evolutionary history of hexaploid tall fescue is complex, as part of a species group with varying ploidy levels and exhibiting distinct ecogeographical morphotypes. To evaluate both naturally occurring variation and host grass taxon specificity, diversity was determined in collections representing multiple meadow fescue and tall fescue accessions. Initial screening with a minimal set of endophyte-specific simple sequence repeat (SSR) genetic markers detected endophyte incidence in 33% of 701 tested accessions. Subsequent analysis identified N. coenophialum genotypes within Continental and rhizomatous hexaploid and octoploid tall fescue [F. arundinacea subsp. atlantigena (St.-Yves) Auquier] accessions. Festuca arundinacea taxonomic group 2 and FaTG-3 endophytes appeared to be restricted to Mediterranean hexaploid and decaploid tall fescue [F. arundinacea cirtensis (St.-Yves) Gamisans] hosts. Endophytes of meadow fescue were confirmed as belonging to N. uncinatum. This study has elucidated host specificity of fescue endophyte taxa and supported models for host-symbiont coevolution. A substantial number of candidate novel endophytes have been identified that are suitable for metabolic characterization and deployment by inoculation in fescue breeding programs.