*Schardl, Christopher L.; McDonald, Bruce A.; Leuchtmann, Adrian. Host-specific populations of Epichloë typhina, and a test of the phylogenetic species recognition method. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-39.
The Epichloë and Neotyphodium species are, respectively, sexual and asexual fungi that maintain constitutive, systemic symbioses with many grasses. These endophytes range from the more virulent and contagious sexual species, to mutualistic but asexual species that are only transmitted vertically. Extensive molecular phylogenetic studies have indicated two trends in evolution of epichloë endophytes: Interspecific hybridization is common but not universal in the evolution of Neotyphodium species, and host specialization is common in the evolution of Epichloë species. A possible exception to host specialization is the broad-host-range and relatively virulent species, Epichloë typhina, as currently defined based largely on interfertility relationships. Therefore, we undertook a study to test if E. typhina comprises cryptic host-specific species, and to test the concordance of phylogenetic species with interbreeding populations.
Populations of Epichloë typhina were surveyed from four common host species in a transect across Switzerland, and sequences were determined from intron-rich regions of their genes for beta-tubulin (tubB) and elongation factor 1-alpha (tefA). No fewer than 20 isolates were analyzed for each host in each location, and more than 200 isolates were analyzed in total. Gene trees were inferred by maximum likelihood and other methods, recombination blocks in the sequenced regions were identified with SNAP Workbench (I. Carbone), and migration rates between locations were estimated with Migrate-n (P. Beerli).
In Cantons Vaud and Zurich, populations of E. typhina were identified in Dactylis glomerata, Poa trivialis, and P. nemoralis. Infected D. glomerata was also found in Canton Schaffhausen. E. typhina in Brachypodium pinnatum was identified in Canton Zurich. Values of Nm (N = effective population size, m = migration rate) indicated that populations were panmictic. No tubB or tefA haplotypes were shared between isolates from different hosts. A recombination block was identified in tubB, requiring removal of one third of the informative sites for phylogenetic analysis. The tubB gene tree placed isolates from each Poa species into a separate clade, isolates from B. pinnatum into two distinct clades, and isolates from D. glomerata in a group that was paraphyletic to the ex P. trivialis clade. The tefA gene tree indicated distinct clades for isolates from each host.
The results strongly supported the hypothesis that E. typhina, as currently defined, is an assemblage of cryptic host-specific species. However, a phylogenetic species recognition method failed to distinguish these host-specific populations of E. typhina. We conclude that in some cases population studies may be preferable over phylogenetics for species recognition.
Keywords: Poaceae, Clavicipitaceae, Plant-fungus interaction, Host specificity
*Institution: University of Kentucky
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