Relationships of Epichloe typhina isolates from different host grasses

Abstract

Epichloë typhina comprises interfertile strains associated with several grass species in tribes Poeae, Aveneae and Brachypodieae. Molecular phylogenetics indicate that E. typhina is paraphyletic to E. sylvatica and E. clarkii. Although interfertility barriers are evident between E. typhina and E. sylvatica, E. clarkii is interfertile with E. typhina. However, E. clarkii is associated specifically with Holcus lanatus (Aveneae). We addressed the possibility that E. typhina is a complex of genetically isolated populations distinguishable by host specificity. Populations of E. typhina were sampled from three Cantons on a transect from southwest to northeast Switzerland, and from 1-3 host species in each Canton. No fewer than 20 isolates were obtained from each host at each location. The intron-rich 5'-end of the beta-tubulin gene was sequenced from each isolate, and all of the sequences were aligned for phylogenetic and coalescence analyses. There was no indication of geographic isolation of the populations, but no haplotypes (sequence variants) were shared between isolates from different hosts. Therefore, E. typhina appears to be a complex of genetically isolated sympatric populations that are specific for different hosts. Keywords: Brachypodium species, Clavicipitaceae, Dactylis glomerata, Epichloë, epichloë endophytes, grasses, host specificity, molecular phylogenetics, Poa species, Poaceae, population genetics