Epichloë in South America: how many, where and why?

IANNONE L.J.

San Juan

Congreso; 11 th Imternational Mycological Congress; 2018

International Mycological Association

Some grasses in the subfamily Pooideae establish symbiotic associations with endophytes of the genus Epichloë (Clavicipitaceae). Whereas some species produce stromata with perithecia that abort the development of the florets causing total or partial sterility in the host, in other cases the endophyte colonizes the ovary to be spread in the seeds of the host. This association is considered to be mutualistic because the endophytes may provide the host with enhanced growth and resistance to abiotic stresses and produce alkaloids against herbivores. In this work, we studied the genus Epichloë in native grasses from South America, considering its diversity, host range, distribution and effect for the host plant. The presence of Epichloë was studied in field collected plants and herbarium material. When possible, the endophytes were isolated and characterized morphologically and genetically by mean of phylogenies of nuclear genes and detection of alkaloid-biosynthesis genes. The distribution of the different lineages was modelled using climatic variables. The effect of Epichloë on the growth of some hosts and its capacity to establish associations with mutualistic, pathogenic and soil fungi was studied by comparing Epichloë-infected plants (E+) with Epichloë-removed plants (E-). In Argentina and Uruguay, where surveys were performed more intensively, Epichloë was detected in 41 grass species, and at least eight more hosts species were identified along Cordillera de los Andes from Venezuela to Argentina. Although sexual species of Epichloë have not been reported from this region, molecular phylogenies have revealed that all the host species are associated with endophytes that evolved from the hybridization between different sexual species. Gene sequences and genetic profiles revealed at least 19 genotypes grouped in eight different lineages. In general, each host species can be associated with different endophytes and different endophytes may co-exist in the population as observed in Phleum alpinum or Bromus pictus, or to present different distribution areas as with endophytes of Bromus auleticus. Wide host-range endophyte lineages, endophyte diversity in individual host species, and relationships between endophytes from different host species in the same community suggest the occurrence of horizontal transmission between hosts, multiple independent hybridization events, or both. In Bromus setifolius and B. auleticus the endophyte increases plant growth and promotes seed germination. The association with Epichloë promotes mycorrhizal colonization and growth and confers resistance to the smut fungus, Ustilago bullata. Epichloë endophytes have also impact on the diversity of other endo-symbionts such as dark septated endophytes, mycorrhizal fungi, endophytic actinomycetes, and on free living soil fungi. Considering the high diversity of grasses and environments as well as the recent and fast radiation of the Pooideae in South America, it is likely that many other host and Epichloë species remain to be discovered in South America, a region that offers the opportunity to study evolutionary and ecological aspects of the symbiosis between grasses and Epichloë endophytes.