Evolution and ecology of Epichloë in South America

IANNONE L.J

Salamanca

Congreso; 10th International Sympossium on Endophytes of Grasses; 2018

Only 45 of the more than 900 species of grasses in the subfamily Pooideae from South America are known to be associated with endophytes of the genus Epichloë. Most of our knowledge about the diversity and distribution of endophytes and host species is restricted to Argentina and Uruguay where 39 host taxa have been reported. However, grasses asymptomatically hosting Epichloë have been detected along the Cordillera de los Andes from Venezuela to Argentina. Thus, it is likely that many other host species remain to be discovered. 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 have revealed at least 19 genotypes grouped in eight different lineages in this region. The E. festucae x E. typhina hybrid species E. tembladerae is the most commonly reported endophyte, associated with at least 22 host species. However, other E. festucae x E. typhina hybrids, E. typhina x E. amarillans and E. festucae x E. aff. elymi x E. typhina hybrids, and E. typhina subsp. poae non-hybrid lineages have been also detected associated with more than one host species. The detection by PCR of alkaloid and mating type genes shows genetic variability within each endophytic lineage and also establishes that at least three E. typhina subsp. poae and two E. festucae genotypes were involved in the hybridization events that gave origin to the South American endophytes. In general, each host species can be associated with different endophytes and the diversity of endophytes in each host species increases with the number of isolates studied. For instance, in Bromus auleticus at least 10 endophytic genotypes were detected. 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 B. 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. Some host species are reported to be toxic to cattle, and although none of the characterized endophytes should produce ergopeptines or lolitrem B, other indole-diterpenes or ergot alkaloids may be produced by some endophytes. Most of these endophytes produce peramine and E. pampeana and E. cabralii both produce lolines, but so far we lack clear evidence of their impacts on insects.The symbioses between Epichloë spp. and native grasses in Argentina mostly appear to be mutualistic, with positive effects to the hosts. In Bromus setifolius and B. auleticus the endophyte increases plant growth and modify the seed germination under different environmental conditions. Positive endophyte effects are also evident in host interactions with other microorganisms. In B. auleticus the endophyte confers resistance to the smut fungus, Ustilago bullata, and promotes mycorrhizal colonization and growth. Epichloë endophytes have also impact on the diversity of other endo-symbionts such as dark septate endophytes, mycorrhizal fungi , endophytic actinomycetes, and on free living soil fungi. In naturalized commercial forage species such as tall fescue and annual rye-grass the positive effects of Epichloë symbioses have played a significant role on adaptation to environmental conditions in this region. Although the commercialization of endophyte-infected seeds is not allowed in Argentina, all of the naturalized populations of these hosts have high frequencies Epichloë symbiosis. However, our knowledge about the diversity of Epichloë in these hosts is still scarce. Considering the high diversity of grasses and environments as well as the recent and fast radiation of the Pooideae in South America, this region offers the opportunity to study evolutionary and ecological aspects of the symbiosis between grasses and Epichloë endophytes.