Evolution and ecology of Epichloë in South America

IANNONE L.J.

Salamanca

Congreso; 10th International Symposium on Endophytes of grasses; 2018

Institute of Natural Resources and Agrobiology of Salamanca, IRNASA-CSIC

Only 45 of the more than 900 species of grasses in the subfamily Pooideae from South America are knownto be associated with endophytes of the genus Epichloë. Most of our knowledge about the diversity anddistribution of endophytes and host species is restricted to Argentina and Uruguay where 39 host taxa have beenreported. However, grasses asymptomatically hosting Epichloë have been detected along the Cordillera de losAndes 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 haverevealed that all the host species are associated with endophytes that evolved from the hybridization betweendifferent sexual species.Gene sequences and genetic profiles have revealed at least 19 genotypes grouped in eight differentlineages in this region. The E. festucae x E. typhina hybrid species E. tembladerae is the most commonly reportedendophyte, 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 havebeen also detected associated with more than one host species. The detection by PCR of alkaloid and mating typegenes shows genetic variability within each endophytic lineage and also establishes that at least three E. typhinasubsp. poae and two E. festucae genotypes were involved in the hybridization events that gave origin to the SouthAmerican endophytes.In general, each host species can be associated with different endophytes and the diversity of endophytesin each host species increases with the number of isolates studied. For instance, in Bromus auleticus at least 10endophytic genotypes were detected. Different endophytes may co-exist in the populationas observed in Phleumalpinum or Bromus pictus, or to present different distribution areas as with endophytes of B. auleticus. Wide hostrangeendophyte lineages, endophyte diversity in individual host species, and relationships between endophytesfrom different host species in the same community suggest the occurrence of horizontal transmission betweenhosts, multiple independent hybridization events, or both.Some host species are reported to be toxic to cattle, and although none of the characterized endophytesshould produce ergopeptines or lolitrem B, other indole-diterpenesor ergot alkaloids may be produced by someendophytes. 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 andmodify the seed germination under different environmental conditions. Positive endophyte effects are also evidentin host interactions with other microorganisms. In B. auleticus the endophyte confers resistance to the smutfungus, Ustilago bullata, and promotes mycorrhizal colonization and growth. Epichloë endophytes have also impacton the diversity of other endo-symbionts such as dark septate endophytes, mycorrhizal fungi, endophyticactinomycetes, and on free living soil fungi.In naturalized commercial forage species such as tall fescue and annual rye-grass the positive effects ofEpichloë 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 naturalizedpopulations of these hosts have high frequencies Epichloë symbiosis. However, our knowledge about the diversityof Epichloë in these hosts is still scarce. Considering the high diversity of grasses and environments as well as therecent and fast radiation of the Pooideae in South America, this region offers the opportunity to study evolutionaryand ecological aspects of the symbiosis between grasses and Epichloë endophytes.