Diversity of Epichloë in Hordeum comosum from Patagonia, Argentina

Abstract

Hordeum comosum J. Presl is a native, perennial grass widespread in Patagonia and in the Andean regionof South America. This species is an excellent forage grass highly preferred by sheep. A previous local study[1],based on tubB and tefA phylogenies of isolates from northwestern Patagonia distinguished two hybrid lineages,one derived from E. amarillans x E. typhina and the other derived from E. typhina subsp. poae x E. festucae andidentified as E. tembladerae.The objective of this work was to study, at regional scale, the diversity and the potential toxicity to cattleof Epichloë sp. in H. comosum along a gradient of aridity.An exhaustive survey of H. comosum covering an area of 60 000 km² in Patagonia Argentina, that includedthe previously studied area, was performed in January 2015. Four transects from extreme arid to sub‐humidconditions (from 150 to 1200 mm annual precipitation) and collection sites on each transect were establishedaccording to their mean annual precipitation (Wordclim). Each site was classified according to its aridity index (AI=Annual precipitation/Potential evapotranspiration) and classified as: arid, AI<0.2; semiarid, 0.20.5. In each site eight plants were collected. The incidence of endophytes in each population wasestablished by checking the presence of the endophyte by microscopic observation of aniline blue stained culmpiths and seeds of each plant. Endophytes were isolated on Potato Dextrose Agar (PDA) in darkness at 24 °C andsingle spore cultures were obtained for morphological characterization and DNA isolation[2]. The genetic diversityanalyses and phylogenetic relationships of Epichloë sp. isolates were based on calmodulin gene (calM) phylogeny,mating type, and screening by PCR for presence of alkaloid biosynthesis genes (perA, lolC, dmaW and idt genes: G,K,P, Q, F, B, E, J).The incidence of endophytes was variable, ranging from 0 to 100%. Epichloë sp. was detected in 27 of the30 sites, with an average incidence across infected populations of 81%. Populations in semiarid environmentspresented higher incidence of endophytes (100%), whereas those in arid and sub‐humid environments presentedlower values (of incidence) (15‐30%). Even though the isolates presented variability in morphologicalcharacteristics, cal M phylogeny indicated that most of the isolates correspond to E. tembladerae, which wasdetected in all the populations (i.e.: sites), with the exception of the previously E. typhina x E. amarillans isolate.Alkaloid gene profiling indicated that the E. typhina x E. amarillans hybrid was positive for perA, lolC, dmaW andmost of IDT genes (idtE‐). The isolates identified as E. tembladerae were negative for lolC and dmaW genes, all ofthem presented perA and the same IDT genes profile, being positive for idtG, K, P, Q, F, B and negative for idtE andJ, with the exception of one isolate that was negative for all the screened IDT genes.Our results show that in H. comosum chances of hosting Epichloë sp. decrease with aridity. However, thesymbiosis is still maintained in some of the arid and semiarid environments, suggesting long‐term benefits of theassociation. Although different endophyte taxa could be associated with H. comosum, E. tembladerae seems to bethe prevalent species in this host and the diversity of endophytes is not associated with the environmentalconditions of the populations. Only the E. typhina x E. amarillans hybrid could be toxic to cattle producing ergotalkaloids, whereas the IDT gene positive E. tembladerae isolates could only produce terpendole C. Both endophytespecies detected could confer resistance to insects through the production of peramine or some loline in the caseof the E. typhina x E. amarillans hybrid.