The Known Antimammalian and Insecticidal Alkaloids Are Not Responsible for the Antifungal Activity of <i>Epichloë</i> Endophytes
Krishni Fernando | Priyanka Reddy | Simone Vassiliadis | German C. Spangenberg | Simone J. Rochfort | Kathryn M. Guthridge
Asexual <i>Epichloë</i> sp. endophytes in association with pasture grasses produce agronomically important alkaloids (e.g., lolitrem B, epoxy-janthitrems, ergovaline, peramine, and lolines) that exhibit toxicity to grazing mammals and/or insect pests. Novel strains are primarily characterised for the presence of these compounds to ensure they are beneficial in an agronomical setting. Previous work identified endophyte strains that exhibit enhanced antifungal activity, which have the potential to improve pasture and turf quality as well as animal welfare through phytopathogen disease control. The contribution of endophyte-derived alkaloids to improving pasture and turf grass disease resistance has not been closely examined. To assess antifungal bioactivity, nine <i>Epichloë</i> related compounds, namely peramine hemisulfate, <i>n</i>-formylloline-d3, <i>n</i>-acetylloline hydrochloride, lolitrem B, janthitrem A, paxilline, terpendole E, terpendole C, and ergovaline, and four <i>Claviceps purpurea</i> ergot alkaloids, namely ergotamine, ergocornine, ergocryptine, and ergotaminine, were tested at concentrations higher than observed in planta in glasshouse and field settings using in vitro agar well diffusion assays against three common pasture and turf phytopathogens, namely <i>Ceratobasidium</i> sp., <i>Drechslera</i> sp., and <i>Fusarium</i> sp. Visual characterisation of bioactivity using pathogen growth area, mycelial density, and direction of growth indicated no inhibition of pathogen growth. This was confirmed by statistical analysis. The compounds responsible for antifungal bioactivity of <i>Epichloë</i> endophytes hence remain unknown and require further investigation.
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