Plant age and seasonal timing determine endophyte growth and alkaloid biosynthesis

The systemic grass endophyte Epichloë festucae var. lolii produces alkaloids which can protect the host grass Lolium perenne from herbivory. Alkaloid concentrations depend on genetic predisposition of grass and endophyte, and are affected by the environment. However, the role of plant age and seasonal timing remains unknown. We monitored monthly endophyte and alkaloid concentrations in endophyte infected perennial ryegrass over 29 months in a common garden experiment in Germany. Climatic conditions in spring and summer enhanced endophyte growth and alkaloid production, explaining a dominant role of seasonal timing. Alkaloid concentrations also increased with plant age and exceeded the toxic threshold for invertebrates in the first summer and for livestock in the third summer. Our results highlight the key role of plant age and seasonal timing in affecting the toxicity of systemic fungal endophytes of grasses. Endophyte mediated livestock intoxications may increase on European grasslands with global warming.