The effects of carbohydrate supply and host genetic background on Epichloë endophyte and alkaloid concentrations in perennial ryegrass

The ecological effects of novel grass-endophyte associations used in agriculture have not been widely studied. Previous studies of asexual Epichloë-infected Lolium perenne suggest that endophyte concentration is altered in high sugar grasses (HSGs) selectively bred to produce higher concentrations of water-soluble carbohydrates relative to conventional cultivars. We investigated whether differences are due to the effects of altered carbohydrates, or genetic background, by growing multiple cultivars in both high-sugar trait expression and non-expression conditions (using light/temperature treatments). Endophyte and alkaloid concentrations were measured in three HSG and three NSG (normal-sugar grass) cultivars infected with Lp19 or AR37 endophyte strains. Low molecular weight (LMW) carbohydrates had a small effect, explaining <6% of the variation in endophyte concentration. Endophyte concentrations were strongly dependent on plant genotype and fungal strain, with the highest concentrations seen in Lp19, suggesting that the interaction is highly dependent on genetic compatibility. Changes in endophyte concentration due to altered environmental variables and genetic compatibility may have consequences for persistence, toxicity, and invasive potential of endophyte-infected plants.