Allelopathic effects of Epichloë fungal endophytes: experiment and meta-analysis

Host-specific Epichloë spp. are endophytic fungal symbionts of pooid grasses that produce herbivore-deterring alkaloids and alter the grass host’s metabolite and protein profiles. Early observations suggested that Epichloë may have negative allelopathic effects on neighbouring plant species, particularly Trifolium spp. clovers, but subsequent allelopathy tests produced variable results. We examined two hypotheses: (1) Epichloë allelopathy negatively affects other plant species, and (2) Epichloë strains differ in their allelopathic effect. We performed a greenhouse experiment using root exudates from Lolium perenne hosting different E. festucae var. lolii strains to compare their allelopathic effects on native legumes and forbs. We then used meta-analysis to examine the evidence to date for allelopathic effects of Epichloë endophytes. We found very little evidence for negative allelopathic effects of Epichloë in cool-season grasses across a range of methodologies, test plant species, and response measures, and there was little difference among E. festucae var. lolii strains. Negative allelopathic effects were detected only for root hair measures, which were from a single study. Positive effects on biomass were found for some experimental subgroups, including legumes. However, the majority of response variables showed no evidence for Epichloë allelopathy. Although there is currently little evidence for negative Epichloë allelopathic effects, our meta-analysis identified several research gaps. Experiments testing the functional belowground effects of Epichloë presence may help to determine its effects on non-host plant performance via plant-soil feedbacks.