Allelopathic effects of Epichloë fungal endophytes: experiment and meta-analysis
Host-specific Epichloe spp.endophytic fungal symbionts of pooid grasses that produce herbivore-deterring alkaloids and alter the grass hosts metabolite and protein profiles. Early observations suggested that Epichloe 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) Epichloe strains differ in allelopathic effect, and (2) Epichloe allelopathy negatively affects other plant species. We performed a greenhouse experiment using root exudates from Lolium perenne L. hosting different E. festucae var. lolii (Latch, M.J. Chr. & Samuels) C.W. Bacon & Schardl 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 Epichloe endophytes. We found little difference in effect among E. festucae var. lolii strains and very little evidence for negative allelopathic effects of Epichloe in cool-season grasses across a range of methodologies, target plant species, and response measures. 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 Epichloe allelopathy. Although there is currently little evidence for negative Epichloe allelopathic effects, our meta-analysis identified several research gaps. Experiments testing the functional belowground effects of Epichloe presence may help to determine its effects on non-host plant performance via plant-soil feedbacks.