An appraisal of the protection conferred by foliar Epichloë endophytes against root herbivores in plants: A meta-analysis

Abstract

The role of foliar endophytes in modulating plant interactions with herbivores has been less investigated in belowground than aboveground environments. We studied how foliar Epichloë endophytes influence plant performance in the presence of root herbivores. We hypothesize that the endophyte-mediated increase in host performance in the context of root herbivory is due to the stimulation of plant growth in response to the herbivore attack (i.e., tolerance) and the presence of antiherbivore alkaloids in belowground tissues (i.e., resistance). We conducted a quantitative analysis of published results in relation to plant-Epichloë-root herbivore interactions and quantified the overall effects of endophytes on both biomass of plants in the presence/absence of root herbivores and performance of root herbivores. To gain further insights into plant-herbivore resistance, we assessed the in planta distribution of Epichloë-derived alkaloids and the responses of these compounds to the root herbivory. Endophytes increased plant growth in both presence/absence of root herbivores. Epichloë also reduced the herbivore performance, although the effect was dependent on the plant-endophyte association and herbivore type. Epichloë-derived alkaloids were generally less concentrated in belowground compared to aboveground plant tissues. However, the belowground:aboveground ratio for loline alkaloid concentrations was higher in plants in presence than absence of root herbivores, suggesting a local induction of resistance. Our results suggest that foliar Epichloë endophytes enhance plant tolerance to root herbivory by promoting plant growth and reducing root herbivore performance. The observed resistance may be partially explained by the action of Epichloë-derived alkaloids that are present in belowground tissues.