Performance of young endophyte-free and endophyte-infected tall fescue (Festuca arundinacea) plants under partial and total submergence

Context Tall fescue (Festuca arundinacea Schreb.) is a valuable temperate forage grass. Tall fescue plants associated with Epichloë fungal endophytes are successfully spreading in grassland regions that are recurrently exposed to flooding. Aims We asked whether the association with fungal endophytes increases plant performance under water excess. Methods In a greenhouse experiment, we evaluated the differential performance of young endophyte-infected and endophyte-free tall fescue plants in response to 14 days of partial and total submergence. We included a wild local population and a cultivar, each with their respective fungal endophyte: the common endophyte and a safe (non-toxic) endophyte (AR584). Key results Relative to control (non-submerged) plants, and regardless of endophyte status, total submergence resulted in a significant growth reduction. At the end of the partial submergence period, the number of leaves per plant increased (21%) in the presence of the safe endophyte AR584 but decreased (18%) in the presence of the wild endophyte. Moreover, under partial submergence, the presence of wild endophyte decreased pseudostem dry weight by 10%. Conclusions Our results show that the presence of either the wild or the safe endophyte did not increase the performance of young tall fescue plants under submergence conditions. Implications Although all endophyte-free and endophyte-infected tall fescue plants survived submergence treatments, we cannot rule out that Epichloë endophytes might improve plant fitness under longer stressful submergence conditions. Future research should explore how endophytes modulate host performance under water excess, considering different phenological plant phases and/or co-occurrence with other stress factors (e.g. high temperatures).