Horizontal transmission, persistence and competition capabilities of Epichloë endophytes in Hordelymus europaeus grass hosts using dual endophyte inocula

The Epichloae (Ascomycota, Clavicipitaceae) are endophytes of grasses consisting of haploid species, and heteroploid interspecific hybrids that are prevalent in many natural host grass populations. Hybrid formation may involve somatic fusion of different mycelia in planta, but this has never been tested. We used Hordelymus europaeus as an experimental system, which naturally hosts several hybrid and non-hybrid endophytes. Seedlings were inoculated with mixed inocula including a hybrid and a non-hybrid strain from H. europaeus, and two sexual Epichloë species from other hosts. Evaluation of endophyte infection 13 months after inoculation detected a high rate of multiple infections within tillers, but no novel hybrid endophyte. The hybrid strain was also found in plants that had not received such inoculum suggesting horizontal transmission. Epiphytic conidia detected on leaf tissues were responsible for contagious spread. This observation may offer an explanation why hybrid endophytes are prevalent in natural populations of H. europaeus.