Can the defensive mutualism between grasses and fungal endophytes protect non-symbiotic neighbours from soil pathogens?

Abstract

It is proposed that Epichloe endophytes have a role protecting host grasses against pathogens. However, it is unclear whether this protection is extended to other non-symbiotic plants. Here we explored the effect of the asexual fungal symbiont, Epichloe occultans, on the interaction between Lolium multiflorum host plants and soil pathogens, and its potential positive side-effect on neighbouring plants. We conducted two microcosm experiments to assess the endophyte effect on seedling establishment of the host grass and other non-symbiotic grasses in the presence of soil pathogens. With an in-vitro experiment, we tested whether the endophyte inhibits, during seed germination, the growth of these pathogens. Independently of pathogen identity, the endophyte improved host establishment (6 %). The endophyte also enhanced the establishment of the neighbouring grass Bromus catharticus (≈20 %) only in soil with Rhizoctonia solani. The endophyte in seed reduced the growth (≈20 %) of two out of four pathogens (Fusarium acuminatum and R. solani). We conclude that asexual endophytes could protect host grasses against pathogens but most importantly, that they can have protective effects beyond their hosts. Since effects depended on pathogen and plant identity, more experiments are needed in order understand the ecological meaning of these positive side-effects.