Symbiosis with systemic fungal endophytes promotes host escape from vector-borne disease
Plants interact with a myriad of microorganisms that modulate their interactions within the community. A well-described example is the symbiosis between grasses and Epichloë fungal endophytes that protects host plants from herbivores. It is suggested that these symbionts could play a protective role for plants against pathogens through the regulation of their growth and development and/or the induction of host defences. However, other endophyte-mediated ecological mechanisms involved in disease avoidance have been scarcely explored. Here we studied the endophyte impact on plant disease caused by the biotrophic fungus, Claviceps purpurea, under field conditions through (1) changes in the survival of the pathogen´s resistance structure (sclerotia) during overwintering on the soil surface, and (2) effects on insects responsible for the transportation of pathogen spores. This latter mechanism is tested through a visitor exclusion treatment and the measurement of plant volatile cues. We found no significant effects of the endophyte on the survival of sclerotia and thus on disease inocula. However, both pathogen incidence and severity were twofold lower in endophyte-symbiotic plants than in non-symbiotic ones, though when insect visits were prevented this difference disappeared. Endophyte-symbiotic and non-symbiotic plots presented different emission patterns of volatiles suggesting that they can play a role in this protection. We show a novel indirect ecological mechanism by which endophytes can defend host grasses against diseases through negatively interacting with intermediary vectors of the epidemic process.
KeywordsMutualism Pathogen transmission Disease avoidance VOCs Epichloë occultans
In loving memory of Professor Rolando J.C. León. Diego Vazquez and Amy Austin provided useful comments on earlier versions of the manuscript. This work was funded by the University of Buenos Aires (UBA), the National Research Council (CONICET) and the National Scientific and Technological Promotion (FONCYT). L.I.P. holds a Research Scholarship from the National Research Council of Argentina.
Author contribution statement
LIP, MO and PEG conceived and designed the experiments. LIP, AGA and HJM performed the experiments. LIP and AGA analyzed the data. LIP wrote the manuscript and all authors provided editorial advice.
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