Arbuscular mycorrhizal fungi make endophyte-induced plant volatiles perceptible.

Abstract

Most cool season grasses are commonly associated with asexual endophytes and arbuscular mycorrhizal fungi (AMF). These two symbionts are known to provide different benefits to the host plant through altering its phenotype when they are present. In isolation, either of them can affect the volatile organic compounds (VOCs) emitted by the host grass, but their interactive influences on this trait are unknown. We hypothesized that changes in host grasses VOCs profile induced by the presence of asexual endophytes within aerial tissues, depend on whether these plants are also colonized by AMF. We designed a factorial greenhouse experiment, in which we identified and quantified VOCs emitted by Lolium multiflorum plants with contrasting levels of infection with the endophyte Epichloë occultans (low < 5% and high > 95%), growing in pots with sterilized soil that could be inoculated or not with AMF. Results showed that total VOCs emission in plants with high infection levels of E. occultans doubled the emission of plants with low levels of the endophyte, but only in plants previously inoculated with AMF. The green leaf volatile Z3-Hexenyl acetate dominated the blend. Its emission was three times higher in plants with high level of association with both types of symbionts compared to plants with high level of AMF but low level of endophyte. We found a similar trend for the monoterpene β-ocimene. Our results point out the importance of considering the contribution of different types of symbionts when studying the interaction of plants with their natural enemies or the benefits provided to the host in different ecological contexts.