An arbuscular mycorrhizal fungus and a root pathogen induce different volatiles emitted by roots.

Plants are in permanent contact with various microorganisms and are always impacted by them. To better understand the first steps of a plant's recognition of soil-borne microorganisms, the early release of volatile organic compounds (VOCs) emitted from roots of in response to the symbiont or the pathogenic oomycete was analysed. More than 90 compounds were released from roots as detected by an untargeted gas chromatography-mass spectrometry approach. Principal component analyses clearly distinguished untreated roots from roots treated with either or . Several VOCs were found to be emitted specifically in response to each of the microorganisms. Limonene was specifically emitted from wild-type roots after contact with spores but not from roots of the mycorrhiza-deficient mutant . The application of limonene to mycorrhizal roots, however, did not affect the mycorrhization rate. Inoculation of roots with zoospores resulted in the specific emission of several sesquiterpenes, such as nerolidol, viridiflorol and nerolidol-epoxyacetate but application of nerolidol to zoospores of did not affect their vitality. Therefore, plants discriminate between different microorganisms at early stages of their interaction and respond differently to the level of root-emitted volatiles.