Could mycorrhizal symbiosis prepare the grapevine to withstand subsequent biotic stresses through changes in the volatilome and ionome of leaves?

Searching alternatives to chemicals to protect vines against biotic stresses, while minimizing environmental impact, is a priority. The association of grapevines with arbuscular mycorrhizal fungi (AMF) is a promising tool, since AMF can change volatilome (VOCs) profile and improve mineral status of grapevine. Whether the inoculation of Tempranillo (T) and Cabernet Sauvignon (CS) with beneficial microorganisms (AMF and plant-growth promoting rhizobacteria, PGPRs) improved the nutritional status and the levels of VOCs in leaves thus reinforcing the constitutive defences of this crop against potential biotic stresses was evaluated. VOCs were isolated and analysed by headspace-solid-phase microextraction and gas chromatography-mass spectrometry. Minerals were determined by inductively coupled plasma optical emission spectroscopy, while proteins, sugars, phenolics, starch and proline spectrophotometrically. More than 40 VOCs were detected in the leaves of T and CS, mostly synthesized via the lipoxygenase-hydroperoxide lyase pathway. The total amount of VOCs was higher in CS than in T, as were pentyl leaf volatiles, some green leaf volatiles (GLVs) and VOCs synthesized via the shikimate pathway. Mycorrhizal association increased the concentration of GLVs only in CS. AMF favoured the accumulation of 2-hexenal and 3-hexenal in CS, but reduced VOCs synthesized via the mevalonate pathway in T. Mycorrhization increased copper in leaves of T, but reduced iron in CS. Soluble leaf phenolics also decreased in CS associated with AMF. AMF (in the presence of PGPRs) triggered subtle and cultivar-specific changes in the ionome and volatilome of leaves in T and CS, which may be linked to different resistance levels. VOCs synthesis in response to pathogen attack cannot be excluded.