Influence of Drought Stress and PGPR Inoculation on Essential Oil Yield and Volatile Organic Compound Emissions in Mentha piperita

Considering that inoculation with beneficial rhizobacteria promotes biomass and secondary metabolite biosynthesis and also the fact that drought stress can increase their production, we determined the effects when both of these situations were combined in EO yield. In addition, the levels of endogenous phytohormones and the gene expression of enzymes related to monoterpenes biosynthesis were measured. The experimental results showed that inoculation with PGPR in stressed plants produced the same effects on trichome density, the EO main components and total yield as in plants only inoculated or with moderate stress alone. In addition, the VOC emissions of inoculated stressed plants did not vary the release amount in relation to uninoculated stressed ones. The results observed have suggested a way of improving aromatic plant productivity, particularly that of peppermint, by managing drought stress through the inoculation of plants with PGPR. This inoculation under moderate drought stress is appropriate when the purpose of the crops is to obtain plants with a high secondary metabolites yield.