Research PaperInducing phenolic production and volatile organic compounds emission by inoculating Mentha piperita with plant growth-promoting rhizobacteria

- Root-associated bacteria increase VOCs emission and phenolic content in peppermint plants.
- Effects of bacterial inoculation on VOCs emission have received little attention.
- Few studies have examined effects of rhizobacteria on total phenolic content.
- %R of main compounds are different in VOCs than in Essential Oils.
- Inoculation with rhizobacteria affect secondary metabolites biosynthesis.

Plant growth-promoting rhizobacteria (PGPR) work primarily by improving the nutrient status of plants and increasing plants' phytohormone production. Although this response has been demonstrated in many plant species, it is not well understood in aromatic plant species. To examine the effect of PGPR strains on the emission of volatile organic compounds (VOCs), total phenolic production and phenylalanine ammonia-lyase (PAL) activity, shoots of peppermint (Mentha piperita) plants were inoculated or co-inoculated with strains of beneficial rhizobacteria.VOC emissions for the inoculated groups were ∼3-fold higher than for controls. Co-inoculated plants produced the greatest increase in VOC emission in comparison to singly inoculated and control plants. The synthesis of phenolic compounds in leaves of all the treated plants was enhanced in comparison with controls; and higher activity of the PAL enzyme was observed in inoculated plants. In view of the economic importance of VOCs and phenolic compounds for a variety of applications in the food and cosmetic industries, P. fluorescens, B. subtilis and P. putida SJ04 have the potential to improve the productivity of cultivated aromatic plants. Better understanding of the processes that affect secondary metabolites accumulation will lead to increased yields of these commercially valuable natural products.