Increase of secondary metabolites content in peppermint in response to inoculation with plant growth-promoting rhizobacteria and foliar feeding insects.

CAPPELLARI, L., CHIAPPERO, J., GIORDANO, W., BANCHIO, E.

Congreso; XIII Congreso Argentino de Microbiología General (SAMIGE); 2018

Peppermint (Mentha × piperita) is cultivated worldwide for production of essential oils (EOs) and fresh or dried herbs, and is one of the most important EO crops.Many species of bacteria, most of which are found in the rhizosphere (the narrow region of soil associated with the roots of plants), have beneficial effects on plant growth and on crop yield and quality. Such bacteria, collectively termed ?plant growth-promoting rhizobacteria? (PGPR), promote plant growth through both direct and indirect mechanisms. Rachiplusia nu is a major defoliator commonly found in Argentina. The larval stage of R. nu can cause severe damages to aromatic plants. Plants display a diverse array of inducible changes in secondary metabolites following insect herbivory or PGPR inoculation. The objective of this work was to determine the effect of inoculation of rhizobacteria and feeding of herbivorous insects on the production of secondary metabolites in M. piperita. M. piperita young shoots were transferred to test tubes containing sterile distilled water and rooting hormone (alpha naphthalene acetic acid). After one week, plantlets were transferred to plastic pots containing sterile vermiculite. After 7 days the plants were inoculated with PGPR strains Bacillus subtilis GB03 or P. putida SJ04. Thirty days after inoculation, the plants were exposed to 6 larvae of R. nu (Lepidoptera, Noctuidae) for 5 hs (enough time to generate considerable damage, approximately 30%). Levels of the main monoterpenes pulegone, menthone and menthol, EOs yield and phenolic content were assessed 48 h after wounding. The biosynthesis of the major EO components was increased in inoculated or insect-damaged plants. EO yield and amounts of the main monoterpenes was similar in inoculated plants than in control plants exposed to insects. The content of phenolic compounds was similar in leaves of inoculated and non-inoculated plants damaged by herbivores. Better understanding of the processes that affect secondary metabolites accumulation will lead to increased yields of these commercially valuable natural products.