Increase of Essential Oil Yield in Mentha piperita by Inoculation with Plant Growth-Promoting Rhizobacteria

Abstract

Peppermint (Mentha piperita) is one of the most important EO (essential oil crops) and is cultivated worldwide. It is composed primarily of monoterpenes, whose medicinal properties are mainly due to their EO composition, accumulated in glandular trichomes. Nowadays, agriculture relies heavily on the use of synthetic chemicals, such as fertilizers and pesticides, to achieve high yields but without taking into account their deleterious effects on the environment. However, there is an interesting biotechnological alternative using microorganisms to increase the availability and intake of nutrients by crops and to control phytopathogenic organisms and herbivorous insects. The group of bacteria termed plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere and stimulate plant growth and development by direct or indirect mechanisms. Thus, in the search for new strategies of plant production to optimize essential oil (EO) yield, inoculation with PGPR is an interesting candidate. We present here an integrated summary of our experimental findings from an analysis of the community of fluorescent Pseudomonas strains in the rhizosphere of commercially grown Mentha piperita, including the effects of inoculation and co-inoculation with different PGPR strains (native and wild type) ontotal EO yield and glandular trichome density. The qualitative and quantitative composition of the main monoterpenes (menthol, menthone, pulegone, limonene and linalool) were also analyzed the effects of the volatile emitted by PGPR rhizobacteria on EO production. The various PGPR strains (Bacillus amyloliquefaciens GB03, Pseudomonas fluorescens WCS417r, Azospirillum brasilense SP7, Pseudomonas putida SJ04-SJ25-SJ48) and co-inoculations evaluated produced significant increases in the production of EO in peppermint plants, but at different magnitudes. Bacterial inoculants are thus an effective biotechnological tool for stimulating the secondary metabolism in plants. Application of these techniques may contribute to environmental conservation, increased crop productivity and sustainable agricultural practices