An overview of plant growth promoting rhizobacteria and their influence on essential oils of medicinal plants: a review article.

One of the important and necessary practices for improving nutrients availability in sustainable agriculture is using microorganisms. Beside the negative effects of chemical fertilizers on the soil and human health, plant growth promoting rhizobacteria are known as an alternative to supply the organic nutrients of plants during the past two decades. Enriching soil fertility by eco-friendly methods in medicinal plants could well-support plants growth and production. Most studies found that bio-fertilizers such as plant growth promoting rhizobacteria (PGPR) could promote physio-morphological characteristics and yield of medicinal plants. The mechanisms of plant growth promoting rhizobacteria could be summarized in symbiotic and associative nitrogen fixation, solubilization and mineralization of nutrients, production of phytohormones, vitamins, and antagonistic components against pathogens which enhance plant resistance to the stress and non-stress conditions. This paper also argued that beside the soil type, environmental variables, soil management practices, and microbial interactions, plant species could affect bacterial diversity and composition of the rhizosphere. Three major secondary metabolites of medicinal plants such as Terpenoids, phenolics and alkaloids were also increase due to the impact of microorganisms in metabolic pathway of plants such as Jasmonic acid signaling pathway. Thereby, significant increases in growth and yield of medicinal plants in response to inoculation with PGPR could be one of the promising approaches in sustainable agriculture.