Plant growth promoting Rhizobacteria (PGPR): a review

Soil microbial communities are often difficult to characterize, mainly because of their immense phenotypic and genotypic diversity. In the last ten years, a number of PGPR that have been identified has seen a great boost, mainly because the role of the rhizosphere as an ecological unit has gained importance in the functioning of the biosphere and also because mechanisms of action of PGPR have been deeply studied. A putative PGPR qualifies as PGPR when it is able to produce a positive effect on the plant upon inoculation, hence demonstrating good competitive skills over the existing rhizosphere communities. PGPR influence direct growth promotion of plants by fixing atmospheric nitrogen, Solubilizing insoluble phosphates, secreting hormones such as IAA, GAs, and Kinetins besides ACC (1-Aminocycloprapane-1-carboxylic acid) deaminase production, which helps in regulation of ethylene. Induced systemic resistance (ISR), antibiosis, competition for nutrients, parasitism, production of metabolites (hydrogen cyanide, siderophores) suppressive to deleterious rhizobacteria are some of the mechanism that indirectly benefit plant growth.