Rhizobia are of enormous agricultural and economic values because they provide the major source of nitrogen input in agricultural soils. Beside nitrogen fixation, many rhizobial strains exert plant-growth-promoting traits such as the production of phytohormones, siderophores and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase as well as the solubilization of inorganic phosphate. These make rhizobia become valuable for both legumes and non-legumes. Effective rhizobial strains have been screened and used as inoculants for improving plant growth. The application of rhizobia as biofertilizer ensures success in crop productivity and reduces the need for artificial fertilizers that are expensive and cause environmental problems. Coinoculations of rhizobia and other plant-growth-promoting rhizobacteria (PGPR) have shown the significant increase in plant-growth promotion. Several rhizobial strains have also been reported for their bioremediation abilities.
Keywords: Acetylene Reduction Activity (ARA), Biofertilizer, Biological nitrogen fixation (BNF), Bioremediation, Co-inoculation, Endophyte, Inoculant, Plant-growth-promoting rhizobacteria (PGPR), Rhizobia, Symbiotic effectiveness.