Plant Growth Promoting Rhizobacteria Improving the Legume–Rhizobia Symbiosis

Abstract

The legume-rhizobia symbiosis is considered the most important nitrogen-fixing interaction from an agricultural point of view. However, biotic and abiotic factors can modify critical parameters of both the legumes and the rhizobia. These changes may lead to differences in the molecular dialogue, consequently reducing the symbiotic effectiveness. Therefore, optimal performance of the N-fixing symbiosis will be guaranteed by selection of both symbiotic partners for adaptation to the target environment. The symbiotic process can be negatively affected by many other rhizosphere interactions, resulting in important ecological, economic, and nutritional losses. The application of agricultural techniques that are friendly with the environment, based on the use of plant growth promoting rhizobacteria (PGPR), can increase the efficiency of the symbiotic process. The use of these beneficial microorganisms could reduce the use of polluting chemicals allowing sustainable production of legumes. Co-inoculations of appropriate rhizobia together with PGPR may profoundly increase the crop yield by different mechanisms. The negative effects of environmental stresses on the legume-rhizobia symbiosis may further be significantly diminished by applying mixtures of rhizobia and PGPR.