ABSTRACT
Plant growth-promoting rhizobacteria (PGPR) have been studied by metagenomic approaches, but the nodule microbiomes have been fundamentally studied by culture-dependent methods with the simple objective of selection of plant growth-promoting bacteria to be used in agronomic practices. Rhizobia may promote the crop growth by direct or indirect mechanisms. Direct mechanism of plant growth promotion occurs when rhizobacteria mobilize the essential nutrients from soil or modulate the level of hormones within a plant. Co-inoculation with rhizobia and non-legume PGPR is becoming an important agronomic practice in the development of sustainable agriculture. The most widely exploited plant bacteria symbiotic relationship is the N-fixing rhizobia and legumes. Phytohormones such as indole acetic acid, cytokinins, and gibberellins producing capacity of several rhizobacteria were demonstrated by various researchers worldwide. Induced systemic resistance and enhanced expression of plant defense-related genes by rhizobia is one of the important mechanisms against pathogens to minimize disease in pulse crops.
