PGPR secondary metabolites: an active syrup for improvement of plant health

Abstract Plant-growth-promoting rhizobacteria (PGPR), arise the mechanism of interaction with each other on plants surfaces and plants make the association with a guild of PGPR during the evolution. These associations are results of crosstalk through signaling cascade of various PGPR colonized on same plant surfaces. The rhizosphere of the plant is very active and rich microbial habitat, due to the release of various nutritive substances through plant root exudates. These root exudates shape the presence of microbial community in surroundings. The presence of nutritional substances also plays significant role in gathering and performance of microbial community in the rhizosphere. However, the plants and microbes influence each other by releasing the inhibitory molecules as molecular signals for making of parasitic, antagonistic and competitive interactions. These signals play an essential role and decide the fate of mutualism and other associative interactions of plants and microbes. Various secondary metabolites from both plant and microbes are also involved in these interactions. In the present chapter, we have tried to explore the role of secondary metabolites produced by plant growth promoting rhizobacteria and fungi as an active syrup for plant growth, health and defense.