Abstract

Plant Growth Promoting Rhizobacteria (PRGR) are the rhizosphere bacteria that help  in the enhancement of plant growth by a variety of mechanisms like phosphate solubilization, siderophore production, biological nitrogen fixation, rhizosphere engineering, production of 1-Aminocyclopropane -1carboxylate deaminase (ACC), quorum sensing(QS) signal interference and inhibition of biofilm formation phytohormone production, exhibiting antifungal activity, production of volatile organic compounds (VOCs), induction of systematic resistance, promoting beneficial plant microbe symbiosis, interference with pathogen toxin production etc. It is generally free living, soil borne bacteria. The potentiality of PGPR is continuously increasing as it offers us a good way to replace the chemical fertilizers, pesticides as well as directly or indirectly influence the whole morphology of the plants and play a vital role in crop protection, growth promotion and in the improvement of soil health. Some well known PGPR Strains are Pseudomonas, Bacillus, Azospirrillum, Rhizobium and Serratia species. Different strains of PGPR are capable of secreting antifungal metabolites (AFM) like siderophore, chitinase and hydrogen cyanide. For example Pseudomonas fluorescens belonging to PGPR class produce siderophore and control Phythium ultimum and Pseudomonas stuzeri produce chitinase which lyse the cell wall of Fusarium solani. Antifungal metabolites produced by these Rhizobacteria were identified as antibiotics ( iturin, surfactins, fengycin, DAPG, Phenazine etc, ), cell wall degrading enzymes( proteses, chitinases, cellulases), plant growth promoting enzymes and hormones  (indole-3-Acetic Acid, ACC-deaminase, phosphatase, nitrogen fixation), N-acylhomoderine lactones and sideophore. Due to synthesis of antifungal metabolites PGPR also used as a biocontrol agent in case of many diseases for instance, it degrades fusaric acid produced by Fusarium sp. That is a causative agent of wilt. They also help plants to be resistant against biotic stresses via direct antagonism to pathogens or by induction of systematic resistance to pathogens. It mostly trigger induced systematic resistance via methyl jasmonate and methyl salicyclate in plants.