Secondary metabolites of fluorescent pseudomonads in biocontrol of phytopathogens for sustainable agriculture

Plant growth promoting rhizobacteria (PGPR) belonging to the group "fluorescent pseudomonads" play very important role in sustainable agriculture. They are well known to assist plants' health by diverse mechanisms. Potential of fluorescent pseudomonads to protect plants from a range of phytopathogens is of prime importance and gained momentum in agri-biotechnology. At global level commercialization of fluorescent pseudomonads in the form of bioinoculants for the management of several plant diseases is now considered to be very effective. Fluorescent pseudomonads are being used as effective biocontrol agents (BCA) against an array of phytopathogens. They have great potential as BCA because of the ability to produce a variety of secondary metabolites. Therefore, the objective of this review is to describe and assess the roles of secondary metabolites produced by fluorescent pseudomonads in controlling the phytopathogens and enhancing the plant health. Prominent secondary metabolites involved in biocontrol by fluorescent pseudomonads include phenazines (PHZ), 2, 4-diacetylphloroglucinol (DAPG), pyoluteorin (PLT), pyrrolnitrin (PRN), cyclic lipopeptides (CLPs) and volatile organic compounds (VOCs) such as hydrogen cyanide (HCN). These metabolites are known for antifungal, antibacterial, antiviral, antitumor and anti-nematicidal properties. Better contemporary techniques for extraction, purification and characterization may unveil the mechanisms of action of these metabolites and enable to utilize them in future bioformulations so as to replace harmful synthetic chemicals (in agriculture).