Impact of plant growth promoting rhizobacteria Serratia nematodiphila RGK and Pseudomonas plecoglossicida RGK on secondary metabolites of turmeric rhizome

Abstract

Plant growth promoting rhizobacteria (PGPR) are diverse group of soil bacteria that live in the rhizosphere of plants. The current research focuses on the plant growth promoting potential of two strains, Serratia nematodiphila RGK and Pseudomonas plecoglossicida RGK isolated from the rhizospheric soil of the turmeric plant. Both of these bacterial strains found to have the capacity to solubilize phosphate, zinc and potassium as well as potential to produce indole acetic acid, siderophores, nitrogen fixation, ammonia, hydrogen cyanide (HCN) and exopolysaccharide synthesis. Further, they showed the salinity tolerance up to the 6–7% NaCl and antibiotic sensitivity to Gentamycin, Kanamycin, Streptomycin, Tobramycin, and Amikacin. The isolate Pseudomonas plecoglossicida RGK also has shown antifungal activity against fungal pathogen of turmeric Pythium aphanidermatum. Treatment of turmeric rhizomes with separate and by combination of both strains demonstrated remarkable increase growth parameters of turmeric as compared to control. They improved the growth metrics of the plant such as the number of leaves, shoot height, rhizome biomass as well as phenolic, flavonoid content, and free-radical (DPPH) scavenging ability. As compared to the untreated plants, PGPR treated rhizomes showed higher amounts of secondary metabolites, primarily curcumin and additional compounds such 4-Hydroxy-2-methylacetophenone, 2,4-Di-tertbutyl phenol, aR-Turmerone, and (Z) -gamma-Atlantone. The detection of a phenolic compound, 4-Hydroxy-2-methylacetophenone, in a consortium-treated turmeric plant, which has significant biological activity is reported for first time. The use of different microbial strains in a single formulation is a new and developing trend for sustainable agriculture.