Isolation of plant growth promoting rhizobacteria and their impact on growth and curcumin content in Curcuma longa L.

The isolation of plant growth promoting rhizobacteria (PGPR) associated with the rhizosphere of Curcuma longa L. and evaluation of plant growth promotion potential, salinity tolerance, antibiotic sensitivity, antimicrobial properties and their correlation with the potential effect on the growth and biochemical ingredients was investigated. Nine strains (Bacillus subtilis CL1, Bacillus sp. CL3, Burkholderia thailandensis CL4, Agrobacterium tumefaciens CL5, Klebsiella sp. CL6, Bacillus cereus CL7, Pseudomonas putida CL9, Pseudomonas fluorescens CLI2 and Azotobacter chroococcum CL13 have been identified. All such strains solubilized tri-calcium phosphate and produced Indole acetic acid, ammonia but only 66% of the strains produced siderophores. Strains CL1, CL9 and CL12 tolerated maximum NaCl (6%) relative to strain CL5 (1%). The strains were sensitive to the antibiotic chloromphenicol followed by erythromycin and most of these effectively inhibited growth of Escherichia coli, Aspergillus niger and Alterneria alternata. Based on salinity tolerance, antimicrobial activity and antibiotic resistance Pseudomonas fluorescens strains were used as inoculants to demonstrate their effects on plant growth. PGPR significantly enhanced leaves number, stem height, stem and rhizome fresh biomass as well as the pharmaceutically important curcumin content. Curcumin is the most important constituent of curcuminoids recognized for their biological activity, food safety and the broad range of pharmaceuticals.