Halotolerant potassium solubilizing plant growth promoting rhizobacteria may improve potassium availability under saline conditions

Environmental change is one of the primary issues faced by the farming community. Low rainfall and high temperature in arid and semiarid regions lead to the development of secondary salinisation, thus making the problem more severe. Under saline conditions, sodium is the most crucial cation that competes with potassium (K) and adversely affects plant metabolism by inhibiting plant enzymatic activities. Potassium-solubilising bacteria (KSB) play a vital role in solubilising fixed potassium and making it accessible to plants. In the current study, 42 KSB strains were isolated from paddy rhizosphere soil grown under salt-affected conditions. The plant-growth-promoting (PGP) properties of these rhizobacteria were also evaluated. Thirteen KSB strains, positive for all tested PGP traits, were evaluated for potassium solubilisation under sodium stress, namely, 0%, 3%, 5% and 7% NaCl stress. The five best strains (Acinetobacter pittii strain L1/4, A. pittii strain L3/3, Rhizobium pusense strain L3/4, Cupriavidus oxalaticus strain L4/12 and Ochrobactrum ciceri strain L5/1) based on the K-solubilising potential were identified by amplification, sequencing and bioinformatic analysis of the 16S rDNA sequences. The maximum potassium solubilisation was measured at 30 °C and pH 7 with glucose as carbon source. The application of these KSB strains significantly improved the shoot length, fresh weight, dry weight and chlorophyll contents of paddy plants grown under saline conditions. Hence, these strains could be halotolerant KSB bioinoculants that can be used to protect plants against salt stress.