Regulation of antioxidant production, ion uptake and productivity in potato (Solanum tuberosum L.) plant inoculated with growth promoting salt tolerant Bacillus strains.

The exchangeable sodium (Na+ ) in salt affected soils is a major constraint in potassium (K+ ) availability to plants that disturb ion transport and inhibit plant growth, adversely. Salt tolerant plant growth promoting rhizobacteria (PGPR) may regulate the Na+ /K+ efflux and increase K+ uptake by the plant from the soil. Therefore, a pot study was performed to examine the effect of salt tolerant PGPR Bacillus sp. alone and in consortium, on antioxidant enzyme activity, ion uptake and potato (Solanum tuberosum L.) tuber yield in normal and salt affected soils. We observed that Bacillus sp. (strains SR-2-1 and SR-2-1/1) solubilized insoluble phosphorous and produced indole-3-acetic acid while only SR-2-1/1 produced ACC deaminase in culture medium supplemented with various concentrations of NaCl (0-6%). In the pot experiment, the consortium treatment of strains was found to increase relative leaf water contents whereas decreased the electrolyte leakage and antioxidant enzyme activity both in normal and salt affected soils. Similarly, consortium treatment decreased Na+ whereas increased K+ , Ca+2 , K+ /Na+ and Ca+2 /Na+ in plant dry matter in both soils. It has been investigated that inoculation of PGPR significantly (p < 0.05) increased plant biomass, number of tubers per plant and tuber weight as compared to un-inoculated plants in both soils. In addition, PGPR inoculation enhanced auxin production in root exudates of young potato plants and bacterial population dynamics in both soils. Na+ ion regulation (R2  = 0.95) and tuber weight (R2  = 0.90) in salt affected soil were significantly correlated with auxin production in the rhizosphere. Results of this study conferred that consortium of Bacillus strains (SR-2-1, SR-2-1/1) enhanced auxin production in the rhizosphere of potato plants and that ultimately regulated antioxidant enzyme production and uptake of Na+ , K+ and Ca+2 in potato plants resulted into a higher tuber yield in both normal and salt affected soils.