Mining of halo-tolerant plant growth promoting rhizobacteria and their impact on wheat (Triticum aestivum L.) under saline conditions

Plant growth promoting rhizobacteria have the potential to mitigate abiotic stressors to improve plant productivity. The current study was conducted to isolate and characterize halo-tolerant PGPR strains from the native plants of Khewra salt mine in Pakistan. Two halo-tolerant bacterial strains (SBN01 and SBN02) were purified, examined in vitro for their plant growth-promoting traits, and inoculated on wheat plants to evaluate their beneficial effects. Both isolates were able to produce indole-acetic acid in tryptophan-supplemented media, both were N2 fixers and capable of solubilizing phosphate. These isolates also showed positive results for catalase, gelatinase, and ammonia, except for protease activity. Based on 16S rRNA gene sequence analysis, SBN01 and SBN02 isolates showed 100% homology with Alcaligenes faecalis. Inoculation studies on wheat plant showed that these isolates maintained ionic imbalance by regulating Na+ and K+ ions and significantly increased growth parameters and plant biomass by decreasing reactive oxygen species induced lipid peroxidation while increased accumulation of osmolyte, photosynthetic pigments and improved photosystem II efficiency as compared to uninoculated plants. These results showed that isolated halo-tolerant rhizobacterial strains could improve plant growth and enhance tolerance during a stressful environment. Thus, they can be used as potential cost-effective candidates for growing wheat in salt-affected areas.