Salt-tolerant rhizobacteria-mediated induced tolerance in wheat (Triticum aestivum) and chemical diversity in rhizosphere enhance plant growth

Salt-tolerant isolates Bacillus pumilus, Pseudomonas mendocina, Arthrobacter sp., Halomonas sp., and Nitrinicola lacisaponensis isolated from high saline habitats exhibited plant growth-promoting traits like P solubilization and indole acetic acid (IAA), siderophore, and ammonia production. These isolates were inoculated in wheat to assess microbe-mediated responses and plant growth promotion in salt affected soil. Maximum shoot and root length (33.8 and 13.6 cm) and shoot and root biomass (2.73 and 4.48 g dry weight) was recorded in plants inoculated with B. pumilus after 30 days. Total chlorophyll content was maximum in the leaves of the plants treated with Halomonas sp. (24.22 mg g⁻¹ dry weight) followed by B. pumilus (23.41 mg g⁻¹ dry weight) as compared to control (18.21 mg g⁻¹ dry weight) after 30 days. Total protein content was maximum in Arthrobacter sp. inoculated plant leaves (3.19 mg g⁻¹ dry weight) followed by B. pumilus (2.47 mg g⁻¹ dry weight) as compared to control (2.15 mg g⁻¹ dry weight) after 30 days. Total carotenoid content was maximum in plants inoculated with Halomonas sp. (1,075.45 and 1,113.29 μg g⁻¹ dry weight) in comparison to control (837.32 and 885.85 μg g⁻¹ dry weight) after 15 and 30 days. Inoculation of bacterial isolates increased presence of individual phenolics (gallic, caffeic, syringic, vanillic, ferulic, and cinnamic acids) and flavonoid quercetin in the rhizosphere soil. The concentration of IAA in rhizosphere soil and root exudates was also higher in all treatments than in control. Accumulation of phenolics and quercetin in the plants played a cumulative synergistic role that supported enhanced plant growth promotion of wheat in the stressed soil.