Halotolerant Bacillus Aryabhattai Strain PM34 Mitigates Salinity Stress and Enhances the Physiology and Growth of Maize

Abstract

Maize is a versatile cereal underpinning global food security and industrial applications. Salinity impedes plant growth and productivity of crops by disrupting the ionic and osmotic balance and hormonal regulation. The present study aimed to examine the potential of plant growth-promoting rhizobacteria strains PM34 (B. aryabhattai) in mitigating salinity stress in maize. The selected rhizobacterium exhibited notable tolerance to NaCl, thriving in concentrations ranging from 0.5 to 1.5 M in LB medium. The efficient B. aryabhattai PM34 strain demonstrated siderophore production capabilities (55.64–50.46%), phosphate solubilization (24.42–21.23 µg.mL⁻¹), secretion of indole-3-acetic acid (81.29–58.31 µM.mL⁻¹) and 1-aminocyclopropane-1-carboxylate deaminase (2.12–1.08 µM/mg protein/h) and exopolysaccharides production (680–810 µg.mL⁻¹) at concentrations from 0 to 750 mM salt stress. PM34 inoculation significantly enhanced maize growth, including improvements in shoot length (19.88–50%), root length (16.32–44.84%), fresh weight (23.53–37.93%), dry weight (10–25.71%) and leaf area (20.25–40.91%) at salinity stress 0 to 300 mM in PM34 inoculated plants as compared to non-inoculated plants. PM34 inoculated plants showed increase in chlorophyll a (2.72–32.88%), b (10.09–86.36%), total chlorophyll (9.87–47.98%), and carotenoids (26.39–66.13%) content as compared to non-inoculated plants. Moreover, improvement in the activities of antioxidant enzymes superoxide dismutase (35.03–55.14%), peroxidase (60.94–22.86%), catalase (20.31–30.24%), ascorbate peroxidase (9.03–15.34%) and the accumulation of osmotic regulators proline (11.47–16.21%) and glycine betaine (10.12–20.25%), when compared to non-inoculated controls under salt stress conditions. Furthermore, maize augmented with halotolerant bacteria displayed reduction in electrolyte leakage (14.81–28.65%), malondialdehyde (20.92–37%), and sodium uptake (9.43–36.98%) when subjected to salt stress. These results contribute to the theoretical foundation and can be concluded that the inoculation of this PGPR can alleviate the adverse effects of salinity stress on maize.