Insights into the beneficial effect of plant growth-promoting rhizobacteria (PGPR), Bacillus thuringiensis , on ecophysiological and biochemical characteristics in maize ( Zea mays L.) under boron toxicity

High boron (B) levels, which are characteristic of arid and semi-arid regions around the world, are a key factor restricting crop growth and productivity in agricultural soils. However, the utilization of plant growth-promoting rhizobacteria (PGPR) can stand out as a promising strategy for plants to combat the deleterious effects of B stress. In our study, we evaluated whether PGPR strain Bacillus thuringiensis (Bt) Se13 plays a beneficial role in improving the ecophysiological and biochemical features of B-stressed maize plants. A pot experiment consisting of two levels of B (0.5 and 5 mM) with or without Bt was conducted. The most striking consequence from our findings is that Bt inoculation is most effective at higher B concentrations (5 mM) rather than lower B concentrations (0.5 mM). Higher B concentrations lowered the plant growth, leaf relative water content (RWC), and photosynthetic pigment levels in maize. However, malondialdehyde (MDA) and hydrogen peroxide (H2O2) content, and the activity of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) increased at higher B concentrations. On the other hand, B. thuringiensis Se13 inoculation reduced the levels of oxidative stress markers in 5 mM B-stressed maize. Furthermore, it remarkably raised the growth characteristics, photosynthetic pigment contents, protein and proline accumulation, and antioxidant enzyme activities of plants exposed to 5 mM B toxicity. Overall, our study revealed that B. thuringiensis is potential candidate for promoting the plant growth and ameliorating the effects of boron toxicity in maize by modulating the growth attributes, osmolyte production, and antioxidant defense system.