Bacillus subtilis HG-15, a Halotolerant Rhizoplane Bacterium, Promotes Growth and Salinity Tolerance in Wheat (Triticum aestivum)

Abstract

Background : Certain plant growth-promoting bacteria (PGPB) reduce salt stress damage in plants. Bacillus subtilis HG-15 is a halotolerant bacterium (able to withstand NaCl concentrations as high as 30%) isolated from the wheat rhizoplane in the Yellow River delta. A qualitative and quantitative investigation of the plant growth-promoting characteristics of this strain confirmed nitrogen fixation, potassium dissolution, and ammonia, plant hormone, 1-aminocyclopropane-1-carboxylic acid deaminase, and proline production abilities. B. subtilis HG-15 colonization of wheat roots, stems, and leaves was examined via scanning electron microscopy , rep-PCR, and double antibiotic screening.Results : Compared with a no B. subtilis HG-15 treatment control, in rhizosphere soil inoculated with the HG-15 strain, the pH (1.08–2.69%), electrical conductivity (3.17–11.48%), and Na + (12.98–15.55%) concentrations significantly decreased ( p < 0.05). Inoculation with the HG-15 strain increased the total N, available N, organic matter, K + , Ca 2+ , and Mg 2+ concentrations in the rhizosphere soil of wheat. Under non-salt stress (0.15% NaCl), low-salt stress (0.25% NaCl), and high-salt stress (0.35% NaCl) conditions, respectively, this strain also significantly increased ( p < 0.05) the dry weight (17.76%, 24.46%, 9.31%), fresh weight (12.80%, 20.48%, 7.43%), plant height (7.79%, 5.86%, 13.13%), root length (10.28%, 17.87%, 48.95%), and other wheat parameters. Through redundancy analysis and Pearson correlation analyses, photosynthesis, biomass accumulation, and osmotic regulation by the wheat plants showed a significant negative correlation with pH, EC, and Na + concentrations in rhizosphere soil.Conclusions : Our results indicated that B . subtilis HG-15 can effectively improve the growth of wheat and elicit induced systemic tolerance in these plant, thus, showing its potential as a microbial inoculant that can protect wheat in salt stress conditions. Furthermore, we determined that the rhizoplane of saline-alkali land plants is an important reservoir for salt-tolerant PGPB.