Abstract: Soil salinization has intensified in recent years across major agricultural regions of China, posing serious threats and highlighting a lack of sustainable management strategies. To obtain biocontrol bacteria suitable for saline soils that exhibit both salt tolerance and growth-promoting traits, this study isolated and screened a bacterial strain, ZF526, from salinized soil samples collected in Inner Mongolia. Based on a polyphasic taxonomic approach combining morphological observation, physiological and biochemical characterization, and multi-gene phylogenetic analysis, the isolated strain was identified as B. pumilus. Tolerance assays against a spectrum of salts revealed that strain ZF526 could grow in LB liquid medium supplemented with high concentrations of NaCl（16%）, KNO₃（20%）, Na₂SO₄（16%）, MgCl₂（6%）, NaHCO₃（8%）, or Na₂CO₃（4%）. Furthermore, the strain exhibited multiple plant growth-promoting traits, including the ability to solubilize phosphorus, release potassium,nitrogen-fixing, and produce ACC deaminase. In vitro antagonism tests also demonstrated its high inhibitory efficacy against phytopathogens such as P. capsici and B. cinerea. Consistent with these in vitro properties, a pot experiment confirmed that treatment with the ZF526 bacterial suspension significantly alleviated salt stress and promoted cucumber plants growth. Under normal conditions without NaCl addition, the treatment increased leaf area and plant height by 22.98% and 25.06%, respectively. Under salt stress with NaCl addition, the salt injury index was reduced by 27.83%, while leaf area and plant height were enhanced by 26.09% and 24.12%, respectively. In summary, B. pumilus ZF526 represents a valuable microbial resource with salt tolerance, plant growth-promoting, and biocontrol potential, providing a promising strain for the microbial improvement of saline-alkali soils.

Key words: Bacillus pumilus, growth-promoting, salt-tolerant, biological control