Salt-tolerant plant growth-promoting bacteria enhanced the growth and alleviated salt toxicity to maize by increasing K + /Na + homeostasisPlant growth-promoting bacteria enhanced the growth and salt resistance in maize

The use of plant growth-promoting bacteria is an eco-friendly way to improve crops’ tolerance to salinity. To obtain more effective bacteria, halotolerant bacteria with plant growth-promoting attributes were isolated and screened out from salt-affected areas. Their abilities to alleviate salt stress on maize were further evaluated. The results showed that 11 of 268 strains displayed at least three plant growth-promoting traits, and some of them promoted growth, decreased Na+ accumulation and increased K+/Na+ ratios of maize seedlings under salt stress. The elongation and biomass of maize seedlings were significantly correlated to K+/Na+ ratios of maize seedlings after strain treatment, not the P-solubilization of strains. The maize seedling growth, Na+ and K+ accumulation were affected by indole-3-acetic acid levels that plant growth-promoting bacteria secreted. Among 11 strains, Hm18 and Pt07 which belong to Bacillus altitudinis and Pantoea agglomerans, respectively, increased maize seedling growth and K+/Na+ ratio in maize seedlings. Strains Hm18 and Pt07 alleviated growth inhibition and cell membrane injuries of maize seedlings caused by salt stress in soil. Additionally, Hm18 and Pt07 reduced Na+ accumulation and increased K+/Na+ ratios in maize under soil conditions as well. Overall, plant growth-promoting bacteria alleviated the detrimental effects of maize seedlings caused by salt stress through increasing K+/Na+ ion balance, which correlated to indole-3-acetic acid produced by bacteria. Hm18 and Pt07 increased salt tolerance and growth of maize seedlings grown in saline soil. These results provided potential beneficial bacteria resources for maize production in saline soil.