Promotion of maize seedling growth by Enterobacter asburiae PW2 under salt stress

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that directly or indirectly enhance plant growth, crop yields and stress tolerance. In this study, the maize variety 'Ningdan 33' was used as the experimental material. Strain PW2, isolated from salinized soil in Yinchuan, Ningxia, was identified as Enterobacter asburiae based on morphological, physiological, and biochemical characteristics as well as 16S rRNA gene sequencing. Pot experiments demonstrated its potential for salt tolerance and growth promotion in maize. The strain can grow in environments with 2.0%-10.0% NaCl and at pH 8.0-11.0, while exhibiting multiple plant growth-promoting traits, such as nitrogen fixation, potassium solubilization, siderophore production, ACC deaminase activity, and IAA synthesis. Under salt stress conditions, inoculation with PW2 significantly promoted maize seed germination, seedling growth, and root system development. Compared to the control group, inoculation with PW2 suspension significantly increased plant height, root length, nitrogen content, and the fresh and dry weights of both shoots and roots. Furthermore, PW2 inoculation significantly enhanced antioxidant enzyme activities in maize leaves and roots. Specifically, the activities of POD, SOD, and CAT in leaves increased by 92.75% (p = 4.0×10^-7), 21.79% (p = 0.008), and 17.28% (p = 0.010), respectively, while those in roots increased by 54.32% (p = 2.0×10^-6), 19.36% (p = 0.041), and 37.80% (p = 0.002), respectively. Conversely, the MDA content in leaves and roots decreased by 19.53% (p = 0.0058) and 32.91% (p = 0.006), respectively. Additionally, the contents of soluble sugar, soluble protein, and proline in both leaves and roots increased significantly. Collectively, these results indicate that strain PW2 effectively mitigates oxidative damage caused by salt stress through enhanced antioxidant defense and improved osmotic regulation, thereby promoting maize growth.