Plant growth promotion and alleviation of salinity stress in Capsicum annuum L. by Bacillus isolated from saline soil in Xinjiang

To maintain the growth and development of pepper in saline condition, candidates of plant growth promoting rhizobacteria (PGPR) were isolated, and detected to plant growth promoting (PGP) potential under salt stress was investigated. Thirteen bacterial strains with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, WU-1–13, were isolated from saline soil in Xinjiang, China. The isolates were shown to belong to the genera Bacillus by partial sequencing analysis of their respective 16 S rRNA genes. Seven isolates had the ability to solubilize phosphate. Moreover, the amount of solubilized phosphate was significantly high (P < 0.05), which ranged from 157.33 μg/mL to 922.41 μg/mL. All tested bacterial strains were shown to produce a large amount of ACC deaminase and NH3. Furthermore, nine strains were detected for siderophore production. On the aspect of extracellular enzyme, all bacterial isolates produced lipase, amylase and cellulose, whereas only a minority produced chitinase (15.4%) and 10 isolates produced β-glucanase or protease. In growth room experiments, the results showed that the strain WU-5 exhibited better growth promotion of pepper seedlings in terms of fresh weight (75.60%), dry weight (86.68%), shoot length (12.12%) and root length (146.52%) over the control under saline stress followed by WU-13. Furthermore, seedlings accumulated high amounts of proline induced by the different PGPR inoculation treatments to alleviate the negative effects of salt stress. Further growth-promoting assays under different salt stress were set up to confirm that the fresh and dry weight, shoot and root length of pepper plants inoculated by three strains all were significantly higher than non-inoculated control under different saline stress. In summary, the results demonstrated that WU-9, which induced high levels of proline production and antioxidant enzyme activities, and three strains (WU-5, WU-9 and WU-13) can be of great value in maintaining the growth and development of seedlings on saline lands.