Salt-tolerant and plant-growth-promoting bacteria isolated from high-yield paddy soil

Growth and productivity of rice is negatively affected by soil salinity. However, some salt-tolerant bacteria improve the health of plants under saline stress. In this study, 305 bacteria were isolated from paddy soil in Taoyuan, China. Among these, 162 strains were tested for salt-tolerance; 67.3%, 28.4%, and 9.3% of the strains could grow in media with NaCl concentrations of 50, 100, and 150 g/L, respectively. The phylogenic analysis of 74 of these 162 strains indicates that these bacteria belong to Bacillales (72%), Actinomycetales (22%), Rhizobiales (1%), and Oceanospirillales (4%). Among 162 strains, 30 salt-tolerant strains were screened for their plant-growth-promoting activities under axenic conditions at 3, 6, 9, and 12 g/L NaCl; 43%-97% of the strains could improve rice germination energy or germination capacity, while 63%-87% of the strains could increase shoot and root lengths. Among various plant-growth-promoting bacteria, TY0307 was the most effective strain for promoting the growth of rice, even at high salt stress. Its promotor effects were associated with its production of 1-aminocyclopropane-1- carboxycarboxylate deaminase, indole acetic acid, and siderophores; induction of proline accumulation; and reduction of the salt-induced malondialdehyde content. These results suggest that several strains isolated from paddy soil could improve rice salt tolerance and may be used in the development of biofertilizer.