Screening Of Plant Growth Promoting Rhizobacteria And Its Promoting Effect On Rice Growth Under Saline-alkali Stress

With the impact of climate warming and human activities,the yield of crop in the world has shown a downward trend,and rice as the main food crop,has been greatly affected,among which the most serious is the reduction of rice yield caused by soil salinization.The main method to improve rice yield in traditional agriculture is to promote the growth of rice by using industrial fertilizers,but there are many hidden dangers.For example,the excessive use of fertilizers leads to a series of problems such as soil fertility decline,high cost and environmental pollution.Therefore,for many countries.it has become the focus to research obtain green,long-tern and low-cost microbial fertilizers that can resist saline-alkali stress.while the plant growth promoting rhizobacteria which can effectively promote growth have been paid more and more attention.This experiment aim to extract has the phosphate-solubilizing,indole acetic acid production.iron element.ACC acid deaminase ability from the rhizosphere bacteria.We isolated nine strains from the rhizosphere of rice which has good characteristics,finally selected by means of pot experiment 1 strain named ND3.The experimental results showed that the soluble phosphorus and iaa-producing capacity of strain ND3 reached 601.01mg/L and 11.36 g/ml,ACC deaminase activity was 256.05 mol α-KB mg-1 h-1,respectively,and the strain was able to grow normally in the medium containing 1.25 M NaCl and pH 10.Through morphological observation,physiological and biochemical indexes and 16S rDNA sequence analysis,strain ND3 was preliminarily identified as a bacterium of Pseudomonas sp.Then the pot experiments were carried out to verify the growth promoting ability of the strain.The results showed that the plant height,root length,aboveground and underground dry and fresh weight of rice seedlings inoculated with strain ND3 were significantly increased under stress or without stress,the contents of chlorophyll,free proline and soluble protein in leaves were significantly increased,and the content of malondialdehyde was significantly lower than that of uninoculated seedlings.The activities of some antioxidant enzymes such as superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)were significantly enhanced in the absence of saline-alkali stress,which reduced the accumulation of reactive oxygen species in rice seedlings and promoted the normal growth of seedlings.However,in the presence of saline-alkali stress,the activity of each antioxidant enzyme was decreased compared with that of the control bacteria,indicating that after inoculation with strain ND3,the oxidative stress of rice seedlings under saline-alkali conditions was alleviated.In this study,a saline-alkali resistant rhizosphere growth promoting strain was screened out.which could effectively promote the growth of rice in saline-alkali soil,providing reference for the application of rhizosphere growth promoting bacteria as microbial fertilizer in the future.