Study On Isolation Of Salt-tolerant Plant Growth-promoting Rhizobacteria And Their Promotion Effect On Wheat Seedling Under Salt Stress

The growth of plants is seriously influenced by salt stress,which is a major factor restricting agricultural productivity.Plant growth promoting rhizobacteria(PGPR)may tightly interact with plant and so can alleviate the salt stress,improve resistance of plants to salt stress and stimulate plant growth.Due to the special climate and geographical environment,the salt content of the desert soil is usually higher,where may be an important source of salt-tolerant plant growth-promoting bacteria.This study applied spread and streak plating to isolate PGPR on selective media of Ashby and inorganic-phosphorus,from Inner Mongolia desert plant rhizosphere soil.Salt tolerance(Na Cl)of the isolates was detected by plate culture.16 S r RNA gene sequence homology comparison analysis was carried out to identify the taxonomic postion.Plant growth-promoting traits were characterized using selective media or colorimetry.These traits included nitrogen-fixation,inorganic-phosphorus-solubilizing,organic-phosphorus-solubilizing(phytate-phosphorus-solubilizing),siderophore-producing and ACC-deaminase –producing.The strains were selected for further study,which can promote the germination of wheat,and they was made into bacterial fertilizer granule(according to strain number representated a single strain,VK and CK respectively on empty carrier particles and blank control of no particles of bacterial manure or empty carrier)for pot experiment,respectively.Those strains with efficient effect were combined to construct consortia for granular fertilizer(JF)and applied in potplanting.The physicochemical indexes of rhizosphere soil and wheat seedling growth were analyzed to reveal the effect and mechanism of PGPR on wheat seedlings under salt stress.The main results and conclusions are as follows:1.A total of 165 strains of PGPR were isolated and pure cultured from plant rhizosphere soil samples: 87 strains of phosphorus-solubilizing bacteria and 78 strains nitrogen-fixing bacteria,which divided into 34 genera,with the abundance of >6% Ochrobactrum(23.64%),Bacillus(11.52%),Pseudomonas(7.88%),Paenibacillus(7.27%),Arthrobacter(7.27%)and Enterobacter(6.06%).81.82% of the strains were able to grow well on the 3% Na Cl R2 A plate.A total of 30 salt-tolerant PGPR possessed multiple promoting traits,namely nitrogen-fixing,inorganic phosphorus-solubilizing,organic phosphorus-solubilizing(phytate-phosphorus-solubilizing),siderophore-producing,and ACC-deaminase-producing.They predominated by the genus Ochrobactrum,Bacillus and Enterobacter.The 13 PGPR with the most remarkab traits ability were screened for further experiments.2.Effect of PGPR single bacteria on the wheat germination test under salt stress: 8 of the 13 PGPR could promote the germination of wheat seeds and had a significantly growth-promoting effect under the different concentrations of salt stress.The plant height,root length and dry weight of wheat seedlings were increased by 3.19-30.64%,5.38-63.63% and 6.30-51.10% respectively.3.Effect of PGPR single bacteria inoculated in potted wheat under salt stress: The growth-promoting effect of different PGPR on the wheat is different under the same concentration of salt stress,while effect of the growth of same PGPR on wheat is also different under the different concentrations of salt stress.Out of them,the strain BN9 increased the dry weight of wheat above ground part,rhizosphere soil available nitrogen content and available phosphorus content and the dry weight of wheat underground and the rhizosphere soil organic matter content under 0,100,200,and 300 mmmol/L Na Cl.BN9 significantly increased the plant height only under 100 mmmol/L Na Cl.4.Effect of the consortia on wheat seedlings under salt stress: JF consortia granular fertilizer(strains BN9,BP11,FYP1101,SN0509 and SP0114)could promote the growth of wheat under under 0-300 mmmol/L Na Cl.The consortia coulde play growth-promoting role in wider range of salinity was wider and the growth-promoting effect was more stable than that of single strain used.In conclusion,the major PGPR with strong salt tolerance and multiple growth-promoting traits were of the genus Ochrobactrum,Enterobacter and Bacillus in desert soil.They promoted on the growth of wheat seedlings under salt stress,especially after the combination of different strains,which may be resulted from the improvement of soil nutritionand increased plant hormones,etc.