Screening Of Saline-alkali Tolerant Rhizohacteria And Their Effects On Growth Promotion And Disease Resistance Of Pepper

Salinization of soil is a serious worldwide problem that restricts the production of agriculture and forestry and the construction of ecological environment.The current trend is that the scope of saline alkali soil is expanding,and the utilization rate is very low.It is an effective and eco-friendly method to use PGPR to reduce the damage caused by saline-alkali stress.In this study,36 strains of bacteria were isolated from the rhizosphere soil of Phragmites communis in Binzhou,Shandong Province.Most of them were tolerant to salt and alkali stress.The PGP function of these 36 strains was identified,and the result showed that 24 strains had the ability of proteolysis and the effect was stable;6 strains had the ability of phosphorus dissolution;6 strains produced IAA;16 strains had the ability of nitrogen fixation;20 strains produced NH₃;22 strains produced ACC deaminase;2 strains produced exopolysaccharide;4strains had the ability of iron carrier;12 strains had antagonistic effect on different fungal pathogens.Four strains were obtained by cross-screening according to different PGP functions.The strains were identified by their colony morphology,physiological and biochemical characteristics,and 16S r RNA gene sequence.The GJB-9 strain was identified as Pseudomonas argentinensis,GJB-10 as Enterobacter cloacae,GJB-14 as Bacillus aerius and YJB-15 as Bacillus siamensis.Seed germination test showed that the four strains of PGPR can effectively promote the germination of Chinese cabbage seeds.Pot experiment of pepper was carried out to verify the effect of salt alkali solution（Na Cl:Na₂SO₄:Na HCO₃:Na₂CO₃=1:1:1:1）on the growth of pepper.The results showed that saline-alkali stress greatly affected the physiological parameters of pepper without inoculation and hindered their growth.The physiological and biochemical parameters of pepper plants treated with PGPR were improved,and the disturbance caused by salt and alkali stress was significantly reduced.After inoculation,the plant height,stem diameter,biomass accumulation,chlorophyll content were significantly increased,and the contents of proline,soluble sugar and soluble protein in leaves were increased,the water absorption of pepper was also improved,and the root activities were increased.The content of malondialdehyde was decreased,while the activities of antioxidant enzymes in leaves and roots were increased significantly,which indicated that the oxidative damage induced by H₂O₂ and O^2-were reduced,the damage of membrane system caused by membrane lipid peroxidation was prevented,the quality of pepper fruit was improved,the activities of urease,sucrase and phosphatase in soil were increased,the fertility was improved,and the growth of microorganisms in the soil were promoted.This study also conducted pepper pot experiments on the control effect of some obtainted PGPR on pathogenic fungi,and the results showed that their had a certain control effects on Phytophthora capsici.Therefore,as salt tolerant PGPR,strains of GJB-9,GJB-10,GJB-14 and YJB-15 can improve the growth of plants,and have the potential to be used as biological fertilizer in saline alkali soil.