Isolation And Identification Of Saline-alkali Tolerant Plant Growth Promoting Rhizobacteria And The Effects On Maize Growth

Soil microorganisms are used to improve saline soils,promote crop growth,alleviate plant salt stress,and improve soil ecology by screening saline-tolerant inter-rhizosphere growthpromoting bacteria is an important development direction for saline land management.In this study,we screened and isolated inter-rhizosphere microorganisms in saline soils,and screened plant inter-rhizosphere probiotic strains with probiotic functions through strain probiotic function identification.Using mixed salt to simulate saline environment,a pot test of single bacterial agent maize plants was conducted to test plant biomass,agronomic trait index plant leaf enzyme activity and inter-rhizosphere soil enzyme activity,and four strains with better growth-promoting effect were screened for compound bacterial agent,and the potential of compound bacterial agent application was evaluated.The strain with the most obvious growthpromoting effect,R5,was optimized for fermentation,and the fermentation medium formulation and fermentation conditions were optimized.The main results are as follows:（1）In this study,552 saline-tolerant strains were isolated and purified from coastal saline soil samples from Guangrao County and Wudi County,Binzhou City,Shandong Province,using Gibbons medium.And a small conservatory of saline-tolerant strains was established with this.All the 552 strains can grow on Gibbons medium with Na Cl concentration of 10%,and all the 552 strains can grow normally in Gibbons medium with p H 9.Through the identification of strain promotion-related traits,134 strains of bacteria with phosphorus solubilization（inorganic phosphorus）ability,117 strains of bacteria with phosphorus solubilization（organic phosphorus）function,152 strains of potassium soluble bacteria,and 165 strains of IAA-producing bacteria were obtained.（2）These 9 strains were identified by morphology,physiology and biochemistry,molecular identification of 16 S r DNA sequences and construction of phylogenetic tree.The strains R5 and R12 were identified as Priestia aryabhattai,strain R14 was Bacillus zanthoxyli,strains R33 and W4 were Bacillus siamensis,strain W8 was Bacillus tequilensis.,.Strain W19 was Delftia lacustris,and strains W26 and W38 were Bacills megaterium.After excluding the redundant strains,a total of six strains,R5,R14,R33,W8,W19 and W26,were selected for pot experiments to verify the salt tolerance promotion effect of single strains on maize plants.（3）The pot experiment of maize plants with a single fungicide showed that all six fungicides could promote the growth of maize plants under the treatment of 9 g/kg mixed salt concentration,and the stalk thickness,plant height,above-ground weight and below-ground weight of maize seedlings were increased to different degrees.The malondialdehyde content of the plants in the experimental group treated with the mycorrhizal agents was significantly reduced,with a maximum reduction of 42.78% under the treatment of 9 g/kg mixed salt solution;the antioxidant enzyme activities including CAT,SOD and POD were increased under different salt concentrations,and the plant roots were more developed.The results of the assay on the inter-root soil enzyme activities showed that the sucrase,protease and catalase activities of the plants with the application of six mycorrhizal agents were enhanced under the treatment of 9g/kg mixed salt solution,and the mycorrhizal agents W8,W19 and W26 also had a good enhancement on the soil urease activity.The application of mycorrhizal agents had enhanced and improved the fertility of the soil.（4）The composite mycorrhizal agents were constructed based on R5,W19 and W26.The stalk thickness,plant height,above-ground weight,and below-ground weight of maize seedlings applied with the composite mycorrhizal agents increased to different degrees,and the malondialdehyde content in plant leaves decreased significantly,indicating that the mycorrhizal agents were able to alleviate the salt stress on the plants.Plant leaf antioxidant enzyme system and inter-root soil enzyme activity also increased significantly.（5）Optimal fermentation medium: 3% of maltose,0.75% of soybean flour and 0.6% of magnesium sulfate;optimal fermentation conditions: optimal temperature 37°C,optimal p H7.5 and 2% inoculum.