Screening Of Plant Growth-Promoting Rhizobacteria To Enhance Salt Stress Tolerance Of Crops And Their Effects In Field Experiment

Excellent germ resources are an important prerequisite for the development of new microbial fertilizers.Soil is a huge germ resource bank,which contains a large number of microorganisms.The purpose of this study was to screen functional strains from rhizosphere soil that could enhance the salt tolerance of crops,and to develop special microbial fertilizer for saline-alkali soil by using the strain resources.So as to enhance salt stress tolerance of crops,increase the yield of crops on saline-alkali soil.The main results were summarized as follows:1.The rhizosphere soil samples of 13 saline-alkali plants from different sources were collected.After extracting the soil suspension,127 strains of Bacillus were isolated from the soil samples by dilution coating method,which could grow rapidly on the solid LB medium.Rhizosphere growth-promoting bacteria T1-8 and T4-9 were screened by water culture experiments of maize and wheat respectively.The pot experiments of maize and wheat were carried out to verify the function of the strain.The growth indexes of plants inoculated with strains T1-8 and T4-9 were significantly higher than those of the control.After 16S rDNA system identification,strains T1-8 and T4-9 were Bacillus sp.,respectively Bacillus paralicheniformis and Bacillus megaterium.The growth-promoting characteristics of strains T1-8 and T4-9 were analyzed.Both strains had certain growth-promoting ability.The strain T4-9 had strong ability of iron carrier production and IAA production.The IAA production of strain T4-9 reached 60.82 mg/L.The strains T1-8 and T4-9 were labeled with GFP by electrophoresis.The number of colonized strains in the rhizosphere of hydroponic maize and wheat was counted under fluorescence microscope after dilution coating.The results showed that both strains colonized 106 CFU/g roots in the rhizosphere of maize and wheat,and the colonization of strain T1-8 reached 107 CFU/g roots in the rhizosphere of wheat.2.The changes of physiological characters of maize plants under salt stress were determined.Compared with the control,the osmotic regulators TSS in maize plants increased significantly after inoculation of functional strains T1-8 and T4-9.TSS has the function of maintaining osmotic pressure of maize.The content of MDA decreased significantly.MDA was one of the most important products of membrane lipid peroxidation,and it was found that the osmotic regulators TSS in maize plants increased significantly after inoculation of functional strains T1-8 and T4-9.Physiological studies on physiology and resistance are common indicators;POD activity decreases,POD can be used as a physiological indicator of tissue aging;potassium ion content in maize plants increases,sodium ion content decreases.3.Bacillus strain T1-8 was tested for liquid fermentation.The optimum proportion of components in liquid fermentation medium of strain T1-8 was molasses 5%,soybean meal powder 0.72%,sodium chloride 0.5%,potassium dihydrogen phosphate 0.1%,calcium chloride 0.1%,magnesium sulfate 0.1%,ferrous sulfate 0.05%,zinc sulfate 0.05%,manganese sulfate 0.05%.The pH value was adjusted to 7.5.The inoculation rate was 10%.The liquid fermentation temperature was 35℃ and the shaking speed was 180 rpm.And the optimum proportion of T4-9 liquid fermentation medium components was molasses 5%,soybean meal powder 0.72%,sodium chloride 0.5%,potassium dihydrogen phosphate 0.1%,calcium chloride 0.1%,magnesium sulfate 0.1%,ferrous sulfate 0.05%,zinc sulfate 0.05%,manganese sulfate 0.05%.The pH value was adjusted to 7.0.The inoculation rate was 5%.The culture temperature was 35℃ and shaking speed was 180 rpm.The special microbial organic fertilizer in saline-alkali soil developed by strains T1-8 and T4-9 had more than 0.2 billion/g of effective viable bacteria,5%of total nitrogen,phosphorus and potassium nutrients and 45%of organic matter,which conforms to the national standard of bio-organic fertilizer.4.The results of field experiment of microbial organic fertilizer showed that the application of microbial organic fertilizer of strains T1-8 and T4-9 could significantly increase the yield of Maize on saline-alkali soil,with the maximum increment of 26.70%and 17.04%respectively,whether in 3‰,4‰ or 5‰ saline soil,and compared the changes of soil physical and chemical properties before and after maize planting with those without organic fertilizer.The content of organic matter increased and the pH and salinity decreased in the soil treated with organic fertilizer.