Isolation Of Salt-tolerant Plant Growth-promoting Bacteria And Thier Promotion Effect On Alfalfa Seedlings

Soil salinization seriously affects the growth of crops and restricts the development of global agriculture and animal husbandry.Plant growth promoting bacteria(PGPB)employ several mechanisms such as producing phytohormone(IAA)and 1-amino-cyclopropane-1-carboxylate(ACC)deaminase,solubilizing phosphorus and potassium,fixing nitrogen,producing siderophore and hydrolase.PGPB can improve plant resistance to salt stress and promoting plant growth.In this study,salt-tolerant PGPB were isolated and the reclaimed soil of salt pans and identified.And system atically studied the impact of the strains on the growth and physiology of alfalfa by pot experiment in the interest of provide a theoretical basis for further research and use of plant growth promoting bacteria to produce biogenic agents.The main results are as follows:(1)In this study,60 saline-tolerant strains were isolated and purified from reclaimed soil of salt field,among which 36 strains can grow on 10% salinity.Through the identification of strain promotion-related traits,17 strains can product IAA,16 strains with ACC deaminase secretion,24 strains with iron carrier capacity were obtained,19 strains had the ability to fix nitrogen,6 strains with inorganic phosphorus solubilization function,12 strains with organic phosphorus solubilization function and 9 strains have the ability to dissolve potassium.(2)The 14 strains were identified by 16 S r DNA sequence analysis.Strains L131B01,L232B01 and L322B01 are Bacills megaterium,strains L222B01,L241B01 and L354B03 are Bacillus licheniformis,strains L243B02 and L341B03 are Bacillus aerius,strains L121B01 and L242B04 are Bacillus mycoides,strains L122B01,L141B02 and L232B01 are Bacillus acidicola.The 8 actinomycetes with better growth-promoting strains were identified by the same method.Strains L122F01,L342F01 and L451F01 are Streptomyces tauricus,strain L131F02 is Pseudarthrobacter oxydans,strain L232F01 is Streptomyces tendae,strain L244F01 is Streptomyces collinus,strains L251F01 and L352F01 are Streptomyces caeruleatus.According to the interbacterial antagonism experiment,strain L322B01,L354B03,L232F01 and L352F01 were selected for alfalfa growth promotion.(3)The effects of growth promoting bacteria on the growth of alfalfa were determined by seed germination and pot experiment.The results showed that the germination rate of seeds soaked with different bacterial solution was improved in different degrees compared under 0,100 and 200 m M Na Cl salt stress.The height,root length,fresh weight and dry weight of alfalfa seedlings were significantly increased by inoculating single and compound inoculant(P<0.05).(4)A pot experiment was conducted to investigate the growth-promoting effects of inoculation with single and compound plant growth-promoting bacteria on alfalfa seedlings.The results showed that the chlorophyll and soluble protein contents in alfalfa leaves were significantly increased,the activity of antioxidant enzymes was improved and the content of malondialdehyde was reduced to alleviate the harm of salt stress on alfalfa seedlings.The results of the assay on the inter-root soil enzyme activities showed that the sucrase,protease and catalase activities of the alfalfa were effectively increased by inoculating bacterioides,which indicated that inoculating bacterioides could improve soil fertility.