Screening And Identification And Optimization Offermentation Conditions Of Antagonistic Actinomycetes On Astragalus Membranaceus Root Rot Isolated From Saline-alkali Soils In Dunhuang

Astragalus membranaceus is a perennial legume plant.It is rooted in medicine and is a medicinal herb with high medicinal value.In recent years,with the increase of the planting area of A.membranaceus,the diseases caused by the root rot of A.membranaceus are increasingly serious,which seriously restricts the yield and quality of A.membranaceus.The root rot of A.membranaceus is a root rot disease caused by Fusarium oxysporum and Fusarium solani.At present,the disease prevention and control method is mainly based on chemical control and then combined with some agricultural management measures.However,the long-term use of pesticides causes pathogens to develop drug resistance and greatly damage the ecological environment.Because of its advantages of no pollution,low cost,and low resistance to pathogenic bacteria,biological pesticides have gradually attracted the attention of researchers.Among them,actinomycetes are the main biocontrol bacteria,and antibiotics produced by actinomycetes are widely used in medicine and agriculture.In this study,a strain A12-2-11 with biocontrol effect on A.membranaceus root rot is isolated and screened from saline-alkali soils in Dunhuang,Gansu Province.The strain A12-2-11 with high antagonistic to pathogen is identified and optimized its fermentation conditions,and selected of carrier for microbial inoculant.This will enrich bacterial strains for biological control of root rot of A.membranaceus.The specific findings are as follows:1.Among 321 actinomycetes strains were isolated and purified from collected saline soil samples by the dilution-plate method and scribing-plate method from 5kinds of medium.From the Gao No.1 medium isolated actinomycetes strains was the most,a total of 146 strains.From the L01 soil sample isolated actinomycetes strains was the most,a total of 124 strains.2.The isolated actinomycetes were preliminary screened using the confrontation culture method and F.oxysporumwas used as target bacteria.The results showed that a total of 18 strains of actinomycetes with strong antibacterial activity were screened from them,accounting for 5.60 % of the test actinomycetes.The most was strainA12-2-11,the inhibition maximum diameter of it was 32.50 mm.3.The 18 strains of actinomycetes obtained from the preliminary screening were screened by the growth speed rate method,and the highest mycelial growth inhibition rate of strain A12-2-11 was 41.77 %.Broad-spectrum experiment on strain A12-2-11,the results showed that it had different degrees of bacteriostatic effect on the five plant pathogens tested.4.On the basis of morphological,physiological and biochemical characteristics as well as 16 S r DNA sequences analysis,the strain A12-2-11 was identified as Streptomyces longisporoflavus.5.In this experiment,the fermentation conditions affecting the antibacterial activity of the antagonistic strain A12-2-11 were optimized,and the physicochemical properties of the strain’s fermentation filtrate were determined.The results show the optimum culture conditions were with a medium of sucrose 10 g/L,(NH4)2SO4 10g/L,KH2PO4 1 g/L,Na Cl 10 g/L,Ca CO3 1 g/L,p H 8.The strain A12-2-11 had strongest inhibition activity in the condition of fermentation temperature was 28 ℃,10 % inoculation volume,the medium volume in the flask was 50 m L/250 m L and fermentation period was 4 d.The fermentation filtrate of strain A12-2-11 had a certain stability for UV and sunlight,and it was can maintian activity under 121℃,there was no obvious change in the activity of fermentation filtrate after storage from different conditions.6.The suspension of strain 12-2-11 was mixed with different combinations of carriers and cultured for 7 d、14 d、30 d、45 d.And the analysis will be based on water content,p H value,number of viable bacteria and number of bacteria.The results showed that,the(3)combination: activated carbon and flower soil.It was relatively stable in the water content,p H value,the number of effective live bacteria and the number of bacteria.So it can be considered for the subsequent experimental microbial carriers.