The Alleviating Effect Of Microbial Fertilizer On Replant Problem Of Astragalus

The medicinal plant Astragalus has been continuously planted in the same soil for more than one year,which will cause continuous cropping obstacles.Roots of Astragalus will secrete autotoxic substances and pathogenic microorganisms will infect the roots of Astragalus.At the same time,the physical and chemical properties of Astragalus soil will change,which will affect Astragalus adversely affect growth.In order to alleviate the problem of continuous cropping obstacles of Astragalus,we identified and verified the autotoxic substances in the rhizosphere soil of Astragalus,and isolated the antagonistic bacteria of the autotoxindegrading bacteria and the pathogenic bacteria of Astragalus,and combined the degrading bacteria and the antagonistic bacteria to make microbial organic fertilizer,applied to the soil of continuous cropping Astragalus,so as to alleviate the problem of continuous cropping obstacles of Astragalus.The main results of this study are as follows:1.Firstly,the method of ultrasonic low temperature extraction was used to extract small molecule metabolites from the soil of 1-3 years of continuous cropping of Astragalus and blank soil,and then the species of the obtained substances were identified by HPLC-MS.Potential autotoxic substances whose contents increased with the extension of continuous cropping years were identified by correlation analysis.18,40,52 and 64 compounds were identified from blank soil,soil with continuous cropping for 1 year,continuous cropping for2 years and continuous cropping for 3 years,and phenolic acid compounds were positively correlated with the continuous cropping years of Astragalus.Through the seed germination experiment,it was found that the four phenolic acids at 400 mg/L,4-hydroxycoumarin,phydroxybenzoic acid,p-methoxybenzoic acid and cinnamic acid,had the most obvious inhibitory effect on the germination of Astragalus seeds.The germination rate of Astragalus was decreased by 7.6%,80.46%,39.08% and 56.51%.The effects of these four substances on the growth of Astragalus seedlings were verified by pot experiments,and it was found that all four substances could inhibit the growth of Astragalus seedlings,and the inhibitory effect of4-hydroxycoumarin was the most obvious.The plant height,root length and dry weight of astragalus treated with 400 mg/kg 4-hydroxycoumarin decreased by 85%,70% and 90%,respectively,compared with the control plants.2.A total of 19 strains of phenolic acid-degrading bacteria were isolated from the rhizosphere soil of Astragalus membranaceus using the screening medium.The 19 strains of degrading bacteria were initially screened and screened again,and 5 strains with broad substrate spectrum and high degradation efficiency were obtained.B7,X1,B6,R4 and R3.Through Gram staining,it was determined that the five degrading bacteria were all Gram-negative bacteria,and then a series of physiological and biochemical identifications were performed on the five bacteria,including nitrate reduction reaction,compound hydrolysis reaction,simple polysaccharide assimilation reaction,and organic acid assimilation reaction.The reaction and the detection of cytochrome oxidase confirmed the physiological and biochemical characteristics of the five strains.Finally,the five strains were assigned to Stenotrophomonas,Pseudomonas,Ensifer,Streptomyces and Cupriavidus.Five bacterial pure cultures were inoculated into the inorganic salt degradation medium,and it was found that the five degrading bacteria could degrade four phenolic acids,but the degradation abilities were different.The degradation ability of five kinds of bacteria was tested.The results showed that the five kinds of bacteria had the strongest degradation efficiency of cinnamic acid and p-hydroxybenzoic acid,and the degradation ability of p-methoxybenzoic acid was weak.Stenotrophomonas sp.B7 degraded p-hydroxybenzoic acid.Formic acid was the most efficient,Pseudomonas sp.X1 was the most efficient in degrading cinnamic acid and 4-hydroxycoumarin,and Ensifer sp.B6 was the most efficient in degrading p-methoxybenzoic acid.3.The synthetic flora constructed by four rhizobacteria can significantly reduce the incidence of root rot in Astragalus.When the four rhizosphere bacteria constructed the flora in different proportions,the efficacy of the synthetic flora was not affected.When the four rhizosphere bacteria were inoculated into the rhizosphere of Astragalus in the form of single inoculation and synthetic flora,all of them could reduce the incidence of Astragalus root rot to a certain extent.The control effect is the best,better than all single inoculation.The synthetic flora also has a good growth-promoting effect,among which the promoting effect on the fresh and dry weight of Astragalus is better than that of all the monocultures.Among the four Astragalus rhizosphere beneficial bacteria we selected,two high-abundance bacteria,S.maltophilia and R.radiobacter,have growth-promoting properties such as producing IAA and dissolving inorganic phosphorus,and have the effect of directly inhibiting the growth of pathogenic bacteria.Two low-abundance bacteria,O.pecoris and A.kashmirensis,could not directly inhibit the growth of pathogenic bacteria,but the PAL,PPO,chitinase activities and JA activities of Astragalus PAL,PPO,chitinase activities and JA and other ISR process-related enzyme and hormone activities under the treatment of O.pecoris and A.kashmirensis Significantly increased,indicating that the two low-abundance bacteria participated in the control of root rot by activating the plant ISR response.4.The pure cultures of 5 kinds of phenolic acid degrading bacteria and 4 kinds of pathogenic bacteria antagonistic bacteria were inoculated in sheep manure organic fertilizer in proportion,and fermented under appropriate temperature and humidity conditions,and the number of effective viable bacteria in the final organic fertilizer met the requirements of microbial fertilizer production.Successfully obtained microbial organic fertilizer.The microbial organic fertilizer and organic fertilizer were added to the soil of Astragalus membranaceus that had been continuously planted for one year.It was found that microbial organic fertilizer and organic fertilizer could promote the growth of Astragalus membranaceus.Compared with the control,the plant height,root length and dry weight of the plants treated with microbial organic fertilizer were increased by 32.6%,44.3%,32.3%.