Study On The Antibacterial Mechanism Of Streptomyces Bull On Soil-borne Diseases Of Corn And Its Effect On Soil Remediation Of Continuous Cropping

With high productivity and strong adaptability,corn is one of the three major crops in the world at present.It is also considered to be an important food crop in China and is widely planted throughout the country.However,due to the continuous cropping of corn soil for many years,corn diseases occur,leading to a large amount of corn production,and the problem of quality damage is even more serious.Among them,corn stem rot caused by Fusarium graminearum is a typical disease.In order to repair corn soil,currently,microbial agents are the most ideal method for bioremediation of continuous cropping soil,and they are widely used due to their advantages of low cost,green environmental protection and strong extensibility.In this study,a strain of actinomycetes with the best antagonistic effect on corn stem rot pathogen was screened for purification and identification.The bacteriostasis and promotion of life of this strain were tested and the bacteriostasis mechanism was studied.After applying antagonists with different concentrations to the soil for a period of time,compared with CK,the antagonists had different effects on the basic physical and chemical characteristics of the soil,biological characteristics,as well as the bacterial community structure,and the restoration ability of microbial agents on continuous cropping soil.The results are as follows:1.Isolate and screen actinomycetes from the rhizosphere soil of corn disease,and obtain a strain with the best antagonistic effect against Fusarium graminearum,which causes corn stalk rot,by using the plate confrontation method,with an inhibition width of 17.1 mm,Combined with physiological and biochemical characteristics and16 S r DNA gene sequence alignment to determine that this antagonistic strain is Streptomyces bullus,and named G1.2.In the study of the antibacterial and growth promotion of Streptomyces bull and its antibacterial mechanism,it is found that when the concentration of the fermentation broth of the strain is 50%,the inhibition rate of hyphae and spore germination can reach up to 95% and 99%.Inhibit the formation of most sclerotia,the morphology of the inhibited hypha is aberrated,the hypha is broken,and the branches increase;in addition,it produces metabolites such as glucanase,chitinase and carboxymethyl cellulase;Streptomyces bull(G1)It can produce indole acetic acid and hydroxamic acid-type siderophores,the contents of which are 76.20 mg/L and 59.12 μg/m L,respectively;strain G1 shows positive reactions on culture media such as ammonia production,nitrogen fixation,and potassium dissolution.The antagonistic strain has a significant effect on the growth of Fusarium graminearum.3.Applying different concentrations of Streptomyces bulls,soil p H value,organic matter,and available nutrient content all increase significantly with the extension of the cultivation time.When the cultivation reaches 75 d,the 3% treatment is the best,and the continuous cropping of corn is the best soil.The p H value increased by 16.52%,and the content of organic matter,alkaline hydrolysis nitrogen,available phosphorus,and available potassium increased by 18.86%,28.21%,19.46%and 34.60%;its urease activity and catalase activity were positively correlated with incubation time,Increased by 118.81% and 39.39%.The microbial agent effectively improves the physical and chemical properties and biological properties of the soil,and shows a better effect of repairing the continuous cropping soil.4.This study used the I11 lumia Mi Seq high-throughput sequencing method to clarify the effect of different concentrations of Streptomyces bullus on the microbial bacterial community structure in corn soil.It was found that the microbial diversity of the soil decreased after the inoculum treatment.Compared with the blank control,the relative abundances of Actinobacteria,Firmicutes and Proteobacteria in the soil dominant bacteria phyla treated with Streptomyces bulls were increased by 0.68%.And 2.81%,4.45% and 3.52%,0.80% and 5.86%;the relative abundance of Arthrobacter and Massilia in the dominant genus increased by 4.61% and 4.40%,2.46% and 7.41%;The relative abundance of Burkholderiales and Xanthomonadales in the order of the dominant bacteria increased by 0.58% and 7.66%,0.61% and0.86%;The relative abundance of Sphingomonadaceae and Oxalobacteraceae in the dominant bacteria family increased by 1.66% and 1.78%,2.02% and 8.63%.A series of experimental results show that an appropriate amount of microbial agents can effectively improve the structure of soil bacterial community,increase the abundance of its dominant populations,and improve the soil ecological environment.