Screening And Identification Of Antagonistic Bacteria Against Wheat Take-all And Preliminary Study On Biocontrol Agents

Wheat Take-all is one of the main fungal diseases which cause a large-scale reduction of wheat in various regions,and its propagation speed is fast and destructive.At present,the application of chemical pesticides is the main means to control Take-all,but because it may cause ecological and environmental problems and food safety issues,the use of microbial preparations to control the disease has become a new choice.In this study,the antagonistic bacteria were isolated and screened from the rhizosphere soil of healthy wheat,and their antibacterial activity against the pathogen was studied in vitro and in vivo,and the fermentation conditions of the antagonistic bacteria were optimized,and the bacteriostatic spectrum of the antagonistic bacteria was carried out.And preliminary preparate antagonistic bacteria-related wettable powder.This study provides antagonistic strains for the biological control of Take-all and provides a method for its application in actual production.The main findings are as follows:1.Twelve antagonistic bacteria were isolated by gradient dilution method and plate confrontation method.The inhibitory effect of XJ-3 and XJ-4 on the pathogen was more than 60.00%.The effect of XJ-4 strain was better.The strains XJ-3 and XJ-4 can cause the hyphae of the Take-all to be swollen,deformed and abnormal,and the inhibition rate of the fermentation broth is 70.20%and 74.27%,respectively.2.XJ-3 and XJ-4 were identified as Bacillus velezensis by morphological characteristics,physiological and biochemical characteristics and molecular identification based on gyrB gene.3.By single factor experiment,the optimum growth temperature of XJ-3 and XJ-4 were 28? and the pH value were 6.0.The optimal fermentation conditions for producing antibacterial metabolites by XJ-3 were 33?,initial pH 7.0,rotation speed 175 rpm,and culture for 4 days.The optimal fermentation conditions for the production of antibacterial metabolites by XJ-4 were 33?,initial pH 7.0,rotation speed 225 rpm,5 days.4.Both XJ-3 and XJ-4 showed inhibitory effects on the pathogenic fungi of Colle to trichum,Botrytis,Rhizoctonia,Gibberella and Fusarium,respectively.The test pathogenic fungi showed inhibitory effects and both had broad-spectrum antibacterial activity.5.The pot experiments showed that XJ-3 and XJ-4 promoted the growth of wheat seedlings,compared with the control group,both plant height and dry weight are increasing.The effect of XJ-4 was more obvious.XJ-3 and XJ-4 had obvious control effects on wheat inoculated with Wheat Take-all.The root irrigation with XJ-3 and XJ-4 alleviates the dwarfing of the affected wheat plants and the degree of blackening of the base and roots of the neck.The average control effects were 51.29%and 52.46%,respectively.6.The spore content of XJ-3 and XJ-4 WP was 1.23 ×109 CFU/g and 1.88 × 109 CFU/g,the wetting time was 52 s and 50 s,the suspension rate was 78.8%and 81.5%,respectively.They are both in line with national standards.