Screening And Antagonistic Mechanism Of Antagonistic Bacteria Against Fusarium Graminearum Preliminary

Fusarium head blight?FHB?is a disease caused by Fusarium graminearum Schw that can be erupted in a short period of time,seriously affecting wheat quality and yield,causing serious damage to economic losses.In this study,We collected a series of bacterial strainsfrom different soils and isolated and identified these samples,bacterial strains antagonistic to Fusarium graminearum were obtained by screening,and some related experiments were carried out on the antagonistic mechanism and biological characteristics of these strains..The experimental results are as follows:A total of 88 strains isolated from 9 regions were identified as:Pseudomonas aeruginosa?Paenibacillus polymyxa?Microbacterium?Brevibacterium,Brevibacteriu m?Achromobacter and Pseudomonas.From the isolated and identified strains,the st rains A19,B23,C24 and I2 which can effectively antagonize Fusarium graminearu m were screened by the sputum culture method,and the inhibition rates of the four antagonistic bacteria were 47.32%,43.50%,45.66%and 51.11%respectively.Accor ding to the identification,strains A19,B23 and C24 are Pseudomonas aeruginosa,and strain I2 is Paenibacillus polymyxa.By investigating the growth of the four antagonistic strains screened in this experiment within 24 hours,it can be seen that the OD₆₀₀00 of strains A19,B23 and C24 can reach about 1.6 in 24 hours,but the OD₆₀₀00 of growth period of strain I2 is 0.66,so the pair The culture conditions of strain I2 were optimized.The results showed that the N source,C source and inorganic salt of the most suitable strain I2 were tryptone,sucrose and magnesium chloride respectively.The suitable conditions for strain I2 were:rotation speed200 rpm,pH 6.0,inoculum of bacterial seed solution 1%,The amount of liquid is 50 mL?150 mL Erlenmeyer flask?.This study explored the effects of biocontrol bacteria on Fusarium graminearum from a molecular point of view.Eight related genes related to pathogenicity,mycelial growth,spore growth,and toxin synthesis in Fusarium graminearum were screened out.The 8genes were verified by qRT-pcr expression under the action of four antagonistic bacteria.The results showed that the relative expression of FgCdc15 and Fg Rab7 was>1under the antagonistic action of strain A19,and the relative expression of the other six genes was<1.The relative expression of FgMCA1 was>1 under the antagonistic effect of strain B23,The relative expression levels of the seven genes were all<1;the relative expression of the genes FgMCA1,FgCdc15 and Fg Rab7 was>1 under the antagonistic effect of strain C24,and the relative expression of the other five genes was<1;the gene under the antagonism of strain I2 The relative expression levels of Fg?NAC and FgMCA1were>1,and the relative expression levels of the remaining 6 genes were all<1.Since the antagonism of strain I2 was significant in this experiment,the antagonistic effect was better than the other three strains.Therefore,the antagonistic substance of strain I2 was initially investigated in this experiment.The results showed that the volatile substances and lipopeptides of strain I2 were not found which can effectively antagonize the wheat scab,but when the ammonium sulfate precipitation method is adopted,when the ammonium sulfate concentration reaches 80%and 90%,the hyphae of the scab is an unhealthy growth state.This can provide a certain direction and lay a foundation for further investigation of the antagonistic mechanism of strain I2 against Fusarium graminearum..