Study On Screening And Identification Of High-Efficiency Antagonistic Bacteria Against Botrytis Cinerea And Its Antifungal Mechanism

Gray mold is a serious fungal disease in agricultural production,the causal agent is Botrytis cinerea,which has a wide host range and is susceptible to develop fungicide resistance,seriously affecting the yield and quality of agricultural products.In order to control B.cinerea in a green and efficient way,a series of experimental studies were conducted in this study,including screening and identification of efficient antagonistic bacteria,determination of antagonistic fungal inhibitory metabolites,isolation and purification of antimicrobial substances,identification and analysis of volatile substances,and antifungal and probiotic effects.1.In this study,11 strains with antagonistic effect on B.cinerea were screened by the plate confrontation method,and then a highly efficient and stable strain WZ5 was obtained by the thesis disc ring method,with an inhibition circle diameter of 30.5 mm against Staphylococcus griseae within 5-7 d.After morphological identification,physiological and biochemical determination and 16 S r DNA sequence analysis,the strain WZ5 was confirmed to be P.jamilae.2.It was found that the sterile fermentation broth of strain WZ5 severely affected the growth of mycelium and germination of spores of B.cinerea,fungal inhibition rates of 85.5% and 37%respectively.In experiments on cucumber leaves in vitro,the fermentation solution showed good antifungal activity when diluted to 20 times,with an in vitro control effect of 89.92%;the indoor tomato pot experiment had a preventive effect of 84.79%;the therapeutic effect was a little worse than the preventive effect,at 76.35%.When the fermentation solution was diluted to 50 times,it also had a certain growth-promoting effect on the plants.3.The optimal fermentation conditions for strain WZ5 were defined: 16 h seed culture,60 h fermentation time,3% inoculum,32℃ incubation temperature,50/250 m L loading volume,200 rpm shaking speed,initial p H 7.4.The antifungal metabolites were determined by crude extraction and antifungal activity,and the antifungal substances were mainly lipopeptides,which were purified and identified as Iturin-A.It also contained antifungal proteins,which were purified and identified as copper amine oxidase.5.It was found that the volatile substances produced by strain WZ5 had antifungal activity.38 monomeric compounds were obtained by GC-MS,among which 2,5-dimethylpyrazine had strong antifungal activity,with 100% plate inhibition and 33.54% fumigation inhibition at a concentration of200 μg/m L,respectively.In conclusion,the secondary metabolites and volatile substances produced by P.jamilae WZ5 screened in this study can have an inhibitory effect on B.cinerea,and can directly destroy the mycelial structure of B.cinerea,with efficient inhibition activity and some promotion effect.