Screening Of Antagonistic Bacillus Against Rice Blast And Study On Biocontrol Mechanisms

Rice blast caused by Magnaporthe oryzae B.Couch is considered to be the most destructive and widely distributed disease and a major cause of crop loss in rice production system. Although efforts are being made to control this disease, application of environmentally benign biocontrol agents is a promising alternative and important strategy to be used to reduce the negative environmental impact caused by the use of chemical fungicides. The aim of the present study was to screen the beneficial bacteria that had Significant control effect against rice blast and to research the main biocontrol mechanism of the bacteria, so as to provide effective strains and practical guidance for industrialization of biofungicides.248bacterial isolates were collected from the rice plants from different rice growth regions of China, and the antifungal activities of these isolates were evaluated under in vitro and in vivo conditions against M. oryzae. The results of control test showed that3strains (RL263、 RL115and RT312) could reduce the incidence and severity of the disease in the potted experience.The results of4years field trials showed RL263and RL115evidently reduced rice blast development and yield loss. Bacillus RL263and RL115were identified as Bacillus amyloliquefaciens respectively through physiological biochemical characters and nucleotide sequence analysis based on16S rRNA and partial gyrA gene.The biocontrol mechanisms of strain RL263and RL115controlling the rice blast were studied. RL263and RL115were capable of producing cellulose, amylase, protease, siderophores and could form biofilm.The colonization ability of the strains was determined in pot experiment by gfp-labeled mutants. The colonization quantity of the strains could maintain about105cfu/g in phyllosphere of rice after15days of inoculation.Filtrate and crude protein of B. amyloliquefaciens RL263showed comparable inhibitory activities on conidial germination and appressorial formation of M. oryzae. Then the compounds which have the same molecular weight as that of surfactin in the resin extract of supernatant of RL263were purified and detected by HPLC-MS. PCR detection also showed that RL263contained genes involved in biosynthesis of antibiotics:sfP, which indicated that surfactin was the crucial compounds responsible for its antifungal activity.