Preliminary Study On Bacillus Pumilus 223 As Potential Biocontrol Bacteria To Rice Sheath Blight

238 endophytic bacterial strains were isolated from the leaves of rice which were collected from ten different regions of Zhejiang province. 15 bacterial strains showed antagonistic activities against the pathogen Rhizoctonia solani in vitro, which causes Rice Sheath Blight. Among them, one antagonistic strain which was isolated from Fuyang , Zhejiang , China showed the strongest antagonistic activities, and it was named as strain 223. Based on the analysis of morphological, physiological characteristics and 16S rDNA gene sequences, it was identified as Bacillus pumilus.Bacillus pumilus 223 showed strong antagonistic activities to Rhizoctonia solani, the treated mycelium became thick and short, the tip was flat. In greenhouse, three days after the inoculation of sclerotium, the Bacillus pumilus 223 liquid culture, Validamycin and their mixture were sprayed on rice seedlings, respectively. The control effect of Bacillus pumilus 223 liquid culture was 37.19%, 29.12% and 25.08%, respectively, which was investigated after sprayed ten, fifteen and twenty days. That of Validamycin was 37.87%, 28.33%, 23.36% and that of their mixture was 39.97%, 31.58%, 27.45%.Bacillus pumilus 223 could grow at PDA, KMB and LB solid media, but the shape and colour of bacterial colony varied on different media. It couldn't grow at NA solid media. The PDA media was confirmed as the best by the detection of antagonistic activities. The antagonistic substance which was extracted from the cultured PDA solid medium with 2% NaCl or 2% glucose solution showed good antagonistic activities to Rhizoctonia solani. But the antagonistic substance was neither extracted from the cultured PDA solid medium with distilled water or organic solution like chloroform, nor detected in cultured liquid medium.The shape and colour of Bacillus pumilus 223 bacterial colony could change as the incubation at PDA solid media, the maximal antagonistic activities to Rhizoctonia solani were detected at 16-24h after inoculation. The antagonistic substance was sensitive to proteinase E and proteinase K, whereas insensitive to Pepsin. The activity was stable during temperature at 65℃for 30min, but lost completely at 80℃for 30min. The antagonistic substance was showed to retain the activity within the pH range of 2-12, and the optimum pH for the activity was about 7.0. The maximal activity was obtained by ammonium sulfate precipitation with 70% saturation.