The Application Of Bacillus Biocontrol Agents And 6% Validamycin·Osthole To Control Rice Sheath Blight Disease

The rice sheath blight caused by Rhizoctonia solani is devastating disease and responsible for severe economic losses in rice production throughout the world. The validamycin is widely used to control this disease. Because of the abuse of this fungicides, the drug-resistant strains has appeared and led to the gradually decline of the control effect. In this study, the biocontrol agents were applied to control this disease. This research would help to reduce the amount of validamycin, and also reduce the risks caused by drug-resistant strains.Several Bacillus spp. representing typical Plant growth-promoting rhizobacteria have been widely studied and applied as efficient, stable biocontrol agents due to their ability to produce antimicrobial substances and induce the resistance of plants. The first purpose of this study was to identify the Bacillus strains by using molecular method. The 16S rRNA and gyrB gene sequence were used to construct the phylogenetic tree. The results had showed that the GBSC56 was belonged to the species of Bacillus atrophaeus, but NMSL88 was only identified as the number of the B. cereus group. The antimicrobial test has showed that the GBSC56 and NMSL88 had strong antagonistic activity to Xanthomonas oryzae pv. oryzae and Sclerotinia sclerotinorium. The MALDI-TOF-MS analysis was used to identify the antimicrobial substance produced by these two Bacillus strains. The results had illustrated that both GBSC56 and NMSL88 could produce lipopeptides surfactin and fengycin. These two typical lipopeptides had strong antibacterial and antifungal activity, respectively.In this study, the Bacillus strain FZB42 was find to have strong antagonistic activity. So, the biocontrol agents, which active ingredients was FZB42, was attempted to control the rice sheath blight caused by R. solani. And the water soluble powder of validamycin A was used as the control. The results had showed that this Bacillus biocontrol agents had a good effect on control rice sheath blight. The control efficiency had reached to 70.34%, when the rice was treated with 50 ml/667m2 of the Bacillus biocontrol agents. This control effect was 0.9% lower than the treatment treated with 40 g/667m2 of 16% water soluble powder of validamycin A. The statistics analysis had indicated that the effect between the Bacillus biocontrol agents and validamycin A had no significant difference at 0.05 or 0.01 level. This study showed that Bacillus biocontrol agents could be used as the substitute for the validamycin.This study also mixed the biocontrol agent osthole, chemical fungicides difenoconazole azole with validamycin to enhance the control efficiency and reduce usage of validamycin. The results showed that treatment of 6% validamycin A·osthole WP with 60 g/667m2 had the best control effect on rice sheath blight, and the control efficiency reached to 82.3%. The control efficiency reduced with a corresponding 10 percentage points, when usage was reduced to 40 g/667m2. While treatment of 12% difenoconazole azole·validamycin A WP with 30 g/667m2 showed the worst control effect on rice sheath blight, and the control efficiency was only 60.31%. The control efficiency increased with 5 percentage points, when usage was increased to 40 g/667m2. In addition, the control efficiency showed no significant difference with 10% validamycin A and the mixed formulations validamycin A·osthole. Furthermore, the experimental results also indicated that biopesticides osthole could enhance control efficiency and reduce usage of validamycin, while chemical pesticides difenoconazole did not have such effect. This study may help to prolong service life of validamycin.