Screening, Mutation Breeding And Antifungal Spectrum Determination Of An Antagonist Bacterial Strain To Magnaporthe.grisea

Because of the serious loss of rice production induced by rice blast, easy loss of resistance of the rice varieties to rice blast, and environmental polution by chemical pesticide, the study on the biological control of Magnaporthe grisea is important. Bacillus subtilis has the antagonistic activity to M.grisea. So, it will be significant to search out one Bacillus subtilis strain which has strong antagonistic activity to Magnaporthe grisea in nature to prevent rice blast and protect the ecological environment.Seven hundred and twenty-two bacteria strains were isolated from soil samples which were obtained from the rhizosphere of rice near the yellow river. Screening the colony which is similar to the Bacillus subtilis DB403 in form, color, and size, one hundred and two bacteria strains were obtained. Forty three bacteria strains which inhibited the growth of fungal mycelium were screened by fermentation supernatant inhibiton test. Among these forty three strains, twenty seven strains have strong antagonistic activity to Magnaporthe grisea. Seven strains were identified to be similar to Bacillus subtilis through their morphologic, physiological and biochemical characteristics among these twenty-seven strains. The bacterium which has the strongest antagonistic activity against Magnaporthe grisea was identified with 16S rDNA sequence, and proved to be 99% similarity with Bacillus subtillis 16S rDNA sequence in Genbank. The strain was named to be Bacillus Subtitles strain BS501a.In order to improve its antagonistic activity, BS501a was treated by N⁺ ion implantation and ⁶⁰Coγ-ray mutagenesis. After screening, re-screening, and data analyzing by spss16.0 and genetic stability test for 5 generation, mutant strain BSC45 still kept 1.2364-fold antagonistic activity to Magnaporthe grisea than BS501a. The antagonistic spectrum of BSC45 was determined by bacteria colony comfrantation test, and the result showed that the antagonistic spectrum of BSC45 was broad. KM mice were used to detect the biological safety of strain BSC45. The result of the acute toxicity test of the fermentation supernatant powder of BSC45 proved that it was low toxicity. So this study is essential for BS501a to be researched and developmented to be Biocontrol Agenst.