Biocontrol Mf-91 Major Rice Disease Control Effect Rhizosphere Microbial Diversity And Rice Quality Impact

This study was aimed at screening the potential biocontrol strains which antagonism to R. solani and M. oryzae, etc and investigating the biological characteristics, fermentation antibiotic activity, control efficiency on rice sheath blight and rice blast of the potential biocontrol strain MF-91, the main results were summarized as follow:1Isolate of the biocontrol strain.In this research,486bacteria and269fungi were isolated and purified from different ecological soil samples. After primary screening test of tablet confrontation method,12bacteria and2fungi which had certain function of antagonism against R. solani or M. oryzae were verified. According to the comparison, it was found that the growth inhibition ratio of antagonistic bacteria against M. oryzae was over80%, such as B4, B8, B18, B31, B34, B73and B74, etc. The inhibitory effect of supernatants of bacterial culture was100%on the spore germination of M. oryzae. Meanwhile, the similar iinhibitory effect on the mycelia growth of R. solani, Sclerotinia sclerotiorum, Fusarium graminearum, Colletotrichum gloeosporioides and Fusarium oxysporum f. sp. Cucumerinum was also be detected. This group of antagonistic bacteria was identified as Bacillus subtilis, and the strains of B1, B43, and B44were belong to Bacillus pumilus, with better inhibitory effect against the M. oiyzae mycelial growth and spore germination, but little inhibition against R. solani. As Streptomyces, B48and B59possessed obvious inhibitory effect against M. oryzae, but not so obvious against the spore germination. As the Antagonist Fungi MF-91has better effect of inhibiting the R. solani and Sclerotinia scleotiorum etc. And MF-91fermentation had better inhibitory effect against the spore germination and appressorium formation of M. oryzae. Thus, it was identified as the Chaetomium aureum.2The biological characteristics of biocontrol strain MF-91.The investigation of the biological characteristics of biocontrol strain MF-91showed that it was extensive adaptability and it could grow normally on most of media. The optimum temperature for mycelium growth was30to35℃on PDA medium and initial pH was9.0to11.0. The optimum temperature for sporulation were25to30℃. on the oat medium,6.0to8.0was the best initial pH value.3The control efficiency of MF-91fermentation against rice diseases.According to the vitro studies, it was verified that MF-91fermentation had marked inhibitory effect on R. solani and M. oryzae. The inhibitory effect could be much more obvious as the fermentation concentration increasing. When the concentration of fermentation was just over10%of the medium, it could competely inhibited the growth of R. solani and M. oryzae spore germination. As tested via Pott anti-efficiency and field efficiency methods, MF-91fermentation had certain control efficiency of rice sheath blight and rice blast.4The antibiotic activity of different conditions on the MF-91fermentation.MF-91fermentation solution was treated under varying conditions, i.e., different inital pH, different collecting time, different heat treatment, different light treatment, proteinase treatment, and the changes in the antibiotic activity of the solution was observed by detecting the mycilium growth rating of R. solani. Results showed that the inhibitory effect of MF-91fermentation solution was significant highest and stable under the condition of pH5-6after culturing6days. Some of the antibiotic substances in the MF-91fermentation liquid had good thermal stability, it causes less impact to its antibiotic activity while treating under the condition of100centigrade temperature. While it was unstable after treatment by light, its antibiotic activity was decreased50%after24hours to light, the antibiotic activity of MF-91fermentation solution had changed little after being treated with protease K.5The influence of MF-91fermentation on the diversity of rice rhizosphere microorganisms and rice qualityThe rice rhizosphere fungi and bacterialflora structure treated by fermentation broth were investigated by PCR-DGGE methods. The results suggested that MF-91fermentation had less impact to the variety of rice rhizosphere microorganisms and would was not changed the original soil microflora structure.According the detection of rice quality, it was found that low concentration treatment of MF-91fermentation broth to rice had less influence on the rice quality, while high concentration could decrease the rice chalkiness as well as improve its quality.