| 1. Isolation , screening of biological baceria and studing of their biological characteristic. In our study, 481 bacterial strains were isolated from 179 soil samples collected from fieldsin GanSu, from which 89 bacterial strains antagonistic highly against 16 strains of plant pathogenic fungal. From the isolates 3(F-152, Q-28 and O-39) strains with obvious inhibiting activity to Phytophthora capsici and the root-colonizing density are highest were screened as the biocontrol bacteria by using the method of the inhibiting zones combined with root-colonizing capacity of the 3 isolates.The biological characterisitic of 3 biocontrol bacteria had been studed. The results showed, the optimum growth time, temperature and PH values were 20~28h, 30~37℃ and 6~8. The optimum growth concentration of NaCL and sucrose in the media of F-152 were 0.17% and 9%, but Q-28 and 0-39 were 1.5% and 3 %.2. Idenification of the biocontrol bacteria.Accroding to observation of characteristic of culture and morphology, physiological and biochemical test, 3 strains belonged to Paenibacillus polymyxa. But diffence of their characteristic of culture , morphology and biochemistry showed 3 biocontrol bacteria were diffent strains. The sequence of the two strains'(F-152 and 0-39) 16S rDNA were found to be homogeneous at the rate of 99% to the members of Paenibacillus polymyxa. (Accession number were AY302439 and AY359622 in GenBank), which conformed with the result of identification of morphology and biochemistry. F-152 and 0-39 were deposited with China Center for Type Culture Collection (CCTCC), bearing CCTCC Accession Number M206041 and M206042.3. Studies on the population fluctuation of biocontrol bacteria in pepper root and rhizosphere soil.Experiments showed that the colonizing capacity of biocontrol bacteria in pepper root and rhizosphere soil had positive relationship to the introduced strains concentration. The higher biocontrol bacteria concentration introduced, the bigger population of biocontrol bacteria the colonizing concentration of biocontrol bacteria in pepper root and rhizosphere soil reduced at first, then raised and decreased gradually again, and keeped a stable leving at 10~3~10~5cfu/g root or soil. In comparison with inoculation of biocontrol bacteria only, inoculation of Phytophthora capsici had a negativest effect on colonization of F-152, secdonly 0-39, had an unconspicuous effect on colonization of Q-28. The effect of inoculating biocontrol bacteria before Phytophthora capsici was smaller than that of inoculating Phytophthora capsici and biocontrol bacteria together and inoculating biocontrol bacteria after Phytophthora capsici.4. Studies on control efficiency of biocontrol bacteriaIn the plate tests, inhibiting rate of the culture filtrate of the biocontrol bacteria against Phytophthora capsici was lower than fermented liquid sterilized. The germination precent of pepper seeds was obviously advanced. In the greenhouse tests, the biocontrol effectiveness of 0-39, Q-28 and F-152 was best as 90.63%, 88.40% and 67.04% by drenching root with fermented liquid, which applying method was inoculated biocontrol bacteria at first, inoculated Phytophthora capsici on sixth days, inoculated biocontrol bacteria again on eighth days and inoculated biocontrol bacteria third when Phytopathora blight broke out.5. Breeding of multi-functional strains by protoplast fusion between F-152 and B-21. Protoplast fusion between F-152(Rif\ Em') and B-21(Rif > Em+) was studied, and discussedthe optimum conditions of preparation and regeneration of protoplast and protoplast fusion. At last, screened out 3 strains of fusants which inhibiting rate of the culture filtrate against Phytophthora capsici was between their parents from 55 stable fusants. But a study on colonization and control efficiency of fusants has to be advanced.
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