Study On The Biological Control Of Antagonistic Bacteria Against Cucumber Fusarium Wilt

The cucumber fusarium wilt disease is very serious in Sichuan. To biologically control it, we have attempted to screen antagonistic bacteria against fusarium wilt disease strain from seedling rhizosphere of cucumber. Among of them, some strains showed the strong antagonistic ability to the crop pathogens. Furthermore, the antagonistic spectrum, physiological and biochemical characters, classification statuses in microbiology, growth curves and the best condition of growth were studied in this research. According to the fermentative condition, the field control and growth-promoting tests were conducted. In addition, the research of antagonistic mechanism was done, and the antagonistic proteins were isolated, purified and sequenced about N-terminus of peptides.The main results are summarized as below:1. Over one hundred bacterium strains were screened from rhizosphere of cucumber seedlings. Three strains, A54, L37 andYll showed the antagonism against the disease, the inhibition zone width of A54, L37, Yl 1 reached 9mnK lOmnu 8.5mm, respectively.2. In the test of antagonistic specture of bacteria against the crops pathogens , the result showed three strains, A54, L37, Yl 1 could inhibit the growth of eleven plant pathogenic fungi. The inhibition zone width against the rhizoxotonia.sondi and wheat fusarium graminearum reached over 10mm.3. A54, L37, Y11 were identified as Pseudomonas atutzeri, Bacillus subtilis, Bacillus licheniformis respectively through classification methods.4. The growth curves of those strains were consistent with the characters of typical bacteria including 4 phases: lag phase, exponential phase, stationary phase and decline phase .The growth and antagonistic effect of the strains were affected by the culture media, temperature, pH and oxygen factors.5. The control effects against the cucumber fusarium wilt were studied in the condition of different spraying concentration and time. The results indicated that the best sprayingconcentration was 108 cfu/ml and the best spraying time was 3 days after inoculating cucumber fusarum wilt. The best control effect of A54, L37, Yl 1 was 52%, 55.36%, 48.24% respectively.6. It showed three antagonistic bacteria could promote growth of cucumber more obviously than CK in three physiological indexes and five morphological indexes in the promoting test, and different treatment showed different effect obviously.7. The screened strais showed greatly control effect against cucumber downy mdilew and cucumber powdery mildew disease. The diseased index of cucumber downy mdilew descended 12.3% in A54, while the diseased index of cucumber powdery mildew descended 20.8% in L37.8. The antagonistic mechanism was studied. Two antagonistic proteins from L37 and one antagonistic protein from Yll were purified by ammonium sulfate fraction, DEAE-Sepharose, Sephdex G-100, SDS-PAGE. And they were detected as 43kD-protein, 15kD-protein from L37 and 32kD-protein from Yll.9. The research on the biological character of panegonxitic protein demonstrated that the protein were both stable against temperature and proteinases. The proteins could inhibite the growth of plant pathogenic fungi, such as twisting, deformation, massed and uneven cytoplasm.