| The tobacco is a kind of important economic crops. Tobacco wildfire caused by Pseudomonas syringae pv. tabaci is a worldwide important disease. It is widely distributed throughout the tobacco planting area of china, and the disease severity is high in some provinces. For the resistance of planting varieties to tobacco wildfire is low, the main way to control the disease still keeps taking chemical pesticide. Thus, it causes the drug-resistant development, environmental pollution, and the exceeded heavy metals contents in tobacco leaves, and so on, finally impacts the disease control effect, ecological safety and mankind health. In this paper, trials for searching biological control of tobacco wildfire disease are designed, mainly for screening antagonistic strains, evaluation of resistance in greenhouse and antagonistic metabolic products analysis, determination of antifungal or antibacterial spectrum, physiological and biochemical characteristics of antagonistic and 16S rDNA sequence analysis. Major findings of the study are as follows.1. The preliminary screening of antagonistic strains against P. syringae pv. tabaci120 isolated laboratory strains have been screened by plate spraying method. Preliminary screening,29.17 percent of total number of test strains are screened out, showed that 35 strains have antagonistic effcet on P. syringae pv. tabaci,14 strains of which are actinomycetes and 21 strains of which are bacteria.2. Evaluation of resistance to tobacco wildfire disease in greenhouse16 strains antagonists whose resistant effect is good in agar plate confrontation test were chosen to use for greenhouse pot experimental. Spraying antagonist 20 days later,14 strains were found with a good antagonistic effect on tobacco wildfire disease, and the relative efficiency over 60%; Farther test were carried out by spraying antagonist vaccinating before and after vaccinating. The results showed that,6 strains had prevention effect better than cure effect. Greenhouse control disease test indicated that, bacterial suspension, sterile fermentation filtrate of antagonists and agricultural streptomycin kept good control effect on tobacco wildfire disease with relative efficiency over 68%, The strain YCD2-7-2 had better effect and more stable than others in both treatments, with relative efficiency over 90%.3. The antimicrobial effect of antagonistsAntimicrobial spectrum test indicated that the antagonistic spectrum of the four strains was much broad, with a good antagonistic effect on 25 tested plant pathogens and the inhibition zone radius ranged from 2.0 to 26.6 mm. Itb80 was the best, which had good antagonistic effect on 19 pathogenic fungi, such as Botrytis cinerea, Phomopsis vexans, Thielaviopsis basicola, Sclerotium rolfsii., and so on. The best inhibition on the pathogens Botrytis cinerea was up to 22.0 mm. And the strain had antagonistic effect on 3 of plant pathogenic bacteria and the inhibition zone ranged from 5.6 to 15.6 mm. Followed by Itb162 strains, which have better antagonistic effect on Oospora lactis Fr. var. parasitica and Sclerotinia sclerotiorum, on Xathomonas campestris pv. citri., Pseudomonas angulata and Ralstonia solanacearum with the inhibition zone ranged from 5.0 to 12.6 mm. Two anti-actinomycetes strains (YCD1-7-1 and YCD2-7-2) showed good antimicrobial activity on Xathomonas campestris pv. citri and Pseudomona angulata with the inhibition zone over 20mm;4. The taxonomy of antagonistic strainsBased on colonies’properties, morphological, physiological and biochemical characteristics, and 16S rDNA phylogenetic analysis, strains Itb80 and Itb 162 were identified as Bacillus subtilis. Strains YCD1-7-1 and YCD2-7-2 were identified as Streptomyces griseus.5. Analysis of the metabolic products of the four strainsThe results showed all of the strains had good biocontrol effects, and all of them could produce active substance for biocontrol, such as proteases, siderophores and so on. But it was found that they were unable to produce cellulases. |
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