Study On The Isolation And The Metabolites Of Soil Antagonistic Organisms In Some Greenhouse Of Cucumbers In Shandong Province

In agriculture production, plant pathogens often cause millions of dollars loss each year. How to control these diseases and maintain the normal growth of plants is always the highlight. Application of chemical pesticides is one of the effective measures to control the diseases and plays an important role in crop protection. However, the unreasonable use of pesticides caused many problems, such as the pollution of, soil, water and atmosphere, the increased residue of pesticide in food damages human health and life directly, results in the unbalance of ecological environment, and leads to the resistance and resurgence of the pest frequently. So, effective and safe alternative control measures are needed. Biological control with natural antagonistic organisms is a potential non-chemical tool for crop protection against pest. Biological control is perceived as safe to the environment and human health and can avoid the side effects largely.In our study, 105 soil samples were gathered from greenhouses planted vegetables in Taian, Dezhou, Weifang, Yantai, Jinan etc. With Ascochyta citrullina as the target pathogen, from these samples 36 antagonistic bacterial strains and 22 antagonistic actinomycete strains were isolated by using confronted culture method from dilutions of soil solution. The result showed that the relevance of screening rates of antagonistic organisms in soil and times of planting was very marked. 3 strains of bacteria and 3 strains of actinomycetes were chained after being screened again on the chitinolytic ability. Further study with antagonistic microses was carried.1. In the inhibiting spectrum test of antagonistic microbes against crops pathogens, the result showed the strains of D24, G8, A9 and T111 could inhibit the growth of ten plant pathogenic fungi. The inhibiting rate against the Ascochyta citrullina and Sclerotinia scleotiorum could reach over 80%.2. Yield of antimicrobial substance produced by antagonistic microbes were affected by medium, culturing temperature, pH and culturing times. The optimum conditions for producing antimicrobial substance by the strain of D24 and G8 were on bean seeding juice medium, initial pH 8.0-9.0 and cultured at 28℃. The optimum conditions for producing antimicrobial substance by the strain of Sh34 were on bean seeding juice medium, initial pH 7.5-8.5 and cultured at 31℃. The optimum conditions for producing antimicrobial substance by the strain of T111 were on LB medium, initial pH 7.5-8.5 and cultured at 34℃. The optimum conditions for producing antimicrobial substance by the strain of A9 were on NA medium, initial pH 8.5-9.5 and cultured at 26℃.3. On the basis of observation of colony and cell morphology, biochemical test, Grain stain reaction and the 16SrDNA sequence analysis, the strains of Sh34 and G8, were identified as Bacillus.subtilis. The strains of T111 and A9 were identified as Streptomyces based on their morphology, culture characteristics.4. The vivo trial in greenhouse showed that rates of pathogen inspection in the cucumber were 32.5%, 37.5%, 57.5% and 30% respectively after being treated by the fermentative broths of strains G8, D24, T111 and A9. Inhibited effect was obvious after being treated by the strains T111, G8, D24 in the plant, which was accordance with results of vitro trial. Therefore, the antagonistic metabolite of soil organisms was an important factor to affect antagonistic effect.