Study On Antimicrobial Activities And Mechanism Of The Extract From Chinese Yam(Dioscorea Opposita Thunb.) To Cucumber Powdery Mildew

It was observed for several crop seasons that Chinese Yam(Dioscorea opposita Thunb.) plants did not infected by cucumber powdery mildew in the field although this disease was prevalent and many other plants such as cucumis, solanaceaes and garlic, onion, leek plants were infected seriously. In order to study the antimicrobial activities and the mechanism of the extract from Chinese Yam (Dioscorea opposita Thunb.) to cucumber powdery mildew, some experenments were manipulated.Step Ⅰ, Chinese yam seedlings inoculated by the conidium of the cucumber powdery to identify if the yam seedlings could be infected by the powdery mildew.Step Ⅱ, the antimicrobial activities of the leaves disk of cucumber’s cotyledon was detected by the extraction of Chinese yam leaves and tubers by distilled water, ethanol, acetone, ethyl acetate respectively.StepⅢ, the effected extraction was screened preliminary for cucumber powdery mildew from different concerning extraction of yam leaves and tubers.Step Ⅳ, the antimicrobial activities was investigated respectively by spraying different treatment of yam leaves extractions on cucumber seedlings. Four kinds of enzymes activity as POD、PPO、PAL、SOD was detected respectively after spraying the extraction of yam leaves in different treatments. The results as fowllowed:First, Chinese yam plants can not be infected by cucumber powdery mildew. It was indicated that Chinese yam plants could not be infected by cucumber powdery mildew.Second, Three different kinds of yam leaves all have low stomata density (238.56-354.19No./mm2), rich wax content(17.56-27.53mg/g) and high phenols content (15.94-20.31mg/g).Third, there were some certain antimicrobial activities of the extraction of Chinese yam leaves and tubers by distilled water, ethanol, acetone, ethyl acetate respectively to cucumber powdery mildew by the leaves disk of cucumber cotyledon infection. However, there was phytotoxicity for the cucumber cotyledon by one time of extractions of ethanol, acetone and ethyl acetate respectively except the extraction of distilled water. So ten times extraction concentration of the Chinese yam leaves and tubers was selected as the working concertration for advanced study respectively.Fouth, there was antimicrobial activities of the extraction from Chinese yam leaves and tubers respectively to the cucumber powdery mildew by detection in pots. Ethanol-extraction from yam leaves and tubers was the most effective for the cucumber powdery mildew, and then it was acetic-extraction then acetone then distilled water-extration. The extraction of Chinese yam leaves was more effective than the extraction of the tubers of four different solvents.Fivth, the enzyme activity of POD, PPO, PAL, SOD of cucumber seedlings was detected respectively treated by spraying extractions of yam leaves after infected Id,3d,5d,7d,9d,11d by the cucumber powdery mildew as the control was not treated by the extractions of yam leaves. The changes was observed that the enzyme activity of POD, PPO, PAL, SOD increased significantly after treated by extractions of yam leaves and was all increased first and then decreased. The order of changes of four kinds of defensive enzyme activity in the cucumber leaves after treated by different extrations from yam leaves by four kinds of solvents from strong to weak was:ethanol>ethyl acetate> acetone> distilled water.