Study on Suppressness Effect of Vermicompost to Soil-borne Disease of Cucumber Seedlings

Vermicomposting is a biological degradation of organic wastes by earthworms. Some earthworms can consume a wide range of organic residues such as sewage sludge, animal wastes and crop residues. The end product is known as earthworm cast or vermicompost. Recently, the use of vermicompost as an organic fertilizer for the cultivation of plants has been examined. The aim of this study was to investigate the suppressive effect of vermicompost produced from cattle manure by Eisenia fetida against some soil-borne vegetable plants seedling diseases. So the application of vermicompost can be enlarged,and the most important is that it will decrease the use of chemical pesticide in agricultural production.The methods used in this study contained culture plate analysis and pot bioassay to test the suppressive effect of vermicompost,the pot experiments had 6 treatments: CK (autoclaved soil), 10%V (10% Vermicompost+autoclaved soil), 20%V, 30%V, 50%V, 20% autoclaved Vermicompost. Every treatment repeated for 3 times, the cucumber was infected by Rhizoctonia solani or Fusarium oxysporum. And to isolate microbial communities using diluted flat plate techniques. Microbial activity was monitored by measuring the rate of hydrolysis of fluorescein diacetate (FDA). FDA is hydrolyzed by a number of enzymes in living cells, such as proteases, lipases and esterases. The reaction yields water-soluble fluorescein from water insoluble FDA. \;The results showed that when adding vermicompost to the center of PDA medium coated with Fusarium oxysporum conidia suspension, A large inhibition zone surrounded it after 15~20days cultivation, the vermicompost induced a strong inhibition of growth of Fusarium oxysporum on agar plates. Whereas the medium without vermicompost and with sterilized vermicompost were all covered with white mycelium. At the same time, a cucumber seedling bioassay was developed, It indicated that the disease incidence was lower when amended with vermicompost. The decrease of disease incidence was connected to the amount of vermicompost in the potting media. When the substrate consisted of 20% of vermicompost, best suppression occurred, the biological control effect was about 96.1%( P 0.05). In addition, the mean fresh weights and plant height of the plants had similar trends. All these suggested that addition of vermicompost with different doses had definite relationship with the suppression of some soil-borne vegetable plants diseases. \;This study also investigated the suppression mechanisms. Because of no suppressive effect was observed in the PDA medium added with sterilized vermicompost and when sterilized vermicompost addition to autoclaved soil with pathogen,no obvious suppression occurred in pot experiments, it seemes that vermicompost lost its suppressive activity after heating sterilized. In another experiment, when 10%~20% vermicompost added into the diseased soil ( Fusarium wilt of cucumber), the total number of plant pathogen ( Fusarium oxysporum ) were significantly lower than the control diseased soil and the total numbers of microorganisms (fungi, actinomycetes and bacterium) were also significantly higher especially the amount of actinomycetes was about 100 fold higher than the control soil. Similarly, with the addition of vermicompost, the microbial activity was also higher than non-vermicompost diseased soil. So the decrease of plant pathogens and the higher microbial activity and numbers of microorganisms in the vermicompost-diseased soil mixture account for improving the competition for resources including space and nutrition of all the soil microorganisms with the plant pathogens. Furthermore, two antagonistic actinomycetes strains have been isolated from the suppressive vermicompost. The vermicompost was obtained by putting earthworm into autoclaved culture plate for six hours after surface-sterilized the worm in 50%~60% ethanol and then dipped into autoclaved water for 5 minutes. The two strains are Streptomyces syringini and Streptomyces globisporus. The two strains exhibit strong inhibition to many plant soi