Biocontrol Of Sweet Potato Stem Nematodes Using Streptomyces Men-myco-93-63

In the experiment the mechanisms of Streptomyces Men-myco-93-63 fermentation filtrate against sweet potato stem nematodes were studied by investigating the knocking-down rates of Ditylenchus, the chemotaxis of Ditylenchus and biocontrol of the disease in the greenhouse test etc.An isolation method for the pathogen that is fit for measuring the knocking-down rates of Ditylenchus was obtained by optimizing Baermann Isolation. By increasing oxygen content in the water, changing containers and ultrasound etc., an isolation may obtain several ten thousands nematodes with survivor rates above 90% in suspensions. The dispersity and homogenization of the nematode suspensions were suitable for the research on microscope.The fermentation filtrate was used to measure the knocking-down rates of Ditylenchus with different concentrations and different time periods etc. The results showed that the knocking-down rates of the fermentation filtrate were not significantly with that of the water.Effect of the fermentation filtrate on the chemotaxis of Ditylenchus to sweet potato juice was tested on agar plate. The filter paper stripes soaking up with sweet potato juice extract or mixture of sweet potato and the fermentation filtrate were place on the one side of water agar plate and Ditylenchus suspension was inoculated on another side of plate at an interval 3 cm distance. The results showed that Ditylenchus were attracted toward the sweet potato juice but were not attracted by the mixture of sweet potato and the fermentation filtrate according the distribution rates of Ditylenchus on 0-2 cm area nearby filter paper stripes. The number of Ditylenchus was significantly higher in the area treated by the sweet potato juice than that by mixture of sweet potato and the fermentation filtrate. It is deduced that the fermentation filtrate can obviously reduce the chemotaxis between Ditylenchus and sweet potato juice.Protection effect and therapeutical effect of the fermentation filtrate was detected by inoculating sweet potato tubers. The results showed that therapeutical effect was not significantly higher than that of CK according the rates of the disease areas. But protection effect was significantly higher than CK and same to avilamycin treatment. We suggest that the fermentation filtrate has protection effect against Ditylenchus.