| Ditylenchus destructor Thonre. has been one of the serious diseases of sweet potato in the north of China, leading to 10%-60% production loss or no harvest. The symptom is culm short, root rot, even the total destruction when serious. Present research mainly concentrates on chemical control and biocontrol, there was little concentrating on pathogenic substances. In this paper, a preliminary study of D.destructor isolation conditions was conducted and D.destructor pathogenic substances were isolated and analysed, to provide a theoretical basis of effective control to the disease.D.destructor was collected in Zanhuang, gaoyi, Qiu County, Lulong, Baoding market; Hebi, Pingdingshan, Xuchang Henan; Linyi Shandong. Soil samples were obtained by 5 points (small block) or "Z" word method (large block), the depth of soil samples was roughly the same to the sweet potato root. Preliminary study of the D.destructor morphology was done separately. Nematodes was collected by Bellman funnel, shallow dish and density centrifugation method,2,500 rpm centrifugal separation, for 5 min in 35% sucrose concentration, to separate nematodes from other samples, the rate was more than 90 percent.Nematode was cultured with sweet potato chips, Botrytis cinerea, sweet potato pieces, sweet potato and potato, and the callus tissue. The callus culture wasted time and effort; sweet potato cultivation need more time than the sweet potato chips cultivation; it would decompose in sweet potato chips cultivation, and it is difficult for separation; Botrytis spore culture was used in this experiment. Nematode morphological was identificated to be D.destructor.1%(w/V) 5-methoxy-N,N-dimethyl tryptamine (DMT),5%(V/V) DMSO were used in this study to stimulate the production and secretion of nematode secretions, TCA/acetone and ammonium persulfate were used to collect secretions. The pathogenic substances existed in the component of ammonium sulphate precipitation and TCA/acetone precipitation, and the pathogenicity of ammonium sulphate precipitation is better than TCA/acetone precipitation. Pathogenicity to sweet potato was detected in conditions as different pH, UV in different time, different temperatures, different concentrations of ions, as well as the concentration of material. The results showed that, the strongest pathogenic pH value was 6.2-6.6. When the pH increased or decreased the pathogenicity was decreased. There was strong pathogenicity on the sweet potato-chips when the temprature was 20℃to 45℃, and 30℃was the strongest. Pathogenicity was weakened when the temperature rised or fall. The pathogenic activity was strong after treated at 50℃for 30 min, but it was significantly reduced after treated at 70℃for 30 min and completely lost after treated at 100℃for 30 min. The experiment results indicated that the protein substances were unstable to the temperature and pathogenic activity reduced gradually with temperatrue increased. The pathogenic activity reduced significantly after exposured at 40 W UV from 50 cm for 10 min, it was almost completely lost its pathogenic activity after exposured for 60 min. It indicated that the substances were unstable to ultraviolet radiation and pathogenic activity reduced gradually with the increasing radiation time. It was obviously influential to the activity of pathogenic substances after adding zinc sulfate, cupric sulfate and magnesium nitrate in certain concentration. Protein substances in 80μL/mL added 0.0025 mol/L zinc sulfate and cupric sulfate play highly role in athogenic activity; and protein substances added 0.0025-0.05 mol/L magnesium nitrate play the strongest role in athogenic activity. |
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