The Pathogen Isolation, Identification And Fungicides Screening Of Cucumber Root Rot In Laboratory

Recently Cucumber root rot, a kind of soil-borne disease, becomes more and more serious in many cucumber-planting areas. The disease could result in cucumber root rot, and directly affected the production and the yield of cucumber. To elucidate the causal agents and occurrence of the disease, 88 isolates of the possible pathogen were purified from diseased cucumber plants in Tianjin city suburbs and rural areas during 1999 to 2002. Three kinds of fungi, Phytophthora melonis, Fusarium oxysporum and F. solani were identified from the isolates. The pathogenicity of the fungi was tested in greenhouse. The results showed that Phytophthora melonis was the pathogen, but Fusarium oxysporun and F. solani could help the occurrence of the disease and make it more serious. The test also had shown that there were no cucumber cultivars resistant to Phytophthora melonis, however some cultivars resistant to the two Fusarium fungi were found in the test.The biological characteristic of the three fungi were studied in the laboratory. The proper temperature for the growth of P. melonis, F. oxysporum and F. solani was 25 ~ 35 , 20~32 and 25~35 respectively. The best temperature for the growth of the three fungi was 32 , 28 and30 respectively. The suitable pH value range for the two Fusarium growth was pH6~8. Different content of nitrogen, phosphorus and potassium in the medium had little effect on the growth of the two Fusarium pathogens.The sensitivity of P. melonis to metalaxyl was tested in laboratory, and the results indicated that all the isolates tested were sensitive to the fungicide. The virulence of other 9 fungicides to P.melonis also was identified and the results had shown that 25% WP Metalaxyl, 58% WP Metalaxyl -MZ and 60% WP Flumorph were more effective to the fungus, and the EC50 were 0.115 g -mL-1, 0.905 g -mL-1 and 2.202 g -mL-1 respectively. Amistar, Sandofan, Mancozeb and Cymoxanil Mancozeb had less virulence to P. melonis, but Hymexazol and Prompamocarb hydrochloride had little effect.