Diagnosis And Screening Chemicals To Control Of Tobacco Root And Stem Diseases In Fujian Province

Tobacco root and stem diseases are the general name of tobacco root diseases and tobacco stem diseases, these diseases caused heavy losses in major tobacco production regions of Fujian province. Tobacco root and stem diseases were investigated and studied during 2006～2008 in Fujian, and the chemicals were screened for the control of tobacco root and stem diseases, expected to provide basis for control these diseases effectively. The results were as follows:1. Tobacco root and stem diseases were investigated and identified in major tobacco growing regions of Fujian. The major kinds of tobacco root and stem diseases were confirmed by symptoms observation, pathogens isolation and identification and pathogenicity test, these diseases include tobacco fusarium root rot, tobacco bacterial wilt, tobacco damping-off, tobacco sore shin, tobacco anthracnose. The results indicated that tobacco fusarium root rot and tobacco bacterial wilt were major root and stem diseases in Fujian tobacco growing regions, and the symptom characteristics of different tobacco root and stem diseases were described and differentiated.2. The occurrence of tobacco black shank was confirmed in Fujian tobacco growing regions, tobacco black shank was't founded in Fujian tobacco growing regions where we investigated, as the results of investigated proposed that it's not suitable for advocate overall control tobacco black shank in Fujian tobacco production.3. Tobacco fusarium root rot as a new disease was founded in Fujian tobacco growing regions and we were systematic studied of the disease. The results indicated that tobacco fusarium root rot was an important tobacco root and stem disease, incidence about 20.0%, occurrence period from April to May. Three kinds of Fusarium were isolated from the samples of tobacco fusarium root rot and were identified as Fusarium oxysporum, F. solani, F. semitectum by morphology. Results of pathogenicity test showed that all three Fusarium were able to infection tobacco, and F. oxysporum was the dominant pathogen that had stronger pathogenicity to tobacco than the others. F. oxysporum biological characteristic research indicated that the optimum temperature for growth of the pathogen was 25～30℃, the optimum pH value for mycelial growth, Sporulation and spore germination were in the range of 5～7. Rresistance of main cultivars to F.oxysporum was determined, the results indicated that Cuibi 1,K326,Yuyan87 all susceptible to F.oxysporum.4. Chemicals were screened for control the pathogens of tobacco root and stem disease by inhibitory tests in vitro and pot test, the results indicated that Metalaxyl-mancozeb 58% WP had good inhibitory effect on Pythium aphanidermatum, EC50 values was 15.8μg·mL-1, the control effect in pot test was 60.3%, Trichloroisocyanuric acid 90% had good inhibitory effect on Ralstonia solanacearum, EC50 values was 9.9μg·mL-1, the control effect in pot test was 60.3%, which significantly better than streptomycini sulfas 72% WP that commonly used in field, and have the advantages of low cost, non-pollution and non-phytotoxicity that can be further used in field control test. Difenoconazole 10% EC and myclobutanil 12.5% EC both have good inhibitory effect on Rhizoctonia solani, Colletotrichum gloeosporioides and F. oxysporum. 12% compounded agent EC was prepared by mixture 3.2mL 12.5% myclobutanil EC with 1mL 10% Difenoconazole EC( the ratio of effective concentration was 4:1) that had good inhibition effect on the pathogens, results of pot test indicated that 1500-fold of 12% compounded gagent EC had good control effect of tobacco root and stem diseases, and with low cost.