| Tobacco is one of the most important economic crops in Guizhou province. Recently,with the increasing tobacco planting area, tobacco brown spot disease which does great harm to the quality of tobacco leaves occurs frequently. The local farmers' cultivate activities and economic benefits are affected subsequently. At present, the prevention and control of tobacco brown spot disease mainly depends on chemical method, thereby it tests the local ecological environment severely. In order to control the tobacco brown spot disease appropriately, typical leaves which infected by this disease were collected from Qingzhen city during the period of tobacco growth from 2014 to 2015 in this study, and the pathogenic fungi was identified by microscopy, separated and purified. The pathogenic determination and molecular biology identification had been carried out. The laboratory toxicity of(Alternaria sp.)was tested by three kinds of chemical reagents and three kinds of biological agents.In order to screen effective extracts which controlling Tobacco brown spot,41 kinds of Chinese herbal medicines were crude extracted using microwave methods, ultrasonic methods, and steam distillation respectively.The field trial of this research was done using chemical pesticides, biological pesticides and herbal extracts,which had good inhibition effects indoor.The main results were as follows:1. According to the results of morphologic determination, molecular identification and pathogenicity, the pathogenic fungi of tobacco brown spot disease in this study was Alternaria fungi(Alternaria sp.) of the Deuteromycotina. In order to screen effective agents to prevent and control tobacco brown spot disease, six kinds of fungicides indoor virulence levels were tested by using mycelium growth rate method, including trichoderma viride,1%phenazino-1-carboxylic acid,80% ethylicin, 37% difenoconazole,99% hymexazol and 40%dimethachlon. The results showed that the six kinds of agents had some inhibiting effect on mycelial growth of(Alternaria sp.).1% phenazino-1-carboxylic acid had the maximum inhibition effect, and it's inhibition rate, EC50 and correlation coefficient was 100%, 1.9746?g/mL and 0.997497 respectively. 37% difenoconazole had the minimal inhibitory concentrations, it was 1.2597 ?g/mL.2. 41 kinds of Chinese herbal medicine in 30 families were crude extractedrespectively by three different methods, aiming on determine preliminary inhibition effect of A. alternata indoor. The results showed that the best extract method was the ultrasonic extraction, inhibition rate of 10 kinds of crude extracts was 100% like motherwort etc.,inhibition rate of 7 kinds of crude extracts are more than 90% like rhizoma arisaematis etc.Following is the microwave extraction, only rhizoma coptidis had stronger inhibitory effect,their inhibition rate was 91.15%.The best inhibition effect using steam distillation was rhubarb, paris polyphylla and cinnamon, the inhibition rate was 69.93%, 68.14% and 63.07%respectively.3. By using mycelia growth, laboratory toxicity was tested by crude extracts of 17 kinds of Chinese herbal medicines, inhibition rate were more than 90%. The results showed that the minimum inhibition concentrations(EC50) was 4.0287 mg/mL of rhizoma coptidis,the second one was 4.4680 mg/mL of asarum. The correlation coefficient was 0.978315 and0.978315, respectively, they have good linear relationship. By using mycelia growth,laboratory toxicity of crude extracts of 2 kinds of Chinese herbal medicine were tested,whose inhibition rate were more than 70%. The results showed that the minimum EC50 values of rhizoma coptidis was 7.0773 mg/mL.4. Field plot experiment was carried out by using 1% Phenazino-1-carboxylic acid,37% difenoconazole, extracts of coptis chinensis/realgar/ginkgo by microwave extraction,40% dimethachlon single-dose and their compound medicament. The results showed that 7kinds of single-dose had certain role in preventing and controlling tobacco brown spot disease. Chemical fungicide-37% difenoconazole was superior to conventional drugs-40%dimethachlon, whose controlling effect was 74.61%.The controlling effect of crude extracts from ginkgo which diluted 400 times was 67.57%, relative controlling effect of extracts from coptis chinensis and realgar were 62.83% and 54.62% respectively; Biological fungicide-1%Phenazino-1-carboxylic acid's controlling effect was 66.18% when diluted 1500 times; 37%difenoconazole extracts of coptis chinensis/ginkgo were 72.82% and 75.36% respectively. |
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