Risk Analysis On Resistance Of Rhizoctonia Solani To Propiconazole And Carbendazim In Guangxi

Rice sheath blight caused by fungus Rhizoctonia solani Kuhn was the most important disease of rice in Guangxi. In order to analyze resistance risk of chemical fungicide in the case of applying to control the rice sheath blight in large-scale, some study related to risk assessment of fungicide resistance was carried out in this paper, by using material of chemical fungicide Propiconazole and Carbendazim, and by reference to Jinggnagmycin which was proved as a low risk fungicide. The study contents were consisted of the functional property of the fungicide, and the dosage effect of the fungicide, and the property of the fungicide stressing on the fungus to induce variation, and competitiveness analysis of isolates in a environment condition containing the fungicide, and so on. Some work on a method of artificial disease was also carried out. The main results were as follows.1. A method of artificial disease on detached rice leaves that was available to determine control effect of fungicide was developed and improved. The points in operation of the method were to fix and cultivate the detached leaves inside a special equipment, and to inoculate at lower part of the leaves with mycelium disc grown less than48hours, and to keep in condition of high humidity and to measure lesion height3days post inoculation. All intact and green leaves of rice plant with growth period above6-leaf stage were suitable for the method. Some advantages of the methods were as follow. The detached leaves kept unfold normally. The operation of fungus inoculation, spraying fungicide and survey result was easy and simple. The disease symptom on the leaves was clear and the control effect was easy to identify.2. The functional property of fungicide applied in control of disease rice sheath blight was detected. Results were showed as follow. A highly effective protection was showed in all 3fungicides of Jinggnagmycin, Propiconazole and Carbendazim for the control of the disease, and relative low therapeutic effect was showed in the3fungicides. The control effect was due to growth inhibiting of mycelium for Propiconazole and Carbendazim, and the control effect was due to virulence weakening of the fungus for Jinggnagmycin.3. Dosage effect of the fungicides applied in control of disease rice sheath blight was detected. The concentration used by production was3.4times,23.8times and17times as the concentration for control effect at90%for three fungicides Jinggnagmycin, Propiconazole and Carbendazim, respectively, an overdose application for the three fungicides in production. Control effect of all three fungicides to disease caused by isolates with high resistance was low, while control effect of the fungicides to disease caused by isolates with low resistance was high.4. No variation was found in isolate of the fungus induced by Jinggnagmycin-stress. A decline of virulent was found in the isolate induced by Jinggnagmycin-stress. A variant with1.6times resistance as its wild type to Propiconazole was found in isolate induced by Propiconazole-stress, but hereditary variation of the variant was not found, and no decline of virulent was found in the variant. A variant with2.15times resistance as its wild type to Carbendazim was found in isolate induced by Carbendazim-stress, but hereditary variation of the variant was not found, and A decline of virulent was found in the variant.5. Competitiveness of isolates with different resistance to fungicide was detected with plate medium contained fungicide or with detached rice leaves contained fungicide. Results showed that a competitive advantage was found in resistant isolates, while a disadvantage was found in sensitive isolates.A prediction of low risk of resistance of R. solani to chemical fungicides Propiconazole and Carbendazim could be made on the results all above.