| Rice blast,rice false smut and rice sheath blight are the three most serious diseases of rice,causing the reduction of rice yield and quality.At present,the major strategy to control those three diseases are the use of chemical fungicides.However,due to the difference occurrence time and commonly fungicide of those three diseases,and the long-term large-scale use of a single fungicide easily leads to the development of fungicide resistance,it’s brought serious hidden dangers for controlling those diseases.In this study,we monitor the resistance of the three major rice diseases to several common fungicides,and screen single fungicides and their combination synergistic hat have good control effects on Pyricularia oryzae,Ustilaginoidea virens and Rhizoctonia solani.This study can provide a theoretical basis for the control of the three major rice diseases.The results of research are as follows:1 Sensitivity baseline and resistance monitoring of tebuconazole to Ustilaginoidea virens in Sichuan and Chongqing:The mycelial growth rate method is used to determine the sensitivity of 100 isolates of Ustilaginoidea virens isolates from Sichuan-Chongqing region from 2018 to tebuconazole The results showed that the EC50 was between 0.0178 and 0.1282μg/m L,with an average value of 0.0567±0.0222μg/m L,the least sensitive isolate is 7.2 times the most sensitive isolate.The sensitivity and the sensitivity frequency distribution of 100 Ustilaginoidea virens is unimodal and continuous,so this study we use 0.0567±0.0222μg/m L as the baseline for tebuconazole of Ustilaginoidea virens in the area Sichuan and Chongqing.The minimum inhibitory concentration of tebuconazole on 30 isolates of Ustilaginoidea virens was between 0.2-0.8μg/m L,and 1μg/m L was determined as the differential dose of tebuconazole-resistant and tebuconazole-sensitive isolates of Ustilaginoidea virens in monitoring the resistance.The result shows that the 683 isolates of Ustilaginoidea virens are all sensitive,and no field-resistant isolates was found.2 Sensitivity baseline and resistance monitoring of thifluzamide to Rhizoctonia solani in Sichuan and Chongqing:The mycelial growth rate method is used to determine the sensitivity of 100 isolates of Rhizoctonia solani isolates from Sichuan-Chongqing region from 2018.to thifluzamide The results showed that the EC50 was between 0.0077 and 0.1053μg/m L,with an average value of 0.0384±0.0207μg/m L,the least sensitive isolate is 13.68 times the most sensitive isolate.The sensitivity and the sensitivity frequency distribution of the 100 Rhizoctonia solani is unimodal and continuous,so this study we use 0.0384±0.0207μg/m L as the baseline for thifluzamide of Rhizoctonia solani in the area Sichuan and Chongqing.Calculating the resistance index of Rhizoctonia solani to thifluzamide,the results showed that the determined 194strains of Rhizoctonia solani resistance index ranged from 0.1997～2.7409,and the average resistance index is 0.9703±0.4703,all less than 10.The tests show that there are no isolate resistant to thifluzamide in the Sichuan-Chongqing region.3 Resistance monitoring of Pyricularia oryzae to isoprothiolane,pyraclostrobin and tebuconazole in Sichuan and Chongqing:Differential dose method is used to determine the resistance levels of 44 Pyricularia oryzae isolates from Sichuan-Chongqing region to isoprothiolane,pyraclostrobin and tebuconazole in 2018.In this test,50μg/m L are used as the differentiation dose to distinguish isoprothiolane resistance,1μg/m L are used to distinguish the pyraclostrobin resistance,and 4μg/m L are used to distinguish the tebuconazole resistance.The results showed that no isolates resistant to isoprothiolane,pyraclostrobin and tebuconazole were found.4 Screening out fungicides for control of Pyricularia oryzae,Ustilaginoidea virens and Rhizoctonia solani:The Indoor toxicity determination and effectiveness in field experiments are used to sreen out several effective fungicides against rice blast,rice false smut and rice sheath blight.First,the mycelial growth rate method is used to determine the toxicity of 9 common fungicides to Pyricularia oryzae,Ustilaginoidea virens and Rhizoctonia solani.The results showed that tebuconazole,fluconazole,propiconazole,prothioconazole,azoxystrobin,and pyraclostrobin has great inhibitory activity,and the EC50 is less than 1μg/m L.The field efficacy test of these 6 fungicides showed that 430 g/L tebuconazole SC and 125 g/L fluconazole SC has the best control effect,the control efficacy against rice blast was 73.35%and 75.57%,the control efficacy against rice false smut was 83.59%and 82.77%,and the control efficacy against rice sheath blight was 82.57%and 77.41%,both of which were greater than70%,followed by 250 The g/L pyraclostrobin EC has 65.67%,74.57%,and 69.01%control effects on three diseases,all of which are greater than 65%.Therefore,tebuconazole,fluconazole and pyraclostrobin are recommended as effective fungicides for controlling these three diseases in the field.5 Screening out fungicides combination for controlling Pyricularia oryzae,Ustilaginoidea virens and Rhizoctonia solani:The screened tebuconazole,fluconazole,propiconazole,prothioconazole,azoxystrobin,and pyraclostrobin are binary compounded according to different mechanisms of action.First,the Horsfall method is used to select the ratio with a virulence ratio greater than 1,and then the Wadley method is used to test synergistic ratio of compound fungicide.Laboratory experiments shows that the synergistic compound are as follows:The five mass ratios of the tebuconazole and azoxystrobin combination have an additive effect on the inhibition of Pyricularia oryzae and Rhizoctonia solani:,and has a synergistic effect at a mass ratio of 2:1,the synergistic ratio was 1.5777 and 1.5941;the combination of fluconazole and azoxystrobin has an additive effect on the inhibition of Ustilaginoidea virens and Rhizoctonia solani by a mass ratio of 3:1 to 9:1,and has a synergistic effect at a mass ratio of 5:1,the synergistic ratio was 1.8500 and 1.5419;the combination of propiconazole and pyraclostrobin have an additive effect on the inhibitory effect of Ustilaginoidea virens and Rhizoctonia solani in 4 mass ratios measured,and has a synergistic effect at a mass ratio of 2:1,the synergistic ratio was 1.5232 and 1.7065.6 Synergistic activity of mixtures of fluconazole and azoxystrobin against Rhizoctonia solani:The results of synergism mechanism showed that the combination of fluconazole and azoxystrobin（5:1 m/m）exhibited synergistic activity against the weight of mycelia,sclerotia production and sclerotia germination of Rhizoctonia solani.The Conductivity method method,TBA method,and coomassie blue staining method are used to further determine the effects of the compound and each single fungicides on cell membrane permeability,lipid peroxidation,and soluble protein.The result shows that hat the compound has synergistic effect on accelerating membrane lipid peroxidation and inhibition of soluble protein. |
