Sensitivity Of Sclerotium Rolfsii To Two SDHIs Fungicides And Risk Assessment Of Resistance To Benzovindiflupyr

In recent years,the occurrence of stem rot of peanut caused by Sclerotium rolfsii has been aggravated year by year due to continuous cropping of peanuts,straw returning and climate warming,which has seriously affected the high-quality development of peanut industry in China.At present,the application of chemical fungicides is a common strategy to control stem rot of peanut.However,at present,there are few registered fungicides used to control stem rot of peanut in China,and all the registered fungicides used to control stem rot of peanut are single target fungicides.Long-term use of fungicides with the same action mechanism will inevitably lead to the development of fungi resistance,thus increasing the difficulty of later control.Therefore,it is urgent to screen new efficient and safe fungicides for controlling stem rot of peanut.A new succinate dehydrogenase inhibitor(succinate dehydrogenase inhibitor;SDHI)benzovindiflupyr and isopyrazam have been used to control many plant diseases,but their application potential to control stem rot of peanut has not been explored.In this study,the isolates from Henan,Shandong and Hebei provinces were used as research materials,and the application potential of benzovindiflupyr and isopyrazam was explored by mycelium growth rate method,pot experiment and correlation analysis of sensitivity,and the resistance risk of S.rolfsii to benzovindiflupyr was further evaluated.The main results are as follows:1.The sensitivity of 246 strains of S.rolfsii to benzovindiflupyr was determined by mycelium growth rate method.The results showed that benzovindiflupyr had strong inhibitory activity against S.rolfsii,the EC50 value ranged from 0.01 to 0.57 mg/L,and the average EC50 was 0.12 ± 0.05 mg/L.There was no difference in the sensitivity of S.rolfsii to benzovindiflupyr in different regions.Twenty-three sclerotia of S.rolfsii were randomly selected,and the inhibitory effect of benzovindiflupyr on sclerotia germination was determined.The results showed that benzovindiflupyr also showed strong inhibitory effect on sclerotia germination,with an average EC50 of 2.38±1.04 mg/L,and benzovindiflupyr with a concentration of 10 mg/L could completely inhibit sclerotia germination.Through indoor pot experiment,it was found that the protective effect of benzovindiflupyr was obviously superior to the curative effect,and its protective effect(93.99%)at the concentration of 100mg/L was more than twice that of the curative effect(45.07%).In addition,the protective or curative efficacy of benzovindiflupyr at the concentration of 50 mg/L(89.87%,20.39%)is equivalent to that of the control fungicide thifluzamide at the concentration of 100 mg/L(86.39%,16.21%),which shows that benzovindiflupyr has great application potential in controlling stem rot of peanut,but in order to achieve better results,In order to delay the development of resistance to benzovindiflupyr,the fungicides that can be used alternately with benzovindiflupyr were screened.The results showed that there was a positive correlation between benzovindiflupyr and isopyrazam and mefentrifluconazole,but there was no correlation between benzovindiflupyr and picoxystrobin,pyraclostrobin,tebuconazole,boscalid,carboxin and thifluzamide,which indicated that benzovindiflupyr could be used alternately with six fungicides such as pyraclostrobin and tebuconazole,thus delaying the development of resistance of S.rolfsii.2.that sensitivity of S.rolfsii to isopyrazam was measure by mycelium growth rate method,and the distribution range of EC50 value was 0.03-6.56 mg/L,and the difference between the highest value and the low value was 218 times.There is no difference in the sensitivity of stem rot of peanut fungus to isopyrazam in different regions,but many strains resistant to isopyrazam were found in the field.Isopyrazam had a strong inhibitory activity on sclerotium germination of S.rolfsii,with an average EC50 of 3.89±1.64 mg/L(n = 28).Pot experiments showed that 100 mg/L,200 mg/L and 300 mg/L of isopyrazam had good control effects on stem rot of peanut.Correlation analysis showed that there was a positive correlation between isopyrazam and tebuconazole or boscalid,but there was no correlation between isopyrazam and pyraclostrobin,mefentrifluconazole,picoxystrobin,carboxin and thifluzamide.The relative conductivity of sensitive hyphae of S.rolfsii increased after the treatment with different concentrations of isopyrazam,and the degree of increase was positively correlated with the concentration of the fungicide.Compared with the relative conductivity of sensitive strains,the change degree of the conductivity of the strains resistant to isopyrazam is small,and even there is no significant difference between the low concentration of isopyrazam and the blank control.After the treatment with 0.5 mg/L isopyrazam,the succinate dehydrogenase activity of sensitive strains decreased significantly,and there was no significant difference between the succinate dehydrogenase activity of isopyrazam-resistant strains and the blank control.3.The risk of resistance to benzovindiflupyr was evaluated by domesticating resistant strains with chemicals in the laboratory.Eight strains resistant to benzovindiflupyr were finally obtained by continuous domestication in medium containing sublethal concentration of benzovindiflupyr for several generations.After the resistant strains were continuously transferred in fungicide-free PDA medium for 10 generations,there was no difference in sensitivity between the first generation and the tenth generation,which indicated that the fungicide resistance of the above strains could be stably inherited.The resistance factor(RF value)of 8 benzovindiflupyr-resistant strains was between 21.58 and 35.08,and their resistance degree was moderate.Through fitness test,it was found that the mycelium growth rate of resistant strains decreased,the number and dry weight of sclerotia decreased,but the pathogenicity increased.The results showed that the resistance of S.rolfsii to benzovindiflupyr was at a low risk level.However,with the exception of picoxystrobin,benzovindiflupyr-resistant strains can reduce the sensitivity to carboxin,thifluzamide,boscalid,isopyrazam and pyraclostrobin.In addition,after the fusion of the resistant strains with their parent strains or with the hyphae of strains in the same affinity group,the sensitivity of the fused strains to benzovindiflupyr was significantly reduced,which indicated that the fusion of the resistant strains to benzovindiflupyr in the field with the hyphae of sensitive strains would increase the difficulty of controlling stem rot of peanut.