Sensitivity And Resistance Molecular Mechanism Of Fusarium Head Blight To Pydiflumetofen

Fusarium head blight（FHB）,caused by Fusarium graminearum species complex,is a fungal disease that seriously damages wheat yield and quality.It not only causes huge economic losses,but also produces mycotoxins that seriously harm human and animal health.Pydiflumetofen is a new type of succinate dehydrogenase inhibitor（SDHIs）developed by Syngenta Company.It was registered and used in China in 2020,with high efficiency and wide bactericidal spectrum.It has been reported that the agent has high indoor inhibitory activity and excellent field control effect against F.graminearum.In order to clarify the application potential of this agent in the control of F.graminearum and explore the molecular mechanism of resistance,two aspects were studied:The current status of the susceptibility of F.graminearum to pydiflumetofen and the field control effect of pydiflumetofen and its compound;Induction of resistance of F.graminearum in laboratory and the function of FgsdhC and FgsdhC2 genes were studied.The main results were as follows:The EC₅₀ values of 105 strains of F.graminearum from four farms in Jiangsu province ranged from 0.009 to 0.168μg/m L,with an average EC₅₀ value of 0.065±0.027μg/m L.The frequency of sensitivity showed a single peak curve,and no resistance groups were found.The frequency of resistance of F.graminearum strains to carbendazim in four farms ranged from 29%to 57%.No mutants showing resistance to phenamacril were detected.The control effects of 200 g/L pydiflumetofen suspension agent on Fusarium head blight were 86.49%and 90.27%,respectively,with one application of 50 m L/667 m² in the early flowering stage and two application of 30 m L/667 m² in the early flowering stage and the full flowering stage.The control effect of 275 g/L pydiflumetofen and propiconazole suspension on Fusarium head blight was 92.43%and 93.51%,respectively,with one application at the initial stage of flowering of 60 m L/667 m² and two application at the initial and peak stage of flowering of 40 m L/667 m².The two fungicides have good control effect on Fusarium head blight.We selected 10 strains of F.asiaticum strains,4 strains F.graminearum strain indoor induced resistance,received 92 strains pydiflumetofen resistant mutants,through to the parent strain and succinate dehydrogenase in the mutant gene（Fgsdh A,Fgsdh B,FgsdhC,Fgsdh D,FgsdhC2）sequencing and comparison analysis,a total of 7 mutation types were obtained,of which 7%were Fgsdh B whose（Histidine）was mutated to（Tyrosine）,and 4%were Fgsdh B groups（Histidine）mutated to（Leucine）,71%were FgsdhC2（Alanine）mutated to（Valine）,showing high resistance,11%were FgsdhC2（Arginine）mutated to（Lysine）,2%were FgsdhC2（Valine）mutated to（Phenylalanine）,1%was FgsdhC2（Leucine）mutated to（Phenylalanine）,4%of Fgsdh D（Aspartic）mutated to（Asparagine）.There were two sdh C genes in F.graminearum,named FgsdhC and FgsdhC2,respectively.In PH-1 strain,colony morphology,spore morphology and pathogenicity were seriously affected after FgsdhC gene was knocked out,but these biological characteristics were not affected after FgsdhC gene was knocked out,indicating that these two genes have different functions,and FgsdhC gene is an essential gene for the growth of Fushun wheat.FgsdhC2 cannot replace the function of FgsdhC gene.Fluorescence quantitative analysis showed that after FgsdhC gene was knocked out,the expression of FgsdhC2 gene increased by more than 500 times.After the knockout of FgsdhC2 gene,the expression level of FgsdhC2 gene did not change significantly,suggesting that FgsdhC2 gene was regulated by FgsdhC2 gene.FgsdhC2 gene expression was upregulated by 159.48 and slightly upregulated by Fgsdh A,Fgsdh B,FgsdhC and Fgsdh D after PH-1 strain was treated with0.075μg/m L pydiflumetofen,suggesting that the mechanism of action of pydiflumetofen was significantly related to FgsdhC2.FgsdhC gene with A83V mutation was transferred into PH-1△FgsdhC to obtain the transformant expression resistance.The mutation at position 83 of FgsdhC gene can lead to resistance of F.graminearum to pydiflumetofen.FgsdhC2 gene with A73V mutation was transferred into PH-1△FgsdhC2,and the transfter showed no resistance.The function of the transfter is still under further study.The average EC₅₀ value of F.graminearum to pydiflumetofen in Jiangsu province was determined to be 0.065±0.027μg/m L,which could be used to monitor the sensitivity of F.graminearum to pydiflumetofen in future.The mutants that showed no resistance to cyanene could be used to control Fusarium head blight.Pydiflumetofen and its compound had good control effect on wheat scab.FgsdhC gene is the key gene for the growth and development of mycelia,and FgsdhC2 gene is related to the combination of agents.The FgsdhC2,Fgsdh B and Fgsdh D mutants induced by F.asiaticum and F.graminearum strains in China were all mutated on FgsdhC2,Fgsdh B and Fgsdh D,but no mutation was found on FgsdhC.The results provided a theoretical basis for the scientific use of the insecticide to control wheat scab,and provided a research basis for delaying the emergence of drug resistance and the development of new agents.