Resistance Risk Assessment For Fusarium Verticillioides To Pydiflumetofen

Fusarium verticillioides is one of the dominant species of maize cob rot,which not only reduces the yield and quality of cereal crops,but also produces fungal toxins that pose a serious health risk to humans and animals.The main target of SDHIs（succinate ehydrogenase inhibitors）fungicides is complex II of the mitochondrial respiratory chain,which is an important part of the tricarboxylic acid cycle.Pydiflumetofen is the latest generation of SDHIs fungicides with a broad spectrum of fungal inhibition.Fusarium verticillioides is sensitive to pydiflumetofen,but the risk of resistance to this agent is not yet known,so it is important to investigate this mechanism for proper application in the field and for safety in production.（1）Using 189 strains of Fusarium verticillioides isolated from eleven areas collected from five provinces across the country from 2018 to 2020.A sensitive baseline for pydiflumetofen was established by determining the medium concentration(EC₅₀)of inhibition of mycelial growth by pydiflumetofen,and no resistant strains were found with an average value at 0.0508μg/m L.（2）More than 50 resistant strains were obtained by using UV to induce resistant strains of pydiflumetofen.The genes encoding the succinate dehydrogenase（SDH）subunit of the resistant strains were sequenced and compared,and four strains with point mutation SdhC1^A83Vwere found in the C1 subunit of SDH subunit（SdhC1）and 17 strains with point mutation SdhB^S202Fand one strain with point mutation SdhB^W205Gin the B subunit（SdhB）,with three different amino acid changes.（3）The RF values（resistance multiplicity）and resistance inheritance of resistant strains were measured,and the test results showed that the RF values of the resistant strains with point mutation SdhC1^A83V（three randomly selected strains）were all greater than 1000,indicating that such mutations cause high resistance;one of the resistant strains with point mutation SdhB^S202F（three randomly selected strains）had RF>1000 and two had RF<10;point mutation SdhB^W205Gresistant strain（only one strain was obtained）RF<10;RF values of resistant 8 generations strains were measured after 8 generations of transfer,and there was no significant difference in RF values compared to the initial resistant strain,indicating that the resistance of all resistant strains can be stably inherited.（4）The biological phenotypes of the resistant strains were determined,as well as the suitability of fumonisin B1 production and pathogenicity,and the test results showed that there was no significant difference in the growth rate,conidial production and fumonisin B1 production of the resistant strain with point mutation SdhC1^A83Vcompared with the wild type 7600;the resistant strain with point mutation SdhB^S202Fonly had a lower conidial The resistant strain with the point mutation SdhB^S202Fhad lower conidial production than the wild type strain;the resistant strain with the point mutation SdhB^W205Ghad significantly lower growth rate,conidial production,and fumonisin B1 production than the wild type strain;all the resistant strains had denser marginal mycelium compared to the wild type7600.（5）The susceptibility of the above resistant strains to abiotic stress factors was studied,and the results showed that the resistant strains with point mutations SdhC1^A83V,SdhB^S202F,SdhB^W205Gwere more sensitive to osmotic stress（KCl,NaCl）,metal ion stress（LiCl,CaCl₂）,oxidative stress（H₂O₂）,cell wall stress（CaCl₂）,and cell wall stress（CaCl₂）than the wild type 7600),cell wall stress（Congo Red）,and 32℃ high temperature environment were not significantly different;after 60 days of growth in 4℃ low temperature environment,they could grow normally and there was no significant change in the inhibition rate when transferred again.（6）Using the same and different types of fungicides to explore the interactive resistance,the results showed that the occurrence of point mutations SdhC1^A83V,SdhB^S202F,SdhBW205G to pydiflumetofen resistant strains and（Benzimidazole）fungicide carbendazim,（DMI）fungicide tebuconazole was not found interactive resistance;with the same fluopyram existed No cross-resistance was found with the fungicides carbendazim and tebuconazole.（7）Inoculation of spores of the resistant strain on maize was studied for pathogenicity.The results showed that the pathogenicity of the resistant strains with point mutations SdhC1^A83V,SdhB^S202Fand SdhB^W205Gdid not change compared with the wild type.