Antimicrobial Spectrum Determination And Resistance Risk Assessment Of Novei Succinate Dehydrogenase Inhibitor Fungicides

Botrytis cinerea、Sclerotinia sclerotiorum、Fusarium fujikuroi、Corynespora cassiicola、Fusarium graminearum and Fusarium pseudograminearum are important crop pathogenic fungi in China,which not only cause serious yield loss to crops,but also make a serious threat to the quality of agricultural products.For a long time,fungicides have always been the most effective emergency measure to control plant disease.However,with the extension of the fungicides time and the increase of fungicides dose,pathogens will develop a certain level of resistance to modern selective chemical fungicides under the pressure of long-term chemical selection,resulting in the reduction or loss of disease control effectiveness.People try to improve the disease control efficiency by increasing the dosage and frequency of fungicides use,which leads to excessive pesticide residues and aggravated ecological environmental pollution.Therefore,in order to control fungicides resistance,people develop new high-activity fungicides on the one hand,and develop the application technology of existing fungicides on the one hand.After the ergosterol biosynthesis inhibitors and methoxyacrylate fungicides,succinate dehydrogenase inhibitors（SDHIs）have the largest market share and the broadest market prospects,with a novel site of action and broad antifungal spectrum.It affects the respiratory chain electron transfer system of fungi by acting on protein complexⅡ,and hinders its energy metabolism,thereby inhibiting the growth of fungi,leading to their death.In this study,five new succinate dehydrogenase fungicides,pyraziflumid,flubeneteram,penthiopyrad,isopyrazam,and fluindapyr are selected to determine its antifungal activity against six pathogens,S.sclerotiorum,B.cinerea,F.fujikuroi,F.pseudograminearum,F.graminearum,and C.cassiicola,using the mycelial growth rate method.The baseline sensitivity of S.sclerotiorum and B.cinerea to flufenoxamide and bifenazone were established respectively,and the risk of resistance to flufenoxamide was evaluated.The results were as follows:（1）The mean EC₅₀values of pyraziflumid against B.cinerea,S.sclerotiorum,F.fujikuroi,F.graminearum and F.pseudograminearum were about 0.0472μg/m L,0.0186μg/m L,3.0749μg/m L,99.08μg/m L and more than 100μg/m L respectively.In summary,pyraziflumid had excellent control efficacy on the mycelial growth of B.cinerea and S.sclerotiorum,and also inhibited the mycelial growth of C.cassiicola and F.fujikuroi,but it had no control efficacy on the mycelial growth of F.pseudograminearum and F.graminearum.（2）The mean EC₅₀values of flubeneteram against B.cinerea,S.sclerotiorum,F.fujikuroi,F.graminearum and F.pseudograminearum were about 0.1492μg/m L,0.3583μg/m L,0.8646μg/m L,26.84μg/m L and 62.6016μg/m L respectively.In general,flubeneteram had excellent control efficacy on the mycelial growth of B.cinerea,S.sclerotiorum and F.fujikuroi,and also inhibited the mycelial growth of C.cassiicola,but the inhibitory effect on the mycelial growth of F.pseudograminearum and F.graminearum is relatively poor.（3）The mean EC₅₀values of penthiopyrad against B.cinerea,S.sclerotiorum and F.fujikuroi were about 1.0554μg/m L,0.2882μg/m L and 0.8159μg/m L respectively.The mean EC₅₀values of penthiopyrad against F.graminearum and F.pseudograminearum were greater than 100μg/m L.Overall,penthiopyrad had excellent control efficacy on the mycelial growth of B.cinerea,S.sclerotiorum and F.fujikuroi,and also inhibited the mycelial growth of C.cassiicola.But it had no control efficacy on the mycelial growth of F.pseudograminearum and F.graminearum.（4）The mean EC₅₀values of isopyrazam against B.cinerea,S.sclerotiorum,F.fujikuroi,F.graminearum and F.pseudograminearum were about 0.5053μg/m L,0.1907μg/m L,0.1469μg/m L,28.60μg/m L and 36.96μg/m L respectively.In summary,isopyrazam had excellent control efficacy on the mycelial growth of B.cinerea,S.sclerotiorum and F.fujikuroi,and also had a certain inhibitory effect on the mycelial growth of C.cassiicola,but the inhibitory effect on the mycelial growth of F.pseudograminearum and F.graminearum is relatively poor.（5）The mean EC₅₀values of fluindapyr against B.cinerea,S.sclerotiorum and F.fujikuroi were about 2.0568μg/m L,0.5664μg/m L and 21.10μg/m L respectively.The mean EC₅₀values of penthiopyrad against F.graminearum and F.pseudograminearum were greater than 100μg/m L.Overall,fluindapyr had the best control effect on the mycelial growth of S.sclerotiorum,followed by B.cinerea.The inhibitory effect on the mycelial growth of F.fujikuroi and C.cassiicola was poor,and fluindapyr almost had no mycelial growth inhibition effect of F.pseudograminearum and F.graminearum.（6）The mycelial growth rate method was used to determine the sensitivity of 98 S.sclerotiorum to pyraziflumid.The EC₅₀values ranged from 0.0007 to 0.0845μg/m L,with the means EC₅₀value of 0.0179±0.0174μg/m L.The sensitivity of 115 S.sclerotiorum to flubeneteram was determined.The EC₅₀values ranged from 0.0030 to 2.5378μg/m L,with the mean EC₅₀value of 0.4122±0.6329μg/m L.The sensitivity of 113 B.cinerea to flubeneteram was determined.The EC₅₀values ranged from 0.2346 to 7.4175μg/m L,with the mean EC₅₀value of 2.2536±1.6107μg/m L.The sensitivity of 97 B.cinerea to pyraziflumid was determined.The EC₅₀values ranged from 0.0371 to 0.9903μg/m L,with the mean EC₅₀value of 0.3058±0.2095μg/m L.（7）Nine flubeneteram-resistant mutants were obtained by chemical taming with the resistance factor（RF value）ranged from 7 to 39μg/m L.The mycelial growth and sclerotinia production capacity of the flubeneteram-resistant mutants obtained by the chemical taming of the agent were significantly reduced compared with the parent strains.In addition,flubeneteram had good protective and curative activities on the detached oilseed rape leaves,and the protective activity is greater than curative activity.