Monitoring And Risk Resistance Assessment Of Colletotrichum Panacicola From Ginseng To Difenoconazole And Tebuconazole In Northeast China

Ginseng antharacnose caused by Colletotrichum panacicola is one of the diseases that cause seriously damage to ginseng in recent years.The occurrence of this disease leads to the decline of yield and quality of ginseng,which causes great economic losses to ginseng production.Chemical control is the main control measure for this disease,with the increasing dosage and frequency of application,not only accompany with the fungicide-resistance of pathogens risk but also a series of problems such as environmental pollution.Difenoconazole and tebuconazole are commonly used special fungicides against all kinds of anthracnose in crop production.However,the fungicide-resistance of C.panacicola to difenoconazole and tebuconazole is not very clear.Therefore,the sensitivity of C.panacicola to the two fungicides was carried out and sensitivity baselines were established,fungicide-resistance levels of C.panacicola to two fungicides,and the fungicide-resistance risk assenment of the two fungicides in Jilin and Liaoning province were evaluated and the cross resistances between these two fungicides and other five fungicides were determined,so that to provide scientific basis for the prevention and control of antharacnose on Panax ginseng and the mitigation of fungicide-resistance generation for these two fungicides.The results of this study are mainly as follows:1.The sensitivity of 109 strains of C.panacicola isolated from 2019 and 2021 in Northeast China to difenoconazole and tebuconazole were determined by mycelial growth rate method.The sensitivity baselines were established according to the principle that the frequency of population sensitivity of strains accorded with normal distribution.The sensitivity baseline of C.panacicola to difenoconazole and tebuconazole were 0.4044±0.1996μg/m L and 0.1717±0.0045μg/m L,respectively.The C.panacicola populations from different geographical sources have different sensitivity to the two fungicides.2.The MIC of difenoconazole and tebuconazole to C.panacicola were determined and the resistance of field strains to both fungicides were monitored,and evaluated for the resistance level of strains in each region according to the criterion for resistance risk assement established by Xian Fei.MIC of difenoconazole and tebuconazole against C.panacicola were determined as 200μg/m L and 80μg/m L based on the growth ability of 109 sensitive strains growing on different concentrations of fungicide-containing plates.Through monitoring the resistance of 435 strains of C.panacicola in Jiling and Liaoning province,the resistance frequencies of C.panacicola to difenoconazole was 0.22%.Only one low resistance strain to difenoconazole was found;the resistance frequencies to tebuconazole was zero,and the resistance strains were not found.3.Seven mederate resistant mutants to difenoconazole and one low resistance mutant,two mederate resistant mutants to tebuconazole were generated by chemical induced method,which can be inherited stably.The resistance risk assements of C.panacicola to these two fungicides was evaluated by comparing the biological characters such as mycelial growth rate,sporulation capacity,spore germination rate,mycelial dry weight,pathogenicity,temperature,Na Cl,glucose and p H.The biocompatibility fitness of the resistance mutants to difenoconazole and tebuconazole are lower than that of their parental stains,which showed that difenoconazole and tebuconazole can currently be recommended to control C.panacicola with a low risk of resistance,and it may not become a dominant strain in the field.In order to avoid the development of resisitant strains into field dominant strains under the pressure of high concentration of fungicide selection,the rational use of difenoconazole and tebuconazole should be paid attention to in production.4.The EC₅₀values from different fungicides against C.panacicola were obtained by testing the sensitivity of C.panacicola to difenoconazole,tebuconazole and other five fungicides including azoxystrobin,pyraclostrobin,trifloxystrobin,propiconazole and prochloraz.The lg EC₅₀values of difenoconazole or tebuconazole were taken as the abscissa,and the lg EC₅₀values of one of other five fungicides were taken as the ordinate,and the regression equations were established.Spearman correlation analysis showed that there was no positive cross resistance between difenoconazole and other three fungicides including azoxystrobin,pyraclostrobin and enoxastrobin,but there was positive cross resistance with enoxastrobin and prochloraz;there was no positive cross resistance between tebuconazole and other three fungicides including azoxystrobin,pyraclostrobin,and enoxastrobin,but there was positive cross resistance with enoxastrobin and prochloraz.When the resistant strains of difenoconazole and tebuconazole appeared in the field,it was not suitable to combine or alternate with azoxystrobin,pyraclostrobin and trifloxystrobin to control or slow down the resistance.5.The test results from point mutation detection of target gene CYP51A and CYP51B in difenoconazole-resistant and tebuconazole-resistant mutants by squence alignment analysis,it was found that no mutation site was detectedin the CYP51A and CYP51B gene in difenoconazole and tebuconazole resistant mutants of C.panacicola.Therefore,it is speculated that the fungicide-resistance of C.panacicola populations resistant to the difenoconazole and tebuconazole may not be related to the point mutation of the target gene.