Evolution Of Azoxystrobin And Dimethomorph Resistance In Potato Pathogen Phytophthora Infestans

Phytophthora infestans is one of the most devastating pathogen that causes late blight disease of potato and tomato worldwide.Research on the evolution of P.infestans resistance against fungicide is limited in this era.In this study,two genotypes A1 and B1 were selected for studies on the evolution of resistance to azoxystrobin,a Qol site fungicide and dimethomorph that is carboxylic acid amide(CAA)fungicide.Two sensitive cultivars Favourita(FV)and Bintje(BJ)were selected for aggressiveness test of P.infestans isolates.Average initial EC50 of both isolates to azoxystrobin(AZO)and dimethomorph(DMM)was 0.13(±0.02)and 0.19(±0.01)μg/ml respectively.The EC50 of both fungicides was selected for initial treatment of isolates.The isolates were passaged on a fresh medium each week for one year,with increasing concentration at 0.1-2 and 0.2-2 μg/ml for DMM and AZO respectively.After one-year pathogens were retrieved on rye-B agar medium(RBAM)to assess the sensitivity and aggressiveness.The EC50 for isolates treated and untreated progenies for each transfer of AZO fungicide was 0.14-0.16 and 0.07-0.6 μg/ml,respectively.The EC50 for isolates treated and untreated progenies for each transfer of DMM fungicide was 0.12-0.2 and 0.10-0.63μg/ml,respectively.The ranges of resistance factors(RF)for each transfer to DMM and AZ were 0.82-5.28 and 0.46-4.38 respectively.The results indicate that adaptation in fungicide treated progenies to DMM and AZO.The aggressiveness of treated and untreated isolates was measured by the percentage of leaf area covered by lesion(PLACL)on both potato cultivars.The aggressiveness of A1 and B1 parental isolates was weaker on FV but stronger on BJ,compared to DMM fungicide treated progenies.The aggressiveness of A1 parental isolates was higher on FV and BJ leaves,in contrary,aggressiveness of B1 parental isolates were higher on FV leaves but smaller on BJ leaves as compared to progenies of A1 and B1 those treated with AZO fungicide.It was concluded that tolerance in progenies of both isolates to both fungicides was negatively correlated with aggressiveness on Bintje.It was observed that aggressiveness on FV leaves was positively correlated to AZO tolerance in progenies of A1 isolates while negatively correlated to progenies of B1 isolates.Additionally,aggressiveness on FV was negatively correlated to DMM tolerance in progenies of A1 isolates but positively correlated to progenies of the B1 isolate.Pleiotropic expression in,sensitivity and aggressiveness may be owing to the different genetic background of pathogens,host and fungicide mode of action.No mutation was found in cellulose synthase 3(PicesA3)gene in DMM fungicide treated progenies compared to parental isolates.Overall,the conclusion of this study shows that low resistant risk of P.infestans to dimethomorph and azoxystrobin fungicides.