Study On The Resistance Of Pythium Aphanidermatum To Matalaxyl

Along with the wide use of systemic fungicides,the issues of fungicide resistance have become increasingly serious.We should attach importance to the problem of decreasing efficiency when using chemical methods.The sensitivities of Pythium aphanidermatum to different fungicides were determined,the resistant risks of metalaxyl-resistant mutants were assessed,and the cross-resistance between matalaxyl and other 3 fungicides were also analyzed.The results are as follows:The sensitivities of the 20 Pythium aphanidermatum strains to metalaxyl and azoxystrobin were determined by the method of colonial growth rate.The results showed that Pythium aphanidermatum strains gathered from different places have different sensitivities to metalaxyl,and one strain was resistant to metalaxyl.Meanwhile,the EC₅₀ value of azoxystrobin ranged from 0.1336μg/ml to 0.7363μg/ml for Pythium aphanidermatum,and the mean EC₅₀ value was 0.3173μg/ml.The distribution of sensitivities showed that no resistant strains be discovered.3 metalaxyl-resistant isolates were obtained from sensitive strain of Pythium aphanidermatum through mutagenesis of metalaxyl and ultraviolet radiation.The resistant factors of isolates obtained by mutagenesis of metalaxyl were 7.72 and 5.38 respectively,and that of isolate obtained by ultraviolet radiation was 21.35.All metalaxyl-resistant isolates were genetically stable.The results of the resistant risk study in vitro showed that metalaxyl-resistant isolate obtained from field had no significant differences with metalaxyl-sensitive isolate in mycelium growth,spore generating and disease index.Although metalaxyl-resistant isolate obtained by ultraviolet radiation had significant differences with metalaxyl-sensitive isolate,it still had relatively high fitness.The results showed that Pythium aphanidermatum have high resistant risk to metalaxyl in vitro,which suggested that we should resort to effective measures when using fungicides so as to prevent fungicide resistance. The results of cross-resistance showed that metalaxyl have no cross-resistance with azoxystrobin, mancozeb,propamocarb.Fungcides having no cross-resistance should be rotated and mixed together when dealing with turf diseases.