Study On Of The Resistance Of Puccinia Striiformis F.sp.Tritici To Triadimefon In Six Provinces Of China

As a major disease of wheat,wheat stripe rust caused by Puccinia striiformis f.sp.tritici(Pst),occurs widely in the wheat plantations all around the world.Triadimefon is primary fungicide for chemically controlling wheat stripe rust.In China,due to the longterm large-scale and single application of triadimefon since 1980 s,Pst may have become resistant to triadimefon.However,relevant resistance has never been tested accurately or systematically under the laboratory environment.In this study,fungicide resistance test of120 Pst isolates from six provinces was determined,which were collected from the main oversummer and winter producing areas.Meanwhile,the triadimefon resistant and sensitive isolates were selected therefrom,and subjected to susceptibility test using other triazole and non-triazole fungicides.Since the conventional triadimefon dosage is no longer sufficient to control the resistant strains,corresponding adjustment is needed regarding the chemical control scheme and specific layout of resistant varieties,so as to effectively control the resistant strains prior to wide spreading.Main results of this study are as follows:1.The triadimefon resistance of 120 Pst isolates from the main oversummer and winter producing areas in six provinces was determined.Some isolates already appeared resistance to triadimefon.The average EC50 values of triadimefon against the isolates were: 0.397μg/ml(Yunnan Province),0.284 μg/ml(Guizhou Province),0.475 μg/ml(Hubei Province),2.374 μg/ml(Sichuan Province),1.771 μg/ml(Gansu Province),and 3.369 μg/ml(Qinghai Province).For oversummer areas(including three provinces),the average EC50 was 2.411μg/ml,while that for the winter producing areas(including another three provinces)was0.385 μg/ml.A total of 36 resistant isolates were found,with an overall resistance frequency of 30%.The resistance frequency was 60% for oversummer areas,whereas was 0% for the winter producing areas,revealing an overall higher resistance level in oversummer areas.2.Two triadimefon resistant isolates and two sensitive ones were selected for susceptibility test with five triazole fungicides and two non-triazole fungicides.The tested isolates exhibited considerably higher EC50 for the non-triazoles(prochloraz and azoxystrobin)than the triazole fungicides,and produced distinct cross-resistance to triazole fungicides.The EC50 values of these five triazoles against triadimefon resistant isolates were all higher than the triadimefon sensitive ones.Besides,all the tested isolates exibited the EC50 values for flutriafol,diniconazole and tebuconazole lower than their EC50 values for triadimefon,indicating higher fungicidal efficiencies of flutriafol,diniconazole and tebuconazole than triadimefon.