Study On Resistance Of Some Plant Pathogens To Fungicides

By the method of plate growth rate,the toxicities of carbendazimthiram and azoxystrobin to Pyricularia grisea(Cooke) Sacc,Sclerotinia sclerotiorum(Lib.) de Bary and some other pathogens were bioassayed.The EC₅₀ of carbendazimthiram to Rhizoctonia solani Kuhn,Colletotrichum gloeosporioides(Penz.) Penz.Et.Sacc.S. sclerotiorum,P.grisea and Alternaria solani(E.et M.) Jones et Grout were 0.5321, 1.7136,4.0644,7.1520 and 8.3404 mg/L,respectively.The EC₅₀ of carbendazimthiram to Verticillium dahliae Kleb,Bipolaris maydis(Nisikado et Miyake) Shoem and A. alternate were 21.7142,22.5703,37.5912 mg/L,respectively.The EC₅₀ of azoxystrobin to R.solani,S.selerotiorum,and P.grisea were 0.0190,0.0722 and 0.2261mg/L, respectively.The EC₅₀ of azoxystrobin to V.dahliae and A.alternate were 12.8993 and 54.3598 mg/L,respectively.In the regression equation of carbendazimthiram and azoxystrobin to some pathogens,b value of carbendazimthiram was higher than that of azoxystrobin.The EC₉₅ of azoxystrobin to S.sclerotiorum,B.maydis and A.alternate were higher than those of carbendazimthiram.Selected by carbendazimthiram consecutively for 9 and 12 generations,the resistance ratio of R.solani was 22.12 and 25.24,respectively.While selected by azoxystrobin consecutively for 9 and 12 generations,the resistance ratio was 16.10 and 126.97,respectivelyResults of resistance selection on P.grisea by carbendazimthiram and azoxystrobin showed that the resistance did not increase significantly.Selected S.sclerotiorum by carbendazimthiram and azoxystrobin the life activity declined,the resistance selection could not continue.Preserved the R.solani that was selected for 12 generations,the resistance had reduced after 2 months of preservation.Studies on the biological characters of the R. solani showed that the R.solani had no significant difference with the sensitive strain in the aspect of plate growth rate in different culture media and different temperatures,and in the aspect of the amount of scleratiniose. The EC₅₀ of kresoxim-methyl,difenoconazole and thiram to R.solani were 0.2701. 0.7662 and 5.3925 mg/L,respectively.The Co-toxicity Coefficients of mixture of thiram and triadimefon(1:1,3:1) were 144.0769 and 90.4538,respectively.The resistance of S.sclerotiorum from Sichuan province to carbendazim and dimetachlone was monitored by the method of minimum inhibition concentration(MIC). For the 428 isolations,resistance profile to carbendazim was as following:21.26%was sensitve,26.16%was low resistant,52.57%was high resistant,32.48%was very high resistant.Resistance profile of 369 isolations to dimetachlone was as following:23.58% was low resistant,44.72%was middle resistant,and 31.70%was high resistant.Results of bioassay showed that EC₅₀ of prochloraz,iprodione and diethofencarb to S.sclerotiorum was 0.02,0.04 and 12.8957mg/L,respectively.