Effect Of Chiral Triazole Fungicide Tebuconazoleand Difenoconazoleon Growth And Production Of FB₁ By Fusarium

Fusarium proliferatumis an important plant pathogen that caused seedling blight,stalk rot,and ear rot.During infection,F.proliferatum producesecondary metabolities,such as fumonsins B₁（FB₁）,that pose a serious threat to human and animal health.Triazole fungicides are widely used as the ergosterol-biosynthesis-inhibiting（EBI）fungicidestokillharmfulbacteria.Manytriazolefungicidesareof complex structure and chirality,which always possess one or two chiral centers,it can exist in two or four stereoiso meric forms.The raceme and enantiomers are identical in chemical structural formula but different in stereostructure and optical rotation performance,resulted to differ in stereoselective toxicity,the processes of absorption,distributionand degradation in organisms and environment.Now the effects of enantiomers on the output of mycotoxins by pathogens with respect to enantioselectivityha ve received limited attention.Thus,in the present study,the enantiomers of tebuconazoleand difenoconazole were used to evaluate the occurrence of enantioselectivityat different environmental factorson（i）growth rate,（ii）fumonisin production and（iii）the expression of FUMsgene by isolates of F.proliferatum,in order to provide basis for risk assessment of fungicides.The contents was as follows:1.Effect of chiral triazole fungicide tebuconazoleand difenoconazole on growth of F.Proliferatum（AF291057.1）at different temperatures and water potentials were tested by means of mycelium growth rate method,respectively.The EC₅₀concentrationsof（+）-tebuconazole was 6.72-91.07 mg/L,the EC₅₀concentrations of（-）-tebuconazole was0.17-1.31 mg/L,the EC₅₀concentrationsof（±）-tebuconazole was 0.32-8.03 mg/L;At the same culture condition,（+）-tebuconazole was about140.11 times less effective than（-）-tebuconazole.TheEC₅₀concentrationsof（2R,4R）-difenoconazole,（2S,4S）-difenoconazole,（2R,4S）-difenoconazole,（2S,4R）-difenoconazole and the racemate of difenoconazole respectively were 0.50-4.43 mg/L,8.71-74.23 mg/L,0.93-7.98mg/L,1.61-17.29 mg/L and 1.99-4.96 mg/L;At the same culture condition,（2R,4R）-difenoconazole’s activity was the highest,（2S,4S）-difenoconazole’s activity was the lowest,the biggest difference ofsublethal dose was 30.80 times.2.Effect of chiral triazole fungicide tebuconazoleon FB₁ mycotoxin production byF.Proliferatum（AF291057.1）had significant difference at different aw/temperatureregimens.Under the effect of EC₅₀,when the water activity was constant at 0.99,prduction of FB₁under the action of（-）-tebuconazolerespectivelyhad 3.52,4.57,1.54 times more than under the action of（+）-tebuconazole at 25℃,30℃,35℃;When the water activity was constant at 0.97,production of FB₁ under the action of（-）-tebuconazolerespectivelyhad 2.30,1.73times more than under（+）-tebuconazole at 25℃,35℃;When the water activity was constant at 0.95,production of FB₁ under the action of（-）-tebuconazolerespectivelyhad1.14,1.22 times more than under（+）-tebuconazole at 25℃,30℃.Under the same conditions,（-）-tebuconazole was more contributed to the production of FB₁.3.Effect of chiral triazole fungicide difenoconazole on FB₁ mycotoxin production byF.Proliferatum（AF291057.1）had some influenceat different aw/temperatureregimens,butthe diversity was not remarkable.At 25℃,30℃,0.99 a_w and 25℃,0.97 a_w production of FB₁ under the action of（2S,4S）-difenoconazole was lowest,and the effect of（2R,4R）-difenoconazole was exactly the opposite.But under the rest environmental factors,the law was not obvious.4.Effects of chiral triazole fungicide tebuconazole on FUM1,FUM6,FUM19 genes expression in F.proliferatum at different temperatures and water potentials were tested by RT-PCR.Under the different environmental factors,relativeFUM1,FUM6 and FUM19genes expression of F.proliferatumwere lower under the action of（+）-tebuconazole than under the action of（-）-tebuconazole,which performanced the same change trend with the production of FB_1.5.Effects of chiral triazole fungicide difenoconazole on FUM1,FUM6,FUM19 genes expression in F.proliferatum at different temperatures and water potentialswere tested by RT-PCR.Under the different environmental factors,there was no clear regularity of FUM1,FUM6,FUM19 genes expression under the action of difenoconazole’s enantiomers.FUMsgene expression and fumonisin production was not relevant.