Inhibitory Effects Of Propiconazole On Sclerotinia Sclerotiorum And Penicillium Digitatum

Sclerotinia sclerotiorum and Penicillium digitatum are two devastating necrotrophic plant pathogenic fungi.S.sclerotiorum causes Sclerotinia stem rot?SSR?disease on oilseed rape,peanut and soybean plants,and P.digitatum causes green mold disease on citrus fruits.At present,propiconazole has been registered in China as a mixture for the control of SSR,but has not yet been registered for the control of green mold disease.This dissertation focused on the biological activities and physiological effects of propiconazole on S.sclerotiorum and P.digitatum.These studies have important implications for the judicious application of propiconazole in controlling SSR and green mold disease.Relative sensitive baseline of S.sclerotiorum to propiconazole was established by measuring the effective concentration causing 50%mycelial growth inhibition(EC₅₀value)of propiconazole for isolates collected in 2008?N=75?and 2014?N=75?.The frequency distributions of the EC₅₀ values for isolates collected in 2008 and 2014 fitted normal distribution?P=0.119 and 0.502,respectively?.The mean EC₅₀ values for isolates collected in 2008 and 2014 were 0.338±0.174?g/mL?mean±standard deviation,SD?and 0.315±0.135?g/mL?mean±SD?,respectively.There was no significant difference?P=0.375?in EC₅₀ values between 2008 and 2014.The preventive efficacy of 40?g/mL propiconazole against SSR on potted rapeseed was 82.4%,and the curative efficacy of 80?g/mL propiconazole was 50.7%.Light microscopic observations showed that propiconazole caused hyphal tips to branch more and hyphal length to become shorter between two adjacent septa.Propiconazole significantly?P<0.05?increased mycelial cell membrane permeability and mannan content of S.sclerotiorum mycelia.The frequency distributions of the natural logarithms of EC₅₀ values of propiconazole against P.digitatum for 118 isolates indicated that 18 isolates were resistant to propiconazole.The frequency of propiconazole resistance was 15.25%,and resistance ratios ranged from 2.7 to 6.5.The mean EC₅₀ values for isolates relatively sensitive to propiconazole was 0.104±0.039?g/mL?mean±SD?.There was a positive correlation?R²=0.7537,P<0.001?in EC₅₀ values of P.digitatum between propiconazole and imazalil.The control efficacies of 200 and 400?g/mL propiconazole against green mold were 63.1%and 84.3%,respectively.Citrus fruits dipped in propiconazole at 40 and 100?g/mL produced significantly fewer?P<0.05?conidia and the conidia were less pathogenic.Studies with propidium iodide showed the membrane integrity was damaged for 25.6%of conidia produced on PDA amended with 0.1?g/mL propiconazole.Fluorescence microscopy observations of P.digitatum conidia stained with 2,7-dichlorofluorescin showed that propiconazole induced the generation of intracellular reactive oxygen species?ROS?.Transmission electron microscopy observation showed that the mycelial cell wall became thicker for mycelia grown on PDA amended with 0.05?g/mL propiconazole.Compared with the propiconazole-sensitive isolates HBWH-22(EC₅₀=0.049?g/mL)and HBWH-26(EC₅₀=0.051?g/mL),no mutation or repeat sequence insertion was found in the sequence of the CYP51 gene of the two propiconazole-resistant isolates JXGZ-2(EC₅₀=0.429?g/mL)and JXGZ-179(EC₅₀=0.675?g/mL),but the relative expression levels of the CYP51 gene were 1.57?P=0.029?and 1.63-fold?P=0.007?higher,respectively,than the average expression level of the two sensitive isolates.