Toxicity on different life stages and mode of action of four SBI fungicides against wheat Fusarium graminearum

The toxicities of four sterol biosynthesis inhibitors (SBIs) against different life stages of wheat Fusarium graminearum were determined by using the mycelium growth rate and conidial germination methods, and the mode of action was investigated by field trial. The results of bioassay showed that the sensitivity of different life stages of wheat F.graminearum to four SBIs was different significantly, and the sensitivity from high to low was mycelium growth and sporulation > germ tube growth > conidial germination. The EC50 values of tebuconazole to mycelium growth, sporulation, germ tube growth and conidial germination were 0.686, 0.191, 3.532 and 3.825 μ g/mL, respectively; that of prochloraz were 0.063, 0.305, 0.827 and 36.581 μ g/mL, respectively; that of difenoconazole was 0.873, 3.659, 5.687 and 79.465 μ g/mL, respectively; and that of diniconazole was 1.961, 33.658, 41.881 and 54.986 μ g/mL, respectively. The influence of four SBIs on the morphology of mycelial growth and conidial germination were observed by microscope, four SBIs could cause wheat F.graminearum mycelium abnormal growth, such as the frequent increase of secondary branches, the inhibition of new branch hypha growth at the top, local constriction or enlargement in mycelium, the digestion of germ tube and mycelium. The results of field trial showed that the protective control efficacies of tebuconazole at 100 g a.i./hm2, prochloraz at 200 g a.i./hm2 and difenoconazole at 200 g a.i./hm2 against Fusarium head blight (FHB) disease were 77.15% -79.26%, and the curative control efficacies were 70.64%-70.77%, suggesting the fungicides were effective when using either before or after the invasion of F.graminearum.