| This paper investigated the safety evaluations of tebuconazole and difenoconazole treatments on maize seedlings and the control effects of these two chemicals on maize head smut by applying as seed treatments. In the chilling stress treatment, effects of these two chemicals on maize emergence rates and seedlings development were analysed, then stability and safety of these two chemicals were got. This study set up a fast and convenient analysis methods of tebuconazole residues in maize plant, to analyse the dynamic distribution of this chemical in maize seedlings treated in chilling stress, the results are as follows.1. Effects of seed-immersion method of two chemicals on emergence rates and seedling developments were studied. The results showed that the emergence rates of maize were not affected using different concentrations of tebuconazole and difenoconazole; but the plant height of maize seedlings were inhibited and the height of maize seedlings treated with tebuconzaole; the contents of chlorophyll and soluble sugar were significantly increased in maize seedlings treated with lower than 300μg mL-1 tebuconazole. Compared with tebuconazole treatment, the inhibition of maize seedlings height were showed when the difenoconazole concentration was higher than 300μg mL-1, the effects of difenoconazole on seedlings development were more beneficial than tebuconzaole, and the respiration of maize seedling roots were enhanced treated with difenoconazole. All above results indicated that the safety of maize seedlings development treated with difenoconazole was better than tebuconazole.2.Tebuconazole and difenoconazole applied as seed treatments at various rates on maize, the head smuts were effectively controlled by field results, the effects to control the diseases could reach higher than 70%, and the maize yields increased. The recommended dosage of difenoconazole seed coating was 0.30 g a.i/kg,and tebuconazole was 0.24 g a.i/kg, and the better results were got.3. In order to study the effects of seed treatment on the emergence of maize seeds and the growth of maize seedlings at chilling stress, active ingredient coated maize seeds at different dosage were chilling stressed, using optimum temperature (25℃/20℃, day/night) as control. At 25℃/20℃,the seed treatment of tebuconazole and difenoconazole could improve the emergence of maize seeds, increase the contents of chlorophyll in the seedlings. and have no negative effect on seedling height and fresh weight. But at chilling temperature 17℃/6℃,15℃/0℃,10℃/0℃, the seed treatment of tebuconazole and difenoconazole could inhibit the emergence of maize seeds and the development of seedlings. Deterioration of peroxidation to membrain lipids and degradation of chloroplasts induced by chilling stress were observed in seedlings that seed-coated by tebuconazole and difenoconazole. The results showed that treatment of difenoconazole was relatively safer than tebuconazole to maize seeds because difenoconazole could inhibit the leakage of electrolytes from leaves,but tebuconazole can worsened the leakage of electrolytes. Moreover, difenoconazole could enhance the respiration of roots which benefit the recovery of chilling stressed seedlings, but tebuconazole inhibited the respiration instead.4. The dynamic distribution of tebuconazole in plant maize seedlings indicated that the distribution contents of tebuconazole in the whole maize plant,seed coat, stem and leaf / bud, roots in chilling stress were higher than in the ambient temperature; the degradation rate of tebuconazole in maize seedlings in chilling stress was significantly lower than in ambient temperature treatment. By determination of tebuconazole contents in the seed coat of maize, leaves and stems / shoots, roots ,the results showed that the concentration of tebuconazole was largest during germ and radicle formation (before tiller appearance), this concentration might be closely related to the regulation of tebuconazole on maize seedlings growth in the late.
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