| In this paper, several quaternary ammonium compounds were selected as research object. In order to ascertain their application potential in the control of vegetable diseases and provide theoretical and practical basis for their actual application, We tested their toxicities on fungi and bacteria, studied the effect of quaternary ammonium compounds on a part of biological characteristics of Botrytis cinerea and Sclerotinia sclerrotium, researched their effect mode and mechanism on pathogens, and also studied their field efficacy on vegetable diseases and the safety evaluation on the growth of tomato and cucumber.The toxicity action of five quaternary ammonium compounds to B. cinerea, Alternaria solani, S. sclerrotium, Fusarium oxysporum and Mycosphaerella melonis was tested by the mycelium growth rate method. The toxicity of five quaternary ammonium compounds to Sphaerotheca fuliginea was tested by spraying fungicides on the seeding cucumber 96 hours after the Sphaerotheca fuliginea spore suspension was inoculated. And the minimal inhibitory concentration method was adopted to evaluate the toxicity of five quaternary ammonium compounds to Pseudomonas solanacearum and Xanthomonas campestris. Dodecyr dimethyl benzyl ammonium chloride and double-stranded quaternary ammonium salt which had high antifungal activity were obtained. The results indicated that the two fungicides both had obvious inhibition activity on mycelial growth. All the EC50 values were under 10μg/mL respectively,which was equal to that of conventional control fungicides or slightly lower than that. EC50 values to S. fuliginea and M. melonis was from 10μg/mL to 20μg/mL. However the toxicity to Fusarium oxysporum was relatively lower than to others with EC50 values were 20～25μg/mL. Comparatively, the toxicity to bacterias was higher than that to fungi. The inhibition activities to X. campestris and P. solanacearum were higher than that of copper acetate and equal to that of streptomycin sulfate with the minimal inhibitory concentration was under 7.5μg/mL. The results of the effect of two fungicides to B. cinerea, S. sclerrotium showed that dodecyr dimethyl benzyl ammonium chloride and double-stranded quaternary ammonium salt had strongly inhibition to mycelium growth and conidia germination. The dry mycelium weight inhibition rate was over 90% and conidia germination inhibition ratereached 100% at the concentration of 20μg/mL. Double-stranded quaternary ammonium salt inhibated the sporulation obviously with the inhibition rate reached 95% at the concentration of 40μg/mL. The sclerotium formation numbers were influenced in different extent. Double-stranded quaternary ammonium salt presented 70% and 50% inhibition rate at the concentration of EC90 to S. sclerrotium and 40μg/mL to B. cinerea, respectively. They had small influence to sclerotium weight and germination.The toxicity stability experiment results indicated that their toxicity were very stable and less influenced by hydrolysis and photolysis.In the study of effect mechanism, the influence of quaternary ammonium compounds on the mycelial growth form, conidia germination form, the cell wall structure of fungi, the permeability of cell membrane, the respiration of mycelial and conidia was observed and tested. And we also discussed the influence of quaternary ammonium compounds on the production of PG, PMG and Cx of B. cinerea. The results indicated that mycelial and conidia growth displayed deformed. After being treated by fungicides at the concentration of 40μg/mL, mycelial obviously became wide, internode became short and expanded, the pots of branches was shrinkable, the intracellular materials was aggregated, the conidia germ tubes became short, wide and expanded, the number of germ tubes was reduced. We also found that the cell wall surface emerged many different ventages by SEM observation. The conductivity of pathogen liquid increased significantly with the time prolonging after being treated by dodecyr dimethyl benzyl ammonium chloride and double-stranded quaternary ammonium salt. It showed that quaternary ammonium compounds could increase the permeability of cell membrane and induced much intracellular electrolytes extravasate from the cell and the fungicides entered into it. At the action of quaternary ammonium compounds, they could induce enzyme activity lost and protein denaturation and the normal physiological and biochemical activity such as the respiration of mycelial and conidia and the production of enzyme were all influenced. During the experiments, we found that the respiration of mycelial enhanced significantly after five minutes being treated by fungicides, and being inhibited and terminated with the time prolonging. The production and activity of PMG and PG were inhibited significantly after 4 days at the concentration of 2.5μg/mL and 5μg/mL respectively. And production and activity of CX were inhibited at the concentration of 5μg/mL. Comparatively, the inhibiton of double-stranded quaternary ammonium salt was much stronger than dodecyr dimethyl benzyl ammonium chloride.Field efficacy and safety appraise were carried in this study. Results showed that 10% dodecyr dimethyl benzyl ammonium chloride AS and 10% double-stranded quaternary ammonium salt AS had excellent efficacy on the control of tomato grey mould, cucumber powdery mildew and cucumber sclerotium disease at the dosage of 60g/hm2～90g/hm2. And the field efficacy was equal to that of procymidone and myclobutanil. The application security on tomato was higher than that on cucumber. The security appraise experiments show that security dosage is less than 100mg/L in cucumber seeding growth period and mild growth period,and security dosage on tomato is less than 200mg/L in grown period in tomato seeding growth period and mild growth period.
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