| Gallic acid (GA), which has anti-bacteria, anti-oxidation and anti-cancer effects, is a phenolic compound in plants. We found that GA has a relatively strong inhibitory effect on Xanthomonas oryzae pv. oryzicola in our early experiments. But, there were not any reports on the antibacterial mechanism of gallic acid against X. oryzae pv. Oryzicola and its control effect on rice bacterial leaf streak. In this dissertation, the effects of GA on the cell structure and function, energy generation and metabolism substance biosynthesis of X. oryzae pv. Oryzicola and the time of residue and inhibitory effect on the pathogens of GA on the leaves of rice were tested. Meanwhile, the control effect of GA on rice bacterial leaf streak was also tested. The main results are as follows:1. The minimum inhibition concentration (MIC) of GA agaisnt X. oryzae pv. oryzicola was tested by using liquid dilution method. The result showed that MIC was 200μg/mLwhen the bacteria concentration at 107 CFU.2. The morphological structure of X. oryzae pv. oryzicola treated with 200μg/mL GA under scanning electron microscope and transmission electron microscopy showed that the morphology of the pathogens distorted, with a coarse surface and severely damaged cell wall. There were clear dents and vesicular irregular heaves on the cell. To analyze the damage level of the cell membrane after treatment with GA, the conductivity of the pathogen culture liquid, the activity of lactate dehydrogenase and the changes of the content of macromolecular substances in the cell were tested. The results showed that, afer treatment with GA, electrolyte and macromolecules in the cells leaked out, and fluorescence intensity of the cell decreased to 58.24%. Meanwhile, the activity of Lactate dehydrogenase in the cell increased. It indicated that GA not only altered the permeability of cell membrane of X. oryzae pv. oryzicola, but also undermined the integrity of the cell membrane.3. The respiratory inhibition experiment revealed that the respiratory inhibition rate of GA, propanedioic acid, iodoacetic acid and trisodium phosphate were 8.20%,29.22%, 16.74% and 19.94%, respectively.The superpose rate of GA added to propanedioic acid, iodoacetic acid and trisodium phosphat against the respiratory of the pathogen were 11.34%, 21.88% and37.45%, respectively. Because of the lowest superpose rate in the cell treated with GA and propanedioic acid, it indicates that GA might inhibit the tricarboxylic acid cycle of bacteria. After GA treatment of 400μg/mL, the amount of pyruvate in the pathogen culture liquid was 2 times higher than that of the control. Meanwhile, GA could inhibit the activity of some ezymes related with cell respiratory. The malate dehydrogenase, succinate dehydrogenase and NADH oxidase of the bacteria 2h after treatment with GA of 400μg/mL were obviously inhibited, the control group wrer 2-3 times as high as that of the drug group.4. GA did no effect on the activity of extracellular hydrolytic enzyme of the pathogen, but it could obviously decrease the activity of cellulase, pectinase and protease. Isotope labeling incorporation method was applied to measure the variation of nucleic acid content and protein biosynthesis in the pathogen before and after treatment with GA. The results showed that when baterial cell treated with GA of 400μg/mL, the incorporation inhibition rate of DNA, RNA and protein were 51.48%,37.09%,62.38% respectively., which means that GA could obviously restrain the biosynthesis of nucleic acid and protein of the pathogen.5. High performance liquid chromatography (HPLC) was used to detect the residue of GA in (on) the rice leaf after treatment with GA. The results showed that GA could not infiltrate into rice leaf, and only resided on the surface of the leaf. The residue time of GA on rice leaf was tested in greenhouse, and found that the higher the concentration was, the longer the residue time gave. The residue time of GA on the leaf at the concentration of 100 mg/L was 16 days, while that of GA at the concentration of 200 mg/L was 24 days, and that of GA at the concentration of 400 mg/L was 28 days. By in vivo inoculation of pathogens, the effective inhibitory time of GA against the pathogen in greenhouse was 16 days.6. The half effective concentration (EC50) of GA on the pathogen was 50.223μg/mL, and that of 75% mancozeb WG,77% cupric hydroxide WG,27.12% copper dihydroxosulphate SE,250g/L tebuconazole EC and 20% thiodiazole-copper SE was 0.0451μg/mL, 0.3637μg/mL,5.4217μg/mL,7.9336μg/mL and 34.605μg/mL, respectively. The half effective concentration (ECso) of mixture of GA and thiodiazole-copper at the proportion of 1:1 on the pathogen was 26.9672μg/mL.7. In the rice plants treatment with GA before inoculation with bacteria, the control efficacy of GA at the concentration of 200mg/L,300mg/L,400mg/L and the mixture of GA and thiodiazole-copper at the concentration of 100mg/L,200mg/L,300mg/L were 65.06%,67.75%,70.92%,67.37%,71.34% and 75.45%, respectively. In the rice plants treated with GA after inoculation with bacteria, the control efficacy of GA at the concentration of 200mg/L,300mg/L,400mg/L and the mixture of GA and thiodiazole-copper at the concentration of 100mg/L,200mg/L,300mg/L were 63.98%,66.31%,68.08%,64.59%, 67.22% and 71.82%, respectively, the preventive effectiveness rates of the mixture of GA and thiodiazole-copper at the concentration of 300mg/L was the best in all of treatments, but its control efficacy was not difference with that of thiodiazole copper, In field experiments, the control efficacy of GA at the concentration of 200mg/L,300mg/L,400mg/L and the mixture of GA and thiodiazole-copper at the concentration of 100mg/L,200mg/L, 300mg/L were 57.76%,60.42%,65.13%,57.64%,63.87% and 67.66%, respectively. The control efficacy of the mixture of GA and thiodiazole-copper at the concentration of 300mg/L was the best in all of treatments, but its control efficacy was not difference with that of thiodiazole copper and bismerthiazol. |
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