Inhibitory Effect Of Active Substances From Amaranthus Tricolor Against Acidovorax Avenae Subsp. Citrulli

Watermelon bacterial fruit blotch (BFB Acidovorax avenae subsp. citrulli) is one of the restrict entry quarantine diseases in China. In recent years, this disease has erupted in succession in many parts of China and the watermelon planting industry has suffered huge economic losses. So far, people failed to find an effective method of controlling Watermelon bacterial fruit blotch. Based on previous studies, using three-colored amaranth as a test material and extracted the active substances from three-colored amaranth to control BFB. Studies include:①the inhibitory mechanism of active substances controlling Acidovorax avenae subsp. citrulli;②the germinations of active substances acting on contaminated seeds;③the physical and chemical properties of the active substances. The main results are as follows:(1) Extracting three-colored amaranth with ethanol, water, acetone and ethyl acetate, the inhibitory effect of active substances which were extracted with ethyl acetatet is especially remarkable; the inhibitory effect of active substances which were extracted with ethanol was not significant; active substances which were extracted with acetone and water had no inhibitory effect. Amaranth antibacterial active substances present in the roots, stems, leaves. However, the inhibitory effect among them reached a very significant difference. The antibacterial substances of leaves are the highest and the inhibition rate reached45.4%; the second is the root, the inhibition rate reached30.4%; the inhibition rate of stem reached22.3%. the pastes of three-colored amaranth active substances which were extracted with ethyl acetatet were dissolved with Ethanol, water and different concentrations of ethanol, the paste which was dissolved with ethanol had a significant inhibitory effect, the inhibition rate was48.6%:the paste which was dissolved with water had the worst inhibitory effect, the inhibition rate was only9.1%; the inhibitory effect of the paste which was dissolved with16.6ethanol was significantly better than50%、25%、12.5%. Toxicity regression equation for active substances on Acidovorax citrulli as follows:y=1.6675x+1.4153, EC50=141.1mg/mL.(2) Followed by the inhibition effects of active substances against Acidovorax avenae subsp. citrulli:Slowed the pathogen growth rate of Acidovorax avenae subsp. citrulli; reduced the utilization of the sugar during the growth. The protein content of bacteria solution with active substances had increased, while the protein content of bacteria solution without active substances had reduced. The result of scanning electron microscopy showed that the active substances damaged cell’s structural; the bacteria blurred, had been dissolved, broken and died gradually. Different concentrations of active substances affected the enzyme activities of Acidovorax avenae subsp. citrulli POD、 CAT、SDH、 MDA. The higher concentrations of active substances are the lower POD, CAT, SDH, MDA activities are. And the changes of the four enzymes all showed very significant differences.(3) The active substances had a certain influence on the germination of seeds contaminated. The germination potential rates of sterile seeds. contaminated seeds、 contaminated seeds treated with ethano、 contaminated seeds treated with active substances were87.3%、47.2%、48.0%、60.0%respectively and The germination rates were93.3%、44.7%、58.7%、90.0%respectively. The germination potential rates and germination rates of contaminated seeds treated by active substances and healthy seeds were almost the same, there were no significant differences. But there were significant differences in the germination potential rates and germination rates between contaminated seeds treated by active substances and contaminated seeds. The germination potential rates of contaminated seeds which treated by low、 medium, high concentrations of active substances were64.7%.51.3%、46.0%respectively and The germination rates were90.7%、62.0%、49.3%respectively. These indicate that the active substances had a high activity.(4) Adjusting active substances pHto3、5、7、9、11.We found that the active substances had inhibitory effect on Acidovorax avenae subsp. citrulli. when the pH adjusted to3,5,7, the inhibition rates were32.7%、30.9%、17.0%respectively. When we adjusted active substances pH to9and11, the extract had no inhibitory effect. The antibacterial active substances have a good thermal stability; the activity did not change in50℃-80℃and the inhibition rate remained at36.0%. When the temperature reaches90℃inhibitory effect of the active substances significantly reduced; when the temperature reached100℃the active substances almost had no significant inhibitory effect. Amaranth antibacterial active substances with high stability under UV irradiation; under different lengths of time to ultraviolet radiation, the inhibition rate remained at around38.0%.the effects of active substances with salt and sugar compared with extracts active substances without salt and sugar was not obvious; the inhibition rate of active substances with salt remained at around33.0%; the inhibition rate of active substances with sugar remained at around36.0%. These indicate that the active substances had stable physicochemical properties The above results showed that:the active substances have a good inhibition in low concentration and the active substances have stable physicochemical properties. Therefore, three-colored amaranth has the potential to develop as a botanical pesticide, and has great promotion and application value.