| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 101 === The southern corn rust of maize (Zea mays L.) caused by Puccinia polysora is a destructive disease of major economic losses in almost maize production areas of the world. Although several fungicides have been found to give good control of the disease, high concern for adverse effects of pesticides on human health and the environment makes the development of alternative methods for disease management an urgent need. The purposes of the study were to evaluate the effect of Eichhornia crassipes (water hyacinth) extract and emulsified plant oils on control of P. polysora. The extracts of E. crassipes showed varied inhibitory effects on spore germination of plant fungal pathogens, however, they all showed significantly effectiveness in inhibiting urediniospore germination and germ tube elongation of P. polysora. The methanol-soluble extract of E. crassipes was concentrated under reducing pressure and further divided into ethyl acetate-, n-butanol- and water-soluble fractions by using liquid-liquid partition. All fractions were concentrated and evaluated their antifungal activity. At a concentration of 100 ppm, ethyl acetate-soluble extract showed significantly effectiveness in inhibiting 96.7% urediniospore germination of P. polysora. To identify the active components, the ethyl acetate-soluble extract was concentrated and subjected to column chromatography with silica gel using n-hexane, ethyl acetate and methanol as eluents with increasing polarity, and activity fraction then subjected to normal phase high performance liquid chromatography using hexane and ethyl acetate as eluents with increasing polarity. Three fractions (EA-06-03-01, -02, -03) were obtained and then tested individually for antifungal activity. The concentration of EA-06-03-03 at 1,000 ppm was found to completely inhibit urediniospore germination of P. polysora. Nuclear magnetic resonance (NMR) analysis of EA-06-03-03 was identified as 4-hydroxybenzaldehyde. In addition, the 6 kinds of plant oils were evenly emulsified by high speed homogenization for control of southern corn rust. Each of emulsified plant oil showed significantly effectiveness in inhibiting germ tube length of urediniospore and pustule formation of P. polysora. At a concentration of 1,000 ppm, sunflower oil was significantly effective in inhibiting 40.5% germ tube length of urediniospores and 66.7% pustule formation of P. polysora. The effectiveness of sunflower oil was increased with increase in concentration. 18-carbon fatty acid compound (C18-FA) was selected from four different carbon chain length of fatty acid compounds by using antifungal activity tests. The C18-FA was able to cause germ tube deformed at 250 ppm, reduce percentage of appressorial formation on stomata of corn leaf surface at 500 ppm, and completely inhibit urediniospore germination at 5,000 ppm. Evaluation for efficacy of 4 kinds of sunflower oil emulsions obtained from mixing with different ratios of C18-FA and sunflower oil on urediniospore germination of P. polysora was conducted. Sunflower oil emulsion (SFOC18605), a mixture of C18-FA and sunflower oil by 5 : 60 ratio (w/v), at a concentration of 100-fold dilution was significantly effective in inhibiting 93-97.1% pustule formation of P. polysora on corn leaf surface. The particle size of sunflower oil emulsion could influence its efficacy on reducing urediniospore germination. Sunflower oil emulsion (SFOC18605) with the particle size of 500 nm at a concentration of 100-fold dilution showed complete inhibition of urediniospore germination of P. polysora, but it didn’t present fungicidal effect. Spraying sunflower oil emulsion (SFOC18605) on corn leaf surface one day prior to inoculation of urediniospores showed the better efficacy on control of southern corn rust than spraying it one day after inoculation. Furthermore, weekly spraying sunflower oil emulsion (SFOC18605) on corn leaf surface for 2 times showed the best efficacy on control of southern corn rust.
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