| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 103 === The essential oils of pomelo peel and lemon eucalyptus fallen leaves extracted by steam-distillation revealed that the essential oil content of pomelo peel and lemon eucalyptus fallen leaves was 7.2% and 0.74%, respectively. The chemical composition of the two essential oils analyzed by GC-MS showed that the major component of pomelo essential oil was limonene (96.27%) while the major components of lemon eucalyptus essential oil were citronellal (43.69%) and citronellol (17.06%). The antifungal activity of essential oils against 9 plant pathogens was tested by the volatile activity assay. The results of volatile activity assay showed that, 1X pomelo could decrease the growth of Botrytis cinerea GBS3-93 and GBS1-104 to 92.7% and 100.0%, respectively; however, it enhanced the growth of Penicillium digitatum Cmep1-3. Moreover, 10X lemon eucalyptus essential oil could decrease the growth of all tested pathogen at the rate of 96.6%-100.0%. Based on the results of poisoned food assay, which showed that PDA containing 100X pomelo essential oil could decrease the growth of Colletotrichum higginsianum PA01, B. cinerea GBS3-93 and GBS1-104 at the rate of 89.8%, 81.1% and 73.4%, but enhanced the growth of P. digitatum Cmep1-3. In contrast, PDA containing 1,000X lemon eucalyptus essential oil could completely inhibit the growth of most tested pathogens. Furthermore, the spore germination inhibiting tests showed that 50X pomelo essential oil could inhibit over 92.6% spore germination of 5 tested pathogens while facilitate spore germination of P. digitatum Cmep1-3(>65.4%). In contrast, 500X lemon eucalyptus essential oil could inhibit over 80.1% spore germination of all tested pathogens. In this study, adding 100X pomelo essential oil, or 1,000X and 10,000X lemon eucalyptus essential oil to PDA containing 1,000 mg a. i./L azoxystrobin showed enhanced efficacies on inhibiting azoxystrobin resistant and sensitive B. cinerea isolates. This effect could also be observed in the experiment which added 100X pomelo essential oil or 1,000X and 10,000X lemon eucalyptus essential oil into PDA containing different concentrations of azoxystrobin. Phytotoxicity tests of essential oils on cucumber, Chinese cabbage and strawberry leaves showed that 20X pomelo and 100X lemon eucalyptus essential oil would damage the leaves of cucumber and strawberry. The control efficacies of anthracnose of Chinese cabbage and cucumber, and gray mold of strawberry indicated that spraying essential oils 1 hour after inoculation would reduce the disease severities of gray mold on strawberry fruit; however, spraying 50X pomelo and 500X lemon eucalyptus essential oils 1 hour before inoculation increased the disease severity. This study showed that pomelo and lemon eucalyptus essential oils are potential disease-control agents to reduce the risk of fungicide-resistance.
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