| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作系所 === 96 === Litsea cubeba（Lour.）Pers. is a small tree with ginger-spicy fruits in the Lauraceae family. It is native to China, Indonesia, Taiwan and other parts of Southeast Asia. The purposes of this study are to evaluate the antifungal activities and allelopathy potential of essential oils and their major compounds extracted from the leaves, fruits and twigs of L. cubeba. In addition, antioxidant activities were also evaluated for essential oils, hot water extracts and ethanol extracts from the leaves, fruits and twigs. Essential oils were extracted by steam distillation, and their chemical compositions were analyzed by GC/MS. The results of GC/MS showed that the dominated volatile compounds of leaf, fruit and twig essential oil are eucalyptol (33.5%), citral (55.4%) and citronellal (15.4%), respectively. Three types of fungi, wood decay fungi, tree pathogenic fungi and molds were used in the antifungal tests. The results of antifungal tests showed that fruit essential oil processed the strongest antifungal activity against wood decay fungi, tree pathogenic fungi and molds with the ranges of 50% inhibitory concentrations (IC50) of 23.3-113.4 µg/ml, 62.6-508.0 µg/ml and 82.4-179.9 µg/ml, respectively. Citral, the most abundant compound in fruit essential oil, also processed excellent antifungal activities with the ranges of IC50 values of 42.3-75.4 µg/ml, 62.0-162.6 µg/ml and 192.5-318.4 µg/ml against wood decay fungi, tree pathogenic fungi and molds, respectively. Morphological alteration of fungal hyphae treated with citral was examined by Scanning Electron Microscope. Structural alteration of fungal hyphae treated with citral was found, indicating that cell wall permeability might be dramatically changed, resulting in the dysfunction of fungal cells. Allelopathy potential was investigated in vitro by examining the inhibitory effect of essential oils and their compounds on the growth of Brassica chinensis and Lactuca sativa. Results indicated that twig essential oil processed the highest allelopathy potential among three oils, and citronellol effectively inhibited the radical growth of B. chinensis (IC50 < 200 µg/ml) and L. sativa (IC50 < 200 µg/ml). Antioxidant tests were carried out by DPPH free radical scavenging and ferrous ion chelating assays. All three essential oils, hot water extracts and ethanol extracts revealed weak ferrous ion chelating activities, but twig hot water extract and leaf ethanol extract performed excellent DPPH free radical scavenging ability with the 50% effective concentration (EC50) of 18.7 and 25.3 µg/ml, respectively. In this study, L. cubeba demonstrated outstanding antifungal activities, phytotoxicity and excellent free radical scavenging capabilities. It is worthy of further study to develop as environmentally-friendly fungicides, herbicides or even health supplements.
|
|---|
