| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 94 === Michelia formosana (Kanehira) Masamune & Suzuki is one of the five precious hardwood trees in Taiwan. The objectives of this study were to evaluate the influence of extractives on the decay resistance of M. formosana wood and analyze the antifungal compounds of heartwood extract and leaf oil. After decay tests with white rot fungus Lenzites betulina and brown rot fungus Laetiporus sulphureus, weight losses of heartwood specimens were less than 2% against 2 kinds of rot fungi. Heartwood demonstrated high decay resistance against wood rots. However, weight losses of extracted heartwood specimens were increased significantly after decay test. It indicated that the ethanolic extract had a strong influence on the decay resistance of heartwood. Antifungal activities of ethanolic extracts obtained from M. formosana were in the following order: heartwood > leaf > sapwood > bark. Result inferred that the heartwood ethanolic extract exhibited the highest antifungal activity. Further more, antifungal activities of n-hexane, EtOAc, n-BuOH and H2O-soluble fractions obtained from heartwood ethanolic extract were assessed, the activities observed were in the order of n-hexane > n-BuOH > EtOAc > H2O-soluble fractions. These results indicated that the antifungal compounds mainly existed in the n-hexane-soluble fraction. One sesquiterpenoid, (+)-epi-cubenol, and two alkaloids, liriodenine and annonbraine, were isolated from active subfractions. (+)-epi-Cubenol and annonbraine were isolated from M. formosana for the first time. According to the antifungal test of liriodenine, IC50 values of liriodenine against white rot fungi L. betulina and T. versicolor were 0.76 and 3.50 μg/mL, respectively. And IC50 values of liriodenine against brown rot fungi L. sulphureus, G. trabeum and F. pinicola were all lower than 2.0 μg/mL. It demonstrated that liriodenine has an excellent antifungal activity.
Five compounds, 4, 5-epoxy-β-caryophyllene, linalool, guaiol, bulnesol and β-elemol, were isolated from the active fractions of leaf essential oil, which also possesses antifungal activity. Amoung these compounds, guaiol, bulnesol and β-elemol have better antifungal activities against white rot fungus L. betulina and brown rot fungus L. sulphureus.
According to the above results, four antifungal compounds, liriodenine, guaiol, bulnesol and β-elemol, were obtained from heartwood extract and leaf essential oil of M. formosana. These compounds which could effectively inhibit the growth of white rot fungi and brown rot fungi, are of great potential as natural wood preservatives.
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