Abstract
BackgroundSequoia sempervirens (D. Don) Endl.) (redwood) has the potential to be grown in New Zealand in commercial forestry operations and is valued for its naturally durable heartwood. A viable redwood industry based on planted forests can only be achieved if the timber produced meets quality expectations, in particular durability. Natural durability is highly variable among trees. Also, a within-tree pattern of low durability close to the pith has been observed. Natural durability is preliminarily caused by secondary metabolites deposited into the cell walls during heartwood formation. The exact nature of the compounds responsible for natural durability in redwood is unknown.MethodsSamples of heartwood from 22 different trees were obtained, ground and extracted using a range of solvents. The ability of some of these extracts to reduce the growth of two fungi (Gloeophyllum trabeum and Trametes versicolor) was tested in vitro. Information on the composition of the extracts was obtained using infrared spectroscopy and gas chromatography.ResultsFungicidal properties were found in solvent extracts of ground S. sempervirens heartwood samples at concentrations comparable to those known to be present in intact wood. The entire acetone-soluble extracts and ethyl-acetate-soluble fraction of the ethanol extracts caused the greatest reduction in the growth of both fungi tested. Large variations in acetone-soluble or ethanol-soluble extract content and fungicidal activity among trees were found. Agatharesinol and sequerin-C appear to be trace compounds in the dried extracts of S. sempervirens.ConclusionsFurther work is needed to identify the key compounds contributing to the natural durability of S. sempervirens.
Highlights
The deposited secondary metabolites are known as heartwood extractives as they can be extracted by various solvents from the heartwood
This article (a) reviews the existing literature regarding the natural durability of S. sempervirens heartwood and the extractives compounds in this material and (b) provides some experimental data on the quantity and bioactivity of various S. sempervirens extracts and their variability
This suggests that either water-soluble extracts play a prominent role for the natural durability of this timber or that the fungi present in those environments are more tolerant to the extractives present in S. sempervirens heartwood
Summary
Extractions: S. sempervirens heartwood was extracted using an Accelerated Solvent Extractor (Thermo) equipped with 33 mL cells. Each solution was placed in a water bath (80°C) until no solvent odour was noticeable to remove fungicidal effects of the extraction solvent. Statistics: Solvent controls showed that potentially remaining solvent traces had no significant effect on the growth of the individual fungi so the control data were pooled (n = 30) to calculate the reference growth rate. As no statistically significant differences were found between the duplicate extractions using a F-test, the respective data were pooled (n = 10) to calculate the average absolute growth rate for each fungus and solvent extract. Standard errors of the ratios were estimated (Kendall et al 1994)
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