| Summary: | The heartwood of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) is known to be relatively resistant to attack by wood-destroying fungi. Previous investigations on other species has established various heartwood extractives as the primary deterrents to decay. Several extraneous fractions from Douglas fir were isolated and evaluated for fungicidal activity in order to determine the precise factor influencing the durability of this species.
An acetone, ether and water extraction of Douglas fir heartwood meal provided five separate components, namely: a dihydroquercetin, free acid, neutral, phlobatannin and carbohydrate fraction. A bioassay of these materials was made using Fomes annosus (Fr.) Cke., Lentinus lepideus Fr. and Poria incrassata (B.&C.) Curt. as the test fungi. Both a cellulosic and a non-cellulosic substrate were employed. Small wood blocks from which certain extractives had been removed were used for the cellulosic substrates, whereas malt agar impregnated with varying concentrations of the extraneous materials represented the non-cellulosic media. The degree of effectiveness of each component as a fungicide was expressed numerically.
Dihydroquercetin was found to be the most potent fungicide, completely inhibiting growth of the most sensitive fungus at a concentration of slightly less than 0.5 per cent.
This value compares favorably with experimental results previously reported with phenolic extractives of the genus Pinus. On the basis of these data, timber selected for its high dihydroquercetin content could be expected to have an extended service life when used under conditions favoring decay. The possibility of breeding highly resistant genetic types is also discussed briefly. === Forestry, Faculty of === Graduate
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