Potential contributions of lignans to decay resistance in western red cedar

Abstract

Recent work examining the correlations between heartwood extractives in western red cedar and decay resistance in ground-contact field tests identified two compounds that were moderately correlated with decay resistance—plicatic acid and an unknown compound. The aim of the present work was to identify the latter compound and to further probe the correlation between both of these lignans and decay resistance. Chromatographic and mass spectral data indicated that the latter compound was plicatin—the lactone of plicatic acid. Extractives fractions containing plicatic acid, plicatin, and polymeric lignans, believed to be derived from these compounds, were impregnated into ponderosa pine sapwood blocks and evaluated for their ability to resist decay by two brown-rot fungi. Impregnation of plicatic acid, plicatin, their combination, or polymeric western red cedar extractives in pine sapwood did not inhibit decay by the fungi evaluated. However, both plicatic acid and plicatin had high radical scavenging activity, and moderate ferrous iron chelating activity. It is proposed that these compounds contribute to decay resistance not as fungicides, but rather via alternative pathways. These could include interference with redox cycles associated with decay, and restricting moisture by reducing cell wall void volume.