Inhibition of basidiospore germination by western redcedar heartwood extractives

• An improved method for evaluating the impact of chemicals on basidiospore germination is described.
• Beta-thujaplicin and thujic acid were associated with the inhibition of basidiospore germination.
• The lignan plicatic acid was not associated with the inhibition of basidiospore germination.

Understanding the relationship between extractives and decay resistance in western red cedar (WRC) is essential for breeding durable planting stock. To date, most such work has focused on resistance to mycelial attack. However, this is potentially misleading since WRC is largely used in above-ground applications where basidiospore germination is the primary way in which the wood is initially colonized. Efficacy against basidiospores is likely a critical factor affecting wood’s decay resistance in above-ground applications. In this study the effect of selected extractives on basidiospore germination was evaluated. Partially-extracted WRC veneer samples, and spruce samples treated with beta-thujaplicin, thujic acid, or plicatic acid were used. Beta-thujaplicin and thujic acid were associated with significantly reduced rates of Gloeophyllum sepiarium, Fomitopsis palustris, and Dichomitus squalens basidiospore germination. Plicatic acid was not associated with any effect on basidiospore germination. Planting stock that generates heartwood with high concentrations of thujaplicins and thujic acid should be selected to yield wood that will be resistant to basidiospore germination.