Preliminary The Role of Extractives Involved in the Natural Durability of Domestic Softwood*l

It is generally known that natural durability of heartwood is different among wood species. It has been explained mainly by the presence of antifungal extractives in durable wood and many researchers have isolated and identified the relevant extractives. However, all isolated extractives did not always exhibit the high antifungal activity in vitro against test fungi, and the involvement of some other factors such as synergistic or additive effect of few substances and/or their hydrophobic effect to inhibit the fungal growth in heartwood 1). Also, Rudman reported that heartwood extractives from durable species were not always toxic against broad spectrum of wood-decay fungi but rather specific to limited species2). In this study, growth-inhibiting effect of extractives, water uptake of wood after extraction, decay resistance and behavior of fungal hyphae in wood after extraction were investigated in several parts from oute ~ sapwood to inner heartwood, using sugi and hinoki as typical domestic softwood species