Characterization of cell wall morphology and water-soluble extractives in Japanese larch decayed by white-pocket-rot fungi

Porodaedalea chrysoloma (Fr.) Fiasson & Niemelä is a basidiomycete that can cause white-rot decay in Japanese larch (Larix kaempferi) heartwood. P. chrysoloma is a white-rot fungus with a unique pattern that causes white-pocket-rot in the xylem of Japanese larch. However, the mechanism by which P. chrysoloma yields the pattern of white-pocket-rot in Japanese larch heartwood remains unclear. Thus, this study investigated the changes in the cell wall morphology, water-soluble extractives such as arabinogalactan, and cell wall chemical components of Japanese larch decayed by P. chrysoloma in the natural environment. P. chrysoloma caused a distinct decay pattern characterized by white-pocket-rot in Japanese larch heartwood. The expansion of the white decayed area on the surface of the wood at the cross-section decreased the volumetric density of Japanese larch. Observations based on optical microscopy revealed that this fungus attacks mainly earlywood cells in the Japanese larch heartwood. In addition, Infrared spectroscopy was used for the determination of the chemical components of the cell wall and revealed that white-pocket-rot–causing P. chrysoloma degraded the structure of lignin and hemicellulose compared with the crystalline structure of cellulose in the cell wall. In addition, we focused on the water-soluble extractives deposited in Japanese larch during the formation of heartwood. The hot-water extractives were isolated from Japanese larch heartwood, and the amount of arabinogalactan was significantly decreased during the early-decay stage, indicating that P. chrysoloma may have been used as a nutrient source for mycelial growth before the decay of the chemical components of the cell wall, such as cellulose and hemicellulose