An Unusual Decay Pattern in Brown-Rotted Wood

Abstract

Brown rot and white rot are two major types of wood decay caused by Basidiomycetes. Brown rot fungi primarily degrade cellulose and hemicellulose while white rot fungi degrade lignin as well as other wood components (Cowling, 1961; Eriksson, 1981; Nilsson, 1974). Fungi that cause white rots frequently have been separated into two groups: simultaneous rot fungi that degrade cellulose, hemicellulose, and lignin at approximately the same rate (Liese, 1970), and white-pocket rot fungi that preferentially degrade lignin leaving appreciable amounts of cellulose (Blanchette, 1980a, b, 1982; Otjen and Blanchette, 1982). Brown rot fungi, when cultured on wood, produce a diffusible factor that results in cellulolytic degradation at considerable distances from fungal hyphae (Cowling, 1961; Liese, 1970; Wilcox, 1970). Although cellulose is degraded in wood, most brown rot fungi cannot degrade pure isolated cellulose (Highley, 1977b; Nilsson, 1974). The presence of lignin and hemicellulose in the wood substrate appears to induce the synthesis of cellulose degrading enzymes (Highley, 1977a; Kirk and Highley, 1973; Nilsson, 1974) or possibly a nonprotein degrading system (Koenigs, 1974), by the majority of wood destroying brown rot fungi. Only a limited number of brown rot fungi, adapted to wood products deterioration, can degrade pure cellulose (Nilsson and Ginns, 1979). White-pocket rot fungi selectively remove lignin from wood leaving substantial amounts of cellulose in isolated areas (Blanchette, 1980a, 1982; Otjen and Blanchette, 1982). Wood surrounding the white pockets is sound (Blanchette, 1980a, b; Otjen and Blanchette, 1982). The formation of white pockets and patterns of selective delignification have been described for Phellinus pini (Thore: Fr.) A. Ames in conifers (Blanchette, 1980a, 1982) and Inonotus dryophilus (Berk.) Murr. in oaks (Otjen and Blanchette, 1982). Brown-rotted wood with white pockets was obtained from a dead Engelmann spruce (Picea engelmannii Parry) (FIGS. 1, 2) in the Uinta Mountains of Utah, Wasatch National Forest. The white-pocket decay was identical to that caused by P. pini. Apparently, while the tree was standing, P. pini caused a considerable amount of heart rot. After windfall, a brown rot fungus colonized the wood. Since