Comparison of wood decay among diverse lignicolous fungi

Abstract

In decay tests with 98 isolates (78 species) of lignicolous fungi followed by chemical and anatomical analyses, the validity of the generally accepted, major decay types (white, brown, and soft rot) was confirmed, and no new major types proposed. We could distinguish soft rot from other decay types based on anatomical and chemical criteria, without reliance on cavities or recourse to taxonomy of causal agents. Chemically, soft rot of birch could be distinguished from white rot by lower Klason lignin loss, and from brown rot by much lower alkali solubility. Anatomically, erosion of birch fiber walls in soft rot was distinguished from that in white rot by the angular erosion channels, V-shaped notches and diamond-shaped, eroded pit apertures that predominated in the former and their rounded forms in the latter.Substantial decay was caused by fungi representing eight orders in addition to the Aphyllophorales. Members of the Exidiaceae generally caused low weight losses and anatomical and chemical patterns of degradation characteristic of white rot. Isolates of Auricularia auricula-judae also caused a white rot, with high weight losses and unusual, branching microcavities that were oriented longitudinally in the S2 cell-wall layer. Ten species of the Dacrymycetales caused a brown rot like that caused by some Aphyllophorales; most caused high weight losses.Among white-rot fungi on birch, a relationship was observed between strongly selective delignification and strongly selective utilization of mannose. Among brown-rot fungi on birch, the top two polyose sugars (not including glucose) in order of selectivity were galactose>mannose; among soft-rotters they were arabinose>xylose. On pine, distinctions were not so clear, but some differing trends were evident.Previously unreported selective delignifiers were found in the Auriculariales, Agaricales, and in two orders of gasteromycetes. Selective delignification was most pronounced at low weight losses. Certain decay features similar to those in the Ascomycota were found in the Auriculariales, consistent with hypotheses that place that order near the phylogenetic root of Basidiomycota. A sequence of origins of decay types is proposed.