Invasion of wood by basidiomycetous fungi II. Obliterated differences between pathosism and saprophytism on pre‐degraded wood substrates in monoxenic culture

Abstract

AbstractMycelial production and linear extension growth of 41 wood‐destroying basidiomycetous fungi (WBF) whose pathogenicity and kratovirulence levels permitted their subdivision into 7 fungal categories was determined on nonsterile and autoclaved wood dust materials from fresh, discoloured (nondecay), and decay wood samples. The resident microflora of nonsterile wood meals compels the intruding WBF mycelium to mobilize its entire competitive ability when going to colonize a contaminated substrate. This demand excludes the pathogenic WBF from utilizing the non‐sterile substrates but allows for extensive development of the fresh‐wood and successive saprophytes that afford the required kratovirulence level. On sterilized wood dust, any differences in the growth patterns of pathogenic and saprophytic WBF vanish immediately. Sterile fresh wood samples from host and nonhost trees the latter being never infected in the field allow for widely uniform mycelial production by fungal species with wide or extremely narrow host range. Some fungi display, in addition, a strong substrate preference to certain natural host tree species or their close relatives. No correlation was found between the total exoenzymatic activity reported for the fungus concerned and its mycelial production. Top values of mycelial formation were observed in fungi with lowest enzymatic activity as well as in producers of normal enzyme quantities while some brown‐rot fungi showed extremely restricted mycelial output although they are known for enzymatic activities to be highest.Among the 41 fungal species listed, 25 prefer certain particular nondecay and decay wood samples to fresh wood meal although the general rule is a higher mycelial production on fresh wood. The addiction to pre‐degraded wood can be traced, surprisingly, throughout all fungal categories with the tendency to abate in saprophytic ones. The brown‐rot fungi are more frequently stimulated by the discoloured nondecay wood while white‐rot fungi tend to prefer decay wood samples. The partially diminutive mycelial production in certain brown‐rot fungi means no defect in vitality or wood‐decay capacity. The weekly linear extension growth figure LE7 of the fungal mycelia can reach top values throughout the 7 fungal categories. No relationship was detected between rapid mycelial growth and both kratovirulence level or pathogenic potency. Fungi most reliably transplanted to raw substrates have medium‐sized LE7 figures. It is concluded that the striking differences between pathogenic and saprophytic members of WBF they display in their competitive ability immediately vanish in the absence of substrate microorganisms. The in vitro tests neither reveal differences in a striking host substrate specificity, the preference to fresh or decay wood, mycelial dry matter production, general enzymatic particularities, and weekly mycelial growth rate.