Anatomical and physico-mechanical characteristics of Cenostigma pluviosum var. pelthophoroides (Fabaceae) wood decayed by Ganoderma australe (Basidiomycota, Polyporales)

Abstract

Sibipiruna (Cenostigma pluviosum var. pelthophoroides) trees are common in the São Paulo city urban forest, but they may cause accidents when deteriorated by wood-decaying fungi due to trunk rupture and tree fall. Therefore, this study aimed to evaluate anatomical, physical, and mechanical changes in sibipiruna wood attacked by Ganoderma australe. Adult trees with basidiomata of this fungus and at imminent fall risk were macro and microscopically analyzed to investigate wood biodeterioration and resistance mechanisms (compartmentalization). Physical and mechanical tests (specific gravity, mechanism of resistance and static bending) were performed. In sibipiruna trees, degradation was observed in the heartwood, being more intense in the region near the pith and more extensive at the stem base, from where basidiomata were collected. Fungal attack was characterized as white pocket rot, i.e. non-selective to cell wall components, causing erosion of the S2 layer from the cell lumen. Decaying wood was also attacked by xylophagous insects, like the subterranean termite Coptotermes gestroi and wood-boring beetles. Wood compartmentalization was characterized by accumulation of extractives. White rot caused significant reductions in specific gravity, modulus of rupture and modulus of elasticity, which justify the rupture of trees when subjected to external forces, such as strong winds.