Incipient decay of Quercus serrata sapwood by Lentinus edodes and its inhibition by an antagonistic hyphomycete, Leptodontidium elatius

Abstract

Incipient decay of Quercus serrata by Lentinus edodes and its inhibition by Leptodontidium elatius were investigated by scanning electron microscopy. Rapid accumulation of L. edodes hyphae in earlywood vessels was a prerequisite to efficient decay of sapwood. In the early stages of decay, selective removal of lignin and other amorphous wall components occurred in the vessels and surrounding tissues, including vasicentric tracheids and wood fibres. Thus, bundles of cellulose microfibrils, having lateral dimensions of 15–50 nm, became recognizable. Disintegration of cellulose microfibril bundles appeared to begin with longitudinal and (or) transverse splitting of the bundles, and then the walls became progressively thinner. In ray parenchyma cells, end walls were susceptible to the fungal degradation, but lateral walls, particularly the innermost layer, were relatively resistant. Hyphae of L. elatius grew in close contact with the vessel wall and exuded slime material to create a distinct microarea (mycosphere) around them. In the vessels precolonized by this hyphomycete, the growth rate of L. edodes hyphae was drastically reduced to less than 20% of that in antagonist-free vessels. Possible roles of the slime material in this antagonism are discussed. Key words: wood decay, Lentinus edodes, Leptodontidium elatius, antagonism, mycosphere.