Investigation of the extracellular mucilaginous materials produced by some wood decay fungi

Abstract

The morphology of the extracellular mucilaginous material (ECM) produced by Coniophora puteana and Coriolus versicolor during colonization of Scots pine and beech was studied using SEM. Wood specimens were examined in the frozen hydrated (FH) condition using low-temperature SEM, and in the freeze-dried (FD) and critical point dried (CPD) state, using conventional SEM. All techniques produced artifacts but the ECM was best preserved when examined in the FH state. Very little difference was observed between FH and FD preparations, but critical point drying damaged the ECM extensively. Copious amounts of ECM were produced by both fungi. It was found to line much of the lumen surface, establishing contact between the mycetium and the wood substratum. Most aerial hyphae were coated with ECM, appearing glued together in a bundle-like fashion. The ECM thickness varied within the same wood cell and from one cell to another. A peculiar granular pattern, in which the ECM was definitely involved, was seen on occasion to encircle the infecting hyphae where they contacted the wood surface. Other morphological patterns of ECM distribution were also observed. Calcium oxalate crystals of varying shapes and sizes were often seen associated with the mycelia and mucilage of the two fungi in beech but not in Scots pine. The probable roles played by the ECM in wood decay mechanisms are discussed.