Effects of substrate on laboratory spalting of sugar maple

Spalting is the coloration of wood caused by fungal colonization. Woodturners, craftspeople, and artists appreciate spalted wood for its aesthetic appeal and uniqueness. Laboratory-induced spalting aims at a repeatable procedure in which wood is inoculated with selected fungi to obtain natural color with high aesthetic appeal, low weight loss and good machinability. Vermiculite (a natural clay with a high capacity for water holding and cation exchange) has been the primary incubation substrate for spalting research despite soil being the standard substrate for soil block decay testing. In this research, we explored the differences between these two substrates and their effects on the growth of spalting fungi on sugar maple (Acer saccharum) wood. Five fungi, Trametes versicolor, Xylaria polymorpha, Arthrographis cuboidea, Ceratocystis pilifera, and Ceratocystis virescens, were tested for their weight loss and spalting abilities on 14-mm sugar maple cubes incubated in both soil and vermiculite. Weight losses from all fungi were either unaffected or reduced by incubation in vermiculite compared to soil. In vermiculite, X. polymorpha produced more zone lines and A. cuboidea produced more pigment than blocks incubated in soil. Growth in vermiculite decreased weight loss of blocks inoculated with T. versicolor and X. polymorpha, while bleaching was unaffected regardless of substrate. External blue stain was higher on blocks inoculated with either Ceratocystis species and incubated in soil. These results indicate that vermiculite is a better substrate for spalting regardless of fungus due to the higher external pigmentation, lower weight loss, and better color contrast on the sugar maple blocks incubated in this substrate.