The dark side of fungal competition and resource capture in wood: Zone line spalting from science to application

On wood surfaces and in planar section, zones lines appear as narrow and sharply delineated dark lines within wood visibly altered (“spalted”) by the decay process. In intact wood, zone lines define an irregular volume of decaying wood. They are primarily aggregations of melanised hyphae that enclose wood being decayed by a single genetic individual of a wood decay fungus. In the industry for speciality wood products, zone lines are highly valued, especially for decorative pieces produced from wood turnery. While zone lines are commonly found in naturally infected wood, they can also be induced under controlled conditions. Although with great economic potential for application, there is currently no spalting process to produce zone lines on a commercial scale for niche furniture and construction markets. Successfully spalting wood in a defined timeframe that meets industry expectations requires a knowledge of fungal species, wood colonisation strategies, fungal decay processes along with wood behaviour (i.e. its hygroscopicity), anatomy and wood mechanical properties in relation to fungal decay. This review identifies current limitations of zone-line spalting and looks at a novel approach to inducing wood by combining genetic individuals from the same fungal species, enabling the operator to homogenise the spalting method.