Modification of the growth habit of the softwood disfiguring fungus Ophiostoma piceae by monoterpene vapors

Monoterpenes form part of the natural defenses against pathogenic fungi in conifers. As a result of exposure to kiln-drying, up to 50 percent of the monoterpene content of softwood timber can be lost. This paper reports an in vitro investigation of the effect of high monoterpene vapor concentration on the formation of pigmented mycelium and coremia/perithecia by Ophiostoma piceae, a common cause of stain in timber. Of five commonly occurring monoterpenes tested, alpha -pinene, beta -pinene, A3-carene, and myrcene caused relatively small radial growth rate reductions but had considerable inhibitory effects on mycelial pigmentation and coremia/perithecia formation. These monoterpenes were also associated with thickening of mycelia and secretion of slime onto the colony surface. In contrast, limonene failed to induce these effects, instead stimulating formation of coremia/perithecia. In combination with the many other changes in wood caused by kiln-drying, the reduction in monoterpene content may contribute to a modified susceptibility to disfiguration by stain fungi.