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ABSTRACT
Disrupting nitrogen acquisition by targeted chemicals is a potential strategy for controlling fungal growth of sapstaining fungi in wood. Detailed analyses of pine and aspen sapwood confirmed that very little of the limited available nitrogen is inorganic. Since proteins are the primary nitrogen source in wood, and proteolytic activity was detected in wood infected with the staining fungus Ophiostoma piceae, proteinase inhibitors were tested for their effect on fungal growth. Heavy metals and several chelators inhibited growth on artificial media containing protein or inorganic nitrogen, suggesting that they were toxic to the fungus rather than specific to the proteinase. However, chymostatin, hen egg white, and the commercial sapstain control product PQ-8 appeared to be specific proteinase inhibitors, because they caused a decrease in growth on a protein-supplemented medium that induces proteinase production, but had little effect on growth in a medium containing inorganic nitrogen. Visual assessment of lodgepole pine sapwood inoculated with O. piceae also identified hen egg white and PQ-8 as effective inhibitors of fungal growth on wood. Other pure chelators and serine proteinase inhibitors performed poorly on wood. The results suggested that developing targeted antifungal compounds willrequire knowing more about the unique physiology of the microorganisms that colonize wood.
About 130 species of fungi worldwide are known to cause a discoloration of sapwood commonly called sapstain (16). Most species belong to the ascomycetes, many to the genera Ceratocystis or Ophiostoma or to the Fungi Imperfecti (31). It has long been known that sapstain in lumber can be prevented either by kilndrying, a process that reduces the moisture content of wood, or by treating the wood with chemicals (30). Kiln-drying is not always feasible. It can cause drying defects in high-value lumber, the cost may not be recoverable in higher lumber prices, and it may not be feasible for lumber with large dimensions (10). Although more environmentally acceptable chemicals are now being used, they still have a broad spectrum of biocidal action. Consequently, there remains a need for effective antifungal agents with lower environmental toxicity and higher specificity for sapstain fungi.
Little nitrogen is available to fungi colonizing wood (22). Nitrogen constitutes from 0.01 to 0.3 percent of the dry weight of wood, depending on the tree species, the individual tree,...
