Fungal invasion of cellulosic skeletal substrates with a hierarchical structure of wood

Wood serves as a renewable resource; however, its sustainability is threatened by wood-rotting fungi, a type of filamentous fungi. Although its decay mechanism has been widely investigated, essential factors controlling fungal responses are poorly understood owing to the complex wood architecture mainly formed by cellulose microfibrils, hemicellulose, and lignin. This study aimed to explore the effects of wood structure and chemical components on wood-rotting fungi using chemically simplified wood substrates. Cellulose-based substrates were successfully prepared from wood sections of Cryptomeria japonica by removing non-cellulosic components while maintaining the inherent wood structure. Confocal microscopy analysis combined with Hough transformation after decay tests revealed a clear tendency of hyphae to elongate along tracheids on cellulosic substrates with wood structures. Furthermore, scanning electron microscopy demonstrated that hyphae passed through bordered pits without completely destroying the pit structure. These results indicate that wood structure is the dominant factor in hyphal responses and that the physical forces of tip growth and enzymatic degradation of components contribute simultaneously to fungal invasion in wood. This study demonstrates the usefulness of single-component substrates with preserved wood structures as new evaluation materials for studying wood-rotting, potentially facilitating research on decay for wood preservation.