Differential Fungal Susceptibility of Aspergillus oryzae to Aomori Hiba Heartwood and Sapwood

The antifungal properties of wood are often attributed to extractives that differ between heartwood and sapwood; however, quantitative evaluation methods remain limited. In this study, we investigated differences in fungal susceptibility between heartwood and sapwood of Aomori Hiba (Thujopsis dolabrata var. hondae) using solvent extraction, fungal growth inhibition assays, and digital image analysis. Heartwood and sapwood were distinguished based on anatomical characteristics and color, and extractives were obtained using ethanol as the solvent. Antifungal activity was evaluated against Aspergillus oryzae by monitoring fungal growth on culture media. Quantitative image analysis was applied to grayscale images to assess fungal growth inhibition, enabling objective comparison between samples. The results demonstrated that heartwood extracts consistently exhibited stronger fungal growth inhibition than sapwood extracts, which correlated with higher extractive contents. Image-derived metrics effectively captured differences in fungal growth that were not readily discernible by visual inspection alone. These findings demonstrate that digital image analysis can be effectively integrated with fungal susceptibility assays and extractive measurements to provide a practical framework for preliminary screening of antifungal potential in wood-derived materials.