Experimental investigation of the humidity effect on wood discoloration by selected mold and stain fungi for a proper conservation of wooden cultural heritages

Unfinished interior wood members in wooden cultural heritages undergo severe discoloration by fungal attack during the summer rainy season. The prevention of fungal discoloration is crucial in the conservation of wooden cultural heritages. It is important to investigate discoloration properties of major mold and stain fungi under different relative humidity conditions to prevent discoloration damage. Among the 54 ascomycetes isolated from wooden cultural heritages in Korea, Aureobasidium pullulans, Cladosporium cladosporioides, Coniochaeta velutina, and Graphiopsis chlorocephala were selected as test fungi because of their particularly strong discoloration intensity on wood. For each fungal species, the minimum relative humidity and exposure period for discoloration were investigated. It was found that A. pullulans and Cl. cladosporioides started to grow and discolor at 75% relative humidity within 3 weeks to 4 weeks, and Co. velutina and G. chlorocephala grew and discolored at relative humidity values greater than 95%. Therefore, the prevention of fungal discoloration of interior wood members by A. pullulans and Cl. cladosporioides for the proper conservation of wooden cultural heritages can be achieved by maintaining an indoor relative humidity of 75% or less during the summer rainy season.