Mycological Characteristics of Dryadomyces sulphureus Isolated from Ambrosia Beetles

A fungal strain designated ARI-24-A9 was isolated from ambrosia beetles collected from apple orchards in Korea. The strain was characterized using culture, morphological, and molecular phylogenetic approaches to determine its taxonomic identity. When cultured on potato dextrose agar (PDA) and malt extract agar enriched with 1% Difco yeast extract (YEME) media at 25℃ for 7 days, the colony diameter ranged from 72.3–74.0 mm on PDA and 82.1–85.3 mm on YEME. The colonies exhibited a golden-yellow center with a characteristic growth pattern. Growth condition tests revealed that the optimal temperature and pH for colony development were 30℃ and pH 4–5, respectively. Most hyphae were hyaline with an average width of 2.9 μm, whereas thicker, pale brown hyphae with a width of up to 7.4 μm were observed in aerial mycelium-forming regions. These culture and morphological characteristics were consistent with those of Dryadomyces sulphureus. Molecular analyses using four genetic markers (internal transcribed spacer, ITS; large subunit ribosomal RNA gene, LSU; small subunit ribosomal RNA gene, SSU; β-tubulin, β-TUB) revealed that ARI-24-A9 shared over 99% sequence similarity with D. sulphureus and formed a highly supported clade with this species in both single-locus (ITS) and multilocus (LSU, SSU, β-TUB) phylogenetic trees. These findings confirmed that ARI-24-A9 is conspecific to D. sulphureus. This is the first known instance of D. sulphureus recovered from an ambrosia beetle in Korea.