Isolation and Characterization of Botryosphaeria kuwatsukai on Apple in Korea
Gwang-Jae Lim1, Kallol Das1, Hyeong-Jin Noh2, Seong-Keun Lim1, Chang-Gi Back3, Seung-Yeol Lee1*, Hee-Young Jung1, and Seong Hwan Kim2
1College of Agriculture and Life Sciences, Kyungpook National University, Korea
2College of Sciences & Technology, Dankook University, Korea
3College of Life Sciences and Biotechnology, Dankook University, Korea
During the screening of the fungal pathogens, the isolates designated as KNUF-23-MG32, KNUF-23-YC8, and KNUF-23-MJ82 were isolated from apple trees collected in Jeollanam-do and Gyeongsangbuk-do in Korea. The cultural and morphological characteristics of those isolates were very similar to the genus Botryosphaeria. The representative strain KNUF-23-MG32 produced abundant aerial mycelia which turned gray to dark gray and olive-green on PDA. Conidiogenous cells have granular contents, hyaline, subcylindrical, and 12.7-23.5×4-6.6 μm. Conidia were hyaline, aseptate, smooth, granular contents, fusiform or irregularly fusiform, with the diameter of 20.0-30.2×5.9-8.2 μm. These characteristics resembled those of Botryosphaeria kuwatsukai CBS 135219, while distinct from B. dothidea KACC 45481 and B. sinensis HMAS 246714T. Pathogenicity tests were conducted with the strain KNUF-23-MG32, rot symptoms and dark-brown discolorations were observed, re-isolated from the lesion and confirmed Koch’s postulates. The phylogenetic analysis was performed with the closest species using sequences derived from the internal transcribed spacer (ITS) regions, translation elongation factor 1-alpha (TEF1α), and partial β-tubulin (TUB2). The phylogenetic tree showed that the three strains closely clustered with the different strains of B. kuwatsukai (DUCC15305, DUCC1528, and CBS 135219). The cultural, morphological characteristics along with the phylogenetic analysis revealed that the isolates were consistent with the previously identified B. kuwatsukai. Therefore, this is a new report of Botryosphaeria kuwatsukai as apple ring rot pathogen in Korea.