Characterization and pathogenicity of sweet potato (Ipomoea batatas) black rot caused by Ceratocystis fimbriata in Korea Narayan Chandra Paul & Sang-Sik Nam & Aardra Kachroo & Yun-Hee Kim & Jung-Wook Yang Accepted: 6 June 2018 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2018 Abstract Black rot disease was observed in sweet po- tato in Korea during a disease monitoring survey in 2017. The symptoms were black, small, circular, and slightly sunken lesions in the initial stages, leading to enlarged black spots and perithecia with long necks that appeared as dark bristles in the later stages. The causa- tive agent was isolated on potato dextrose agar (PDA) and stored at the Sweet Potato Research Laboratory, Bioenergy Crop Research Institute, RDA, Muan (SPL17100 and SPL17101). The cultured organism produced cylindrical single-celled conidia after 5 days of incubation at 25 °C with a conidial size of 8.5–65.2 × 2.6–7.3 μm. Brownish, globose, and thick-walled aleuroconidia were produced with an 11.9–17.0 × 8.3– 12.2 μm size. The perithecia were globose and dark brown with long thin necks tapering from the base to the apex. Morphologically, the fungus was identified as Ceratocystis fimbriata, which was well supported by the combined phylogenetic analysis of the sequences of the internal transcribed spacer (ITS), large subunit (LSU), and elongation factor 1-α (EF-1α) genes. Pathogenicity tests were conducted, and Koch’s postulates were confirmed. Keywords Ceratocystis fimbriata . Molecular phylogeny . Morphology . Pathogenicity . Sweet potato Sweet potato [Ipomoea batatas (L) Lam.] is one of the most widely cultivated tuber crops in the world and is popular in tropical and subtropical countries in Asia, the Pacific Islands, Latin America, and Africa (Loebenstein and Thottappilly 2009). This crop has helped sustain people during hard famine-like times such as wars worldwide and disasters in Asia. Therefore, the sweet potato is regarded as the Bpoor man’ s crop^ (Clark et al. 2013). Sweet potato is an excellent source of pro-vita- mins, vitamin C, potassium, iron, and calcium (Clark et al. 2013). Therefore, the popularity and consumption of sweet potato are also increasing in Korea. However, many fungal diseases cause losses during the cultiva- tion, storage, and marketing of sweet potato. Black rot, one of the most significant diseases of sweet potato, normally transmits through storage roots to plants and then to the roots again. The disease, which is caused by Ceratocystis fimbriata, is a significant threat to the production of sweet potato worldwide (Muramoto et al. 2012). Sweet potato has been used as animal feed from ancient times, and this is increasing in Asia (Clark et al. 2013). However, C. fimbriata induces the produc- tion of phytoalexin, which may be toxic to animals (Clark, 1980; Wamalwa et al. 2015). Ipomeamerone, a Eur J Plant Pathol https://doi.org/10.1007/s10658-018-1522-8 N. C. Paul : S.<S. Nam : J.<W. Yang (*) Bioenergy Crop Research Institute, National Institute of Crop Science, Rural Development Administration, Muan 58545, Republic of Korea e-mail: hg369732@korea.kr A. Kachroo Department of Plant Pathology, University of Kentucky, Lexington, KY, USA Y.<H. Kim Department of Biology Education, IALS, Gyeongsang National University, Jinju, South Korea