Sclerotium rolfsii Causes White Rot on Taro in Korea

Taro (Colocasia esculenta L.) is grown throughout the world primarily for its tubers, which become edible after cooking. Taro stems are often used in a traditional soup in South Korea. In September 2012, a suspected white rot of taro occurred in a farmer's fields in Jinju, South Korea. Infected plants gradually withered, a white mycelial mat appeared, and numerous sclerotia developed on the surface of petioles near the soil line. The heavily infected petioles rotted and the entire plant eventually died. The freshly isolated pathogenic fungus was grown on potato dextrose agar (PDA) and examined microscopically. Aerial mycelia usually formed many narrow hyphal strands 4 to 8 μm wide. The white mycelia formed a typical clamp connection structure after 6 days growth at 25°C. The sclerotia were white at first, gradually turned dark brown, and were 1 to 3 mm in diameter. Small globoid sclerotia formed abundantly on PDA after 18 days of growth. Ten 2-month-old potted taro plants were inoculated with S. rolfsii-colonized agar discs directly at the base of each plant and kept at 25°C in a greenhouse to test pathogenicity. Three taro plants were inoculated similarly with uncolonized agar discs as controls. Eight days after inoculation, blight symptoms were observed, and S. rolfsii was reisolated from the artificially inoculated plants. The control taro plants remained healthy. We amplified and sequenced an internal transcribed spacer (ITS) rDNA region of the isolate using the ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) primers to confirm the identity of the fungus (2). The resulting 684-bp sequence was deposited in GenBank (Accession No. KC491876). A comparison with other sequences available in the GenBank database revealed that the ITS sequence shared 100% similarity with Sclerotium rolfsii sequences (HQ420816 and JN017199). Based on the symptoms, mycological characteristics, ITS sequence analysis, and host plant pathogenicity, this fungus was identified as S. rolfsii Saccardo (1). To our knowledge, this is the first report of white rot in taro caused by S. rolfsii in Korea. References: (1) J. E. Mordue. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 410, 1974. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, New York, 1990.