First Report of Sclerotinia sclerotiorum Causing Sclerotinia Rot on Codonopsis lanceolata in Korea

Abstract

Lance asiabell or deodeok (Codonopsis lanceolata L.) is native to East Asia such as Korea, China, Japan, and Russia. In Korea, roots of the plant are widely used as a food and medicine because of its high content of beneficial ingredients such as saponin. In May 2018, Sclerotinia rot symptoms on 2-year-old lance asiabell plants were observed in a field in Jeju (33.51° N, 126.84° E), Korea. Symptoms affecting the crown were water-soaked lesions associated with characteristic white cottony mycelia. Secondary symptoms such as wilting and bleaching were also observed on above-ground tissues. The incidence of diseased plants was approximately 10% in the field. Ten sclerotia were collected from the soil around the diseased plants, surface sterilized with 1% NaOCl for 1 min, and then rinsed twice in sterilized distilled water. The sclerotia were placed on water agar and incubated at 20°C for 5 days in the dark. Four isolates were obtained from mycelium grown from each sclerotium and were cultured on potato dextrose agar (PDA) at 20°C for 3 weeks in the dark. All isolates produced irregular and black sclerotia (1.8 to 4.5 mm in size) on a PDA plate. Based on morphological characteristics of mycelia and sclerotia, all isolates were tentatively identified as Sclerotinia sclerotiorum (Kohn 1979). To confirm the morphological identification of all isolates, DNA sequencing of the internal transcribed spacer (ITS) region of rDNA was carried out using ITS1 and ITS4 primer pair (White et al. 1990). The 505-bp products of nucleotide sequences obtained from four isolates (NC18657 to NC18660) were deposited in GenBank with accession numbers MK418968 to MK418971. The ITS region sequences of the four isolates were 100% identical with GenBank reference accession number KF859933 of S. sclerotiorum CBS 499.50. Pathogenicity assays were conducted using two isolates (NC18657 and NC18659) on the lance asiabell seedlings. Five healthy 2-week-old seedlings were inoculated by placing a sclerotium with PDA plug (3 × 3 mm) around the stem. The same number of seedlings were noninoculated controls and received noncolonized PDA plugs. Plants were maintained in the growth chamber at 20 ± 3°C with a 14-h photoperiod. After 4 weeks, all inoculated seedlings wilted. Black irregular sclerotia with white mycelium were observed on the soil surface. No symptoms were observed in the control plants. The fungus was consistently reisolated from the sclerotia formed on the soil surface, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of S. sclerotiorum causing Sclerotinia rot on lance asiabell in Korea. Further studies are needed to develop integrated management of the disease on the host in Korea.