First report of sclerotinia stem rot of fennel caused by sclerotinia sclerotiorum in Korea

I. Y. Choi, J. H. Kim, B. S. Kim, M. J. Park, Hyeon-Dong Shin

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Abstract

Fennel (Foeniculum vulgare Mill., family Apiaceae) is widely cultivated and used as a culinary spice. During winter of 2013-2014, fennel (cv. Florence) grown in a plastic greenhouse in Gongju (36°29′42.2″ N; 127°02′00.8″ E), Korea, exhibited typical symptoms of Sclerotinia rot. Initial symptoms were water-soaked lesions on stems at the soil line. The lower stems in contact with soil developed a brown decay and leaves on these stems became chlorotic. Dark-brown stem lesions enlarged and a cottony mycelium covered the affected area, followed by crown rot and wilt a few days afterward. About 50% of plants withered or died before harvest due to the disease. Whitish aggregates of mycelia developed into sclerotia that were 2 to 8 mm in diameter outside and inside affected stems. Stem tissues were surface-disinfested with 1% sodium hypochlorite, and segments were transferred onto potato dextrose agar (PDA). Resultant colonies were white or faint gray and floccose, with black sclerotia (3 to 8 mm in diameter) forming on the colony surface near the margin. A representative isolate was deposited in the Korean Agricultural Culture Collection (Accession No. KACC47724). Based on morphological and cultural characteristics, the fungus was identified as Sclerotinia sclerotiorum (Lib.) de Bary (Mordue and Holliday 1976). Fungal DNA was extracted with a DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA). The complete internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS1/ITS4 and sequenced. The resulting sequence of 558 bp was deposited in GenBank (Accession No. KJ614565). A BLAST search revealed that the sequence of the Korean isolate shared 100% identity to those of S. sclerotiorum (e.g., JN013184, KF859932, and DQ329537). A pathogenicity test was achieved by placing PDA plugs (9 mm2) from a 7-day-old culture on the stems of three healthy plants (cv. Florence) at the soil line. Three plants inoculated with noncolonized PDA plugs served as controls. Plants were enclosed in plastic bags that had been sprayed with water on the inside to maintain high humidity and kept in the greenhouse at 16 to 20°C. After 3 days, all inoculated stems became discolored, soft, watery, and covered with white mycelia, whereas control plants remained symptomless. S. sclerotiorum was consistently reisolated from the symptomatic tissue, fulfilling Koch’s postulates. Pathogenicity tests were repeated twice with similar results. Sclerotinia stem rot of F. vulgare caused by S. sclerotiorum has been recorded from India, Taiwan, New Zealand, and Italy (Panchal et al. 2012; Farr and Rossman 2015). To our knowledge, this is the first report of Sclerotinia stem rot on F. vulgare in Korea. Our continuous observations during the winter season (December, January, and February) suggest that low temperatures (4 to 10°C at night), high humidity, poor ventilation, and continuous cultivation in nonheated plastic greenhouse cultivation systems can increase the incidence and severity of Sclerotinia stem rot on fennel plants.

Original languageEnglish
Pages (from-to)223
Number of pages1
JournalPlant Disease
Volume100
Issue number1
DOIs
Publication statusPublished - 2016 Jan 1

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ASJC Scopus subject areas

  • Plant Science
  • Agronomy and Crop Science

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