First Report of Southern blight of Formosan Michelia Seedlings in Taiwan

Formosan michelia (Michelia compressa (Maxim.) Sargent) is a native, giant evergreen tree in Taiwan. This species is used for afforestation, provision of shade in domestic situations, used in parks, and also for furniture. During the summer of 2004, a sudden wilt of 1-year-old plants was observed in a nursery of northern Taiwan. Initial symptoms included stem necrosis at the soil line, yellowing, and tan discoloration of leaves. As stem necrosis progressed, infected plants wilted and died. Necrotic tissues were covered with whitish mycelium that differentiated into reddish brown spherical (1 to 2 mm in diameter) sclerotia. Sclerotium rolfsii was consistently recovered from the surface of symptomatic stem sections that were disinfected for 1 min in 0.5% NaOCl and then plated on potato-dextrose agar amended with 100 ppm ampicillin. Pathogenicity of two S. rolfsii isolates was confirmed by inoculating 1-year-old Formosan michelia seedlings grown in pots. Inoculum consisted of mycelium and sclerotia of the pathogen placed on the soil surface around the base of each plant. Noninoculated plants served as controls. All plants were kept in a growth chamber at 25 to 35°C with relative humidity >95%. Inoculated plants developed symptoms within 14 days while control plants remained symptomless. Sclerotia developed on infected tissues, and S. rolfsii was reisolated from symptomatic tissues. This disease has been observed on many species of plants (1), but to our knowledge, this is the first report of southern blight of Formosan michelia seedlings caused by S. rolfsii in Taiwan. Reference: (1) Y. P. Tsai, ed. List of Plant Diseases in Taiwan. The Plant Protection Society of the Republic of China and The Phytopathological Society of the Republic of China, 1991.