First Report of Sclerotium rolfsii on Island Ash Seedlings in Taiwan

Island ash (Fraxinus formosana Hay.) is a large, semideciduous tree in Taiwan. It is used for forestation, a shade tree, and producing wood for furniture. During the summer of 2001, a sudden wilt of 1-year-old plants was observed in a nursery in northern Taiwan. Initial symptoms included stem necrosis at the soil line and yellowing and tan discoloration of the leaves. As stem necrosis progressed, infected plants wilted and died. Necrotic tissues were covered with white 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 (PDA) amended with 100 ppm of ampicillin. Pathogenicity of two S. rolfsii isolates was confirmed on 1-year-old island ash seedlings grown in 12.7 cm- (5-in) plastic pots in a sterilized mixture of peat moss and vermiculite (3:1). Seedlings were inoculated with mycelia and sclerotia of the pathogen grown on PDA. Three plants each were inoculated with four disks (5 mm) of agar with mycelium and three were inoculated with 10 sclerotia that were 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 and >95% relative humidity. The test was repeated once. All 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 Island ash 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.