First Report of Sclerotium rolfsii on Star-cluster (Pentas lanceolata) in Taiwan

Star-cluster (Pentas lanceolata (Forssk.) Deflers) has recently become popular as a bedding plant in Taiwan. During the summer of 2000, a sudden wilt of 60-day-old plants was observed in a nursery in Tainan City (southern Taiwan). Initial symptoms included stem necrosis at the soil line and yellowing and tan discoloration of 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 plated on potato dextrose agar amended with 100 ppm streptomycin sulfate. Pathogenicity of three isolates of S. rolfsii was confirmed by inoculating 90-day-old plants of P. lanceolata that were grown in pots. Three plants each were inoculated with a 5-mm plug of agar with mycelium or two sclerotia of the pathogen. Inoculum was placed on the soil surface against the stem of each plant. Three noninoculated plants served as controls. All plants were kept in a growth chamber at 20 to 30°C with relative humidity >85%. The pathogenicity test was repeated. Inoculated plants developed symptoms within 7 days, while control plants remained symptomless. Sclerotia developed on infected tissues and S. rolfsii was reisolated from symptomatic tissues. Although this disease has been observed on many species of plants (1), to our knowledge, this is the first report of southern blight of P. lanceolata caused by S. rolfsii in Taiwan. Reference: (1) Tsai, Y. P., 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.