First Report of Pyricularia grisea Causing Gray Leaf Spot on Lily in Korea.

Abstract

Lily is an economically important ornamental crop in Korea. In August 2008, severe leaf spot symptoms were observed on an oriental Lily 'Action' in a plant nursery in Daegu, Korea. Disease incidence was 20 to 30%. Initial symptoms were olive green-to-brown lesions on the leaf that developed into tan, elliptical, necrotic lesions. On severely infected leaves, lesions coalesced and killed the entire leaf blade. Infected leaves were surface disinfested with 70% ethanol for 30 s and 2% chlorox for 15 min before plating 1 cm2 sections onto potato dextrose agar. Hyphae appeared 5 days after inoculation and pure culture. Conidia were hyaline, transversely septate with one to three septa; most had two. Conidia were obpyriform and measured 29 to 46 μm long and 7 to 17 μm wide. Mycelia morphology and conidia production were consistent with that described previously for Pyricularia grisea (1). Koch's postulates were fulfilled by spraying five, healthy, vegetative-stage plants with 2 × 105 conidia per ml of sterile distilled water plus 0.05% Tween 20. As a control, five similar plants were sprayed with sterile water plus 0.05% Tween 20 only. Plants were placed inside plastic bags to maintain high relative humidity and incubated in a growth chamber at 25°C under fluorescent light for 14 h and at 20°C in darkness for 10 h. After 3 days, the plastic bags were removed and plants were maintained under the same conditions. Initial symptoms were observed 7 days after inoculation. Ten days after inoculation, disease symptoms on inoculated plants were similar to those previously described in the nursery. Control plants did not show any symptoms. Fungi isolated from these lesions had the same morphological characteristics as the ones isolated previously from plants in the nursery. To our knowledge, this is the first report of gray leaf spot on lily caused by P. grisea in Korea.