Research Note: Common fungal diseases of native butterfly orchids (Phalaenopsis sp.)

Abstract

Specimens of the most common fungal diseases of native butterfly orchids were collected in Baybay, Leyte and the diseases and their casual organisms were also identified. Sclerotium rolfsii Sacc. grew radially showing profuse, white, aerial, straight mycelia and brown sclerotial bodies in potato dextrose agar (PDA). Colletotrichum sp. exhibited creeping, whitish, straight mycelia with circular growth and produced abundant spores. Sporulation was observed after two days of growth in PDA. Phytophthora sp. showed suppressed growth and did not sporulate in PDA; it displayed creeping, whitish, cottony mycelia with radial growth pattern. However, abundant sporangia were produced in onion agar (OA) and after immersion in sterile water for 2 to 4 days under laboratory condition. Incubation periods of S. rolfsii, Colletotrichum sp. and Phytophthora sp. were observed 2-3 days, 10-11 days 9-12 days, respectively, after inoculation. Yellowish intact rotted portions characterized the disease caused by S. rolfsii while circular to oblong, sunken, necrotic lesions were produced by Colletotrichum sp. Watersoaked lesions incited by Phytophthora sp. gradually turned blackish and sunken with irregular border and shape. Of the three fungal pathogens, S. rolfsii was the most destructive with the highest severity.