Marasmiellus inoderma Causes Basal Rot of Golden Shower Orchid. Y. K. Fong, Singapore Botanic Gardens, Singapore 259569 . S. Anuar, Singapore Botanic Gardens, Singapore 259569; F. R. Sanderson, PNG Oil Palm Research Association, P.O. Box 36, Alo-tau, Milne Bay Province, PNG; I. Nuss, Botamynus-Botanic Mycological Institute, Fuerstenstrasse 2, D-93098 Mintraching, Germany; D. N. Pegler, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK; and F. Y. Tham, School of Science, Nanyang Technological University (Bukit Timah), Singapore 259569. Plant Dis. 80:822. Accepted for publication 10 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0822C.
The Golden Shower orchid, Oncidium Goldiana (O. flexousom Sims. x O. sphacelatum Lindl.) is part of an orchid cut-flower industry that grossed S$25.06 million in Singapore in 1994. This popular yellow orchid is susceptible to a lethal basal rot that affects up to 30% of the plants in some Singapore nurseries. The characteristic disease symptom is a golden-brown lesion that first appears at the base of the pseudobulb. The dark brown margin advances gradually until the whole pseudobulb turns golden brown. Infection progresses up the leaves until they become yellow, then brown. The final symptom is dry rot. Under moist and humid . field conditions, many small basidiocarps form on infected plant parts. The fungus was identified as Marasmiellus inoderma (Berk.) Singer, a pantropical species often associated with monocotyledonous hosts. Two single-basidiospore isolates were used to inoculate pseudobulbs of unin-fected Golden Shower orchid plants. Characteristic disease symptoms developed after 3 weeks whereas all the control plants remained healthy. The fungus was reisolated from the inoculated diseased plants; therefore, the basal rot of Oncidium Goldiana is attributed to M. inoderma. This is believed to be the first report of M. inoderma as a pathogen on an orchid species.