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First Report of Leaf Blight of Chinese Ground Orchid (Phaius tankervilliae) Caused by Botrytis cinerea in India

Chinese ground orchid (Phaius tankervilliae Banks:Blume) is a beautiful, terrestrial orchid, which belongs to the family Orchidaceae. It is used as a cut flower, which lasts for 4 to 5 weeks. This species is considered endangered and rare in nature. In June of 2007, potted plants of P. tankervilliae in Shillong, Meghalaya (northeast India; maximum temperature 24°C, minimum temperature 18°C, and 83.5% relative humidity) exhibited leaf blight. Symptoms included water-soaked lesions and dense, gray mold growing on infected tissues. Thirty-six percent of the plants surveyed were found to have this disease. For isolation, diseased tissue was surface disinfested by soaking it in 0.5% sodium hypochlorite for 1 min, air dried, plated on potato dextrose agar, and incubated at 20°C. Mycelia were initially white but later turned gray. Mature, unicellular, ellipsoid, hyaline conidia (6.3 to 8.2 × 9.6 to 11.4 μm) were formed in botryose heads. Hard, black, irregular-shaped sclerotia (average size 1.8 × 2.3 mm) were formed after 15 days. On the basis of these morphological characters, the pathogen was identified as Botrytis cinerea Pers.:Fr. (1). Pathogenicity was confirmed by spraying plants with a spore suspension (10⁶ spores per ml), which were then maintained under high humidity for 48 h at 20 to 22°C by covering with cheesecloth. Five potted plants were inoculated and five were sprayed with sterile water. Lesions and spore masses that were identical to those observed appeared 5 to 6 days after inoculation. Water-treated control plants remained asymptomatic. B. cinerea was reisolated from inoculated plants. A literature search revealed no previous record of this disease in India. So, to our knowledge, this is the first record of B. cinerea on P. tankervilliae in India.

References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CMI, Kew, Surrey, England, 1971.