|| A virus causing necrotic spots and necrotic flecks on the leaves of Vanda orchids in Japan was identified as cymbidium mosaic virus(Cymv) on the basis of host range,stabilly in crude sap, particle morphology, serological test and physico-chemical properties. The virus was transmitted by sap inoculation to 12 of 57 species in 6 of 12 families tested, but not by aphid Mizus persicae or through seeds. Systemic infection occurred in all Orchidaceae plants tested and only one in non-orchidaceae (Sesamum indicum). In Tetragonia expansa sap, the infective at a dilution of 10-5 but not at 10-6, after heating at 65℃ for 10 min, and was still active after 1 month aging in vitro. Flexuous rod particles, c. 475×13nm,
were observed.In ultrahtin sections of leaf tissues from diseased plants, virus particles were found to aggregate in the cytoplasm. The molecular weight of the protein submit and RNA determined by gel electrophoresis, was 27.8×103 and 2.2×106, respectively. Double-stranded RNAs with estimated molecular weight of 5.4×106, 4.0×106, 3.6×106 and 3.0×106 were isolated from infected plants.