Abstract1. A serological survey carried out in 13 orchid nurseries in Puerto Rico revealed the presence of tobacco mosaic in association with Cymbidium mosaic in variegated Cattleya flowers and in leaves of Cattleya, Epidendrum, and Calanthe. 2. Cattleya flowers showing mild pigment disturbances were shown to contain CMV only in serologically detectable amounts. Most flowers displaying gross color-breaking were shown to contain in addition, TMV. 3. No definite symptom pattern could be associated with a positive serological reaction, but a large majority of samples displaying the necrotic symptoms of Cymbidium mosaic in Cattleya were serologically positive. The nonreliability of visual observations for virus diagnosis in orchid leaves is further stressed. 4. The limitations of the precipitin test in relation to the present study are discussed.
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