Virus incidence increased from 10 to more than 95 percent in a field-planting of Dioscorea spp. between 1903 and 1964. The predominant symptom consisted of dark-green bands of tissue bordering the main veins, while the interlaminate areas of the leaves were yellowish-green. The virus was mechanically transmitted to Dioscorea composita, D. floribunda, Crolalaria striata, Nicoliana glutinosa, and N. tabacum was a symptomless host. Symptoms observed on D. friedrichshalii and D. spiculiflora in the field were similar to those observed on other Dioscorea spp. in the greenhouse. C. striata, a common weed in Puerto Rico, may serve as a reservoir for the virus. The virus was not transmitted with a tuber-culling knife from diseased to healthy tubers, but transmission was effected through tuber-grafts. The virus could not be inactivated in vivo with high temperature treatments of the tubers. Preliminary evidence suggested that the virus is transmitted by the cotton aphid (Aphis gossypii).