Introduction. Research on diseases now known to be caused by, or associated with, geminiviruses includes several early studies which have become classics in the literature of plant pathology. Curly top virus (CTV), the cause of major diseases in several crops in the western United States and the Mediterranean, has been the subject of considerable study since the early 1900s (Bennett, 1971). The relationship of the leafhopper vector (Circulifer tenellus) to disease spread was understood before 1910, and significant progress was made before 1950 in developing control measures based upon genetic resistance in crop species, improvements in crop management and control of vectors with insecticides (Bennett, 1971; Goodman, 1981). There is a similar history for maize streak virus (MSV), which causes one of the most important diseases of maize in Africa. Maize streak disease was the subject of serious research, notably by H. H. Storey and co-workers, beginning in the 1920s (Bock et al., 1974; Rose, 1978).