Odu B.O; Shoyinka S.A; Hughes J. d’A; Asiedu R and Oladiran A.O
Yams are an important staple food in Africa. Nigeria produced about 70% of 33 million
MT of yams produced globally in 1996. Pests and diseases are still major production constraints.
Five viruses have been reported to infect yams in Nigeria: yam mosaic poty virus (YMV), Dioscorea alata potyvirus (DAV), cucumber mosaic cucumovirus (CMV), Dioscorea dumetorum potyvirus
(DdV) and Dioscorea alata badnavirus (DaV). YMV, infecting D. rotundata and D. alata in all the yam-growing areas of Nigeria, was found to cause severe chlorosis, veinal chlorosis, green vein banding, shoe-stringing, leaf distortion and severe stunting. It is transmitted both mechanically and by Aphis spp. DAV is transmitted to test plants by A. craccivora and Rhopalosiphum maidis. It causes mottling, green vein banding, severe chlorosis and leaf distortion. DaV-infected plants have distorted and crinkled leaves. The symptoms of the viruses, their transmission, diagnosis, distribution and possible effects on yam production in Nigeria are discussed.