Isolation, characterisation and identification of a potyvirus from Dioscorea alata L. (water yam) in Nigeria

A yam potyvirus was isolated from Dioscorea alata samples collected in Nigeria. The virus was not transmissible mechanically but was transmitted by Aphis craccivora to four cowpea cultivars (Ife Brown, IT84S-2114, IT82E-10 and TVu2657), and from which it could be mechanically transmitted between the cowpea cultivars. In infectivity-tests using cowpea extracts, the virus had a dilution end point of 10(-4), a thermal inactivation point of 60-65 degrees C and longevity in vitro of 2 days at room temperature. The virus coat protein had an estimated molecular weight of 32 100 daltons. The virus was identified as an isolate of Dioscorea alata virus (DAV; syn. yam virus 1) due to its biological characteristics and its serological reaction with antiserum raised against DAV. The virus is not related to yam mosaic virus, but distantly related to blackeye cowpea mosaic virus and cowpea aphid-borne mosaic virus.