Two serotypes of Sweetpotato feathery mottle virus in Uganda and their interaction with resistant sweetpotato cultivars

Isolates of Sweetpotato feathery mottle virus (SPFMV, genus Potyvirus, fami ly Potyviridae) were obtained in several districts of Uganda from sweetpota to plants infected with the sweetpotato virus disease (SPVD), the most impo rtant disease of this crop in Africa. A monoclonal antibody (MAb 7H8) raise d against the coat proteins (CP) of a mixture of the SPFMV strain C (United States) and the isolate SPV-I. (West Africa) distinguished Ugandan SPFMV i solates into those detectable and not detectable by the MAb. These two sero types differed in prevalence in different districts of Uganda and in two co mmon sweetpotato cultivars. Both serotypes could be transmitted simultaneou sly by single aphids. The serotypes differed in their ability to systemical ly coinfect sweetpotatoes that were infected with Sweetpotato chlorotic stu nt vints (SPCSV, genus Crinivirus), the virus required to induce SPVD in SP FMV-infected plants. One sweetpotato breeding line. resistant to SPFMV from the New World, was infected by graft-inoculation with all SPFMV isolates f rom Uganda. Another SPFMV-resistant sweetpotato line became infected with S PFMV and developed SPVD only following coinoculation with SPCSV.