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Two Serotypes of Sweetpotato feathery mottle virus in Uganda and Their Interaction with Resistant Sweetpotato Cultivars

First author: Ministry of Agriculture, Animal Industry and Fisheries, c/o Kawanda Agricultural Research Institute, P.O. Box 7065, Kampala, Uganda, and Institute of Biotechnology, University of Helsinki, Finland, and Department of Plant Biology, Genetic Centre, Swedish University of Agricultural Sciences (SLU), Box 7080, S-750 07, Uppsala, Sweden; second and fourth authors: Department of Plant Biology, SLU, Uppsala, Sweden, and Institute of Biotechnology, University of Helsinki, Finland; and third author: Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, U.K.

Isolates of Sweetpotato feathery mottle virus (SPFMV, genus Potyvirus, family Potyviridae) were obtained in several districts of Uganda from sweetpotato plants infected with the sweetpotato virus disease (SPVD), the most important disease of this crop in Africa. A monoclonal antibody (MAb 7H8) raised 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 isolates into those detectable and not detectable by the MAb. These two serotypes differed in prevalence in different districts of Uganda and in two common sweetpotato cultivars. Both serotypes could be transmitted simultaneously by single aphids. The serotypes differed in their ability to systemically coinfect sweetpotatoes that were infected with Sweetpotato chlorotic stunt virus (SPCSV, genus Crinivirus), the virus required to induce SPVD in SPFMV-infected plants. One sweetpotato breeding line, resistant to SPFMV from the New World, was infected by graft-inoculation with all SPFMV isolates from Uganda. Another SPFMV-resistant sweetpotato line became infected with SPFMV and developed SPVD only following coinoculation with SPCSV.