Natural wild hosts of sweet potato feathery mottle virus show spatial differences in virus incidence and virus-like diseases in Uganda.

Sweet potato feathery mottle virus (SPFMV, genus Potyvirus) is globally the most common pathogen of sweetpotato. An East African strain of SPFMV incites the severe 'sweetpotato virus disease' in plants co-infected with Sweet potato chlorotic stunt virus and threatens subsistence sweetpotato production in East Africa; however, little is known about its natural hosts and ecology. In all, 2,864 wild plants growing in sweetpotato fields or in their close proximity in Uganda were observed for virus-like symptoms and tested for SPFMV in two surveys (2004 and 2007). SPFMV was detected at different incidence in 22 Ipomoea spp., Hewittia sublobata, and Lepistemon owariensis, of which 19 species are new hosts for SPFMV. Among the SPFMV-positive plants, approximately 60% displayed virus-like symptoms. Although SPFMV incidence was similar in annual and perennial species, virus-like diseases were more common in annuals than perennials. Virus-like diseases and SPFMV were more common in the eastern agroecological zone than the western, central, and northern zones, which contrasted with known incidence of SPFMV in sweetpotato crops. The data on a large number of new natural hosts of SPFMV detected in this study provide novel insights into the ecology of SPFMV in East Africa.