The incidence of sweet potato virus disease and virus resistance of sweet potato grown in Uganda

Sweet potato virus disease (SPVD) was common (25-30% average incidences), a nd farmers recognised it as an important disease, in sweet potato crops in southern Mpigi, Masaka and Rakai Districts in Uganda, but SPVD was rare in Soroti and Tororo Districts. Whiteflies, which are the vector of sweet pota to chlorotic stunt crinivirus (SPCSV) a component cause of SPVD, were corre spondingly common on sweet potato crops in Mpigi and rare on crops in Toror o. However, aphids, which are the vectors of sweet potato feathery mottle p otyvirus (SPFMV), the other component cause of SPVD, were not found colonis ing sweet potato crops, and itinerant alate aphids may be the means of tran smission. Different sweet potato cultivars were predominant in the differen t districts surveyed and four local cultivars obtained from Kanoni in S. Mp igi, where whiteflies and SPVD were common, were more resistant to SPVD tha n four cultivars from Busia in Tororo District, where whiteflies and SPVD w ere rare. However, nationally released cultivars were even more resistant t han the local cultivars from Kanoni. Yield results and interviews with farm ers indicated that farmers in S. Mpigi were making compromises in their cho ice of cultivars to grow, some key factors being SPVD susceptibility, and t he yield, taste, and marketability, duration of harvest and in-ground stora bility of the storage roots. These compromises need to be included in an as sessment of yield losses attributable to SPVD.