First identification of a sweet potato begomovirus (sweepovirus) in Uganda: characterization, detection and distribution

Sweet potato begomoviruses diverge basally from all other begomoviruses and have been named sweepoviruses. In 2009, a sweepovirus was detected for the first time in sweet potato crops in Uganda by using the indicator plant Ipomoea setosa and generic primers in a polymerase chain reaction (PCR). An isolate was cloned and sequenced, the first fully sequenced genome of a sweepovirus from mainland Africa. At the nucleotide level, this isolate differed from other sweepoviruses by at least 13%, discriminating the Ugandan isolate as a new species which has been tentatively named Sweet potato leaf curl Uganda virus (SPLCUV). In infected sweet potato plants, SPLCUV showed an uneven distribution; it was detected more often in samples from the midrib and lamina of middle and lower leaves, and reversion to healthy tissue occurred, especially in shoots of cv. New Kawogo. This appears to be the first report of resistance to a sweepovirus in sweet potato. While it was only detected at relatively low efficiency by PCR, use of I. setosa plants as an indicator of sweepovirus infection in sweet potato plants was as efficient as using real-time quantitative PCR (qPCR). Storage of dry leaves for 84 days and dried DNA extracts for 21 days did not affect the ability of PCR and qPCR to detect it. Sweepovirus(es) was detected frequently using generic primers in cultivars Ejumula, New Kawogo and 318L in eastern and central Uganda.