Symptoms, aetiology and serological analysis of sweet potato virus disease in Uganda

Sweet potato virus disease (SPVD) is the name used to describe a range of severe symptoms in different cultivars of sweet potato, comprising overall plant stunting combined with leaf narrowing and distortion, and chlorosis, mosaic or vein‐clearing. Affected plants of various cultivars were collected from several regions of Uganda. All samples contained the aphid‐borne sweet potato feathery mottle potyvirus (SPFMV) and almost all contained the whitefly‐borne sweet potato chlorotic stunt closterovirus (SPCSV). SPCSV was detected by a mix of monoclonal antibodies (MAb) previously shown to react only to a Kenyan isolate of SPCSV, but not by a mixture of MAb that detected SPCSV isolates from Nigeria and other countries. Sweet potato chlorotic fleck virus (SPCFV) and sweet potato mild mottle ipomovirus (SPMMV) were seldom detected in SPVD‐affected plants, while sweet potato latent virus (SPLV) was never detected. Isolates of SPFMV and SPCSV obtained by insect transmissions together induced typical symptoms of SPVD when graft‐inoculated to virus‐free sweet potato. SPCSV alone caused stunting and either purpling or yellowing of middle and lower leaves when graft‐inoculated to virus‐free plants of two cultivars. Similarly diseased naturally inoculated field plants were shown consistently to contain SPCSV. Both this disease and SPVD spread rapidly in a sweet potato crop.