Simon C. Jeremiah, Richard W. Gibson, Raphael P. Msabaha
Crops of sweet potato and cassava were examined and farmers interviewed in Mara, Mwanza, Shinyanga and Kagera regions in the Lake Zone of Tanzania. Sweet potato virus disease (SPVD) affected sweet potato crops in all four regions and was shown by enzyme linked immuno- sorbent assays (ELISA) to be caused by infection with the aphid-borne sweet potato feathery mottle virus (SPFMV) and the East African strain of the whitefly-borne sweet potato chlorotic stunt virus (SPCSV). SPVD was especially common in sheltered fields and in Kagera region where it averaged 50% incidence at Kyaka near the Uganda border. Whiteflies were also abundant on many crops, again especially in sheltered locations, but their numbers were significantly correlated with SPVD incidence only in Kagera region. Most sweet potato farmers regard as high yielding landraces were susceptible to SPVD. Cassava mosaic disease was also observed in all four districts and was also common in Kagera. Most cassava farmers stated that they selected planting material from disease- free plants and a few also stated that they rogued diseased cuttings for the first few months after crop establishment. However, whiteflies were rare on cassava plants and most mosaic disease appeared to derive from farmers planting infected cuttings rather than from whitefly-borne infection.