In a survey of most sweetpotato-growing areas of Uganda, virus-like diseases were observed in all districts surveyed. Out of 338 fields sampled in 35 of the then 42 districts, 219 (65%) had some plants with symptoms. The most common symptoms included vein clearing, mottling, leaf distortion, yellowing, stunting and leaf strapping. Particularly high viruslike disease incidences (means of 34-86%) were encountered in districts around Lake Victoria and in the Rift Valley in southern and western parts of Uganda; particularly low incidences were encountered in the east and north of Uganda. Using four formats of enzyme-linked immunosorbent assay in combination with immunoelectron microscopy and polymerase chain reaction assays, five viruses were identified. Sweet potato feathery mottle virus (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV) were most commonly detected, being found in about 90% of samples. Sweet potato mild mottle virus at 10%, Sweet potato chlorotic fleck virus (SPCFV) at 8% and Sweet potato caulimo-like virus (SPCaLV) at 0·07% were more rarely detected. Most infections were multiple, SPCSV + SPFMV constituting > 90% of all double infections. Triple infections, involving mainly SPFMV, SPCSV and either SPMMV or SPCFV, and quadruple infections of SPFMV + SPCSV + SPMMV + SPCFV were observed in < 10% of the diseased samples. The identification of SPCaLV is the first evidence of its occurrence in Africa.

Abs tract. Twenty-six cowpea lines were field evaluated for resistance to Xanthomonas campestris pv vignicola for two seasons in two locations of Uganda following artificial inoculation. Disease development varied significantly (P=0.001) with the cowpea lines in both locations, and higher disease incidence was observed during the first rains than in second rains. The genotype-by-environment interaction was, however, non-significant during the two seasons. During the first rains, the highest disease incidences (54.96%) and (54.53%) were recorded in the lines IT82E-12 and SLA 59, respectively. During the second rains, however, the highest disease incidence (65.85%) was recorded in the line Ife Brown. Based on AUDP C values, lines were grouped into four categories, i.e. resistant, moderately resistant, moderately susceptible and susceptible. The lines IV 1075 and Icirikukwai were consistently classified as resistant in both seasons.

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