Changes in the incidence and severity of Cassava mosaic virus disease, varietal diversity and cassava production in Uganda

A survey in 1994 assessed the incidence and severity of Cassava mosaic virus disease (CMD) in Uganda and the changes that had occurred since the previous survey in 1990-92. Three counties in each of 27 districts were selected and 15 fields were assessed per county. CMD occurred in each of the 1215 fields surveyed and the overall incidence within fields was 64% compared with 52% in the same districts in 1990-92. Mean incidence differed significantly between districts and between counties within some districts. The incidence and severity of CMD had increased in 20 and 23 of the 27 districts, respectively, compared with 1990-92, indicating the continued progress of the epidemic that was first reported in Uganda in 1988. In all but three districts, there had been a decrease in the total area of cassava. The number of different varieties that predominated in one or more fields had increased in 17 districts compared with 1990-92, although the total number of varieties encountered was little changed. Ebwanateraka was again the most widely grown variety but it was recorded less frequently and predominated or was co-dominant in only two districts in 1994 compared with seven in 1990-92. The biggest decrease in the cultivation of Ebwanateraka had occurred in districts where there was a high incidence of CMD in 1990-92.