ANALYSIS OF TEMPORAL DISEASE PROGRESS OF AFRICAN CASSAVA MOSAIC-VIRUS

Forty-nine disease progress curves of African cassava mosaic virus rec orded in Ivory Coast (West Africa) of monthly plantings between 1981 a nd 1986 were analyzed. The Gompertz model was the most appropriate to describe the epidemics, and analysis of the parameters of the fitted m odels indicated that the maximum rate of disease increase was reached an average of 2 mo after planting and that the rate of disease progres s has a seasonal component. There was a large increase in disease inci dence from November to June and a relatively small increase between Ju ly and October. About 70% of the variation was related to changes in w hitefly numbers and to fluctuations in temperature and radiation. Othe r possible causes were changes in whitefly activity, virus concentrati on in plant reservoirs, and plant susceptibility to infection. By cont rast, in this tropical, humid climate with a short dry season, the imp act of the rain-induced parameters was limited. Whatever the overall d isease incidence, a reduction in the rate of spread with age occurred.