ANALYSIS OF TEMPORAL DISEASE PROGRESS OF AFRICAN CASSAVA MOSAIC-VIRUS

Forty-nine disease progress curves of African cassava mosaic virus recorded in Ivory Coast (West Africa) of monthly plantings between 1981 and 1986 were analyzed. The Gompertz model was the most appropriate to describe the epidemics, and analysis of the parameters of the fitted models indicated that the maximum rate of disease increase was reached an average of 2 mo after planting and that the rate of disease progress has a seasonal component. There was a large increase in disease incidence from November to June and a relatively small increase between July and October. About 70% of the variation was related to changes in whitefly numbers and to fluctuations in temperature and radiation. Other possible causes were changes in whitefly activity, virus concentration in plant reservoirs, and plant susceptibility to infection. By contrast, in this tropical, humid climate with a short dry season, the impact of the rain-induced parameters was limited. Whatever the overall disease incidence, a reduction in the rate of spread with age occurred.