This paper reports the main conclusions of a series of experiments
concluded at Adiopodoume in the forest zone of the Ivory Coast between
1980 and 1990 on the temporal spread of African cassava mosaic virus
(ACMV). The experiments sought to gain a better understanding of the
epidemiology of the disease it causes and to facilitate the assessment
of control measure. The course of ACMV epidemics over time was shown to
depend closely on crop age and planting date. These relationships were
expressed mathematically and ACMV progress curves were modeled
combining a direct interaction between an overall exponential
decreasing susceptibility to infection with crop age and a sinusoidal
temperature-driven seasonal fluctuation in amount of spread from
outside sources. After being validated using 1930s data from Kiwanda in
Tanzania, this model was extended to incorporate host plant resistance,
spread within plantings and yield losses. Simulation studies showed
that when reversion (non-systemicity of the virus) does not occur and
when cuttings are not selected preferentially from healthy plants,
disease incidence increased in successive plantings of the same clonal
stock and ultimately reached 100%. This occurred whatever the degree of
host resistance, albeit after different periods. By contrast, with
reversion and/or cutting selection, disease incidence may reach
equilibrium values below 100% in resistant cultivars. At such
equilibria, the effects of reversion and/or cutting selection balance
the new virus transmissions by whiteflies. This emphasizes the
potential of resistant cultivars to control ACMV by exploiting their
ability to revert, as such cultivars not only suffer yield loss when
infected, but are less likely to become heavily infected, even after
many cycles of crop production