Abstract:

A comprehensive survey of the incidence of ACMD was carried out, between 1990 and 1992, in all the 32 important cassava growing administrative districts of Uganda. The incidence varied between districts, counties within districts and also between fields within a county. Overall incidence in the country as a whole was 57%. Incidence in individual fields ranged from 0% in districts in the wetter and more humid Lake Victoria (southern) region to 100% in districts in the drier short grassland savannah regions in the east, north and west. The differences in incidence are related to the main agroecological regions of the country and were associated with differences in climate and abundance of whitefly vectors. Infection of local selections (Ebwanateraka, Senjonjo, Bao, Bukalasa 11) and improved genotypes (TMS 30786, TMS 30337, TMS 60140, TMS 60142, TMS 30395 and TMS 30572) was studied during the 1990-1992 seasons in four locations in different agroecological regions and in on-farm trials in northern Luwero. There were significant differences in ACMD incidence and adult whitefly populations between locations and between genotypes in location. The local varieties and TMS 30786 were quickly infected and final incidence reached 90%-100% in some locations. In contrast, TMS 30395, TMS 30572 and TMS 60142 sustained very little infection and symptoms tended to become inconspicuous even disappear during the later stages of growth, varieties also harboured low whitefly populations. ACMV was multifactorial and due to components, that of infection, or a These Resistance to delayed time reduced the rate of infection, restricted symptom Variations expression, and probably to resistance to the vector, between locations were associated with differences in whitefly populations.