Host resistance and epidemiology of African cassava mosaic virus disease in different agroecologies of Uganda

The African cassava mosaic disease (ACMD) is a major production constraint of cassava in Uganda. It is caused by a geminivirus (ACMV) that is transmitted by the whitefly vector (Bemisia tabaci) and disseminated by man through infected cuttings. Studies were conducted in four locations (i.e., Namulonga, Nakasongola, Masindi and Lira) to understand the effect of date of planting, varietal resistance and inoculum level on the incidence and deveelopment of ACMD in the context of formulating plausible control strategies. The locations represented four different agroecologies of Uganda; Namulonge for the humid, wet and low ACMV pressure zone, Nakasongola for dry savanna and high ACMV pressure zone, Masindi in the humid tall grassland and Lira for the humid short grassland both of intermediate ACMV infection pressure. Two improved cassava varieties Nase I and Nase 2 and a local cultivar (Ebwanatereka) were used in the planting date studies. Planting was done in 1993 during the first and second rains referred to as March-June and August-October, respectively. Results showed seasonal variation in ACMD incidence. Plantings made during the first rains had higher ACMD incidence than those during the second rains plantings. October plantings showed the lowest while the April and May plantings had the highest ACMD incidence. ACMD development was related to agroecologies. Also noted was the significant variation in susceptibility to infection among the varieties. Improved varieties were more resistant than the local variety.