Effects of Cassava Mosaic Virus Disease on the Growth and Yield of Cassava - Some Highlights from Makerere Experiments

African Crop Science Journal, Vol. 7. No. 4, pp. 511-522, 1999 Effects of Cassava Mosaic Virus Disease on the Growth and Yield of Cassava - Some Highlights from Makerere Experiments Code Number: CS99042 ABSTRACT: A series of experiments is described in which the effects of cassava mosaic disease (CMD) on the growth and yield of cassava were evaluated. Four cassava varieties of differing resistance/susceptibility were used. These were Ebwanatereka (Susceptible local), Nase 2 (Moderately resistant/improved), SS4 and Migyera (Resistant/improved). The results showed significant differences between varieties and their mixtures both in the incidence and the amount of disease that developed. Ebwanatereka had the highest CMD incidence while SS4 had the lowest. Varietal mixtures consistently and significantly decreased the incidence of CMD and the population of adult whiteflies compared to their corresponding pure stand treatments. Stage of infection significantly affected the yield of the susceptible variety, Ebwanatereka. The earlier the infection, the greater was the effect of CMD. However, the stage of infection did not appear important in the resistant varieties. Compensation occurred in all varieties although significantly more compensation was achieved in Ebwanatereka. The health status of the immediate neighbours significantly influenced the losses sustained. Application of NPK fertiliser significantly increased the incidence of CMD in Nase 2 and Migyera compared with the unfertilised treatments. However, little difference was apparent in Ebwanatereka which became almost totally infected in all treatments. Adult whitefly populations were increased significantly by the application of NPK in Nase 2 and Ebwanatereka, whereas no effect was observed in Migyera. The implications of these findings in the epidemiology and management of CMD and the scope for future research are discussed. KEYWORDS: Bemisia tabaci, CMD, leaf area index, Uganda Copyright 1999, African Crop Science Societ