Mkumbira, J; L. Chiwona-Karltun, J. Saka, A.R.K. Mhone, N.M. Mahungu, M. Bokanga; L. Brimer, H. Rosling & U. Gullberg
Cassava is grown m diverse agro-ecologies in tropical Africa. Cyanogenic glucosides (CG) in cassava is determined by both the genotype as well as the environment. Changes in cassava CG levels due to environmental effects are important in areas where cassava is utilised with minimum processing. Factors that affect cassava root CG and taste were studied in farmers’ fields in Nkhata Bay, a lake Malawi shore district in Northern Malawi in 1996. A total of 40 cassava fields for 30 cassava farmers were used. Root CG levels and taste were determined at Mkondezi Agricultural Research Station and soil nutrient determination was done at Chitedze Agricultural Research Station. Mean root taste scores for cool cassava cultivars had strong correlation with soil nitrogen content (r=0 9), soil pH (r=-0.79), root dry matter content (r=0.64), root weight (r=0.83) and cassava plant age (r=0 78). In contrast, cassava root cyanogenic glucoside content had no significant correlation to any of these variables. There was also no correlation between taste and cyanogenic glucoside content. CG content for bitter cassava cultivars had weak significant positive correlation with phosphorus (r= 22), root weight (0.24) and cassava plant age (0.29). Root taste had no significant correlation with all but plant age (r=0.2). Unlike the cool cultivars, there was strong positive correlation between taste and CG (r=0.87) for the bitter cultivars. There is no consistent trend that can be observed in the means of the cuitivars for each agro-ecological determinant. This may indicate that a combination of factors is involved in the agro-ecology hence multivariate analysis of the data obtained would be more suitable. However, there is indication that cassava plants grown in dambo, places without anthills and those planted on ridges had relatively low mean CG content.