Farmers perceptions on the causes of cassava root bitterness in konzo-affected areas of Mtwara Region, Tanzania

The agronomic factors influencing increased cyanogenic glucoside levels, particularly in bitter cassava varieties during periods without water stress, in areas where konzo (a cassava cyanide related paralytic disorder also called spastic paraparesis) persists, are hardly known. However, through their assessment of bitter taste, farmers may have noticed factors unrelated to water stress and variety type that additionally influence cassava root cyanogenic glucoside content in these environments. Bitterness in cassava is usually associated with high cyanogenic glucoside levels. Using some konzo-affected areas in Mtwara region of Tanzania as a case study, a survey was thus carried out to identify the factors, hitherto overlooked, that may additionally influence cyanogenic glucoside levels in cassava. A total of 120 farmers were interviewed. A number of factors unrelated to water stress and variety type that could be additionally influencing cyanogenic glucoside production in cassava plants were mentioned. The mentioned factors included nutrient poor soils, plant age at harvest, weeds, piecemeal harvesting, and branch pruning; the factors, respectively, constituted 14.2%, 7.5%, 0.8%, 0.8%, and 0.8% of the total responses given. The revealed factors constitute permanent environmental characteristics and commonly used crop management practices by farmers living in konzo-prone Mtwara region of Tanzania that could be additionally resulting in high cyanogenic glucoside levels in cassava, regardless of water stress.