Characterization of cassava (Manihot esculenta Crantz) varieties in Nigeria and Tanzania, and farmers’ perception of toxicity of cassava

Cassava (Manihot esculenta Crantz) roots in endemic and non-endemic areas for cassava associated neurological syndromes in Nigeria and Tanzania were characterized for levels of cyanogenic compounds, taste, weight and farmers’ perception of toxicity. Mean cyanogenic compounds (mg HCN eq/kg dry wt) in cassava roots was 133 (range 8–1063) in Nigeria ( n = 97 ) , but 61 (range 22–244) in Tanzania ( n = 57 ) , P<0.0001. 13% of cassava varieties in Nigeria were bitter, compared with 12% in Tanzania. Mean cyanogenic compounds (mg HCN eq/kg dry wt) was 103 (range 27–543) in bitter roots compared with 105 (range 8–1064) in sweet roots (P>0.05). Sweet cassava predominates in Nigeria and Tanzania. Mean weight (range) was 405 g (49–3100) for roots of cassava planted at altitude<100 m above sea level, but 298 g (25–2300) for roots of cassava planted at altitude >100 m above sea level, P = 0.02 . Multivariate model shows significant relationship of levels of cyanogenic compounds in cassava roots and altitude, weight of roots and country. High cyanogenic cassava varieties were present in the endemic area in Nigeria, where the altitude is low, but low cyanogenic cassava varieties were present in the endemic area in Tanzania, where the altitude is high. Both sweet and bitter cassava were consumed raw by farmers, who do not perceive bitter cassava as a toxic crop. The practise of delayed harvesting of cassava for food security is low in both countries.