Farmers’ perceptions on the causes of cassava root bitterness: A case of konzo-affected Mtwara region, Tanzania

In areas where konzo (a cassava cyanide related paralytic disorder) persists, the agronomic factors causing increased cyanogenic glucoside levels in cassava, during periods without water stress, are hardly known. However, through their assessment of cassava root toxicity, using its bitter taste, farmers may have noticed factors unrelated to water stress that additionally influence the cyanogenic glucoside content of cassava cultivated in these areas. Increased cassava root bitterness is often associated with an increase in cyanogenic glucoside levels, making it a good indicator of changes in root cyanogenic glucoside content. Bitter cassava varieties that are preferentially planted by people living in most konzo-affected areas, are an additional known contributor to high cyanogenic glucosides. It is water stress that further increases the inherent toxicity of the planted bitter cassava varieties. Using konzo-affected Mtwara region in Tanzania as a case study, a household survey was carried out to identify the overlooked agronomic factors that additionally influence cyanogenic glucoside levels in cassava cultivated in konzo-affected areas. A total of 120 farmers were interviewed and they mentioned a number of factors unrelated to water stress, as agronomic factors that influenced cassava root bitterness and hence cyanogenic glucoside production in cassava. The mentioned factors included; certain soil characteristics (14.2%), plant age at harvest (7.5%), poor weeding (0.8%), piecemeal harvesting (0.8%), and branch pruning (0.8%). The revealed factors constitute permanent environmental characteristics and crop management practices commonly used by farmers living in konzo-affected Mtwara region in Tanzania. The revealed factors could be contributing to increased cyanogenic glucoside levels in cassava, during periods without water stress in areas where konzo persists.

在木薯疯（konzo，一种与木薯氰化物相关的瘫痪性疾病）持续流行的地区，无水分胁迫时期内导致木薯氰苷（cyanogenic glucoside）含量升高的农艺因子仍鲜为人知。然而，农户可通过木薯块根的苦味评估其毒性，借此留意到该地区种植的木薯中，除水分胁迫外另有其他因素会影响氰苷含量。木薯块根苦味加剧通常与氰苷含量升高相关，因此苦味可作为块根氰苷含量变化的良好指示指标。在多数受木薯疯影响的地区，农户优先种植的苦味木薯品种，是导致氰苷含量偏高的另一已知因素；而水分胁迫则会进一步提升已种植的苦味木薯品种的固有毒性。本研究以坦桑尼亚受木薯疯影响的姆特瓦拉地区为案例开展农户调查，旨在识别木薯疯流行地区中，除水分胁迫外额外影响木薯氰苷含量的被忽视农艺因子。本次调查共访谈120名农户，农户提及了多项与水分胁迫无关的农艺因子，这些因子会影响木薯块根苦味，进而影响木薯的氰苷生成。提及的因子包括：特定土壤特性（14.2%）、收获时植株株龄（7.5%）、除草不及时（0.8%）、分期采收（0.8%）以及枝条修剪（0.8%）。上述识别出的因子均为坦桑尼亚姆特瓦拉木薯疯疫区农户日常采用的永久性环境特征与作物管理措施。在木薯疯流行且无水分胁迫的时期，上述因子可能会导致木薯氰苷含量升高。