Department of Soils and Geological Sciences, Sokoine University of Agriculture, Morogoro, Tanzania.
The International Institute of Tropical Agriculture, Dar es Salaam, Tanzania.
PLoS One. 2019 May 13;14(5):e0216708. doi: 10.1371/journal.pone.0216708. eCollection 2019.
Soils in areas affected by konzo (a cassava cyanide intoxication paralytic disorder) are predominantly infertile and probably unable to supply cultivated cassava with the nutrients it needs to achieve optimal growth. Soil nutrient supply in these areas could also be influencing cyanogenic glucoside production in cassava, however there is hardly any knowledge on this. An assessment of soil nutrient levels on crop fields in konzo-affected areas was therefore carried out to determine their adequacy for optimal cassava growth. Konzo-affected Mtwara region of Tanzania, was used as a case study. Whether soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas and how it could be doing this, was additionally investigated. To investigate this, correlations between total hydrogen cyanide (HCN) levels (a measure of cyanogenic glucoside content) in cassava roots and various soil nutrient levels on crops fields were carried out. This was followed by an investigation of relationships between cases of cassava cyanide intoxication and soil nutrient levels on crop fields from which the consumed toxic cassava roots had been harvested. Cases of cassava cyanide intoxication were used as a proxy for high cyanogenic glucoside levels in cassava roots. Logistic regression analysis was used in the latter investigation. Other important non-nutrient soil chemical characteristics, like pH and soil organic carbon, were also included in all analysis performed. The results revealed that most soil nutrients known to have reducing effects on cassava cyanogenic glucosides, like potassium (mean = 0.09 cmol/kg, SD = 0.05 cmol/kg), magnesium (mean = 0.26 cmol/kg, SD = 0.14 cmol/kg) and zinc (mean = 1.34 mg/kg, SD = 0.26 mg/kg) were deficient on several crop fields. The results also showed that cyanogenic glucosides in cassava roots could be increased with the increased supply of sulphur in soils in bitter cassava varieties (rs = 0.593, p = 0.032), and with the increased supply of P in soils in all cassava varieties (rs = 0.486, p = 0.026). The risk of cassava cyanide intoxication occurring (and thus high cyanogenic glucoside levels in cassava) was found to be likely increased by cultivating cassava on soils with high pH (X2 = 8.124, p = 0.004) and high iron (X2 = 5.740, p = 0.017). The study managed to establish that cassava grows under conditions of severe nutrient stress and that soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas of Mtwara region. Despite the multiple soil nutrient deficiencies on crop fields, low soil fertility was however not the only probable cause of increased cyanogenic glucosides in cassava, as high soil nutrient levels were also found to be potential contributors.
在受科酮病（一种木薯氰化物中毒性麻痹疾病）影响的地区，土壤通常贫瘠，可能无法为种植的木薯提供生长所需的全部养分。然而，这些地区的土壤养分供应情况也可能影响木薯中氰苷的产生，但目前对此几乎没有任何了解。因此，对科酮病地区的作物田土壤养分水平进行了评估，以确定其是否适合木薯的最佳生长。坦桑尼亚姆特瓦拉地区的科酮病地区被用作案例研究。此外，还调查了土壤养分供应是否会影响在受科酮病影响的地区种植的木薯中氰苷的产生，以及它可能会产生怎样的影响。为了进行调查，对木薯根中的总氢氰酸（HCN）水平（氰苷含量的衡量标准）与作物田中的各种土壤养分水平进行了相关性分析。然后，调查了从食用有毒木薯根的作物田中采集的中毒病例与土壤养分水平之间的关系。木薯氰化物中毒病例被用作木薯根中氰苷含量高的替代指标。在后者的调查中，使用了逻辑回归分析。还对其他重要的非营养性土壤化学特性（如 pH 值和土壤有机碳）进行了分析。研究结果表明，在多个作物田中，几种已知对木薯氰苷具有还原作用的土壤养分（如钾（均值=0.09 cmol/kg，标准差=0.05 cmol/kg）、镁（均值=0.26 cmol/kg，标准差=0.14 cmol/kg）和锌（均值=1.34 mg/kg，标准差=0.26 mg/kg））都存在缺乏的情况。研究结果还表明，在苦木薯品种中，随着土壤中硫供应量的增加，木薯根中的氰苷（rs=0.593，p=0.032）和在所有木薯品种中，随着土壤中磷供应量的增加，木薯根中的氰苷（rs=0.486，p=0.026）也会增加。研究发现，在 pH 值高（X2=8.124，p=0.004）和铁含量高（X2=5.740，p=0.017）的土壤中种植木薯，可能会增加木薯氰化物中毒（即木薯中氰苷含量高）的风险。研究表明，木薯在严重的养分胁迫条件下生长，土壤养分供应会影响姆特瓦拉地区科酮病地区种植的木薯中氰苷的产生。尽管作物田中的土壤存在多种养分缺乏，但土壤肥力低并不是导致木薯中氰苷含量增加的唯一可能原因，因为高土壤养分水平也可能是潜在的原因之一。
