Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: a case of konzo-affected Mtwara region, Tanzania

Imakumbili, M. L. E.; Semu, E.; Semoka, J. M. R.; Abass, A.; Mkamilo, G.

doi:10.1101/464594

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bioRxiv · 10.1101/464594

Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: a case of konzo-affected Mtwara region, Tanzania

Imakumbili, M. L. E.·Semu, E.·Semoka, J. M. R.·Abass, A.·Mkamilo, G.

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Abstract

Soils in areas affected by konzo (a cassava cyanide intoxication paralytic disorder) are predominantly infertile and probably unable to supply cassava the nutrients it needs to achieve optimal growth. The soil nutrient levels in these areas, could also be influencing cyanogenic glucoside production in cultivated cassava, however there is hardly any knowledge on this. An assessment of soil nutrient levels on cassava fields in konzo-affected areas was therefore carried out to determine their adequacy for optimal cassava growth and how this influences cassava cyanogenic glucoside production. Konzo-affected Mtwara region, in Tanzania, was used as a case study area. Correlations between total hydrogen cyanide (HCN) levels in cassava roots and various soil nutrient levels on cassava fields were carried out and relationships between cyanide intoxication and soil nutrient levels on fields from which toxic cassava roots had been harvested were also investigated. The results showed that cassava grows under conditions of severe nutrient stress in the region. Soil nutrients found to be deficient on most fields, like potassium (mean = 0.09, SD = 0.05 cmol/kg), magnesium (mean = 0.26, SD = 0.14 cmol/kg) and zinc (mean = 1.34, SD = 0.26 mg/kg), are known to reduce cyanogenic glucoside levels in cassava roots when adequate in soils. Cyanogenic glucoside levels in cassava roots however increased by high levels soil phosphorous (rs = 0.486, p = 0.026 for all varieties) and sulphur (rs = 0.593, p = 0.032 and rs = 0.714, p = 0.047; for bitter and sweet cassava varieties, respectively) on these soils. The likelihood of cassava cyanide intoxication was also increased on fields with high pH and iron levels. High levels of sulphur and phosphorus, to very high levels of iron occurred on some fields. How soil nutrient supply influences cassava cyanogenic glucoside production in the konzo-affected areas was established.

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Imakumbili, M. L. E., Semu, E., Semoka, J. M. R., Abass, A., Mkamilo, G.. 2018-11-07. Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: a case of konzo-affected Mtwara region, Tanzania. https://doi.org/10.1101/464594

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