Biology subjects

Imakumbili, M. L. E.

Publications and source records attributed to Imakumbili, M. L. E..

3 recordsLinked to original sources

bioRxiv2019

Cyanogenic glucoside production in cassava: The comparable influences of varieties, soil moisture content and nutrient supply

Varieties and soil moisture content are the two agronomic factors mostly pointed out as influencers of cyanogenic glucoside production in cassava. The role of soil nutrient supply is however often overlooked or minimised, despite its known influence on cyanogenic glucoside production. A pot experiment was hence carried out to determine whether soil nutrient supply had an equal influence on cyanogenic glucoside production in cassava, as varieties and soil moisture content. The cassava varieties, Kiroba (a sweet cassava variety) and Salanga (a bitter cassava variety), were used in the experiment, together with three soil moisture treatments that respectively induced severe moisture stress, moderate moisture stress and no moisture stress (optimal soil moisture conditions where plants were kept well-watered). The soil nutrient treatments used depicted conditions of low (no fertiliser), moderate (25 N mg, 5 P mg, 25 K mg /kg) and high (25 N mg, 5 P mg, 25 K mg /kg) nutrient supply. A sole K treatment was also included (25 K mg/kg). Total hydrogen cyanide (HCN) levels in cassava leaves were used to indicate the effects of the three factors on cyanogenic glucoside production. The results of the study showed that nutrient supply had a significantly (p < 0.001) equal influence on cyanogenic glucoside production, as varieties (p < 0.001) and soil moisture content (p < 0.001). Cyanogenic glucoside production was however found to be differently influenced by soil moisture content (M) and nutrient supply (N) in both Salanga (MxN, p = 0.002) and Kiroba (MxN, p < 0.001). Leaf HCN levels of unfertilised Salanga and Kiroba were respectively increased by 1.8 times and 2.7 times their levels under optimal soil moisture conditions. Thus, under severe moisture stress, low soil fertility was found to have an increasing effect on leaf HCN levels in both varieties. A high supply of N, P and K, however also had an increasing effect on leaf HCN in both varieties regardless of soil moisture conditions. Leaf HCN levels in Salanga ranged from 95.5 mg/kg to 334.5 mg/kg and in Kiroba they ranged from 39.3 mg/kg to 161.5 mg/kg, on a fresh weight basis. The study managed to demonstrate that soil fertility had an equally important influence on cyanogenic glucoside production, just like varieties and soil moisture content. The study also showed that the effects of nutrient supply on cyanogenic glucoside production in various cassava varieties is dependent on changes in soil moisture content and vice versa.

plant biology↗

bioRxiv2018

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

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.

pharmacology and toxicology↗

bioRxiv2018

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.

pharmacology and toxicology↗