Determination of Cyanogenic Compounds Content in Transgenic Acyanogenic Kenyan Cassava (Manihot esculenta Crantz) Genotypes: Linking Molecular Analysis to Biochemical Analysis

Abstract

Being the fourth most important crop in the developing countries surpassed only by maize, rice and sugarcane as a source of calories, cassava (Manihot esculenta Crantz) is doubtlessly a famine reserve crop due to its drought tolerance, ability to grow on infertile soils and its ability to recover from disease and pest attacks. However, this important tuber crop has a fair share of demerits, among which is the fact that all parts of the plant contain toxic levels of cyanogenic glycosides, which have to be removed by laborious processing before cassava can be safely consumed. Conventional methods for removal of cyanogenic glycosides in cassava have seldom been successful for decades. Genetic engineering holds the key to overcoming majority of these limitations in order to produce cassava plants in which desirable traits are optimized and undesirable traits downregulated. The objective of this study was to determine the levels of cyanogenic compounds in three Kenyan cassava genotypes along with an exotic modelcultivar in which cyanogenic glycosides had been downregulated via RNA interference approach in an earlier study by the authors. Cassava roots from transgenic and wild type genotypes were harvested, peeled, cut to pieces and washed three times with cold water, following cyanogenic compounds were extraction by homogenization in acid extraction medium. The supernatant obtained after centrifugation of the homogenate was analyzed for cyanogenic compounds content by spectrophotometric procedures. From this study, transgenic cassava lines with cyanide content three folds less than the cyanide content in the wild type relatives were produced. This confirmed RNAi mediated downregulation of expression of cytochrome P450 genes responsible for biosynthesis of cyano-glycosides previously undertaken by the authors in an earlier study