Abstract:
Cassava (Manihot esculenta Cranzt) is an important food security crop for resource poor rural communities particularly in Africa. Little is however known about variability of critical root nutritional, biochemical quality traits and molecular diversity of Kenyan cassava germplasm. This led to a study whose objective was to determine the nutritional quality traits of different genotypes of cassava cultivated in the central Rift Valley region of Kenya and to identify genetic constitution of cassava accessions from different regions of Kenya using molecular tools. Roots from fourteen accessions comprising Kenyan local landraces and improved clones were screened for their nutritional traits including the contents of cyanogenic glycosides, protein and the micro nutrients iron and zinc while another 69 accessions were tested for molecular diversity using Simple Sequence Repeats (SSRs). Trait stability and the effects of the environment on the expression of the nutritional traits were evaluated using various genotype (G) x environment (E) interaction study models. There were significant (p<0.05) differences in all the nutritional traits in the three test sites of Baringo, Kericho and Nakuru in Kenya. Contents of cyanogenic glucosides in both roots and leaves, total root proteins, root iron and zinc ranged from 31.8 ppm to 90.8 ppm; 20.8 ppm to 154.4 ppm; 1.15 % to 3.47 %; 17.81 ppm to 59.69 ppm and 39.39 ppm to 118 ppm, respectively. The sites were also significantly (p<0.05) different from each other with the highest cyanogenic content in leaves and roots expressed at the Nakuru site. Regression coefficients (bi) obtained ranged from -2.21 to 2.29 for all traits combined while sensitivity to environmental change (SE2i) revealed that cassava genotypes differed in their level of sensitivity. The root cyanide trait had the highest mean SE2i which indicated that it was the least stable quality trait in the cassava germplasm. The observed values for protein and mineral contents suggest the potential for improving the nutritive value of local cassava germplasm. Seven pairs of micro satellite (SSR) primers previously developed from cassava were used to detect polymorphic 21 alleles in a sample of 69 accessions. The cluster analysis of similarity matrix obtained at 68 % with SSR data showed that the 69 accessions were grouped into five marker based groups. This study proved that SSRs could be used to identify cassava accessions as well as in the assessment of level of genetic relatedness among accessions.
