CHARACTERIZATION OF CASSAVA (Manihot esculenta Crantz) GERMPLASM IN KENYA

Abstract

Cassava (Manihot esculenta Crantz) is a crucial income crop and staple food crop, providing substantial carbohydrates for millions globally and supporting small-scale farmers in Kenya. Due to incorrect characterization of the phenotypic and genetic materials available, the gene pool for cassava in Kenya are frequently overestimated or underestimated. Therefore, this study sought to characterize cassava germplasm in Kenya. Specific objectives were to; characterize and delimit cassava germplasm based on their phenotypic traits, investigate the genetic diversity among the cassava germplasm using molecular markers and also to determine the cyanide concentration levels in leaves, peels and pulp among cassava germplasm in Kenya. A total of 131 cassava accessions were collected from 7 major purposefully selected cassava growing Counties in Kenya. Each cassava accession was represented by a single plant. This plant was divided into 3- 10 pieces and planted in single rows. Plants from this main plot were collected and planted in three sites. In each plot, three rows of five plants were planted. Data collection on phenotypic traits was done at 3, 6, 9 and 12 months. Twenty-one qualitative and four quantitative phenotypic data were collected and subjected to multivariate analysis. At a statistical significance of p≤0.05, the data was subjected to cluster analysis and dendogram construction. From the main plot, apical leaf samples from 40 proportionately sampled accessions were taken for evaluation of genetic diversity and population structure using start-codon-targeted (SCoT) molecular markers. Cluster analysis and dendogram development was done to establish the accessions' genetic variability. A total of 32 samples were processed for cyanide content analysis using picrate paper and spectrophotometric methods. In a field survey, 32 cassava sample accessions were randomly collected from various farms in Migori County for cyanide determination. Phenotypically, a dendrogram generated categorized these accessions into four clusters with Cluster 1, 2, 3 and 4 containing 72.5%, 16.0%, 3.1%, and 8.4% of the genotypes, respectively. Out of the 25 phenotypic traits assessed, 11 principal components accounted for 71.58% of the genetic variation. A total of 119 fragments were amplified, with 89.9% being polymorphic, indicating moderate genetic diversity. The dendrogram grouped the accessions into two clusters at a 0.35 genetic similarity coefficient. Moderate genetic variation among the accessions was revealed by SCoT markers. The study also revealed significant variations in cyanide levels across different cassava parts and accessions. The spectrophotometric method recorded average cyanide levels of 5.89 mg/L, 7.42 mg/L and 8.20 mg/L in leaves, peels and pulps respectively while the picrate paper method showed 3.13 mg/L, 5.44 mg/L, and 7.97 mg/L. The highest cyanide concentration was found in Nyarkadera leaves (26.93 mg/L), Kazanzwara peels (17.82 mg/L) and Nyatanga pulps (26.93 mg/L). The lowest levels were in Nyatanga-002, Nyakanyamkago, and Kasukali leaves (0.40 mg/L), Kasukali peels (1.19 mg/L) and Mzungu pulps (0.40 mg/L). Moderate positive correlations (r=0.547 and r=0.570) between cyanide concentrations in leaves and peels, and a strong positive correlation (r=0.936) in pulps was established. Thus, cassava germplasm in Kenya exhibits moderate diversity, with molecular data revealing clearer differentiation among this germplasm. In addition, the germplasm shows significant cyanide variation necessitating integrated genetic and biochemical breeding approaches. Thus, these results may assist breeders and farmers in optimizing cassava germplasm utilization, ultimately contributing to food security.