GENETIC IMPROVEMENT OF ROOT YIELD AND NUTRITIONAL QUALITY OF CASSAVA (Manihot esculenta Crantz) IN SIERRA LEONE
Cassava storage root is a major staple. However, the tuber is poor in nutrients especially micronutrients. The study was conducted to improve the nutritional status of cassava with farmers’ preferred traits in Sierra Leone. The specific objectives were i) to assess adoption challenges, perception and preferences for provitamin A cassava among cassava value chain actors in Sierra Leone. ii) to estimate genetic diversity within provitamin A cassava germplasm using morphological, molecular tools and i-check device for establishing a collection in Sierra Leone. iii) to determine performance and stability of total carotene content and dry matter of selected provitamin A cassava accessions across environments.vi) to characterize F1 progenies for total carotenoid, iron and zinc and protein content using biochemical tool. v) to estimate the combining ability of 12 cassava parents and their F1 progenies for mealiness, dry matter, number of roots and fresh root yield. A participatory rural appraisal (PRA) was conducted in Bombali, Kailahun and Moyamba districts, to identify farmers’ and consumers’ adoption challenges, perceptions and preferences for provitamin. High production cost, low yield, scarcity of planting materials, high cost of fertilizers and agro-inputs, drudgery in peeling and processing and limited access to micro finance loan schemes, were identified as major challenges for provitamin A cassava adoption. The respondents show willingness to accept and adopt provitamin A cassava due to its perceived nutritional quality. A total of 188 cassava accessions cultivated in the southern part of Sierra Leone were assessed using molecular tools and the i-check device. The Cassava accessions were grouped into eight distinct clusters based on the morphological data while they grouped into nine distinct clusters based on the molecular analysis. A significant positive correlation was found between the morphological and molecular data sets (r = 0.104; p < 0.034) but the correlation was rather weak. Thirty provitamin A accessions with higher total carotenoid contents were selected to form a collection. The collection evaluated in 3 environments for the GGE biplot analyses for dry matter content (DMC) and total carotenoid content (TCC) showed significant variation among the Genotypes, Environments and their interaction. Genotypes TR-1182 and TR-1313 had the highest performance for DMC and TCC. Njala was identified as an ideal environment for selecting superior genotype for total carotenoid content and Pendembu as ideal for dry matter content. The performance of 868 F1 progenies (obtained from five crosses involving eight genetically diverse parents) was evaluated for selection of varieties with increased level of micro nutrients. F1 progeny 13 and 33 from cross IITA-TMS-IBA 120004 x IITA-TMS-IBA 120003 recorded the highest (28.0 μg-1) and lowest (6.0 μg -1) values for total carotenoid content with a grand genotypic mean of 14.7 μg -1. F1 progeny 41 and 12 from cross IITA-TMS-IBA 088693x IITA-TMS-IBA 088747 recorded the highest (8.1%) and lowest (4.2%) crude protein content with a grand percentage mean of 5.4%. F1 progeny from cross IITA-TMS-IBA 96/1165 x IITA –TMS-IBA 011368 recorded the iron content with a ranged 45.0 ppm to 59.2 ppm and harvested progeny with the grand mean 12.6 ppm. F1 progeny from cross MM96/81791 x IITA-TMS-IBA 088747 had the highest zinc concentration ranging from 4.5 ppm to 17.7 ppm with a grand mean 8.5 ppm. Micro nutrients analysis on F1 progenies revealed that there is variation for quality traits in cassava. In addition, a 12 x12 diallel study revealed highly significant differences for dry matter, number of roots and fresh root yield at P < 0.01, and 0.05 respectively. General combining ability (GCA) variance was significant for fresh root yield while estimates of specific combining ability (SCA) variance was highly significant for dry matter and number of storage roots. The significant difference observed for most of the traits for the parents and their F1 progeny revealed that genetic diversity exists among the germplasm and Progenies from crosses IBA120004 x IBA961165, IBA 961165 x I088693 and IBA120004 x IBA961165 were the best combiners for number of storage roots, mealiness and fresh root yield.