GENETIC ANALYSIS FOR HIGH STARCH, DRY MATTER CONTENT AND STORAGE ROOT YIELD IN CASSAVA (Manihot esculenta Crantz)
Although cassava (Manihot esculenta Crantz) has benefited from a significant amount of research, there still exist gaps in knowledge on its starch and dry matter content. Studies were conducted to access farmers’ and end-users preferences and also to evaluate improved cassava genotypes for high starch content, high dry matter content and high storage root yield in Sierra Leone. Participatory Rural Appraisal (PRA) was conducted among 360 respondents that comprised farmers, processors, marketers and consumers in 12 chiefdoms in Sierra Leone using focus group discussion and semi-structured interviews. Identified important attributes with cassava production, processing and utilization were high storage root yield, poundability, root taste, dry matter content, resistance to pests and diseases, starch content, and maturity period. These selection criteria reflected the degree of importance attached to multiple needs and priorities, as well as their context in production environments and farming systems. Genetic diversity was assessed among 102 cassava genotypes using a total of 22 agro-morphological traits (11 qualitative and 11 quantitative traits) and 5,600 SNP markers. Significant differences were observed for the quantitative traits. Based on cluster analysis for the qualitative traits, the genotypes were classified into five groups while the dendrogram for the quantitative traits produced four main clusters. The molecular marker based cluster analysis classified the accessions into three main groups. There was a positive correlation between starch percentage and dry matter content. Twenty six genotypes high with dry matter content, starch content and storage root yield were selected and evaluated in three locations for one year to assess genotype by environment interaction effect (GEI) on the expression of dry matter content, starch yield and storage root yield. Analysis of variance indicated significant variation among genotypes, locations and their interactions for fresh storage root yield, dry matter content and starch yield. Fresh storage root yield, dry matter content, starch yield and the other traits evaluated were predominantly under genetic control. Furthermore, twenty four F1 families generated from a line x tester mating design revealed a high degree of variation between and within families for all the traits assessed at the seedling stage. Additive gene effects were predominant in the expression of dry matter content and most of the other traits. The physiochemical and functional properties of starch were significantly different within the F1 progenies. The starch content ranging between 61.13 to 69.98% was significant and positively correlated with percentage sugar. Amylopectin was also perfectly correlated with amylose. Individual F1 progenies had higher peak viscosity, set back viscosity and viscosity at breakdown suggesting inherent genetic and biochemical differences among families used in the study. Promising F1 progenies from the seedling stage evaluation would be evaluated in clonal trial, preliminary yield trial and advanced further to multi-location trials where superior genotypes would be selected for improved cassava production in Sierra Leone.