Molecular Relatedness and Morpho-Agronomic Characteristics of Congolese Accessions of Cassava (Manihot esculenta Crantz) for Breeding Purposes

Abstract

Cassava serves as primary staple food of millions of people in the tropics and subtropics, and is used as a carbohydrate source in animal feed. Knowledge of agro-morphological characteristics and genetic relatedness is essential for an efficient recombination of varieties in a breeding program. The objective of the present study was to determine genetic relatedness and morpho-agronomic differentiation among Congolese cassava collection for breeding purposes. The morphological and agronomic characters were highly variable among accessions. Every accession could be differentiated from any other one. There were significant genotypes x location interactions for storage root yields. Root weights were positively correlated with the number of roots per plant. In general, all the improved varieties were tolerant or resistant to the Cassava Mosaic Virus (CMV) while the local (non-improved) varieties were susceptible. But the reaction to Cassava Bacterial Blight (CBB) confirmed that genetically improved accessions are susceptible and local varieties are resistant. Molecular analysis revealed that the accessions analyzed were genetically distant with 80% of genetic distance values estimated above 0.5. One local accession was an out-group that was separated from the main groupings with 100% degree of confidence. More importantly, there were no associations between genetic relationships and morphological similarities based on lobe shape, leaf colour, petiole colour, petiole orientation, and stem colour. Although the Congolese cassava genepool is small, there is enough variability to sustain a breeding program without new introductions of germplasms.