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.
ABSTRACT
Mutation breeding in crop plants is an effective approach in improvement of crop having narrow genetic base such as groundnuts (Arachis hypogaea L.). Determination of effective irradiation dose is prerequisite for mutation breeding and development of genetic variability by induced mutation. Three groundnuts (Arachis hypogaea L.) genotypes (JL12, JL24 and Kimpese) were irradiated to the absorbed doses of 100, 200, 400 and 600 Gy for effective dose determination and to compare their sensitivity to different doses of gamma irradiation in a completely random design. It was found that, irradiation reduced significantly germination and survival percentages of seedlings in higher doses and this reduction was more pronounced in JL 24 cultivar. This sensitivity expresses himself distinctly to the rank of stem lengths and roots. Results show a negative interrelationship indeed between doses of irradiation applied and lengths of stems and roots. With attention to LD50 data, our results indicated that optimum doses were 200 Gy for JL12 and Kimpese, and 100 Gy for JL24. We concluded that JL24 are more sensitive to gamma irradiation than JL12 and Kimpese.