Despite the importance of cassava for food security in semi-arid areas of Kenya, there is a lack of information regarding gene action determining yield of local varieties. Therefore the objective of this study was to estimate the combining ability for yield and associated secondary traits by crossing popular local varieties with some varieties from IITA using a NC II mating design. The F1 progenies were evaluated in a seedling trial laid out as a 7 × 7 simple lattice with two replicates. Results indicated significant variation among progenies for shoot weight, root number, root weight, root yield, biomass, harvest index, percentage dry matter, dry matter yield, cyanide content, and resistance to cassava mosaic disease and green mites. Average fresh root weight at 6 mo ranged from 1.1 kg to 1.4 kg plant-1. To a great extent SCA effects (57 to 75%) explained variation for shoot weight, root weight, harvest index, dry matter content, root cyanide content and resistance to cassava mosaic, while GCA effects (55%) were more important for root number. Thus, our results suggested that non-additive gene action was more important than additive gene action in influencing yield and most of its associated traits in this cassava population. Overall, the results suggested that the success of cassava breeding in the semi-arid areas would depend on the ability of breeders to assemble heterotic groups of germplasm that combine well in order to achieve early vigour, disease and pest resistance, root quality and high yield potential.
Key words: Cassava, Yield, Secondary traits.
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