Gene action controlling farmer preferred traits in cassava varieties adapted to mid-altitude tropical climatic conditions of western Kenya

Information on genetic inheritance of farmer preferred traits is fundamental in selection of parents and breeding strategies for an effective participatory plant breeding. Forty sibs representing each of the 24 full-sib families generated using 6 × 4 North Carolina II mating design from ten popular cassava varieties grown in mid-altitude tropical climatic conditions were evaluated in two distinct environments using α-lattice design. Crosses, general and specific combining ability (GCA and SCA) effects and their interaction with environment were significant for most traits evaluated indicating significant genotypic, additive, non-additive gene action and their interaction with environment. Significance of genotypic, GCA, SCA effects and their interaction with environments imply selection of superior genotypes and parents should be based on multi-location evaluation. The presence of both additive and non-additive gene action for most preferred traits indicates the need to have specific breeding strategies that exploits both gene actions. However, the importance of additive over non-additive gene action varied between traits indicating the need specific breeding approaches for these traits. Over 50% of variability within the crosses for all traits evaluated except height to first branching, plant height and branching level was due to SCA effect indicating the importance of non-additive gene action. The GCA effects for the parents did not generally correlate with their per se performance also the best performing crosses were not always developed from parents with high GCA effects. These implied selection of parents based on their per se performance may not necessarily lead to development of superior hybrids.

► Over 50% of variability within crosses was due to non-additive gene action.
► GCA effects for parents did not correlate with their per se performance.
► Best performing crosses were not always from parents with high GCA effects.