Combining Ability Analysis of Storage Root Yield and Related Traits in Cassava at the Seedling Evaluation Stage of Breeding

Abstract

Selection of genotypes at the seedling evaluation stage of cassava breeding for advancement is largely based on high heritability traits. Moreover, combining ability and family data at this stage are rarely analyzed, leading to a loss of potential genetic information. This study was conducted to estimate the general combining ability (GCA) of nine cassava parents and specific combining ability (SCA) of their crosses for storage root yield (SRY) and related traits, as well as to determine the gene action controlling these traits. Thirty-six full-sib cassava families were developed from a 9 x 9 half-diallel mating design and evaluated in a 6 x 6 triple lattice design. The family mean squares (MS) were significantly different for all traits assessed, suggesting significant differences among families for all traits. The GCA MS were significant for all traits, whereas SCA MS were significant for only storage root number (SRN). Percentage sum of squares attributable to GCA accounted for >50.0% of variability expressed by families in five of the seven traits studied, indicating predominance of additive gene effects in controlling expression of most traits. Parent CT4 was the best general combiner for SRY, SRN, and resistance to cassava brown streak and mosaic diseases, while crosses NASE3 x CT2, CT5 x CT3, and NASE3 x CT4 had desirable SCA effects for SRY. Correlation analysis indicated a possibility of selecting for SRY and quality traits simultaneously. Simultaneous selection of these traits at the seedling generational stage of cassava breeding could reduce the cassava breeding cycle.