Diallel analysis of early storage root yield and disease resistance traits in cassava (Manihot esculenta Crantz)

Abstract

Little progress has been made in determining the combining ability and gene action controlling early storage root yield (SRY) and disease resistance traits in the Ugandan cassava germplasm. Such information is important in the selection of parents and breeding strategies for an effective breeding programme. The objective of this study was to estimate the general combining ability (GCA) of nine cassava parents and their specific combining ability (SCA) for early SRY and disease resistance traits, as well as to determine the gene action controlling these traits. Thirty-six full-sib cassava families were generated from a 9×9 half-diallel mating design and were evaluated in two distinct environments in Uganda using a 3×12 row by column design. Family, GCA and SCA effects and their interactions with environments were significantly different for most traits, indicating, respectively significant differences in the mean performances of the families, additive and non-additive gene action in the expression of the traits, and the non-additive influence of the environments. The relative importance of additive and non-additive gene action varied between traits, indicating the need for specific breeding strategies for each trait. Parents with desirable GCA effects for most traits were developed from cassava introductions from South America, highlighting their importance and possibility of widening genetic variability of African cassava germplasm. The GCA effects for the parents did not always correlate with their per se performance, implying that selection of parents based on their per se performance may not necessarily lead to development of superior hybrids.