Sweetpotato is in the botanical family Convolvulaceae. It is the only crop plant of major economic importance for food among the approximately 50 genera and more than 1000 species of the family, which may be due to the Agrobacterium infection which occurred in evolutionary times of the crop. It is a nutritious food, low in fat and protein, but rich in carbohydrates. The potential of sweetpotato in food security and global well-being has been well recognised. It is a staple food for millions of people and the seventh most abundant crop globally after wheat, rice, maize, potato, barley and cassava. However, its utilisation is very low in Ghana compared to the other root and tuber crops such as cassava, yam and cocoyam. Consumers in Ghana prefer non-sweet sweetpotatoes with high dry matter content. Conversely, locally available clones have very sweet taste, which limit their consumption as a staple food. Recently introduced orange-fleshed varieties, which possess the vitamin A precursor to combat vitamin A deficiency at relatively cheaper cost, have low dry matter content that is not preferred. Lack of varieties with end-user-preferred traits has been the main reason for the low utilisation of sweetpotato in Ghana. There is a need to develop farmer- and consumer- preferred sweetpotato varieties to increase the crop’s utilisation in Ghana.

Sweetpotato breeding until recently was exclusively based on estimates of heritability of the traits concerned. Estimates of heritability indicate that superior parents tend to pass on desirable additive genes to their progeny. The expected amount of superiority is realised in subsequent generations only if the genetic effects are additive. In cross-pollinating crops such as the sweetpotato, combinability, or the ability of a parent to pass on desirable genes to a hybrid progeny, is more important. Knowledge on the gene action influencing high dry matter, high starch and non-sweetness therefore becomes critical in sweetpotato improvement or cultivar development. 

Mating designs that estimate general combining ability (GCA) and specific combining ability (SCA) of quantitative traits are important in breeding heterozygous crops. The North Carolina II (NCII) mating design has been used to study inheritance in sweetpotato, but the diallel mating design may provide more genetic information on a complex crop such as the sweetpotato. Diallels, in addition to estimating GCA and SCA variance components from a set of randomly chosen parental lines, can also be used to obtain estimates of genetic effects for a fixed set of parental lines from multiple environment experiments.

Diallel cross is used for determining cumulative gene effects of breeding populations, and also provides information on heterosis. Heterosis provides a basis for the formation of genetic pools. The mode of inheritance for some production and utilisation constraints in sweetpotato has been studied using diallels.

Method 4 has been used for inheritance studies in sweetpotato but, Gardner and Eberhart proposed an alternative analysis (GEAN II) for diallel crosses from heterogeneous parents. GEAN II is useful in evaluating n varieties and their n(n – 1)/2 F1 crosses. Variation among entries (genotypes) is apportioned into entries (genotypes) and mid-parent heterosis (Gardner & Eberhart 1966; Hallauer & Miranda Fo 1988; Murray et al. 2003). Heterosis is further subdivided into variety heterosis which indicates GCA, average heterosis and specific heterosis which indicates SCA.

This study used diallel mating design to estimate GCA and SCA effects, to elucidate the gene action controlling storage root dry matter, starch and sugar content in sweetpotato and heterotic potential of the traits to facilitate the crop’s improvement for increased utilisation.