Extending the cacao (Theobroma cacao L.) gene pool with underrepresented genotypes: growth and yield traits

The narrow level of diversity of cacao varieties that are currently cultivated in West Africa has been suggested as one of the major problems to yield improvement of the crop in its major production countries. In this study, combining abilities and heritability for growth and yield traits in 12 underrepresented cacao parents of diverse genetic groups were estimated using these as females in crosses with three tester parents. Progenies obtained from a North Carolina II (NC II) incomplete factorial mating design together with three standard varieties were evaluated in a randomized complete block design with four replications at two contrasting locations for three growth traits (percentage survival, trunk cross-sectional area in the juvenile stage (TCSAj), and jorquette height) and four yield traits (bean weight, number of beans per pod, bean yield, and yield efficiency). Mean performance of the progenies was significant (p < 0.05) for all the traits involved and progenies of some specific crosses performed better than the best standard variety. The female GCA, male GCA, and SCA male x female interaction effects were significant, which suggest that both additive and dominant effects are important in the inheritance of traits. Heritability was moderate to high (H-2 = 0.35-0.70) for broad sense and low (h(2)ns = 0.17-0.30) for narrow sense. This indicates that even though the expression of traits is controlled by genes, it may partly be influenced by the environment. Parental clones A1/197 and DOM 3 which had significant positive GCA effect consistently produced progenies with high SCA values for most of the traits. Results from the study indicate that the underrepresented cacao clones represent a suitable genetic resource for broadening parental clones of current cacao varieties cultivated in Ghana and beyond.