Abstract
The understanding of the generated hybrids’ breeding value gives a measure of probable advances in a breeding program. Four cocoa genotypes (testers) were crossed with two distinct lines (T65/7 and T86/2). The parents and the hybrids were separately established in randomized complete block design with six replications. The fourteen genotypes were evaluated for pod length (PL), weight (PW), beans/pod (NoB), bean length (BL), width (Bwi) and thickness (BT). The treatment, parent, crosses and Line x Tester sources of variation were significant (P ≤ 0.05). Hybrids from the same maternal parent differed significantly (P < 0.05) for the six traits. Contribution to the total variance of PL, PW and Bwi were in the following order: Tester > Line x Tester > Lines. The highest general combining ability (0.42) occurred in T65/7 for PW; the least (-0.081) occurred in T86/2 for PL. Cross combination T65/7xT57/22 produced the highest specific ability of combination (4.33) for NoB. Variance of GCA and SCA were significant (P < 0.05) for the six traits. The GCA/SCA ratios revealed the inheritance of PL, PW, Bwi and BT to be additive. Non-additive gene effect controlled NoB and BL. Heterosis for the six traits ranged between -17.82% for BT (T65/7xT57/22) to 52.40% for PW (T65/7xT53/8). Increased productivity in cocoa is possible through hybrid breeding programs.
Highlights
It is known that breeding success at tree crops is slow; scaling the process of the right parents’ choice for generating high quality hybrids is another challenge
Hladni et al (2008) remarked that the act of obtaining plant genetic resources with desirable traits for pairing as male and female parents, to produce superior F1 progeny over the existing genotypes, is a main precondition for designing a model in hybrid breeding program
The critical information guides the choice of the right parent(s) and elucidates the nature and magnitude of gene actions determining the phenotypic expression of traits in the resultant crosses (Rashid et al, 2007; Salgotra et al, 2009; Sanghera and Hussain, 2012; Sarker et al, 2002)
Summary
It is known that breeding success at tree crops is slow; scaling the process of the right parents’ choice for generating high quality hybrids is another challenge. A concerted breeding effort on tree crops, such as cocoa, often leads to significant improvement in quality, yield and other economic traits. Effective breeding will take advantage of available genetic resources into an improvement program to achieve high level of heterosis for desired traits. The success in crop breeding through hybridization is dependent on the identification, selection and utilization of the right parents. Heterosis conceals inferior genes in a hybrid; its utilization is effective for the genetic improvement of different traits. Information on combining abilities through Line x Tester mating design guide breeders to select parental stocks with good GCA and SCA for polyclonal and biclonal seed gardens, respectively. The objectives of the present study include: to investigate combining ability of six cocoa clones for some pod and bean traits, to identify parents with desirable GCA, cross combinations with desirable SCA and to understand the nature of gene action involved in the studied pod and bean characters
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