Theor Appl Genet (1995) 90:534-541 9 Springer-Verlag 1995 L. A. S. Dias 9 P. Y. Kageyama Combining-ability for cacao ( Theobroma cacao L.) yield components under southern Bahia conditions Received: 6 July 1994 / Accepted: 9 August 1994 Abstract The objective of this study was to assess five cacao cultivars (selfs) and 20 hybrids with regard to their general- and specific-combining ability for yield compo- nents using method 1, model I, of the dialM analysis system. The selfings and the hybrids were obtained through controlled crossings, tested in the field in a random block design with four replications and plots containing 16 plants. The experiment was set up in the Centro de Pesquisas do Cacau, in Itabuna, Bahia, Brasil, in 1975. The characteristics studied were: the number of healthy and collected fruits per plant (NHFP and NCFP), the weight of humid seeds per plant and per fruit (WHSP and WHSE), and the percentage of dis- eased fruits per plant (PDFP), for 5 years (1986-1990). The F-test values, highly significant for general combin- ing ability (GCA) and specific combining ability (SCA), demonstrated the existence of variability for both effects. However, the effects of SCA were greater than those of GCA, when compared in terms of the average squared effects. This condition held for the characteristics NHFP, NCFP and WHSP, which shows the relative importance of the non-additive genetic effects over the additive effects. The reciprocal effects did not show significance. Breeding methods which explore the addi- tive portion of genetic variance should be employed for obtaining higher-yielding cacao and high seed weight. For this, the segregant populations should involve cul- tivars CEPEC 1, SIAL 169 and ICS 1. Combinations involving the cultivar ICS 1 presented the most favor- able results for the characteristics WHSP and WHSF, Communicated by P. M. A. Tigerstedt L. A. S. Dias ([~) Esta~gto Experimental "Filog6nio Peixoto', Centro de Pesquisas do Cacau, C.P. 102, 29.900, Linhares, ES, Brasil P. Y. Kageyama Departamento de ci~ncias florestais, Eslaq/USP, C.P. 09, 13418- 900, Piracicaba, SP, Brasil where the hybrid SIAL 169 x ICS 1 and its reciprocal were outstanding. Key words Theobroma cacao L. 9 Combining ability Yield components 9 Genetic improvement Introduction The development of superior hybrids has made a signifi- cant contribution to Brazilian cacao productivity. Hy- brid cacao trees have permitted the renewal of crops with high and early yielding materials that also show some resistance to diseases. The hybrid type selected for commercial-scale production was similar to the inter- varietal corn hybrid; a non-conventional hybrid syn- thesized from non-inbred clonal progenitors. The progenitor clones, however, differ as to their combining ability for yield and, frequently, the yield ability of the clones per se is not associated with their performance as progenitors. Difficulties such as these were overcome by introducing combining-ability tests. With these tests a part of the randomness of the hybrid- ization process was eliminated and the demand for area and for the time needed to assess the hybrid cacao trees was reduced. In combining-ability studies the design most com- monly utilized is the diallel design. In diallel analyses, Sprague and Tatum (1942) introduced the concepts of general combining ability (GCA) and specific combining ability (SCA). The GCA is a measure of the additive genic action, while the SCA is assumed to be a deviation from additivity. The combining ability in cacao for the characteristics of yield and resistance to diseases has been studied by a number of authors (Sofia et al. 1974; Ojo 1982; Baez 1984; Engels 1985; Monteiro et al. 1985; Mora 1987; Pardo and Enriquez 1988; Tan 1990). The present study was undertaken for the purpose of estima- ting the general- and specific-combining ability of five cacao cultivars (sells) and their 20 hybrids, at advanced ages.