Combining-ability for cacao (Theobroma cacao L.) yield components under southern Bahia conditions

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 components using method 1, model I, of the diallel 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 WHSF), and the percentage of diseased fruits per plant (PDFP), for 5 years (1986-1990). The F-test values, highly significant for general combining 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 additive portion of genetic variance should be employed for obtaining higher-yielding cacao and high seed weight. For this, the segregant populations should involve cultivars CEPEC 1, SIAL 169 and ICS 1. Combinations involving the cultivar ICS 1 presented the most favorable results for the characteristics WHSP and WHSF, where the hybrid SIAL 169 x ICS 1 and its reciprocal were outstanding.

Avaliação e seleção de híbridos de cacaueiro em Rondônia

“…Quanto ao caráter número médio de frutos coletados por planta (NMFCP), por exemplo, PA 150 x SIC 864 mostrou a quarta maior média em 1986, e o pior desempenho, em 1988. A presença de interação genótipos x anos é comum em estudos envolvendo genótipos de cacau (Bartley et al, 1982;Pereira et al, 1987;Mariano et al, 1988); contudo, esta interação não foi observada por Almeida (1991) e Dias & Kageyama (1995, 1997 para, pelo menos, algum caráter estudado.…”

“…O bom desempenho deste híbrido pode ser resultante, pelo menos em parte, da inclusão de ICS 1 como um dos genitores, uma vez que outros híbridos incluindo SCA 6, SCA 6 x BE 9 e SCA 6 x BE 10, não apresentaram boas médias quanto a este caráter. O clone ICS 1 também demonstrou capacidade de aumentar a média deste componente de produção, quando em combinações híbridas, em ensaios conduzidos por Pereira et al (1987) e Dias & Kageyama (1995).…”

Genetic distance and its association with heterosis in cacao

“…However, the best performing hybrids with regard to wet seed weight/plant and wet seed weight/fruit were those involving ICS 1, where the SIAL 169 x ICS 1 hybrid and its reciprocal were outstanding (Dias and Kageyama, 1995;1997a). In addition, ICS 1 had a high general combining ability for the same components (Dias and Kageyama, 1995), suggesting a relationship between combining ability effects and parental genetic divergence. Nevertheless, this not expected apparent relationship, as will be shown in the next section, reflects the high additive genetic value of the ICS 1 parent.…”

“…Unfortunately, no data regarding productivity is available from the 250,000 ha of hybrid cacao plantations in Brazil. Hybrid cacao trees, which are non-conventional hybrids synthesized from non-inbred clonal progenitors, allowed for the renewal of plantations with high and early yielding material that also showed some resistance to diseases (Dias and Kageyama, 1995). The major worldwide drawback in cacao hybridization is its empiricism.…”

“…On assessing the divergence between the parents, the data representing five yield components (Table 2) collected over a period of five years was used. Combining ability analysis, agronomic practices, as well as details of performance data records can be found in a previous study (Dias and Kageyama, 1995).…”