QUANTITATIVE INHERITANCE OF SPIKE CHARACTERS IN CASTOR (RICINUS COMMUNIS L.)

Castor oil plant (Ricinus communis L.) is an important oil crop with little research attention in Nigeria. In this research, studies on quantitative inheritance of spike characters in castor, through combining ability and generation mean analyses, were carried out. This was aimed at evaluating prominent seed yield related components for selection and hybridization in castor breeding in Nigeria. The result of combining ability analysis showed significant differences for both general combining ability (GCA) and specific combining ability (SCA) for number of spikes per plant (SPP), effective spike length (ESL), capsules per spike (CPS) and 100-seeds weight. Specific combining ability was important for seed yield (SY) and seed oil content. Broad sense heritability and narrow sense heritability of 28.02% to 99.64% and 10.28% to 72.19% respectively were recorded among the traits studied. The results of scaling and joint scaling tests revealed inadequacy of simple additive-dominance model to explain the mode of gene actions for all the studied traits. The six parameters model revealed that besides the additive and dominance gene actions, epistatic interaction mechanisms have also contributed significantly to the expressions of all the characters examined. These findings suggest heterosis breeding and recurrent selections as appropriate breeding techniques for the improvement of the traits. However, where additive gene actions are to be exploited in selection program for some of the traits, the problem pose by presence of epistasis gene interactions may be overcome through delay in selection to later generation when the major operating genes will be fixable.