Genetic component and combining ability analyses in relation to heterosis for yield and associated traits using three diverse rice-growing ecosystems

Genetically designed analyses for gene governance components, combining abilities, heterosis, inbreeding depression and genetic gains were made utilizing a seven-parent half-diallel mating design having several locally adapted, traditional varieties or land races from three diverse rice ecosystems. Both additive and non-additive genes were found to control the expression of yield and its associated traits. The ratio of sigma(g)(2)/sigma(g)(2) exhibited greater relevance of non-additive gene actions governing yield and its associated traits. Exploitation of heterosis to develop superior rice hybrids using some of the local parents with proven 'gca' (general combining ability) and 'sca' (specific combining ability)' effects has been demonstrated as a potentially better method for grain yield enhancement. Results revealed that per se performance of the parents is a reflection of their 'gca' effects in most of the crosses. Among the genotypes NDR 359 ranked as the top general combiner for yield and its associated traits followed by T 21 and IR 24. Higher yield was found to be greatly associated with morpho-economic traits such as harvest index, biological yield, 100-grain weight and productive tiller number per plant. Most desirable specific combiners for hybridity involved high x low general combiners along with high x high with certain limitations of low x low general combiners (epistatic). The gene distribution estimates indicated the occurrence of asymmetry. The high to moderate estimate of narrow-sense heritability further supported the involvement of both additive and non-additive gene effects for different traits. At least one major group of genes controlled the inheritance of each trait. The photoperiod-sensitive plants with different critical day length were obtained from a particular intermediate sensitive x insensitive cross-combination. The two varieties-NS 19 and Jal Lahri-with intermediate photoperiod sensitivity along with resistance to biotic and abiotic stresses and the third variety Mahsuri which possesses attractive grain quality features have been identified for utilization as donors for candidate genes in rice genetic improvement for targeted ecosystems. (C) 2003 Published by Elsevier B.V.