Five cytoplasmic male sterile (CMS) lines namely IR58025A, BRRI1A, D. ShanA, BRRI9A and IR73328A were crossed with three testers, viz. M.H.63R, M.H.77R and Gui99R in line x tester fashion to produce hybrids and find out the best combinations related to the combining ability effects among the parents and hybrids. Analysis of variance revealed a significant difference among the genotypes and crosses. Variance due to parents was highly significant for all the characters. Variance due to interaction effect of parents and crosses was significant for all the characters except days to 50% flowering and days to maturity. Variance of sea was higher than that of gca for all the characters except number of panicles per m% suggesting the significant role of non-additive gene action on the inheritance of this character. The relative contribution of line, tester and combinations of line x tester interaction of all characters was calculated and found that 1000-grain weight contributed the highest (61.11%) followed by number of spikelet per panicle (58.19%), plant height (53.91%), spikelet fertility (47.23%) and yield per plant (44.02%) in their hybrid. IR73328A/M.H.63R cross combination was the best specific combiner for grain yield per plant. Estimates of gca effects showed that BRRI9A was an excellent general combiner for improving eight characters viz. plant height, effective tiller per plant, days to 50% flowering, number of panicle per m2, panicle weight, number of spikelet per panicle, spikelet fertilityand 1000-grain weight. The cross BRRI9A/Gui99R was found to be a good specific combiner for most of the characters. The cross between good general combiners did not always produce the best specific crosses. Moreover, the predominance of production of thebest specific crosses from high xlow and low xlow combiners indicated the influence of non-additive and over-dominant gene action on the plant stature.
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