Parental selection for high heterosis in sorghum [Sorghum bicolor (L.) Moench]–Combining ability, heterosis and their inter-relationships

Combining ability analysis is routinely used to identify the best combiners among a group of genotypes and superior hybrid combinations along with type of gene action controlling the expression of a quantitative trait. Eighty-four sorghum hybrids generated by crossing seven cytoplasmic male sterile lines and 12 fertility restorers in Line × Tester fashion were evaluated for grain yield and related traits in a replicated trial along with standard checks. Significant heterosis values were observed for all the traits studied, and hybrids displayed up to 139% grain yield advantage over better parent and 76% over standard check. Variances due to general combining ability (gca) and specific combining ability (sca) were significant for days to flowering, panicle length and grain yield indicating role of both additive and non-additive gene action, while plant height and 100-seed weight were completely under additive genetic control. For grain yield 27B, RS 673 and CB 33 were good combiners, while for panicle length 27B, 296B, 2077B, RS 673 and Indore 12 were good combiners among parents. Analysis of combining ability status indicated that combinations of parents with non-significant gca can also result in hybrids with significant sca as well as heterosis for grain yield and other traits. Significant correlations were found between per se performance of hybrids and sca, per se performance and heterosis, and sca of hybrids and heterosis. The study demonstrates that superior hybrid combinations can be identified through appropriate field evaluation, and estimation of combining ability as a tool to identify suitable parents among a set of genotypes has to be relooked at.