Heterosis and combining ability analysis in CMS hybrid rice

Abstract

Combining ability analysis (GCA) enables plant breeders to select parental lines for crossing and provides the opportunity to understand the nature of gene actions involved in the inheritance of desired traits. In this study, we used a line × tester mating design to generate 33 hybrid crosses using 11 restorer (R) and three cytoplasmic male sterile (CMS; A) lines from Philippine CMS hybrid rice germplasm. Single nucleotide polymorphism genotyping was performed using the Cornell-IR LD Rice Array to assess parental genetic diversity. Field performance of the hybrids, parents and standard checks was evaluated for grain yield (Gy) and important morpho-agronomic traits. Overall, the hybrids performed better than the parental lines and checks for the examined traits and exhibited clear hybrid vigor. General combining ability (GCA) analyses revealed a number of good combiners for specific traits, with PR36248-HY-2-5-1R (R4) identified as the best R line for producing high-performing hybrids and improving existing breeding lines. IR73328A (A2) produced the highest performing hybrids among the CMS lines. A preponderance of non-additive gene action was observed for most traits, with the exception of Gy, filled grains and grain width which were mainly controlled by additive genes. Parental genetic distance showed a poor relationship with per se performance, heterosis values and combining ability effects. GCA effects were also poorly correlated with specific combining ability (SCA) effects and hybrid performance, while SCA was positively correlated to heterosis estimates for all traits although it was only correlated with Gy for per se performance. These results indicate that intricate mechanisms are involved in the inheritance of quantitative traits. General sum of combining ability (GSCA) values obtained from both parents for each specific cross were highly correlated to per se performance for all traits that can be used to predict hybrid performance.