Genetic Effects of Grain Quality Enhancement in Indica Hybrid Rice: Insights for Molecular Design Breeding.

Improving rice quality remains a crucial breeding objective, second only to enhancing yield, yet progress in quality improvement lags behind yield. The high temperature and ripening conditions in Southern China often result in poor rice quality, impacting hybrid rice production and utilization. Therefore, to address this challenge, analyzing the molecular basis of high-quality traits is essential for molecular design breeding of high-quality hybrid rice varieties. In this study, we investigated the molecular basis of grain shape, amylose content, gel consistency, gelatinization temperature, and aroma, which influence rice quality. We discovered that quality related alleles gs3, GW7^TFA, gw8, chalk5, Wx^b, ALK^TT, and fgr can enhance rice quality when applied in breeding programs. Polymerization of gs3, GW7^TFA, gw8, and chalk5 genes improves rice appearance quality. The gs3 and GW7^TFA allele polymerization increasing the grain's length-width ratio, adding the aggregation of gw8 allele can further reducing grain width. The chalk5 gene regulates low chalkiness, but low correlation to chalkiness was exhibited with grain widths below 2.0 mm, with minimal differences between Chalk5 and chalk5 alleles. Enhancing rice cooking and eating quality is achieved through Wx^b and ALK^TT gene polymerization, while introducing the fgr(E7) gene significantly improved rice aroma. Using molecular marker-assisted technology, we aggregated these genes to develop a batch of indica hybrid rice parents with improved rice quality are obtained. Cross-combining these enhanced parents can generate new, high-quality hybrid rice varieties suitable for cultivation in Southern China. Therefore, our findings contribute to a molecular breeding model for grain quality improvement in high-quality indica hybrid rice. This study, along with others, highlights the potential of molecular design breeding for enhancing complex traits, particularly rice grain quality.