Characterization and Genetic Analysis of Grain Filling Rate of “Ludao” and Restorer Line C-Bao in Japonica Rice

The objective of this study was to improve the grain plumpness of Japonica hybrid rice (Oryza sativa L.) with large panicles through crossing with a kind of primitive Japonica rice “Ludao”. Grain-filling rates of the P1, P2, F1, F2, B1, and B2 generations that were derived from the reciprocal crosses between a Japonica restorer “C-Bao” and Ludao were investigated at 1-7, 8-14, 15-21, 22-28, 29-35, and 36-42 d after flowering. The average grain-filling rate over whole filling duration was analyzed using the mixed major gene plus polygene inheritance models. According to the reciprocal analysis, no cytoplasmic effect was found for the average grain-filling rate. The largest filling rate appeared in the stage of 8-14 d after flowering in the P1, P2, and F1 generations. The whole filling duration of Ludao was 28 d, which was 14 d shorter than that of C-Bao. The average filling rate of Ludao was larger than that of C-Bao by 50%. Based on analysis of the mean components, the inheritance of average grain-filling rate was in agreement with additive-dominance-epistasis model. Two major genes and some polygenes controlled the average filling rate with additive-dominance-epistatic effects, and the major genes played a pivotal role.