Objective  Genetic improvement on 5 traits of rice through heterosis by hybridizing Indica-Japonica was analyzed.

  Method   Following the NC-II incomplete diallel hybridization protocol, 14 rice parents and 48 hybrid combinations were generated for the analysis. Genetics, heterosis, and correlations of growth period, plant height, spikelet length, spikelet width, and spikelet length-width ratio of the varieties were evaluated according to the additive and dominant genetic effects.

  Result  The ratios of additive variance component to phenotypic variance (V_A/V_P) on the growth period, plant height, spikelet length, spikelet width, and spikelet length-width ratio of the rice were 69.2%, 74.2%, 58.9%, 66.0%, and 63.5%, respectively. The variations of broad-sense heritability (H²_B) and narrow-sense heritability (H²_N) were 59.0%–99.6% and 69.2%–98.9%, respectively, at significant or extremely significant level. The traits were largely controlled by additive effects, little by environmental factors, and only effective for early generation selection in breeding practice. The growth period, plant height, spikelet length, pikelet width, and spikelet length-width ratio of most combinations displayed a heterosis of both negative intermediate and super parent hybrid vigor. The growth period of the hybrids was shortened, the plant height reduced, and the spikelet length-width ratio in between two parents. The growth period was an independent genetic trait, while the plant height somewhat positively correlated with the grain shape.

  Conclusion   In breeding Indica-Japonicahybrids, balancing the benefits gained on the growth period, plant height, grain shape, and other traits through heterosis needed be carefully considered.