Genetic Difference of Parents and Its Relation to Heterosis in Hybrid Rice

Using 7 maintainer lines and 9 restorer lines as the materials, the genetic difference of hybrid rice parents and its relation to F1 heterosis were studied through principal component analysis and cluster analysis of 11 major agronomic characters. The results showed that among all of the 120 genetic distances of the 16 parents, morethan 80% was below 2; the average genetic distances among the 9 restorers and among the 7 maintainers except Xiangxiang 2B were 0. 4793 and 0. 7723, respectively, which indicates that the genetic difference is comparativelysmall in the existing hybrid rice parents, especially within restorer lines or within maintainer lines. The analysis ofCorrelation between the genetic distance of both parents and heterosis of their F1 hybrids showed that there was nota correlation between them among the existing hybrid rice parents. However, it was found that the grain yield of F1hybrids was closely related to that of both parents, especially to the mean grain yield of both parents, indicating thatparental improvement is of great importance to increase hybrid rice yield. Purthermore, the relation betweenparental improvement and heterosis, the approaches to the improvement of parents and the principle of choice of pareals for developing hybrids were also discussed.