Purpose Heterosis and genetic background of indica and japonica hybridization were analyzed to facilitate breeding high quality rice varieties.

Method Parents and 11 hybrid rice were planted in the field to examine the agronomic traits and yield. More than 500g of grain sample were collected from each variety for determinations on hybrid vigor, yield, and grain quality. Cases of rice aspergillus and blast diseases on the plants under field conditions were observed. Grains of the parents and hybrids were sent to a biotechnology company for genome homozygosity and genetic background analyses on indica and japonica segments using high-density gene chips as well as functional gene aggregation.

Result The hybridization and surpassing parent advantages on spike count per plant of the new generation were negative. The hybridization advantage on grain count per panicle was positive in all but Yexiangyouhang 148. It was positive on the surpassing parent advantage for all, except negative for Yexianyou 631 and Yexiangyouhang 148. On the thousand grain weight, the hybridization advantage was positive, but the negative in surpassing the parents. The hybridization and surpassing parent advantages on yield were all positive. The grain quality of the 11 hybrids met or exceeded the standard of three classes of high-quality rice in the frequency division that included Yexiangyou 633being rated in the top grade, Yexiangyou 669, Yexiangyou 6866, Yexiangyou 653 and Yexiangyou 631 in the 2^nd grade, and the rest in the 3^rd grade. There were significant differences in the wholesome grain appearance, chalky grain percentage, grain chalkiness degree, and alkali digestion value, but not in the other quality indicators, between the male parent and the hybrids. The portions of grains in perfect shape and high alkali digestion value were positive, but negative on the chalky grain percentage and chalkiness degree, for the hybrids. The overall disease resistance of the hybrids was more than moderate. Aside from Yexiangyou 653 and Yexiangyou 699 that exhibited moderate to high resistance, the others were susceptible to rice blast. Compared with the parents, the homozygosity of Yexiangyou was significantly decreased, while the indica segment increased relatively with some of the japonica fragments.

Conclusion The combination of Yexian A and indica significantly improved the quality of the hybridized rice. The advantages gained from the hybridization and surpassing parent heterosis on large panicles and plenty grains would ensure a high and stable production of the new rice varieties in cultivation.