Studies on Seed Setting Percentage Stability in F_1 Hybrids between Indica and Japonica Rice Varieties

Based on the study and use of the wide compatibility gene(S5n), some Indic-Japonica hybrids, such as Yayou 2, have been used in rice production in recent years. However, the seed setting percentage of these hybrids appeared unstable in various degrees, which weekened the het erosis of hybrids. In this experiment, some Japonica varieties with S5n were collected and crossed with Indica varieties. The seed setting percentages of hybrids with different seeding dates were observed. The results showed that the seed setting percentages of all hybrids could come to 70% and more. 67% of the hybrids appeared sensitive to the environment. Some hybrids, such as Yayou 2,heading in the second ten-day of September, appeared highly sterile, while all intervarietal hybrids had normal seed setting percentage. Compared with Indica varieties from southeast Asia, those from China showed more stable hybrid seed setting percentage as crossed with 02428, a Japonica variety with S5, and its derivative lines. The hybrids of Indica varieties having some affinity with Japonica, such as Peiai 64S, had good stability of seed setting. The sensitivity of pollen fertility of Indica-Japonica hybrids to the environment resulted in the unstability of seed setting percentage.