Spikelet sterility in F1 Hybrids between Rice Varieties Silewah and Hayakogane.

In order to analyze the cause of the highly spikelet sterility observed in the F1 hybrids between Silewah and Hayakogane, reciprocal crosses between Hayakogane and Silewah were conducted. Since F1 hybrids in the reciprocal crosses showed slmilarly low spikelet fertility, the spikelet sterility in the F1 hybrids was not caused by cytoplasmic male sterility. In addition, the F1 hybrids displayed normal pollen fertility and crossed seed fertility in reciprocal crosses between F1 hybrids, Silewah/Hayakogane and Hayakogane was normal. These results indicated that pollen and ovule of the F1 hybrid were normal. The F1 hybrids between Silewah and Hayakogane showed a large number of indehiscent anthers. Accordingly, it was deduced that the highly spikelet sterility in the F1 hybrlds between Silewah and Hayakogane was mainly caused by indehiscent anthers. When spikelet fertility in the F1 hybrids between pedigrees of Hayakogane and Silewah was examined, the F1 hybrid between Norin 15 and Silewah showed the same extremely low spikelet fertility as that of the F1 hybrid between Silewah and Hayakogane. Furthermore, the F1 hybrids between either Kyowa or Hokuto and Silewah were partially fertile. The slightly decreased fertility was also observed in the F1 hybrids between either Hashiribozu or Matsumotomochi. These F1 hybrids had normal pollen fertility and a number of indehiscent anthers. The F1 hybrids of the remaining pedigrees of Hayakogane crossed with Silewah showed a normal spikelet fertility in F1 hybrids crossed with Silewah. These results suggest that varietal differentiation for spikelet sterllity in the F1 hybrids including Silewah may occur in Japonica rice varieties.