Discovery and preliminary study on photoperiod and temperature sensitive female sterility in rice

Photoperiod and temperature sensitive genic male sterility in rice has been widely reported. But photoperiod and temperature sensitive female sterility of rice has not been reported so far. In this communication, we report a photoperiod and temperature sensitive female sterile mutant, T23fs, which was derived from the progeny of pollen culture derived plant from the cross of C57 (Indica) x 02428 (Japonica). During 1996 to 1998, T23fs was sown at different times under natural conditions of daylength at Guangzhou (23°08� N). It was found that panicles bore few seeds when they headed during mmd-July to late August, and bore seeds at a high rate when they headed during late-September to mid-October. During sterility inducing period, the spikelet set no seeds even when normal pollens of a different variety were sprinkled over their stigmas. The morphology and structure of T23fs spikelets were normal and they opened normally. By iodine staining, germination- test, and pollination-test, it was found that the pollen of T23fs was highly fertile when panicles flowered under favorable growing conditions from July to October. The embryo sacs were observed 3 days and 7 days after self-fertilization by a whole stain-clearing technique. No normal embryos were observed when panicles flowered during mid-July to late August. On the other hand, normal embryos developed when panicles flowered during late-September to mid-October. By using semi-thin section technique, it was found that the structure of embryo sac of T23fs was similar to normal rice, which had one egg cell, two synergids, two polar-nuclei and one group of antipodals. There were two reasons for T23fs sterility. The first was that the zygote could not divide normally (Fig.lA). The second was that zygote could divide normally but the young embryo could not develop normally because of lack of endosperm (Fig. 1B). These results clearly showed that T23fs was a typical photoperiod and temperature sensitive female sterile mutant. The female sterility was caused in the early season with long-daylight and high temperature, and it became fertile in the condition of late season with short-daylight and �low� temperature. We considered that the female sterility of T23fs was different from that in the cross of Indica x Japonica reported by Yokoo (1984), also different from the female sterile mutant reported by Ling et al. (1991).

Photoperiod and temperature sensitive genic male sterility in rice has been widely reported. But photoperiod and temperature sensitive female sterility of rice has not been reported so far. In this communication, we report a photoperiod and temperature sensitive female sterile mutant, T23fs, which was derived from the progeny of pollen culture derived plant from the cross of C57 (Indica) x 02428 (Japonica). During 1996 to 1998, T23fs was sown at different times under natural conditions of daylength at Guangzhou (23°08� N). It was found that panicles bore few seeds when they headed during mmd-July to late August, and bore seeds at a high rate when they headed during late-September to mid-October.

During sterility inducing period, the spikelet set no seeds even when normal pollens of a different variety were sprinkled over their stigmas. The morphology and structure of T23fs spikelets were normal and they opened normally. By iodine staining, germination- test, and pollination-test, it was found that the pollen of T23fs was highly fertile when panicles flowered under favorable growing conditions from July to October. The embryo sacs were observed 3 days and 7 days after self-fertilization by a whole stain-clearing technique. No normal embryos were observed when panicles flowered during mid-July to late August. On the other hand, normal embryos developed when panicles flowered during late-September to mid-October. By using semi-thin section technique, it was found that the structure of embryo sac of T23fs was similar to normal rice, which had one egg cell, two synergids, two polar-nuclei and one group of antipodals. There were two reasons for T23fs sterility. The first was that the zygote could not divide normally (Fig.lA). The second was that zygote could divide normally but the young embryo could not develop normally because of lack of endosperm (Fig. 1B). These results clearly showed that T23fs was a typical photoperiod and temperature sensitive female sterile mutant. The female sterility was caused in the early season with long-daylight and high temperature, and it became fertile in the condition of late season with short-daylight and �low� temperature. We considered that the female sterility of T23fs was different from that in the cross of Indica x Japonica reported by Yokoo (1984), also different from the female sterile mutant reported by Ling et al. (1991).