12. Complementary genes controlling temperature-sensitive sterility in hybrids
between Indica and Japonica types

Hebiao Li1, Aiming Liu1, Linghua Tang1, Qifa Zhang2 and Jiangshi Zou1

                            1) Jiangsu Academy of Agric. Sciences, Nanjing, 210014 China
                            2) State Key Laboratory of Crop Genetic Improvement, Huazhong Agric.
                                University, Wuhan, 430070 China
      In China, some Indica-Japonica hybrid expressing strong heterosis have been used for rice production. Yayou 2 is one of such hybrid varieties. Its seed-setting rate, however, was found to be unstable recently as the expression of heterosis for grain yield is lowered under low temperatures (Li 1993: Ikeda 1994).
    Yayou 2 is derived from crosses between 3037 (Indica) and 02428 (Japonica), and is sensitive to low temperatures. In 1994, the F1, F2 and B1F1 plants were grown in Nanjing in summer (mean temperature being 29.6° for 10 days before heading) and in Hainan in winter (23.8°). In Nanjing, the F1 plants had 80% or higher seed setting, and the F2 and B1F1 plants showed a monomodal distribution of seed-setting rate, as there were no sterile plants. Under the lower temperatures in Hainan, the F1 plants had a mean seed-setting rate of 13.1% only, although the parental strains showed normal fertility. The F2 population showed a bimodal distribution of pollen fertility. There were 157 partly sterile and 143 fertile plants. The seed-setting rate of the F2 population also showed a bimodal distribution; there were of 205 partly sterile and 151 fertile plants. These ratios fit the 9:7 ratio.
    The B1F1 population showed a rather variable frequency distribution of pollen and seed fertilities, which appeared to be either 1:1 or 3:1. From these observations, it may be assumed that the low-temperture sensitivity of the F1 plants is controlled by two complementary genes for sterility, probably one from Indica and the other from Japonica parent.

References

Li Lin, 1993. Effect of temperature on seed setting rate of Yayou 2. Jiangsu Agric. Sciences 2: 18-20.
Ikeda, R., 1994. Research on hybrid rice in Japan - Progress and future directions. J. Agric. Science 49(11):
            478-492.