23. A new thermosensitive radiation-induced male-sterile rice line

Yu-Wei SHEN, Qi-Hua KAI and Ming-Wei GAO

Institute of Nuclear-Agric. Sciences, Zhe'iang Agric- University Hangzhou, 310029 China

The discovery of photosensitive genic male-sterile line (PGMR) Nongken 58S by Shi (1981) has attracted a wide attention of the rice breeders. A number of environment-sensitive male-sterile (EMS) lines have been developed by transferring PGMR genes from Nongken 58S to other Japonica and Indica varieties, and by selection of other spontaneous mutants (Yuan 1990). Mutagenesis was also used as an effective way of developing EMS lines, by which two thermosensitive genic male-sterile lines (TGMR) were obtained (Kato et al. 1990; Oard et al. 1991). In this paper, we report a new Indica TGMR line, 26 Zhaizao S induced by gamma-rays.

In the first-crop season of 1989, we isolated 9 sterile plants from among 4,000 M\2\ plants and 4 sterile plants from 45 M\3\ kubes of 26 Zhaizao. These sterile plants were ratooned for observation of their fertility restoration in the late season. The plants which exhibited fertility restoration was selected, and screened further in 1990 and 1991. In 1991, three plants which headed on July 10 were completely sterile, but their tillers set seeds after mid-Agugust at a rate of 35-40%.

In 1992, one of the three mutants, named 26 Zhaizao S, was studied in the growth chamber of China National Rice Research Institute. Under day-lengths of 12.5 to 14 hrs, its fertility increased as the average temperature rose. At 23.1degC, the seed set upon bagging was only about 1%, but it was 30-40% at 24.1degC. At the average temperature of 30.1degC, the seed-setting rate of bagged plants decreased to 6-10%. However, 90% of the pollen grains stained with KI, suggesting that bagging affected fertilization at such a high temperature. Under the day-length of 15 hrs, the mutant showed low fertility at the three temperatures, especially at 30.1 degC (Table 1).

Table 1. Fertility response of mutant 26 Zhaizao S to day-length and temperature regimes set in a growth chamber (1992) (Each plot consisted of 15 plants)

========================================================================
Day-length   Temperature    % seed setting             % abortive
(hrs)           (degC)       rate upon bagging            pollen
========================================================================
15.0            30.0            0                          50.0
                24.1           16.3+/-6.0                  25.3
                23.1            7.4+/-4.6                  21.7
14.0            30.1           10.1+/-20.9                  8.1
                24.1           39.6+/-9.7                  22.1
                23.1            1.0+/-1.05                 48.5
12.0            30.1            6.1+/-4.2                  13.8
                24.1           32.1+/-10.3                 20.1
                23.1            1.2+/-2.0                  40.4
=======================================================================

The mutant was also observed in the field at Hangzhou in 1992, by sowing every two weeks starting April 30. The plants began flowering on July 25, but failed to set seed. After August 10, the plants became gradually male-fertile. This mutant has a much earlier fertility restoration time than other photo- or thermosensitive male-sterile mutants. A preliminary analysis of the data suggested that the sterility of this mutant between July 25 and August 10 might be due to low temperatures at the time of panicle differentiation. The average temperature for the period June 13 to July 9 was below 23degC.

From the growth-chamber tests and field trials, it is suggested that the sterility of the mutant is induced by temperatures below 23degC. The fertility response of this mutant to temperature is opposite to that of H89-1 and also differs from those of 87NB, 87N1O and 87N123-R\e\ (Zhou 1992).

The mutant, 26 Zhaizao S, has a good productivity and a high rate of stigma exersion. It may be used for hybrid seed production in the two-line system.

References

Kato, H., S. Yanagihara, K. Maruyama and H. raki, 1990. Sterility responses of a rice thermosensitive genic male-sterility in some areas of Japan. Jpn. J. Breed. 40, Suppl. 2: 378-379. (in Japanese)

Shi, M.S., 1985. The discovery and study of the photosensitive recessive male-sterile rice (Orvza sativa L. subsp. japonica). Scientia Agricultura Sinica 2: 44-48. (in Chinese)

Yuan, L.P., 1992. Progress of two-line system hybrid rice breeding. Scientia Agricultura Sinica 23(3): 1-6. (in Chinese)

Zhou, T., 1992. Comparison of photo- and thermo-reactions between different photo- (thermo-) sensitive genic male sterile lines. Hunan J. Agric. Sci. 5: 6-8.