30. A temperature-sensitive male-sterile line found in rice

Zong-Xiu SUN, Shao-Kai MIN and Zhen-Min XIONG

China National Rice Research Institute, Hangzhou, Zhejiang, China

A genic male-sterile mutant, 5460s, wa-s discovered in Fujian Agricultural College from an Indica strain (5460) originally derived from IR54. It was sterile from middle July to early September when planted in Fuzhou (26 deg.05'N), and was considered to be a photoperiod-sensitive male-sterile line (Li et al. 1988; Yang et al. 1988). However, its sterility period is characterized not only by long days but by high temperatures also, and whether the long day or the high temperature is responsible for its summer sterility has remained unknown. To make this point clear, the present experiment was conducted using growth chambers.

The seeds of 5460s and 5460 (control) were provided by Fujian Agricultural College, and the seedlings at 7-leaf stage were transplanted in pots and placed in six growth chambers each with a different combination of three photoperiods (12.0 h, 13.5 h and 15.0 h) and two temperature schemes (low: 27 deg. in mid-day and 22 deg. in mid-night, mean 23.5 deg., and high: 33 deg. in mid-day and 28 deg. in mid- night, mean 29.5 deg.). Relative humidity was adjusted at 75%. More than 10 plants per treatment were observed, their pots being randomized in each growth chamber. Pollen fertility at flowering and self seed fertility (bagged) at maturity were re- corded in each plant.

The control plants (5460) showed normal pollen and seed fertilities throughout the treatments. The fretilities of 5460s plants observed are given in Table 1. Under the low temperature scheme (27 deg. - 22 deg.), all the plants were fertile showing

Table 1. Effects of temperature and day length on pollen and seed 
fertilities of a sterile mutant 5460s, tested in growth chambers 
(1988)
________________________________________________________________
Temperature      Day length    % abortive      % seed
   scheme         (hr)          pollen        fertility
________________________________________________________________
33/28 deg.C         12.0     96.4+/-8.6        2.7+/-4.0
                    13.5     97.9+/-7.1        0.4+/-1.1
                    15.0     99.6+/-1.2        2.2+/-5.1
27/22 deg.C         12.0     49.0+/-9.7       58.4+/-13.5
                    13.5     29.5+/-13.4      65.4+/-15.9
                    15.0     30.2+/-13.1      54.3+/-17.5
________________________________________________________________
higher than 50% pollen and seed fertilities regardless of daylength. Under the high temperature scheme (33 deg.-28 deg.), most of the plants were completely sterile and a few others were highly sterile, abortive pollen being higher than 96.5% and seed fertility being less than 3%. This was also regardless of daylength although there was a slight tendency for percent abortive pollen to be higher at 15.0 h than at 12.0 h/day. Analysis of variance of seed fertility of 5460s showed that the difference cause by temperature was highly significant (F=978).

Although the daylength did not influence fertility much (F= 1.69, non- significant), the interaction between temperature and daylength was significant (F=4.73, P<0.05) as fertility was influenced by daylength only under the temperature scheme. We also found that the embryo sacs of 5460s grown under high temperature could be fertilized and set seeds when pollinated with normal pollen grains.

Accordingly, we have asserted that 5460s is a temperature-sensitive male- sterile line. This line will be useful not only for genetic and physiological studies but also for breeding "two-line hybrid rices", as it will serve as a sterile line in summer and as a maintainer line in autumn.

References

Li, W. M., C. M. Cai and Y. C. Zhou, 1988. A photoperiod-sensitive genic male-sterile rice newly discovered. RGN 5: 89-90.

Yang, R. C., W. M. Li, N. Y. Wang and Q. H. Chen, 1988. Discovery and preliminary study on indica photosensitive genic male-sterile germplasm 5460a. Chinese J. Rice Sci 3(1): 47-48.