20. Preliminary characterization of fertility-restoring mutants induced from cytoplasmic male-sterile rice

Yu-Wei SHEN, QI-Hua CAI and Ming-Wei GAO

Institute of Nuclear-Agric. Sciences, Zhejiang Agric. University, Hangzhou, 310029 China

Cytoplasmic male sterility (CMS) is caused by an interaction between cytoplasmic and nuclear genes, and is maternally inherited. GMS can be modified by external factors. For instance, male-fertile revertants were obtained through somaclonal variation and mutagenesis in different crops: maize (Brettle et al. 1980), pearl millet (Burton 1977), wheat (He et al. 1989), and rice (Nawa et al. 1987). In this paper, we report the induction of mate-fertile mutants from a CMS line II-32A by gamma-ray irradiation, and their characteristics.

II-32A has the cytoplasm of an Indonesian variety and the nucleus of an Indica variety II-32. In 1988, its seeds were treated with gamma-rays, and in the M, generation found were 8 fertile plants. Stable fertile plants were selected from the progenies of these plants. Some of the fertile plants thus obtained were compared with the maintainer line II-32B (Table 1). The agronomic characters of these mutants were almost identical to those of II-32B.

One of the fertile revertants, T24, showed segregation into fertile and male-sterile plants in a 3:1 ratio (165:54). As these mutants have male-sterile cytoplasm, they must have fertility restoring genes in their nucleus. T24 would be heterozygous for the gene. The 3:1 ratio indicates that the fertility restoring ene is dominant.

To test the above hypothesis, the mutants were crossed with Zhenshan 97A

Table 1. Characters of fertility-restoring mutants and line II-32B (1992)
=============================================================================
Character             T18            T21            T24            II-32B
                   (II-32R-1)     (II-32R-2)     (II-32R-3)
=============================================================================
Plant height (cm)   97.8+/-6.1    87.1+/-5.3      95.6+/-5.6     91.5+/-5.6
Tillers/plant       10.1+/-3.6     7.5+/-1.3       9.6+/-3.2     10.0+/-1.3
Spikelets/panicle  114  +/-9.7   161  +/-15.6    103  +/-10.7   134  +/-14.2
Filled grains       94  +/-5.3   111  +/-13.2     80  +/-9.1    105  +/-11.1
Seed setting        83.5          68.8            78.4           77.9
Days to heading    113           112             113            111
Grain length (mm)    9.05+/-0.13   8.70+/-0.21     8.83+/-0.24    8.56+/-0.23
Grain width (mm)     3.01+/-0.13   2.98+/-0.13     3.12+/-0.11    3.11+/-0.13
Length/width ratio   3.01          2.92            2.83           2.75
=============================================================================
     All lines had purple glume tips.



Table 2.  Characters of F\1\ plants of Zhenshan 97AxT18 and other crosses
(1992, early season)
===============================================================================
Character      Zhenshan 97A  II-32A   Zhenshan   II-32A   Zhenshan    11-32A
                 xTl8         xTI8    97A x T21    T21    97A x T24     xT24
===============================================================================

Plant height 
       (cm)    89.2+-2.8  99.8+-3.9  72.3+-2.3  75.2+-3.9  87.5+-4.3  92.3+-4.9
Tillers
    /plant     11.5+-3.8   9.1+-4.6   7.8+-3.3  14.2+-3.8  10.4+-3.1   9.3+-2.0
Spikelets
    /panicle  110  +-9.5 130  +-18  131  +-16  129  +-4.2 129  +-14  132  +-18
Filled grains 101  +-8.4 101  +-11  108  +-13  102  +-9.2 105  +-11  108  +-15
Seed setting   89         79         83         79         81         81
Days to 
   heading    106        113        108        108        105        111
Range of % 
   seed set.   85-97      74-85      80-86      70-84      79-85      77-85
===============================================================================

(a WA-type CMS line) and II-32A. The results showed that the fertility of both Zhenshan 97A and II-32A was restored to normal level in the F\1\ plants (Table 2). However, II-32A X T24 cross produced fertile and sterile F\1\ plants in a 1:1 ratio (20 fertile:22 sterile). This verifies the above conclusion.

In the F\2\ populations of the fertile mutants crossed with II-32A or Zhenshan 97A, however, the fertility variation was continuous and only a small part of plants showed fertilities over 70%. This suggests that the fertile mutants have two genes for fertility restoration, similarly as found in a restorer line of Zhenshan 97A (Gao 1980). These fertile mutants would be useful for looking into the mechanism of cytoplasmic male sterility.

References

Brittell, R.I.S., E. Thomas and D.S. Ingran, 198O. Reversion of Texas male-sterile cytoplasmic maize in culture gives fertile T-toxin resistant plants. Theor-Appl-Genet. 58: 55-58.

Burton, G. W., 1977. Fertile sterility-maintainer mutants in cytoplasmic male-sterile pearl millet. Grop Sci. 17: 635-637.

Gao, M. W., 1980. Preliminary analysis of genotype of wild-abortive type cytoplasmic male-sterile Indica rice. Acta Genetica Sinica 8: 66-74.

He, P.R., Z.D. Li and S.X. Li, 1989. Male-sterility reversion from T-type cytoplasmic male-sterile wheat induced by ⁶⁰Co gamma-rays. Acta Genetica Sinica 16: 1-6.

Nawa, S., Y. Sano, M. Yamada and T. Fujii, 1987. Cloning of the plasmids in cytoplasmic male-sterile rice and changes of organization of mitochondrial and nuclear DNA in cytoplasmic reversion. Jpn. J. Genet. 62: 301-314.