23. Male sterile mutants induced through irradiation of egg cells in rice

P. PLAHA, G.S. KHUSH and D.S. BRAR
International Rice Research Institute, P. O. Box 933. 1099 Manila, Philippines

Cytoplasmic-genetic male sterility system has been commercially exploited for the production of F1 hybrids in a number of crop plants. More recently, major progress has been made in developing high yielding hybrid rice varieties using CMS based on wild abortive (WA) cytoplasm. However, due to some inherent limitations of CMS, breeders are exploring the possibilities to use TGMS (thermo-genic male sterility) and PGMS (photoperiod genic male sterility) to develop two-line rice hybrids (Virmani 1996). In this communication, we report the isolation of male sterile mutants in rice by irradiating egg cells with gamma-rays.

Panicles of cultivar IR36 were emasculated and subsequently irradiated with 7.5kR gamma-rays followed by pollination with a dominant purple leaf rice as marker. A totof about 12,000 M1F1 seeds were produced from which 5,150 M1F1 plants were obtained. These M1F1 plants were harvested individually and plant-to-row M2F2 progenies were raised.

At flowering, progenies were visually scored for segregation for male sterility and fertility. Pollen sterility in each segregating progeny was examined by staining pollen with 1.0% IKI. Plants with less than 10% pollen stainability were considered as male sterile and those with more than 60% as fertile. At maturity the behaviour of the progenies was reconfirmed on the basis of seed set. The sterile plants of the progenies either did not set any seed or set only a few seeds. Of the 5,150 progenies, 29 (0.55%) were found to segregate for male sterility (Table 1). In each of these progenies, male sterility was found to be governed by a single recessive gene. Four progenies (23424, 23546, 23704, 23995) had a few but only sterile plants. The fewer number of plants is due to rare seed set in the respective M1F1 plants. These four progenies could be CMS. All male sterile progenies are under investigation to determine the nature of male sterility.

Reference

Virmani,S.S.,1996. Hybrid rice. Adv.Agron. 57:377-462.

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Table 1. Segregation pattern of male sterile progenies in the M2F2 generation

Progeny no.

Fertile plants

Sterile plants

χ2

20765

26
7
0.253
20783

24

9

0.091

20915

25

9

0.039

20919

28

6

0.980

21099

27

6

0.818

21201

30

8

0.316

21309

30

8

0.316

21588

25

8

0.010

21827

25

8

0.010

22079

27

7

0.353

22234

29

6

1.152

22305

27

7

0.353

22313

27

7

0.353

22661

26

8

0.039

22662

28

6

0.980

22663

26

8

0.039

23009

26

7

0.253

23118

26

4

2.178

23383

15

5

0.000

23386

26

7

0.253

23393

20

4

0.889

23424

0

4

12.000

23459

20

10

1.111

23470

12

4

0.000

23474

17

6

0.014

23486

12

4

0.000

23546

0

5

15.000

23662

26

5

1.301

23673

19

5

0.222

23704

0

3

9.000

23872

15

5

0.000

23995

0

1

3.000

24221

19

4

0.710