South China Institute of Botany, Academia Sinica, Guangzhou, 510650 China
A female-sterile mutant (164V) was found among 140 R3 plants obtained from a somaclone (164) of IR50, in 1986. Its major characters were as follows:
1) The pistil lacked stigma and style and consisted of ovary only (Fig. 1A). Some ovaries had an embryo sac, but others were full of parenchyma cells. The mutant plant set no seed (Fig. 1D). The ovaries were not functional.
Fig. 1. Spikelets of the female-sterile mutant obtained. A. Scanning
electromicroscopic photo of a spikelet having no stigma and style in the
pistil. B. Section of a spikelet with long lemma, short palea (p) and two
ovaries. C. Section of a spikelet with more than two ovaries. D. A
female-sterile panicle (left) and a normal panicle (right) of somaclonal line
164.
2) The anthers degenerated to varying degrees. In about one fourth of spikelets of a panicle, all anthers degenerated and the stamens consisted of filaments only. The maximum nuniber of anthers per spikelet was four. Of 77 spikelets observed, those having 4, 3, 2, 1 and 0 anthers were 3, 8, 26, 20 and 20, respectively. But the anthers contained functional pollen grains which were stained by iodine normally. When a normal plant was pollinated with the pollen of the mutant, F1 seeds were obtained.
3) In the spikelets, the lemma was over-developed while the palea was under- developed becoming a small piece (Fig. 1B). Some spikelets had two or more than two ovaries (Fig. 1B, C).
Six F1 plants (164N/164V) were obtained, which showed normal phenotype and set seed with seed fertilities ranging from 48% to 89%. The F2 plants segregated into 436 normal: 22 female-sterile types, showing a good fitness to a 15:1 ratio. This suggests that the female-sterile mutant is controlled by two independent recessive genes.
The somaclone producing this mutant was derived from seed callus culture of the variety IR50. In the R1 and R2 generations, all plants were normal although there were only 30 R2 plants. Probably, the female-mutant was induced during in vitro culture.
Female-sterile mutants have been found in the progeny of distant crosses in wheat (Yuan 1987) and rice (Yokoo 1984). But its induction from culture does not seem to have been reported previously.
References
Yokoo, M., 1984. Female sterility in an Indica-Japonica cross of rice. Jpn. J. Breed. 34: 219- 227.
Yuan, S., 1987. Studies on the induction of alien cytoplasm to abortion of pistils and stamens in Tritictim durum hybrid. Acta Bot. Sinica 7: 170-176.