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D.H. Ling, C.Y. Liang, Z.R. Ma and M.F. Chen
South China Institute of Botany, Academia Sinica, Guangzhou 510650, China
Two fertile revertants were obtained in somaclones of male-sterile plants 91-20 and 194A, respectively. 91-20 was a male-sterile mutant obtained in R2 generation of somatic cell culture of IR54 (Ling et al. 1987), and 194A was a male-sterile line of an Indica variety developed from the BT cytoplasm type of Shinjyo (1969) by cytoplasmic transfer. Young panicles (0.5 to 1 cm in length) of male sterile plants were cultured in the MS medium supplemented with NAA and kinetin, 2mg/1 each (Table 1). In this medium, buds were formed in the young panicles by reinitiation of vegetative growth and they developed into plantlets without callus formation, as reported by Ling et al. (1983). We call this process "SBUD" (spikelet budding).
The fertile revertant from 91-20 was obtained in this manner. On the other hand, the young panicles of 194A were cultured in the MS medium supplemented with 2, 4-D and kinetin, 1mg/1 each, for callus induction, and the calli were transferred to a regeneration medium that was MS with NAA and kinetin, 2mg/1 each. One of the regenerated plants of 194A was fertile.
A total of 94 plants were obtained by "SBUD" from somaclones of male-sterile plants of IR54, IR8 and IR24 (Table 1). In addition, 32 plants were regenerated from 194A. When they reached the mature stage, two plants from 91-20 and one from 194A were found to be fertile. Their seed fertilities were 87.5% for 91-20 and 78.1% for 194A, while the original male-sterile plants had 0% and 1.5% fertilities, respectively. It was also found that one "SBUD" plant from 91-20 (coded 91-20p) had a different expression of male sterility. The original 91-20 plant produced no pollen grain in the anthers, but 91-20p had aborted pollen grains in the anthers.
In the case of 91-20, the processes of mutation and reversion can be summarized as follows: A normal plant of IR54 produced male-sterile segragants in the R2 generation after the young-panicle culture with callus formation, which had no pollen grain. Their "SBUD" culture of young panicles produced three kinds of plants, that were fertile, male-sterile with abortive pollen, and male sterile without pollen grains.
In maize, a fertile reversion was obtained from a male sterile plant with T- cytoplasm through in vitro culture with Helminthosporium maydis toxin treatment (Umbeck and Gengenbach 1983). It seems that culture in vitro is an effective method of inducing male sterility and also its reversion.
Table. 1 Fertility reversion derived from "SBUD" plants of male-sterile
mutants
References
Ling, D.H., W.Y. Chen, M.F. Chen and Z.R. Ma, 1983. Direct development of plantlets from immature panicles of rice in vitro. Plant Cell Reports 2: 172- 174.
Ling, D.H., Z.R. Ma, M.F. Chen and W.Y. Chen, 1987. Male sterile mutant from somatic cell culture of rice. Theor. Appl. Genet. 75: 127-131.
Shinjyo, C., 1969. Cytoplasmic genetic male sterility in cultivated rice Oryza sativa L. 2. The inheritance of male sterility. Jpn. J. Genet. 44: 149-156.
Umbeck, P.F. and B.G. Gengenbach, 1983. Reversion of male sterile T-cytoplasm maize to male fertility in tissue culture. Crop Sci. 23: 584-588.
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