39. Utilization of microspore-derived plants for genetic analysis in rice

Department of Botany, National Taiwan University, Roosevelt Road, Taipei, Taiwan 107, ROC

This communication summarizes our results on genetic analysis of rice plants produced from anther culture (Chen et al. 1982, 1983). Four traits each controlled by a recessvie gene, glutinous endosperm (wx), narrow leaf (nal), ligulelessness (lg), and long glume (g), were selected as markers for the analysis. Previous studies showed that nal and lg were in linkage group 11 and their distance was approximately 19 map units (Yen et al. 1968); wx is in linkage group I and g in linkage group IV (Takahashi 1964). The anthers of hybrids heterozygous for two unlinked (wx and lg; Ig and g) and linked (nal and lg) genes were cultured according to the method described by Chen (1977, 1978). Chromosome numbers of the plants obtained from anther culture were determined and the haploid and diploid plants were subjected to genetic analysis.

Progeny tests showed that all diploids but one were homozygous for both loci. The homozygous diploids were likely of microspore origin, where the haploid chromosome complement of microspores was doubled spontaneously during in vitro development. The exceptional plant was homozygous for lg+ but was heterozygous for the waxy locus. Indirect evidence suggested that a mutation at the wx locus in a spontneously doubled haploid cell during culture might have resulted in this exceptional plant.

Chi-square tests of the haploids and homozygous diploid plants further revealed the following facts: 1) In plants produced from all hybrids, the ratio of the dominant to recessive states of each character fitted the expected 1:1 gametic ratio, indicating that there has been no competition among the microspores with different genotypes during in vitro development. 2) In plants derived from heterozygotes for two unlinked genes, the frequency distribution of the four genotypic classes fitted a 1:1:1:1 ratio. 3) In plants derived from heterozygotes for two linked genes (nal and lg), the ratio of the four genotypic classes departed significantly from the 1:1:1:1 ratio, and the pooled data for haploids and diploids yielded a recombination value of 9.3 +/- 1.47 percent between nal and lg. This value was quite close to that estimated from the F\2\ data by the author (8.5 +/- 1.33%) although it differed from a 19% value reported by Yen et al. (1968).

These results indicate that meiotic events, such as segregation, independent assortment, and recombination of linked genes, occurring in the donor plants can all be detected in the microspore-derived progeny. The significance of this work would be that it provides a theoretical basis for the utilizatin of another culture for rice breeding and demonstrates the feasibility of using the gametophyte derivatives of higher plants for gene mapping. Because fertilization is bypassed in the procedure, this new method of gene mapping may have some special advantages.

Chen, C. C., 1977. In vitro development of plants from microspores of rice. In Vitro 13: 484-489. 1978. Effects of sucrose concentration on plant production in anther culture of rice. Crop Sci. 18: 905-906.

Chen, C. C., W. L. Chiu, L. J. Yu, S. S. Ren, W. J. Yu, and M. H. Lin, 1983. Genetic analysis of anther-derived plants of rice: Independent assortment of unlinked genes. Can. J. Genet. Cytol. 25: 324-328.

Chen, C. M., C. C. Chen, and M. H. Lin, 1982. Genetic analysis of anther-derived plants of rice. J. Hered. 73: 49-52.

Takahashi, M., 1964. Linkage groups and gene schemes of some stricking morphological characters in Japanese rice. In IRRI (ed.), Rice Genetics and Cytogenetics, p. 215-236. Elsevier, Amsterdam.

Yen, S. T., M. H. Lin, and S. C. Hsieh, 1968 Genic analysis in rice. IX. Linkage relations of another induced dwarfness gene d\31\. Bot. Bull. Acad. Sinica 9: 69-74.