22. Linkage analysis of an F1 sterility gene in Japonica / Indica cross of rice
Plant Breeding Laboratory, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka, 812-8581 Japan

We studied hybrid sterility in a cross between Japonica and Indica rice varieties using chromosome segment substitution lines (CSSLs). CSSLs enable us to clarify the effect of a single gene on the substituted chromosome in quantitative genetics. In this study, we describe the map position of a locus for F1 sterility found in a Japonica-Indica hybrid.

Kubo et al. (1999) developed IR24 (Indica variety) chromosome segment substitution lines (CSSLs) in Asominori (Japonica variety) genetic background by successive backcrossing and marker-assisted selections. In the BC3F2 and BC3F3 populations for developing the CSSLs, segregation of partial spikelet sterility was observed. The BC3F3 segregant was backcrossed with Asominori to identify and localize the causal gene on RFLP map. BC4F1 population segregated into highly fertile (>90%) and partially sterile (71-90%) plants (Fig. 1). There were 26 highly fertile and 28 partially sterile plants. The segregation ratio agreed with 1:1 ratio, suggesting that spikelet sterility was controlled by a single nuclear gene. To determine the chromosomal position of this gene, RFLP genotypes of the individuals were observed. At RFLP marker L688 on chromosome 6, the partially sterile plants were heterozygous, whereas the highly fertile plants were homozygous for Asominori alleles, indicating that the sterility gene was closely linked to L688 on chromosome 6. The sterility gene was tentatively designated as S26 (t); its location on the RFLP map is shown in Fig. 2.

The hybrid sterility gene S5 (Ikehashi and Araki 1986), which is universally accepted as a factor for female gamete abortion in Japonica-Indica hybrids, is located near RFLP marker R2394 tightly linked with L688 (Liu et al. 1997). There is a possibility that S26(t) is allelic to S5 because the positions of these genes are almost the same.

This study was supported by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.


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