Rice Genetics Newsletter, Vol. 18

Rgn18

22.	Linkage analysis of an F₁ sterility gene in Japonica / Indica cross of rice
	T. KUBO and A. YOSHIMURA 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.

References

Harushima, Y., M. Yano, A. Shomura, M. Sato, T. Shimano, Y. Kuboki, T. Yamamoto, S.Y. Lin, B.A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamamoto, Y. Nagamura, N. Kurata, G.S. Khush and T. Sasaki, 1998. A high-density rice genetic linkage map with 2275 markers using a single F₂ population. Genetics 148: 479-494.

Ikehashi, H. and H. Araki, 1986. Genetics of F₁ sterility in remote crosses of rice. In Rice Genetics. IRRI, Manila, Philippines pp. 119-130.

Kubo, T., K. Nakamura and A. Yoshimura, 1999. Development of a series of Indica chromosome segment substitution lines in Japonica background of rice. RGN 16: 104-106.

Liu, K.D., J. Wang, H.B. Li, C.G. Xu, A.M. Liu, X.H. Li and Q. Zhang, 1997. A genome-wide analysis of wide compatibility in rice and the precise location of the S5 locus in the molecular map. Theor. Appl. Genet. 95: 809-814.