Sobrizal et al. (1999) developed the Oryza glumaepatula introgression lines in the background of O. sativa cv. Taichung 65. During the process of development, we observed that the pollen semi-sterile plants segregated in a BC₄F₁ population. To study the inheritance of this trait, a BC₄F₁ plant showing pollen semi-sterility was backcrossed with Taichung 65. The BC₄F₁ plant used for backcrossing was found to have retained O. glumaepatula chromosomal segments on chromosomes 4, 7 and 9, when the BC₄F₁ generation of O. glumaepatula introgression lines was genotyped using 106 RFLP markers scattered in 12 chromosomes (Sobrizal et al. 1999). One hundred and four BC₅F₁ plants were grown and the pollen fertility was studied. There were 50 normal and 54 semisterile plants (Fig. 1). This segregation ratio agreed with monogenic segregation ratio (1:1), indicating that the F₁ semi-sterility was controlled by a single gene. Furthermore,

linkage analysis was carried out using RFLP markers located on chromosomes 4, 7 and 9. The result suggested that the gene controlling F₁ pollen semi-sterility was located between RFLP markers R1789 and C213 on chromosome 7 and co-segregated with RFLP marker C1340 (Fig. 2).

So far, two genes controlling pollen sterility, S12 and S22(t), in the hybrids of O. sativa and O. glumaepatula have been reported. The chromosomal location of S12 is unknown (Sano 1994), whereas S22 is located on the short arm of chromosome 2 (Sobrizal et al. 2000). Doi et al. (1999) reported that the F₁ pollen semi-sterility gene S21, identified in backcross progeny of O. sativa and O. glaberrima is also tightly linked with RFLP marker C1340 on chromosome 7. There is high possibility that S21 is allelic to the F₁ pollen semi-sterility gene found in this study. However, the gene identified in this study was tentatively designated as S23(t) until the allelic relationship is verified.

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

References

Doi, K., K. Taguchi and A. Yoshimura, 1999. RFLP mapping of S20 and S21 for F₁ pollen semi-sterility found in backcross progeny of Oryza sativa and O. glaberrima. RGN 16: 65-68.

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Sano, Y., 1994. Pollen-killer in rice. Japan J. Breed. 44 (suppl. 1): 298.

Sobrizal, K. Ikeda, P.L. Sanchez, K. Doi, E.R. Angeles, G.S Khush and A. Yoshimura, 1999. Development of Oryza glumaepatula introgression lines in rice, O. sativa L. RGN 16:107-108.

Sobrizal, Y. Matsuzaki, P.L. Sanchez, K. Ikeda, and A. Yoshimura, 2000. Identification of a gene for male gamete abortion in backcross progeny of Oryza sativa and Oryza glumaepatula. RGN 17 (in press).