22. Identification of a gene for male gamete abortion in backcross progeny of Oryza sativa and Oryza glumaepatula

Plant Breeding Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan

During the development of a series of Oryza glumaepatula introgression lines obtained from crosses of O. sativa L. (cv. Taichung 65) with O. glumaepatula Steud. (Acc. IRGC105688) and continuous backcrossing with Taichung 65 as the recurrent pollen parent (Sobrizal 1999), a locus for F1 pollen semi-sterility was found.

A BC4F2 population 231 was used for analysis of the F1 pollen semi-sterility. The parental BC4F1 plant of the BC4F2 population 231 was found to have retained O. glumaepatula chromosomal segments on chromosomes 1, 2, 7, 9 and 10 when the BC4F1 generation of O. glumaepatula introgression lines was genotyped using 106 RFLP markers scattered on 12 chromosomes (Sobrizal 1999). The BC4F2 population 231 showed clear-cut bimodal distribution for pollen fertility when classified into normal and semisterile plants (Fig. 1). There were 32 normal and 36 semi-sterile segregants. Semi-sterile plants showed approximately 50% pollen fertility and normal spikelet fertility.

Segregation analysis between semi-sterility and RFLP markers on chromosomes 1, 2, 7, 9 and 10 revealed that the pollen semi-sterility was associated with the RFLP marker S910 on chromosome 2 in the BC4F2 population 231 (Table 1). At S910 locus, the 32 plants showing normal pollen fertility were homozygous for Taichung 65 alleles and the other 36 plants showing pollen semi-sterility were heterozygous. The observed segregation ratio agreed with the expected 1:1 ratio, and we assume that the gametes carrying the allele of O. glumaepatula and Taichung 65 are equally transmitted through female side but only the gametes with the allele of Taichung 65 are transmitted through male side. In fact, no plant homozygous for O. glumaepatula alleles at S910 was observed in the BC4F2 population 231, suggesting that the pollen grains carrying O. glumaepatula allele aborted. These

results demonstrated that the pollen semi-sterility was under monogenic control and the locus was tightly linked with RFLP marker S910 on the short arm of chromosome 2 (Fig. 2).

Sano (1994) also found S12, a gene for pollen sterility, in the backcross progeny of O. sativa and O. glumaepatula. In case of S12, the pollen grains carrying O. sativa allele aborted. Since no other gene for pollen semi-sterility or hybrid sterility on chromosome 2 has been reported, the new gene for pollen sterility was designated as S22(t).

The S22(t) causing male gamete abortion in the heterozygous condition is responsible for one of the reproductive barriers. Hence, it limits the utilization of O. glumaepatula specific traits in improving rice varieties. Understanding the nature of this gene as well as the other genes for reproductive barriers between O. sativa and O. glumaepatula is useful for using the O. glumaepatula genome for improving rice varieties.

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


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