利用一套以粳稻品种Asominori为遗传背景、籼稻品种IR24为染色体片段供体的覆盖全基因组的CSSL群体，研究了籼粳亚种间组合Asominori/IR24和02428/IR24杂种小穗低育性的遗传基础。结果发现，Asominori/IR24组合的育性主要受第5染色体上的2个育性位点S-24(t)和S-31(t)及第6染色体上的 S-5位点控制，其中S-31(t)为本研究发现的新育性位点，粳稻品种02428带有该位点的亲和性基因。02428/IR24组合的低育性主要受S-24(t)花粉育性位点的影响。育性基因的表达受遗传背景的影响，在粳稻遗传背景中，S-24(t)位点处在Si/Sj杂合基因型时可使杂种小穗育性下降70%左右，而S-31(t)和 S-5为杂种半不育位点。在籼粳全基因组杂合遗传背景中，当S-5i/S-5j基因型置换成S-5i/S-5i基因型后，亚种间杂种小穗育性可平均提高22.5%，接近正常育性水平。在S-5i/S-5j遗传背景中，S-24(t)和S-31(t)的Si/Si纯合基因型不能改善亚种间杂种的小穗育性。说明S-5位点是影响亚种间小穗育性的关键位点，在亚种间杂交稻育种中，必须首先克服S-5位点造成的育性障碍。提出了等位基因置换法克服水稻籼粳亚种间杂种小穗低育性的技术策略。
The two rice indica/japonica combinations, Asominori/IR24 and 02428/IR24, have strong heterosis, but low seed-setting rates. To understand the genetic bases of the sterility of the two hybrids，a study for identification of gene loci causing hybrid sterility were carried out by using a set of CSSL population with genetic background of japonica variety Asominori and chromosome substitution segments of indica IR24. The results showed that the sterility of Asominori/IR24 is mainly controlled by three gene loci, namely S-5 on chromosome 6, S-24(t) and S-31(t) on chromosome 5, and that of 02428/IR24 is influenced by S-24(t), a locus conferring pollen fertility. S-31(t) was first identified and tentatively nominated, and furthermore, a neutral gene on S-31(t) was also identified in a japonica variety 02428, which had been well documented with a neutral allele S-5n on S-5. The genetic background has a great effect on expression of fertile genes. In the japonica background, S-24(t) at Si/Sj heterozygous genotype could decrease spikelet fertility by about 70%, but S-31(t) and S-5 were two loci of hybrid semi-fertility. In the heterozygous genetic background of indica/japonica hybrid, the F1 seed setting rate could be averagely increased by 22.5% when S-5i/S-5j genotype replaced with S-5i/S-5i, which improved the F1 fertility near to normal level, but S-24(t) and S-31(t) did not have the significant substitution effects when S-5 was at S-5i/S-5j genotype. Therefore, S-5 was proved to be a key locus conferring spikelet sterility of rice indica/japonica hybrids. Finally, an alternative strategy named “alleles substitution method” was put forward to overcome low spikelet fertility in exploiting rice inter-subspecific heterosis.
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