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CROP BREEDING, GENETICS & CYTOLOGY

Identification of Hybrid Sterility Gene Loci in Two Cytoplasmic Male Sterile Lines in Rice

^a Graduate School of Agric., Kyoto Univ., Kyoto 606-01, Japan
^b Centre for Plant Breeding and Genetics, Tamil Nadu Agric. Univ., Coimbatore 641 003, India

ikehashi{at}kaias.kyoto-u.ac.jp

In hybrid rice (Oryza sativa L.) breeding, spikelet sterility is a barrier to attaining enhanced heterosis in crosses between different groups or subspecies of rice. Our objective was to identify the hybrid sterility gene loci (HSGLi) in two indica cytoplasmic male sterile A lines (`IR58025A' and `IR62829A') and their corresponding maintainer B lines (`IR58025B' and `IR62829B'). To detect the HSGL, three testers, `IR36' (indica cultivar), `Dular' (indica wide compatibility variety [WCV]) and `Nekken 2' (japonica WCV) were crossed to the two groups in the form of IR36/WCV//B and A//IR36/WCV. The level of spikelet fertility in the F₁ progeny of three-way crosses was differentiated by morphological and isozyme marker genes at the known HSGLi, S5, S7, S8, and S15 on chromosomes 6, 7, 6, and 12, respectively, and by two new HSGLi, on chromosomes 3 and 11. The levels of pollen fertility were differentiated by specific marker alleles among segregating genotypes in the cytoplasmic male sterile (cms) background. The presence of marker alleles from IR36 was associated with high pollen fertility, while marker alleles from Dular and Nekken 2 were associated with low pollen fertility due to the effect of HSGLi in the cms background. The effect of dominant and recessive restorers from IR36 was not estimated due to lack of appropriate markers. To alleviate problems of hybrid sterility, the level of sterility should be tested in crosses between maintainers and restorers before the former are used for backcrossing to create new cms lines.

Abbreviations: cms, cytoplasmic male sterile • HSGLi, hybrid sterility gene loci • Rfs/rfs, fertility-restoring gene • WA, wild abortive • WCG, wide compatibility gene • WCV, wide compatibility variety