15. Mapping of genes for slender kernel using Oryza glumaepatula introgression lines in rice
  SOBRIZAL and A. YOSHIMURA

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

A Brazilian wild rice, Oryza glumaepatula (IRGC 105668), and a Japonica cultivated rice, cv. Taichung 65, were used for mapping of genes for slender kernel. Oryza glumaepatula kernels are 10.0 mm long and 2.5 mm wide; Taichung 65 kernels are 7.8 mm long and 3.8 mm wide. During the development of Oryza glumaepatula introgression lines with O. sativa cv. Taichung 65 genetic background (Sobrizal et al. 1999), plants segregated for slender kernels in BC4F2 populations 01WGA49 and 01WGA51.

In 01WGA49 population, 21 plants had slender kernels and 34 plants had normal kernels. The sizes of slender and normal kernels were 8.3 x 3.1 mm and 7.8 x 3.8 mm, respectively (Fig. 1A). The population 01WGA49 has retained O. glumaepatula chromosomal segment on chromosomes 2, 8, 9 and 10. Linkage analysis between slender kernel and RFLP markers on chromosomes 2, 8, 9 and 10 was conducted. Out of 21 plants with slender kernels, 20 plants were homozygous for O. glumaepatula allele at C560 of chromosome 2 and one plant was heterozygous. Out of 34 plants with normal kernels, ten were homozygous for Taichung 65 allele at C560 and 24 were heterozygous. These results indicate that slender kernel was controlled by a single recessive gene, and tightly linked with RFLP marker C560 on chromosome 2 (Fig. 2A). O. glumaepatula had a recessive allele at this locus. One slender kernel plant carrying the heterozygous allele at C560 was considered as a recombinant between the loci of slender kernel and C560. Since no other gene for grain shape on the long arm of chromosome 2 has been reported, the new gene for slender kernel was designated as sk1(t). The gene sk1(t) was mapped between RFLP markers C679 and C560, with map distances of 2.8 cM and 1.5 cM, respectively (Fig. 2A).

In 01WGA51 population, the sizes of slender and normal kernels were 7.8 x 3.4 mm and 7.8 x 3.8 mm, respectively (Fig. 1B). The population 01WGA51 have retained O. glumaepatula chromosomal segment on chromosomes 2 and 5 (Sobrizal et al. 1999). Linkage analysis between slender kernel and RFLP markers on chromosomes 2 and 5 revealed that slender kernel co-segregated with RFLP marker C1004 on the short arm of chromosome 5 (Fig 2B). At C1004, 17 plants with normal kernels were homozygous for Taichung 65 allele and 39 plants with slender kernels were heterozygous or homozygous for O. glumaepatula allele. These results suggest that slender kernel was controlled by a single dominant gene. O. glumaepatula

had a dominant allele at this locus. Kajiya et al. (1995) reported that wgl(t) gene for wide glum, identified from the backcross progeny of Nipponbare and Kasalath, is tightly linked with RFLP marker Y1060L on the short arm of chromosome 5. There is a high possibility that wgl(t) is allelic to the slender kernel gene found in 01WGA51 population. This gene was tentatively designated as Sk2(t) until the allelic relationship is verified. The Sk2(t) was mapped between RFLP markers Y1060L and R566 on the short arm of chromosome 5 (Fig. 2B).

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

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