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.
Harushima, Y., M. Yano, A. Shomura, M. Sato, T. Shimano, Y. Kuboki, T.
Yamamoto, S.Y. Lin, B.A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamamoto,
Y. Nagamura, N. Kurata, G.S. Khush and T. Sasaki, 1998. A high-density
rice genetic linkage map with 2275 markers using a single F2
population. Genetics 148: 479-494.
Kajiya, H., M. Yano and T. Sasaki, 1995. Molecular tagging of the gene
wgl(t) conferring glum width in rice. Japan. J. Breed. 45
(Suppl. 1): 77.
Kurakazu, T., Sobrizal and A. Yoshimura, 2001. RFLP Mapping of the genes
for awn on chromosomes 4 and 5 in rice using the Oryza meridionalis
introgression lines. RGN 18: 28-30.
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.