Culm length of rice is an important agricultural character related to
the lodging resistance. To date, more than 60 dwarf mutants have been
reported, but D53 is the only dominant mutation among them. Here
we report a new dwarf mutant controlled by a dominant gene.
A mutant, KA-902 derived from cv. Taichung 65 mutagenized with methyl-nitrosourea
(MNU), showed a semi-dwarfism and twisted leaves (Fig. 1 a and c). The
progenies of selfpollinated KA-902 segregated three different phenotypes,
wild, semi-dwarf and extreme dwarf types (Fig. 1 a, b and d). Semi-dwarf
type was similar to the parent KA-902 and extreme dwarf type was sterile.
We found no segregation from any wild type progeny, whereas semidwarf
type progenies segregated the three phenotypes (Table 1). Thus semi-dwarf
KA-902 would carry a heterozygous dominant dwarf gene.
To confirm the inheritance mode of KA-902, we crossed the semi-dwarf type
plant with an indica cv. Kasalath. The F1 plants showed
two different phenotypes, wild and semi-dwarf
types in the ratio of 1: 1. In the F2 progenies
of wild type F1, all plants were normal, but these of semi-dwarf
type F1 were segregated into the three different phenotypes
These results reveal that the semi-dwarfism of KA-902 is controlled by
the single dominant dwarf gene, and its homozygote shows the extreme dwarf
phenotype. The extreme dwarf type seedlings were frequently lethal. This
may cause the low frequency of this dwarf type at
maturity (Table 1 and 2).
The phenotype of KA-902 differs from that of D53 mutant reported
as tillered dwarf (Iwata et al. 1977, 1978, Iwata and Omura 1984). Then
we designated tentatively this mutant gene Twisted dwarf1 (Td1).
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groups for 6 genes newly described. Japan. J. Breed. 27 (Suppl.
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Iwata, N., T. Omura and H. Satoh. 1978. Linkage studies in rice. The sequence
of genes at the eight and eleventh linkage groups. Japan. J. Breed. 28
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