1) Department of Agronomy, Nanjing Agricultural University, Nanjing 210095 China
2) Institute of Crop Breeding and Culture, Chinese Academy of Agricultural sciences, Beijing, 100081 China
A Japonica strain, KL908 characterized by short stature, profuse tillering, and small panicles with small grains, was introduced from Kyushu University, Japan in 1988 through the courtesy of Drs. Tze-Xuan Wang and N. Iwata. Its dwarfism is controlled by a dominant gene. In 1989 to 1993, KL908 was crossed with six tall varieties with diverse eco-agronomic traits, and genetic analysis was carried out with regard to plant-height in F`1`, F`2`, F`3`, B`1` (backcrossed to KL908) and B`2` (backcrossed to a tall parent) generations. Plant height was measured from ground surface to the panicle tip not including awns. The materials were divided into three categories: tall with more than 120 cm heights, semidwarf or intermediate with 80-120 cm heights, and dwarf with less than 80 cm height.
The dwarfism of KL908 appeared to be controlled by one or two dominant genes depending on the genetic background of the material. The potential of dominance was rather weak as the stature of F`1` plants approximated the mid-
Table 1. Segregation patterns for plant height in hybrid progenies of
KL908 (dwarf) crossed with different varieties
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Cross Mean height, cm F`2`, plant no. Height B2,plant no.
KL908 x P`1` P`2` F`1` Dwarf Tall Chi2 B`1`cm Dwarf Tall Chi2
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Kuidao 2.2 3.4
(Japonica) 68 156 108 347 135 85 138 108
(3:1) (1:1)
Wase-aikoku 1.4 1.6
57 125 97 488 145 77 81 99
(Japonica) (3:1) (1:1)
Yancheng- 3.2 0.1
ngmangzi 63 138 92 494 138 74 84 79
(Japonica) (3:1) (1:1)
Cungu 1.3 0.6
57 159 96 664 195 77 101 89
(unknown) (3:1) (1:1)
Ketan nangka 0.1 0.0
(Javanica) 68 201 94 146 119 (9:7) 92 32 96 (1:3)
Nanjing 6 0.1 0.8
(Indica) 68 162 121 263 199 92 12 50
(9:7) (1:3)
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B`1`: backcross with KL908; B`2`: backcross with tall parent.
parent value and tended toward tall parents. The expression of the dwarfing
genes fluctuated according to genetic background, as shown in Table 1.All dwarf plants from segregating populations produced tall and dwarf or semidwarf segregants, or homozygous dwarf progenies, but did not produce fixed tall progenies. Three semidwarf lines were selected, which showed their recessiveness when testcrossed to a tall variety (Table 2).
Table 2. Testcross of semidwarf lines with tall variety, Nanjing 6
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Plant No. of F`1` plants with Nanjing 6
Semidwarf line height plants Height Deviation No. of
(cm) observed (cm) from Nanjing 6 plants
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91-120-1 105 6 158 -4 6
91-120-2 105 6 148 -14 11
91-1119-1 82 7 154 -8 8
91-1119-2 86 18 150 -12 14
91-1147-1 95 18 163 +1 22
91-1147-2 103 18 166 +4 35
Nanjing 6 (tall) 162 18
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The origin of recessive genes for semidwarf stature cannot be explained.
Neither KL908 nor the tall parents carry sd-1 or other recessive dwarfing
gene. Probably, KL908 has some recessive genes for dwarfism together with
the dominant dwarfing gene. The inheritance of dominant dwarfism has been
reported by lwata et al. (1977), Heu et al. (1988) and Koh and Heu
(1993). But there remain questions as to the genetic structure of dominant
dwarfism.References
Heu, M. H., Y. K. Kim, H. J. Koh and B. H. Kwon, 1988. The segregation mode of plant height in the crosses of rice cultivars, XII. Genetic segregation of dominant dwarf gene D-53. Korean J. Breed. 20(2): 155-159.
Iwata, N., H. Sato and T. Omura, 1977. Linkage studies in rice. Linkage relationship for 6 newly described genes. Japan. J. Breed. 27 (Suppl. 1): 250-251. (in Japanese)
Koh, H. J. and M. H. Heu, 1993. A new dominant dwarfing gene in rice. RGN 10: 77-79.