Department of Agronomy, National Chung-Hsing University Taichung, Taiwan 40227, ROC
During recurrent backcrossing of Taichung 65 (abbr. T65) to early-heading donor parents, Tatung-tsailai (A) and Bozu 5 (B), a line similar to T65, (7)ea was obtained from cross A, and another similar line, (15)eb was obtained from cross B. These T65-like lines both showed a heading time about three days earlier than that of T65 and bred true. Their plant height was similar to that of T65. When they were intercrossed, 7 early-heading offtypes occurred out of 2455 F`2` plants (Tsai 1990). One of the early-heading offtypes (AB-60) produced in its progeny several lines differing in heading time, ranging from "E-type" three to six days earlier-heading than the isogenic line of T65 with gene Ef-1a, and "e'-type" four to six days earlier than T65 carrying ef-1, to a late-heading type 15-25 days later than T65. An e'-type plant, AB-60e'-3 (abbr. e'-3) had a heading time 4 to 9 days earlier than T65 and its plant height was 15-19 cm shorter than that of T65 (Tsai 1990). The F`1` plants between T65 and e'-3 showed intermediate heading time between the parents, indicating partial dominance of the earliness gene of line e'-3. But the height of the F`1` plants was similar to that of T65. The F2 population segregated into 1 e'-3(early): 2 intermediate: 1 T65-like (late) for heading time, and 3 tall (T65-like): 1 short (e'-3 like) for plant height (Table 1).
Table 1. F`1` and F`2` data for plant height in crosses of T65 with three
semi-dwarf lines (difference from T65 in parentheses)
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F`2` Plant number
F`1` Mean
T65-like sd-7 like sd-1 like Total Chi2 Expected
Cross (2nd crop) 97-105 cm 87-97 cm 71-82 cm ratio
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cm
T65xsd-1 88 (-11) 129 282 148 559 1.3 1:2:1
T65xsd-7 100 109 40 149 0.3 3:1
T65xe'-3 99 (-1) 113 35 148 0.2 3:1
(sd-8)
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An early-heading line, T65(20)Ef-1a headed about 6 days earlier than line
e'-3, and showed semi-dwarfism similarly as e'-3. The F`1` plants between
T65(20)Ef-1a and e'-3 headed three days earlier than T65(20)Ef-1a and
were similar to the parents in semi-dwarfism. Their F`2` population
segregated into 3 early (Ef-1 type): 1 late (e'-3 type) for heading time, and
the plants of e'-3 type segregated further into 3 tall (T65-like): 1
semi-dwarf (e'-3 like). The Ef-1a gene has a pleiotropic effect to reduce
plant height (Tsai and Oka 1965). When a plant had ef-1 in place of Ef-1,
its height is recovered to the stature of T65. The early-heading segregants
of T65(20)Ef-1a x e'-3 were all semi-dwarfs and a 1/4 part of late-heading
plants (e'-3 type) were also semi-dwarfs. The occurrence of tall and
semi-dwarf plants in the late-heading class suggests that the parental lines
have different genes for plant height. The semi-dwarfing gene carried by
line e'-3 is denominated as sd-x.Taichung Native 1 (TN1) is known to have the Dee-geo-woo-gen gene, sd-1 (Suh and Heu 1978; Kikuchi and Ikehashi 1984; linkage group 1). The gene was introduced into T65 by 8 backcrosses and a near-isogenic line T65sd-18 was produced. This line was about 26 cm shorter in height than T65. Its F`1` plants with T65 were 11 cm shorter than T65, and the F`2` segregated into 1 tall: 2 intermediate: 1 short types. The allele of T65, sd-1+ is incompletely dominant over sd-1.
On the other hand, a semi-dwarf mutant line, D65-312 was obtained after X-ray irradiation (40 Kr) of T65 seed. This line was about 16 cm shorter and 3 days earlier-heading than T65 (Tsai 1989). Its F`1` plants with T65 showed a similar height to T65, and the F`2` segregated into 109 T65-like: 40 dwarf plants, giving a good fit to the 3: 1 ratio. The semi-dwarfing gene of this mutant was symboled sd-7. It was located on chromosome 5 (Tsai 1991). Crossing experiments showed that sd-1 and sd-7 were independent, and that homozygotes for both had a much reduced plant height. Mean heading time and plant height of lines with these semi-dwarfing genes are summarized in Table 2.
Table 2. Mean plant height and days to heading of T65 and its near-isogenic
lines with a semidwarfing gene (difference from T65 in parentheses)
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Line Plant height (cm) Days to heading
1st crop 2nd crop 1st crop 2nd crop
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T65 102(=O) 99(=O) 127(=O) 88(=O)
T65sd-1`8` 76(-26) 73(-26) 128(+l) 87(-1)
T65sd-7`5` 90(-12) 85(-14) 124(-3) 82(-6)
e'-3(sd-8) 95(-7) 82(-17) 115(-12) 77(-11)
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1st crop: planted in winter, 2nd crop: planted in summer.
To test the allelism of semi-dwarfing genes, crosses were made between e'-3
and T65sd-1`8`, and between e'-3 and T65sd-73. The F`1` plants between e'-3
and T65sd-1 had an intermediate height between T65 and e'-3, and the F`2`
plants varied from tall (T65-like) to very short (double dwarf). When plants
with intermediate heights were pooled, the F`2` segregation pattern fitted 3
tall: 12 intermediate: 1 short ratio (Table 3). Letting the dwarfing gene of
e'-3 be sd-x, the F2 data show that sd-x and sd-1 are independent. Although
both genes are recessive, their heterozygotes like the F`1` plants show
semi-dwarfism possibly due to some interaction of two recessive genes.
Table 3. Expected and observed frequencies of F`2` plants in crosses of line
e'-3 with sd-8 and two other semi-dwarf lines
a) e'-3xT65sd-1`8`
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Genotype Frequency No. of plants
sd-8 sd-7 expected Expected Observed
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+ + + + 1/16_
| 3/16
+ sd-8 + + 2/16_| 26.4 34
+ + + sd-7 2/16_
+ sd-8 + sd-7 4/16 |
+ sd-8 sd-7 sd-7 2/16 | 12/16 105.7 99
sd-8 sd-8 + sd-7 2/16 |
sd-8 sd-8 + + 1/16 |
+ + sd-7 sd-7 1/16_|
sd-8 sd-8 sd-7 sd-7 1/16 1/16 8.8 8
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Differences between expected and observed numbers did not reach the 5% level
of significance.
b) e'-3 XT65sd-7`3`
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Genotype Frequency No. of plants
sd-8 sd-7 expected Expected Observed
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+ + + + 1/16_
| 5/16
+ sd-8 + + 2/16_| 44.7 47
+ + + sd-7 2/16_
+ sd-8 + sd-7 4/16 |
+ sd-8 sd-7 sd-7 2/16 |
| 10/16 89.4 86
sd-8 sd-8 + sd-7 2/16 |
sd-8 sd-8 + + 1/16 |
+ + sd-7 sd-7 1/16_|
sd-8 sd-8 sd-7 sd-7 1/16 1/16 8.9 10
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Differences between expected and observed numbers did not reach the 5% level
of significance.
Further, line e'-3 with sd-x was crossed with T65sd-7. The F`1` plants were
somewhat shorter (by 4 cm) than T65, and the F`2` segregated into 5 tall: 10
intermediate: 1 short classes when plants with intermediate heights were
pooled, as shown in Table 3. These experimental results indicate that gene
sd-x is independent of both sd-1 and sd-7. It is symboled sd-8 tentatively.The agronomic characters of these lines are summarized in Table 4. Gene sd-1 shortens the upper internodes rather strongly, but sd-7 and sd-8(t) both shortens the second to fifth internodes moderately. Gene sd-8(t) seems to increase spikelets per panicle.
Table 4. Character values of T65 and its semi-dwarf lines
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1st crop, 1992 2nd crop, 1991
Character _______________________________ _________________________________
T65 T65sd-1`9` T65sd-7`4` e`-3 T65 T65sd-1`9` T65sd-7`4` E`-3
(sd-8) (sd-8)
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Length, cm
Plant height 97.O 71.4 81.8 81.1 99.4 68.0 85.1 84.2
Panicle 22.2 20.4 21.5 20.8 22.5 20.0 20.7 19.1
Internode 1 41.8 32.5 41.1 40.1 39.8 25.8 38.1 38.3
" 2 21.4 12.4 15.1 14.0 21.3 13.8 17.1 16.2
" 3 9.3 4.4 2.4 4.0 10.0 5.3 6.4 6.5
" 4 2.7 1.2 0.7 1.0 4.0 1.8 1.0 2.5
" 5 0.8 0.5 0.4 0.5 1.0 0.7 0.6 0.8
Panicles/plant9.0 7.3 6.7 6.2 8.7 9.9 11.6 8.7
Spikelets/panicle139 119 135 185 144 106 139 162
Spikelet length6.8mm 6.8 6.7 6.4 7.0 6.9 6.8 6.4
" width 3.3 3.4 3.5 3.3 3.5 3.5 3.3 3.3
1000 grain wt.25.09 24.9 24.7 18.6 25.4 21.0 22.5 20.6
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ReferencesKikuchi, F. and H. Ikehashi, 1984. Semidwarfing genes of high-yielding rice varieties in Japan. RGN 1: 93-94.
Suh, H. S. and M. H. Heu, 1978. The segregation mode of plant height in the cross of rice varieties, XI. Linkage analysis of the semi-dwarfness of rice variety "Tongil". Korean J. Breed. 10: 1-6.
Tsai, K. H., 1989. An induced dwarfing gene, sd-7(t), obtained in Taichung 65. RGN 6: 99-101.
Tsai, K. H., 1990. Unusual mode of inheritance of heading time and occurrence of weak plants observed in rice. Japan. J. Breed. 40: 133-146.
Tsai, K. H., 1991. Tight linkage of gene sd-7(t) and d`1` found in a cross of Taichung 65 isogenic lines. RGN 8:104.
Tsai, K. H. and H. I. Oka, 1965. Genetic studics of yielding capacity and adaptability in crop plants. 1. Characters of isogenic lines in rice. Bot. Bull. Acad. Sinica 6: 19-31.