14. Evolutionary significance of chromosome 7 in an annual type
of wild rice
M. Eigluchi1 and
Y. Sano2
1) National Institute of
Genetics, Mishima. 411 Japan
2) Plant Breeding Institute,
Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan
In order to look into the genetic divergence between
wild and cultivated rice, a segment of chromosome 7 was examined after
introducing it into a cultivated form from a common wild rice by successive
backcrossings. An annual type of wild rice from India
(W107) was crossed to a near-isogenic line of Taichung 65 (Japonica
type from Taiwan) with g (long empty glume) and lg (liguleless)
which was used as the reccurent parent (T65glg) in back-crosses.
W107 like most of the common wild rice has red pericarps (Rc) and
short empty glumes (g+) and T65glg has white pericarps
and long empty glumes. The two dominant genes which are located on chromosome
7 were used to transfer the chromosome segment with Re and g+.
The genetic divergence due the segment was studied since weedy forms frequently
show red pericarps even after introgression, suggesting the adaptive significance
of the segment under natural conditions.
Two other dominant genes were detected to be located
on the segment in question. One was responsible for short stature only
in the vegetative phase (tentatively called Ssv) while no difference
in culm length was observed at the flowering stage. Dominant dwarfism expressed
at the vegetative phase has not been reported so far. The other gene was
responsible for late heading at Mishima (tentatively called Lh)
while plants with Lh(t) headed earlier than T65glg under
a short-day treatment. This indicates that the dominant gene may be a photosensitivity
gene. Ratios of 3:1 were repeatedly observed from BC3 F2
to BC5 F2 showing that short stature and late heading,
both are controlled by single dominant genes in the genetic background
of cultivated rice. The allelism tests between Lh(t) and other known
photosensitivity genes remain to be studied.
The segregation in B5 F2 showed
that Ssv(t) and Lh(t) were linked to both g and Rc (Table
1 ). The linkage relations were estimated as shown in Fig. 1. Distorted
segregations were detected for Rc and Lh(t), showing significant values
in c2 (Table 1). Although the mechanism for the distortion is
unknown, the frequency of phenotypes with Rc decreased most severely
in the B5 F2 than the expected value (60.8%,
significant at 1%) as shown in
Table 1. Linkage relations among the 4 loci, g, Ssv(t), Rc
and Lh(t) on
chromosome 7 in the BC5 F2 between T65glg
and W107
| Gene
combination
(A)
(B) |
No. of
phenotypes |
Recombination
value (sd) |
X2
(df=3) |
| AB |
Ab |
aB |
ab |
Total |
| Ssv(t) |
g |
Obs. |
84 |
5 |
10 |
31 |
130 |
0.17(0.04) |
6.0 ns |
|
|
Exp. |
87.4 |
10.1 |
10.1 |
22.4 |
|
|
|
| Ssv(t) |
Rc |
Obs. |
68 |
21 |
11 |
30 |
130 |
0.29(0.05) |
16.6** |
|
|
Exp. |
81.4 |
16.1 |
16.1 |
16.4 |
|
|
|
| Lh(t) |
Rc |
Obs. |
75 |
10 |
4 |
41 |
130 |
0.13(0.03) |
15.8** |
|
|
Exp. |
89.6 |
7.9 |
7.9 |
24.6 |
|
|
|
| Ssv(t) |
Lh(t) |
Obs. |
70 |
19 |
15 |
26 |
130 |
0.34(0.05) |
11.5** |
|
|
Exp. |
79.2 |
18.3 |
18.3 |
14.2 |
|
|
|
| Rc |
g |
Obs. |
66 |
13 |
28 |
23 |
130 |
0.40(0.06) |
17.8** |
|
|
Exp. |
76.7 |
20.8 |
20.8 |
11.7 |
|
|
6.0 ns |
| Lh(t) |
g |
Obs. |
67 |
18 |
27 |
18 |
130 |
0.46(0.06) |
6.0* |
|
|
g |
74.5 |
23.0 |
23.0 |
9.5 |
|
|
|
Note; The genotype of F1 was g+ Ssv(t) Rc Lh(t)/g
Ssv(t)+ rcLh(t)+.
ns shows non-significance.
* and ** show significance at 5% and 1%, respecitvely. Fig. 2,
suggesting that the introduced segment is quickly eliminated when backcrossed
with T65glg.
