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other dwarfing genes might be presented, but could not be identified at present. This has
agreed with breeder experiences in China and CIMMYT when crossing Chinese wheats with
known CIMMYT germplasm.
A notable change in the frequencies of three dwarfing genes was observed when
comparing cultivars released before and after 1990 (Table 7). Overall, the frequencies of
Rht-
B1b
and
Rht-D1b
have increased, from 8.6 to 32.2%, 36.2 to 53.4%, respectively, while the
frequency of
Rht 8
remains constant over time. Before 1990,
Rht-B1b
was only presented in
Zone II with frequency of 15.2%,
Rht-D1b
was not presented in Zone III, and its frequency
has increased significantly in all four zones. It is also interesting to observe that frequency of
Rht 8
has reduced in Zone III and V, but significantly increased from 20.0 to 48.0% in Zone I.
This is agreement with breeding experience in China since both
Rht-B1b
and
Rht-D1b
has
strong effect on reducing plant height in comparison with
Rht 8
(Zhuang, 2003). Our study
indicated that plant height has reduced from ca 110 to 80 cm in Beijing, from ca 110 to 75-85
in the Provinces of Hebei, Henan, Shandong, and Shaanxi, from ca 120 to 90 cm in Jiangsu
and Sichuan Provinces, respectively.
Based on pedigree analysis,
Rht-B1b
in Chinese wheat is derived from two sources, viz..,
Norin 10 and the Italian introduction St2422/464. The identity of
Rht-B1b
in these two
sources still needs to be confirmed. Suwon 86 carrying both
Rht-B1b
and
Rht-D1b
, and
Chinese cultivars, Huixianhong and Yaobaomai, are the primary sources of
Rht-D1b
in
Chinese wheats. It is likely that in Youbaomai derives from an unknown introduction. Italian
instructions such as Funo, Abbondanza, Lovrin 10 and Chinese landraces are the major
sources of
Rht 8
.
Table 7. Frequency (%) of
Rht-B1b
,
Rht-D1b
and
Rht8
in varieties released before and
after 1990
Gene Zone I Zone II Zone III Zone V Total
Rht-B1b
0
a
/32.0
b
15.2/32.5 0/60.0 0/13.0 8.6/32.2
Rht-D1b
20.0/40.0 51.5/63.9 0/26.7 20.0/47.8 36.2/53.4
Rht 8
20.0/48.0 39.4/53.0 60.0/20.0 60.0/43.5 41.4/47.3
a
and
b
are percentage of various genes in varieties released before and after 1990, respectively.
Table 8. Distribution of 1B/1R translocation in Chinese wheat cultivars among
difference regions
Zone I II III V Total
No. of cultivars tested 3
a
/22
b
18/80 9/10 5/15 35/127
No. of cultivars with 1B/1R translocation 0/13 0/33 0/2 0/3 0/51
Frequency of 1B/1R translocation (%) 0/59.1 0/41.3 0/20.0 0/20.0 0/40.2
a
and
b
are number (percentage) of 1B/1R translocation in cultivars released before and after 1980,
respectively.
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