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In the past few years
studies on the composition of HMW glutenin subunits of the Chinese
wheats and its relation to bread baking quality have been made by
several institutes, among them. Hebei Agric. University's work
deserves mention. The HMW glutenin subunits composition of 5071
common wheats (comprising 922 landraces, 2292 breeding lines and 1818
exogenous materials) were determined by SDS-PAGE and the
corresponding Zeleny sedimentation value and other related quality
indices were scored in a period of three years. They found that: (1)
The main subunits variations in the three loci of homeologous
chromosome 1 were: for Glu-A1 --- Null,1,2*; for Glu-B1
--- 7+8, 7+9, 6+8, 7, 20, 21, 22, 17+18, 14+15, 13+16, 13+19; for
Glu-D1 --- 2+12, 3+12, 4+12, 5+10. Some rare or new allelic
variations such as 2+10, 2.2+12, 6+9, etc. were also found. (2) The
main subunits in the three loci were listed in Table
3. The
frequencies of good quality subunit 5+10 in Chinese landraces and
improved varieties or lines were 3.7% and 15.7%, respectively. (3)
The main subunit combinations in the three loci for landrces were
Null, 7+8, 2+12, with a frequency of 74.8%; for improved vareities
were Null, 7+8, 2+12 (18.8%); Null, 7+9, 2+12 (16.7%); and for
foreign varieties were Null, 7+9, 5+10 (14.0%); Null, 7+9, 4+12
(10.5%); Null, 7+8, 5+10 (7.5%), respectively. (4) Multiple
regression analysis between glutenin subunits determined and their
corresponding 12 quality indices revealed that 5+10 gave the best
performance, and 2* ranked next. As judged from the 3 main bread
baking quality indices, namely sedimentation value, valorimeter value
and bread score, in a subset data from 126 varieties, the magnitute
of effect for each subunit in Glu-A1 was in the order of 2*
>l>Null; in Glu-D1 was 5+10>4+12>2+12; and in
Glu-B1 was 7=20>7+8>22>7+9. (5) A new Glu-1
quality score system was suggested as follows (Mao 1992, to be
published):
|
|
Score
|
Glu-A1
|
Glu-B1
|
Glu-D1
|
|
|
|
5
|
|
|
5+10
|
|
|
|
4
|
2*
|
|
|
|
|
|
3
|
|
7,20
|
|
|
|
|
2
|
1
|
7+8
|
4+12
|
|
|
|
1
|
Null
|
22
|
2+12
|
|
|
|
0
|
|
7+9
|
|
|
Wheat breeders in China have confronted for many years two problems,
namely, poor or not so diversified genetic backgrounds and lack of
superior parental materials. Henceforth they are getting more and
more interests in population improvement and germplasm
development.
Population improvement
There has been a small nation-wide network in this area aiming at
the improvement for either single breeding objective or multiple,
comprehensive breeding objectives by using Taigu dominant male
sterile gene-, Ms2. In addition to the recurrent selections
for scab resistance mentioned before, many breeders have paid
considerable attention to the improvement of salt tolerance and yield
performance as well. Shanxi AAS in a study of half-sib selection vs
phenotypic selection for 4 cycles indicated that the former gave a
higher genetic gain than the latter (Table
4) (Wang et al
1991). Recently Institute of Crop Breeding and Cultivation, CAAS, has
been successful in developing a genetic material called Aibai (dwarf
dominant male sterile) which linked Ms2 with Rht10
tightly on the sams chromosome 4DS with 0.18 crossing-over unit.
This provides a genetic marker for male sterility. The progeny of
Aibai always segregates into one tall, male fertile: one dwarf, male
sterile and the plant stature of them is quite different. Such a
material will facilitate the use of Ms2 gene because it can
shift the time of recognition for male steriles from the normal to as
early as shooting stage which will save much time and labor in
roguing off the male fertiles. The dwarf male steriles serve readily
as good reciever of any pollens available and can avoid the defect
that ordinary Ms2 carriers used to recieve pollens more
frequently from the plants taller than themselves and make the
reduction of plant stature very difficult.
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