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Germplasm development
Presently all the major breeding units in China pay much
attention to the development of superior parental stocks and regard
it as an indispensable part of the breeding program. They are trying
hard to develop germplasms with specifically valuable properties such
as integrating disease resistance, dwarfness, earliness and high
yield potential in combinations of any two or three of them, and also
with multiple resistance of diseases and other stresses. For
instance, Pangzhihua Municipal Agric. Res. Inst., Sichuan Province,
has developed some long-spiked materials with 30 and more cm long and
more than 30 spikelets; large-spiked and big-kerneled types with
20-28 cm long, 70-130 kernels per spike and 90-100 g per 1000 kernel
weight; etc. These are very attractive to the development of super
high- yielding varieities (Liu 1992, personal communication).
At the same time, various amphidiploids (including amphiploids),
alien addition, substitution and translocation lines and other
intermediate materials which are of value in genetic studies and
breeding programs were developed by wheat geneticists. The following
descriptions are cited mainly from a review by Li and Hao (1992) with
a few supplementary notes.
Besides the man-made triticales, 29 different amphidiploids or
amphiploids were developed from crossing wheats with their 13 wild
relatives including Aegilops caudata, Ae. comosa, Ae.
crassa, Ae. aucheri, Ae. ovata, Ae. speltoides, Ae. tauschii,
Ae. triuncialis, Ae. umbellulata, Ae. ventricosa, Agropyron
elongatum, Ag. intermedium, and Haynaldia
villosa.
A series of alien addition, substitution and translocation lines
were subsequently generated by either crossing some of the above
amphidiploids or amphiploids with wheats or crossing wheats directly
with the alien species followed by backcrossing. They are important
steps in introgressing valuable alien genes. For example, Hao and He
(1990) reported 14 alien addition lines each carrying an additional
pairs of chromosomes from EE or XX genomes of Ag.
intermedium by crossing octoploid wheat-wheatgrass
hybrid with wheat (He et al 1989). Liu et al (1988) produced five
addition/substitution lines each carrying one pair of V2, V3, V4
(addition)/V5 (substitution), V6 and V7 chromosomes, respectively,
from Haynaldia villosa. Ma et al (1990) obtaines 3 addition
lines of 1R, 4R and 5R through crossing octaploid triticale with
wheat. Hu et al (1989) and Tao and Hu (1990) got 1B/1R, 1D/1R, 4D/4R,
and 6D/6R substitution lines by crossing hexaploid triticale with
wheat followed by anther culture and subsequent chromosome doubling.
Li et al (1986) and Mu et al (1986) were successful in developing
seven substitution lines with blue-grained marker gene transferred
from 4Ag to 2D, 3A, 3D, 4D, 5A, 6A, and 7A, respectively, by crossing
Elytrigia (Agropyron) elongata with wheat and
backcrossing to wheat followed by subsequent gamma-ray and fast
neutron radiations. Most of these intermediate materials possess good
resistance to one or more of the following diseases such as stripe
rust, leaf rust, stem rust, powdery mildew, and barley yellow dwarf
virus. Some of them are being used in breeding programs. For
instance, Xin et al (1991) in cooperation with the scientists of
CSIRO, Australia, have been successful in introgressing BYDV
resistance (which has not been found in the genus Triticum) to
several common wheat varieties from Zhong 4 [an amphiploid from
wheat-Thinopyron (Agropyron) intermedium
hybrid with 2n=56] and L1 (a French addition line from
Taft 46 which is also an octoploid wheat-Thinipyron intermedium
hybrid) through a combined efforts of ph gene-added
chromosome engineering, somaclonal variation through tissue culture
and conventional breeding.
In order to make alien gene transfer to wheat more effectively,
severa important "tool" materials for genetic study, gene location
and chromosome engineering have been established. For example, eight
monosomic series of common wheats, ie, Jinghong 1, Zhong 7902,
Fengkang 13, Abbondanza, Yangmai 1, Beijing 10, Gangmai 8 and Sumai 3
were produced by separate institutes. This would facilitate the use
of aneuploid technic in genetic studies under different ecological
conditions. Li et al (1986) created seven blue-grained monosomics
(2D, 3D, 4D, 5A, 6A and 7A) and 6 self-fertile nullisomics (2D, 3A,
3D, 4D, 5A and 6A) after introgressing the blue-grained gene
of Elytrigia elongata
to wheat. Xie et al (1991) furtherly developed 18 self-fertile
nullisomics except 2B, 4B and 7D from extensive screenings in large
population of the progenies of Abbondanza monosomic
series. Li et al (1990) also established a new procedure --
nullisomic backcrossing method -- for rapid production of alien
substitution lines. In the production of Triticum-Aegilops
amphidiploids, Xu and Dong (1992) observed that two accessions of
tetraploid wheats, namely T. persicum PS5 and
T. durum DR14, have the ability to produce unreduced gametes
when crossed with Aegilops species and this character was
transmitted to the amphiploids and to their hybrids with common
wheats. Fan et al (1990) were successful in incorporating Ms2,
kr and ph1b genes into a "triplex." All these "tool"
materials provide a sound and convenient basis for alien gene
transfer in wheats.
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