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In regard to breeding
methodology, intervarietal hybridization in the usual way
supplemented by induced mutation, dihaploid breeding and wide cross.
During the past 10 years, supporting researches such as testing for
disease resistance, stress tolerance and quality, evaluation and
development of parental stocks, population improvement and genetic
studies on economically important traits have been allocated with
appropriate resources. Fig.1
illustrates the conventional procedures of wheat breeding adopted in
China.
The Chinese wheat breeding program is characterized as: being small
in scale but intensive (one breeding unit used to grow approximately
a F2 population of less than 200 thousand plants and 6000
F3 and later generation progeny lines all togather
annually before initial yield trial); pedigree method adopted with
small spacing; emphasizing more on field observation and early
generation selection; and testing the selected varieties in the
fanner's field as early as possible for approval in production. So it
takes 8-10 generations from crossing to the time when a variety has
finished the regional test. Hereby recent advance in the following
areas is briefly described.
Breeding for disease resistance
This is the main theme in wheat breeding in which three important
diseases, i. e. stripe rust, powdery mildew and scab, are
emphasized.
Stripe rust and powdery mildew
Stripe rust is a nation-wide disease except in the northeastern
spring wheat region. From the beginning of 1950's China began to
release in succession its own cultivars resistant or tolerant to
stripe rust. For the nation as a whole, stripe rust has essentially
been under control in the last 20 and more years except in the middle
part of Shaanxi, mid- southern Gangsu and the southwestern provinces
where physiological races used to variate from time to time due to
special ecological conditions prevailing in these areas. Recently
powdery mildew has become increasingly important as a result from the
inreased application of nitrogenous fertilizers and the expansion of
irrigated wheat lands. As there was pratically no breeding work in
the past on powdery mildew, nearly all the varieties released for
commercial production are susceptible to the disease with some
exceptions from Guizhou province. When the 1BL/1RS derivatives such
as Lovrin 10, Predgornaia 2, Kavkaz, etc. were first introduced from
Romania in the early 1970's, they showed quite a good resistance to
the prevailing races of stripe rust, leaf rust and powdery mildew as
they carried Yr9, Lr26 and Pm8 resistance genes
and matured normally under various heat-stressed environments as
well. So all the breeders across the country gave special preference
to them and used them extensively in breeding programs as a source of
multiple resistance. Consequently, an overwhelming majority of
varieties recently released for production in various winter and
spring wheat regions were new derivatives from the above-mentioned
old 1BL/1RS translocation lines. This would inevitably result in a
monotonous spectrum of disease resistance which is highly vulnerable
to the attack of new fungal races. It is now reported everywhere that
a lot of cultivars carrying 1BL/1RS resistance genes have lost
their-resistance to the diseases. This has become a great threat to
wheat production and a big challenge to the breeders too. Therefore
wheat breeders and pathologists are anxious in looking for
second-line sources of resistance which can be readily utilized in
breeding programs. A disease testing group of the Beijing
Agricultural University after extentive testings and genetic analyses
has provided a recommendation list of new resistance genes and their
carriers togather with some information on their mode of inheritance.
Table1
shows the main sources of resistance to stripe rust and powdery
mildew in the comming years, at least in North China.
Within the list Luqiyou and C39 give the best performance because the
former is nearly immune to stripe rust in F1 and the latter carries
three genes for powdery mildew resistance. Currently these new genes
of resistance are being incorporated into the recommended varieties
(Yang et al 1992, to be published). Meanwhile, Jiangsu Academy of
Agricultural Sciences (hereinafter abbreviated as AAS) has identified
CI12633, CI12632 and TP114 which carry Pm2 and Pm6 are
effective in the control of powdery mildew in Nanjing area (Yiao et
al 1990). Durum wheat and triticale breeders from the Institute of
Crop Breeding and Cultivation, CAAS, indicate that certain durum
wheats and many triticales are also good sources of resistance to
powdery mildew, among them 6R of rye deserves attention (Zeng and Xin
respectively, personal communications). It is reported that a common
wheat line named Yangxiaohe1-1,developed by Guizhou Agricultural
College from a cross involving false wild oat, common wheat and rye,
shows good resistance to powdery mildew in Sichuan and Guizhou
provinces and might carry a new gene(s) (Li and Huang 1991).
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