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The use of embryo rescue in wheat breeding was introduced primarily for the
production of interspecific and intergeneric crosses. Since one of the most common
reasons in interspecific and intergeneric crosses is embryo abortion, also in case of
successful fertilization in wide hybridization the seeds are weak, seed development
is not perfect or the seed produced are not viable. Embryo rescue has been very suc-
cessful in overcoming these main barriers in many plant species (Collins and
Grossser 1984 ).
Artificial media is an important factor in embryo rescue procedure. Young
embryos need a more complex media compared to a mature one. Generally, the
Murashige and Skoog (Murashige and Skoog 1962 ) and Gamborgs B-5 (Gamborg
et al. 1968 ) media are used. The concentration of the media depends upon the devel-
opmental stage of the embryo. Sometimes growth regulators, vitamins and amino
acids are used in the media (Reed 2005 ).
Embryo rescue is an important procedure utilized in the production of haploids
through elimination of chromosomes following wide hybridization. In wide hybrid-
ization when the fertilization occurs the pollen parents chromosomes are eliminated
afterwards by the seed parent. To obtain a viable haploid the embryo needs to be
rescued. The chromosomes of haploid can be doubled to obtain a double haploid
(Bridgen 1994 ). Embryo culture can also avoid dormancy problems if the dormancy
is due to seed coat, thus shorting the breeding cycle by rescuing the embryo. Sharma
and Gill ( 1983 ) reported a reduction of generation time by 40 days.
The success of development of an embryo depend on many factors; along with
other factors one of the most important factor is plant genotype, differences were
found among different cultivars (Collins and Grosser 1984 ). In addition to this, light
and temperature also effect the development of a reduced embryo.
8.7 Wide Hybridization
Genetic diversity of the wheat gene pool has been narrowed down in the last four
decades. One reason of this narrowing down is the result of selection of pure line,
high yielding and responsive to high input varieties. In ancient times and before the
spread of narrow based modern cultivars, there was a lot of genetic diversity in the
landraces grown by farmers; sometimes the crops planted by farmers were mixtures
of landraces: modern wheat breeders have emphasized pure-line cultivars, narrow-
ing the genetic diversity. Few types of diversity can be measured in the perspective
for breeding programs (Smale 1996 ).
During the Green Revolution, wheat lost a lot more genetic diversity as emphasis
was placed on pure lines with higher yields. The improved wheat varieties growing
in most of the farmers’ fields (in certain area/country) are somehow similar. Despite
the fact that these varieties are high yielding and are economically of great impor-
tance but mostly have the same mechanism of resistance to most of the wheat dis-
eases. Some disease breaks out or mutation in pest population may cause severe
stress resulting devastating crop failure, varieties having similar background will be
Q. Sohail et al.