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Life Science Research and Sustainable Development ISBN: 978-98-84663-33-9

simpler or quicker than the standard backcross procedure if the characteristic is available in
avariety. This is more so because the desirable mutations are often associated with undesirable
side effects due to other mutations, chromosomal aberrations, sterility, etc. As a result, one or few
backcrosses with the parent variety may be necessary to bring the desirable mutant allele in an
acceptable genetic background.
Mutagenesis has been successfully used to improve various quantitative characters, including
yield. Several varieties have been developed by this technique. However, there is no critical
comparison available to show that the same improvement would not have been broughtabout by
the conventional hybridization programmes. F1 hybrids from intervarietal crosses may be treated
with mutagens in order to increase genetic variability by inducing mutations and by facilitating
recombination among linked genes. But this method has not been widely used.
In developing countries, mutation breeding is widely used, but in Europe it is mainly
confined to clonal and ornamental crops. For example, mutagenesis is the principal source of
genetic variation in chrysanthemum and banana breeding programmes. This is because most
breeders believe that the characteristics of mutation breeding, viz.,
a. The need for large (105 to 106) M2 populations,
b. Associated detrimental effects of mutations, and
c. The existence in germplasm of the so called 'novel' mutant alleles,
mitigate against the incorporation of this technique into conventional breeding programmes.
In mutagenesis, the yields of new varieties released over a period of years (developed
through conventional breeding approaches) show anaverage increase of -1 % in case the major
field crops. Development of a new variety using mutagenesis would require about 7 years;
therefore, the mutant variety must show an increase of -7% in yield over the parent variety. An
increase of this magnitude is unlikely from modificationof a single gene or trait unless it is critical
for plant performance, e.g., disease or insect resistance.

Limitations of mutation breeding
Apart from all this desirable genetic recombination initiated in mutation breeding, there has
certain limitations of the technique; these limitations are summarized as under.
1. The frequency of desirable mutations is very low, about 0.1 per cent of the total mutations.
Therefore, large M2 and subsequent populations have to be grown and carefully studied.
This involves considerable time, labour and other resources.
2. The breeder has to screen large populations to select desirable mutations. Therefore, efficient,
quick and inexpensive selection techniques are required to screen large populations.
3. Mutation breeding is more easily applied to such characters where quick screening
techniques are available, e.g., disease resistance. But in the case of characters where elaborate
tests are required, e.g., quality characteristics, mutation breeding is virtually impractical. For
this reason, mutation breeding has been more successful with those characteristics where the
mutant phenotype is distinct and easily detectable.
4. Desirable mutations are commonly associated with undesirable side effects due to other
mutations, chromosomal aberrations, etc. The mutant lines often have to be back crossed to
the respective parent varieties to remove these defects. This increases the time requirement
of mutation breeding programmes and involves additional labour, time and expenditure.
5. Often mutations produce pleiotropic effects. The chief procedure for reducing or eliminating
pleiotropic effects is to transfer the gene into different genetic backgrounds by hybridizing

https://jesjalna.org/Zoology-Publications/index.html 13 Department of Zoology, J. E. S. College, Jalna