Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 173

jor component of today research on molecular genetics and genomics. Specific se-
quences like transposons can be randomly inserted into a genotype through genetic
crossing, which when inserted within a gene, blocks its transcription, thereby caus-
ing loss of phenotype. The gene then can be identified by using the sequences of
transposon, a technique known as transposon tagging. A variety of other techniques
including RNA interference, gene trap, activation tagging and virus induced gene
silencing are based on the same principle of knocking out the phenotype through
inactivation either at DNA or RNA level to establish gene-phenotype relationship.
Discussion of such techniques is beyond the scope of discussion and will primarily
concentrate on the application of mutation induction for crop improvement purpose
only. International Atomic Energy Association (IAEA) has categorized its mutant
variety database of 3,220 (as on December 2008) varieties according to six breeding
methods namely:
1. Development of commercial cultivars through direct mutagenesis of genotype
(2,738 genotypes),
2. Development of variety using mutant line as one of the parents in crossing pro-
gramme (375 genotypes),
3. Development of variety through crossing of two mutants (28 genotypes),
4. Development of hybrid variety using mutant genotype as one parent (26
genotypes),
5. Development of variety through mutation of segregating generation (53
genotypes).
The first category includes 273R varieties and involves all the released variety
through mutagenesis of seed, vegetative propagules and cultured tissues. Among
the other classes, more success have resulted from using mutant line as parent in
breeding programme as well as mutagenesis of breeding nurseries. Country wise,
China ranks first in development of new varieties through induced mutagenesis
and is well ahead of other countries in numbers. Many of these mutant varieties
have been developed in rice, the principal food crop of India, China and other some
Asian countries, through induced mutagenesis of seed as well as anther culture.
Major commercial mutant varieties of China have been developed in rice, wheat,
maize, Capsicum , cotton, tomato and groundnut. India ranks second after China,
developing about 240 mutant varieties of different crops through direct mutagenesis
of which major varieties have been developed for rice, wheat, barley, pearl millet,
jute, groundnut, soybean, chickpea, mung bean, cowpea, black gram, sugarcane,
chrysanthemum, rose and Dahlia . Additionally, about 50 varieties have been devel-
oped through using mutant lines in breeding programme. Indian mutation breeding
programme became successful in the sixties with development of mutant varieties
in wheat and rice and thereafter flourished in the next decades where new mutants
have been developed in about 60 agricultural and horticultural crops. The major
methods of mutation breeding in India involve irradiation with gamma rays, X-rays
and treatment with EMS. Major Indian Institutes involved in mutation breeding are
Bhabha Atomic Research Centre (BARC) in Mumbai, Indian Agricultural Research