Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 151

Table 4.1 Three important plant breeding strategies
Breeding
Methods

Source of genetic
variation

Transmission,
expression and
inheritance

Nature of gene
action

Breeding
generations

Mutation
breeding

New alleles
artificially
and randomly
created from
endogenous
genes

Induced mutations
subject to diplon-
tic and haplontic
selection

Mostly recessive
alleles

About 2-3
generations

Recombinant
breeding

Recombination
of gene alleles
from parental
varieties

No selective
transmission;
co-segregation
of closely linked
alleles

Dominant,
recessive
alleles, and
QTLs

About 10
generations

Transgenic
breeding

Insertion of new
genes or
modification
of endogenous
genes

Expression of trans-
genes subject to
position effect or
silencing

Mostly domi-
nant alleles

About 3
generations

QTL-Quantitative trait loci

leles that do not persist in germplasm pools and the induction of new gene alleles
for a commercial variety such that new varieties carrying desired mutation alleles
can be directly used as a commercial variety. Also, the limited genetic changes
of any single plant of a mutated population and the often recessive nature enable
breeders to develop a new variety in a short breeding cycle. The limitation being its
limited power in generating the dominant alleles which might be desired; its less
effectiveness than cross breeding for a trait needs for a combination of multiple
alleles, such as tolerance to abiotic stresses. The low mutation frequency requires
growing and screening a large population for selection of desired mutants at a rea-
sonable confidence. This becomes very expensive for traits that have to be evalu-
ated through laborious phenotypic analysis (Roychowdhury 2011 ; Roychowdhury
and Tah 2011 ).
The knowledge of the extent to which the desirable characters with economic
values are heritable is a prerequisite for any crop improvement programme (Roy-
chowdhury and Tah 2011b ; Roychowdhury et al. 2011a ). Breeders have continually
retained their interest in the grouping of the germplasm and the pedigree of selected
cultivars since the information might be particularly helpful in effective breeding
strategy determination (Ali et al. 2011 ). For this purpose, inducible mutation, using
chemical or physical mutagens, is a suitable source of producing variation through
mutation breeding procedure (Domingo et al. 2007 ; Roychowdhury and Tah 2011a )
which can produce several improved mutant varieties with high demanding eco-
nomic value (Din et al. 2004 ). From implicational point of view, it is quite possible
to induce gene-mutation artificially with the help of some potent chemical muta-
gens to create any new variation in crops.