International Journal of Horticulture, 2017, Vol.7, No.22, 180-204
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Chromosomal mutations:
Mutation due to changes in chromosomal structure are called as chromosomal
mutations. It is used for transferring characters from other species and genera and diploidization of polyploids.
Somatic mutations:
Mutations due to changes in buds and somatic tissues used in propagation are called as
somatic mutations.
Cytoplasmic mutations:
Mutation due to changes in cytoplasmic characters are called as cytoplasmic mutation.
Genome mutations:
Mutations due to alteration of chromosome number (polyploidy, haploidy, aneuploidy) are
called genome mutations.
Spontaneous mutations:
Mutations occurring in natural population at a low rate automatically are called
spontaneous mutations. The frequency of spontaneous mutation is very low.
.
Spontaneous mutations are caused
by atomic rays and particles, electric currents, hybridity, polyploidy, aging factors, nutritional deficiencies, high
temperature, natural mutagens, injuries, disease and insect attacks etc. Spontaneous mutations have been reported
in
Oenothera, Godetia, Paeonia, Bougainvillea, Dahlia,
Rose etc.
Induced mutations:
Artificial mutations caused by a treatment with certain physical or chemical agents are
called as induced mutations.
Mutagens:
The physical or chemical agents causing mutations artificially are called mutagens. Mutation is
caused by physical and chemical mutagens. Physical mutagens are alpha rays, beta rays, X-rays, gamma rays,
neutrons and UV rays. Chemical mutagens are 5-bromouracil, 5-chlorouracil, mustard gas, sulphur mustard,
nitrogen mustard,ethyl methane sulphonate (ems), methyl methane sulphonate (mms), ethylene oxide, ethylene
imine,
azasorine, mitomycin c and streptonigrin etc. are used.
Mutagenesis:
It is the treatment of a biological material with a mutagen to induce mutations.
Mutation breeding:
It involves the mutation inductions and isolation of mutants for crop improvement.
Mutation in cross pollinated crops:
Cross pollinated crops are heterozygous and open pollinated and thus
detection of mutant is difficult. The method of handling the
M
2
and M
3
generations is same as self-pollinated
crops except selfing is done to check out crossing.
Mutation in asexual propagated crops:
These plants are heterozygous and so mutation from dominant to
recessive are easily detected and chromosomal mutation is common. The mutated plant becomes a chimera ecto-,
meso- and endo-chimera depending upon variation in epidermal tissues. The chimeric structure is the most
important factor in mutation breeding and so, less differentiated primordial are treated. Chimeric formation is
avoided by irradiating the youngest possible stage of bud. Suitable propagation methods like budding, stooling
are selected and the shoots of mericlinal chimera are also pruned.
Mutagenic treatments:
Physical mutagens like X-rays and gamma rays are preferred over chimeric mutagens
for better penetration and more chromosomal rearrangements.
Applications of mutation breeding includes
elimination of defective characters, higher yield through production
of superior cultivars, increase in variability, exploitation of mutated genes in heterosis, induction of male sterility
for use in hybrid seed production, production of sports or chimeras, induction of polyploids, diploidization of
polyploids, breaking of undesirable linkage, production of haploids.
Mutation breeding in plants:
Ornamental plants are ideal for application of mutations induction techniques
because many economically important traits like flower characteristics or growth habit are easily monitored after
mutagenic treatment. Most of ornamental species are heterozygous and propagated vegetatively which allows the
detection, selection and conservation of mutants in the M
1
generation; for example the origin of moss rose was a
