Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 165

mutation in both the alleles simultaneously is product of individual probabilities
of mutation and therefore, is extremely low. It is not possible to identify a reces-
sive mutation in M l stage; only dominant mutations can be identified. However,
due to occurrence of this expression is also sectorial, or may not be observable. A
breeder should attempt to screen mutations in M 2 generation, where the mutation
will segregate generating homozygotes for recessive or dominant alleles. The M l
plants should not be allowed to cross pollinate, because recombination will lead to
generation of new variability that will be difficult to separate from effects of muta-
tion (Roychowdhury 2011 ).
M 1 GenerationMaintenance
The treated seeds need to be handled with care. The seeds treated, with physical mu-
tagens can be stored before sowing. However, the seeds treated with chemical mu-
tagens should be washed thoroughly and be planted as soon as possible. If the seeds
cannot be plowed soon for various reasons such as weather or long transport, the
seeds should be dried in shade to a moisture content of about 13 % as soon as pos-
sible without causing any damage to the seeds. Soil conditions can have consider-
able influence on survival and growth of the M 1 . Nitrogen fertility of the soil should
be normal or slightly sub-normal to limit excessive vegetative growth. However,
other nutrients should be at optimum levels. The time of sowing should be slightly
later (2 or 3 weeks) than normal so as to reduce excessive vegetative growth. The
purpose of isolation of the M 1 is to avoid the introduction of genetic variability
other than that induced with the mutagenic treatment. Most mutagen treatments will
induce some pollen sterility increasing the amount of out crossing. M 1 population
should be planted 75-100 m apart from the parental or other genotypes of the same
crop species. If the crop is frequently insect pollinated, as with some legumes, the
required isolation may he greater and other means of isolation may be required.
Mutagen treated M 1 materials normally flower over a longer period than the control
materials. A slightly later sowing of M 1 material than the parental genotype will
permit separation of flowering times. When mutation breeding is practiced with a
limited number of M 1 types of a crop, it may be possible to grow M 1 treatments side
by side since F 1 hybrids may not occur or could easily be recognized by means of
marker traits such as flower, plant or spike colour. Mechanically isolation can be
achieved by bagging spikes in cereals using plastic or paper bags to prevent cross-
pollination and bird damage. M 1 generation can also be grown in a green house or
in the screen enclosures to achieve control over pollination by insects. Methods of
harvesting the M 1 populations will depend on the pattern of ontogenetic develop-
ment in the species, the methods of screening and the generation to be screened
for mutants. In case the seed yield from each branch is reasonably adequate, it is
suggested that each primary branch may be harvested separately. In case of cereals,
individual plant or spike can be harvested (Roychowdhury 2011 ; Roychowdhury
et al. 2011c , 2012 ).