Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 166

ManagementofM 2 Population
Sowing of M 2 generation depends upon the method of harvesting of M 1 generation.
Two methods of sowing M 2 generation can be followed. Firstly, M 1 plant to row,
where all seeds produced from a single plant are grown in row. The success of its
use will depend, to a large extent, on how well the branching has been controlled
because it tends to dilute the yield of M 2 mutants. Second method is of M 1 spike
or branch to row, which offers the greatest precision with regard to the origin of a
mutant when the material treated is genetically homogeneous as regards the non-
mutant allele and when outcrossing is controlled.
Mainly three types of screening/selection techniques can be employed for the
selection of mutants in M 2 and subsequent generation viz. visual, mechanical/physi-
cal and other methods (Roychowdhury et al. 2012 ). Visual screening is the most
effective and efficient method for identifying mutant phenotypes. Visual selection
often is the prime basis for selecting for disease resistance, earliness, plant height,
colour changes, ion-shattering, adaptation to soil, climate, growing period etc.
Mechanical or physical selection can be used very efficiently for seed size, shape,
weight, density, etc., using appropriate sieving machinery. In other category, chemi-
cal, biochemical, physiological, physio-chemical like screening procedures may be
needed for selecting certain types of mutants. Low alkaloid content mutants can he
selected using colorimetric tests. Colorimetric, chromatographic or electrophoresis
techniques may be used to select isolate protein variants.
PropagationandEvaluationofMutants
When a mutant appears promising, seed multiplication for extensive field testing is
necessary. The mutant, the mother strain and other varieties with which it is intend-
ed to compare, should produce comparable seed properties for the basic trial seed.
Mutants of vegetatively propagated plants can be multiplied by the usual method
for the crop in question such as cuttings, grafting, budding, layering, bulbs, tubers
etc. The methods of testing mutants in comparative trials are essentially the same
as for any other newly developed strain. It is intended to find whether the mu-
tant promises to become a variety surpassing the value of the mother strain and of
the best available variety (a) in at least one property or (b) by a better combina-
tion of different characters; mutants of growth rhythm, growth habit, structure
and yield components should be tested in a wide range of environments such as
locations, soil, water and nutrient conditions, seed rates, planting, distances, sowing
dates etc.