Mutants 35 and 115-Nayab are early maturing and produced amber coloured grain whereas, mother cultivar Nayab is red grained. This means that loci determining red grain colour and earliness on 3D chromosome were simultaneously mutated on both the chromosomes (SAWHNEY et al. 1971). Simultaneous mutation of two copies of genes is expected to be a rare event since two hit events are unexpected with gamma rays and fast neutrons. Mutants which are simultaneously changed for grain colour and maturity, could be due to pleiotropic effects of a single mutation although such effects are unlikely. The radiation has also removed a major defect such as apical sterility of mother cultivar Nayab. The isolation of amber seeded mutant with early maturity is of great interest because of plant type now produced could economically be used to enlarge the areas of cultivation.

Response to selection for quantitative characters is directly proportional to the function of its heritability and its genotypic variance. Heritability enables a plant breeder to recognise the genetic differences among strains and genotypic variance indicates the potential for the improvement of a population. Keeping in view these points the estimates of genotypic variance, heritability and genetic gain expected from selection were obtained separately for each quantitative character and are shown in Table 3.

All the metrical traits have displayed considerable increase in genotypic variance, heritability and genetic gain expected from selection. All the mutant strains exhibited highest genotypic variance for yield. This could be due to large number of high yielding mutants (Table 2). Similar conclusions have been drawn by LARIK (1979b) and LARIK et al. (1980a). They noticed that M₂ families derived from six hexaploid wheat cultivars after irradiation treatments showed an increase of mean values and genotypic variance. The heritability (hw) and genetic gain expected from selection (Gs) displayed almost the same tendency as the genotypic variance (sigma_p²). This indicates that greater gain from selection for yield are anticipated in the mutant stains derived from different cultivars. While studying the magnitude of genotypic variance and heritability estimates for yield among randomly selected EMS-treated lines of barley cultivars with diverse yields and adaptation patterns at individual sites in M₄ generation, GHAFOOR ARAIN (1973) reached the similar conclusion.

It is therefore imperative from breeders point of view to select the yield components traits showing high heritability values among the mutated material. Thus, improvement of bread wheat, like any other crop, essentially depends on the induction and fixation of positive variation in a given agricultural environment. Mutation breeding is only one of the current methods of wheat improvement and can produce desirable results when combined with selection or with other methods of manipulating genetic variation (BROCK 1977).

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