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b. Mean performance: Data means and percent deviations of selected levels (H. M and L) from the control in the two mutant types (SS and GH) are given for different traits in Tables 3 and 4. The situation in mutant selected from DS mutagenic treatment is remarkable. The high level (H) of (SS) type showed a highly significant increase compared with the control for all traits studied. Regarding the grain yield and harvest index, both showed the highest improvement percent than the mother cultivar with values of 287.40 and 125.61%, respectively. This is mainly due to the presence of higher frequencies of positive mutants as a result of mutagenic effect. HUSSEIN & ABDALLA (1981) in field bean found that M2 plants selected for high yield showed a higher response to selection. The results of nonselected traits, i.e. number of spikes/plant, number of kernels/spike and 100-kernel weight, relatively showed some improvement, consequently. On this ground, it could be said that these increases may be attributed to genetic correlation or the micromutation effects in the positive direction. The remainder levels (M and L) of the same mutant type (SS) showed irregular deviations (positive or negative) concerning the parent variety. In general, these deviations were insignificant with regard to all traits except the number of spikes/plant in the medium level (M). Regarding the (GH) mutant type i.e. grain yield and harvest index, the higher selected level (H) showed a highly significant marked increase over the control in the two traits. The percent productivity were 72.71 and 63.58% respectively. 100-kernel weight showed indirect increase than the control, with a highly significant value (39.22%), while the remaining traits i.e. number of spikes/plant and number of kernels/spike failed to shift the population means significantly. KASSEM et al. (1976) reported that both chemical and physical mutagens failed to shift the population means of grain yield and number of kernels/spike. On the other hand, the yield and yield component traits in the lowest level (L) of (GH) mutant type did not even reach the level of the mother cultivar. Whereas, three out of five traits, in the medium level (M), showed insignificant increase over the control; the other two revealed a reduction. However it could be concluded that the response of yield and yield components to mutagenic treatment was more pronounce in positive (H) than in negative (L) direction, since selection intensity for higher traits could be attributed to the micromutations. KRULL & BORLAUG (1970) found that grain yield was improved at various levels through intensive selection. SIDDIQUIet al. (1981) obtained three wheat mutants that gave higher mean yield compared to the mother cultivar and one mutant with the lowest yielding genotype. HUSSEIN & ABDALLA (1981) in field bean experiments found that some induced mutants increased seed yield of more than 40%. |
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