| In the present material, the mean values for different traits in treated
material did not show any change/shift compared to their control values
except in few cases in M1 generation. On the other hand, the
coefficients of variations were increased in treated populations compared
to their controls in almost all the cases (Table 1).
Also, there was increase in variance with the increase in radiation dose,
however, the relationship between variance and dose was not linear. The range for different traits has been given in Table 2. This table clearly supports the increase in variance, as the range was also enlarged in almost all the doses. Thus, by using mutagenic treatments, we can increase variability. However, ultimately the breeder will be interested in the variability which is in the desired direction. For example, reduced plant height will be desirable to overcome lodging problem particularly in varieties like WH-147. Similarly for other traits studied, the increase in mutation spectrum on positive side is desirable which is required for higher production. This type of variability particularly in M2 generation can be utilized for breeding better types. We have isolated a number of plants having desirable traits from M2 generation and will be tested for their purity in successive generations. Dwarf mutants isolated during this study particularly in variety WH-147 deserve special mention since some of them simultaneously had other desirable traits also like more number of tillers, high grain yield etc. Differential effectiveness of radiation dose and response of varieties in producing variability were observed in this study. The average coefficients of variation for different varieties pooled over doses for different traits has been given in Table 3. The results indicate that the maximum variance was observed for grain yield per plant followed by tillers per plant both in M1 and M2 generations. Though, there were differences in variatal response with regard to different traits, however, on overall basis variety WH-147 appeared to be the most radiosensitive followed by S 308 and HD 2009. Similarly, the coefficients of variation were pooled over varieties for different doses of different traits (Table 4). Here also, there were differences for different traits like the maximum variation for tillers, spikelets and grain yield was observed in 30 KR while 20 KR gave maximum variation for plant height. From overall picture, we can conclude that the maximum variability was generated in 30 KR treatment. In 40 KR, either it was constant or reduced. Further, it can be confirmed that there was increase in variation with the increase in dose, however, the increase in variance did not have linear relationship with the increase in dose. |
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