| Results and Discussion The data on various genetic parameters of induced variabliity are presented in Table 1. The range of variability for 1000-grain weight, specific gravity, grain hardness, and yield/plant were 24.560-49.60, 1.063-1.643, 9.420-14.820 and 7.342-22.275 respectively. When these values are compared with parental means for each character it is quite clear that considerable variability has been generated by Co60 gamma-rays at two moisture levels for all the characters. A precise idea of variability can be had by C.D. values at 5 per-cent level. The genotypic coefficient of variability (GCV) ranged from 0.836 to 17.776 for sepecific gravity and yield/palnt respectively. In all the cases phenotypic coefficient of variability was higher than the corresponding GCV values. Thus high genetic coefficient of variability induced through gamma-rays for grain hardness, 1000-grain weight and grain yield provides wide basis for genetic improvement in wheat. Since, the efficiency of selection would depend upon the magnitude of variability that is heritable and caused by genetic factors the higher values, therefore, of heritability accompanied by high genetic advance for the characters studied should be quite valuable. In our study, heritability estimates were found to be high for grain hardness (73.592) and 1000-grain weight (71.174), moderate for grain yield (43.180) and low for specific gravity of grains (16.666). Genetic advance at 5 per-cent selection intensity ranged from 22.178 to 2.343 for 1000-grain weight and specific gravity of grains respectively. Thus high heritability accompanied by high values of genetic advance was achieved for grain hardness and 1000-grain weight. Genetic improvements, therefore, can be achieved with care for these characters. ANAND et al. (1970) also found high heritability and high genetic advance for grain hardness in a collection of 80 different strains of wheat from diverse sources. Observations of GANDHI et al. (1964) on 90 wheat varieties were also similar for 1000-grain weight and grain yield. Negative association (Table 2) between grain hardness and specific gravity reveals that combined selection for these two physical characters can not be operated because they inherit independently. Similarly grain yield does not seem to have any bearing with these two grain characters as association of grain yield with these characters is negative. On the basis of our findings we conclude that hard wheats possess low grain yield. Association of grain hardness and specific gravity of grains with 1000-grain weight was observed to be non-significant as has also been reported by ANAND et al. (1970). Significant positive association between 1000-grain weight and yield/plant at genotypic levels observed here is in agreement with the findings of SIKKA and JAIN (1958) and GANDHI et al. (1964), who emphasized the importance of test weight in grain yield. Non significant association between these characters at phenotypic levels indicates that association is influenced by environmental conditions. Coheritability values for different pairs of characters are presented in Table 3. Coheritability values of 1000-grain weight with specific gravity and grain yield were positive whereas coheritability of grain yield with specific gravity and hardness; specific gravity with grain hardness; and grain hardness with 1000-grain weight were negative. Coheritability value of 1000-grain weight with grain yield was highest whereas it was moderate in case of other pair of characters. Negative coheritability for certain character pairs indicate that they are not inherited jointly and thus correlated response should not be expected in selection experiments for one character. In contrast, high and positive joint inheritance between 1000-grain weight and grain yield suggests that significant improvements in grain yield can be obtained by practicing selection for 1000-grain weight. (Received June 1, 1974) |
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