| Results and Discussion The estimates of narrow sense heritability (percent) for four characters calculated through two methods in four wheat crosses are presented in Table 1. There were differences between the heritability values of three out of total four characters studied (except for 1000 grain weight) in all the four crosses when F2/F3 combination was used in the two methods of estimating heritability. In almost all cases showing differences in the heritability values, the standard unit method overestimated heritability as compared to the normal parent progeny regression method. But for 1000 grain weight the two methods gave almost similar estimates of heritability. However, the differences in the heritability values obtained through these two methods in F3/F4 combination were smaller as compared to those in F2/F3 combination. This might be due to the fact that in F3/F4 combination, the phenotypic variance of parents may be almost equal to the phenotypic variance of their progeny. For calculating genetic advance, the heritability values obtained from F2/F3 combination were only used. The values showing differences between expected and actual genetic gains for four characters in four wheat crosses are given in Table 2. These values under standard unit method were higher than those obtained through normal parent-progeny regression method, indicating again that the standard unit method overestimated heritability values for grain yield and its component traits in wheat and subsequently overestimated the expected genetic advance from selection. Hence, one should be careful while calculating heritability or expected genetic advance in early segregating generations and should use only standard procedure for calculating these genetic parameters. References FREY, K. J. & T. HORNER. 1957. Heritability in standard units. Agron. J. 49: 59-62. LUSH, J. L. 1940. Intra-sire correlations or Tegressions of off-spring on dam as a method of estimating heritability of characteristics. Proc. Amer. Soc. An. Prod: 293-301. SMITH, J.D. & M.L. KINMAN, 1965. The use of parent-offspring regression as an estimator of heritability. Crop Sci. 5: 595-596. |
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