| Results and Discussion The range, mean, phenotypic coefficient of variation, genotypic coefficient of variation, per cent heritability in broad sense and expected genetic advance as per cent of mean of F5 progenies following three selections method in a three-way wheat cross for six metric traits are presented in Table 1. The range of distribution in SSD progenies was, in general, higher than the progenies developed through pedigree selection for almost all the traits, while bulk selection showed lower range of distribution for almost all the traits. The mean values of F5 progenies produced by pedigree selection and SSD methods were significantly better in comparison to the F5 progenies produced by bulk method. However, no significant differences existed between the mean values of F5 progenies developed through pedigree selection and SSD methods. Hence these two procedures sppeared to be equally effective methods of handling the segregating generations of this wheat cross. It can also be suggested that SSD method may be used as an alternative to pedigree selection when it is not feasible for a breeder to handle large populations owing to the limited resources available. Several previous workers (KNOTT & KUMAR 1975, TEE & QUALSET 1975, WRIGHT & THOMAS 1976) also observed that the SSD procedure was often superior or was at least equally efficient to pedigree and bulk methods of selection in wheat. However, SNEEP (1977) pointed out that SSD method is affected by genetic drift and as a consequence many genotypes are lost. As regards the phenotypic and genotypic coefficients of variation, the pedigree selection gave slighly high values than SSD method. The lowest values of phenotypic and genotypic coefficients of variation were recorded for bulk selection. This might be due to strong intergenotypic competition within the population. As there were large differences between phenotypic and genotypic coefficients of variation for tiller number, grain number and grain yield per plant, so these three characters were more influenced by the environment. It can be seen from Table 1 that the heritability values for plant height and days to heading were relatively higher. On the other hand, these values for grain yield and tillers per plant were smaller indicating that these two characters were more influenced by environment. The values of heritability and genetic advance (as per cent of mean) calculated in SSD procedure were higher than those in pedigree selection for all the traits except for grain yield where slightly higher genetic advance was obtained in pedigree selection than in SSD procedure. Bulk selection showed lower values of heritability and expected genetic advance for almost all the traits. In majority of cases, there was association between high heritability and higher genetic advance but in few cases like days to heading and plant height, there was no association between high heritability and high genetic advance. This was due to high or low amount of phenotypic standard deviation. Hence, on the basis of results of the present study, it can be suggested that both the pedigree selection and single-seed-descent method are effective in handling the segregating generations of this wheat cross. References JOHNSON, H.W., H.F. ROBINSON and R.E. COMSTOCK. 1955. Agron J., 47: 314-318. KNOTT, D.R. and J. KUMAR. 1975. Crop Sci., 15: 295-299. SNEEP, J. 1977. Euphytica, 26: 27-30. TEE, T.S. and C.O. QUALSET. 1975. Euphytica, 24: 393-405. WRIGHT, G.M. and G.A. THOMAS. 1976. New Zealand Wheat Rev. 13: 46-49. |
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