| The estimated components of genetic variation (Table
4) showed that both D and H1 were found to be highly significant. This
indicated the role of both additive and non-additive components in the control
of grain weight. The magnitude of the component H1 was slightly
higher than the D component under E1 and E2 whereas
reverse was true under late sown E3. Similarly the estimated
degree of dominance was more than unity except in E3, suggesting
over dominance and thus greater role of non-additive gene effects. The ratio
H2/4H1 indicated slight deviation from symmetrical
distribution of genes with positive and negative effects in E1
and E2, while in E3 symmetrical distribution was observed.
The ratio h2/H2 indicated that a large number of dominant
genes or gene groups were governing this character. The estimates of gca effects pointed out that none of the parents were the good general combiners for both grain number and grain weight. This is evidently so because of the fact that grain number and grain weight are negatively correlated. (Sikka & Jain, 1958; Gandhi et al. 1964; Paroda & Joshi, 1970). In fact, many plant breeders have believed that breaking of this negative correlation offers one of the most important means to bring about further spurt in the yield productivity of wheat. In the present study also, although substantial heterosis for both grain weight and grain number/ear was simultaneously obtained in certain cross combinations, none of the promising F1 hybrids combined the high grain weight of Sonalika and grain number of Kalyansona. In a situation, where additive and non-additive genetic variations are significant, the most suitable breeding procedure would be one which mops up the additive genetic variance and at the same time maintains certain degree of heterozygosity. Therefore, it is desirable to practice recurrent selection, by intermating the most desirable segregants, alternately with selection, as suggested by Dwivedi & Singh (1980). References DWIVEDI, S. L. and R. B. SINGH 1983. Population improvement in wheat. Indian J. Genet. 40: 585-592. GRAFIUS, J. E. 1959. Components of yield in oats: a geometrical interpretation. Agron. J. 48: 419-23. GRIFFING. B. 1956. Concept of general and specific combining abillty in relation to diallel crossing systems. Aust. J. Biol. Sci. 9: 463-493. HAYMAN, B. I. 1954. The theory and analysis of diallel crosses. Genetics. 39: 789-801. KNOTT, D. R. and B. TALUKDAR. 1971. Increasing seed weight in wheat and its effect on yield, yield components and quality. Crop Sci. 11: 280-83. KRONSTAD, W. E. and W. H. FOOTE. 1964. General and specific combining ability estimates in winter wheat. Triticum aestivum Vill; Host. Crop. Sci. 4: 616-619. Mc NEAL, F. H. 1960. Yield components in Lemhi x Thactcher wheat cross. Agron. J. 52: 348-49. MUTRY. B. R. 1965. Heteresis and combining ability in relation to genetic divergence in flue-cured tobacco. Indian J. Genet. 25: 45-56. PARODA, R. S. and A. B. JOSHI. 1970. Genetic architecture of yield and components of yield in wheat. Indian J. Genet. 30: 298-314. RANDHAWA. A. S. and K. S. GILL. 1978. Response to selection for the improvement of grain yield in a winter x spring cross of wheat. Crop lmprov. 5: 11-20. REHMAN. A. 1979. Heterosis and combining ability in wheat under normal and late plantings. 5th Intern. Wheat Genet. Symp : 695-699. SCHMIDT, J. W., KUNG-PING P. SHAC; VIRGIL A. JOHNSON and ROBERT F. MUMM. 1978. Diallel cross analysis of yield components in hard red winter wheat. 5th Intern. Wheat. Genet. Symp: 656-662. SHARMA. D. and D. R. KNOTT. 1964. The inheritance of seed weight in a wheat cross. Canal J. Genet. Cytol. 6: 419-425. SHARMA, J. C; ZIAUDDIN AHMAD and A. N. KHANNA 1978. Combining abilities in relation to wheat breeding. Indian J. Genet. 38: 77-85. SINGH, K. B., D. SHARMA and P. D. MEHINDIRATTA, 1969. Study of combining ability and genetic parameters for yield and its components in wheat. Jap. J. Genet. 44: 367-377. SINGH, V. P., R. S. RANA, M. S. CHAUDHARY and D. SINGH. 1985. Genetics of Kernel weight under different environments. Wheat lnform Serv. 60: 21-25. TANDON, J. P., R.S. JOSHI and K. B. L. JAIN. 1970. Comparison of graphic and combining ability analysis of diallel crosses in wheat. Indian J. Genet. 30: 91-103. THOMBRE, P. G.,K. S. GILL and G. S. NANDA 1980. Combining ability in wheat over generations and plant densities. Indian J. Genet. 43: 448-453. |
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