| The seedling height decreased proportionally with increasing concentration
of the mutagen used either individually or in combination. However, combined
treatments produced maximum inhibitory effect in both genotypes. Adverse
effects of both mutagens were much more pronounced on root growth than on
shoot growth. The extent of the injury in seedling growth with increase
in dose was not the same in the two genotypes, indicating differential genotypic
response. Pollen and seed fertility also decreased with the increase in
the concentration of the mutagen revealing a linear dependence of these
traits on dose as reported earlier (SHARMA et al. 1979; NILAN et
al. 1977). Low pollen and seed fertility at higher doses and in combination
treatments could be due to translocations and other cytological anomalies
induced by these treatments (LARIK 1975). In combination treatments independent action of two mutagens leads to an additive effect. This effect gets modified depending upon the nature of interaction of mutagens in a combination treatment. If one of the mutagens exposes previously protected sites or creates favourable condition to enhance the activity of other, more than additivity, a synergistic effect would result. If, on the contrary, two mutagens merely compete for the same site, the effect will be less than additivity (AASTVEIT 1968). Present results show negative synergism (less than additivity) which confirm the findings of AASTVEIT (1968). CHOPRA & SWAMINATHAN (1966) made analogous studies in common wheat suggested that "recovery, rather than induction appears to be the major obstacle for obtaining synergistic effects". References AASTVEIT, K. 1968. Mutation in Plant Breeding, 11, FAO/IAEA, Vienna 5-14. ALEXANDER, M. P. 1969. Stain Technol. 44: 117-122. AUGUSTINE, V. J., K. PALANICHAMY and E. A. SIDDIQ. 1975. Rad. Bot. 15: 267-277. AWAN, M. A., C. F. KONZAK, J. N. RUTGER and R. A. NILAN. 1980. Crop Sci. 20: 663-668. BHASKARAN, S. and M. S. SWAMINATHAN. 1961. Genetica 32: 1-32. CHOPRA, V. L. and M. S. SWAMINATHAN. 1966. Ind. J. Genet. 26: 59-62. GAUL, H. 1977. Manual on Mut. Br. IAEA! FAO, Tech. Rep. Sr. 119: 87-96. KHAN, I. A. 1981. J. Cytol. Genet. 16: 125-130. KONZAK, C. F., M. NIKNEJAD, I. WICKHAM and F. DONALDSON. 1975. Mutation Res. 30: 55-62. LARIK, A. S. 1975. Genetica Polonica 16: 295-300. MYHILL, R. R. and C. F. KONZAK. 1967. Crop Sci. 7: 275-277. NILAN, R. A. 1954. Genetica 39: 943-953. NILAN, R. A., A. KLEINHOFS and C. F. KONZAK. 1977. Ann. N. Y. Acad. Sci. 287: 367-384. NILAN, R. A., A. KLEINHOFS and C. SANDER. 1976. Proc. 3rd. Int. Barley Genet. Symp. Verlag Karl Thiemig, Munich, pp. 295-300. SHARMA, N. P., A. PATNAIK and P. J. JACHUK. 1979. Exp. and Environ. Bot. 19: 117-121. SINGH, R. B., B. D. SINGH, R. M. SINGH and VIJAY LAXMI. 1978. Ind. J. Genet. P1. Breed. 38(3): 380- 389. SMITH, H. H. 1958. Bot. Rev. 24(1): 1-24. |
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