| Differential radio-sensitivity among the different
varieties of bread wheats R. P. CHANDOLA and M. P. BHATNAGAR Botanical Section, Agriculture Department, Rajasthan, Jaipur, India From the comparison between the different varieties of bread wheats regarding their response to the evolution of mutations evaluated in terms of yield of the M2 progenie-s it has been found that different doses of gamma-rays have a positive differential effect on different genomes and varieties. Yield has been considered to be an important factor with regard to the radiation response because its being controlled by many of its components. It thus involves more than a simple gene alteration. Varieties of hexaploid wheat, Kharchia, RS 31 - 1, C 591, Jaipur Local and RS 9 - 11, and one tetraploid wheat, Malvia Ekdania, were included in a study of evolution of useful mutations in these varieties. Seeds were subjected to three doses of gamma-rays viz. 10,000 r, 20,000 r and 30,000 r at the Cobalt - 60 facility of the Indian Agricultural Research Institute, New Delhi, India in 1959. Yield of 100 M2 progenies with equal number of plants of each ear progeny and controls in each of the above mentioned varieties were recorded under field conditions. The treatments were also screened for various mutations. Spontaneous mutations were not observed in any of the large control materials. The results of the present study indicate that Kharchia is relatively most sensitive than the other varieties when range of yield in various progenies is used as an index of sensitivity. In all cases except in Kharchia 10,000 r and Malvia Ekdania - 10,000 r there is a decline in the yield of the treatments as compared to the controls. Among the treatments themselves the decline in yield is directly proportional to the higher dose of gamma-rays. Different treatments of a variety when collectively are compared in the same way to each other show a different pattern of yield range. Differences of sensitivity as indicated by these studies show that radio - sensitivity depends not only on the kind and number of genomes but also on the kind of alleles present in any particular material. The lower efficiency of the tetraploid wheat Malvia - Ekdania to produce much less number of mutations due to its lesser mutagenic specificity is also reflected in the studies. Since the tetraploid wheat being more stable is more likely to be less effected by gamma-rays in comparison to the hexaploid it necessarily implies that a lower range of yields be obtained in the treated material of such a variety. Such results showing more stability in the tetraploid wheat have been reported by FUJII (WIS. No. 7 p 11, 1958). The restricted group of mutations observed in our tetraploid material lends support to MACKEY'S (Hereditas 40 : 165 - 180, 1954) contention that the 'diploid sector' of the germ plasm of bread wheat is limited and the polyploidy while imposing a restriction on the morphological frame permits a more varied and subtle differentiation within this frame. |