| Induction of chlorophyll deficient mutations in Secale
cereale B. C. JOSHI, D. SINGH, S. KUMAR, H. C. BANSAL and Sarla VARMANI Division of Genetics, Indian Agricultural Research Institute, New Delhi, India Seeds of self fertile diploid Secale cereale (2n=14) were treated with the mutagens gamma rays, nitrosomethyl urea (NMU) and ethyl methanesulphonate (EMS). Gamma rays were delivered from Cobalt60 in the Gamma Cell 200 of Atomic Energy of Canada, Ltd., at a dose rate of 5.1 kR/minute. For EMS and NMU treatments seeds were soaked in aqueous solutions of the mutagens for 20 hours. Irradiated or chemically treated seeds were immediately sown in the field to give M1 generation. In each treatment 300 seeds were sown. Three spikes per M1 plant were used to raise M2 generation and score chlorophyll deficient mutations. In Table 1 are given the sample sizes and chlorophyll mutation frequencies for different doses of gamma rays, EMS and NMU. The response to gamma rays in the range of doses from 7.5 kR to 15 kR is linear. With NMU (10-2 to 10-3) and EMS (0.1 and 0.2 percent) generally more mutations are induced as the dose increases but the relationship is complex. Ninety-two percent of the chlorophyll mutations were of three types: albina, striata and tigrina. Out of these, on an avarage, about 79 percent were striata, 15 percent albina and 6 percent tigrina. The frequencies of chlorophyll mutations induced by gamma rays, EMS and NMU among these three classes of mutants obtained, by pooling the data for all the concentrations of each of the chemical, are given in Table 2. It is seen that with both EMS and NMU the frequencies of albina (8.9, 11.5 percent) and striata (89.3, 80.2 percent) are comparable. However, frequency of tigrina is higher with NMU (8.3 percent) than with EMS (1.8 percent). The frequencies of the three kinds of mutations with gamma rays are markedly different from that obtained with EMS and NMU, the frequency of albina being higher (37.8 percent) and that of striata being lower (56.8 percent). The spectrum of induced chlorophyll mutations in rye differs significantly from that observed in diploid barley (Hordeum vulgare, 2n=14). In barley, albina, tigrina and striata mutations account for an average of only about 56 percent of the total chlorophyll mutations. In this 56 percent portion of the mutant population the three types of mutations induced by gamma rays, EMS and NMU occur with frequencies given in Table 3. As seen from the Table, in barley, with all the three agents the albina mutation is predominant (53 to 69 percent) and the frequencies of striata (3 to 17 percent) and tigrina (27 to 34 percent) are very low. (Received June 17, 1971) |