Relative mutagenic effects of ionizing radiations and alkylating chemicals in rice

Abstract

Studies were undertaken on the relative mutagenic effects of three ionizing radiations (X-rays, gamma rays, fast neutrons) and five alkylating chemicals (DES, EMS, MMS, NMH, MNNG) in rice. Observations on seed germination, seedling survival, seedling height, seed fertility and chlorophyll deficient chimeras were made in the IV^ generation. The M3 generation was grown as M, ear progenies. Chlorophyll mutation frequency, segregation percentage and mutant spectrum were estimated. The mutagenic effectiveness and efficiency were also worked out. Germination of seeds was not affected by radiations even at high doses. Chemical mutagens inhibited germination. Radiation induced lethality was manifested subsequent to germination, whereas lethality induced by chemical mutagens was expressed mostly through inhibition of germination. Seedling height was reduced fay mutagen treatments • Gamma rays and NMH were more effective in this respect Radiations induced high degreesof sterility than chemical mutagens. Fast neutrons induced more sterility per unit dose than sparsely ionizing radiations. Chlorophyll deficient sectors were more frequent in M; plants after treatment with NMH and EMS. NMH, however, was more effective than EMS in this respect. Mutation frequency estimated on M,ear basis was as efficient as that on M.J plant basis because the study was confined to pre-formed ears. Gamma rays fast neutrons, EMS and NMH had induced high frequencies of chlorophyll mutations. Per unit dose, fast neutrons was more effective than gamma rays and atequimolar concentrations NMH was more effective than EMS. The mean segregation percentages were higher after treatment with radiation than with chemical mutagens. The spectra of mutants differed between radiations and chemical mutagens. Albina was the most frequent type following irradiation. In chemical mutagen treatments, the frequency of albina was low and that of viridis was high. Radiations were more effective than chemical mutagens• Mutagenic effectiveness decreased with increase in doses of mutagens. This was due to the failure of mutation frequency to increase proportinately with increase in mutagen doses. Mutagenic efficiency was higher for radiations when estimated on the basis of lethality and injury whereas, based on sterility, chemical mutagens were more efficient. Mutagenic efficiency also decreased with increase in doses of mutagens. The most effective as weli as efficient radiation was fast neutrons Among chemical mutagens the most effective was NMH whereas the most efficient was EMS.