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.