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We investigated the usefulness of ion beams for mutation breeding in rice (Oryza sativa L.) by comparing the efficiency (i.e., the ratio of desirable mutations to plant damage such as lethality and sterility), mutation rate, spectrum, and optimum dose to that of gamma rays. Rice seeds were irradiated with carbon ions (mean linear energy transfer = 76 and 107 keV/µm), helium ions (9 keV/µm), and gamma rays, and their survival and fertility were examined in the M 1 generation. The frequency of chlorophyll mutations and their types (albina, xantha, and viridis) were examined in the M 2 generation, using the M 1 -plant progeny method. The efficiency of ion beams either equaled or exceeded that of gamma rays. In addition, the mutation rate of ion beams was higher than that of gamma rays. Thus, ion beams appeared to efficiently induce mutants with little radiation damage. No remarkable difference was observed in the relative frequencies of each type of mutation among 3 types of ion beams and gamma rays, thus suggesting that there was no difference in the spectrum. A shoulder dose, which hardly affected survival, was sufficient to efficiently obtain mutants for both types of radiation.

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