Optimization of ion-beam irradiation for mutagenesis in soybean: effects on plant growth and production of visibly altered mutants

Ion-beam irradiation is attracting increasing attention as a new mutagen. Here, we describe for the first time the dose response and mutagenic effects of ion-beam irradiation in soybean. We irradiated the hilum side of dried mature soybean seeds with 320-MeV carbon ions within a 0.25–20-Gy range. The growth or seed production of the irradiated plants was profoundly affected. In particular, the number of plants that survived until seed-set decreased with the increase of the irradiation dose and was very low in plants irradiated at doses higher than 5.0 Gy, whereas the frequency distribution of the number of seeds produced by each seed-setting plant was not affected by lower doses of irradiation. Based on these results, we produced plant populations irradiated at 2.5 Gy and 5.0 Gy on a large scale to obtain M2 seeds. Despite the duplicate composition of the soybean genome, which originated from tetraploids, chlorophyll-deficient mutants were detected with a frequency of 0.47% in the M2 generation of plants irradiated at 5.0 Gy. These results demonstrate that irradiation of the hilum side of dried soybean seeds with carbon-ion beams at a dose range around 2.5–5.0 Gy induces genetic changes while also allowing the production of a considerable number of seed-setting plants, suggesting that these irradiation conditions are suitable for producing a mutant population potentially useful for breeding and/or identifying gene function.