Use of radiation in soybean breeding

Experiment on using gamma radiation for soybean improvement were started with Sansai and S.J.2 cultivars in 1970. The seeds were treated with 5 to 30 krad; 15 krad was an appropriate working dose, S.J.1, Wakashima, and Cutler-71 cultivars were later included. Outcrossing in the irradiated Sansai varied from 0.04 to 0.18 percent. Yellow seedling mutants were observed in M2 in many cultivars with mutation frequencies ranging from 0.09 to 0.53 percent. White-flowered mutants were obtained in the purpled-flowered Wakashima with a frequency of 0.15 percent. White-flowered mutants were also observed in S.J.2. In brown-hilum cultivars, 0.09 percent of black hilum mutants were observed in Wakashima and 0.14 percent in S.J.2, respectively. A lethal Sansai mutant with an extreme reduction in plant growth was obtained. An increase in protein content was approximately 2 to 3 percent. An increase, as well as a reduction of about 1 percent oil content were observed in S.J.2 and Sansai mutants. The fatty acid composition of mutants and mutation-derived lines of both cultivars were determined. There was 1 to 4 percent reduction of oleic acid in S.J.2. mutants, but 2 to 6 percent increase in Sansai mutants. S.J.2 mutants had an increase of approximately 2 to 4 percent in linoleic acid. Conversely, Samsai mutants had approximately 2 to 4 percent reduction in linoleic acid and less than 1 percent reduction in linoleic acid. In respect to change in yield of mutant lines, it was not possible to obtain any single mutant line which yield significantly higher than that of the control. The seed yield of mutant lines was always lower than that of the control. Soybean mutation experiments for inducing rust resistance in the followering soybean cultivars, namely G 8375, Wakashima G 8377, G 8586, and G 8587 are being carried out.