The study was carried out to evaluate the affect of proton beam radiation on production of bulbil and tuber including change of endogenous gibberellins, of Dioscorea opposita Thunb. The yield of bulbils and tubers from non- and irradiated D. opposita Thunb at doses of 5, 10, 15 and 20 Gy were determined. Endogenous gibberellins were also quantified by GC/MS analysis. D. opposita tubers irradiated at 15 Gy produced higher bulbil production than non-irradiated plants. Enlarged bulbil (above size diameter 4 mm) was significantly increased at 15 Gy. Bioactive endogenous GA4 was dominant in bulbils and tubers irradiated with proton beam rather than GA1 . Major gibberellins biosynthetic pathways in bulbils and tubers of D. opposita plants were non C-13 hydroxylation route. From the results of this study, 15 Gy proton beam radiation was suggested as an optimal dose that can produce high amounts of bulbil for mass production of D. opposita plant.

The survival rate and thermal, crystal, and physicochemical properties of starches in chinese yam tubers irradiated to proton beam were determined. Survival rate was decreased with increased proton beam irradiation. Amylose content of D. opposita starches from different proton beam ranged from 13.2% to 17.8%. D. opposita starch at 5 Gy showed the highest δHgel values (12.0 J/g) while D. opposita starch at 25 Gy showed the lowest values (10.1 J/g). Several parameters such as PKV (peak viscosity), HPV (Hot peak viscosity) and CPV (Cooling peak viscosity) decreased with the increase in irradiation dose. The degrees of crystallinity of the D. opposita starches at 5, 10, 15, 20 and 25 Gy were 37.2, 38.3, 38.9, 39.2 and 39.9%, respectively. It might be deduced that proton beam irradiation causes changes of starch, especially at high dose irradiation.