Effects of ⁶⁰Co-γ radiation on the seed germination and seedling growth of Bromus catharticus

In order to investigate the effects of different doses of ⁶⁰Co-γ on the seeds and seedlings of Bromus catharticus, we compared the seed germination index, root morphology index, seedling morphology, and physiological index of B. catharticus treated with different doses of ⁶⁰Co-γ (0, 50, 100, 150, 200, 250, and 300 Gy). The main results obtained were as follows. In terms of seed germination and seedling morphological indices, we found that in response to an increase in radiation dose, the germination potential of seeds showed a trend of initial increase and subsequent decline, reaching a maximum value of 32% at a radiation dose of 50 Gy. In addition, percentage B. catharticus seed germination and seedling height and root length at 50 Gy radiation, and seedling leaf length at 50 and 100 Gy radiation, were slightly higher those of the control. In contrast, at all other radiation doses assessed, these indices were lower than those of the control group. Although the leaf width and stem diameter of seedlings exposed to 150 Gy radiation were higher than those of the control seedlings, the leaf area of seedlings at this dose was smaller than that of control seedlings. The root surface area and volume of seedlings were found to be inversely proportional to the radiation dose, although there were no significant differences in mean root diameter between seedlings subjected to ⁶⁰Co-γ radiation and control treatments (P > 0.05). At the higher radiation doses of 250 and 300 Gy, seedling mortality approached 100%. With respect to the physiological and biochemical indices of seedlings, the contents of proline (Pro), malondialdehyde (MDA), and chlorophyll (Chl), as well as the activities of catalase (CAT) and superoxide dismutase (SOD), were significantly affected by exposure to ⁶⁰Co-γ radiation (P < 0.05), showing a trend of initial increase and subsequent decline in response to exposure to an increasing radiation dose. Membership function analysis indicated that optimal seed germination and seedling growth were obtained in response to ⁶⁰Co-γ radiation mutagenesis at doses of 50 and 100 Gy. Moreover, the semi-lethal dose of ⁶⁰Co-γ radiation for B. catharticus was calculated to be approximately 224 Gy. The results obtained in this study will provide a theoretical basis and technical guidance for the innovative development of B. catharticus germplasm resources.