Abstract: [Objective] This study aimed to clarify the effects of Na₂CO₃ and boric acid on seed germination and seedling growth of sweet sorghum. [Methods] Two forage sweet sorghum cultivars, Zhongke Tian 438 and 968, were used as experimental materials. Using ultrapure water as the control, two experimental groups were established, Na₂CO₃ was tested at 0, 10, 20, 40, 80, 120 and 200 mmol/L, and boric acid at 0, 1, 2, 5, 10, 15, 25, 50 and 70 mmol/L. Germination tests were conducted under constant temperature 25 ℃ and dark conditions, daily germination counts were recorded. At the end of the test, radicle length, plumule length, fresh weight, and dry weight were measured. Germination percentage, germination potential, germination index, vigour index, salt injury rate, and seedling water content were calculated. The effects of Na₂CO₃ on seed germination and seedling growth were fitted using linear regression and exponential regression equations to determine critical concentrations. The membership function method was applied to evaluate the suitable boric acid concentration for sweet sorghum. [Results] For cultivar 438, germination rate, germination potential, and germination index were significantly lower than those of the control at Na₂CO₃ concentrations of 40, 80, 120, and 200 mmol/L （P<0.05）. Radicle length and fresh weight were significantly lower at concentrations of 20, 40, 80, 120, and 200 mmol/L （P<0.05）. At Na₂CO₃ concentrations of 80, 120, and 200 mmol/L, the germination rate, germination potential, and germination index of cultivar 968 seeds were significantly lower than those of the control group （P<0.05）; while at concentrations of 10, 20, 40, 80, 120, and 200 mmol/L, both plumule length and radicle length of cultivar 968 seedlings were significantly lower than control group （P<0.05）. Based on linear regression fitting, the suitable saline alkali concentration, semi lethal concentration, and lethal concentration for cultivar 438 seeds were 34.52, 87.90, and 206.66 mmol/L, respectively; for cultivar 968 seeds, the corresponding values were 46.82, 79.84, and 186.85 mmol/L. Boric acid within the tested range had no significant effect on germination rate of either cultivar （P>0.05）. At a boric acid concentration of 1 mmol/L, plumule and radicle lengths of cultivar 438 and radicle length of cultivar 968 were significantly higher than those of the control （P< 0.05）. However, at boric acid concentrations of 5, 10, 15, 25, 50, and 70 mmol/L, radicle length, plumule length, and fresh weight of cultivar 968 were significantly lower than control group （P<0.05）. Similarly, at boric acid concentrations of 10, 15, 25, 50, and 70 mmol/L, these parameters of cultivar 438 seeds were significantly lower than those of the control （P<0.05）. The membership function analysis indicated that the optimal boric acid concentration for both cultivars was 1 mmol/L. [Conclusion] Cultivar 968 sweet sorghum seeds showed better adaptability to mild saline-alkali stress, while cultivar 438 exhibited stronger tolerance to moderate and severe saline-alkali conditions. Within the tested concentration range, 1 mmol/L boric acid promoted seedling growth of both sweet sorghum cultivars and can be recommended as a suitable concentration for seedling cultivation of these varieties.

Key words: Na₂CO₃, boric acid, sweet sorghum, germination, seedling