Effect of gibberellic acid treatment and cold stratification on breaking combined (physiological + mechanical) dormancy and germination in Sassafras tzumu (Hemsl.) Hemsl seeds

Sassafras tzumu (Hemsl.) Hemsl., known as Chinese sassafras, is an exclusive species of tree found in China, belonging to the Sassafras genus in the Lauraceae family. Its primary mode of propagation is through seeds, which possesses a profound dormancy and irregular germination. In its natural environment, it takes approximately 2–3 years for the seeds to emerge from the ground and begin germinating. Consequently, a rapid and effective method for breaking dormancy would greatly benefitsbn edjhn the production of S. tzumu seedlings. The objective of this investigation was to identify the optimal treatment for breaking dormancy. The S. tzumu seeds were subjected to gibberellic acid (GA₃) treatment and cold stratification. The findings indicated that the dormancy type of Sassafras tzumu seeds was combined (physiological + mechanical) dormancy. After 6 months of cold stratification, the germination percentage of seeds treated with various concentrations of GA₃ (200 mg/L, 500 mg/L, and 1000 mg/L) all exceeded 50 %. Among these treatments, the most effective method was the application of 200 mg/L GA₃ in combination with 5 months of cold stratification, resulting in a germination percentage of 55 %. During the process of cold stratification, soluble proteins, soluble sugars, starch, and fat were broken down into smaller molecules to support embryo growth. Interestingly, the content of soluble sugar exhibited an upward-downward trend, while the content of soluble protein displayed a downward-upward trend. The release of dormancy in S. tzumu seeds was jointly regulated by various endogenous hormones. The content of GA₃ demonstrated an upward-downward trend, while the ABA content exhibited a continuous decline with a brief upward trend. In contrast, the IAA content displayed a continuous upward trend, and the ZR content showed no significant change. The ratios of GA₃/ABA, IAA/ABA, and ZR/ABA all displayed an upward trend.