Seed Germination Response to Temperature, Cold Stratification Period, and Gibberellin Treatment in Spiraea fritschiana

To improve the germination of Spiraea fritschiana seeds for mass propagation, we evaluated the effect of a range of temperatures, cold stratification periods, and gibberellic acid (GA3) treatments on three germination characteristics. Final germination percentage (FGP) increased as the temperature for seed germination increased, up to 30°C, while the mean germination time (MGT) and the mean number of days to 30% germination (T30) decreased when seeds were germinated at 25-30°C. The optimum germination temperature of S. fritschiana seeds is approximately 30°C considering FGP, MGT, and T30 together. FGP increased with the duration of cold stratification up to a period of 6 weeks, but declined after 8 weeks of cold stratification, as prolonged cold stratification can induce dormancy with a resultant decline in germination. Pretreatment with 6-8 weeks of cold stratification or soaking seeds in distilled water or 500 mg·L-1 GA3 for 24 h accelerated and increased the germination of S. fritschiana seeds, regardless of temperature. However, further study might be required to evaluate the effect of GA3 concentrations lower than 500 mg·L-1 on the promotion of germination in S. fritschiana seeds.