Abstract: [Objective] Wild shrub Daphne giraldii mainly grows on half-shaded half-sunlighted gentle slope with an altitude from 2 500 to 2 600 m of Qilian Mountains. In order to adapt to cold winter and cool summer in Qilian Mountains, the seeds of D. giraldii have developed a strong dormancy. This study was intended to explore methods of breaking the seed dormancy and improving germination rate of the D. giraldii seeds, therefore to provide theoretical basis and technical support to the propagation from seeds.[Method] Different seed treatments such as biological identification of germination inhibitors of D. giraldii seeds, immersing seeds in GA₃ and 6-BA solution, low temperature sand stratification and dry storage were employed to study the types of and the causes for dormancy, and methods of breaking dormancy of D. giraldii seeds were investigated in this study.[Result] The results indicated that:1) The viability of newly collected D. giraldii seeds were 84.6%, but not germination at all, indicating that there was obvious dormancy phenomenon in freshly collected D. giraldii seeds. The process of water absorption, including quick soaking, stable soaking and saturated soaking stages, of D. giraldii seeds was in line with the Logistic curve, and the seed testa had no serious impact on water absorption of the seeds. 2) Alcohol extract and water extract of seed testa, endotesta and embryo had different degree of inhibitory activity on seed germination rate and radicle length of Chinese cabbage(Brassica pekinensis) seeds. The water extract of testa had more obvious inhibition effects than alcohol extract on the germination and the radicle length of Chinese cabbage seeds under the same condition. The alcohol and water extract of embryo completely inhibited the germination of Chinese cabbage seeds at the concentrations of 0.1 g·mL^-1 and 0.15 g·mL^-1, however the inhibitory effect of water extract of embryo were significantly lower than alcohol extract at the concentration of 0.05 g·mL^-1, showing significantly inhibition in germination and radicle length. The alcohol extract of endotesta had extremely significant inhibition in germination and radicle length of Chinese cabbage seeds, but the water extract had less inhibition at all concentrations. These indicated that the main reason of the seed dormancy of D. giraldii might result from the joint effect of water-soluble germination inhibitory substances in seed testa, both water-soluble and alcohol-soluble germination inhibitory substances in embryo and alcohol-soluble germination inhibitory substances in endotesta. 3) The scanning by electron microscopic showed that the surface cells of the control seeds were smoother and the shape was more regular, the longer columnar cells constituted the palisade tissue, but some holes were found on the surface cells of the seeds after the low temperature sand stratification at 5℃ for 90 days, favorable for seeds to germinate. [Conclusion] Soaking seeds in GA₃ and 6-BA solutions, low and warm temperature dry storage all could not obviously improve the germination of newly collected D. giraldii seeds, but sand stratification at 5℃ for 90 days could break seed dormancy effectively and the germination rate could reach about 80%. The dormancy of newly collected D. giraldii seeds is a type of comprehensive dormancy.

Key words: Daphne giraldii, seed dormancy, seed germination, low temperature sand stratification