Dormancy breakage in Cercis chinensis seeds

The seeds of Cercis chinensis Bunge are important for reproduction and propagation, but strong dormancy controls their germination. To elucidate the causes of seed dormancy in C. chinensis, we investigated the permeability of the hard seed coat and the contribution of the endosperm to physical dormancy, and we examined the effect of extracts from the seed coat and endosperm. In addition, the effectiveness of scarification methods to break seed dormancy was compared. Cercis chinensis seeds exhibited physical and physiological dormancy. The hard seed coat played an important role in limiting water uptake, and the endosperm acted as a physical barrier that restricted embryo development in imbibed seeds. Germination percentage of Chinese cabbage [Brassica rapa subsp. chinensis (L.) Hanelt] seeds was reduced from 98% (control) to 28.3% and 56.7% with a seed-coat extract and an endosperm extract, respectively. This demonstrated that both the seed coat and endosperm contained endogenous inhibitors, but the seed-coat extract resulted in stronger inhibition. Mechanical scarification, thermal scarification, and chemical scarification had positive effects on C. chinensis seed germination. Soaking non-scarified seeds in gibberellic acid (GA3) solution did not promote germination; however, treatment with exogenous GA3 following scarification significantly improved germination. The optimal method for promoting C. chinensis seed germination was soaking scarified seeds in 500 mg·L−1 GA3 for 24 h followed by cold stratification at 5 °C for 2 mo.