Causes and Breaking of Seed Dormancy in Flowering Dogwood (Cornus florida L.)

Cornus florida seeds show strong dormancy. In this study, we investigated the causes of the dormancy by assessing the permeability of the stony endocarp, the germination of seeds after mechanical dissection, and the effect of endogenous inhibitors. Water uptake by intact and cracked seeds during imbibition showed that the endocarp formed a strong barrier for water absorption. Meanwhile, extracts from endocarp decreased the germination frequency of chinese cabbage seeds from 99.3% (control) to 2.7%. Therefore, the endocarp was the mechanical barrier and contained endogenous inhibitors for seed germination. However, the germination percentage of decoated seeds and dissected seeds with the exposed radicle were only 13.3% and 28.7%, respectively. It was found that the endosperm also played a role in seed dormancy. Extracts from endosperm decreased the germination frequency of chinese cabbage seeds from 99.3% (control) to 53.0%. By contrast, extracts from embryo did not affect the germination of chinese cabbage seeds. When tested with the excised embryos, germination percentage was up to 85.3% at the 16th day of incubation. Taking these results together, we concluded that the endocarp and endosperm were responsible for seed dormancy in C. florida . To break the seed dormancy of C. florida , stratification and soaking in sulfuric acid are the effective means. The highest germination frequency was achieved by immersing seeds in 98% sulfuric acid for 10 minutes, then soaking the seeds in 500 mg·L −1 gibberellic acid (GA 3 ) for 72 hours before cold stratification at 5 °C for 60 days.