Seed dormancy-break and germination of Cynanchum forrestii (Asclepiadaceae), an endemic medicinal species of southwest China

Cynanchum forrestii is an over-harvested medicinal plant species in China. At present, wild resources of this species urgently need to be conserved and cultivated to meet the demand of the pharmaceutical industry. However, information on reproduction and propagation is not available. Here, different treatments were assessed to develop an effective protocol for facilitating seed germination of this species. Once seeds were released from physiological dormancy, using 25/15 degrees C with a 12-hour light period promoted germination. Seeds cold stratified at 4 degrees C for 90 days and 120 days germinated to 87 and 91%, respectively, and mean germination time was 11.53 and 10.52 days, respectively. The combination of 60 days cold stratification and 200 mg L-1 GA(3) significantly increased germination from 11% (fresh seeds) to 87%. Among four concentrations used, 200 mg L-1 GA(3) was the most effective for promoting germination of 90-day dry-stored seeds. Taken together, cold stratification for 90 days or more is recommended as a practical measure to break innate dormancy of this species.