Seed dormancy and storage behaviour of the Hawaiian endemic Coprosma kauensis (Rubiaceae)

Context: Seed banking is the most efficient and cost-effective method of preserving plant germplasm, but not all species can be conserved by conventional practices. Further, restoration of plant populations from seeds often is hindered by a lack of a priori knowledge of seed dormancy and germination requirements. Aims: Our objective was to determine seed desiccation, initial freezing tolerance and the dormancy-breaking and germination requirements of Coprosma kauensis, a dioecious shrub endemic to Kauai Island in Hawaii. Methods: The effects of temperature and gibberellic acid (GA3) on germination of fresh seeds were tested in light/dark at 15/5, 25/15 and 20/10°C with and without treatment with GA3. To test effects of desiccation and initial freezing on germination, seeds were dried to 15% relative humidity at 15°C and then stored at -20°C. Key results: Regardless of incubation temperature and treatment (or not) with GA3, final germination ranged from 78 to 88%; however, time to 50% germination decreased at 20/10°C for seeds treated with 500 ppm GA3. There was no significant difference in final germination percentage between freshly harvested seeds and those desiccated, nor of those desiccated and then subsequently frozen at -20°C. Conclusions: Fresh seeds of C. kauensis exhibit a low degree of nondeep physiological dormancy. They can germinate over a range of temperatures, but germination speed is increased by GA3. Fresh seeds are desiccation and freeze tolerant (after 6 months storage). Implications: This vulnerable Kauai endemic species easily can be propagated from seeds. Future studies should investigate long-term longevity at various storage temperatures.