Extending Populus seed longevity by controlling seed moisture content and temperature

The poplar species Populus davidiana and P. koreana are widely grown in plantations and as biofuel resources, but little is known about ex-situ seed conservation in poplar. To identify the optimal long-term seed storage conditions for these species, we evaluated the viability of seeds with different seed water contents (SWCs) at various storage temperatures and time periods. P. davidiana seeds with <6% SWC could be stored at room temperature (RT) for 4 weeks, while P. koreana seeds showed no storability at RT. P. davidiana seeds with 3% SWC showed 74% viability after 36 months of storage at 4°C, while those with 9–18% SWC showed >89% viability after 48 months of storage at -18°C. Long-term storage at -80°C was best for P. davidiana seeds with a wide range of SWCs (3–24%), with 91–98% of normal germination after 48 months of storage. However, the normal germination of P. koreana seeds with 3–24% SWC declined to <20% after 36 months of storage, even at -18°C and -80°C. No significant difference was observed between seeds immersed vs. not immersed in liquid nitrogen for both species. Our findings increase the possibility for long-term seed conservation for both Populus species.