Cryopreservation of conditionally dormant orthodox seeds of Betula pendula

To evaluate the feasibility of long-term cryopreservation of Polish provenances of silver birch (Betula pendula), the sensitivity of conditionally dormant seeds to extreme desiccation and/or the ultra-low temperature of liquid nitrogen (LN; -196A degrees C) was evaluated. The critical water content (WC) of desiccated seeds and the high-moisture freezing limit of seeds desiccated or moistened to various WCs and frozen for 24 h or for 2 years in LN was also determined. Germination tests revealed no critical WC for seeds [to 0.02 g H(2)O g(-1) dry mass (g g(-1))]. Seeds tolerated freezing in LN within specific safe range of WC 0.02-0.23 g g(-1) (nuts). Seeds desiccated to the safe WC and stored in LN for 2 years had similar or higher germination as seeds stored at -3A degrees C for 2 years, depending on provenance. Therefore, long-term cryopreservation of B. pendula seeds in gene banks is feasible.