Cryopreservation of dormant European ash (Fraxinus excelsior) orthodox seeds.

We investigated the sensitivity of dormant Polish-provenance Fraxinus excelsior L. seeds to extreme desiccation and liquid nitrogen (LN, -196 degrees C). Germination and seedling emergence tests revealed that the critical water content (WC) of the desiccated seeds was 0.04-0.06 g H(2)O g(-1) dry mass, g g(-1) (0.04 g g(-1) in the germination test and 0.06 g g(-1) in the seedling emergence test). The seeds that were within the safe WC range (0.06-0.24 g g(-1) in the germination test and 0.08-0.24 g g(-1) in the seedling emergence test) tolerated freezing in LN. A 2-year seed storage period in LN after desiccation to a safe WC did not decrease the germination after thawing as compared with a 2-year seed storage at -3 degrees C. When the seeds were stored in LN after dormancy breaking, the germination rate after storage was lower, because the seeds had to be desiccated to the lower level (~ 0.11 g g(-1)) within the seeds' safe WC range after stratification (before storage). Secondary dormancy was induced in seeds that were desiccated after stratification. The results of this study confirm the feasibility of long-term cryopreservation of European ash seeds in forest gene banks.