Preservation of the genetic resources of Fraxinus excelsior L. in cryopreservation

According to the IUCN, Fraxinus excelsior L. is a near-threatened species due to the spread of Ash dieback disease. Thus, it is important to preserve the genetic resourse of this species. Seeds and plant organs storage under cryopreservation conditions  is a very efficient method to maintain the germplasm of plant species for a long time. Ash seeds were collected from Sangdeh region of Mazandaran province, Iran. Three dehydration treatments were applied to store ash seeds in the cryopreservation. The treatments were 30% glycerol pretreatments, vitrification, and desiccation which were used before entering to liquid nitrogen. After 24 hours, the treated seeds were removed from liquid nitrogen and thawed. Then, they were evaluated for viability and seed germination traits in coimparison to the control. The highest seed viability (92%) and germination (36%) were related to desiccation treatment. The moisture content of F. excelsior seeds at maturity was 5%(w/w). For desiccation treatment, the seeds were placed in a desiccator containing silica gel under vacuum conditions. The moisture content of the seeds decreased by 1.66% compared to the ripening time. Reducing the amount of seed moisture prevents crystallization and rupture of plasma membranes in liquid nitrogen. Glycerol 30% and vitrification treatments were also successful, but probably damaged the seed embryo and reduced the seed survival rate. Due to higher efficiency and no need to use chemicals, the collected ash seeds successfully cryopreserved in the Cryo-Bank of the Research Institute of Forests and Rangelands, Iran, to preserve for a long term and to prevent the extinction of this valuable and unique species.