Abstract
Floodplain forests as one of the most endangered ecosystems in Europe have recently been impacted by fungal pathogens Phytophtora sp. and Hymenoscyphus fraxineus (chalara). Grey poplar (Populus × canescens Aiton Sm.) can be used as one of well adapted tree species for the reforestation of withering stands of ash (Fraxinus sp.). A unique population of grey poplar (Populus × canescens Aiton Sm.) characterized by desirable phenotypic traits was used for this purpose. The gender distribution was asymmetric; out of 155 individuals, 113 were female. Out of 33 different genotypes determined in the population, 15 were used as a source of approved forest reproductive material. Vegetative reproduction methods (ex situ clonal reproduction by micropropagation and cuttings) were developed and used, to rapidly initiate the recovery of forest stands of grey poplar. In total, 940 explants were successfully micropropagated and adapted to natural conditions, to ensure a genetically diverse source of viable plants used for reforestation. Moreover, we used methodological procedures of micropropagation for setting up cryopreservation technique. With respect to long-term storage of valuable grey poplar genotypes, modulation of gene expression by cold hardening during cryopreservation revealed significant changes in a few candidate genes involved in plant cellular processes.