Desiccation tolerance and cryopreservation of seeds of black poplar (Populus nigra L.), a disappearing tree species in Europe

Abstract

Black poplar (Populus nigra L.) is a widely distributed species that plays a crucial role in riparian forest ecosystems. Due to a reduction in its natural habitats and hybridization with introduced poplar species clones, its genetic pool is decreasing and efforts are required to preserve this species. Seeds of black poplar are short-lived and quickly lose viability during conventional storage in gene banks. Therefore, in order to preserve ex situ the genetic diversity of this species, the feasibility of seed cryopreservation in liquid nitrogen (at −196 °C, LN) for periods of 24 h and 2 years was investigated. Seeds were harvested from three individual trees (two provenances) and desiccated to different levels of water content (WC) in the range of 0.02–0.35 g g−1 (g H2O/g dry mass, g g−1) prior to immersion in LN. Seed germination was assessed after each treatment. P. nigra seeds tolerated desiccation to WC 0.07 g g−1 but after severe desiccation to WC <0.05 g g−1 exhibited a significant reduction in germination. Results indicated that all black poplar seeds, regardless of origin, year of harvesting and seed quality, could be cryopreserved for 24 h when their WC was in the range of 0.11–0.17 g g−1. Physiology of P. nigra seeds showed in this paper is consistent with attributes of intermediate seed storage behavior. This study provides a foundation for using cryopreservation for the ex situ conservation of P. nigra seeds.