Submitted to: International Society for Horticultural Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 13, 2013
Publication Date: August 13, 2013
Citation: Xia, K., Hill, L.M., Decorte, A., Zhou, Z., Walters, C.T. 2013. Cryopreservation of recalcitrant seeds: factors affecting survival of embryonic axes from four Quercus (Fagaceae) species native to the US or China. International Society for Horticultural Science Meeting. p. 107. Technical Abstract: Numerous tree species of economic and environmental importance are facing pressures from diseases or pests, climate change or habitat fragmentation. Seed banking to preserve the genetic diversity within these species would aid conservation. However, several tree species produce recalcitrant seeds, which do not tolerate sufficient drying to survive conventional seed banking. Cryopreservation of recalcitrant plant embryos is becoming increasingly successful, especially for species native to temperate climates. Large size of some axes, high metabolic activity and differential survival of root and shoot tissues are among the major challenges that impede routine cryostorage of recalcitrant embryos. Quercus (oaks) represents a large genus of trees and shrubs with over 450 species occurring in temperate and tropical climates, mostly in the Northern Hemisphere. The broad distribution of oaks provides an ideal opportunity to investigate interactions between various recalcitrant physiology traits and cryo-exposure methods. Successful cryopreservation methods have been reported for seeds of Q. robur, a European species, as well as for seeds of Aesculus hippocastanum, a tree species having seed development and distribution patterns that are similar to several temperate Quercus species (e.g., P. Chmielarz or J. Wesley-Smith and colleagues). Building on past cryopreservation work, we compared responses to desiccation and cryoexposure among embryonic axes of four Quercus species that are native to either US temperate areas (Q. gambelii and Q. rubra) or Chinese subtropical semiarid areas (Q. franchetii and Q. schottkyana). Freshly excised embryonic axes contained 1.0 to 1.5 g H2O/ g dry mass and survived drying to 0.14 g H2O/ g dry mass (US species) and 0.30 g H2O/ g dry mass (Chinese species). Embryonic axes from the US endemics were 3 to 7 fold larger than the Chinese endemics, and the size influenced how rapidly embryos could be cooled to liquid nitrogen. In a multifactoral experiment to understand the interactions of water content and cooling rate on survival after cryoexposure, we found highest survival in axes dried to their limits of desiccation tolerance and cooled at 5 or 0.5oC/sec compared to 50-100 oC/sec. Higher survival was obtained for the US species (95-100%) compared to the Chinese species (0-53%), but damage to the plumule was frequently observed in all species. Our results demonstrate a wide range of seed physiologies within Quercus and immediate feasibility of cryopreservation for some species endemic to the temperate areas.