Ex situ Conservation and Ontogenesis of Torreya taxifolia Embryos

Neusa Steiner, Federal University of Santa Catarina, Emily Coffey, Atlanta Botanical Garden, Jason Ligon, Atlanta Botanical Garden, Lisa Hill, USDA-ARS, Emma Dorr, USDA-ARS, Laurie Blackmore, Atlanta Botanical Garden, Christina Walters, USDA-ARS

Torreya taxifolia Arn (Taxaceae) is an ancestral evergreen tree on the brink of extinction. This dioecious plant is found in the Florida panhandle and is threatened by a fungal pathogen. Ex situ conservation of the remaining genetic diversity of the species is hampered by an unusual seed development pattern. Seeds naturally shed from trees with an apparently immature embryo, and germination often requires complex dormancy-breaking cues. The seed has been categorized as recalcitrant (i.e., sensitive to desiccation), but this interpretation may hinge on the developmental stage of the embryo when desiccation challenges were applied. In this collaboration, we seek to map out the reproductive pathway, from initiation of strobili (cones) through pollination, embryo growth, naturally shedding from trees, and embryo changes post-shedding, using morpho-histological characterizations. Recently, we assessed the feasibility of using in vitro methods to complete embryo maturation and induce germination of immature-appearing embryos excised from freshly shed seeds. We found that we could obtain normal growth in vitro, assessed as development of shoots and roots, from embryos using a two-step process involving a maturation medium, with ABA as the active ingredient, followed by a germination medium that is based on the common woody plant (WP) medium. In contrast, this two-step process only gave rise to embryogenic cultures when embryos were excised from seeds that had been stored for 9 months at 4ºC. Having achieved a means to test viability and germination of T. taxifolia embryos, we are now poised to test survival and normal development of embryos exposed to cryogenic conditions following drying treatments or cryoprotectant solutions. Ultimately, we hope to develop robust cryopreservation and recovery methods to allow effective germplasm banking of this unique species.