Developing seed cryobank strategies for Tabebuia heptaphylla (Bignoniaceae), a hardwood tree of the Brazilian South Atlantic Forest.

The conservation of Tabebuia heptaphylla, an economically significant, endangered tree of the South Atlantic Forest is confined to arboreta. Although its seeds are orthodox, they do not withstand long-term storage in conventional seed banks, motivating the development of cryopreservation for this species. Seeds within the moisture content (MC) range of 7.5 percent (0.08 g water g dry mass) to 8.4 percent (0.09 g water g dry mass) germinated after storage in liquid nitrogen (LN). Storage duration (15 min to 26 weeks) and rewarming regime (slow and rapid) did not significantly influence germination, which ranged between 54-67 percent. As no additional cryoprotective treatments were required, the protocol is time-, cost- and technically-efficient. Because transport of seeds in LN is problematic for safety, logistic and technical reasons, the feasibility of implementing germplasm transfer using T. heptaphylla seeds recovered from cryobanks was also tested. Viability was not negatively affected in seeds that had been rewarmed, recovered and maintained at room temperature for 2 weeks, allowing safe germplasm transfer in the unfrozen state. The vigor of seedlings from cryopreserved seeds, which was evaluated 90 days after transfer to soil was not influenced by LN storage compared to the controls.