Cryopreservation of Paphiopedilum exul (Ridl.) Rolfe seeds using encapsulation-vitrification and encapsulation-dehydration methods

Paphiopedilum exul (Ridl.) Rolfe seeds were cryopreserved using encapsulation-vitrification method (EV) and encapsulation-dehydration method (ED). For EV method, P. exul seeds were dehydrated with PVS2 solution for 0, 20, 40, 60, and 120 min. For ED method P. exul seeds were dehydrated with a laminar air-flow cabinet for 0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h. Dehydrated P. exul seeds were plunged into liquid nitrogen (LN) for 1 h. All treatments were cultured on ½ MS agar medium in dark condition at 25±2°C for 8 w, and then moved to culture in light condition at 25±2°C for another 8 w (white fluorescent at intensity of 37 µmol m^‑2 s^‑1 for 16 h d^‑1). For control treatment, dehydrated P. exul seeds were done with the same step of EV and ED methods, but were not plunged into LN. The results showed that the optimum treatment for EV method was using PVS2 solution for 40 min. It gave seed germination percentage at 29.68% and growth index (GI) at 2.03. For ED method, the optimum treatment was using a laminar air-flow cabinet for 2 h. It gave seed germination percentage at 14.02% and GI at 2.2. When comparing seed germination percentage and GI of EV and ED conditions with unpaired t-test, the suitable treatment for cryopreservation P. exul seeds was EV methods that used PVS2 solution for 40 min in dehydration step.