Cryopreservation of Bletilla formosana seeds (Orchidaceae) by desiccation

- Practical protocol for orchid seed long-term conservation was established.
- The advantages of the two desiccation methods are simple, low cost and non-toxic.
- Provided potential cryopreservation methods for other orchid species.
- Endangered Bletilla formosana seed can be preserved long term.

The development of a long-term conservation method is crucial for orchid germplasm preservation and the orchid industry in general. Mature Bletilla formosana (Hayata) Schltr. capsules were harvested 3 months after pollination (3MAP) and used as cryopreservation materials. Water content of freshly harvested seeds was initially high (49.5%) before decreasing significantly within 1-4 h, and stabilizing 1 d (1.9%) after silica gel desiccation. The viability and seed germination rates of fresh seeds were 89.9% and 76.8%, respectively. The viability and germination rates of untreated fresh seeds placed directly into liquid nitrogen (LN) for cryopreservation decreased to 2.3% and 1.8%, respectively. However, the viability and germination rates of fresh seeds desiccated by silica gel for 24 h prior to cryopreservation were 86.8% and 68.5%, respectively, and those desiccated by air-drying for 24 h at room temperature were 84.9% and 68.6%, respectively. The pretreatment of B. formosana seeds in a sucrose solution and vitrification prior to being placed into LN was found to be unsuitable for cryopreservaton. The water content of seeds with air-dried for 24 h (24.8%) was close to those that were dried with silica gel for 1-2 h (21.9-31.2%). Both desiccation methods are recommended for long-term storage of B. formosana. Fresh harvested seeds of B. formosana can be desiccated for 2 h by silica gel or air-drying for 24 h in laboratory conditions prior to cryopreservation as a practical desiccation method for the long-term conservation of orchid seeds. In addition, B. formosana seeds with 1.9-24.8% water content were found to be suitable for cryopreservation.