Long-term preservation of Dendrobium chrysotoxum Lindl. using encapsulation method

The species Dendrobium chrysotoxum Lindl., a wild orchid native to north and northeast Thailand, is rapidly depopulated in its natural stand by ingathering for trade within the country. This causes it to become a rare or endangered species in the near future. Long-term preservation is an alternative approach for conservation of plant genetic resources which can be applied to this species. This study was aimed to optimize the conditions for seed germination, protocorm induction and proliferation, and preserving D. chrysotoxum protocorms via encapsulation-dehydration method. Seeds successfully germinated on solid ND medium in the absence of plant growth regulators. Solid ND medium supplemented with 4 mg/l BA was found to promote protocorm proliferation. The proliferation rate was 85%. The seed-derived protocorms were successfully cryopreserved as the following protocol. The protocorms were encapsulated with Ca-alginate and then precultured in liquid ND medium supplemented with 0.25 M sucrose for 1 week in the dark at 4 °C. They were further precultured in liquid ND medium supplemented with 0.75 M sucrose for 2 days in the dark at 4 °C and dehydrated by air-drying for 5 h and subsequently placed in a freezer at -80 °C for 2 weeks. TTC staining exhibited viability rate of 64%.