Cryopreservation Development of Some Endangered Thai Orchid Species

Abstract

Thailand is the origin of about 1, 300 tropical orchid species and 180–190 genera. Deforestation and over-collection of wild Thai orchids for trade has placed orchid species at a risk of extinction. Therefore, the conservation as well as sustainable use is urgently needed to conserve orchids by various means. The genera Paphiopedilum and Dendrobium cruentum are listed in Appendix I of CITES. At the Department of Plant Science, Faculty of Science, Mahidol University, various methods of cryopreservation and conservation of Thai orchid species have been carried out. For cryopreservation, recent methods were used, namely, vitrification (dehydration in PVS2 solution, consisted of 30% glycerol, 15% ethylene glycol and 15% dimethyl sulfoxide, prepared in modified Vacin and Went liquid medium), encapsulation-dehydration (encapsulation in calcium alginate beads followed by air-drying in a laminar air-flow cabinet), encapsulation-vitrification (encapsulation in calcium alginate beads followed by dehydration in PVS2 solution), droplet-vitrification (fast freezing from small drops of PVS2 solution on aluminium strip) and cryo-plate (a combination of encapsulation and droplet on very fast freezing aluminium plate) dehydrated with silica gel and drying beads. Application of these methods in seeds was successful in Dendrobium chrysotoxum (99%, vitrification), D. cruentum (32%, vitrification), D. draconis (95%, vitrification), D. hercoglossum (80%, encapsulation-vitrification), Doritis pulcherrima (62%, vitrification), Rhynchostylis coelestis (85%, vitrification), Vanda coerulea (67%, vitrification), as well as in protocorms of D. cruentum (33%, vitrification; 27%, encapsulation-dehydration), D. cariniferum (15%, encapsulation-vitrification), Grammaytophyllum speciosum (14%, encapsulation-vitrification), Rhynchostylis gigantea (19%, vitrification), V. coerulea (40%, encapsulation-dehydration), Seidenfadenia mitrata (67%, vitrification) and Arundina graminifolia (76% and 74%, cryo-plate dehydrated with drying beads and silica gel, respectively; 33% droplet-vitrification; 64% encapsulation-dehydration with drying beads or silica gel). Cryopreserved seeds and protocorms were able to develop into normal seedlings. These techniques appear to be promising for the cryopreservation of some Thai orchid germplasm.