Conservation of some endangered Thai orchid species using cryopreservation

Abstract

Thailand is the origin of about 1,300 tropical orchid species and 178 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 genus Paphiopedilum and Dendrobium cruentum are listed in Appendix I of CITES. This paper reviews the protocol development using different cryopreservation methods for endangered Thai orchid species. At the Department of Plant Science, Faculty of Science, Mahidol University, various methods of conservation of Thai orchid species are implemented. For cryopreservation, recent methods were used, namely vitrification (dehydration in PVS2 solution, consisted of 30% (w/v) glycerol, 15% (w/v) ethylene glycol and 15% (w/v) 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 aluminum strip) and cryo-plate (a combination of encapsulation and droplet on very fast freezing alminium plate). Application of these methods in seeds was successful in Dendrobium chrysotoxum (99%, vitrification). Dendrobium cruentum (32%, virification), Dendrobium draconis (95%, vitrification), Dendrobium hercoglossum (80%, encapsulation-vitrification). Doritis pulcherrima (62%, vitrification). Rhynchostylis coelestis (85%, vitrification), Vanda coerulea (67%, vitrification), Arundina graminifolia (82%, D cryo-plate; 74%, encapsulation-dehydration), Paphiopedilum exul (Ridl.) Rolfe (30%, encapsulation-vitrification; 14%, encapsulation-dehydration), as well as in protocorms of Dendrobium cruentum (33%, vitrification; 27%, encapsulation-dehydration; 22%, encapsulation-vitrification; 68%, V cryo-plate), Dendrobium cariniferum (15%, encapsulation-vitrification), Grammaytophyllum speciosum (14%, encapsulation-vitrification), Rhynchostylis gigantea (19%, vitrification), Vanda coerulea (40%, encapsulation-dehydration), Seidenfadenia mitrata (67%, vitrification), 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), Acampe rigida (17%, V cryo-plate; 74%, D cryo-plate) and in pollinia of Dendrobium signatum (56 and 50%, V cryo-plate and D cryo-plate, respectively). Cryopreserved seeds, protocorms and pollinia were able to develop into normal seedlings. These methods appear to be promising techniques for cryopreservation of some Thai orchid species.