Ex situ Conservation and Cryopreservation of Orchid Germplasm

Abstract

Premise of research. Orchids are among the most enigmatic of plant species. Yet the Orchidaceae comprises more species at risk of extinction than any other plant family. The collection and storage of orchid germplasmprincipally seeds and associated mycorrhizal fungi but also protocorm-like bodies using encapsulation and vitrification techniques-allows for secure ex situ conservation. This article reviews the approaches and techniques used for the ex situ conservation of orchid germplasm, with a focus on seed banking and the use of cryopreservation techniques to improve the longevity of germplasm.Pivotal results. It is increasingly apparent that cryopreservation-the storage of germplasm at ultra-low temperatures (e.g., in liquid nitrogen)-is required for the long-term and low-maintenance conservation of all types of orchid germplasm. For orchid seeds, desiccation tolerance is common, but longevity in storage is poor. Cryopreservation of orchid seeds shows promise, but some complexities in low-temperature storage behavior still require explanation and resolution. The application of more advanced cryopreservation techniques, including encapsulation-dehydration and vitrification, is becoming increasingly common. These techniques provide for the simultaneous storage of orchid propagules with their compatible fungus, while for seeds, vitrification techniques show potential for improving tolerance to the stresses of cryopreservation. Conclusions.A renewed focus on describing the low-temperature storage physiology of orchid seeds to more precisely define the relationship between seed water content, storage temperature, and seed survival is required, as is perhaps the wider adoption of the use of cryoprotectants for seeds. This research, coupled with the development of improved methods of seed viability testing, will support the growing work of germplasm banks to protect orchid biodiversity in the face of habitat loss and potential species extinction.

Seed banking of terrestrial orchids: evaluation of seed quality in Anacamptis following 4‐year dry storage

“…; Merritt et al . ). Extrinsic factors, directly or indirectly caused by human activities, include habitat change, loss and destruction, climate change, weed invasion and illegal collection.…”

“…Many species are intrinsically rare, with rarity often linked to ecological specialisation (Swartz & Dixon ; Merritt et al . ). The total dependence of orchids on pollinators and/or mycorrhizal associations for sexual reproduction and seed germination up to maturity often results in fragmented and restricted populations, which are at risk of genetic erosion or extinction and are more vulnerable to habitat change (Seaton ; Merritt et al .…”

“…The total dependence of orchids on pollinators and/or mycorrhizal associations for sexual reproduction and seed germination up to maturity often results in fragmented and restricted populations, which are at risk of genetic erosion or extinction and are more vulnerable to habitat change (Seaton ; Merritt et al . ; Swartz & Dixon ). Orchids produce thousands of tiny seeds with a morphophysiological dormancy (Baskin & Baskin ) and with a generally low frequency of in situ germination.…”

Tamaño y viabilidad de semillas: implicancias en la evolución y conservación de Phaius tankervilleae (Orchidaceae)

“…En la familia Orchidaceae se han identificado 880 géneros y más de 25.000 especies, convirtiéndose en la mayor familia de plantas con flores (Givnish et al 2015), de las cuales, un gran número de especies se encuentran en riesgo de extinción. La conservación de germoplasma de orquídeas, específicamente semillas, representa una forma segura de conservación ex situ (Merritt et al 2014).…”

Seed cryopreservation, in vitro propagation and ex vitro growth of Cattleya walkeriana Gardner, a vulnerable ornamental orchid

“…Orchids are endangered by a combination of factors: over-collecting for trade as ornamental and medicinal plants, unsuitable agriculture and forestry practices, urbanization, habitat destruction caused by fragmentation or degradation of natural ecosystems, and climate changes that may promote extreme events. Hence, the development of ex situ conservation of orchid germplasm is a promising alternative to protect and conserve native species (Meritt et al, 2014;Popova at al., 2016).…”