Frozen beauty: The cryobiotechnology of orchid diversity.

Orchids (Orchidaceae) are one of the most diverse plant groups on the planet with over 25,000 species. For over a century, scientists and horticulturalists have been fascinated by their complex floral morphology, pollinator specificity and multiple ethnobotanical uses, including as food, flavourings, medicines, ornaments, and perfumes. These important traits have stimulated world-wide collection of orchid species, often for the commercial production of hybrids and leading to frequent overexploitation. Increasing human activities and global environmental changes are also accelerating the threat of orchid extinction in their natural habitats. In order to improve gene conservation strategies for these unique species, innovative developments of cryopreservation methodologies are urgently needed based on an appreciation of low temperature (cryo) stress tolerance, the stimulation of recovery growth of plant tissues in vitro and on the 'omics' characterization of the targeted cell system (biotechnology). The successful development and application of such cryobiotechnology now extends to nearly 100 species and commercial hybrids of orchids, underpinning future breeding and species conservation programmes. In this contribution, we provide an overview of the progress in cryobanking of a range of orchid tissues, including seeds, pollen, protocorms, protocorm-like bodies, apices excised from in vitro plants, cell suspensions, rhizomes and orchid fungal symbionts. We also highlight future research needs.