Recent advances towards the application of biotechnology in in vitro conservation (slow growth and cryopreservation) of genetic resources of rare and endangered ornamental plants

Every year hundreds of new cultivars are produced and introduced. Each ornamental plant is a valuable genetic pool that is used as a source for breeding program. In the last decade there has been an alarming increase in the number of disappearing and dangered species. Several valuable ornamental plants such as Fritillaria imperialis, Buxus hyrcana, Lilium ledebourii, Taxus sempervirens and some orchids are in danger of extinction. Some of these species have medicinal value in addition to aesthetic value. Therefore, the rapid development of approaches to long-term preservation of germplasm of these species under extinction seems to be necessary. Many of these plants are preserved in seed banks or as live plants in natural conditions. These preservation methods are unreliable, hard and costly. Therefore, complementary in vitro approaches represent an important tool for ex situ conservation of plants germplasm. Today, the conservation of ornamentals germplasm can take advantage of innovative techniques which allow preservation in vitro (slow growth storage and cryopreservation) of plant material. Periodic subcultures decrease in slow growth storage. Cryopreservation is the storage of explants at ultra-low temperature (−196°C/−321ºF). At such temperature, all the biological reactions within the cells are hampered; hence the technique makes available the storage of plant material for theoretically unlimited periods of time. Cryopreservation is the only technique currently available for the long-term preservation of the germplasm of plant species that are vegetatively propagated or has recalcitrant seeds. In recent years, some cryopreservation methods based on vitrification of intracellular solution such as encapsulation-vitrification and droplet-vitrification and the use of aluminum cryo-plate (D and V types) have been developed. Today, the encapsulation-dehydration technique is most often used. In the future, combined techniques, DNA conservation, survey of genetic stability of cryopreserved species, especially chimeras, cryotherapy and finding a simple, reliable and inexpensive approach and simpler regeneration of preserved explants will probably be the much popular. Unlike micropropagation, there is not much study on cryopreservation of ornamental plants especially those under danger of extinction and rare. Thus, the aim of this review paper is to evaluate different in vitro conservation and cryopreservation techniques and their use for the storage, breeding and exchange of genetic sources of ornamental plants especially those under the threat of extinction.