Cryopreservation of Endangered Ornamental Plants and Fruit Crops from Tropical and Subtropical Regions

Abstract

Horticultural crops comprise various economic species extending from fruits, nuts, vegetables, spices and condiments, ornamentals, aromatic, and medicinal plants. Ornamental and fruit plants are produced mainly for their nutritional and aesthetic values, respectively. Unfortunately, many tropical and subtropical species are in danger of extinction because of climate change and (a)biotic stresses. It is imperative to preserve the germplasms of these species for the present and future genetic improvement programs. Cryopreservation, i.e., maintenance of tissues at the ultralow temperature of liquid nitrogen, is a promising long-term preservation technique, alternative to seed or in vitro banks, which can be applied for both vegetatively and generatively (through seeds) propagated crops, including those with recalcitrant seeds. It is a technology of choice not only for the preservation of plant biodiversity but also for virus elimination in the proficient administration of large-scale micropropagation. The main advantages of cryopreservation are the lowering of in vitro culture expenditures, needed space, contamination risk, and operator errors. However, tropical species are temperature delicate and one of the foremost challenging issues is preconditioning treatments that stimulate physiological reactions to sufficiently enhance tolerance to dehydration and cryogenic procedures. In recent years, several cryopreservation methods based on encapsulation-vitrification, droplet-vitrification, the use of aluminum cryo-plates, and cryo-mesh have been established. Combined cryo-techniques, gene/DNA conservation, as well as studies on perceiving bio-molecular events and exploring the multistage process from the beginning to end of cryopreservation are receiving more emphasis. The development of cryobiomics delivers a conceptual framework to assess the significance of cell signaling mechanisms on cellular functions, the influence of cryoinjury factors on sample viability, and the implications for genetic stability following cryo-storage. The aim of this mini-review article is to provide a succinct synthesis of the developed cryogenic procedures and their use for the storage and exchange of genetic resources of tropical and subtropical horticultural crops, particularly fruit crops and ornamental plants under the threat of extinction.

Keywords: cryo-mesh; cryo-plate; genetic resources; genetic stability; in vitro conservation; omics technologies; regeneration; stress.

Figure 1

Global fruit production in 2020 [28].

Figure 2

Cryopreservation steps of the encapsulation-dehydration, encapsulation-vitrification, and droplet-vitrification techniques: (A) preculture of nodal explants on the medium with an increased sucrose and ABA concentration; (B) shoot tip encapsulated in calcium alginate; (C) osmotic dehydration of encapsulated explants in a concentrated sucrose solution; (D) air drying of explants; (E) dehydration in PVS; (F) cryotube with aluminum foil strip and attached shoot tip; (G) cryobank in the Botanical Garden of the Polish Academy of Sciences in Warsaw, Poland; (H) recovery of explants on a cytokinin-supplemented medium. Bar = 1 cm (except for Figure 2(B)—1 mm).

Figure 3

Schematic representation of different cryopreservation protocols.

Figure 3

Schematic representation of different cryopreservation protocols.