Managing plant genetic resources using low and ultra-low temperature storage: a case study of tomato

Ex situ preservation of plant genetic resources is essential. Tomato is one of the most important vegetable crops on the market. However, the genetic diversity of the clade is limited and suffering from genetic erosion phenomenon. Genebanks experience alleles loss on regeneration of small samples, genetic drift, and somaclonal variation in in vitro cultures. Therefore, the development of more efficient ex situ preservation protocols is required. Storage of accessions at low temperatures allows for the reduction of cell metabolic activity and medium or even long-term preservation. Working and active collections of tomato seeds can be stored at + 5 °C, at reduced humidity. Medium-term storage of seeds and pollen can be performed at freezing temperatures (− 20 °C or − 80 °C). This, however, is highly limited as it requires special freezers and can affect the fecundity of the specimens. As for long-term storage, cryopreservation in liquid nitrogen (− 196 °C to c.a. − 140 °C) is also effective. Over time, several cryopreservation techniques have been successfully applied with tomato pollen, seeds and shoot tips, including: slow cooling (not common anymore), desiccation, encapsulation-dehydration, droplet-vitrification and V-cryo-plate. Despite those studies reported high survival and no morphological variation of cryopreservation-recovered shoots, some differences between cryopreserved and non-cryopreserved samples, revealed by biochemical, ultrastructural and molecular analyses, were observed. The intensity of those alternations was depending on the cell type, cultivar or plant generation. In the future, more attention could be focused on cryoprotection of embryogenic tissues and application of novel cryopreservation techniques, e.g. vacuum infiltration vitrification.