Cryopreservation of fruit germplasm

Most temperate fruit species are genetically heterozygous and vegetatively propagated. Active collections of fruit genetic resources in Germany are generally maintained in the field, e.g., as potted plants for Fragaria and as trees for pome and stone fruit species. The plant material in active collections should be kept in duplicate to ensure security in case of disease or environmental disaster. The aim of this study was to develop an efficient complementary conservation strategy for fruit genetic resources. Although costly, fruit tree cultivars can be duplicated as field collections at a second site within the framework of the German Fruit Genebank, which is a decentralized fruit-specific network. Wild species accessions, particularly those of the genera Malus spp. (apple) and Fragaria spp. (strawberry) as well as strawberry cultivars, can also be duplicated by means of cryopreservation. In the current study, long-term cryopreservation was initiated for 194 Fragaria genotypes. A protocol combining vitrification with cold acclimation was effective and highly reproducible, with an average regrowth rate of 86%. In Malus, a general cryopreservation protocol based on dormant winter buds was adopted. Based on the results provided in this study, a combination of traditional ex situ conservation and cryopreservation can greatly improve the stability and security of fruit germplasm conservation.