Cryopreservation of winter-dormant apple buds: establishment of a duplicate collection of Malus germplasm

The clonal wild-species Malus collection at the Julius Kühn-Institute, Institute for Breeding Research on Fruit Crops, Germany, comprises 507 accessions of 46 species and represents one of the largest collections in Europe. Cryopreservation was applied to 77 accessions of 31 species and hybrids in the Malus collection using a winter vegetative-bud method. No significant differences were observed in the recovery of the two controls, untreated buds and desiccated buds, however, cryopreservation significantly decreased bud recovery, independent of the rootstock used for chip budding. Data from this investigation showed an effect on recovery of year and genotype between and within species. Of the 77 accessions, 62 had living buds, and recovery was >40 % for 37 and these averaged 68.5 % recovery. The initial moisture content, dehydration time, and morphology of the buds had no significant influence on recovery. The higher percentage of recovery in one experimental year was possibly the result of secondary buds that grew despite lethal injury to the primary meristems. Adaptations to the general protocol and the handling details were successful, and the cryopreservation of dormant buds will now be part of the conservation strategy for Malus genetic resources in Germany.