Cryopreservation of Malus germplasm using a winter vegetative bud method: results from 1915 accessions.

Cryopreservation using a winter vegetative bud method is being applied to the Malus collection maintained in the field at the USDA-ARS Plant Genetic Resources Unit, Geneva, New York. Winter hardy materials are sent to the USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO, for processing. To date 1915 accessions, representing 30 species and 16 interspecific hybrids, have been tested. The NCGRP minimum standard for cryopreservation is 40% viable buds, as determined by grafting. For M. x domestica 95% of the accessions tested have been cryopreserved. For species other than M. x domestica, 83% have met the criterion. Eight lines were collected, cryopreserved and recovered through grafting each year. Data from this set showed an affect of year and cultivar on success. There was no strong relationship between viability after cryopreservation and phylogeny. For North American species success after cryopreservation was related to geographical origin.