Prioritization ofMalusaccessions for collection cryopreservation at the USDA-ARS National Center for Genetic Resources Preservation

Abstract

The USDA-ARS National Plant Germplasm System maintains a grafted collection of apple accessions representing 48 taxa in Geneva, NY. Dormant buds of many of these accessions have been routinely cryopreserved at the USDA-ARS National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, CO. In the standard procedure, dormant buds are sent to NCGRP in mid-winter. Scions are cut into 35 mm bud sections and desiccated at -5°C to a moisture content of 25 to 30% (fresh weight basis). Desiccated single-bud sections are then sealed into polyolefin tubes containing 10 to 12 sections each, slow cooled at -1°C h-1 to -30°C, held at -30°C for 24 h, and then placed into the vapor phase of liquid nitrogen (LNV) for long term storage. For viability testing, the buds from one polyolefin tube are rehydrated at 2°C in moist, sterile peat moss and grafted onto rootstocks. For most accessions, this left 3 polyolefin tubes of Malus buds in long-term storage for each accession. For this analysis, successfully cryopreserved accessions were defined as those that have a total of 19 or more predicted viable buds remaining in LNV at NCGRP. Of the 2291 accessions currently cryopreserved at NCGRP, 2052 accessions meet this requirement. Criteria were established to prioritize the apple accessions that are either inadequately backed up at NCGRP or have not yet been processed. These criteria include the likelihood of success in cryopreserving the Malus taxon, the vulnerability of the field trees, the number of viable buds currently stored in LNV, and previous failures in response to the standard procedure.