Prioritization of Malus accessions for collection cryopreservation at the USDA-ARS National Center for Genetic Resources Preservation

Authors: Volk, Gayle; Jenderek, Maria; Chao, Chihcheng

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2016
Publication Date: 10/17/2017
Citation: Volk, G.M., Jenderek, M.M., Chao, C.T. 2017. Prioritization of Malus accessions for collection cryopreservation at the USDA-ARS National Center for Genetic Resources Preservation. Acta Horticulturae. 1172:267-272 doi: 10.17660/ActaHortic.2017.1172.51.
DOI: https://doi.org/10.17660/ActaHortic.2017.1172.51

Interpretive Summary: The USDA-ARS National Plant Germplasm System Apple collection is maintained, in part, as a field collection in Geneva, NY. Field collections of plant genetic resources are expensive to maintain and are vulnerable to climatic, abiotic, and biotic threats. Cryopreservation (long term conservation in liquid nitrogen vapor, LNV) has emerged as a technology by which clonally propagated field collections can be conserved in a safe, secure, secondary location. Apple cultivars can be cryopreserved in the form of dormant buds or as excised shoot tips, with dormant buds often being a more economical choice. There are currently 2291 apple accessions cryopreserved as dormant buds at the USDA-ARS National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, Colorado. Of these, 2052 accessions meet the minimum viability standards. We identified 568 apple accessions that are either inadequately backed up or that have never been processed in need of cryopreservation at NCGRP. We prioritized these accessions based on the vulnerability of the field trees, the number of viable buds currently stored in LNV at NCGRP, and previous failures in response to the standard procedure.

Technical Abstract: The USDA-ARS National Plant Germplasm System maintains a grafted collection of apple accessions representing 49 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 degree Celsius to a moisture content of 25 to 30% (fresh weight basis). Desiccated single-bud sections are then sealed into polyolefin tubes, slow cooled at -1 degree Celsius per hour to -30 degree Celsius, held at -30 degree Celsius 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 degree Celsius in moist, sterile peat moss and grafted onto rootstocks. For this analysis, successfully cryopreserved accessions were defined as those that have 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.