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Home HortScience Saving Apples from Extinction
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FORT COLLINS, CO—In the vast plant germplasm collection program held by the U.S. Department of Agriculture–Agricultural Research Service, researchers work to protect the genetic diversity of plants through a complex system of preservation methods. Although many plant germplasm collections can be stored as seed, a large group of plant genetic resources are clonally propagated crops and need to be stored in a vegetative state in field plantings, liquid nitrogen, or both. These cryopreservation methods safeguard the fragile genetic resources from abiotic and biotic stress.

Malus (apple) is one example of a collection that has benefited from cryopreservation. According to a report published in HortScience, more than 100 Malus accessions were lost to disease in the field gene bank and exist today only because they were cryopreserved as a secure backup and recovered from the stored buds by grafting.

"The cryopreservation of Malus using dormant buds represents one of the easiest methods for cryopreserving clonally propagated plant germplasm collections," explained Maria M. Jenderek from the USDA–ARS National Center for Genetic Resources Preservation. In this cryopreservation method, dormant buds are harvested from field-grown trees during winter dormancy. Single-node segments are slowly desiccated and slow cooled to –30 °C, then stored in liquid nitrogen vapor. To recover the tissue from the cryostorage, the dormant bud segments are slowly rehydrated and chip-grafted onto rootstocks in a greenhouse or in the field.

The study investigated post-cryoviability of dormant buds for three commercial cultivars of Malus domestica grown in three distinct geographic locations: Geneva, New York; Davis, California; and Corvallis, Oregon. The commercial apple cultivars Braeburn, Jonagold, and Liberty (all classified as intermediate in cold-hardiness) were used. "Germplasm collections include genotypes with varying degrees of cold-hardiness and these differences need to be taken into account when applying cryopreservation protocols," explained Jenderek. "Because the degree of cold-hardiness is known to be a factor in the successful use of dormant bud cryopreservation for Malus, it was suggested that material from relatively warmer climates would not respond to cryopreservation as well as material from colder environments."

To test this hypothesis, the research team investigated the effect of growing provenance on cryosurvival of dormant buds in three consecutive years. Dormant winter buds were harvested at the three locations, cryopreserved, and bud viability was tested by grafting. The collective 3-year mean viability for cryopreserved dormant apple buds for the three locations ranged from 63% to 81% of the buds surviving with the highest survival from the Corvallis site; however, the Geneva twigs were exposed to the lowest preharvest temperature. "Based on the data, the growing locations of the apple dormant bud source had little effect on their cryosurvival," the study noted.

"These results suggest that the temperature at the growing location may not hinder application of the dormant bud cryopreservation method with Malus to the extent previously speculated," Jenderek said. "The results lend a favorable prospect for cryopreservation of other dormant woody crops growing at clonal repositories through the United States and the perhaps other countries."


The complete study and abstract are available on the ASHS HortScience electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Effect of Geographical Location, Year, and Cultivar on Survival of Malus sp. Dormant Buds Stored in Vapors of Liquid Nitrogen
Maria M. Jenderek, Phil Forsline, Joseph Postman, Ed Stover, and David Ellis
HortScience 46:1230–1234. [Abstract][Full Text][PDF]

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