The U.S. National Plant Germplasm System’s repositories house collections of plant material that not only preserve our horticultural heritage, but can be used by fruit breeders to develop new and better varieties.
In 1980, the NPGS added clonal genebanks to its network of national repositories. There are now eight genebanks devoted to fruit and nut crops and their wild relatives, which maintain 30,000 accessions representing 1,600 species. Each of these facilities has internationally recognized, globally diverse collections of genetic resources for their assigned crops. Temperate crops, including tree fruits and grapes, are preserved at facilities in Corvallis (Oregon), Davis (California), and Geneva (New York).
Before 1980, fruit and nut germplasm collections in the United States were largely developed and maintained by individual plant breeders at universities, and were often lost when scientists retired, changed the focus of their research, or encountered funding shortfalls. As a result, collections of irreplaceable material, assembled through years of effort, were routinely lost, producing an erratic and insecure network for germplasm conservation. That insecurity lessened in 1980, with the establishment of the first U.S. National Clonal Germplasm Repository in Corvallis. Over the next several years, seven more repositories were built at specifically chosen sites throughout the country.
The mission of NPGS genebanks includes the acquisition, documentation, preservation, evaluation, enhancement, and distribution of plant genetic resources.
This conservation activity improves the quality and production of economic crops important to United States and world agriculture.
Unique cultivars or selections are maintained as growing plants, evaluated for descriptive or useful traits, documented in a national public database, and freely distributed as clonal propagules to researchers and other germplasm users around the world.
While originally conceived as working collections for crop improvement as a hedge against starvation, the genebanks have also provided the raw materials for basic plant genetic research, reservoirs for rare or endangered species, archives of historic cultivars, and educational opportunities for the public. The collections preserve our horticultural heritage for future generations.
Uncover the genes
In his Brief Book: Biotechnology and Genetic Diversity, published in 1985, Stephen Witt quoted a report that compared germplasm collections to “pharmacies filled with miracle drugs without labels.”
We need to uncover the genes lurking in our germplasm that will allow us to develop cultivars able to overcome emerging diseases, adapt to changing climates, improve flavor, enhance nutritional value, and expand production into new environments.
We must not only preserve our vanishing agricultural heritage, but also discover new sources of essential human nutrients, satisfy consumer desires for novel fruits and nuts, and implement reliable methods to identify and fingerprint genotypes. DNA techniques have become useful tools for both identifying clones and for locating the genes associated with useful traits. Our germplasm is only as useful as the information that accompanies it.
The Germplasm Resources Information Network, or GRIN, is the national public database that provides both genebank personnel and germplasm users access to data in the national germplasm collections. Each repository, in consultation with a team of crop specialists, has developed a list of key traits that are of interest to plant breeders. Germplasm users can query GRIN for plants with traits that meet their specialized needs, whether as parents for breeding or representatives of a unique geographic area.
Fruit collections
NCGR-Corvallis, located at Oregon State University, maintains collections of more than 26 genera, including Pyrus (pear). Its collection includes Asian and European pears, and hybrids of the two, as well as ancient cultivars that are at least 400 years old.
NCGR-Davis is located at the University of California, Davis. It holds more than 5,400 plant accessions representing about 15 genera and 175 species with Vitis (grape) and Prunus (stone fruits) accounting for about 75 percent of accessions. Accessions are maintained as two trees or vines each on a 30-hectare field site in Winters, California. The repository for apple, grape, and tart cherry is on the campus of Cornell University in Geneva. The apple collection includes 4,000 accessions with 2,500 of these maintained as trees grafted to EMLA.7 semidwarfing rootstock. The tart cherry collection includes approximately 100 accessions of Prunus cerasus and Prunus fruticosa maintained as duplicate trees on MXM 2 rootstock. The grape collection consists of 1,200 accessions growing in the field as own-rooted plants. These accessions represent mostly North American native species and hybrids that are cold hardy and supplement the 2,800 cold-tender Vitis accessions maintained in Davis, California.
Risk of loss
Repositories must find a balance between maximizing diversity and minimizing the risk of loss. Some crops, like apples and pears, are economically maintained in long-lived orchard collections. Other crops, such as stone fruits, are prone to insect-borne viruses and must be protected in screenhouses to prevent plants from becoming infected. Maintaining multiple plants of each accession as a backup increases the security of the collection, but reduces the space available for additional accessions. Some repositories use in vitro culture as a medium-term back-up strategy for growing plants, while others use cryogenic storage of either apical meristems or dormant buds for long-term back-up.
Distribution of clonal germplasm is more complicated than distribution of seeds. Clonal repositories do not generally distribute finished rooted plants, but scions or cuttings that must be propagated by the recipient. Shipping of requested accessions is therefore dependent on the season when appropriate propagules are available, which might be midwinter for grape cuttings or fruit tree scions. Germplasm is freely available from all NPGS repositories in small quantities for research purposes. Although not certified to be free of all known pathogens, much of the clonal germplasm in NPGS has been tested for the presence of common or important viruses and virus-like pathogens.
Future challenges
A quarter century after their inception, the NPGS Clonal Germplasm Repositories have established national collections representing world diversity of not only commercially important fruit and nut cultivars, but also their wild relatives, which may have genetic traits of unanticipated importance. Regeneration and evaluation of the collections are priorities.
Future challenges include identifying gaps and acquiring plants to fill those gaps. Recent international agreements, such as the Convention on Biological Diversity and the International Treaty on Plant Genetic Resources for Food and Agriculture, have redefined the protocols for exchange of plant genetic resources between countries. National quarantine regulations that prevent the movement of insect and disease pests also impact international germplasm exchange.
Genebank personnel will be challenged to maintain expanding collections with declining resources, and to transition from the acquisition phase to the evaluation phase as collections mature. Eliminating unintended redundancy, filling genetic gaps, and expanding phenotype and genotype data in GRIN will continue to enhance the value of the NPGS fruit and nut collections. An era of enhanced utilization, when mature genebanks expand their partnerships with breeders, researchers, and stakeholders, has arrived for the NPGS clonal repositories.
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