In a Nutshell: Listen to the Summary
The National Clonal Germplasm Repository (NCGR) at Davis is one of 22 federally funded genebanks in the National Plant Germplasm System (NPGS), part of USDA-ARS. NPGS was established in the late 1800s to bring new crops to the United States and help safeguard our systems of agriculture through acquisition, cultivation and storage of plant genetic resources at regional Plant Introduction stations. This early system brought us important crops and varieties like the Meyer lemon and Egyptian cotton.
Today’s NPGS has grown from the early foundations, conserving over half a million unique accessions of every commercial crop grown in the U.S., and making these seeds and cuttings (i.e., germplasm) available to researchers and plant breeders. The NPGS system is a global leader in the science and art of conserving and characterizing crop genetic variation, particularly when it comes to clonally propagated crops like nut and fruit trees. Each NPGS site specializes in particular crop collections, and the NCGR-Davis holds the collections for Mediterranean-adapted fruit and nut crops including fig, grape, kiwi, mulberry, olive, persimmon, pistachio, Prunus (almond, apricot, cherry, nectarine, peach, plum and prune), pomegranate and walnut.
Not Seeds in a Bunker, but Plants in the Ground
NCGR at Davis operates closely with UC Davis. The NCGR leases approximately half of the Wolfskill Experimental Orchard in Winters, Calif. This property belongs to UC Davis and is also home to the tree nut, pomology and strawberry breeding programs, as well as the “Wolfskill” olive production orchard. This interesting site was donated to UC Davis in 1937 by the family of John Wolfskill, with the intended purpose of enriching and preserving pomological crops. Wolfskill was a fruit pioneer in California who settled in the area during the time of the Gold Rush, and his original ranch continues to support important agricultural advances. The NCGR collection includes over 7,000 unique accessions covering over 175 species, grown on a little over 70 acres, managed by eight full-time employees and several part-time UC Davis students. Most of these accessions are propagated clonally through vegetative cuttings, budding and grafting. Occasionally, wild-collected seed lots are incorporated for conservation and evaluation.
The primary mission of NCGR-Davis is to collect, preserve, evaluate, document and distribute germplasm of its assigned crops, listed above. NCGR-Davis also hosts tasting events, gives special interest group tours and leads classroom field trips. By educating students and the public about the importance of genetic variability in crop plants and providing plant material to researchers, we hope to inspire innovation through the art and science of genebanking.
Crop Improvement Requires Germplasm
Germplasm is a collection of genetic materials that include seeds, plant tissues and DNA sequences. At NCGR-Davis, most of the germplasm is maintained in the form of living trees. Accessions of plants are donated to the collection in the form of seeds, cuttings or budwood. These donations are then propagated by rooting or grafting and put into the living collection. Types of accessions at the repository include breeding lines, heirloom cultivars and crop wild relatives. The more genetic variation a collection has, the more likely we are to find resistance to the diseases, pests or unpredictable weather events that growers face. We also may find novel traits for increasing yield, nutritional value, unique flavors, favorable textures or ease of harvest. NCGR-Davis contains a vast library full of germplasm that can be mined for crop development.
Once an accession has enough material for distribution, it is made available through our searchable public database, GRIN-Global. Plant breeders and other career research scientists can request germplasm in the form of cuttings, budwood, pollen, leaves, fruits or seeds, depending on the crop. After research is done on a particular accession, many of our collaborators provide information to the repository that can be added to the public database, opening the door for additional inquiries by other stakeholders. Examples of the kinds of information that can be added to GRIN-Global include flowering or ripening dates, sugar, oil or starch content, images for growth habit, links to cultivar descriptions or scientific publications, level of crop improvement, collection origin, description of habitat and many more. We are constantly updating and improving this database as time permits.
All germplasm from international sources passes through the Animal and Plant Health Inspection Service where it is rigorously tested for pathogens before being transferred to NCGR-Davis. However, we are unable to continually monitor for new diseases in the plant material, so we refer requestors seeking “clean” plant material to reputable commercial nurseries or to Foundation Plant Services at UC Davis.
Importance of Crop Wild Relatives
Nearly all nut and fruit crops grown in the United States were originally domesticated in other parts of the world, called their geographic centers of origin. Wild versions of the domesticated crops still live in these areas, and in many cases other related species are distributed in different environments around the globe. These distant cousins to our commercial agricultural commodities are referred to as crop wild relatives. Crop wild relatives are typically not suitable for either production or consumption, though they may be culturally significant or important as food sources for wild animals. When they are used for crop improvement either through crossbreeding or use as grafted rootstocks, they often hold the key to resistance for both biotic (living) and abiotic (nonliving) factors.
NCGR-Davis focuses on the conservation of North American crop wild relative species by holding distributable forms of plants that have limited accessibility in their wild locations. In some cases, these plants are facing challenges in the wild, such as habitat fragmentation, loss of pollinators and changing environmental conditions.
Impact of NCGR-Davis Germplasm on Pistachios, Walnuts and Almonds
Crop wild relatives in the NPGS system have already led to major discoveries in resistant rootstocks impacting the pistachio, walnut and almond industries. Two pistachio rootstocks (UCB1 and PGII) came from the hybridization of crop wild relative accessions collected in their geographic centers of origin: Pistacia atlantica and P. integerrima. The parents of these crosses were formerly housed at the Chico Plant Introduction Station, one of the original PI stations in the early NPGS system. When the Chico PI Station was closed, the parents were moved to the Kearney Agricultural Center and finally ended up in the NCGR-Davis. The resulting commercially available hybrids are resistant to verticillium wilt and have high tolerance for cold temperatures and saline soils. PGII is now sold under the trademarked name Platinum. Platinum is resistant to Bushy Top.
The RX1 walnut rootstock, developed from wild Juglans microcarpa from the NCGR collection hybridized with J. regia in collaboration with UC Davis and ARS scientists, is resistant to Phytophthora, root rot and is less susceptible to crown gall. Seedlings of this cross segregate for resistance to root lesion nematodes as well. The original accession of J. microcarpa was collected wild in Edwards County, Texas and added to the NCGR collection in 1983. At the time of its collection, it was an interesting crop wild relative with tiny nuts, not expected to make a big impact on the industry. Its full potential as a rootstock parent was not realized until nearly three decades later. It was ultimately patented and released to the public in 2010.
Almond rootstocks containing Prunus mira, a peach crop wild relative collected in China, are showing useful application for nematode resistance. In addition to being useful for rootstocks, some of the accessions in the collection impart other favorable characteristics. Recently, a self-fertile almond cultivar called Yorizane was released. One of the parents of Yorizane, an NCGR-Davis accession called Tuono from Spain, is the major source of self-fertility in nearly all current almond breeding programs.
The Future of Germplasm
NCGR-Davis will continue to partner with breeders and researchers to genetically screen our collection for traits that are more useful to the tree nut industry of the future like self-fertility, low chill, earlier ripening, frost avoidance, increased nutrition, high yield, drought tolerance, salinity tolerance, ease of harvest, marketability, pest resistance, value-added products, byproducts and more. Our team is working hard to optimize the collections using genomic data to inform choices on culling redundancies and identifying gaps where we should target collecting explorations to introduce more novel traits, ensuring the germplasm at NCGR-Davis is the most robust representation of our assigned crops in the world.
Additionally, we are fostering collaborations with botanical gardens and arboretums across the United States to collect more native North American species through the North American Fruit and Nut Tree Crop Wild Relatives Working Group. These species are likely to have adaptations to soil pathogens found in North America and will be particularly well suited for incorporation into rootstock breeding programs. One accession we acquired this year was a wild desert almond relative that is fully dioecious. Like reproduction in pistachios, this species represents the extreme in almond self-incompatibility, having its reproductive flowers on separate plants. Including this extreme-case accession in their studies may help researchers unlock additional mechanisms related to almond infertility.
We do not yet know the full value of the genetic treasures held in NPGS collections. However, we do know they have proven their worth many times as the backbone of crop improvement throughout history. Every crop can point to success stories such as those mentioned above where germplasm provided growers with tangible solutions to major problems. The plants and seeds that we maintain today will hopefully be ready and waiting for the needs of the industry in perpetuity, for generations to come.
Resources
GRIN Global (Search for Accessions Tool) – https://npgsweb.ars-grin.gov/gringlobal/search
