California Citrus Nursery Board

2.2—Trade Information

USDA-ARS National Germplasm Repository for Citrus and Dates

1060 Martin Luther King Blvd.
Riverside, CA 92507
Phone: 951 827 4399; Fax 951 827 4398
Richard Lee, Research Leader and Research Plant Pathologist
Robert Krueger, Curator

The mission of the Germplasm Repository is to provide the genetic diversity necessary for the improvement of citrus, citrus relatives, and dates and to reduce the genetic vulnerability of these crops for the future. The primary objectives of the Repository are to collect, maintain, evaluate, preserve, and distribute pathogen-tested clonal germplasm of Citrus and citrus relatives (Aurantioideae genera), date palms and related species of palm (Phoenix sp.), to carry out research relative to the improvement of methods for the therapy for freedom from pathogens, maintenance and preservation of citrus germplasm, and to maintain an informational file on each accession that is available for distribution. The National Clonal Germplasm Repository for Citrus and Dates (NCGRCD) is unique among the USDA ARS repositories in that this is the only unit which may receive germplasm from foreign and domestic sources, therapy and pathogen-test the accessions, and after release from quarantine status by the USDA APHIS and CDFA, distribute the germplasm as pathogen-tested material. Our operations parallel those of the Citrus Clonal Protection Program (CCPP), but we differ in that we are interested in collecting, maintaining, preserving accessions having diverse genetic traits for use in the future whereas the CCPP concentrates their efforts of varieties which have immediate commercial uses.

The Repository is located on the campus of UCR. The facilities consists of a screenhouse for the maintenance of pathogen-free germplasm (Protected Collection); several greenhouses for pathogen testing, propagation, and maintenance; a laboratory for pathogen testing and germplasm evaluation; and office space. Field collections are cooperatively maintained by the Repository and UCR.

The NCGRCD, Riverside, maintains about 450 accessions in their "Protected Collection." The Protected Collection are accessions which have been therapied, pathogen-tested, and may be distributed upon request. The Protected Collection is maintained as potted plants grafted onto an appropriate rootstock in large containers protected under a screenhouse which is closely monitored for freedom from insects. A limited number of buds are distributed per request, usually about 25 budeyes. Accessions available for distribution are listed in the GRIN database. The Protected Collection increases in size each year as additional varieties are released from quarantine status and added to the collection.

Via a cooperative agreement, the NCGRCD utilizes the University of California, Riverside (UCR) Citrus Variety Collection as a field planting for the purpose of evaluation and as a source of seed, pollen, etc. The trees used for seed collection are tested for freedom from Citrus leaf blotch virus and psorosis by RT-PCR assays and Xylella fastidiosa by PCR assay. This collection contains over 1,100 accessions of citrus and related genera. Over 50 additional cold-sensitive accessions (mostly citrus relatives) are maintained at the UC South Coast Research and Extension Center in Irvine, CA.

The date collection consists of 75 varieties and hybrids of two Phoenix species (P. dactylifera and P. sylvestris). The collection is maintained as two field grown palms per accession at the University of California Coachella Valley Agricultural Research Station at Thermal, CA.


The first steps in germplasm evaluation after establishment in the NCGRCD collection involves the proper identification and/or verification of each species or cultivar. Initial verification will be done by classical botanical and horticultural methods. Molecular characterization of citrus accessions utilizing micro-satellite markers is currently being done in cooperation with Dr. M. Roose, Department of Botany and Plant Sciences, UCR.

Gene descriptor lists have been developed for use in evaluating accessions. These lists include 66 traits of primary importance to the users of the germplasm. Examples include: resistance to important insects and diseases, tolerance to extremes in environmental conditions, ease of propagations, early or late fruit harvest, and fruit quality. Information for these records will be obtained from field observations by Repository personnel and by cooperating research personnel at various institutions and made available on the GRIN website (


All accessions in the Protected Collection undergo indexing for nine virus and viroid diseases: tristeza and seedling yellows, exocortis, cachexia, psorosis, tatterleaf, concave gum complex, and vein enation. Additionally, indexing for freedom from stubborn, a mycoplasma disease is done. Exotic pathogens are tested for using laboratory-based assays, usually PCR-type assays and using a cloned PCR product as a positive control as exotic diseases are not maintained. Accessions with positive symptoms or test results are treated by thermotherapy and/or shoot tip micrografting to eliminate the pathogen(s), then reindexed prior to repropagation. Established trees in the Protected Collection are reindexed at regular intervals and before distributions as required on permits.

More information:

Descriptive information of accessions and/or their evaluations is stored in the USDA-ARS Germplasm Resources Information Network (GRIN), a national database of all plant germplasm. Access to GRIN information is available to the general public through the World Wide Web ( Requests for budwood may be made at

Genetic diversity may be lost through inadequate maintenance of germplasm. The citrus and date Repository provides protection from extremes in environmental conditions and natural insect and disease pests by maintaining germplasm in insect-excluding greenhouses and screenhouses. Within this protected environment, the plants can be kept free of viruses and other pathogens and separate and distinct from the working field variety collection. The citrus collection also is being backed up by cryopreservation at the USDA-ARS National Center for Genetic Resources Preservation, Ft. Collins, CO. The Repository is playing an important role in preserving, maintaining and cleaning germplasm from Florida where the germplasm is now threatened by huanglongbing (citrus greening) and citrus canker.

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