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United States Department of Agriculture

Agricultural Research Service


Location: National Clonal Germplasm Repository for Citrus

2010 Annual Report

1a. Objectives (from AD-416)
Maintain high quality of and upgrade citrus variety collection and citrus relative collection.

1b. Approach (from AD-416)

3. Progress Report
Huanglongbing (HLB): Development of Information Needed for Avoidance and Management: One objective of this project conducted by the National Clonal Germplasm Repository for Citrus and Dates (NCGRCD) and in collaboration with USDA ARS, Ft. Pierce, FL utilizes the citrus variety collection as the source of seed of diverse citrus and citrus relatives to determine if sources of tolerance to HLB exists. Seeds of 80 different selected “core” collection accessions and other citrus and relative species were established as a replicated planting at USDA ARS in Ft Pierce, FL where HLB is present to determine if any of these specific species or varieties exhibit tolerance to HLB. Citrus genotypes that exhibit tolerance will be extremely valuable to determine sources of tolerance genes in order to develop strategies to incorporate HLB tolerance into commercial citrus cultivars. Characterization of Accessions in the Citrus Variety Collection for Polyembryony: We initiated a project to determine whether Citrus accessions in the collection are polyembryonic. Polyembryony, the ability to produce multiple embryos per seed, occurs in some Citrus types and varieties, mostly by a process called nucellar embryony. Nucellar embryos develop asexually by mitotic divisions of cells of the nucellus tissue within the ovules of each flower with seedlings that develop from nucellar embryos being genetically very similar to the seed parent. This contrasts to embryos produced by sexual hybridization, or zygotic embryos which are a hybrid between both parents. Citrus types and varieties that only produce zygotic embryos are known as monoembryonic. This has important implication for citrus breeding since varieties that are entirely zygotic are preferred as seed parents to ensure that crosses will produce a hybrid seed. Presence of polyembryony is also a valuable characteristic for varieties used as seedling rootstocks, since it is advantageous for rootstock seedlings to be genetically the same as the seed parent tree. Although there is some data on which types are monoembryonic, for many hybrid varieties this is not known. This data will be included in the GRIN and citrus variety collection databases and will be summarized for publication. Characterization and Improved Documentation for Citrus Relative Taxa: Completion of the data collection for the 80 different descriptors of the 600 citrus relative trees is making it possible to increase the availability of information on citrus relatives that lacked descriptor data in the past and to clear up any discrepancies in the identifications of taxa. This data will also be used to consolidate the number of trees per taxa. This past year, the NCGRCD watermarked and uploaded photographs of these Citrus relative taxa, and we are continuing to format and upload this large data set as well as all new citrus variety collection accessions into the GRIN system database. ADODR monitored activities by meetings, site visits, e-mail correspondence, and phone calls.

4. Accomplishments

Last Modified: 07/24/2017
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