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United States Department of Agriculture

Agricultural Research Service


Location: Crop Germplasm Research

2010 Annual Report

1a. Objectives (from AD-416)
Objective 1: Strategically expand and improve collections of priority Carya genetic resources and associated information. Sub-objective 1.A: Survey existing U.S. domestic collections of Carya, identify material that would fill gaps in NPGS collections, and begin strategically acquiring and characterizing them. The initial priority is to collect Carya myristiciformis (nutmeg hickory) across its range. Sub-objective 1.B: In cooperation with Federal agency collaborators, state Conservation Reserve Programs, Nature Conservancy and Heritage Programs, and private landowners, designate appropriate in situ reserves and establish additional regional Carya plantings. Objective 2: Conserve and propagate Carya genetic resources efficiently and effectively, and distribute disease-free samples and associated information worldwide. Sub-objective 2.A: With ARS collaborators, develop and apply more efficient and effective strategies for conserving the genetic integrity of Carya genetic resources. Sub-objective 2.B: Optimally maintain orchard plantations of grafted cultivar accessions at Somerville (near College Station), Texas, with duplicate plantings at Brownwood, Texas, and distribute seeds and/or cuttings to requestors. Objective 3: As resources permit, strategically genotype and phenotype Carya genetic resources for priority genetic and horticultural traits. Sub-objective 3.A: Incorporate existing characterization data for Carya into GRIN and/or other databases. Sub-objective 3.B: Incorporate existing horticultural evaluation data for Carya into GRIN and/or other databases. Sub-objective 3.C: Extend ongoing cooperative research to assess the relationship between genetic diversity and geographical distribution in Carya via molecular marker assays, and incorporate genotypic data into GRIN and/or other databases.

1b. Approach (from AD-416)
Efforts to strategically expand and improve collections of Carya genetic resources and associated information will give initial priority to collecting Carya myristiciformis (nutmeg hickory) across its range (Objective 1). Information on the distribution of nutmeg hickory will be obtained from a variety of sources, including published accounts, herbarium voucher information, USDA Forest Service Forest Inventory records, State Conservancy and Heritage programs, and personal information. When possible, seeds, graftwood, and collection records will be obtained from local cooperators. Collection trips will be conducted to targeted locations when needed. Attempts will be made in cooperation with Federal agency collaborators, State Conservation Reserve Programs, Nature Conservancy and Heritage Programs, and private landowners, to designate appropriate in situ reserves. C. floridana (scrub hickory) is the most geographically restricted hickory species in the U.S., and it will serve as a model for rational development of in situ conservation in other species. Samples will be collected from the known range of the species, characterized using available molecular tools, and data will be analyzed for patterns of genetic isolation. Implications for resource management will be interpreted and translated into guidelines for designating functional in situ reserves. Efforts to develop more efficient and effective strategies for conserving the genetic integrity of Carya genetic resources (Objective 2) will involve cooperative efforts to determine feasibility of adapting recalcitrant seed cryopreservation protocols for use in Carya. Work will involve developing protocols for harvesting, handling, shipping, viability testing and storage of pecan pollen, and cryopreservation protocols for dormant buds. To strategically genotype and phenotype Carya genetic resources for priority genetic and horticultural traits (Objective 3), there is a need to develop a relational database with capabilities for efficient management of the spatial descriptors related to original collections, spatial descriptors of repository inventories, and genetic data of the NCGR-Carya collection. A database will be structured to appropriately capture many analyses associated with one inventory, and to allow retrieval in association with other inventories of the same cultivar in forms amenable to statistical analyses. To facilitate data entry for Carya into GRIN and/or other databases, efforts will be made to integrate bar coding into field labeling, and Personal Digital Assistants (PDAs) into field data collection. Efforts to assess the relationship between genetic diversity and geographical distribution in Carya via molecular marker assays will be made using collections made from 19 native pecan populations located from Illinois to Oaxaca, Mexico, and will facilitate assessment of the extent of genetic isolation by distance and reveal patterns consistent with environmental adaptation.

3. Progress Report
In FY 2010, 32 accessions of Carya floridana were added to Repository collections by collecting seed from native populations from across the limited range of this Florida species. In addition, 16 seed accessions were collected from associated Florida populations of Carya glabra. Analysis of DNA extracted from these accessions revealed that geographically distant populations within each of the two species were distinct, but often shared maternal patterns with the related species. This is consistent with limited seed movement between geographic populations, but with interspecific hybridization between species. Seedlings of Carya floridana were incorporated into tests designed to screen diverse pecan seedstocks for resistance to the root knot nematode. Three accessions of Carya texana were collected from Gillespie County, Texas, one of the westernmost populations of the species, and were added to Repository collections by grafting. DNA from these samples was extracted and evaluated, and revealed genetic patterns found only in pecan accessions from Texas and Mexico. DNA was also extracted from diverse Carya accessions from New York, Missouri, and Mexico, revealing patterns consistent with interspecific hybridization between species that are sympatric (overlap in their natural ranges). Thirteen pecan accessions from the University of Georgia Pecan breeding program, including 2 patented accessions, were evaluated using molecular tools known as plastid and nuclear simple sequence repeat (SSR) markers in order to clarify inconsistent reports of parentage. Results established parents and direction of cross for the patented cultivars 'Byrd' and 'Morrill' as 'Wichita' x 'Pawnee', not 'Pawnee' x 'Desirable' or 'Pawnee' x 'Squirrel's Delight' as reported earlier by other workers. Almost 900 dormant bud samples were collected from trees in the Pecan Provenance Orchard in Byron, Georgia; these were indexed and cryopreserved for DNA extraction in two locations (College Station, Texas, and St. Louis, Missouri). Patterns of mortality within the Byron orchard necessitated the propagation at College Station of several accessions to back-up the Byron inventories. More than 1500 nut samples were collected from Repository inventories, evaluated for nut quality, and photographed for verification and posting on the Project web site. The Pecan Cultivar orchard at College Station responded well to hedging (duplication of critical accessions) in FY 2010 with vigorous graftwood production. Protocols are being developed for routine hedging of Repository orchards. Irrigation mainlines and manifolds were extended in FY 2010 to Provenance and Cultivar orchards. Additional storage capacity was added to rainfall collection systems used to collect high-quality water for irrigation of plants maintained in Repository greenhouses.

4. Accomplishments
1. Molecular methods to genetically characterize pecan. Pecans are a valuable U.S. nut crop and a nutritionally healthful food source. The pecan species in the genus Carya are important components of our woodland ecosystems. Understanding the genetic relationships among the Carya species that occur naturally in our North American habitats is important to understanding how these species evolved over time and how they historically expanded their ranges. ARS researchers at College Station, Texas, in cooperation with scientists at Texas A&M University, developed and employed innovative molecular biology methods to obtain new genetic information on pecan, including an accurate determination of the parents of interspecific hybrids that occur in geographically defined populations from Mexico to the northern U.S. This work established for the first time the lack of reproductive isolation in these wind pollinated species, and shows that considerable gene flow has occurred among different populations, even those separated by considerable distances. The genetic tools developed by this work will greatly facilitate efforts to better understand the genetic makeup of pecan, will support development of greatly improved management and preservation techniques for critical U.S. species and populations, will aid in developing safe strategies for introduction of non-native Carya species into the U.S., and will dramatically improve the ability to accurately establish parentage/lineage of important pecan cultivars--many of which are a half-century old or older.

Review Publications
Grauke, L.J., Thompson, T.E. 2010. Pecan: Register of new fruit and nut cultivars - list 45. HortScience. 45(5)739-740.

Last Modified: 06/21/2017
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