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United States Department of Agriculture

Agricultural Research Service


Location: Crop Germplasm Research

2011 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
Project work in FY 2011 focused on the molecular genetic analysis of a broad group of new collections, using markers and techniques developed by this project to characterize populations of origin of materials being added to permanent collections. The distributions of Carya ovata and C. myristiciformis were extended by the discovery of isolated, disjunct populations in the Edwards Plateau region of Texas. Accessions from those populations were added to Repository collections by grafting. Plastid and nuclear single sequence repeat markers confirmed that the entire stand of C. ovata consisted of a single individual regenerating from root-sprouts, while C. myristiciformis revealed hybridity with pecan. Both showed intermediacy between southeastern U.S. and Mexican populations of the same species and offered evidence of mechanisms to survive genetic bottlenecks. Nuts and herbarium vouchers were collected from several Texas walnut populations (Juglans microcarpa, J. major, and J. nigra) to provide germplasm to the National Clonal Germplasm Repository at Davis, CA. Samples were characterized morphologically and genetically, confirming hybridity between species. No evidence of thousand cankers disease was found in any population visited. Cooperative pollination tests were conducted in FY 2011 with researchers at Fort Collins, CO. Pollen stored under various conditions for extended periods of time was tested for efficacy in setting nuts. Pollen stored 18-23 years with viability as low as 1.7% set at least some nuts. The low success of such pollinations argues against use of the technique except for material of high value. More than 600 nut samples were collected from Repository inventories, were destructively evaluated for nut quality, and were photographed for verification and posting on the Project web site. Repository inventories at the College Station worksite were monitored during the dormant season for diameter growth. Bud break and flower development was monitored in early spring. Irrigation mainlines and manifolds were extended to Provenance and Cultivar orchards at College Station during FY 2011, and additional storage capacity was added to rainfall collection systems used to irrigate Repository greenhouse inventories. Graftwood was shipped to international cooperators in Argentina, China, India, and Italy; and to domestic cooperators upon request.

4. Accomplishments
1. Genetic tools establish gene flow in pecan. Molecular methods developed in this program are being routinely used here and by other researchers to obtain definitive genetic information on a diverse group of Carya species from the U.S., Mexico, and China. Plastid microsatellite markers developed for Carya (pecan) can be used on the sister genus Juglans (walnut), and produce useful information, such as revealing evidence of hybridization and genetic diversity related to geographic origin. This accomplishment is important because it confirms a lack of reproductive isolation in these wind-pollinated species and has implications for the breeder regarding the potential for genetic manipulation. These genetic tools are valuable in identifying regional patterns of genetic diversity that must be considered in successful management of native populations and in successfully managing nursery collections. The understanding provided by these methods contributes to the development of strategies for the safe introduction of related Carya species from Asia, and increased resolution for the development of improved pecan cultivars.

Review Publications
Sagaram, M., Lombardini, L., Grauke, L.J. 2011. Variation in anatomical characteristics in leaves of pecan seedstocks from Mexico and the United States. Journal of the American Society for Horticultural Science. 136(2):103-108.

Grauke, L.J., Mendoza-Herrera, M., Miller, A., Wood, B.W. 2011. Geographic patterns of genetic variation in native pecans. Tree Genetics and Genomes. 7(5):917-932.

Last Modified: 06/26/2017
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