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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZING AND CONSERVING THE GENETIC DIVERSITY OF CARYA POPULATIONS

Location: Crop Germplasm Research

2009 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 2009, 23 accessions of Carya (pecans and hickories) were added to Repository collections by collecting from native populations. These included species from Alabama, Arkansas, Missouri, and Texas. One species was from Yunnan, China. The collection strategy for Carya floridana was finalized. Project work included refining of latitude and longitude records for many accessions to facilitate analysis of genetic diversity in relation to geographic origin. In other work, almost 800 nut samples were collected from Repository inventories, were destructively evaluated for nut quality, and were photographed for voucher verification and posting on the Project web site. Work on pecan nut germination established that nuts frozen in compliance with quarantine protocols for elimination of pecan weevil larvae had reduced germinability if moistened for stratification while frozen. An off-site planting established with selected pecan seedstocks in Louisiana was evaluated for establishment and growth in a wildlife forest reserve in comparison with native seedstocks. A new off-site planting of genetically diverse pecan seedstocks, screened on the basis of a specific genetic criterion (maternal haplotype), was established in Maverick County, Texas, in an effort to identify sources of resistance to Cotton Root Rot.


4.Accomplishments
1. Modern Genetic Tools Define Pecan History: Pecan (in the genus Carya) is a valuable U.S. nut crop, and is also an important component of many U.S. ecosystems. Understanding the genetic relationships among Carya occurring naturally in different North American habitats is important in defining how these species evolved over time and how they historically expanded their ranges. The use of molecular biology tools can facilitate genetic research on Carya species to provide a better understanding of Carya history, and also to facilitate development of pecans as a commercial crop. Modern molecular methods including polymerase chain reaction (PCR) techniques were developed and used to obtain definitive genetic information, including patterns of genetic inheritance, on a diverse group of Carya species (from Mexico to the northern U.S.). This accomplishment is important because it established that southern Carya populations are much older than northern populations that were established after Pleistocene glaciation. The genetic tools developed by the work will be valuable in studies to document historical movements of Carya populations, and to better understand critical genetic aspects of the genus Carya that can be exploited in developing better pecan cultivars for use by U.S. farmers.


6.Technology Transfer

Number of Web Sites Managed1

Review Publications
Volk, G.M., Waddell, J.W., Towill, L., Grauke, L.J. 2009. Variation in low temperature exotherms of pecan cultivar dormant twigs. HortScience. 44:317-321.

Last Modified: 7/23/2014
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