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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #443737

Research Project: Manage, Expand, and Evaluate the U.S. National Collection of Temperate-adapted Woody Landscape Plant Germplasm and Associated Descriptive Data

Location: Floral and Nursery Plants Research

2023 Annual Report

Objective 1: Conduct research to develop genetic resource maintenance, evaluation, or characterization methods and, in alignment with the overall NPGS Plan, then apply them to priority woody landscape plant genetic resource and information management. Sub-objective 1.A: Develop and apply molecular markers for analysis of genetic diversity, taxonomic identity, and/or population structure for priority taxa. Sub-objective 1.B: Perform ecophysiological research on seed cryopreservation and dormancy breaking for priority taxa Sub-objective 1.C: In collaboration with ARS and external stakeholders, evaluate the horticultural merit of accessions in the USNA living collections and those collected under sub-objective 2.A Sub-objective 1.D: Conduct research and conservation initiatives with the USNA living collections, as well as collections of other botanic garden collaborators, which highlight the value and utility of ex situ, data-driven collections. Objective 2: Acquire, distribute, and maintain the safety, genetic integrity, health, and viability of woody landscape plant genetic resources and associated descriptive information, including integrating select genetic resources and information from other collections at the U.S. National Arboretum. Sub-objective 2.A: Acquire samples and associated information of select taxa via exploration, contract collecting, and exchange. Sub-objective 2.B: Maintain and backup plant germplasm, including seed viability testing; seed regeneration via controlled pollinations; offsite accession backup; and asexual propagation of valuable clonal accessions. Sub-objective 2.C: Distribute germplasm and information that meet the specific needs of researchers, breeders, conservationists, nursery professionals, and other stakeholders. Sub-objective 2.D: Maintain up-to-date NPGS accession records within GRIN-Global and expand the available resources within GRIN-Global to include relevant information from the USNA Herbarium, the USNA living collections, and genetic and phenotypic information generated by Objective 1 of this project and other FNPRU researchers.

Analysis will be conducted to identify taxonomic, geographic, and genetic gaps within the collections maintained as part of the Woody Landscape Plant Germplasm Repository. Combined with historical GRIN-Global request data and input from stakeholders, new acquisitions will be prioritized to meet contemporary demand from nursery, conservation, breeding, and other research cooperators. High quality germplasm will be identified from in situ populations or ex situ collections and acquired in the most efficient manner. For many acquisitions this will be done through germplasm requests, contract collectors, and ARS expeditions. The storage and maintenance of existing and newly acquired germplasm will utilize multiple sites and methods based on the biology and conservation significance of each taxon. Species with dessication-tolerant seeds (‘orthodox’) will be maintained at -20 degrees C, with a backup sample sent to NLGRP when sufficient quantities allow, and living plants propagated to fulfil research and conservation goals. Species with dessication-intolerant seeds (‘recalcitrant’) will be maintained as living plants as part of the USNA living collections, distributed to stakeholders via GRIN-Global, and shared with external botanic garden collaborators as part of jointly managed ‘meta-collections’. Basic research will be conducted to develop in vitro or shoot-tip cryostorage methods to maintain recalcitrant taxa. Regeneration of seed and clonal inventories will be performed as needed based on regular monitoring of plant health as well as seed quantity and viability in storage. To meet the needs of stakeholders, we will continue to improve the quantity and quality of taxa and associated data maintained in GRIN-Global. This includes the addition of genetic and phenotypic data, images and supporting attachments, and greater connectivity of data from the USNA living and herbarium collections. New initiatives will be developed to improve the utilization of WLPGR germplasm inventories and data, primarily through stakeholder engagement and the cultivation of new GRIN-Global cooperators. Basic and applied research will be conducted to improve the management, availability, and long term conservation of woody plant germplasm. Priority taxonomic groups (Fothergilla, Hamamelis, Ilex, Lindera, Magnolia, Stewartia, and Viburnum) will be acquired in support of diverse research objectives. Genetic markers will be used to assess the population genetic structure of priority North American taxa to guide conservation priorities at the population level and improve the genetic diversity of ex situ collections. We will study seed-aging in storage to optimize seed storage conditions for long-term preservation. For taxa with complex or unknown mechanisms of seed dormancy, we will conduct studies to develop rapid, synchronized germination methodologies to enable broader usage of these taxa in the nursery and plant breeding industries. We will evaluate underutilized species and select clones for potential as new landscape plants, including recently described species that have not entered the nursery trade.

Progress Report
This new project began on March 6, 2023 and represents a continuation of Project 8020-21000-157-000D which ended March 5, 2023. Progress toward milestones and objectives for early FY23 is documented in the report for the terminating project. Please see the report for 8020-21000-157-000D for detailed information. In this project, under Objective 1a, leaf material and herbarium vouchers were collected among all known populations of Hamamelis ovalis, which occurs from eastern Texas to western Florida. When possible, samples were also collected of H. virginiana from nearby localities; these germplasm samples will be used to assess population structure and phylogenetics of the genus Hamamelis. Additional samples were obtained from collaborators that collected from ex-situ collections of botanic gardens and in-situ populations of northern states. Lindera samples were collected from all individuals in the U.S. National Arboretum (USNA) living collections as part of a characterization study of genome size and ploidy across the genus. Additional samples of rare or less cold-hardy Lindera were obtained from ex-situ collections from collaborators in Florida, Georgia, North Carolina, and Pennsylvania. A total of 111 Lindera accessions representing 22 species are part of these characterization efforts. The study identified hexaploid and octoploid taxa in addition to validating previous reports of diploid and tetraploid species. As part of the range-wide characterization of Sassafras albidum, additional samples were collected from Mississippi, Alabama, Georgia, and Florida to improve representation of southern-provenance germplasm. Sassafras sampling has now been completed, DNA were extracted, and we have begun to review data and prepare a manuscript to publish the results. For Objective 1b, a plan was developed to cryopreserve Fothergilla, Viburnum, and Ilex seeds. Seeds will be harvested from USNA living collections and prepared for treatments in September and October of 2023. Dormancy breaking studies were designed and initiated for Fothergilla gardenii, Hamamelis virginiana, Stewartia malacodendron, Stewartia ovata, and Viburnum lantanoides. Accessions for germplasm evaluation projects outlined in Objective 1c were propagated this year to generate material available for distribution to collaborators. Among the clonal selections identified for evaluation, the two Tilia genotypes have been challenging to propagate using traditional cuttings; air layering, tissue culture, and grafting are currently being tested to produce new clones. Novel forms of Lindera benzoin are being evaluated among a mutagenized seedling group for future selection. Viburnum nudum ‘Little Cherub’ is being multiplied in vitro. The four known species of Fothergilla are being propagated via seed and cuttings for interspecific evaluation. Under Objective 1d, two Magnolia ashei orchard plantings were initiated. At the USNA, approximately 20 trees representing the central, “Holmes Creek” population were planted as a conservation orchard. A second planting representing individuals from across M. ashei’s range was initiated at the Beltsville Agricultural Research Center, and once mature, these plants will be used for cryopreservation backup activities. Seeds were collected from five USNA accessions and added to the seed bank. Significant collecting activities were conducted as part of Objective 2a to acquire germplasm for genebank curation and research projects. A total of 262 new accessions were added to GRIN-Global during the past year, representing 139 unique taxa collected in 25 U.S. states as well as material from Azerbaijan, China, and the Republic of Georgia. Among this project’s priority taxa, we added 2 accessions of Fothergilla, 6 accessions of Hamamelis, 23 accessions of Ilex, 1 accession of Lindera, 10 accessions of Magnolia, 17 accession of Quercus, one accession of Sassafras, and six accessions of Viburnum. A substantial number of Rhododendron collections were also acquired and added to the seed bank, including 32 accessions representing 12 species. All associated herbarium vouchers from collections were deposited in the U.S. National Arboretum Herbarium. For Objective 2b, SOPs were developed to outline seed-intake and maintenance processes and procedures. There are currently 240 seed accessions with quantities below critical distribution thresholds in GRIN-Global. This represents a significant backlog for germination activities, and we decided to prioritize 50 accessions annually to effectively keep up with maintenance needs for the resulting plants. Viability testing was prioritized based on seed age, and the 50 oldest seed accessions were assayed with a tetrazolium test. GRIN-Global inventory records for non-viable seeds were modified to alert collaborators, but the seeds are still available for request because many customers use seeds for morphological research only. 231 new accessions of seed were assessed for viability using x-rays to record percentage of filled seeds. 25 of these new accessions met the criteria for secondary backup at the National Laboratory for Genetic Resources Preservation (NLGRP) in Ft. Collins, Colorado, and were transferred to NLGRP for backup. Nine 15’ x 15’ plots consisting of metal frames and screened enclosures were constructed for controlled seed regeneration activities at South Farm. This doubles the amount of space available for seed regeneration. Five declining Prunus cultivars at the USNA were clonally propagated to ensure backup germplasm is available for replanting into the collection and distributing to stakeholders for off-site backup. A total of 640 germplasm distributions were made as part of Objective 2c. Distributed germplasm was sent to 106 collaborators in 32 states and included 494 unique germplasm accessions representing 240 species. A handout was developed for the repository that outlines our genebank function, diversity of collections, and procedures for requesting germplasm from GRIN-Global. The handout will be shared with new audiences at trade shows and conferences, and the information will be added to the USNA website. A form letter was developed to accompany all outgoing germplasm distributions. This letter provides a similar outline of the repository’s scope and is intended to open a dialog with collaborators to solicit their future needs for germplasm to aid our acquisition activities. We began developing SOPs with the USNA Gardens Unit as part of Objective 2d. We reviewed and provided feedback on updates to the Living Collections Policy and began working with Gardens Unit staff to draft collections. We developed plans for the signature USNA collections. We worked closely with the Gardens Unit plant records staff to begin migrating accession and inventory records from BG-BASE to GRIN-Global to ensure that germplasm data and material is available to cooperators. SOPs were developed for transferring herbarium vouchers and associated data of GRIN-Global accessions to the USNA Herbarium.


Review Publications
King, R., Bassil, N.V., Rounsaville, T.J., Reinhold, L.A. 2023. Sorbus sensu lato: A complex genus with unfulfilled crop potential. Journal of the American Pomological Society. 77(2):110-127.