Location: Floral and Nursery Plants Research
2024 Annual Report
Objectives
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.
Approach
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
Within Objective 1a, DNA sampling of Hamamelis ovalis was completed, representing every population known to exist including new populations discovered in Texas during this project’s survey work. DNA samples from other Hamamelis taxa were provided from ex-situ collections of stakeholders as well as the U.S. National Arboretum (USNA) living plant collection and herbarium vouchers. Having acquired all necessary samples, DNA extraction was initiated for this molecular characterization project. For our genetic study of Sassafras albidum, sequencing work was completed, and a manuscript is in preparation. Also in Sub-objective 1a, Lindera benzoin was initially targeted for analysis of genetic diversity, but we shifted our focus to Persea. Although both Lindera and Persea are members of the Laurel family, Persea endemic to the eastern U.S. are suffering mortality caused by the fungal disease Laurel Wilt. As Lindera appear to be minimally affected by Laurel Wilt, Persea species present a more urgent need for characterization, especially because these species are wild-relatives of avocado, Persea americana. DNA sampling for Persea borbonia, Persea humilis, and Persea palustris was initiated this year to characterize molecular diversity for these eastern North American taxa. These data will inform prioritization of germplasm acquisition to develop core-collections of Persea germplasm.
For Objective 1b, we have significantly increased the taxonomic scope of seed biology and ecophysiology research projects. For seed cryostorage and longevity phenotyping, we have focused on species that cannot be stored using traditional methods. Experiments were designed and initiated to develop protocols for seed storage of Buxus spp., Fagus grandifolia, Magnolia spp., Persea palustris, and Sideroxylon lanuginosum. We have completed experiments to characterize dormancy breaking and germination for Fothergilla gardenii, Magnolia ashei, Sideroxylon lanuginosum, Stewartia ovata, Stewartia malacodendron, and Viburnum lantanoides and have begun manuscript preparation for each of these taxa. We also initiated a study of seed dormancy among North American Ilex, which are known to have challenging, complex, and poorly-studied dormancy mechanisms. Nineteen Ilex accessions representing 12 taxa were initiated as seed cultures this year, and this study will expand in the future to encompass all North American Ilex species. Ilex that germinate as part of this study are being grown on as living plants to collection development at the USNA (Objective 1d) and stakeholder requests for distribution (Objective 2c).
Field evaluation of germplasm as part of Objective 1c is ongoing at the USNA although some focus taxa with slow growth rates have delayed the distribution of test plants to offsite evaluators. In Lindera benzoin, we have made our first round of selections for potentially compact genotypes and plan to initiate field trials next year. In Hamamelis ovalis, our seed-grown plants have set flower buds this growing season and will be subject to preliminary phenotyping and selection next season. In Tilia, all attempts to root cutting of our two clones of interest have failed; however, scions were grafted onto rootstocks of different Tilia species and we anticipate these grafted plants will be ready for distribution next year. In Fothergilla, we focused distribution efforts on the newly-described diploid species Fothergilla milleri, and shared seedlings with five cooperators this year. Our clonal selection of Viburnum was released as the cultivar ‘Little Cherub’ last year, and we continued to propagate and make distributions of this clone.
We continue to utilize the USNA living collections as a source of germplasm for collections-based research as part of Objective 1d. This year we performed a comprehensive review of the USNA Ilex collection and submitted an application to the American Public Garden’s Plant Collections Network as part of their National Accreditation program. Using the USNA collections of Lindera, we completed and published a survey of genome size and ploidy level for 100 genotypes. Although we planned to initiate a similar survey of genome size for Viburnum this year, we have instead chosen to focus on Tilia. This decision was made due to increased demand for Tilia genetic resources from stakeholders. In addition, we noted taxonomic uncertainty among several USNA Tilia that can be resolved by making ploidy determinations, so this work will aid proper identification of accessions to support stakeholder needs. In support of new efforts to study Persea as part of Objectives 1a and 1b, we have relied upon USNA’s sole Persea accession to conduct preliminary research. We used this individual to test DNA stability during shipping in advance of our field sampling efforts in Objective 1a and have made seed collections to initiate embryo storage research as part of Objective 1b. In the process of utilizing this accession we were also able to correct the taxonomic identity to Persea palustris that had been mis-identified as P. borbonia for 30 years.
Acquisition of new germplasm samples as part of Objective 2a was extremely successful over the past year. 377 new accessions of germplasm representing 167 unique taxa were added to the National Plant Germplasm System (NPGS) as part of this project. Each of these accessions were accompanied by comprehensive source data documented in GRIN-Global as well as preserved herbarium vouchers deposited in the USNA herbarium. Notable acquisitions of priority taxa include Hamamelis (11 accessions), Hydrangea (10 accessions), Ilex (63 accessions), Magnolia (six accessions), Quercus (21 accessions), Rhododendron (47 accessions), and Viburnum (15 accessions).
Significant progress was made in seed bank operations including regeneration, testing, and backup of seed accessions as part of Objective 2b. We began testing the viability of existing seedbank accessions using a taxonomic approach, beginning first with the Laurel family whose seeds are generally not suitable for storage. We found 14 out of 16 Lauraceae seed accessions were non-viable. A total of 121 accessions were tested for viability with a focus on Lauraceae, Cornus florida, and Viburnum spp., and 28% of these accessions were deemed non-viable. Because non-viable seeds remain useful to select stakeholders conducting morphometric analysis or molecular research, we created a new maintenance policy code in GRIN-Global to continue our distribution activities for appropriately labeled, non-viable seeds. A total of 37 seed accessions were collected or regenerated at quantities of over 4,000 and backup samples for these accessions were distributed to the ARS National Laboratory for Genetic Resource Preservation in Colorado. Five accessions were initiated this year for controlled seed-regeneration activities, and a total of 16 clonal accessions at the USNA were asexually propagated to backup and replace valuable genotypes showing signs of decline.
We continue to expand stakeholder engagement and germplasm distribution activities as part of Objective 2c. To increase our stakeholder base and be proactive about germplasm availability, we have developed a form letter to accompany all outgoing shipments that provides information about our genebank’s scope and promotes information exchange with stakeholders concerning the disposition, use, and eventual outcomes of distributed germplasm. We added a similar overview of the genebank to the USNA website to further promote our available resources and value to stakeholders. In total, 112 requests for germplasm were fulfilled for 92 unique requestors. Among these requests we distributed 564 accessions items, an average of 5 items per order, representing 264 unique taxa. Seed distributions accounted for the majority (78%) of order-items, followed by cuttings (20%) and live plants (2%). These materials were shipped to customers in 30 U.S. States, and seven countries including Denmark, France, Ireland, Netherlands, South Korea, Switzerland, and the United Kingdom. The five most common usage-requests for our germplasm were reported to be breeding and varietal development (26%); botanical/taxonomic investigation (17%); historical, cultural, and anthropological research (15%); genetic studies (10%); and plant pathological investigations (9%).
For Objective 2d, we continued to make progress coordinating the exchange of plant records data across USNA management units and within the USNA research unit. Over the last year, 6,332 USNA plant accessions including 9,544 associated germplasm inventory records were migrated from the USNA internal plant records system (BG-BASE) to the NPGS database, GRIN-Global. Among those records are 160 USDA Plant Introduction (PI) accession records that were previously missing from GRIN-Global. These 160 PI accessions include 318 germplasm inventory-items that are now publicly accessible to stakeholders for the first time. Through this project’s scientific oversight of the USNA living collections, we have initiated a review and update to the USNA living collections policy that will bring the document more in line with contemporary genebank operations and contain standardized operating procedures to integrate the efforts of the USNA Public Horticulture and Engagement Unit (PHEU) with scientific curation of the living collections.
Accomplishments
1. Genetic survey of cultivated spicebush. Spicebush (Lindera) species are a diverse group of trees and shrubs with applications as medicinal, industrial, and ornamental plants. In the U.S., all native Lindera species are susceptible to the Laurel Wilt pathogen, while some introduced species used as ornamentals are escaping into natural areas; however, breeding and selection to improve these traits is limited by a lack of information on genetics and species relationships in the genus. ARS researchers at the U.S. National Arboretum surveyed the genome size and ploidy level for all spicebush accessions maintained in the National Plant Germplasm System and all taxa known in cultivation in the U.S. The survey identified significant variation in total DNA content and is the first report of species in the Laurel family with up to six and eight sets of chromosomes. The results of this study can be used for breeding efforts to develop plants with resistance to Laurel Wilt, develop sterile or seedless forms of exotic ornamental species, and improve select traits for production of oil, aromatics, and medicinal compounds.