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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #425386

Research Project: Taxonomy of Landscape Trees and Shrubs

Location: Floral and Nursery Plants Research

2016 Annual Report

The long-term objectives of this project are 1) to improve the understanding of interrelationships and the distribution of genetic variation (especially genome size and ploidy level) in understudied groups of specialty crops (primarily woody landscape plants), 2) to further develop the National Arboretum as a scientific resource, and 3) to investigate emerging and suspected invasive woody plants among groups of interest to the nursery industry and to National Arboretum plant introduction programs. These goals will be achieved through the following specific objectives: Objective 1: Identify and characterize genetic resources in understudied priority groups of woody landscape plants, including, but not limited to, Ulmus, Celtis, and Carya, to elucidate their genetic relationships and variation within species. Sub-objective 1.A. Determine taxonomic and genetic relationships among selected species of elms (Ulmus). Sub-objective 1.B. Determine ploidy level and comparative genome size in Carya using flow cytometry. Sub-objective 1.C. Determine the distribution of apomixis and polyploidy in North American species of hackberry (Celtis) and their taxonomy and relationships. Sub-objective 1.D. Resolve taxonomic problems and determine the amount and apportionment of genetic diversity in selected white oaks (Quercus sect. Quercus). Sub-objective 1.E. Carry out research projects to meet needs for taxonomic research expressed by stakeholders, such as the production of regional floras and botanical manuals in collaboration with other scientists and horticulturists. Objective 2: Maintain and enhance the National Arboretum Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Sub-objective 2.A. Maintain and enhance the U.S. National Arboretum Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Sub-objective 2.B. Maintain and enhance the U.S. National Seed Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Objective 3: Determine the identity and basic biological characteristics of selected invasive woody plants in the United States. Apply herbarium records of woody plant introduction and naturalization in the mid-Atlantic area to test statistical models for predicting characteristics contributing to invasive behavior in woody plants.

Investigations will utilize a variety of different data types, primarily morphological data, DNA sequence variation, and variation in single-locus DNA markers within variable sites in the genome, analyzed using phylogenetic analyses and other multivariate statistical methods. Organisms will be studied in the field, herbarium, laboratory, and garden.

Progress Report
In Objective 1A, we worked with a collaborator at the Morton Arboretum in Lisle, Illinois to perform phylogenetic analysis on NextGen sequencing results for elms (Ulmus), identified critical gaps in the sampling, and carried out additional sequencing to fill in these gaps. A thorough survey of genome size in Ulmus was carried out using our flow cytometer. This project will improve our ability to breed and select trees with desirable characteristics. In Objective 1B, data on nuclear DNA content of Carya was acquired for representative plants, but completion of this project was postponed because of partial breakdown of the flow cytometer. When complete, these data will improve our understanding of relationships and potential for crossbreeding in this economically important group of trees. In Objective 1C, representative populations of Celtis were characterized for pollen stainability and genome size. In Objective 1D, additional field work was carried out in the southeastern and south-central states to collect material of selected oaks (Quercus) for preliminary analysis. Material was collected for RADSeq sequencing. In Objective 1E, work was carried out on treatments for the Flora of North America, Flora of Oregon, and Flora of New Mexico; a world revision of the genus Catalpa was completed and submitted; a cooperative agreement was set up with New York Botanical Garden to work jointly on genetic analyses of ash, an important genus of shade trees that is being severely impacted by an introduced insect; and various aspects of phenology (leafout, leaf drop, fruit maturation) were monitored for representative species of woody plants in collaboration with an intercontinental consortium of botanical gardens. In Objective 2, activity in the herbarium and seed herbarium included continuing exchange with other herbaria worldwide, loaning of our specimens to qualified scientists, hosting visitors, and mounting, filing, and databasing of specimens. In addition, the compactors were upgraded with new motors and control systems, and work continued to eliminate the large backlog of unfiled specimens remaining from the period of the building renovation. In Objective 3, we used flow cytometry to survey invasive Hedera with a collaborator at the Smithsonian Institution, and considerable data was collected from collaborators across the United States. Work on the weed risk assessment project slowed as a result of the retirement of one scientist, but collection of data on biological characteristics and native ranges of known invasive and non-invasive exotic woody plants cultivated in the mid-Atlantic states continued.