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United States Department of Agriculture

Agricultural Research Service

Research Project: TAXONOMY AND GENETIC DIVERSITY ASSESSMENT OF LANDSCAPE TREES AND SHRUBS
2011 Annual Report


1a.Objectives (from AD-416)
Objective 1: Accurately identify and characterize existing genetic resources, and elucidate their genetic relationships and genetic variation within species, in understudied groups of specialty crops (primarily woody landscape plants). • Sub-objective 1.A. Elucidate relationships among selected species of elms (Ulmus). • Sub-objective 1.B. Determine whether apomixis occurs in selected species of hackberry (Celtis). • Sub-objective 1.C. Determine whether pollen competition affects the occurrence and frequency of interspecific hybridization in oaks (Quercus). • Sub-objective 1.D. Characterize the evolutionary and systematic relationships for the approximately 11 species of the economically important landscape plant genus Catalpa, culminating in a biosystematic monograph for the genus. • Sub-objective 1.E. Construct an initial systematic and phylogenetic analysis of the evolutionary relationships between the relatively few temperate species of the landscape plant Chionanthus and their many tropical congeners. • Sub-objective 1.F. Carry out research projects relating to other families and genera to reach a broad audience in the form 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.

Objective 3: Investigate the identity and basic biological characteristics of selected invasive woody plants in the U.S.


1b.Approach (from AD-416)
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.


3.Progress Report
Elm research (objective 1A) has concentrated on the Ulmus americana polyploid complex. Further flow cytometry has been carried out, cytogenetics of progeny from triploid elm has been studied, and representative elms have been characterized for different SSR markers in order to select markers that give maximum information about genetic structure in the group. DNA sequencing for representative species of elm is being carried out via a cooperative agreement with the Morton Arboretum (see the subsidiary report, 1230-21000-050-04S, for more information). Additional morphological and flow cytometry work has also been carried out on Celtis (objective 1B). The Quercus pollination project (objective 1C) was abandoned due to reductions in manpower and budget and loss of technical support in pollination of wind-pollinated trees among the project personnel. Catalpa species (objective 1D) have been characterized for morphological characters. Characterization of DNA sequences in collaboration with project 1230-21000-053-00D (Genetic Improvement of Landscape Trees for Disease and Pest Tolerance, Non-Invasiveness, and Ornamental Traits) has not been completed (see this report for details). Accessions of Chinese fringetree (objective 1E) in the United States, representing material now available in this country for breeding and improvement of horticultural material of this species. Representative wild populations of the two North American native species, pygmy and common fringe trees, were collected, and characterization of morphological and DNA variation in the species is underway.

Work in the herbarium (objective.
2)has been limited by the closure of the main building at the National Arboretum for thorough renovation. Arranging for storage of the 800,000 specimens, moving them to their temporary locations, and monitoring these storage sites for insect infestation and humidity has required a major investment of time. Having a renovated building with adequate climate control will benefit the herbarium greatly, however. Most of the collection is inaccessible during the renovation, but specimens of interest have been kept out, and work continues with these. Staff and volunteers have added more than 7000 records to the herbarium database. Herbarium collecting has mainly been carried out through contracts and cooperative agreements with collaborators across the country, which will result in the addition of approximately 3000 specimens of North American cultivated plants of interest to the herbarium.

The invasive risk assessment project (objective.
3)has been delayed due to the retirement of the collaborator on the project. Staff will seek a new collaborator to complete this.


4.Accomplishments
1. Documentation of genetic lines of Chinese fringe tree in the U.S. ARS scientists at the U.S. National Arboretum, Washington, DC and Poplarville, Mississippi genetically characterized the races of Chinese fringe trees now available in the U.S. The Chinese fringe tree is an attractive, spring-flowering tree or shrub with the potential to be a beautiful element in urban gardens. There are now five distinct genetic lines of Chinese fringe trees in the U.S. These genetic lines are immediately available for improvement of the horticultural cultivars of the Chinese fringe trees, which will facilitate the rapid development of new cultivars of this species.


Review Publications
Arias, R.S., Techen, N., Rinehart, T.A., Olsen, R.T., Kirkbride, J.H., Scheffler, B.E. 2010. Development of simple sequence repeat markers for Chionanthus retusus (Oleaceae) and effective discrimination of closely related taxa. HortScience. 46(1):23-29.

Last Modified: 12/22/2014
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