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United States Department of Agriculture

Agricultural Research Service

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

Location: Floral and Nursery Plants Research Unit

2010 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
Variation in chromosome number in American elm (Ulmus americana) was investigated. Plants across the range of the species were examined using flow cytometry, and both diploid and tetraploid races were found. The diploid race was previously unknown, suggesting that much untapped genetic variation remains in this species, one of the most important tree species for the American landscape industry. DNA was extracted from representative American elms, and representative genetic markers are being examined to determine the relationships between chromosomal races.

Investigation of the relationships among chromosome number, pollen formation, and apomixis in the hackberries (Celtis) has continued. This work is important for determining strategies for developing superior cultivars of these native trees, which are tolerant of harsh conditions but underused in the landscape.

Potential parents for oak crosses were characterized for several SSR markers. Flowering material of three oak species was collected and fixed for pollen-tube studies.

Cultivated catalpas and related plants from all over the world were collected. Each collection included cuttings that were rooted in the greenhouse, tissue for DNA extraction, and dried specimens to serve as permanent records of the collections. This material was obtained for assessment of catalpa genetic diversity now in cultivation, and its correct identification. The oldest North American catalpa species in Maryland and Virginia were collected as baseline examples of their genetics. Living material and previous literature were used to develop a morphological character list.

Cultivated and wild fringe trees and relatives in North America were collected. Each collection included tissue for DNA extraction and dried specimens to serve as permanent records of the collections. Chinese fringe trees cultivated in North America were sampled to measure their genetic diversity. Two large populations of native fringe trees in Maryland, two in North Carolina, and one in Texas were intensively sampled for genetic diversity. Living material and previous literature were used to develop a morphological character list.

A new bird's foot trefoil species was discovered during a review of bird's foot trefoil plants from the Cape Verde Islands. The new species is found only in very dry habitats on two islands.

Permanent herbarium specimens were collected and existing herbarium specimens were entered into a database in order to provide research material needed for National Arboretum research projects.

The National Arboretum herbarium is being prepared for upcoming storage while the building where it is located is renovated. Collections and ancillary materials have been checked for storage requirements, alternate storage plans prepared and evaluated, and an agreement with Smithsonian to store some of the most sensitive specimens negotiated.

Information was gathered from the herbarium on past and present cultivation of non-native woody plants in the mid-Atlantic area, to be used to evaluate characteristics that make plants likely to become invasive in our area, and to evaluate models for predicting invasiveness.


4.Accomplishments
1. Demonstration that Ulmus americana consists of at least two chromosomal races. An ARS scientist at Beltsville, Maryland investigated geographical variation in chromosome number in American elm (Ulmus americana). Plants from throughout the range of the species were examined using flow cytometry, and it was demonstrated that both diploid and tetraploid chromosome races are found in the species. The diploid race was previously unknown, suggesting that considerable untapped genetic variation remains in this species, one of the most important tree species for the American nursery industry.

2. Revision of the elm family in Missouri. An ARS scientist in Washington, DC revised the elm family (Ulmaceae) for The Flora of Missouri, a manual published by the State of Missouri to provide up-to-date information on the taxonomy, distribution, and ecological status of all plants in the family that are wild or invasive in Missouri (including most of the species found across the eastern half of the United States), together with a guide for identification, aimed at professional and sophisticated amateur users. The taxonomy, distribution, and ecological status of all species of these groups that grow outside of cultivation in Missouri was reevaluated, based on extensive field and laboratory studies and a thorough reexamination of available herbarium specimens from throughout the eastern United States, and a guide for identification was supplied. These groups of plants include American elm and other important ornamentals, and species that are or may become invasive in the United States.

3. Documentation of genetic markers for Chinese fringe tree races in the U.S. ARS scientists at the U.S. National Arboretum, Washington, D.C. and Poplarville, Mississippi genetically characterized the races of Chinese fringe trees now in the U.S. The Chinese fringe is an attractive, spring-flowering tree or shrub with the potential to be a beautiful element in urban gardens. Identification of the genetic races now available in the U.S. and development of techniques for their identification will speed up their improvement by clearly distinguishing the genetic lines available for improvement and eliminating duplication in improvement studies.

4. Designation of the characteristic collection for the northern catalpa. ARS scientists at the U.S. National Arboretum, Washington, D.C. discovered that the character specimen for the northern catalpa was incorrect. The northern catalpa is one of our most beautiful trees for urban forestry. Its correct identification is vital for its proper utilization and research furthering its improvement.

5. New bird's foot trefoil from the Cape Verde Islands off the western coast of Africa discovered. An ARS scientist at the U.S. National Arboretum, Washington, D.C. discovered a new species of bird's foot trefoil from two islands in the Cape Verde archipelago. This distinctive new species occurs in very dry habitats, and will further our understanding of the biodiversity and biogeography of the archipelago.


Review Publications
Olsen, R.T. and Whittemore, A.T. 2009. Validation of the hybrid flowering cherry Prunus xincam (Rosaceae). Novon. 19:490-493.

Last Modified: 8/22/2014
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