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United States Department of Agriculture

Agricultural Research Service


Location: Floral and Nursery Plants Research

2009 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
Material for DNA extraction from representative elms was collected, and several genes are being sequenced to determine which will be most appropriate for phylogenetic work. Several hundred specimens of hackberry (the genus Celtis) were examined for malformed, aborted pollen and triploid chromosome number, two known indicators of apomixis (that is, the production of seed without pollination) in this group. In North America, the smaller trees (C. tenuifolia, C. pumila, and relatives) are apomictic, while the large trees (C. occidentalis and C. laevigata) reproduce sexually. Flow cytometry was carried out on wild and cultivated elms from the Washington, DC. area, emphasizing the collection in Glenn Dale, Maryland, that will soon be unavailable to us. We confirmed that genomic DNA varies among species, and to some extent within American elm, providing a baseline for future study. Cultivated catalpas and related plants from all over the world were collected for propagation, DNA extraction, and voucher specimens. The oldest North American catalpa species in Maryland and Virginia were located and collected for baseline data. Major museum collections in Boston, New York, Philadelphia, St. Louis, and Washington, DC in the USA and Edinburgh, London, and Paris in Europe were visited for known catalpa localities; all collection and locality data was databased. Cultivated and wild fringe trees and related plants in North America were collected for DNA extraction and voucher specimens. Chinese fringe trees in North America were sampled for genetic diversity. North American fringe trees were sampled in Maryland, North Carolina, and Virginia. One large population in Maryland was intensively sampled as a populational baseline. Selected samples were used to identify genetic markers for the Chinese fringe tree. Major museum collections in Boston, New York, Philadelphia, and Washington, DC were visited for known North American fringe tree localities; all collection and locality data was databased. A new relative of cucumber from Zambia was discovered during identification of new germplasm collections. It was grown out, crossed with its nearest relatives, its morphology determined, and its DNA compared to all cucumbers and melons. Information was gathered on species of plants that have long been cultivated in the mid-Atlantic area. We will determine which of these plants have become invasive in the area and which have not, and perform a statistical study to identify characteristics that can be used to predict invasiveness. Approximately 6,000 records were added to the herbarium database.

4. Accomplishments
1. Revision of three genera of plants in California. An ARS scientist in Washington, DC revised three groups of plants, the maples, buttercups, and mousetails, for The Jepson Manual of the Higher Plants of California, a manual published by the University of California to provide up-to date information on the taxonomy, distribution, and ecological status of all plants that are wild or invasive in California, 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 California was reevaluated, based primarily on a thorough reexamination of available herbarium specimens, and a guide for identification was supplied. These groups of plants include plants with potential as ornamentals, and species that are or may become invasive in the United States.

2. Documentation of genetic markers for the Chinese fringe tree and related plants. ARS scientists at the U.S. National Arboretum, Washington, DC and Poplarville and Stoneville, Mississippi developed 252 molecular markers for the Chinese fringe tree. The fringe tree is an excellent, spring-flowering garden tree or shrub. These molecular markers will be important tools in breeding programs, facilitate accurate identification of cultivars and species, elucidate native population structures, clarify the evolutionary relationships of cultivated and wild species, and aid in identifying genetic variability of dietary supplements derived from fringe trees.

3. Determination of a reported Himalayan catalpa as a North American species. ARS scientists at the U.S. National Arboretum, Washington, DC discovered that an early 20th Century catalpa species, reported to occur in the high Himalayas, is actually the southern U.S. catalpa. They examined dried specimens at the Royal Botanic Garden, Edinburgh, Scotland, and compared them to specimens in the USA and France. Consequently there is no cold-hardy Himalayan catalpa from which to develop new, cold-hardy cultivars.

4. New cucumber relative from Zambia in Africa discovered. ARS scientists at the U.S. National Arboretum, Washington, DC and Ames, Iowa, a scientist at St. Louis University, St. Louis, Missouri, and a state scientist at Ames, Iowa discovered a new relative of cucumber among germplasm from Zambia, Africa. DNA and morphological profiles confirmed the new species, Cucumis zambianus. The most closely related species were artificially crossed with the new species, and failed to yield fertile offspring. The new species was reported to be a wild relative of cucumber and melons with potentially useful genes for cucumber improvement programs. The germplasm is available from the USDA National Plant Germplasm System.

Review Publications
Delprete, P., Kirkbride, J.H. 2008. Clarification of Borreria gymnocephala, Diodia gymnocephala, Diodia schumannii, Borreria flavoriens, and Spermacoce schumannii (Rubiaceae). Journal of Botanical Research Institute of Texas. 3:245-250.

Widrlechner, M.P., Kirkbride, J.H., Ghebretinsae, A.G., Reitsma, K.R. 2008. Cucumis zambianus (Cucurbitaceae): A New Species from Northwestern Zambia. Systematic Botany. 33:732-738.

Whittemore, A.T. 2009. What is Ranunculus gelidus? Journal of Botanical Research Institute of Texas. 3:245-250.

Last Modified: 07/27/2017
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