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United States Department of Agriculture

Agricultural Research Service


Location: Floral and Nursery Plants Research

2013 Annual Report

1a. Objectives (from AD-416):
Develop stress, disease, and pest-tolerant cultivars of common and underutilized landscape trees suitable for urban areas and height-restricted planting sites. Develop disease- and insect-screening assays for identifying resistant parent taxa and hybrid progeny. Identify interspecific and intergeneric barriers to introgression of desired traits into adapted germplasm. Develop non-invasive tree cultivars, via wide-hybridization and inter-ploid crosses, to limit naturalization and gene-introgression into natural populations. Quantify genome sizes and ploidy levels in related taxa and identify parental taxa for interploid crosses. Develop methods for ploidy-manipulation of vegetative meristems to facilitate interploid crosses and ploidy bridges. Use molecular techniques for hybrid verification and genetic-relatedness tests within cultivated germplasm of important tree species.

1b. Approach (from AD-416):
Develop in vitro and in situ disease and insect screening assays for identifying resistant parent taxa and hybrid progeny; determine inter- and intrageneric barriers to introgression of resistance and ornamental traits into adapted germplasm via controlled pollinations and fluorescence microscopy; quantify genome sizes and ploidy levels using flow cytometry and manipulate ploidy level via mitotic inhibitors; verify hybrid and cultivar parentage using molecular markers. Evaluate progenies and make clonal selections for pest resistance, stress tolerances, non-invasiveness, and ornamental traits. Test plants for geographic and climatic adaptability and horticultural traits through cooperative procedures.

3. Progress Report:
This is the final report for this project which terminated in April 2013. On-going studies and new research was incorporated into the new project 1230-21000-061-00D. Significant progress was made in five years towards establishing a long-term urban tree breeding program at the U.S. National Arboretum, focused on disease- and pest-tolerance, non-invasiveness, and novel ornamental traits. Catalpas are an underutilized, urban-tolerant tree with diverse plant genetic resources and potential. Reciprocal hybridizations were conducted between Asian and North American Catalpa to elucidate self-compatibilities, and intra- and interspecific compatibilities, and intergeneric crosses with Chilopsis. Novel hybrids have been developed and advanced populations are being developed to combine disease resistance and ornamental traits. A two-year powdery mildew evaluation of Catalpa germplasm identified new sources of powdery mildew resistance and elite plants for the nursery industry. Two selections have been propagated for further evaluation and potential release. A black gum (Nyssa) breeding program was redirected towards identifying and selecting novel hybrids for leaf spot resistance, improved habit, and fall color. Controlled hybridizations were supplemented with open-pollinated seed from isolation blocks to generate large segregating populations. Molecular identification of the leaf spot organism in Nyssa confirms that the pathogen is host specific and a valid species, Mycosphaerella nyssicola. The hemlock breeding program moved forward, with new interspecific crosses to determine the nature of species incompatibilities within hemlock species. Two screening studies were conducted to determine host plant resistance to the adelgid. Chinese hemlocks and hybrids were resistant to the adelgid. Elite clones with improved habit and growth and adelgid resistance have been propagated for distribution to nursery collaborators. Molecular markers from Chinese fringe tree (Chionanthus retusus), developed with ARS scientists, have been used to analyze genetic diversity among cultivated and non-cultivated Chionanthus species. Chinese fringe trees cultivated in North America fall into five genetically similar groups as determined by DNA markers. Each of these five groups represents a separate introduction of the species into North America. Wild pygmy (C. pygmaeus) and common fringe trees (C. virginicus) were collected in central and northern Florida for DNA and taxonomic analyses. Morphological data were collected in the field, especially from ephemeral characters, such as stem, petiole, and leaf blade colors, that are lost when the specimens are dried for long-term archival storage in the herbarium. Genetic characterizations, using DNA markers, of five populations of the common and pygmy fringe trees are now underway.

4. Accomplishments

Last Modified: 04/29/2017
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