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United States Department of Agriculture

Agricultural Research Service


Location: Floral and Nursery Plants Research

2010 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
A long-term breeding program for Catalpa was established to develop disease-tolerant, non-invasive cultivars with novel ornamental traits. Controlled pollinations were conducted using novel hybrid combinations, including intraspecific, interspecific, and intergeneric crosses. Permanent field plots have been established for evaluating advanced Catalpa and Nyssa crosses. A two-year powdery mildew evaluation of Catalpa germplasm was begun. Genetic diversity and identification of Catalpa germplasm using molecular markers has continued with the addition of new germplasm. Selection has begun on Nyssa hybrids with improved plant habit, fall color, and leaf spot tolerance. Molecular identification of the leaf spot organism in Nyssa confirms that the pathogen is host specific and a valid species, Mycosphaerella nyssicola. A two-year study testing resistance of container-grown Tsuga hybrids to hemlock woolly adelgid was concluded. Test crosses in advanced Tsuga hybrids were conducted for developing advanced generation hybrids. Flow cytometric analysis continues on Catalpa, Celtis, and Ulmus americana. Molecular markers were used to analyze genetic diversity among cultivated and non-cultivated Chionanthus retusus.

4. Accomplishments

Review Publications
Trueblood, C.E., Ranney, T.G., Lynch, N.P., Neal, J.C., Olsen, R.T. 2010. Evaluating fertility of triploid clones of hypericum androsaemum L. for use as non-invasive landscape plants. HortScience. 45:1026-1028.

Last Modified: 10/18/2017
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