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United States Department of Agriculture

Agricultural Research Service


Location: Floral and Nursery Plants Research

2012 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 aimed at the development of disease-tolerant and pest-resistant urban trees has made progress in several genera, including Catalpa, Nyssa, and Tsuga. Additional controlled pollinations in Catalpa and Chilopsis were conducted to expand the genetic base in Chitalpa. First flowering of triploid Chitalpa has occurred facilitating initial screening for elite clones. The Catalpa germplasm and breeding collection is being utilized for taxonomic studies. A review of North American and European botanical collections and nursery industries revealed the breadth and depth of taxonomic issues in Asian Catalpa, particularly the Catalpa bungei-fargesii-duclouxii complex. Controlled pollinations were repeated to create novel hybrid combinations in Tsuga, including intra- and interspecific crosses. A long term test site was established in North Carolina for elite clones of Tsuga to test cold-hardiness and resistance to hemlock woolly adelgid under high inoculation pressure in situ. New Nyssa hybrids were produced from isolation block at the U.S. National Arboretum. Screening of Nyssa hybrids for leaf spot tolerance, improved plant habit, and fall color continued. Additional plantings of Acer, Aesculus, Catalpa, Chitalpa, Celtis, Pistacia and Ulmus have been added to permanent field plots. Plants of a novel dwarf saucer magnolia were distributed to industry cooperators for evaluation.

4. Accomplishments

Review Publications
Brummer, E., Barber, W.T., Collier, S., Cox, T.S., Johnson, R., Murray, S., Olsen, R.T., Pratt, R., Thro, A. 2012. Plant breeding for harmony between agriculture and the environment. Frontiers in Ecology and the Environment. 9:561-568.

Last Modified: 06/24/2017
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