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United States Department of Agriculture

Agricultural Research Service


Location: Floral and Nursery Plants Research

2011 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. Controlled pollinations were conducted on novel hybrid combinations, including intra- and interspecific crosses in Tsuga. A three-year study testing resistance of container-grown Tsuga hybrids to hemlock woolly adelgid was concluded. Elite clones, demonstrating resistance to hemlock woolly adelgid, have been propagated for distribution to nursery collaborators. Isolation blocks of Nyssa continue to yield hybrid seed for building larger populations of advanced hybrids for screening for leaf spot tolerance, improved plant habit, and fall color. A two-year powdery mildew evaluation of Catalpa germplasm was completed which will lead to new sources of powdery mildew resistance and elite plants for the nursery industry. Additional plantings of Aesculus, Catalpa, Chitalpa, Chionanthus, Halesia, Pterostyrax, Pistacia and Nyssa have been added to permanent field plots. Molecular markers from Chinese fringe tree (Chionanthus retusus) 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. These are the genetic strains now available in North America for improvement of the Chinese fringe tree. 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. Molecular genetic characterizations of five populations of the common fringe tree are now underway, and accessions of the pygmy fringe tree will be added to this study. The catalpa germplasm and breeding collection is being utilized for taxonomic studies. Catalpa plants were grown out and observed throughout their complete life cycle. The living plants were compared with dried plants. The dried museum specimens were grouped together into recognizable units corresponding to similar groupings among the living plants. Their vegetative and reproductive organs were examined as living material and compared to the same organs on dried specimens. Suitable, fresh organs were examined in detail to determine the relationships among the organs, their shapes, and sizes. The type specimen for the northern catalpa was reviewed, and its designation was clarified and amplified to insure the proper application of its scientific name. Attempts to extract and characterize DNA from living catalpa tissues were unsuccessful. The techniques will be modified, and the new procedures carried out to collect and characterize catalpa DNA in order to verify species and hybrids in the breeding program.

4. Accomplishments

Last Modified: 08/20/2017
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