Location: Floral and Nursery Plants Research2010 Annual Report
1a. Objectives (from AD-416)
Accelerate development of superior Hydrangea germplasm using wide hybridization, molecular markers, and ploidy manipulations. Develop, evaluate, and release improved germplasm of selected nursery crops species, including Hydrangea, Cornus, Clethra, and Styrax. Investigate physiological constraints with transplanting nursery crops and root system changes for better adaptation into production systems. Develop improved nursery production systems with an integrated approach of bio-plastic containers, plant water and nutrient use, and cultural management.
1b. Approach (from AD-416)
Use wide hybridization to improve H. macrophylla. Use molecular markers for studying genetic relationships and creating genetic linkage maps in Hydrangea. Develop a polyploid series in H. macrophylla. Develop, evaluate, and release improved germplasm of Hydrangea, Cornus, Clethra, and Styrax. Evaluate germplasm for nursery production and landscape potential. Determine root growth, root quality and plant performance in non-traditional nursery containers. Determine transplantability and survivability of bare root trees during nursery production and in post harvest landscape settings. Determine the relationship of cyclic irrigation and low nutrient inputs with container-grown ornamental trees. Determine the influence of irrigation and nutrient inputs on bio-based materials for container nursery production.
3. Progress Report
We continued evaluating progeny derived from hybridizations of Hydrangea macrophylla and Dichroa febrifuga. Hybrids produced from crosses of diploid and tetraploid selections of D. febrifuga were evaluated and backcrossed to H. macrophylla. Four plants derived from crosses of hexaploid D. febrifuga with triploid H. macrophylla were selected and propagated. All four had flowers with sepals ranging in color from pink to purple with streaks of deep green, but differed in plant size and inflorescence form. These are currently being evaluated for potential commercial value. The ploidy level of 20 Hydrangea macrophylla plants obtained from crosses between two diploid cultivars, one of which (‘Trophee’) had previously been found to produce unreduced gametes, was determined. All but one plant were found to be triploids, indicating that unreduced gametes can be used for producing bigleaf hydrangea polyploids. Additional hybridizations were made using ‘Trophee’ and a variety of H. macrophylla cultivars. Two cultivars of oakleaf hydrangea (Hydrangea quercifolia) were released. ‘Ruby Slippers’ and ‘Munchkin’ are compact cultivars with large, full inflorescences that are held above the foliage. Another oakleaf hydrangea selection was propagated for distribution to cooperators for evaluation. Cooperators were allowed to begin propagating a yellow-leafed Clethra alnifolia in anticipation of its release as a cultivar. This plant, which was selected from an F2 population between ‘Compacta’ and ‘Ruby Spice’, is the first chlorophyll-mutant of C. alnifolia described Growth and flowering period evaluation for thirty five Lagerstroemia varieties was completed. An evaluation of nutrient input and irrigation management for container grown trees was continued. Nutrient loss via substrate leaching was influenced by the time of daily irrigation and emitter selection when Acer rubrum ‘Sun Valley’ maple was grown in large nursery containers. Evaluation of application rate and method of application of neonicotinoid insecticides for trunk protection of A. rubrum cultivars from flatheaded borer attack was completed. Bio-based nursery containers were evaluated for structural integrity and subsequent plant growth of selected herbaceous and woody perennials.
1. Release of two oakleaf hydrangea cultivars. Oakleaf hydrangea (Hydangea quercifolia) is a popular summer-flowering shrub that is native to the southeastern U.S. Most cultivars grow 6 to 8 feet in height and are not suitable for use in small gardens; the two smaller-growing cultivars that are commercially available have inferior floral qualities. An ARS scientist in McMinnville, Tenn. developed two compact selections of oakleaf hydrangea (Hydrangea quercifolia) with large, full flower heads that are held above the foliage for maximum visual impact. ‘Ruby Slippers’ grows 4 feet tall and has flowers that age to a bright rose color , while ‘Munchkin’ grows 3 feet tall and has flowers that turn medium pink at maturity. Both cultivars should result in increased sales for nurseries and garden centers. Gardeners will benefit from the availability of new, improved cultivars. These cultivars should be of particular value in small residential landscapes where standard cultivars of oakleaf hydrangea are not suitable.
5. Significant Activities that Support Special Target Populations
Scientists presented educational talks at the Tennessee Small Farm Expo, which was sponsored by Tennessee State University. (an 1890's Historically Black College) Scientists also participated in a Specific Cooperative Agreement with Tennessee State University entitled “Evaluation of Production Practices, Disease Resistance and Insect Control Measures for Nursery Crops”. The objectives of this project are to: 1) develop new and improved ornamental trees and shrubs for the U.S. nursery industry; 2) develop basic genetic and physiological information related to nursery crop species; 3) reduce pesticide use and fertilizer run-off during nursery crop production; 4) develop improved nursery crop propagation methods; 5) evaluate existing germplasm of ornamental trees and shrubs for pest resistance, tolerance of environmental stress, and superior ornamental value; and, 6) develop methods for control of imported fire ant on field-grown nursery stock. Additional details can be found in the annual report for this project. (1230-21000-052-04S)
Li, Y., Windham, M., Trigiano, M., Rinehart, T.A., Reed, S.M., Spiers, J.M. 2010. Assesment of resistance components of bigleaf hydrangeas (Hydrangea macrophylla) to Erysiphe polygoni in vitro. Canadian Journal of Plant Pathology. 31:348-355.