Location: Floral and Nursery Plants Research2009 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
Diploid, tetraploid and hexaploid selections of Dichroa febrifuga were identified. Genetic relationships among Dichroa taxa were analyzed using molecular markers. One species, D. versicolor, was found to be a naturally occurring hybrid between D. febrifuga and Hydrangea macrophylla. Seedlings were obtained by hybridizing H. macrophylla to diploid and tetraploid selections of D. febrifuga. An evaluation of powdery mildew resistance among H. macrophylla cultivars was completed. Cold hardiness of hybrids between Clethra alnifolia and C. cavaleriei was determined. Seed set and germination percentage were recorded for thirty five Lagerstroemia cultivars. 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 with Acer rubrum ‘Sun Valley’. Spring applications of several rates of neonicotinoid insecticides were tested with two sizes of A. rubrum.
1. Evaluation of Bigleaf Hydrangea for Powdery Mildew Resistance. An ARS scientist in McMinnville, Tennessee, in cooperation with University of Tennessee and Tennessee State University scientists, identified cultivars of bigleaf hydrangea (Hydrangea macrophylla) with resistance to a fungal pathogen. Bigleaf hydrangea is a popular ornamental shrub that is cultivated both as a garden and a pot plant, but can become disfigured by powdery mildew during late summer in the landscape and when produced in a greenhouse. This disease is most severe on plants grown in humid, shaded environments. The identification of cultivars with powdery mildew resistance provides information needed by growers in selecting cultivars for production and by landscapers and home gardeners in choosing the best cultivar for their growing conditions. This information will also be of value to plant breeders when selecting parents for developing disease resistant bigleaf hydrangea.