Location: Floral and Nursery Plants Research
2019 Annual Report
Objectives
Objective 1: Characterize and evaluate, breed, select, and release improved germplasm for woody landscape plants that have superior ornamental value, are tolerant of biotic and abiotic stress, and are not invasive. [NP301, C1, PS1B; C2, PS2A]
Sub-objective 1a: Characterize germplasm and develop hybrids or breeding lines in genera currently under investigation, including Buxus, Cercis, Lagerstroemia, Prunus, and Ulmus.
Sub-objective 1b: Propagate and evaluate (in-house and via cooperators) advanced selections of Buxus, Catalpa, Cercis, Nyssa, Lagerstroemia, Prunus, and Tsuga developed in previous cycles.
Sub-objective 1c: Name, release, distribute, and promote new cultivars.
Objective 2: Incorporate modern breeding tools to accelerate the creation, characterization, identification, selection, or evaluation of priority plant materials. [NP301, C1, PS1B; C2, PS2A]
Sub-objective 2a: Test genes for altered plant architecture (developed previously by ARS scientists) in several woody ornamental plant genera.
Sub-objective 2b: Use molecular markers to characterize germplasm or hybrids in Buxus and Tsuga, where phenotypic traits are ambiguous.
Approach
Objective 1: For classical breeding work, parental germplasm will be collected from native habitats, botanical repositories, and commercial sources, and will be evaluated in the polyhouse or field plots. Controlled hybridizations will be carried out in the field or greenhouse by hand or by insects in pollination cages or greenhouses to produce hybrid progeny, to determine compatibility among parents, and to study breeding systems and inheritance of traits of interest. Appropriate reciprocal and test crosses will be conducted for inheritance studies. In addition to traditional evaluations and classical breeding methodologies, several techniques will be used to characterize parental germplasm and develop hybrids. This includes ploidy analysis and manipulation and creating interploid hybrids and wide hybrids in order to develop seedless selections of priority genera. Resultant progeny will be screened for ploidy and evaluated for traits of interest. Promising selections will be propagated and transplanted to the field for further evaluation.
Selections developed during previous project cycles that have performed well will also be propagated. These include elite clones of Buxus, Catalpa, Cercis, Nyssa, Lagerstroemia, Prunus, and Tsuga. Nursery cooperators, botanical gardens, or other cooperators will be chosen based on hardiness zone and production system, and at least three plants of each selection will be sent to each cooperator for evaluation. In consultation with ARS’s Office of Technology Transfer, plants selected for release will undergo stock increase by volunteer cooperators and will be released following the standard ARS administrative approval procedures. Promotional materials will be prepared and distributed. Propagation material will be sent to nurseries upon request until the cultivar is routinely available in the trade.
Objective 2: For the first few years of this five-year plan, we will focus on establishing in vitro cultures of diverse woody taxa that would have the most impact from altered plant architecture (for example maples, crapemyrtles, beech, oaks, elms, flowering cherries). We will attempt to establish many diverse taxa in culture, recognizing that some taxa won’t be successful, and then focus on those few that perform well in terms of multiplication and regeneration using updates of protocols established already in our lab. Explants will consist of shoot tips, dormant buds, or seeds. Different protocols for regeneration, including organogenesis and embryogenesis, will be tested with ARS collaborators.
Appropriate molecular markers will be used in conjunction with classical taxonomy and, when appropriate, ploidy analysis to determine genetic relationships among taxa and verify parentage of hybrids. Efforts will focus on markers in hemlock and boxwood for the first few years.
Progress Report
This is the first full year of this project, with substantial progress made towards all objectives. A new scientist (Research Geneticist) came onboard on April 2019. Progress towards Objectives 1a and 2b includes testing the identity of several boxwood accessions that are currently unknown or have ambiguous taxonomic relationships. Revealing the genetic identity and taxonomic relationships of the remaining material in the boxwood collection will help inform future breeding decisions. This work is being conducted using previously identified molecular markers for boxwood. To address Sub-objective 1a, 80 boxwood hybrids have currently been screened for disease resistance to boxwood blight using a lab-based inoculation assay developed in-house. Work will continue on screening and evaluating the remaining boxwood hybrids developed previously. Additional diagnostic tools are being developed to test manual disease ratings versus computer imaging analyses for more accurate and efficient boxwood blight evaluations. Additional progress towards Objective 1 includes evaluation of Prunus and Lagerstroemia hybrids and selection of at least 35 unique plants to propagate for further evaluation. Progress towards Objective 2 includes establishment of 10 boxwood cultivars in vitro to create a plant tissue culture protocol for boxwood. Shoot tips from these 10 selected boxwood cultivars were established in three different artificial media and are currently under evaluation.
Accomplishments
1. Chinese hemlock accessions in the U.S. show extensive molecular genetic diversity. Hemlocks play an important role in forest ecosystems as well as in cultivated landscapes. The most significant species in the U.S., the Canadian hemlock, is under attack by the hemlock woolly adelgid, an insect that has caused widespread loss of these trees; therefore, finding resistant species of hemlock has become increasingly important. While several Asian species are tolerant to the pest, the Chinese hemlock appears to have the combination of resistance, shade tolerance, adaptability to poor soil, cold hardiness, and vigorous growth that make it especially promising for cultivation in landscapes and possibly managed forest ecosystems. ARS scientists in Beltsville, Maryland, evaluated the molecular genetic diversity of 35 accessions of Chinese hemlock held in collections in the U.S. and determined that significant genetic diversity is available in the existing U.S. collections of T. chinensis, and represents the wild gene pool well. This characterization of germplasm can be important in driving decisions about collections management, breeding methods, and forest or ecosystem management.
