Location: Floral and Nursery Plants Research
2021 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.
Additional resources in the merged project will strengthen the research in the current Objective 2:
Objective 2: Incorporate modern breeding tools to accelerate the creation, characterization, identification, selection, or evaluation of priority plant materials. [NP301, C1, PS1B; C2, PS2A]
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 third full year of the project with substantial progress made towards all objectives. Progress towards Objectives 1a, 1b, 1c includes acquiring, characterizing, breeding, and evaluating accessions in the USNA germplasm collection. Previous boxwood accessions acquired through cooperators have been propagated and are currently under evaluation for key ornamental traits. Four new boxwood cultivars released from Belgian collaborators and two cultivars released by a U.S. nursery have been evaluated for boxwood blight resistance using an in-house boxwood blight leaf assay. All hybrids created in previous years have been evaluated for boxwood blight resistance; advanced selections will be propagated in late summer for further field evaluations by an industry collaborator via a MTRA. The collaborator will also send ARS unreleased boxwood hybrids for blight resistance evaluation using our detached leaf assay. The parentage of recently released industry hybrids are also being determined using phylogenetic and ploidy analysis since they were generated from open pollinated seeds. Additionally, a deep learning model for classification and quantification of boxwood blight is under development using images generated from screening boxwood accessions and hybrids using the detached leaf assay. Additional images are being generated to further train the model using a second version of open-source software. To-date we have achieved 96% accuracy for boxwood blight detection.
Boxwood hybrid seeds generated from last year’s crosses have been planted out in the polyhouses for further evaluation. Creation of new hybrids is underway including collection, stratification, and germination of seeds from controlled cross pollinations and open pollinations. This year 40 interspecific and interploid Buxus crosses have been made with approximately 80% of them currently developing fruit. Additionally, four interspecific Prunus crosses were conducted to generate flowering cherry hybrids segregating for flower shape, plant architecture, and disease resistance.
To address Objective 2 - Incorporate modern breeding tools to accelerate the creation, characterization, identification, selection, or evaluation of priority plant materials - the draft genome and transcriptome of an industry standard boxwood cultivar, Buxus sempervirens ‘Suffruticosa’ has been completed. Two next-generation sequencing platforms were used to generate a draft genome, and RNA was also sequenced to develop a reference transcriptome. A reference genome was developed that will be used for molecular marker and gene discovery that will facilitate breeding of this genus. Further analyses will be conducted to polish the genome and transcriptome that will be made publicly available in the online database Phytozome. This will represent the first published genome for the genus Buxus. Also, under Objective 2, we successfully established in-vitro cultures of four Buxus and three Prunus genotypes for downstream use in biotechnology applications or to facilitate propagation (Prunus).
Accomplishments
Review Publications
Gouker, F.E., Guo, Y., Pooler, M.R. 2020. Using acetone for rapid PCR-amplifiable DNA extraction from recalcitrant woody plant taxa. Applications in Plant Sciences. 8(12):e114-3. https://doi.org/10.1002/aps3.11403.
Gouker, F.E., Fabio, E., Serapiglia, M., Smart, L. 2021. Yield and biomass quality of shrub willow hybrids in differing rotation lengths and spacing designs. Biomass and Bioenergy. 146:105977. https://doi.org/10.1016/j.biombioe.2021.105977.
