Location: Floral and Nursery Plants Research
2023 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 final year of this project, which will expire in late 2023 when the new project plan is implemented. Substantial progress was made towards all objectives. Under Objective 1, we evaluated and selected 15 interspecific Buxus hybrids for advanced selection from the previous year which we have propagated and are evaluating further. The plants will be sent to a cooperating research partner/stakeholder for field testing, landscape evaluation, and boxwood blight resistance evaluation. An MTRA was implemented for this research collaboration. Boxwood hybrids from the 2022/23 breeding season have germinated and have been individually potted for further evaluation. Twenty-one unique interspecific controlled cross pollinations were completed with ripening fruit still being monitored for harvest. This work uses previously generated hybrids from the USNA breeding program to generate BCF1 and F2 populations for cultivar development and genetic mapping populations.
We began propagating a new xChitalpa hybrid for release. This is the first triploid hybrid between Catalpa and Chilopsis from the USNA, and was selected for its pink flowers and tree-like habit. We are also propagating and preparing to release a new dwarf Catalpa introduction selected by a former scientist in this project.
We have 41 diploid, triploid, and tetraploid American elm selections accessioned in conjunction with the USNA Taxonomy Project. Working collaboratively with partners from SUNY College of Environmental Science and Forestry, we sampled leaf, stem, bud and flower life stage of diploid elm between January and May 2023 to send for RNA sequencing for an American elm genome and transcriptome sequencing project. We are currently rooting several cuttings of the accession U. americana “Montgomery” to sequence root tissue for this project.
Under Objective 2, we designed and generated multiple overexpression or silencing constructs for the genes that related to plant architecture in flowering cherry. Some of the overexpression constructs will also be used for ectopic expression in other species, such as crapemyrtle. We are also making silencing constructs for crapemyrtle and gene editing constructs for both flowering cherry and crapemyrtle. We have established an organogenesis-based regeneration system for two genotypes of flowering cherry. We are also applying and optimizing a callus-induced regeneration method developed by a collaborator at Texas A&M University for Lagerstroemia speciosa in genotypes from our breeding program. From this foundational work, we began work to develop an efficient Agrobacterium-mediated transformation method in both flowering cherry and crapemyrtle.
Accomplishments
1. Optimized DNA extraction from herbarium samples. Herbarium specimens are becoming increasingly recognized as a vital resource of genetic information to help answer questions related to taxonomic identity, evolutionary relationships, genetic diversity, and many other aspects across the biological sciences. Preserved collections also provide the opportunity to study taxa from wide geographic distributions, undescribed or even extinct species, as well as samples from remote locations where obtaining in situ samples may be cost- or time-prohibitive, allowing the opportunity for improved phylogenetic or conservation studies. However, extracting usable DNA from herbarium samples is often hindered by the age or condition of the sample and resulting degradation of DNA. ARS scientists from Washington, DC, optimize a DNA extraction protocol for recalcitrant plant taxa to obtain high-quality DNA from preserved herbarium tissue suitable for downstream PCR applications. This protocol, which is simple, fast, and uses standard laboratory-grade chemicals, yields DNA from herbarium specimens that is comparable in quality to that from commercially available kits, and is of sufficient quality and quantity for other applications.
Review Publications
Omolehin, O., Keller, J., Gouker, F.E., Daughtrey, M., Luster, D.G., Pscheidt, J., Hong, C. 2022. Combating an invasive boxwood pathogen – Calonectria pseudonaviculata – in the United States by shifting production to less susceptible cultivars . Plant Disease. https://doi.org/10.1094/PDIS-09-22-2124-RE.
Huang, D., Gao, L., Mcadams, J., Zhao, F., Lu, H., Wu, Y., Martin, J., Sherif, S.M., Subramanian, J., Duan, H., Liu, W. 2022. Engineered cleistogamy in Camelina sativa for bioconfinement. Horticulture Research. https://doi.org/10.1093/hr/uhac280.
Duan, H., Moresco, P., Champouret, N. 2023. Characterization of host-effector transcription dynamics during pathogen infection in engineered late blight resistant potato. Transgenic Research. https://doi.org/10.1007/s11248-023-00340-2.
Bentz, S.E., Gouker, F.E., Olsen, R.T., Pooler, M.R. 2023. Tsuga ‘Traveler’ and ‘Crossroad’ – the first adelgid-resistant interspecific hemlock hybrids. HortScience. 58(3):289–290. https://doi.org/10.21273/HORTSCI16918-22.
Gouker, F.E., Guo, Y.H., Svoboda, H.T., Pooler, M.R. 2023. Optimizing efficient PCR-amplifiable DNA extraction from herbarium specimens. Applications in Plant Sciences. https://doi.org/10.1002/aps3.11521.
Li, X., Tseng, H.T., Hemmings, G., Omolehin, O., Taylor, C., Taylor, A., Kong, P., Daughtrey, M., Gouker, F.E., Hung, C. 2023. Boxwood Epiphytic and Endophytic bacterial communities and their differential responses to systemic and contact fungicides. Microbiology Spectrum. https://doi.org/10.1128/spectrum.04163-22.
Bentz, S.E. 2023. ‘Traveler’ Hemlock. American Conifer Society Bulletin. 40(1):11-12.
