Location: Floral and Nursery Plants Research
Project Number: 8020-21000-087-000-D
Project Type: In-House Appropriated
Start Date: Feb 14, 2023
End Date: Feb 13, 2028
Objective 1. Characterize, evaluate, breed, select, and release improved woody landscape plant germplasm such as ornamental cherry, hemlock, catalpa, elm, boxwood, crapemyrtle, and redbud with superior disease and pest resistance, non-invasiveness, climate resilience, and improved ornamental traits. Sub-objective 1a: Develop and evaluate intra- and interspecific hybrids and breeding populations to use as genetic mapping families and for use in cultivar development, with a focus on Prunus (flowering cherry), Ulmus (elm), Buxus (boxwood), Lagerstroemia (crapemyrtle), and Cercis (redbud). Sub-objective 1b: Propagate and evaluate advanced selections of Prunus, Tsuga, Ulmus, Buxus, Lagerstroemia, and Cercis developed in previous breeding cycles through multi-location, replicated field trials. Sub-objective 1c: Name, release, distribute, and promote new cultivars. Objective 2. Develop genomic resources for genetic mapping of key traits and phenotypic methods for trait characterization and quantification to accelerate breeding and selection in Buxus, Cercis, Prunus, and Lagerstroemia. Sub-objective 2a: Develop and utilize quantitative high-throughput phenotyping methods for ornamental traits and evaluate disease resistance of boxwood hybrids and germplasm. Sub-objective 2b: Create reference genomes by sequencing and assembling genomes of accessions, cultivars, and parental lines of Buxus. Sub-objective 2c: Establish a foundation for genetic mapping, gene identification, and marker-trait analysis by genotyping germplasm and hybrid progeny in Buxus, Cercis, Prunus, and Lagerstroemia. Objective 3. Develop and apply biotechnology to accelerate characterization, identification, selection, or breeding of priority plant materials for key traits, with a focus on disease and pest resistance in Buxus and plant architecture and flowering traits in Prunus. Sub-objective 3a: Establish efficient micropropagation, regeneration, and transformation systems for selected flowering cherry (Prunus) and boxwood (Buxus) genotypes. Sub-objective 3b: Identify genes or genetic elements in flowering cherry and boxwood for targeted traits and use transgenic and gene editing approaches to modify gene expression. Sub-objective 3c: Characterize and evaluate selected transgenic or gene-edited plants.
The approach for Objective 1 uses traditional methods of plant breeding, selection, and evaluation. We will focus on Prunus, Ulmus, Buxus, Lagerstroemia, and Cercis to develop plants that are disease resistant, have superior ornamental or growth characteristics, and are tolerant of abiotic stresses. Controlled intra- and interspecific hybridizations will be carried out by hand or by insects to produce hybrid progeny, to determine compatibility among parents, and to study breeding systems and inheritance of traits of interest. Resultant progeny will be evaluated, and selections will be evaluated in replicated field trials. We will introduce new plants in consultation with ARS’s Office of Technology Transfer (OTT) and stakeholders following standard ARS administrative approval procedures. Promotional materials (fact sheets, press kits for garden writers, information on the USNA website) will be prepared and distributed. Propagation material in the form of rooted cuttings (preferably) or cuttings will be sent to nurseries upon request until the cultivar is routinely available in the trade. The approach for Objective 2 will be based on molecular breeding, genetics, and machine learning methodologies to develop mapping tools and to facilitate trait discovery. We will develop a large image data set of boxwood blight-infected plants to develop a convolutional neural network (CNN) to assist in detecting and monitoring infected boxwood plants. We will also develop a 3D imaging pipeline for measuring plant architecture traits to develop marker-trait associations for breeding and selection. We will use next-generation sequencing technologies to create reference genomes of two boxwood genotypes (B. harlandii 60705 and B. microphylla ‘Little Missy’). We will map QTLs, establish multi-environmental genome-wide association (GWA) mapping trials of B. sempervirens, and develop SNP markers based on genotyping-by-sequencing (GBS) methodologies. In addition to Buxus, we will use GBS or de-novo sequencing and assembly for novel trait discovery in Cercis, Prunus and Lagerstroemia. These traits include growth habit, leaf and flower color, and reblooming traits that can be used for gene-editing technologies in Objective 3. The approach for Objective 3 focuses on developing and utilizing new breeding tools and technologies to characterize, select, and develop superior cultivars of ornamental plants, particularly establishing and optimizing transgenic and gene-editing methods in Prunus and Buxus. We will first establish an efficient in vitro axillary proliferation and regeneration system, including testing selectable markers. We will establish a protoplast isolation and culture protocol and test various developmental regulator genes and growth-regulating factors for their effects on promoting regeneration. Finally, we will develop a genetic transformation system in both genera, focusing on Agrobacterium-mediated transformation and biolistic particle bombardment methods. We will characterize these new transformed and gene-edited plants by PCR and sequencing, propagation to ensure stability, and in growth chambers or greenhouses to assess phenotype.