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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #434613

Research Project: Genetic Improvement of Nursery Crops through Functional Genomics and Breeding

Location: Floral and Nursery Plants Research

2023 Annual Report

Objective 1: Establish long-term experimental hydrangea populations, and develop information management systems and standards for hydrangea phenotyping and genetic mapping to accelerate the development of disease and stress resistant hydrangea cultivars with superior product quality. [NP301, C1, PS1A; NP301, C4, PS4A] Sub-objective 1.A. Establish and phenotype Hydrangea macrophylla experimental populations for identification of disease resistance and ornamental traits. Sub-objective 1.B. Establish, genotype, and phenotype a range-wide Hydrangea quercifolia collection for natural genetic variation for disease resistance and ornamental traits. Sub-objective 1.C. Develop new phenotyping methods for important traits and create associated data management systems for genomic and phenotypic data. Objective 2: Develop, evaluate, and release improved germplasm of hydrangea and other high-value, native, and underrepresented nursery crop species to expand market opportunities for producers, stimulate consumer interest, and mitigate the environmental footprint of nursery production. [NP301, C1, PS1B] Sub-objective 2.A. Accelerate the development of superior Hydrangea germplasm using ploidy manipulations, and wide hybridization. Sub-objective 2.B. Evaluate germplasm including Hydrangea, Osmanthus, and Hamamelis for nursery production and breeding improvement potential. Sub-objective 2.C - Improve resource use efficiency and/or reduce nutrient runoff in container nursery production through data-driven research on substrates, fertilizer, and irrigation.

During the next five years, Hydrangea and Osmanthus selections from previous breeding cycles will be progagated and distributed to cooperators. Germplasm evalutations of new species and cultivars will ensure a broad base for future cultivar development. We will confirm the three major powdery-mildew resistance SNPs in the two most resistant and two most susceptible cultivars using real-time PCR with TaqMan probes. Controlled crosses between the most powdery mildew-resistant and most susceptible cultivar are underway. This F1 mapping population will be genotyped via RT-PCR in the same manner as the mapping parents. This population will be planted in the field for a minimum three-year observation period. During this time, natural powdery mildew incidence and/or induced powdery mildew infection will be recorded. Digital images of each plant will be obtained in regular intervals throughout the growing season. Image analysis will be used to monitor the progression of disease infection and the number and size of new inflorescences. Together, the genotype and phenotype data will be used to refine the genome-wide association analysis, determine the efficacy of marker-assisted selection for powdery mildew resistance at the seedling stage in Hydrangea, and identify plants for further gene expression analysis. For genetic and horticultural analysis of oakleaf hydrangea, we will sample up to 20 populations within each state on a longitudinal/latitudinal cline, as well as representing the full diversity of environments in which the species occurs. Within each of these populations we will sample up to 20 plants. Three to five recently expanded leaves will be collected from selected plants, stored flat in Ziploc bags and stored in coolers with unique identifiers linked with each bag. Plant morphology, location, and other notes will be recorded using the EpiCollect5 web application. Leaves will be shipped overnight via UPS to the USDA-ARS in McMinnville, TN for processing, DNA isolation, and storage. Genotyping-by-sequencing will be performed by the University of Minnesota Genomics core facility. Bioinformatic support will be provided by the ARS NEA Statistics Group. Ten populations per state on a longitudinal/latitudinal cline, as well as representing the full diversity of environments in which the species occurs, will be evaluated for current generation estimates of genetic diversity and levels of inbreeding and for common garden horticultural characterizations in Minnesota, Mississippi, and Tennessee. Each location will evaluate 25-50 individuals of each population (60 populations total) for growth, form, floral, and disease resistance traits. Over 1500 F2 seedlings derived from hybridizations between 'Snow Queen' and the compact cultivars Pee Wee and Sikes Dwarf were evaluated for compact plant habit, quality and quantity of inflorescences, disease resistance and fall foliage color. Seven plants from this population have been selected for compact form and superior floral display. Seed and seedlings from these selected plants will be used for development of disease-screening methods.

Progress Report
This is the fifth and final report for Project 8020-21000-072-000D, which began on 4/14/2018. Significant progress was made on all Objectives, which fall under NP301. Under objective 1.A., we completed linkage mapping of a bigleaf hydrangea F1 population. We tested germination and growth of eight bi-parental F2 mapping populations, developed a new F2 mapping population, and phenotyped through the first year of growth. This well-characterized population will be used for genetic mapping of reblooming and for determining gene-trait associations. Under Objective 1.B., we selected a core collection of oakleaf hydrangea accessions for breeding and trait introgression. Under Objective 2.A., we completed genome sizing of 74 individual plants resulting from unreduced gamete breeding or mutation and continued phenotyping them for floral and disease resistance traits though Year 2. We located 13 incense-cedar populations from geographically and climactically diverse provenances and have identified collaborators to collect seed from each population. Under Objective 2.B., we evaluated 39 bigleaf hydrangea cultivars for resiliency in a full-sun production setting and compared growth, flowering, and disease severity to those grown under 47% shade. The transpiration rate per unit leaf area of 12 bigleaf hydrangea cultivars was measured and correlated with leaf wilting rate and root to shoot mass ratio to identify potentially drought- or heat-tolerant phenotypes. Under Objective 2.C., we completed evaluation of Osmanthus fragrans cultivars through third year of growth. We measured phosphorus leaching and uptake, potting media fertility, and plant growth of five economically important container-grown woody ornamental plant species when produced in substate amended with phosphorus-adsorbing ferrous sulfate. We initiated a greenhouse study to assess the availability of iron and phosphorus to iron-sensitive crops growing in peat amended with ferrous sulfate. We conducted the first of two experiments evaluating the effect of irrigation frequency and container color on root zone temperature, shoot and root growth, and controlled-release fertilizer longevity when growing red-osier dogwood in full sun. We initiated a witchhazel propagation study for which approximately 2000 stem cuttings from nine different witchhazel cultivars are being evaluated for the effect of cutting harvest timing on rooting and overwintering survival. We conducted a preliminary evaluation of rooting success of two incense-cedar cultivars.

1. Reducing phosphorus runoff from container nurseries with a soluble iron amendment. Approximately 80% of U.S. nursery operations produce crops in above-ground containers, an intensive production system that requires daily irrigation and frequent fertilization. Potting media used for container-based nursery production (e.g., pine bark, peat) retain phosphorus poorly; as a result, as much as 60% of the phosphorus fertilizer applied to container-grown nursery crops can leach out of the containers during irrigation and storm events and subsequently enter surface waters as runoff. USDA-ARS researchers in McMinnville, Tennessee, and Wooster, Ohio, developed an inexpensive approach for growers and potting media suppliers to modify pine-bark-based potting mixes to increase its phosphorus retention capacity without negatively impacting plant growth. Adding 3 kg/m3 of ferrous sulfate heptahydrate (FeSO4·7H2O) reduced phosphorus leaching 35% to 57% over the course of a growing season. Adoption of this Best Management Practice can prevent 18 -65 kg/ha P from draining from nursery containers. Costing approximately $2.60 per m3 of potting media, adding 3 kg/m3 of FeSO4·7H2O to pine bark potting media is an inexpensive and scalable production practice that both small and large nursery operations can adopt and include in their state-mandated nutrient management plans.

Review Publications
Alexander, L.W. 2023. Genome size, flowering, and breeding compatibility in Osmanthus. Horticulturae.
Parajuli, M., Liyanapathiranage, P., Neupane, K., Shreckhise, J.H., Fare, D., Moore, B.T., Baysal-Gurel, F. 2023. Tree architecture and powdery mildew resistance of yellow-flowering magnolias in Tennessee, USA. HortScience.
Parajuli, M., Liyanapathiranage, P., Shreckhise, J.H., Fare, D., Moore, B.T., Baysal-Gurel, F. 2022. Cercospora leaf spot resistance of Crapemyrtle cultivars in Tennessee, USA. HortScience.
Shreckhise, J.H., Owen Jr, J.S., Niemiera, A.X., Altland, J.E. 2022. Growth and quality response of four container-grown nursery crop species to low-phosphorus controlled-release fertilizer. HortTechnology. 32(5):447-458.