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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #435012

Research Project: A Horticultural and Genetic Characterization of Oak Leaf Hydrangea (Hydrangea quercifolia Bartrm.) Collected Across Its Range of Occurrence

Location: Floral and Nursery Plants Research

Project Number: 8020-21000-072-05-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Aug 1, 2018
End Date: Jul 31, 2021

1) Describe the distribution of genetic diversity and spatial genetic structure of previously collected populations across the native range of oakleaf hydrangea, and 2) Identify and analyze the full range of existing variation for key horticultural traits and descriptors among selected clones and seedlings derived from seeds collected across the six-state range of occurrence for the species.

Genetic diversity characterization: Genetic diversity characterization will be done at the University of Minnesota Genomics Center (UMGC) in three phases. In Phase 1, we will use the draft genome assembly of H. macrophylla (produced by Lisa Alexander at USDA-ARS) to first identify an ideal restriction enzyme combination for genotyping-by-sequencing (GBS) utilizing an in-silico analysis. In Phase 2, we will use the GBS protocol to sequence 180 individuals (2 from each of 90 populations) across the range of occurrence for the species. In Phase 3, we will use these GBS markers in combination with a set of SSR markers to develop an amplicon sequencing (AmpSeq) marker panel that will allow us to cost-effectively genotype the entire set of collected plants (~1,800 adult plants, 200 seedlings). Extant, adult populations across the range of occurrence for the species (~1,800 genotypes) will be analyzed for the number of alleles/locus, genotyping errors, occurrence of null alleles, observed and expected heterozygosity, fixation index, genetic differentiation, spatial genetic structure, and clonal structure. Seedling populations derived from seeds collected from randomly selected maternal parents in the adult study (~200) will be subjected to the same analysis listed above. Horticultural characterization: (Minnesota). University of Minnesota is currently growing ~15,000 seedlings from sixteen populations collected in 2017 for laboratory-based cold hardiness testing that will commence in the winter of 2019. A freezer-based test of inter-nodal stem hardiness of a subset of the seedlings that is routinely employed in the Hokanson lab will be used. The test will be non-destructive, leaving the plants in-tact for subsequent horticultural characterizations. Based on the laboratory-based cold hardiness assessment, populations that demonstrate higher than average cold hardiness will be targeted for field testing in Minnesota. (Tennessee). In order to observe the maximal amount of horticultural variation, the majority of the horticultural characterizations will be conducted by ARS at the Tennessee State University Otis L. Floyd Nursery Research Center in McMinnville, TN. This will avoid the pre-emptive killing of large proportions of the germplasm due to winter cold in Minnesota. This evaluation will provide an understanding of the range of variation for traits of horticultural/breeding interest in the species. ARS will collect data for a number of horticultural characteristics and GRIN descriptors including, average leaf size, lobe number and sinus depth, leaf color (mid-summer and peak fall), leaf quality (disease), plant form (height/width), date of first flower, average number of inflorescences, average inflorescence width and length, color, peak flower date, date of initial fall foliage color, fall foliage color and rating, plant disease rating, and population mortality rate.