Precipitation, temperature, and population structure influence genetic diversity of Hydrangea quercifolia throughout its native range

Authors: Sherwood, Andrew; Alexander, Lisa; CLARK, MATTHEW - University Of Minnesota; HOKANSON, STAN - University Of Minnesota

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2022
Publication Date: 1/4/2023
Citation: Sherwood, A.P., Alexander, L.W., Clark, M., Hokanson, S. 2023. Precipitation, temperature, and population structure influence genetic diversity of Hydrangea quercifolia throughout its native range. Journal of the American Society for Horticultural Science. https://doi.org/10.21273/JASHS05255-22.
DOI: https://doi.org/10.21273/JASHS05255-22

Interpretive Summary: Oakleaf hydrangea is a flowering shrub native to woodlands of the southeast United States. Oakleaf hydrangea has immense ornamental potential with four-season interest of showy flowers, striking foliage textures, intense fall color, and exfoliating bark. Cultivars are often derived from wild selections either directly or only a few generations removed, leading to little variety in ornamental traits like flower color, flowering time, and disease resistance. USDA scientists in McMinnville, TN, along with partners at the University of Minnesota, collected leaves from 73 oakleaf hydrangea populations across the southeast for genetic characterization. They identified six geographically defined genetic clusters, each with unique alleles. The genetic clusters at the southern extent of the range are small but contain putative adaptive alleles at relatively high frequencies. Many historically documented populations were found to be either extirpated or at risk of extirpation, highlighting the importance of preserving representative germplasm from throughout the species range. Public and private plant breeding initiatives have used this information to make targeted collection of unique alleles for breeding oakleaf hydrangea cultivars with unique traits. Land managers and planners will use this information to conserve this native plant in its natural habitat.

Technical Abstract: Oakleaf hydrangea (Hydrangea quercifolia Bartr.) is an understory shrub native to the southeastern United States. The species occupies a relatively small native range, and little is known about its demography, genetic diversity or needs for conservation. Samples were collected from 188 plants in 73 locations throughout the species range and were genotyped using genotyping by sequencing. A Structure analysis identified 6 genetic clusters which are geographically defined. Although these clusters are weakly differentiated, each has unique alleles. An environmental association analysis revealed that environmental variables explain 11.3% of genetic diversity while population structure explains 13.5%. Further, 231 putative adaptive alleles were identified, the majority of which are correlated with precipitation related variables, indicating that precipitation has an impact on genetic diversity in H. quercifolia. Many historically documented populations were found to be either extirpated or at risk of extirpation. The genetic clusters on the southern extent of the species range are relatively small and contain putative adaptive alleles at relatively high frequencies. These results highlight the importance of preserving representative germplasm from throughout the species range.