The genetic diversity of triploid Celtis pumila and its diploid relatives C. occidentalis and C. laevigata (Cannabaceae)

Authors: HAYES, ANDREW - Agri Food - Canada; WANG, SONG - Agri Food - Canada; Whittemore, Alan; SMITH, TYLER - Agri Food - Canada

Submitted to: Systematic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2022
Publication Date: 6/14/2022
Citation: Hayes, A., Wang, S., Whittemore, A.T., Smith, T. 2022. The genetic diversity of triploid Celtis pumila and its diploid relatives C. occidentalis and C. laevigata (Cannabaceae). Systematic Botany. 47(2):441-451. https://doi.org/10.1600/036364422X16512564801713.
DOI: https://doi.org/10.1600/036364422X16512564801713

Interpretive Summary: The genus Celtis (hackberry, sugarberry) is a group of native trees and shrubs whose tolerance for difficult conditions (heat, cold, poor soil) makes them potentially useful as landscape trees in difficult sites. Finding wild populations with characteristics that could be useful in cultivation has been difficult because our native Celtis species show unusual patterns of variation, partly because many of the plants produce seeds clonally, without crossing with other plants. A team of scientists used DNA markers to study the distribution of genetic variation in all species of Celtis native to the eastern United States, confirming the classification we have used in the past, but also finding unexpected variation in the clonal species. This information will help tree breeders and horticulturalists to identify new sources of genes for these stress-tolerant trees and shrubs.

Technical Abstract: The genus Celtis in eastern North America shows puzzling patterns of variation. While three species are generally recognized, many authors have suggested hybridization may be blurring the boundaries among them. We collected tissue samples from populations of all three taxa across the full range of C. pumila. Flow cytometry data confirm the co-occurence of diploids and triploids across this range, and, at two locations, tetraploids. Microsatellite data confirm that there are two diploid species, C. occidentalis and C. laevigata, and that they do hybridize where they co-occur in southern Missouri and Illinois. Apomictic triploid plants, corresponding to C. pumila (or C. tenuifolia) of recent treatments, showed a low number of multilocus genotypes, consistent with other data indicating they are apomictic. Ordination of SSR data from these triploids showed two clusters which were geographically separate but could not be clearly defined morphologically, though the northern cluster showed some subtle genetic and morphological similarity to C. occidentalis, while the southern group was more similar to C. laevigata. The cluster also included two tetraploid plants, and the sole population of the western C. reticulata that was sampled. While there may be rare gene-flow from the diploids to the triploid, most triploid populations are dominated by one or a few apomictic clonal genotypes.