Characterization of Elm Germplasm of Horticultural Interest
Floral and Nursery Plants Research Unit
2013 Annual Report
1a.Objectives (from AD-416):
Characterize germplasm of elms with potential importance to the American nursery industry, concentrating on recently introduced species and on newly discovered genetic races of native species. Analyze genetic diversity among elm accessions and the phylogenetic relationships among them. Provide genetic markers and taxonomically well-identified and characterized germplasm that will be useful for elm research and breeding in the future.
1b.Approach (from AD-416):
Accessions will be identified according to the latest understanding of elm taxonomy, collecting herbarium specimens at different times of the year to allow coding of characters of the flowers, fruit, and leaves, and winter buds. Genetic diversity and phylogenetic relationships will be analyzed by DNA analysis of appropriate nuclear and chloroplast regions, evaluating new markers as necessary. Genome size and ploidy of representative accessions will be investigated using flow cytometry and (if necessary) chromosome counts.
This year we compared DNA sequences of representative elm accessions for two single-copy nuclear genes, glutamine synthetase (ncpGS) and nitrate reductase (nia), and prepared phylogenies for these two genes. The gene phylogenies share many topographic features, indicating that we are building an understanding of the underlying organismal phylogeny; however, there are some inconsistencies between the sequences, and the reasons for these inconsistencies must be investigated. Additional accessions will be added to the dataset to improve resolution of the phylogeny.
In addition to the sequencing work, we have continued to collect herbarium specimens to preserve flowering, fruiting, and leaf material of elm germplasm in the living collections of the National Arboretum (DC and Maryland) and Morton Arboretum (Illinois). Study of these specimens has allowed us to correct some significant errors in identification of this material, which is used for research and (potentially) for future breeding and commercial release.