Development of new Dutch Elm disease-tolerant selections for restoration of the American Elm in urban and forested landscapes
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In: Sniezko, Richard A.; Man, Gary; Hipkins, Valerie; Woeste, Keith; Gwaze, David; Kliejunas, John T.; McTeague, Brianna A., tech. cords. 2017. Gene conservation of tree species—banking on the future. Proceedings of a workshop. Gen. Tech. Rep. PNW-GTR-963. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 53-63.
The goal of our research and development efforts is to restore American elm (Ulmus americana) as a species in both natural and urban landscapes. Accomplishing this goal requires identification/generation of additional American elm cultivars that are tolerant to Dutch elm disease (DED) caused by Ophiostoma ulmi and O. novo-ulmi, and development of methods to reintroduce American elm along the rural to urban gradient. To accomplish our goal we are screening large survivor trees for DED tolerance, generating DED-tolerant/site-adapted cultivars, generating three regional seed orchards, establishing experimental American elm restoration sites, using elm in the Appalachian Regional Reforestation Initiative, performing operational trials using elm seed along the Mississippi River, comparing local vs. DED-tolerant enriched seedlings, investigating fungal transmission in DED-tolerant selections, and investigating the basis for cold-hardiness in the American elm and the genetic as well as metabolic basis of DED tolerance. In the spring of 2016, branches containing flower buds were collected from large surviving American elm trees in New England. Pollen was collected from the flowers and was used in controlled pollinations with the DED-tolerant American elm cultivars ‘Delaware 2’, ‘Princeton’, R18-2, and ‘Valley Forge’. The mean numbers of seeds produced per cross for each DED-tolerant mother tree ranged from 0.1 to 23 per flower. Scion wood was collected from the branches and used to graft buds and scion wood to potted American elm root stock using several types of grafting techniques. Veneer and top grafting had the highest success rates (30 percent and 22 percent, respectively), followed by bottle grafts (12 percent) and bud grafts (6 percent). Top grafts, veneer grafts, and bud grafts produced the greatest growth and number of cuttings. Plants growing from successful grafts were used to generate clones by vegetative cuttings using the rooting hormone indol-3-butyric acid at varying concentrations. Sixty-five percent of the cuttings had rooted by early August, and 42 percent of the trees that rooted had also produced shoots. Clonally propagated American elm selections generated from crosses among DED-tolerant cultivars, clones of large survivor trees found in Michigan, Ohio, Illinois, and Indiana, and susceptible and tolerant controls were inoculated with a mixture of O. novo-ulmi and O. ulmi spores. For each tree, the combined percentage of the crown exhibiting wilting, chlorosis, or necrosis was visually estimated to the nearest 5 percent. The percentage of the crown exhibiting DED symptoms in trees from the Midwest and New England inoculated trees ranged from 0 to 35 percent at 4 weeks post-inoculation. Control trees (inoculated with water) in both studies exhibited from 0 to 5 percent canopy decline. Trees with high levels of DED tolerance will be released to the tree nursery industry and retained in test plots to constitute a seed orchard. Over the next 6 years approximately 16,000 elm trees—clones of survivor trees and site-adapted progeny from crosses between DED-tolerant elms and elms from the upper Midwest and New England states—will be inoculated.
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Pinchot, C.C.; Flower, C.E.; Knight, K.S.; Marks, C.; Minocha, R.; Lesser, D.; Woeste, K.; Schaberg, P.G.; Baldwin, B.; Delatte, D.M.; Fox, T.D.; Hayes-Plazolles, N.; Held, B.; Lehtoma, K.; Long, S.; Mattix, S.; Sipes, A.; Slavicek, J.M. 2017. Development of new Dutch Elm disease-tolerant selections for restoration of the American Elm in urban and forested landscapes. In: Sniezko, Richard A.; Man, Gary; Hipkins, Valerie; Woeste, Keith; Gwaze, David; Kliejunas, John T.; McTeague, Brianna A., tech. cords. 2017. Gene conservation of tree species—banking on the future. Proceedings of a workshop. Gen. Tech. Rep. PNW-GTR-963. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 53-63.