Elm Hybridization and Dutch Elm Disease

Dutch elm disease, hybridization and genetic diversity of native and invasive elm species

This work started when Dr. Juan Zalapa came to do postdoctoral work in the laboratory under an NSF minority fellowship. Together with Dr. Zalapa and Dr. Guries, the elm breeder at UW-Madison at the time (now retired), we have examined the pattern of hybridization between the native Red elm, Ulmus rubra, and an invasive exotic species, the Siberian elm, Ulmus pumila. We have developed species-specific microsatellite markers that permitted the genetic identification of putative hybrid individuals in contact zones between the two parental species (Zalapa et al. 2008, Molecular Ecology Resources); we have described the genetic diversity of U. pumila present at the UW Arboretum in Wisconsin and planted from seeds originally collected throughout China (Zalapa et al. 2008, Genome). We have confirmed genetically the presence of hybrids between U. pumila and the native U. rubra and identified a pattern of introgression biased towards U. pumila (Zalapa et al. 2009, American Journal of Botany). Finally, we have established the widespread presence of hybrids in naturalized U. pumila populations in Wisconsin and beyond (Zalapa et al. 2010, Evolutionary Applications).  We have collaborated with Dr. Alberto Santini, a forest plant pathologist in Italy, to examine patterns of hybridization between U. pumila and a native European elm, Ulmus minor (Brunet et al. 2013, Biological Invasions). Our results are raising serious concerns about the long-term survival of native elm species in the U.S. and potentially Europe. We also collaborated with a german PhD student who examined whether hybrids existed when U. pumila was planted in regions that did not have native elm species (Hirsch et al. in review, Biological Invasions). Finally, we have examined the impact of Dutch elm disease (DED) on the genetic diversity and level of genetic differentiation among populations of the native Slippery elm, U. rubra, in Wisconsin (Brunet et al. 2016, Conservation Genetics) and determined that DED did not decrease the genetic diversity or increase the levels of genetic differentiation among populations of Slippery elm.

USDA-ARS and Department of Entomology, University of Wisconsin-Madison