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Issue link: https://read.dmtmag.com/i/1163463
Fungus, Beetle, Fungus: Dutch Elm Disease (DED), caused by the fungi Ophiostoma ulmi and Ophiostoma novo-ulmi, continues to weaken and kill American elm trees (Ulmus americana) in forests and cities. "Survivor elms" (mature trees that are still alive in forests and seem to have some natural tolerance to DED) have been used for DED tolerance breeding pro- grams aimed at restoring American elm trees. Breeding programs test DED tolerance of American elm cultivars with laboratory strains of the DED fungi. However, these laboratory strains were collected decades ago and may not be represen- tative of current strains found in the environment. Fungal pathogens evolve alongside their hosts. Therefore, it is likely that the Ophiostoma strains causing DED today are genetically different from those that caused disease decades ago. To determine the genetic variability of Ophiostoma strains currently in the environment, we are col- lecting and studying fungal strains from naturally infected American elm trees. We will sequence the genomes of some of these strains in order to understand the current population genetics of the fungi causing DED in American elms. Fungi have relatively small genomes (~30 Mb). With recent advances in next-generation sequencing (NGS) technologies, we can quickly get whole genome sequencing data for fungi in a cost-effective way. Using several computational approaches, we can analyze the whole genome data to identify fine-scale genetic differences within strains of the same species. Just as there are strains of the flu virus that cause people to get especially sick, there are strong (also called virulent) strains of the DED-causing fungi that kill trees more quickly than others. Ophiostoma strains isolated in the lab will be used in field-based studies on American elm trees to see which strains are the most virulent. By linking the genome sequencing data to field- based studies, we will be able to identify virulence factors in Ophiostoma and ensure that existing breeding programs are selecting for DED toler- ance that will continue into the future. DED-stricken American elm trees in test plot. Photo by USFS U.S. Forest Service Team to Study Dutch Elm Disease Population Genomics in Response to Fungal Strain Evolution By U.S. Forest Service Northern Research Station: Principal Investigators Jonathan Palmer, Jessie Glaeser, Charles Flower, Kathleen Knight, Cornelia Pinchot, and James Slavicek May 6, 2019 30 CityTREES