Beetle, Fungus, Fungus: Research Updates on EAB, DED, and Chestnut Blight

Emerald Ash Borer. A report recently published in the Journal of Economic Entomology offers data on the newest parasitoid wasp released against the EAB beetle: Spathius galinae. One of the authors, Dr. Jian Duan of the Beneficial Insect Introduction Unit at the U.S. Department of Agriculture’s Agricultural Research Service, says including this species in the biocontrol lineup could be a game-changer. “The addition of S. galinae to the current biocontrol arsenal will provide a whole spectrum of protection for surviving ash trees,” he says. To read more, see the summary article by Melissa Mayer in Entomology Today. Photo credit: Jian Duan, Ph.D., USDA-ARS

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 programs 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 representative 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, U.S. Forest Service researchers are collecting and studying fungal strains from naturally infected American elm trees. U.S. Forest Service Northern Research Station Principal Investigators Jonathan Palmer, Jessie Glaeser, Charles Flower, Kathleen Knight, Cornelia Pinchot, and James Slavicek 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. Read more here. Photo Courtesy USFS

Chestnut blight. The American Chestnut Foundation (TACF) is screening American chestnut backcross families for blight tolerance using small stem assays (SSAs). In the small stem assay, the stems of containerized chestnut seedlings are inoculated with the fungal pathogen Cryphonectria parasitica and assessed for differences in blight tolerance between families.

For sixteen weeks post-inoculation, volunteers and TACF staff assessed blight canker severity and survival to detect differences in blight tolerance across families. They also wanted to determine whether a strong correlation exists between the SSA and standard field inoculations.

Results provide reasonable assurance that SSAs can be useful for progeny tests, and potentially as an early screening tool. The use of SSAs by TACF chapters can save valuable resources such as the time and labor required to plant and manage seed orchards, as well as improve the quality of the trees established in orchards. Read the whole story from the TACF publication, Chestnut. Photo of severe canker on chestnut seedling courtesy TACF.

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