Scientists with the U.S. Forest Service and Colorado State University examined a fungus native to North America, the native beetle that carries it, and their host tree and found something surprising: Geosmithia morbida (the fungus) and the walnut twig beetle co-evolved and, while the beetle/fungus complex was once the equivalent of a hang nail for a black walnut tree, it has now become lethal. Research published on November 13, 2014 in PLOS ONE by U.S. Forest Service scientist Dr. Keith Woeste, Colorado State University scientists Dr. Marcelo M. Zerillo and Dr. Jorge Ibarra Caballero, and colleagues, details the origins and spread of Thousand Cankers Disease (TCD), a fungal disease that is threatening the health of black walnut in the Eastern United States. The study provides a detailed look at the genetic diversity of the fungus and how that diversity is distributed on the landscape, allowing scientists to make much stronger conclusions about the sources of TCD spread in the past and in the future. "Black walnut is a species with tremendous economic and cultural significance," said Dr. Michael T. Rains, Director of the Northern Research Station and the Forest Products Laboratory. "To help ensure this species sustains it vibrancy, Forest Service scientists are working with state agencies, other federal agencies, and university partners to advance survey and detection efforts and to understand the genetics of the disease, as well as resistance to TCD." When black walnut trees in California and Arizona began dying of TCD two decades ago, some scientists believed that the walnut twig beetle (image) had acquired a new and probably non-native fungus that was killing the trees. "That wasn't the case," said Dr. Woeste, a research plant molecular geneticist with the U.S.
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