Abstract
Thousand Cankers Disease (TCD) is a disease complex wherein the fungus (Geosmithia morbida) is vectored by the walnut twig beetle (WTB, Pityophthorus juglandis). The disease causes mortality primarily of eastern black walnut (Juglans nigra), although other walnut and wingnut (Pterocarya) species are also susceptible. Black walnut is native to the Eastern and Midwestern U.S. but is widely planted in western states. Total standing volume in both urban and forested settings is approximately 96 million cubic meters, and is valued at $539 billion. Although native to the Southwestern U.S., the range of WTB has expanded considerably. The spread of G. morbida coincides with that of WTB. TCD was introduced into Tennessee in 2010, and has spread to seven eastern states. Trees infected with TCD exhibit drought-like symptoms, making field detection difficult without molecular and/or morphological methods. The recently sequenced G. morbida genome will provide valuable research tools focused on understanding gene interactions between organisms involved in TCD and mechanisms of pathogenicity. With no chemical treatments available, quarantine and sanitation are preeminent options for slowing the spread of TCD, although biological control agents have been discovered. High levels of black walnut mortality due to TCD will have far-reaching implications for both eastern and western states.
Highlights
Juglans spp. and Pterocarya spp. (Fagales: Juglandaceae) trees across the United States (U.S.) and Europe are threatened by an insect-fungal disease complex known as Thousand CankersDisease (TCD)
It has been estimated that the net volume of eastern black walnut growing stock on timberland is between 96 and 112 million cubic meters [25,31]. This figure accounts only for eastern black walnut trees growing within the native range, and does not include transplanted trees grown in the Western U.S In general, eastern black walnut that are categorized as growing stock are eventually harvested for lumber and veneer
This report further indicated high genetic diversity of the pathogen, confirming the hypothesis of multiple introductions from multiple sources [3,39]. Both Zerillo et al [3] and Hadziabdic et al [40] proposed that anthropogenic movement of timber from multiple Thousand Cankers Disease (TCD) infested areas, coupled with high susceptibility of eastern black walnut to disease pressures [7] would support the hypothesis that the pathogen has been recently introduced into the eastern U.S.—the native range of eastern black walnut
Summary
Juglans spp. and Pterocarya spp. (Fagales: Juglandaceae) trees across the United States (U.S.) and Europe are threatened by an insect-fungal disease complex known as Thousand Cankers. (Fagales: Juglandaceae) trees across the United States (U.S.) and Europe are threatened by an insect-fungal disease complex known as Thousand Cankers. The pathogen associated with TCD is a filamentous ascomycete, Geosmithia morbida. Tisserat (Hypocreales: Bionectriaceae) [1]. The pathogen is vectored primarily by the walnut twig beetle (WTB) Pityophthorus juglandis Blackman Curculionidae) [1,2,3]. Another beetle species, Stenomimus pallidus (Boheman) (Coleoptera: Curculionidae), has been identified as a potential vector of G. morbida in Indiana and Ohio [4,5]
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