Differential Virulence Among Geosmithia morbida Isolates Collected Across the United States Occurrence Range of Thousand Cankers Disease

Thousand cankers disease (TCD), first documented in the western United States early 2000s, has spread into nine and seven eastern states northern Italy. TCD incidence severity differ between outbreak localities. Black walnut ( Juglans nigra ) trees, introduced both urban plantation settings States, have been severely impacted as evident by high mortality. However, localities, where J. is native, host-pathogen-vector interactions resulted two different outcomes: trees either die or partly recover followed infection. Recent genetic studies on causal agent, Geosmithia morbida , indicate spatial structure levels of diversity among populations. Using detached branch inoculation assays, we reported differential virulence 25 G. isolates collected across current distribution range disease. As a proxy for virulence, canker area was measured to 7 days after inoculation. Varying degrees were observed tested isolates, which explained their provenance (genetic clusters). Isolates that grouped within cluster 2 n = from 6 States; mean 210.34 mm induced significantly larger than 1 12; all isolates; 153.76 ). Canker sizes varied each not correlated with geographic region (eastern vs. States) but rather isolated state origin. Mean size also differed response originated tree host species. major statistically smaller when compared recovered undetermined species . In sum, increased mortality populations cannot be higher local Plausible explanations disparity include environmental conditions, such prolonged drought, greater population densities twig beetle causing number events individual multiple introductions originating locations. Future experimental evaluation should undertaken quantify influence these factors epidemics.