Measuring quantitative resistance against the walnut twig beetle (Pityophthorus juglandis) in a mapping population of Sparrow x Schessler black walnuts (Juglans nigra)

            Eastern black walnut (Juglans nigra) is an ecologically and economically important tree species. These trees are endemic to the eastern United States, but have been planted widely outside of their native range, where thousand cankers disease (TCD) is responsible for the widespread death of black walnut. The disease is caused by a fungal pathogen (Geosmithia morbida) which is vectored by the walnut twig beetle (WTB, Pityophthorus juglandis), and threatens the health and productivity of black walnut throughout its native range which includes the Central Hardwood Forest Region. Control options are currently limited and focus on managing WTB to halt or slow the spread of TCD. Identifying mechanisms of host plant resistance to WTB, and ultimately TCD, holds promise for managing the disease. Here, we present the preliminary results of an assay designed to quantify resistance to WTB in walnut. This assay involved artificially infesting bolts of walnut with WTB and measuring multiple aspects of physical and chemical defense as well as the impacts on WTB fitness. All bolts used in this assay were taken from a full-sib mapping population of progeny from a cross between two commercial walnut genotypes: Sparrow and Schessler. The results of this study will inform genome association studies which will be used to identify loci with genes responsible for increased or decreased resistance in walnuts.