AUTHOR=Sitz Rachael A. , Luna Emily K. , Ibarra Caballero Jorge , Tisserat Ned A. , Cranshaw Whitney S. , McKenna James R. , Stolz Joshua , Stewart Jane E. 

TITLE=Eastern Black Walnut (Juglans nigra L.) Originating From Native Range Varies in Their Response to Inoculation With Geosmithia morbida

JOURNAL=Frontiers in Forests and Global Change

VOLUME=4

YEAR=2021

URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2021.627911

DOI=10.3389/ffgc.2021.627911

ISSN=2624-893X

ABSTRACT=<p>Thousand cankers disease (TCD) is caused by the walnut twig beetle (<italic>Pityophthorus juglandis</italic>) vectoring the fungal canker pathogen <italic>Geosmithia morbida</italic>, which can result in severe dieback and eventual death to species of walnut (<italic>Juglans</italic> spp.) and wingnut (<italic>Pterocarya</italic> spp.). This disease is most devastating to the highly valued species <italic>J. nigra</italic> (black walnut). This species is primarily grown and harvested for timber production in the Central Hardwood Region of the United States, which comprises part of its native range. Management options for TCD are limited; therefore, finding resistant genotypes is needed. Initial studies on black walnut susceptibility to <italic>G. morbida</italic> documented some genetic variation and suggested potential resistance. Furthermore, <italic>G. morbida</italic> is thought to be native to the United States, which may have allowed for co-evolution. To capture the representative genetic diversity and screen for resistance to <italic>G. morbida</italic>, <italic>J. nigra</italic> families were collected from across the native range. These wild trees, in conjunction with seedlings developed in a black walnut timber improvement program, were planted in a common garden in Fort Collins, Colorado and repeatedly inoculated with <italic>G. morbida</italic> over the course of four years and three growing seasons. Improved seedlings exhibited larger cankered areas than wild <italic>J. nigra</italic> of the same provenance. Cankers induced by <italic>G. morbida</italic> in wild germplasm were smaller on <italic>J. nigra</italic> collected from the western and central portions of the native range compared to those collected from the eastern portion. Although trees from the western and central part of the range still incurred cankers, our findings indicate that variation in genetic resistance to <italic>G. morbida</italic> is present in black walnut. This study was performed with <italic>G. morbida</italic> independent of the walnut twig beetle, but our results suggest the limited <italic>G. morbida</italic> resistance observed in <italic>J. nigra</italic> will prevent the full compromise of black walnut to TCD. Results from this study should be taken into consideration in future black walnut breeding programs.</p>