Detection of Geosmithia morbida on Numerous Insect Species in Four Eastern States

Abstract

Thousand cankers disease is caused by the coalescence of numerous Geosmithia morbida cankers on branches and stems of Juglans species, leading to branch dieback and eventual tree death. The fungus sporulates in galleries of the walnut twig beetle (Pityophthorus juglandis), allowing for acquisition of pathogen propagules and its subsequent transmission to other branches or trees following adult emergence. Recently, G. morbida has been isolated from Xylosandrus crassiusculus and Xyleborinus saxesenii collected in Ohio and Stenomimus pallidus collected in Indiana. These beetles are known to colonize diseased Juglans nigra in these states. In this study, an operational trap survey for ambrosia beetles, bark beetles, and other weevils was conducted in four eastern states, and captured beetles were assayed to detect G. morbida using both culture and PCR-based methods. A new primer pair (GmF3/GmR13), based on the β-tubulin region, was designed for G. morbida DNA detection. The pathogen was detected on 18 insect species using molecular methods, and live cultures were isolated from two species. This is the first report of the pathogen in Illinois and Minnesota.

A duplex real-time PCR with probe for simultaneous detection of Geosmithia morbida and its vector Pityophthorus juglandis

“…Moore et al . ’s [ 15 ] molecular assay, instead, applied conventional PCR for detecting G . morbida on various insect species; this assay, carried out with the G .…”

“…Despite the short time since the discovery of this fungal/beetle complex, epidemiological studies into TCD have proliferated in North America, ranging from susceptibility testing of hosts within the Juglandaceae (members in the genera Juglans and Pterocarya ), to exploring actual and potential insect vectors, and to TCD diagnostics [ 15 – 17 ]. On the European side, on the contrary, TCD is a relatively recent and almost unknown phytosanitary problem.…”

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

“…In contrast, within the native range, TCD has progressed very differently. For example, G. morbida has been detected on a variety of ambrosia beetles, other bark beetles, and weevils in the central and eastern part of J. nigra's native range (Juzwik et al, 2015;Moore et al, 2019), yet mortality has not been documented with these non-walnut twig beetle associations nor have many species of Pityophthorus been documented. These observed differences in TCD dynamics between the western United States and the eastern United States, might mean that TCD has not yet spread to the western part of J. nigra's native range.…”

“…Therefore, to more fully understand the impact of TCD, J. nigra identified to exhibit more resistance in this study should be challenged against high populations of P. juglandis naturally vectoring G. morbida. P. juglandis adaptation to the southwestern portion of the United States likely impacted disease progression, but the presence of G. morbida on additional insects (Warmund and van Sambeek, 2014;Juzwik et al, 2015;Chahal et al, 2019;Moore et al, 2019) could complicate TCD epidemiology, especially in areas where P. juglandis is maladapted.…”

“…The first record of TCD in the native range of J. nigra, occurred in Tennessee in 2010 (Grant et al, 2011). Since the initial accounts, consistent reports were made throughout the eastern United States (PDA, 2012;VDACS, 2011;ODNR/ODA, 2012;Seybold et al, 2012;NCDACS, 2013;Reed et al, 2013;MDA, 2015;Moore et al, 2019), and abroad (Italy) (Montecchio and Faccoli, 2014;Moricca et al, 2019).…”