Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Thousand cankers disease caused by Geosmithia morbida and its insect vector Pityophthorus juglandis first reported on Juglans nigra in Tuscany, Central Italy.

Abstract

As part of a monitoring programme to detect the occurrence of thousand cankers disease (TCD) in Tuscany, Italy, eight-unit Lindgren multiple funnel traps were deployed in April 2018 in various walnut (Juglans nigra) plantations. Two traps baited with walnut twig beetle (Pityophthorus juglandis; WTB) were set up at each site and inspected at 15-day intervals. From the first inspection date, bark beetles were found trapped in a plantation of J. nigra with scattered individuals of J. regia at Rosano, and morphologically identified as WTB. Following this discovery, all trees in the stand were carefully inspected for TCD symptoms and WTB entry and exit holes. Branches with wilt and the typical flagging of TCD, and with WTB holes, were found on J. nigra only. Galleries, adults and larvae of WTB were observed under the bark. Galleries were densely covered with the characteristic whitish mycelium consisting of long, verticillate conidiophores producing yellowish conidia with an average size of 5.5 × 2 µm. The pathogen was isolated on potato dextrose agar from infected wood and from WTB adults and larvae and identified as Geosmithia morbida at the molecular level. Amplicons of both organisms were purified and sequenced (GenBank accession nos. MH620784 [G. morbida] and MH666050 [P. juglandis]). A BLAST search of the ITS and CoxI sequences with the closest sequences deposited in the database revealed a 99% identity of the fungus with the North American and Italian isolates. Sequences of the insect displayed 100% identity with specimens from the USA and Piedmont (Italy). This is thought to be the southernmost finding of TCD in Europe.