First record of Graphium species associated with Euwallaceae perbrevis in Australia

Conrad Trollip; Angus Carnegie

doi:10.1094/PDIS-02-25-0319-PDN

In the wake of the detection of polyphagous shot hole borer (Euwallaceae fornicatus) in Perth, Western Australia, in 2021 (Cook and Broughton 2023), and ongoing surveillance for Fusarium dieback associated with ambrosia beetles in New South Wales (NSW) (Callaghan et al. (2024), there is a growing need to characterize fungal associates of already-established Euwallaceae species in Australia. Historically, plant health diagnostics targeting fungi vectored by tea shot hole borer, Euwallaceae perbrevis, in Australia has focused on Fusarium species, with only Fusarium obliquiseptatum and F. metavorans reported to date (Aoki et al. 2019; Callaghan et al. 2024). No other fungal associates have been reported from this vector in Australia despite the presence of key symbionts found in association with Euwallaceae beetles globally (Lynch et al. 2016, Na et al. 2018). In 2024, three cases of beetle infestation associated with dieback and tree mortality reported to forest biosecurity staff of NSW provided an opportunity for more detailed diagnostic investigations. The first was from Acer paxii at the Royal Botanic Garden of Sydney in April, the second from a stand of Cupaniopsis anacardioides at Lennox Head, northern NSW, in August, and the third from Ficus obliqua at the Royal Botanic Garden of Sydney in November. Isolations were performed from stained wood tissue, beetle galleries, and directly from beetle specimens, similar to described protocols (Lynch et al. 2016). Fusarium obliquiseptatum was confirmed in all cases (data not shown), however, Graphium spp. were readily observed in beetle galleries and in low abundance co-occuring with F. obliquiseptatum on isolation plates. Graphium isolates were recovered by picking conidial spore drops from synnemata and hyphal tipping to produce axenic cultures. Molecular identification was achieved by PCR and sequencing the internal transcribed spacer (ITS) and the translation elongation factor 1α barcoding regions using primers ITS1–ITS4 and EF2F–EF2R, respectively (Marincowitz et al. 2015). Three Graphium taxa were identified, viz. Graphium euwallaceae (DAR 86890) isolated from A. paxii in Sydney, the currently undescribed Graphium sp. II (DAR 86892) isolated from C. anacardioides in Lennox Head, and a putatively novel Graphium taxon, Graphium cf. basitruncatum (DAR 86894), isolated from F. obliqua in Sydney. These detections represent the first records of Graphium species associated with E. perbrevis in Australia. Graphium euwallaceae is a well-established fungal symbiont of E. fornicatus and E. perbrevis globally, previously reported in the United States, Vietnam and most recently in Perth, Western Australia (Lynch et al. 2016, Wright and Kehoe pers. comm.). In contrast, Graphium sp. II has only been previously recorded from a Durio sp. in Thailand (Na et al. 2018). The taxon identified as Graphium cf. basitruncatum is most closely related to G. basitruncatum, originally found in forest soils in the Solomon Islands and Japan (Okada et al. 2000). Graphium species are often regarded as saprobes or nutritional symbionts of ambrosia beetles, however their role in the lifecycle of Euwallaceae beetles and demonstrated pathogenic potential is arguably underappreciated in biosecurity (EPPO 2020, Lynch et al. 2016, Na et al. 2018). Future research in this regard might provide better assessment of the risks posed by fungal symbionts that goes beyond predetermined views of pathogenicity.

First record of Graphium species associated with Euwallaceae perbrevis in Australia

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First record of Graphium species associated with Euwallaceae perbrevis in Australia

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UN Sustainable Development Goals (SDGs)

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