Benchmarking a fast and simple on-site detection assay for the oak wilt pathogen Bretziella fagacearum

Bourgault, Émilie; Gauthier, Marie-Krystel; Potvin, Amélie; Stewart, Don; Chahal, Karandeep; Sakalidis, Monique L.; Tanguay, Philippe

doi:10.3389/ffgc.2022.1068135

Cited by 7 publications

(2 citation statements)

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“…A new onsite test has recently been published (Bourgault et al., 2022) and may be considered in a future revision of this protocol.…”

Section: Detectionmentioning

confidence: 99%

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PM 7/1 (2) Bretziella fagacearum (formerly Ceratocystis fagacearum)

2023

EPPO Bulletin

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Specific scope: This Standard describes a diagnostic protocol for Bretziella fagacearum. 1 This Standard should be used in conjunction with PM 7/76 Use of EPPO diagnostic protocols. Specific approval and amendment: First approved in 2000-09. Revised in 2023-07. Authors and contributors are given in the Acknowledgements section. | I N T RODUC T IONBretziella fagacearum is the cause of oak wilt in the United States. Although the pathogen is mainly reported on Quercus spp., several species in other genera of the Fagaceae (e.g. Castanea mollissima, Notholithocarpus densiflorus) are documented as hosts, either as naturally occurring infections or as the result of artificial inoculation studies (EPPO, 2023a). In 2022, the species was detected on Castanea sativa × C. crenata (Sakalidis et al., 2023). In Quercus spp., red oaks (subgenus Lobatae) are highly susceptible to the fungus, whereas American white oaks (subgenus Quercus) are more resistant to disease development. Bretziella fagacearum is a classic vascular wilt, in which the fungus is confined to the vessels of the outermost xylem ring until the trees become moribund. The most important means of shortdistance spread is through natural root grafts, while above-ground spread occurs through beetles such as Carpophilus sayi or Colopterus truncatus (Coleoptera: Nitidulidae), which are the main vectors. In some areas, Pseudopityophthorus minutissimus and P. pruinosus (Coleoptera: Curculionidae) have also been involved in the spread of the pathogen. Movement of infested firewood is suspected to have been a source of infections in new areas (Davies, 1992). More information on host plants and distribution is available in the EPPO Global Database (EPPO, 2023b).Testing of insect vectors is performed near infested areas in North America. Tests have been described in McLaughlin et al. (2022) and Bourgault et al. (2022).However, the current diagnostic protocol focuses on the testing of symptomatic plant material.A flow diagram describing the diagnostic procedure for Bretziella fagacearum is presented in Figure 1.

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“…A new onsite test has recently been published (Bourgault et al., 2022) and may be considered in a future revision of this protocol.…”

Section: Detectionmentioning

confidence: 99%

“…(2022) and Bourgault et al. (2022). However, the current diagnostic protocol focuses on the testing of symptomatic plant material.…”

Section: Introductionmentioning

confidence: 95%

PM 7/1 (2) Bretziella fagacearum (formerly Ceratocystis fagacearum)

2023

EPPO Bulletin

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Interlaboratory Evaluation of Bretziella fagacearum Molecular Detection Assays to Guide the eDNA Monitoring of Oak Wilt Disease

Gauthier,

Djoumad,

Bal

et al. 2024

Environmental DNA

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Oak wilt disease, caused by the fungus Bretziella fagacearum, can kill mature red oaks within months of infection, severely affecting biodiversity, landscapes, and industries. The disease, originally only present in the United States, was officially reported for the first time in Canada in June 2023. The aim of this study was to suggest a standardized assay and sample processing method to optimize oak wilt detection both in infection centers and ahead of the disease front. Two previously published molecular assays, a Nested PCR and a TaqMan qPCR, were compared to detect B. fagacearum in a variety of samples in a ring trial across five laboratories. Sample types investigated included eDNA from trapped insect vectors (sorted insects and bulk content from traps), infested and healthy oak wood chips, and B. fagacearum conidia dilutions. Results demonstrated that both Nested and TaqMan assays can be used for molecular confirmation of oak wilt, and results are reproducible across different labs. There is a general agreement between both detection assays when testing true‐positive and true‐negative samples. Both methods demonstrated overall good accuracy. The TaqMan assay was more sensitive and detected lower amounts of DNA target. Both tests were 100% specific to oak wood samples, which was the best sample type to use for detection. In general, samples with high Cts were more prompted to yield false negative Nested results. Detecting oak wilt from bulk insect samples was by far more rapid than sorted sap beetles, but resulted in lower detection signals, especially with the Nested assay. The time‐period when the insect traps were set up also had considerable influence on detection results. We hope this study helps to formulate guidelines in oak wilt detection and biosurveillance management.

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