Fast, Field-Based Diagnosis of Laurel Wilt Disease

The redbay ambrosia beetle (Xyleborus glabratus) and a fungal pathogen (Raffaelea lauricola) were first introduced to the U.S. in the early 2000s. Since then, the deadly duo known as laurel wilt disease has cause widespread mortality among redbay (Persea borbonia), sassafras (Sassafras albidum), and avocado (Persea americana) trees in the southeastern U.S.

A team of researchers has developed a molecular, diagnostic test for the disease – one that can be completed rapidly in the field without the need for lab confirmation.

USDA Forest Service scientists Stephen Fraedrich, recently retired, and Bud Mayfield contributed to the study, which was led by Caterina Villari and graduate student Jeffrey Hamilton at the University of Georgia’s Warnell School of Forestry.

First, the researchers developed and tested the new method – a loop-mediated isothermal amplification (or LAMP) assay – in the lab using known isolates of the fungus. They then extracted fungal DNA from tissues of possibly infected wood samples and tested for the presence of the fungus. Pleased with the accurate results, the team carried the study to the field.

Samples were collected from trees showing visual symptoms characteristic of the disease: wilting leaves and dark-streaked sapwood. Using samples of infected sapwood and portable equipment, the researchers were able to conduct DNA extractions and analyses on site.

In under an hour, the LAMP method accurately detected laurel wilt disease in sassafras and redbay. In the past, lab confirmation of diagnostic tests could take upwards of a week. The portable assay is valuable for rapidly and accurately discriminating between laurel wilt, as other potential problems can cause similar visual symptoms.

A broad scale, effective treatment for laurel wilt disease does not exist yet. Rapid detection and tree removal remain the best way to minimize its impacts.

Read the article in Arboriculture & Urban Forestry. For more information, email Bud Mayfield at albert.e.mayfield@usda.gov.