Washington [US] June 2 : A new risk to the ecosystems of North American forests is beech leaf disease. Twelve more US states and Canadian provinces have already experienced its spread since it was initially identified in northern Ohio in 2012. The diseased and dying trees were initially diagnosed based only on their symptoms, which included dark banding along the leaf veins and shrivelled, leathery leaves.
However, nematodes were discovered in sick leaves in 2017, and by 2020 we knew the cause: Litylenchus crenatae mccannii, a newly identified subspecies of the worm-like critter, was unquestionably linked to the symptoms.
Forestry experts will require a quick, precise approach for detecting the nematodes in order to track the progress of the disease, comprehend the nematode's existence among both symptomatic and perhaps asymptomatic trees, and start developing management measures. Before now, anyone working in forest health who wanted to identify a tree would have to go through a lengthy process that involved soaking leaves for twelve hours, further preparing samples, and then examining them under a microscope to look for nematodes. It's a good technique for one expert to analyse one tree, but it can't be applied on a broad scale easily.
In a new report, published by forest health researchers at the Holden Arboretum, the Ontario Forest Research Institute, and the US Forest Service, the team outlines a new tool for detecting these nematodes. Their work appeared in the journal Plant Disease.
The new nematode detection tool utilizes a long-standing laboratory method that can be used to detect DNA specific to a certain organism. In this method, researchers use a short DNA sequence that is specific to the species of interest, called a primer, to identify and then amplify on-target DNA in a sample. The amplification step is a relatively basic laboratory technique, PCR, but the real challenge lies in developing the primer in the first place which is exactly what the researchers have done.
"The new primer will make detection of the North American beech leaf nematode faster and easier, allowing forest health professionals across the US and Canada to keep better tabs on this emerging disease," says David Burke, Vice President for Science and Conservation at Holden Forests & Gardens, who led the work. "Better detection will mean more accurate monitoring and improved research on treatment."
The new primer can be used to differentiate L crenatae from other nematodes that might be found in areas affected by BLD and also allows researchers to estimate the relative degree of nematode infestation between samples.
"We need all the forest professionals we can get working on BLD if we want to nip it in the bud," says Burke. "Our forests may depend on it."
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