Researchers search for microscopic clues to an ecological mystery.

How do you find a culprit you can’t see or track, especially when you don’t know what it is? That’s the problem confronting Ohio State University researchers who are trying to figure out what’s harming the state’s beech tree population.

Discovered in 2012 about 30 miles northeast of Cleveland, the mysterious affliction causes dark green bands on beech leaves, which later wither and fall. It spread rapidly to Pennsylvania, New York and Ontario, Canada, while moving southwest across 11 counties in Ohio. It eventually began killing trees.

Dubbed “beech leaf disease” by OSU professor of plant pathology Pierluigi “Enrico” Bonello, it threatens a common Ohio tree that provides canopy cover, habitat and food for animals, says Carrie Ewing, a graduate student in environmental science at OSU. She and Bonello are members of an international consortium of researchers who are hunting for the cause.

While other scientists focus on a microscopic worm called a nematode, Bonello and Ewing are searching for a microbial suspect. They hope to find differences between genetic samples from healthy and diseased leaves that will point to a known pathogen. The challenges are plentiful, Bonello says. For example, the hunt requires sifting through millions of genetic sequences with scant available funding, other than a small grant for Ewing’s doctoral research. Still, the pair aims to have an initial idea of what’s causing the disease by the end of the year.

The stakes are high. The American beech is vital to its ecosystem, Ewing says, and if the species is lost, it would be very detrimental to those forests, which are widespread throughout the eastern U.S.

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