Prof. Barry Logan, Mistletoe Research in The Scientist

Story posted December 02, 2009

The season for mistletoe is upon us, but the plant's cousin, parasitic eastern dwarf mistletoe, takes no holiday, presenting unwelcome advances of disease for white spruce trees year-round.

Associate Professor of Biology Barry Logan has been studying the deadly relationship between the parasitic mistletoe and its unfortunate host trees for ten years.

His research is the focus of the article, "No Kissing Here," in the December 2009 issue of The Scientist magazine.

The article details how the parasite causes trees to grow twisted, tangled branches called witches' brooms that wreak havoc on the tree's growth and development, and how Maine's coastal forests may be uniquely vulnerable.

The mistletoe, it seems, may be meddling with the tree's hormones. In a not-yet-published study, Logan and his team discovered that needles on infected white spruce branches have twice the concentration of cytokinins as do uninfected branches. These growth-promoting hormones trigger branching and direct the movement of resources into the branch. Infected branches also have significantly reduced concentrations of abscisic acid, a stress-related hormone that some studies have linked to the shedding of old branches. "All of this comes together nicely," Logan says, to explain how witches' brooms form and thrive.
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Infected trees are easy to spot; their "witch's brooms" — tangled masses of branches (inset) — survive while the rest of the host tree appears to suffer.
Exactly how the mistletoe is manipulating the tree's hormones remains to be seen. "I think it's possible that the mistletoe is moving hormones into the host and not just withdrawing resources," he says. He hopes to undertake more hormonal analysis to get to the bottom of the interaction between parasite and host.

In 2009, Logan led a summer research project with Shem Dixon '11, Danielle Marias '10 and Stephanie Schmiege '10.

They traveled to Southport Island to see firsthand the damage done by parasitic eastern dwarf mistletoe at their field site along the coast.

Read more about the summer research project on Southport Island.

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(L. to r.) Professor Barry Logan, Shem Dixon '11, Stephanie Schmiege '10 and Danielle Marias '10 amid infected white spruce trees on the coast of Southport Island in August 2009.

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