Discovery of New Disease Explains the Mysterious Decline of Critically Endangered Tree, Florida Torreya

Healthy Florida torreya with cone full of seeds in garden cultivation. Most Florida torreyas in the wild do not reproduce. Photo credit: Jason Smith, http://edis.ifas.ufl.edu/fr338

In the late 1950s, the Florida torreya (Torreya taxifolia), a conifer growing in a pocket of Florida and Georgia along the Appalachicola River, began mysteriously dying.  A decline in the tree’s populations had been first noted in the early 1900s, but the sudden die-off was unprecedented.  Many believed the die-off was due to the recent construction in 1957 of the Woodruff Dam on the Appalachicola River, which changed water flow and dried out the soil where this tree was growing.  Others thought a disease caused the decline, because cankers and leaf spots usually symptomatic of a fungal infection were reported on many of the trees during and after the population crash.   Alarmed, conservationists applied for protection under the new Endangered Species Act that passed in 1973, and Florida torreya became one of the United States’ first official endangered species in 1984.  After the die-off, some trees began to re-sprout from the original trees’ roots. Decades later, the trees remained small, stunted, and constantly faced with dieback because of some unknown reason.  Because these trees rarely make seed in the wild, Florida torreya’s extinction is imminent, and it remains the rarest conifer in North America, one of the most endangered species in the world, and one of the oldest tree species on Earth.  The tree’s population has declined 99%, from over 350,000 in 1914 to hundreds of individuals today.

A new species of fungal disease has been found to cause the cankers observed on Florida torreya. The cankers cause trees to dieback and then resprout from the roots, without getting big enough to make seeds. Photo credit: Jason Smith et al. 2011, http://dx.doi.org/10.1094/PDIS-10-10-0703

After 50 years of looking for the culprit, scientists have discovered the disease that causes cankers on Florida torreya in the wild, a new species of fungus in the genus Fusarium, a genus including many infamous pathogens.  While no one can easily prove that this disease caused the decline of Florida torreya, its ubiquitous infections on the host tree today, and historical accounts of fungal disease symptoms during the die-off, indicate its potential role.

The discovery of this disease answers one question and creates many more.  Where did this disease come from?  Does it infect other trees?  How does it spread?  Can infection be prevented?  Scientists are now busy collecting the data to answer those questions.


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