A century ago, about half a million torreya trees grew in the wild. Today, there are fewer than 1,000. Is extinction imminent, or can the species be saved?
“I’m more optimistic now, after the Torreya Tree of Life Workshop,” says USDA Forest Service geneticist Dana Nelson. “The workshop brought a large group of enthusiastic people together – lots of good ideas about how to help this species.”
The workshop was jointly organized by the Atlanta Botanical Garden, ProForest, and the University of Florida Institute of Food and Agricultural Services.
The Florida torreya (Torreya taxifolia) has been vanishing since the 1950s. In 1984, it become one of the first plants to be listed as an endangered species.
The primary culprit appears to be a fungus called Fusarium torreyae. Jason Smith, an associate professor at the University of Florida, discovered the fungus in 2010. Scientists think the fungus is native to China.
The fungus causes fusarium stem canker, which eventually kills the tree. The disease also stunts growth – most of the surviving torreya look more like shrubs than trees.
On the second day of the meeting, participants broke into four study groups, each focused on a specific aspect of torreya restoration.
The genetics group resolved to sequence the torreya genome. Doug Soltis and Pamela Soltis, distinguished professors at the University of Florida Museum of Natural History, will spearhead the sequencing efforts.
“Some DNA sequencing is already available,” says Nelson. “There’s been enough sequencing to identify genetic markers.” The markers can estimate the species’ genetic diversity and provide population-level information. The work is underway, led by SRS researchers Tyler Dreaden and Craig Echt and Sedley Josserand at the SRS Southern Institute of Forest Genetics.
Eventually, Nelson and Dreaden hope to screen all the available torreya genotypes for disease reaction. “We’re hoping that some torreya genotypes will have natural resistance to the fusarium,” says Nelson.
The first step is collecting torreya samples. Starting in the late-1980s and early-1990s, researchers collected cuttings from Torreya State Park in Florida. Horticulturists and researchers at the Atlanta Botanical Garden (ABG) planted many of those cuttings in ex situ conservation plantings in north Georgia.
Cuttings have also traveled far from Florida through the ABG – to North Carolina, Ohio, Mississippi and other areas. In addition to conservation plantings, citizen science groups and gardeners have planted torreya in many areas.
Such plantings are helping conserve the genetic variation that was once present in the wild.
Torreya has a tiny natural range – a county in Georgia, plus three in the Florida panhandle. “Most forest tree species have large ranges across many states, if not entire regions,” says Nelson. “So to have a species with such a small native range is an oddity.”
Once the torreya genotypes have been collected, Nelson and Dreaden plan to conduct artificial inoculation trials. “We’ll infect torreya seedlings with fusarium stem cankers in a controlled system,” says Nelson. The trials could identify naturally resistant torreya genotypes.
One of Nelson’s areas of work is pitch canker, caused by a related fungus that affects southern pines. “We’ll modify the pitch canker screening protocol for use with the torreya stem canker trials,” says Nelson.
Torreya has many champions, including renowned biologist E.O. Wilson. Wilson was one of the first to comment on torreya’s plight, in 1957. He returned to Torreya State Park to plant a torreya seedling, and as a guest speaker at the workshop.
Despite efforts to save torreya, extinction looms. With every extinction, the world’s biodiversity shrinks – an incalculable loss.
For more information, email Dana Nelson at email@example.com.