Test plots evaluated for survival and growth; challenges emerge


Dr. Scott Schlarbaum at test location

​Dr. Scott Schlarbaum, leader of the University of Tennessee Tree Improvement Program, shows off an American chestnut sapling bred to be resistant to chestnut blight. Test plots of trees are being evaluated at undisclosed locations in national forests.


KNOXVILLE, Tenn. – Data are coming in to the University of Tennessee’s Tree Improvement Program on how test plantings of American chestnuts in the region fared during this year’s long growing season, which started early due to a mild winter followed by a warm spring.

Test plots of seedlings believed to be blight-resistant and which are now growing at undisclosed locations in southern national forests were evaluated for growth, survival to blight and response to disease and insect problems. The first series of plantings was initiated in 2009, and subsequent growth has been spectacular in some of the seedlings, but scientists are finding the plantings are not without problems.
UT scientists, led by Dr. Scott Schlarbaum, a professor in the Institute of Agriculture’s Department of Forestry, Wildlife and Fisheries, are evaluating the trees, which were produced by three American chestnut breeding programs. The effort will determine the best methodology for restoring chestnuts to Tennessee and Eastern forests and lands. The goal is to achieve trees robust enough to survive chestnut blight as well as threats posed by native and exotic pests.
For example, the rarely seen chestnut softly has been found damaging the seedlings. Exotic or non-native pests, including the chestnut gall wasp and Asiatic oak weevil, have also shown a presence, as has an old problem, root rot disease. Root rot disease was imported from Europe in the 1830s and resulted in the first wave of disease that devastated American chestnuts, taking out the nation’s lowland chestnuts in the 1880s.
Considering these threats, Schlarbaum believes that even blight-resistant chestnuts are going to have a number of challenges in Eastern forests, as scientists work toward successful restoration of the species.
Yet some signs of promise exist. Researchers are using a virus that infects the chestnut blight fungus itself. Trees infected with virus-treated fungus have managed to heal over cankers caused by the blight, enabling trees to fight the disease. The virus has been found to occur naturally in some trees, among them a small stand of 30-year-old American chestnuts growing on land used for agricultural studies by scientists with UT AgResearch. The trees were planted by Dr. Eyvind Thor, the first leader of UT’s Tree Improvement Program.
The trees being evaluated originate from these programs:
• The American Chestnut Foundation, which is working to achieve blight resistance through hybrid trees backcrossed with blight-resistant Chinese chestnuts. Successive generations are then bred with American chestnuts to retain the main characteristics of American trees. UT scientists and Dr. Stacy Clark of the U.S. Forest Service are evaluating hybrids, which are 15/16 American chestnut and believed to carry blight resistance from the Chinese parent. Clark, who worked with the UT Tree Improvement Program while earning her master’s degree, is based in Knoxville at the UT Institute of Agriculture.
• The American Chestnut Cooperators Foundation, which is breeding pure American chestnuts with low levels of blight resistance and kept alive by site selection and introduction of the virus to the chestnut blight fungus. One UT planting of their trees is at the East Tennessee State Nursery. UT is also working with a founder of the organization, Dr. Gary Griffin of Virginia Tech, on thousand cankers disease in black walnuts, which is spreading in East Tennessee.
• The Connecticut Experiment Station, which is the nation’s oldest chestnut breeding program and is working with complex hybrids backcrossed with Chinese and Japanese chestnuts. The Japanese species has resistance to root rot. UT is comparing seedlings from this program planted in containers with trees planted bare root to determine if container-planted trees, whose roots experience less damage during transplanting, can grow as robustly as seedlings planted bare-root. Led by Dr. Sandra Anagnostakis with involvement by former UT tree improvement scientist Dr. Leila Pinchot, now of the Pinchot Institute, the project’s cooperators have planted trees at the Milford Experimental Forest in eastern Pennsylvania and the U.S. Military Academy Reservation at West Point, New York, as well as at various locations in public and private land in Connecticut.
Considering the findings to date, Schlarbaum says, “Given the situation where we have six serious exotic pests that attack chestnut seedlings as well as natural pests, we’re probably looking at chestnuts returning as an occasional tree in the landscape as opposed to groves and groves of chestnuts.”
The push to achieve blight-resistant and robust chestnuts is to restore Eastern forest ecosystems and thus reintroduce an important food source to wildlife as well as grow rot-resistant timber.
In the absence of American chestnuts, Chinese and some of the Asian chestnut trees can be good both for human and wildlife consumption. An experiment conducted in the 1990s by scientists and undergraduates at UT found that wild turkeys recognized American and Chinese chestnuts as food, even after the chestnuts’ long absence. The turkeys preferred smaller sized chestnuts to larger ones, which can approach two inches in diameter. In terms of preference, the turkeys ate chestnuts as often as white and red oak acorns.
Today at the Ames Plantation in southwest Tennessee, which operates as one of 10 UT AgResearch and Education centers, scientists are evaluating the size and quality of Chinese chestnuts through a test population of the trees growing on Ames’ land. Although Chinese chestnuts typically are larger than American chestnuts, some trees produce smaller nuts.
“We’re in the process right now of quantifying what size chestnuts each tree in the seed orchard produces, as well as growing chestnuts from the small-sized nuts to plant as replacement trees in the orchard,” Schlarbaum says.
Most of the trees in this orchard are now producing nuts, and the Tree Improvement Program will use these to supply seed to the East Tennessee State Nursery, which will sell the resulting seedlings to Tennessee landowners.
The UT Tree Improvement Program celebrated its 50th anniversary in 2009 and is one of the longest-running programs of its kind in the nation. Emphasis is on trees for timber, game and nongame wildlife, and forest aesthetics. The program also is advancing scientific knowledge and contributing to education programs at UT and in grades K through 12. You can learn more about the program at its website: http://treeimprovement.utk.edu.
The UT Tree Improvement Program is operated by UT AgResearch, one of four units of the UT Institute of Agriculture. In addition to its agricultural research programs, UTIA also provides instruction, research and public service through the UT College of Agricultural Sciences and Natural Resources, the College of Veterinary Medicine and UT Extension offices in every county in the state.
Dr. Scott Schlarbaum, UT Tree Improvement Program, 974-7993, tenntip@utk.edu