Update on the status of the American chestnut

Richard Hines

Prior to the outbreak of the Chestnut Blight, American chestnut trees once occupied 25% of the entire forest canopy over most of the Eastern United States. Its loss was an ecological disaster and for years researchers have worked tirelessly attempting to find a strain of trees that would be resistant. After years of work there may be hope for the return of this forest giant. Thanks to an understanding of genetics and efforts of numerous scientists along with concerned citizens a solution may be close.

At the KWOA Conference this past March, Rick Caldwell presented the group with the latest findings on how the chestnut is fairing.

Caldwell, who is the Arborist for Bernheim Forest, and President of the Kentucky Chapter of the Chestnut Foundation said, “for the past 35 years, we have been doing traditional crossbreeding between the American chestnut and the Chinese chestnut”. In addition to normal crosses, researchers have been backcrossing trees continually trying to captive more of the American chestnut genetics. Intercrosses have also been used in every effort possible to restore this magnificent tree to the landscape.

Through these efforts, Caldwell said, “we now have a tree that is about 94% American and 6% Chinese”.  Overall, the result to this point is a tree referred to as the B3F3 tree. Through backcrossing three times plus additional intercrossing researchers are now working with a tree that for all practical purposes is 15/16 American Chestnut. The question will continue, how resistant and/or tolerant is this tree to the chestnut blight.

While the group continues working with traditional breeding programs, Caldwell described how the Foundation has a new transgenic tree that researchers at New York State University which has had a wheat gene inserted that has further helped improve resistance. Currently, this new tree is showing about 99% resistance. Before any releases of this new tree can take place or before this is introduced into the breeding program, both the U.S. Department of Agriculture and the Environmental Protection Agency will have to approve the resulting tree. Caldwell added, “this is a very promising direction we are going, combining both transgenic and traditional breeding programs”. The process of developing a transgenic organism occurs when DNA material from another organism is inserted the target organism. In this case, a gene from wheat is being inserted into the experimental chestnut trees. Caldwell indicated that this may be the one that can finally start restoration efforts.

American Chestnut was such a large component of America’s eastern forests when it disappeared that researchers calculated that around 25 billion trees were lost. A tree that was essential to rural families for not only food, livestock feed, but lumber and numerous other wood products was essentially gone. From the standpoint of wildlife, the chestnut was the primary food consistently producing well over 5 to 10X the poundage of mast that oaks and other hardwood trees currently produce.  Unlike oaks, there is no variation in annual mast production due in part to a June flowering date which reduces susceptibility to early spring freezes.

An effort is underway to locate potential sites to establish mother orchards. If you are interested in becoming involved, you can contact Rick Caldwell at rcaldwell@bernheim.org or call him on his cell phone at 502-807-2257.