It is an exciting time in the field of conservation and biotechnology. For the first time, it appears likely that a tree that has been developed with genetic engineering (GE) could be approved by U.S. regulatory agencies for use in restoring a threatened species to the wild. That tree is the American chestnut, a species decimated by disease in the last century. Proponents of American chestnut restoration have waited several decades for this day to come, and anticipation for its release builds with every passing month.
Despite the excitement of many for the chance to once again grow the native chestnut tree, there are some who oppose the use of biotechnology for American chestnut restoration. A recent opinion piece in The Hill expressed concerns held by opponents of the release of GE blight-tolerant chestnut trees, so I will try to address those concerns and provide insight into the efforts to restore the American chestnut.
The American chestnut tree was once a prominent member of eastern American forests, but was effectively lost because of a fungal blight pathogen that hitchhiked to the U.S. on resistant species of Asian chestnuts. Decades of research at SUNY College of Environmental Science and Forestry in Syracuse, N.Y., yielded American chestnut trees called ‘Darling’ that harbor an acid-detoxifying gene from wheat, which allows the trees to survive infections by the blight fungus.
This feat of modern biology enables the conservation of the native chestnut’s genetics without hybridization with other chestnut species. Opponents of ‘Darling’ trees suggest that Chinese-American hybrid chestnuts would be a safer choice, citing concerns of unexpected changes that could come from the GE techniques used to create the blight-tolerant chestnuts.
While American chestnuts bred with Asian chestnut species can have enhanced tolerance to blight infections, many of the important traits of the native chestnut tree are also lost in the process. This is due to the enormous genetic changes that occur when two species hybridize, where the entire genetic structure of the species are reorganized. In contrast, ‘Darling’ American chestnuts maintain their genetic constitution with the small addition of the gene from wheat. Additionally, the genetic sequence (genome) of ‘Darling’ has been mapped and no unexpected genetic changes were caused by the addition of the gene from wheat.
Another concern is the possibility that resistance to blight may not sufficiently persist over time and that the trees eventually may succumb to the infections they were developed to resist. While this is a valid concern, it is unlikely because of the way the wheat gene protects the tree without directly harming the fungus. Also, the end result of this scenario would be the death of GE trees, which is the same outcome currently experienced by wild trees. In other words, there is no added threat, just an extension of the status quo.
While it is impossible to know every possible consequence of planting ‘Darling’ chestnut trees in the forest, it is possible to rule out many hypothesized risks. For example, some of the most sensitive organisms in the chestnuts’ native ecosystem include pollinating insects and amphibians, which suffer from even small exposures to toxins. Experiments were conducted where bumble bees were fed pollen containing the wheat gene and wood frog tadpoles were fed ‘Darling’ chestnut leaves. In both cases, no differences were observed between chestnuts with or without the wheat gene.
These are just two examples of environmental studies performed with ‘Darling’ chestnut trees to test their safety. In all these published studies that looked at interactions with insects, plants, fungi, amphibians and more, no negative effects were observed from the additional gene from wheat. As a result, it is reasonable to conclude that these trees do not present any novel threats to the environment. This is not surprising, since the same gene used in ‘Darling’ chestnuts is naturally found in many species of plants and fungi that live in the eastern forests and other ecosystems. After assessing these studies in a years-long review, the U.S. Department of Agriculture (USDA) has also concluded that these trees do not represent novel risks to the environment. (The USDA’s public comment period on the trees ends Dec. 27.)
The current approach of the American Chestnut Foundation is a multi-pronged strategy that uses biotechnology in conjunction with breeding and biocontrol techniques. ‘Darling’ trees fit into the biotechnology category but there is also a decades-long breeding program that has been incorporating resistance genes from Chinese chestnut into advanced generation hybrid American chestnut trees.
These two approaches aren’t seen as an either/or proposition but as complementary techniques that can be explored in parallel, as well as in combination. The third category is biocontrol, which includes several techniques that mitigate infection damage by treating infected trees with biological agents. Biocontrol helps to maintain existing trees in orchards but has potential for mitigating disease damage in wild ecosystems as well. The combination of these three approaches is known as 3BUR: Biotechnology, Breeding, and Biocontrol United for Restoration. A combined strategy has the best chance at success in American chestnut restoration.
In a time filled with seemingly endless stories about degradation of the environment, the potential restoration of the American chestnut using biotechnology presents a clear example of a positive impact humans can have on the environment. This tree may represent the first of many projects where people can help trees to stand their ground against invasive diseases. But for a start, it will be the return of one of America’s most iconic forest tree species.
Erik Carlson is a research project assistant, teaching assistant and doctoral student at SUNY College of Environmental Science and Forestry and a member of the New York chapter of the American Chestnut Foundation.