American chestnut. Image © Plant it wild

The American chestnut

Touted as a conservation breakthrough, the genetically engineered American chestnut has shown “significant performance limitations,” including poor blight tolerance, slow growth, and higher mortality. Intended to interbreed with remaining wild American chestnuts, its release would be a large-scale experiment with virtually no way to monitor, manage, or reverse it – threatening wild populations and potentially undermining conservation efforts in both the U.S. and Canada.

Why is the American chestnut critically endangered?

The American chestnut (Castanea dentata), once a keystone of North American ecosystems, is now classified as Critically Endangered.1

The primary cause for the decline is chestnut blight, a disease caused by the fungus Cryphonectria parasitica introduced from Asia in the early 1900s.2 Today, numbers of mature trees are dwindling in the US, though less so in Canada. Most survivors are root sprouts that die before reaching maturity, but a few naturally resilient individuals persist.

Habitat fragmentation and land-use change have further reduced suitable habitat, while other tree species have filled the chestnut’s ecological niche, making reestablishment difficult in mature forests.

Can genetic engineering help save the species?

Scientists at the State University of New York’s College of Environmental Science and Forestry (SUNY ESF) have engineered a genetically modified American chestnut containing an oxalate oxidase (OxO) gene from wheat, designed to confer tolerance to the Cryphonectria fungus.

After 13 years of experimentation3, they announced the “Darling 58” GM tree in 20134, with initial support from the American Chestnut Foundation (TACF). However, in December 2023 – after more than a decade of collaboration and over $10 million invested – TACF withdrew its support, citing “significant performance limitations” observed in field tests and a critical labelling error.5

In fact, between 2016-23, mislabelled pollen samples meant researchers had been propagating and testing the wrong GM line, invalidating seven years of research data. The “Darling 54” (D54) variety has the OxO gene inserted on a different part of its genome, giving it significantly different qualities.

SUNY ESF is now seeking regulatory approval to release “Darling 54” into the wild6  – a move opposed by TACF7 and the Canadian Chestnut Council.8

Technical realities and limitations of GM chestnuts

Blight symptoms on an engineered seedling. Image © TACF

Although presented as a fast and efficient conservation solution, the GM chestnut has struggled to meet even its narrow objectives.

  • Trials revealed that modified trees suffered from poor blight tolerance9, stunted growth10, reduced vigour and high mortality10 and greater susceptibility to other diseases.11
  • The OxO gene also addresses only one disease threat; others, such as Phytophthora, ((USDA-APHIS (2022). SUNY ESF Petition (19-309 01p) for Determination of Nonregulated Status for Blight-Tolerant Darling 58 American Chestnut. https://www.aphis.usda.gov/sites/default/files/19-30901p-dpra.pdf)) 
  • In “Darling 54”, a large DNA deletion negatively affects drought and salinity tolerance.9

American chestnuts take 5-7 years to mature (fruit) and over 20 years to establish self-sustaining populations. This long life-cycle slows down the ability to test success, makes mistakes harder to reverse, and raises the risk that genetic modifications could fail amid ecological complexity and ongoing evolutionary change.

Ecological and conservation risks of releasing GM trees

Releasing genetically engineered trees poses unique, irreversible risks that short-term studies and greenhouse trials cannot adequately assess or predict.12

American chestnut pollen can travel hundreds of kilometres, and seeds spread via animals, making containment impossible once GM trees are released. Performance failures could harm genetic diversity,13 and hybridisation with wild chestnuts could introduce permanent maladaptive traits that threaten the survival of remaining wild populations.

Fruit of the American chestnut tree. Image © Canadian Chestnut Council

Cross-border governance and regulatory gaps

In 2020, SUNY ESF petitioned U.S. regulators to approve the commercial release of the “Darling 58”14 and since amended its petition to request release of the “Darling 54” GM chestnut.15 USDA-APHIS has recommended non-regulated status, which would exempt the tree from containment, monitoring, and reporting requirements. Further reviews by other US agencies are needed before the GM tree can be planted outside of research plots.

If approved, GM chestnuts would likely spread into Canada via natural dispersal. The Canadian Chestnut Council opposes the release, warning that it would “put restoration of the American chestnut at risk, in Canada and the United States”.16

"The GM American chestnut has struggled to meet even its narrow objectives."

In Canada, any genetically engineered forest tree is regulated as a “Plant with Novel Traits”17 and must undergo formal risk assessment before open release. However, Canada cannot prevent cross-border pollen or seed drift, and no binding treaty governs the unintentional spread of GM organisms between the two countries.

Equity, profit, and Indigenous Peoples' rights

Though promoted as a public-good restoration, the GM chestnut is tied to private investment and patents. SUNY ESF’s commercial partner, American Castanea18, holds licensing rights and operates through SilvaBio – a Public Benefit Company developing engineered hardwoods. SilvaBio reportedly has over 2,500 engineered seedlings planted in USDA-approved orchards in New York State.19

TACF has warned that profit motives could make seedlings prohibitively expensive, undermining restoration goals.9 Indigenous nations and communities were not meaningfully consulted despite the tree’s cultural and spiritual significance.20

Engineered seedlings beginning to show leaf injury symptoms. Image © TACF
“Decades of work to breed naturally blight-resistant American chestnut trees…would be lost if the D58 GE American chestnut tree is released into the wild.”
— Friends of the Earth US

Alternatives grounded in conservation practice

Conservationists are making progress through non-GM methods. The Canadian Chestnut Council208 and American Chestnut Cooperators’ Foundation21 are identifying and breeding naturally blight-tolerant wild chestnuts and returning them to the forests, reporting thousands of healthy, reproducing specimens. This work could be lost if the GM chestnut tree is released into the wild.

Sources

  1. IUCN Red List of Threatened Species (2018).  https://www.iucnredlist.org/species/62004455/62004469 [↩]
  2. Mlinarec J et al  (2018). Molecular evolution and invasion pattern of Cryphonectria hypovirus 1 in Europe: Mutation rate, and selection pressure differ between genome domains. Virology https://www.sciencedirect.com/science/article/pii/S0042682217303902?via%3Dihub [↩]
  3. Petermann A (2025). The Darling 58 debacle. Earth Island Journal https://www.earthisland.org/journal/index.php/magazine/entry/lessons-from-the-unsuccessful-gm-chestnut-experiment [↩]
  4. Zhang B et al (2013). A threshold level of oxalate oxidase transgene expression reduces Cryphonectria parasitica-induced necrosis in a transgenic American chestnut (Castanea dentata) leaf bioassay. Transgenic Research. https://doi.org/10.1007/s11248-013-9708-5 [↩]
  5. TACF Press Release (2023). https://tacf.org/tacf-discontinues-development-of-darling-58/ ). See also: Chestnut chat: Darling 58 update. 15 Sept. https://www.youtube.com/watch?v=9w_ehgYyxGY [↩]
  6. Federal Register (2025) Availability of a Revised Petition for Blight-Tolerant Darling 54 American Chestnut (Castanea dentata) Developed Using Genetic Engineering. Docket No. APHIS-2020-0021 https://www.federalregister.gov/documents/2025/06/06/2025-10226/state-university-of-new-york-college-of-environmental-science-and-forestry-availability-of-a-revised [↩]
  7. USDA/APHIS (2025). Comment from the American Chestnut Foundation https://www.regulations.gov/comment/APHIS-2020-0030-19911 [↩]
  8. Canadian Chestnut Council comment to USDA/APHIS (2025). https://cban.ca/wp-content/uploads/Response-to-APHIS-to-D54-from-CCC-June-2025.pdf [↩] [↩]
  9. TACF Briefing (2025). Darling 58/54 – Darling 54 FAQ. https://tacf.org/darling-58 [↩] [↩] [↩]
  10. Data presented by Vasiliv Lakoba at TACF Webinar Chestnut Chat 44: 15 Dec 2023 – Darling 58 & Science Strategy Update, Part 1. https://tacf.org/chestnut-chat/# [↩] [↩]
  11. McKenna JR, reporting on experiments from Indiana (2023). TACF Webinar Chestnut Chat 44: 15 Dec 2023 – Darling 58 & Science Strategy Update, Part 1. https://tacf.org/chestnut-chat/#darling-58-update-sept-15-2023 [↩]
  12. Econexus. Discussion of the performance limitations of Darling 58/54 (2024).  https://www.econexus.info/publication/genetically-engineered-american-chestnut [↩]
  13. Campaign to STOP GE Trees et al (2019). Biotechnology  for Forest Health? The Test Case  of the Genetically Engineered  American Chestnut. https://stopgetrees.org/wp-content/uploads/2019/04/biotechnology-for-forest-health-test-case-american-chestnut-report-WEB-1.pdf [↩]
  14. Federal Register (2020) Petition for Determination of Nonregulated Status for Blight-Tolerant Darling 58 American Chestnut (Castanea dentata). Docket No. APHIS-2020-0030 https://www.federalregister.gov/documents/2020/08/19/2020-18135/state-university-of-new-york-college-of-environmental-science-and-forestry-petition-for [↩]
  15. SUNY ESF Progress Report 2024 (2024). https://www.esf.edu/chestnut/progress-report/index.php [↩]
  16. Canadian Chestnut Council (2022). https://cban.ca/wp-content/uploads/Canadian-Chestnut-Council-response-APHIS-D58.pdf [↩]
  17. Government of Canada website. https://inspection.canada.ca/en/plant-varieties/plants-novel-traits/general-public [↩]
  18. SilvaBio (2025). A breakthrough. https://www.silvabio.com/ [↩]
  19. Kamentz A (2024). GMOs could reboot chestnut trees. MIT Technology Review.  https://www.technologyreview.com/2024/10/23/1105275/gmo-chestnut-trees-american-castanea-genetics-revival [↩]
  20. Fu J (2019). Researchers can restore the American chestnut through genetic engineering. But at what cost? The Counter https://thecounter.org/american-chestnut-restoration-genetic-engineering-indigenous-sovereignty-gmo [↩] [↩]
  21. American Chestnut Cooperators’ Foundation (2024). https://accf-online.org/News2024Feb.pdf [↩]