A deadly fungus nearly erased the American chestnut from US forests more than a century ago, transforming one of the region's most important trees into a rare sight. Once widespread across eastern North America, the tree provided food for wildlife and people while its durable wood was prized for construction and furniture. Now, scientists are using advances in genomics to understand the genetic basis of chestnut blight resistance and identify trees with the most promising traits. A study published in Science in February 2026 found that genome-guided breeding could help researchers select resistant trees much earlier. The approach could accelerate restoration efforts, although significant scientific and regulatory challenges remain.
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A deadly fungus nearly erased the American chestnut
The American chestnut (Castanea dentata) was once one of the most important hardwood trees across the eastern US, particularly throughout the Appalachian region. Mature trees commonly reached 50 to 100 feet in height, with some growing even taller over their long lifespans.
The tree played an important role in forest ecosystems. Its nuts provided food for wildlife and people, while its straight-grained, rot-resistant wood was widely used for buildings, furniture, fencing and other products.
The species began its dramatic decline after chestnut blight, a fungal disease caused by Cryphonectria parasitica, was introduced to North America.
The fungus was first identified in 1904
Chestnut blight was first recognised in the US in 1904 in New York City, including at the Bronx Zoo. The fungus subsequently spread through much of the American chestnut's native range.
The disease attacks the bark and cambium of chestnut trees, eventually killing the above-ground portion of infected trees. Young shoots can emerge again from surviving roots, but they are usually infected and killed before reaching maturity.
Within several decades, the once-dominant tree had virtually disappeared as a mature component of eastern forests.
Researchers have been attempting to restore the American chestnut for about a century. One of the main strategies has been conventional crossbreeding.
Scientists have crossed American chestnut with Asian chestnut species, particularly Chinese chestnut, which evolved alongside the blight and possesses greater resistance.
The resulting hybrids are then repeatedly crossed back with American chestnut in an effort to retain the American species' appearance, growth characteristics and ecological traits while incorporating resistance.
However, conventional breeding is slow. Researchers often need to wait years for young trees to mature enough to assess their resistance and other important characteristics.
New genomic research could speed up breeding
A major development came from a study published in Science in February 2026. Researchers investigated the genetic architecture of American chestnut traits and examined how genomic information could improve breeding programmes.
The approach uses genomic selection, in which researchers analyse DNA markers to predict which young trees are more likely to possess desirable traits.
Instead of growing every tree for years before determining whether it is worth testing, breeders can use genomic information to identify promising candidates much earlier.
This could help researchers select better parents, reduce the number of trees requiring extensive field testing and potentially accelerate the restoration process.
Blight resistance involves multiple genes
Scientists have found that resistance to chestnut blight is not controlled by a single genetic switch.
Multiple regions of the genome can influence how a tree responds to the fungus. Other genetic regions affect characteristics such as growth, form and environmental adaptation.
This makes restoration considerably more complicated than simply inserting one resistance gene into the American chestnut.
The new genomic approach aims to understand these combinations and help breeders retain desirable American chestnut characteristics while increasing resistance to the disease.
Surviving trees could hold valuable genetic clues
Although the American chestnut was devastated, some trees have survived in the wild. Their roots can produce new shoots, and a small number of trees have reached significant sizes.
Researchers are studying these survivors to determine whether some possess genetic variants that contribute to greater blight tolerance.
The genomes of these trees could provide additional genetic material for breeding programmes and help scientists understand why certain individuals have survived when most of the population did not.
Scientists are also exploring genetic engineering
Genomic research is being complemented by genetic transformation and gene-editing approaches.
One well-known strategy involved introducing a wheat gene that produces oxalate oxidase, an enzyme that breaks down oxalic acid. The fungus produces oxalic acid as part of its attack on plant tissue.
Earlier research suggested that this approach could improve resistance, but more recent field observations have raised concerns about some trees carrying the gene, including reports of abnormal growth and slower development.
Researchers are therefore investigating additional genes and biological mechanisms rather than relying on one engineered solution.
CRISPR could provide another option
Modern gene-editing technologies such as CRISPR could eventually allow scientists to modify specific genes within the American chestnut itself.
Rather than introducing genetic material from another species, gene editing could potentially alter existing American chestnut genes or reproduce naturally occurring resistance mechanisms found in Asian chestnuts.
However, this remains an area of research. No CRISPR-based American chestnut is currently ready to restore forests on a large scale.
Restoring the tree involves more than disease resistance
Scientists ultimately want to restore a tree that can survive and reproduce in real forests, not merely withstand the fungus under controlled laboratory conditions.
Researchers therefore need to consider growth rate, reproductive ability, genetic diversity, climate adaptation and interactions with other organisms.
This is particularly important because climate conditions across the American chestnut's historic range are changing. A restoration programme will need to preserve enough genetic diversity for future populations to adapt to different environments.
Regulatory barriers remain
Genetically engineered trees face regulatory requirements before they can be extensively tested or released into the environment.
The US Department of Agriculture issued a Request for Information in May 2026 concerning modified organisms subject to the Plant Protection Act. The process could contribute to future changes in how certain genetically modified organisms are regulated.
However, the move does not amount to approval for genetically engineered American chestnuts to be released into forests.
Field trials remain subject to regulatory oversight, particularly because mature trees can produce pollen and seeds that can spread beyond experimental plots.
The American chestnut could eventually return
The latest genomic research does not mean that the American chestnut has already been restored. Instead, it provides scientists with more powerful tools to understand resistance and make breeding decisions.
Genome-guided breeding could accelerate conventional approaches, while genetic transformation and gene editing could provide additional routes for developing resistance. At the same time, surviving American chestnuts remain valuable sources of genetic diversity.
The ultimate goal is to produce trees that combine blight resistance with the growth, ecological characteristics and genetic diversity of the American chestnut.
