Genomic Revolution Offers Hope for Restoring the American Chestnut

For over a century, the American chestnut tree, once a dominant species in eastern North American forests, has been decimated by an invasive fungal disease. Now, a new era of genomic breeding is offering a pathway to restore this iconic tree, potentially returning it to its native range within the coming decades.

The American Chestnut’s Decline

The American chestnut (Castanea dentata) was a vital part of the eastern U.S. Ecosystem and economy. Billions of trees thrived from Maine to Mississippi, providing food for wildlife and humans alike. In the early 1900s, an imported fungal disease, chestnut blight (caused by Cryphonectria parasitica), and root rot (Phytophthora) began to devastate the population. The fungus creates cankers that girdle the trunk, ultimately killing the tree.

Genomic Selection: A Faster Path to Restoration

Traditional breeding methods have been employed to develop blight-resistant chestnut trees, primarily by crossbreeding with the Chinese chestnut (Castanea mollissima), which possesses natural resistance. However, this process is sluggish, as chestnut trees take years to reach reproductive maturity. A new approach, genomic selection, is dramatically accelerating this process.

Genomic selection involves using computer models to associate a tree’s DNA profile (genotype) with its observed resistance to disease (phenotype), such as canker size. This allows breeders to predict a tree’s resistance based on its DNA alone, provided it is related to trees already evaluated in the field. By selecting the most resistant parent trees for breeding and then focusing on their most resistant offspring, breeders can significantly improve disease resistance with each generation. This “recurrent genomic selection” (RGS) is now the primary strategy for breeding disease resistance into American chestnut trees [The American Chestnut Foundation].

Recent Advances and Expected Outcomes

Recent research, including a study published in Science, demonstrates the effectiveness of genomic selection in accelerating American chestnut restoration [Science]. Researchers at Berry College and The American Chestnut Foundation have been instrumental in generating the breeding lines, experimental protocols, and data used in these analyses [Berry College].

According to Jared Westbrook, director of science at The American Chestnut Foundation, genome-enabled breeding is expected to produce the next generation of trees with roughly twice the average blight resistance of current populations, while maintaining approximately 75% American chestnut ancestry [Berry College]. These trees are anticipated to begin producing large quantities of seed for restoration within the next decade [Berry College].

The approach allows breeders to identify promising seedlings before years of field testing, shortening breeding cycles – a critical advantage for a long-lived tree species [Berry College].

Preserving Genetic Diversity

Beyond disease resistance, The American Chestnut Foundation similarly focuses on preserving the regional genetic diversity of remaining wild American chestnut populations. This ensures that reintroduced trees are adapted to local conditions and can continue to evolve and survive in a changing environment [The American Chestnut Foundation].

Looking Ahead

The combination of genomic selection and preservation of genetic diversity offers a promising future for the American chestnut. The revitalization of this iconic tree could have significant ecological and economic benefits, restoring a vital component of eastern forests and providing a sustainable resource for future generations [AP News].