In 1990, the New York Chapter of The American Chestnut Foundation (NY-TACF) and the State University of New York’s College of Environmental Science & Forestry (ESF) began a collaboration to take a complementary approach to traditional breeding: transgenically add new genes to the American chestnut to enhance the tree’s ability to withstand blight. The most effective gene tested to date is a gene from wheat called oxalate oxidase, or OxO. The OxO enzyme breaks down oxalic acid, which is one of the primary “weapons” the blight fungus uses to attack chestnut trees. The result of this research was the development of a transgenic American chestnut tree dubbed Darling 58. Watch this brief animated video about the OxO gene and how it works.

Researchers at ESF have conducted many experiments to confirm the safety of this gene in the American chestnut’s natural environment. Results to date show that there are no significant ecological effects of inserting the OxO gene, apart from enhancing blight tolerance (read more here). There are also no negative human health consequences of inserting OxO, as this gene is naturally present in many food crops and is non-allergenic. Three U.S. federal agencies (USDA, EPA, and FDA) are rigorously evaluating potential environmental and health effects of transgenic American chestnuts. Federal approval must be granted before the trees can be distributed or widely planted. In the 2020 winter issue of TACF’s Chestnut magazine, part 1 of a 3-part series describes tests conducted on the nuts as a food product. Part 2, in the 2020 spring issue, evaluates the safety to wildlife. Part 3, on safety to plants and fungi, can be found here.

If chestnut trees containing the OxO gene are crossed with surviving American chestnut trees, half the offspring will inherit the OxO gene and will have enhanced blight tolerance, just like the transgenic parent.

Figure 1: Blight cankers on first generation progeny of transgenic American chestnut x wild American chestnut. The tree on the left inherited the oxalate oxidase gene and the tree on the right did not inherit the gene. The swollen canker on the transgenic tree indicates an active response to the blight and new growth around the canker, similar to cankers on some Chinese chestnuts. In contrast, the canker looks sunken on the non-transgenic tree where it has completely killed the surrounding tissue.

The resulting progeny will be essentially 100% American chestnut because none of the American chestnut genome has been removed or replaced. This characteristic allows the possibility of rescuing much of the remnant genetic diversity and local adaptations in the surviving population of American chestnut. If federal approval is granted, TACF plans to breed transgenic tree with wild trees over multiple generations to dilute out the transgenic founder genome and increase the genetic diversity of the blight-tolerant population. Read more about our plan here.

TACF’s chapters and staff are currently conserving 1,000 wild-type American chestnuts in orchards to use as parent trees in this diversification effort. To participate in the wild tree conservation effort contact TACF’s regional coordinator from your region. You can also donate to TACF to support restoration using transgenic blight-tolerant trees.

Figure 2: Pollination of wild type American chestnut with transgenic pollen containing the oxalate oxidase gene.

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