Page 19 - Tree Line - North Carolina Forestry Association - Third Quarter 2021

The goal of TACF was to transfer resistant genes
to the American chestnut while retaining all the characteristics of the American tree. Backcrossing with Chinese chestnuts was the first approach that TACF employed. The first step was to produce hybrid trees between American and Chinese chestnut trees that would have the resistant genes. Next, these hybrids would be crossed back to American chestnuts. This process was repeated for three generations, gradually phasing out most of the Chinese characteristics, except resistance. Finally, the third-generation chestnuts would be crossed with each other to ensure that the resistant genes would be inherited by future generations. The final product is a 15/16 American chestnut that breeds true for resistance.
These trees are now being employed in restoration projects by TACF in northern latitudes. Unfortunately, another exotic invasive pest, phytophthora root rot (ink disease), still limits restoration efforts in southern latitudes.
The New York State Chapter of TACF took another approach to developing resistant chestnuts, which involves biotechnology. Scientists at the State University of New York College of Environmental Science and Forestry (SUNY-ESF) in Syracuse have genetically modified chestnuts by introducing a wheat gene. Wheat, and many other grasses, produce an
enzyme called oxalate oxidase that breaks down the destructive chemical of the blight — oxalic acid —
and renders it harmless. There is no evidence that the enzyme is harmful to humans, animals, plants, or the environment. Through a complicated process involving somatic embryos and agrobacterium, the wheat gene
is inserted into tissue that develops into chestnut treelets. After years of research, the ESF scientists
have developed a transgenic American chestnut tree, called “Darling 58”, with inheritable blight tolerance and 100% of its natural genes. To succeed, Darling 58 needs to be bred with wild-type American chestnut trees to diversify the population and provide regional adaptation. However, through a series of petitions, Darling 58 must first be granted “nonregulatory” status from three different federal agencies: USDA-APHIS (Animal and Plant Health Inspection Service), EPA, and FDA. These petitions are now being reviewed.
TACF has established a blueprint for research and restoration of host trees decimated by exotic and invasive pests, of which there are many examples that threaten our North Carolina forests, including the emerald ash borer, balsam wooly adelgid, Asian longhorned beetle, sudden oak death, laurel wilt disease, and the hemlock wooly adelgid (HWA).
Chestnut blight canker WILLIAM POWELL, CC BY-ND
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ncforestry.org / THIRD QUARTER 2021 17