Two-year field testing of genetically engineered American chestnut reveals fungal blight tolerance

The American chestnut (Castanea dentata [Marsh.] Borkh.) was a foundational forest canopy species in eastern North America until an accidentally imported fungal blight (caused by Cryphonectria parasitica [Murr.] Barr.) rendered it functionally extinct across its native range. Biotechnological approaches, such as the bioengineered Darling 54 line, have potential for future restoration of American chestnut, but field-based evaluations of blight tolerance have been limited. Progress has been slowed by the many years it takes for seedlings to grow to saplings, then to full-fledged trees. Current regulatory restrictions also constrain the testing of transgenic chestnuts to within permitted orchards. This research reports on a two-year field trial of Darling 54, their non-transgenic wild-type siblings and Chinese chestnut (Castanea mollissima Blume) controls. The research deployed a randomized block design to test for blight tolerance. In the two years, three replicates each of 261 trees were branch-inoculated with EP-155, a hghly virulent isolate of the fungal blight. Based on canker length, Darling 54 trees consistently outperformed their non-transgenic wild-type siblings and Chinese chestnut. To our knowledge, this is the first report of a multi-year field trial of fungal blight inoculations comparing advanced generation Darling 54 families. This field-based evaluation suggests that reintroduction programs using Darling 54 American chestnuts, which can commence after federal approval, may offer a promising path to success.