“The American chestnut (Castanea dentata) was a foundational forest canopy species in eastern North America until an imported fungal blight (caused by Cryphonectria parasitica) rendered it functionally extinct across its native range. Biotechnological approaches, such as the Darling 54 (D54) transgenic line, have potential for future restoration of American chestnut, but field-based evaluations of blight tolerance have been limited. Field-based evaluation is 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 just within permitted orchards. This research reports on a two-year field trial of four- to five-year-old, T3- and T4-generation transgenic D54(+) saplings and their non-transgenic full-siblings in a permitted orchard in southern Maine. The field trial deployed a randomized block design with wild-type American chestnut and Chinese chestnut (Castanea mollissima) controls. In the two years, 261 trees were branch-inoculated in three replicates with EP-155, a highly virulent strain of the fungal blight. D54(+) trees consistently outperformed their negative siblings and outperformed Chinese chestnut in a limited comparison. To our knowledge, this is the first multi-year field trial of fungal blight inoculations comparing advanced generation D54 families. This field-based evaluation of blight tolerance in D54 transgenic chestnuts contributes to the goal of restoring this iconic species to its eastern North American native range.”

From bioRxiv.