Evaluating transgenic Darling 54 American chestnuts for reintroduction: Insights from survivorship, growth, and respiration in a common garden

The American chestnut ( Castanea dentata [Marsh.] Borkh.), once dominant in eastern North American forests, was devastated by Cryphonectria parasitica . Transgenic Darling 54 chestnuts, engineered with an OxO gene for blight tolerance, retain the native American chestnut’s genome and offer a potential restoration solution. This study evaluates their performance relative to non-transgenic and hybrid chestnuts to determine their suitability for ecological restoration. We measured survivorship, growth, crown morphology, and dark respiration rates of three-year-old trees in a common garden experiment featuring nearly 500 trees across five chestnut types, including Darling 54 transgenic (OxO+) and non-transgenic (OxO-) full-siblings. Statistical analyses assessed the effects of transgene status and maternal lineage on growth performance and respiration. Darling 54 trees exhibited strong survivorship and a favorable growth form comparable to related non-transgenic chestnuts, despite reduced growth rate and initial survival. Elevated leaf respiration was observed in OxO+ trees during late-season measurements, suggesting a potential metabolic cost or pleiotropic effects associated with transgenesis. Overall, Darling 54 trees maintain desirable traits, but reduced growth and intermittently higher respiration rates may indicate a trade-off. Although Darling 54 American chestnuts show promise as restoration trees, additional research is needed to assess blight tolerance, long-term performance under competitive forest conditions, and whether growth constraints persist over time. • Transgenic chestnuts survived and grew well, despite reduced growth overall. • Transgenic trees retain a vertically-oriented crown structure, typical of the species. • Slower transgenic tree growth coincides with periodically stimulated leaf respiration. • Results support using transgenic chestnuts in forest restoration efforts.