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.