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

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 for this functionally extinct tree species. We compared the performance of three-year-old trees in a common garden experiment featuring nearly 500 trees across five chestnut types, including Darling 54 transgenic (OxO+, n = 198) and non-transgenic (OxO-, n = 201) full-siblings, hybrid chestnuts (B3F3 backcross hybrids, n = 34; F1 hybrids, n = 17), and Chinese chestnuts (n = 55). We measured survivorship, growth, crown morphology in August 2024 and dark respiration rates in May and August 2024 to determine the suitability of Darling 54 transgenic trees for ecological restoration. Statistical analyses assessed the effects of transgene status and maternal lineage on growth performance and respiration. Darling 54 OxO+ trees exhibited strong survivorship and a favorable growth form comparable to related non-transgenic chestnuts, despite reduced growth rate and survival. Elevated leaf respiration was observed in OxO+ trees during late-season measurements, suggesting a potential metabolic cost associated with transgenesis. Overall, Darling 54 OxO+ chestnuts maintain desirable traits, but reduced growth and intermittently higher respiration rates may indicate a trade-off. Although OxO+ 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.