Clonal propagation of Oregon ash (Fraxinus latifolia) via somatic embryogenesis

Abstract Key message This first account of Oregon ash somatic embryogenesis identifies unique auxin and abscisic acid responses distinct from green and white ash, advancing clonal propagation techniques for reforestation. Abstract Oregon ash ( Fraxinus latifolia ), the only ash species native to the Pacific Northwest, is vulnerable to the invasive beetle, emerald ash borer (EAB; Agrilus planipennis ). EAB was first detected in North America in 2002, and subsequently spread primarily east of the Rocky Mountains, with greatest concern centered on more abundant and economically valuable ash species, such as green ash ( Fraxinus pennsylvanica ) and white ash ( Fraxinus americana ). Given the devastating effects of EAB on ash populations and limited natural regeneration capacity of Oregon ash, developing reliable propagation methods is essential for restoration efforts. Thus, our objective was to develop somatic embryogenesis (SE) protocols for Oregon ash by evaluating effects of auxin concentration, explant manipulation, and abscisic acid supplementation on embryogenesis induction, proliferation, and maturation. Embryogenesis induction was influenced by the interaction between picloram concentration and explant cutting ( p = 0.03), with optimal rates achieved using 0.2 mg/L picloram with intact embryos (16%) or 0.1 mg/L picloram with excised cotyledons (15%). During proliferation, 2,4-D significantly improved culture growth compared to picloram ( p = 0.03). Genotype also affected Oregon ash proliferation response to varied minute (0.1–10µM) abscisic acid (ABA) concentrations ( p < 0.01).Our findings lay the foundation for understanding SE response in Oregon ash and demonstrate the feasibility of clonal propagation for this species, providing essential tools for conservation efforts as EAB threatens Pacific Northwest ash populations.