LAUSR

Abstract Premise Of the approximately 430 species of oaks (Quercus spp.) that have been assessed, 31% are threatened with extinction and in need of safeguarding. However, oak seeds cannot be seed banked, and thus rely on alternative strategies such as in vitro culture for ex situ conservation. One challenge to this approach is low culture initiation rates. Our objective was to identify factors that may improve the establishment of shoot cultures in vitro using new growth collected from mature trees. Methods Shoot cuttings were harvested from individuals of five different oak species (Q. alba, Q. bicolor, Q. macrocarpa, Q. muehlenbergii, and Q. palustris). Shoots were cultured onto medium with or without 50 µM silver thiosulfate (STS), a known inhibitor of the stress hormone ethylene. Cultures were grown for one month, at which point shoots were assessed for survival. Results Shoot survival was significantly greater in shoots cultured on medium containing STS compared to the control group, with the overall survival rate increasing from 65% to 73%. Discussion Increasing the survival rate of newly established cultures is important in ensuring that material collected from endangered species has the best chance for survival, which is critical for successful ex situ conservation.