In vitro propagation of Douglas maple (Acer glabrum var. douglasii): 1. Role of basal medium formulation and concentrations of supplemental minerals and cytokinin on optimization of shoot multiplication

Abstract

Douglas maple (Acer glabrum Torr. var. douglasii (Hook.) Dippel [Aceraceae]) is a potentially valuable landscape plant that lacks efficacious asexual propagation protocols. We conducted a series of developmental experiments to evaluate basal salts, supplemental minerals, and cytokinins to optimize culture medium formulations. Three commercial formulations of basal salts were evaluated, Driver and Kuniyaki Walnut (DKW), Murashige and Skoog (MS), and Woody Plant Medium (WPM). The DKW medium was superior to the other commercially available nutrient formulations for promoting shoot growth and enhancing node production. Iron supplementation (addition of 45 mg/l) resolved issues of chlorosis associated with reduced microcutting growth and multiplication rates. Supplementation of 12.0 mg/l boric acid resolved shoot tip necrosis problems. Cytokinin optimization with respect to shoot length was evaluated in 3 experiments, in which, BA, kinetin, MT, TDZ, and zeatin were all tested at various concentrations. Autoclaved zeatin at 4 µM or MT at 2 µM were the best 2 cytokinins and concentrations for promoting shoot growth. Two zeatin sterilization methods were tested, autoclaving following addition to medium, and filter sterilizing prior to adding to post-autoclaved medium. Autoclaving media that included zeatin proved to be effective methodology, thus avoiding filter sterilization, which commonly introduces microbial contaminants into media. Overall, Douglas maple growth and development during micropropagation were optimized on DKW medium, supplemented with iron (45 mg/l) and boron (12.0 mg/l) and either 4 µM autoclaved zeatin, or with 2 µM MT. Economic efficiency is improved by using MT, rather than the much more expensive zeatin.