Micropropagation methodology for Douglas Maple (Acer glabrum var. douglasii)

Abstract

Douglas maple (Acer glabrum Torr. var. douglasii (Hook.) Dippel [Aceraceae]) has habitat improvement characteristics that make it valuable for restoration and revegetation. Plants of the species also make very attractive specimen trees in urban landscapes. Recalcitrance during seed propagation reduces the potential of Douglas maple for use in either restoration or landscaping purposes. Herein, we propose a research-based, efficient micropropagation protocol to bypass seed propagation issues and allow production of marketable plants in commercial quantities. Inferences from previous research on maples suggests softwood stems harvested in spring or summer provide the best tissue for culture induction of single-node explants. Nutrient modification of commercial culture medium formulations is critical for preventing deleterious deficiency symptoms. Chlorosis and shoot tip necrosis occur when Douglas maple plantlets are grown on Driver and Kuniyuki Walnut (DKW) medium, which is the most suitable unmodified medium when compared with Murashige and Skoog (MS) and Woody Plant Medium (WPM). Providing relatively low light levels (photon flux of roughly 17 µmols·m⁻²·s⁻¹ (1.58 µmols·ft⁻²·s⁻¹) during microculture prevents abnormal growth and maximizes rate of multiplication. Meta-topolin may be preferable to trans-zeatin as a cytokinin to enhance multiplication for reasons of cost and comparable performance. Reproduction of plantlets is optimized using a 6-wk subculture cycle, wherein an estimated 12-fold explant multiplication rate can be achieved. Rather than rooting plantlets in culture, we found they acclimatized better to ex vitro conditions if rooted ex vitro (up to 92% survival after establishment in pots).