Micropropagation of Douglas maple (Acer glabrum var. douglasii): 2. Light intensity and evaluation of in vitro and ex vitro rooting protocols

Abstract

Douglas maple (Acer glabrum Torr. var. Douglasii (Hook.) Dippel [Aceraceae]) has potential for habitat development in urban landscapes. Efficacious micropropagation methodology would enhance the value of this seed recalcitrant species. Three light intensities—6.6, 16.8, and 36.6 µmols•m⁻²•s⁻¹ (0.65, 1.58, and 3.44 µmols•ft⁻²•s⁻¹, respectively) PPFD—were tested for their effect on Douglas maple chlorophyll content, shoot length, number of nodes, and mean dry weight. Visually, plants appeared darker green under lower light intensity. However, mean dry weight of cultured microcuttings was significantly higher at higher light intensity. We tested in vitro and ex vitro rooting procedures for their ability to produce healthy roots on established microcuttings. IBA concentration (0, 1, 2, 4, and 8 µM) and the length of the initial microcutting propagule (2.0 to 3.0 cm [0.79–1.18 in]) or 3.5 to 4.5 cm [1.38–1.77 in]) were evaluated for enhancing in vitro rooting. Initial microcutting length as a covariate and concentrations of IBA (0.1% and 0.3%) in a talcum powder formulation were evaluated for enhancement of ex vitro rooting. Rooting treatments were assessed by measuring overall survival rate of plantlets after rooting and acclimatization. Greatest survival (92%) occurred with ex vitro rooting with a 0.1% IBA talcum powder treatment. In comparison, the best in vitro rooting treatment (1 µM IBA regardless of microcutting length) yielded just 75% survival after rooting and acclimatization. We verified efficacy of the ex vitro rooting protocol (100% rooting and acclimatization) using a second Douglas maple genotype (treated with 0.1% IBA talcum powder).