In vitro and ex vitro rooting of micropropagated shoots using three green ash ( Fraxinus pennsylvanica ) clones

Abstract

Shoot multiplication using seedling materials was achieved by subculture on Murashige and Skoog salts with Gamborg's B5 vitamins (MSB5) medium containing a combination of 5 μM 6-benzyladenine (BA), 5 μM thidiazuron (TDZ), and 1 μM indole-3-butyric acid (IBA) with three green ash (Fraxinus pennsylvanica) clones, SD1009 (South Dakota origin), SD2002 (South Dakota origin), and KA2018 (Kansas origin). Shoots were rooted using in vitro and ex vitro methods. For in vitro rooting studies, elongated shoots were transferred to rooting plugs supplied with liquid MSB5 medium containing a 3×3 factorial arrangement of two different auxins, α-naphthaleneacetic acid (NAA) and IBA, at three concentrations (0, 5, and 10 μM). The most effective treatment for in vitro root number, root length, and shoot height was 5 μM IBA. The three clones also were tested for ex vitro rooting using a quick dip in 1 mM NAA, 1 mM IBA, or control (no auxin). The maximal ex vitro rooting response occurred when shoot explants of the three clones were dipped in 1 mM IBA. Significant clonal differences were noted in response to in vitro and ex vitro rooting treatments. Rooted plantlets were acclimated to the greenhouse.