Copper Compounds Influence in Vitro Rooting of Birch Microcuttings

Abstract

The effects of woody plant medium (WPM) with various formulations and concentrations of Cu+2 on in vitro rooting and subsequent shoot growth of microcuttings of a Betu pubescens × papyrzfera (birch) clone were monitored for 28 days. Adventitious root initiation and elongation were reduced in magnitude and slowed in development by moderate to high Cu (as CuSO4·5H2O) concentrations, with near zero root regeneration occurring at 157 μm Cu. Shoot growth was also inhibited by 157 μM Cu as cupric sulfate. Copper-toxicity symptoms (senescent leaves, necrotic stems, and bulbous and stunted roots) were significantly increased by moderate to high levels (≥ 79 μm) of Cu as cupric sulfate. Microcuttings responded differently to Cu+2 applied as cupric chloride (CuCl2·2H2O). Root initiation, root elongation, and root branching were increased by moderate concentrations of Cu as cupric chloride. Shoot growth was slightly stimulated by cupric chloride at moderate levels. No significant increase in Cu-toxicity symptoms was observed at concentrations up to 157 μm Cu as cupric chloride. Cupric acetate [Cu(CH3 COO);H2O] and cupric carbonate [CuCO3·Cu(OH)2] produced more severe Cu-toxicity symptoms than cupric sulfate. Root regeneration and shoot growth were inhibited and increased Cu-toxicity symptoms were apparent even with low concentrations (39 μm) of Cu as cupric acetate or cupric carbonate. There was little or no effect on root regeneration when the Cu+2 in cupric sulfate was replaced by different cations, i.e., magnesium sulfate (MgSO4·7H2O), calcium sulfate (CaSO4·2H2O), and sulfuric acid (H2SO4), a result suggesting that the observed responses could be attributed to the Cu+2 concentration. Changes in media pH did not correspond to Cu-toxicity symptoms or alterations in root or shoot growth by the Cu compounds.