Adventitious root formation in hypocotyl cuttings of Picea sitchensis (Bong.) Carr. — the influence of plant growth regulators

summary A simple method for the study of adventitious root initiation on Sitka spruce [ Picea sitchensis (Bong.) Carr.] hypocotyl cuttings is described and was used to examine the effects of plant growth regulators. Twenty‐one‐day‐old seedlings, grown at a low light intensity (15–20 μmol m −2 s −1 ) to stimulate hypocotyl elongation, provided easy to handle tissues which were responsive to root inducing treatments. Spontaneous rooting only occurred at a low frequency on untreated cuttings and reliable rooting depended upon auxin treatment. When continuous auxin treatment was used, indole‐3‐butyric acid (IBA) was more effective than either indole‐3‐acetic acid (IAA) or 1‐naphthaleneacetic acid (NAA), and was optimal between 10 −6 and 10 −5 M. Pulse treatments with 10 −3 M IBA for as little as 10 min were sufficient to stimulate rooting. All other growth regulators examined were inhibitory to IBA induced rooting. 6‐benzylaminopurine (BA) was the most active being inhibitory down to a concentration of 3 × 10 −7 M when it was applied in a mixture with IBA. Pre‐treatment of hypocotyl cuttings with BA prior to auxin treatment demonstrated strong cytokinin ‘carry‐over’ inhibitory effects on rooting. Gibberellic acid A 3 (GA 3 ), abscisic acid (ABA) and 2‐chloroethyl‐phosphoric acid (ethrel) were less potent inhibitors of rooting.