Chemical Stimulation of Floral Initiation in Florists’ Hydrangea

Abstract

Abstract Ancymidol and paclobutrazol (13 weekly foliar spray applications of 100 mg/liter AI) stimulated inflorescence initiation of Hydrangea macrophylla Ser. ‘Merritt's Supreme’ plants under a noninductive continuous photoperiod at 24°C minimum daily temperature. Inflorescence primordia were present on plants having 12-14 subtending leaf pairs. Four expanded leaf pairs prior to initiation of treatments were sufficient to sustain inflorescence development. Plant height was controlled effectively with 10,000 mg/liter daminozide, 50 and 100 mg/liter ancymidol, and 100 mg/liter paclobutrazol treatments. Chlormequat at 3000 mg/liter did not suppress internodal elongation. Number of expanded leaf pairs per plant was significantly less than on control plants for all treatments except chlormequat at 3000 mg/liter. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); β[(4-chlorophenyl)methyl]-α-(l,l-dimethylethyl)-1 H -l,2,4-triazole-l-ethanol (paclobutrazol); butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); [2-chloro- N , N , N -trimethylethanaminium chloride (chlormequat chloride); 1 H -indole-3-butanoic acid (IBA).