Gibberellic Acid Reverses Effects of Excess Paclobutrazol on Geranium

Abstract

Paclobutrazol (PBZ) was applied to `Mustang' geranium (Pelargonium × hortorum L.H. Bailey) as a single growth-medium drench at 0.06 mg a.i./pot or as a single foliar spray at 100 mg·liter -l when the plants had three to four expanded true leaves (34 days after sowing). At these rates, PBZ caused excessive growth suppression but plants flowered earlier than untreated controls. A single foliar spray of gibberellic acid (GA) at 100 mg·liter -l applied 0 (same day), 7, 14, or 21 days after PBZ reversed the growth suppression caused by PBZ. Plants treated with GA 3 0 or 7 days after PBZ were as tall or taller and flowered at the same time as or later than the untreated (no PBZ, no GA 3 ) controls. Plants treated with GA, 14 or 21 days after PBZ were shorter and flowered earlier than untreated controls but were taller than plants treated with PBZ alone. Response to GA 3 was similar whether PBZ was applied as a drench or as a spray. Chemical name used: (+)-(R*,R*)-β([4-chlorophenyl]methyl)-α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol).