Gibberellic acid and cytokinin affect Phalaenopsis flower morphology at high temperature

Abstract

Gibberellin A3 (GA3: 1, 3, or 5 μg/shoot) 6N-benzyladenine (BA: 1, 3, or 5 μg/shoot), or both were applied to the flowering shoots of a white hybrid Phalaenopsis orchid (Leda) when they were 2 to 3 cm (stage 1, no flower primordia) long at high temperature (30 °C day/25 °C night). When flowering shoots were treated with GA3 alone, deformed flowers were more frequent with increasing GA3 concentrations. The occurrence of GA3-induced deformed flowers was prevented by BA at the same dose as GAs when applied 4 days after GA3 treatment. BA (1, 3, or 5 μg/shoot) was also applied 4 days before (time 1) or 4 days after (time 2) GA3 (1 μg/shoot) treatment for regulating plant characteristics. The application of BA at 1 or 5 μg/shoot to stage 1 flowering shoots at time 2 resulted in short internodes between florets, whereas BA application at time 1 had no effect. Simultaneously, BA at 1 or 5 μg/shoot applied at time 1 or time 2 to stage 2 (5 to 6 cm long, two-to three-flower primordia) flowering shoots also shortened internode length between florets as compared to GA3 alone. When a stage 1 flowering shoot was given BA (3 or 5, but not 1 μg/shoot) and then treated with GA3 4 days later, flower count was slightly reduced as compared to treating with GA3 alone. However, a high dose of BA applied at time 1 or time 2 on stage 2 flowering shoots had no effect on flower count. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)], gibberellic acid (GA3).