Benzyladenine promotes flowering in Doritaenopsis and Phalaenopsis orchids

Two experiments were performed to determine how application of the cytokinin benzyladenine (BA) influenced flowering in Doritaenopsis and Phalaenopsis orchid clones. In the first experiment, two vegetative orchid clones growing in 15-cm pots were transferred from a 28 degrees C greenhouse that inhibited flowering to a 23 degrees C greenhouse for flower induction (day 0). A foliar spray (0.2 L m(-2)) containing BA at 100, 200, or 400 mg L-1 or 25, 50, or 100 mg L-1 each of BA and gibberellins A(4) + A(7) (BA+GA) was applied on days 0, 7, and 14. Plants treated with BA alone at 200 or 400 mg L-1 had a visible inflorescence 3-9 days earlier and had a mean of 0.7-3.5 more inflorescences and 3-8 more flowers per plant than nontreated plants. The application of BA+GA had no effect on inflorescence number and total flower number at the rates tested. In the second experiment, three orchid clones received a single foliar spray of BA at 200 mg L-1 at six time points relative to time of transfer from 29 degrees C to 23 degrees C (-1, 0, +1, +2, +4, or +6 weeks). A separate group of plants received a BA application at week 0 but was maintained at 29 degrees C. Inflorescence number was greatest in all three orchid clones when plants were treated with BA 1 week after the temperature transfer. Plants that were sprayed with BA and maintained at 29 degrees C did not initiate inflorescences. The promotion of flowering by the application of BA suggests that cytokinins at least partially regulate inflorescence initiation of Doritaenopsis and Phalaenopsis, but its promotion is conditional and BA application cannot completely substitute for an inductive low temperature.