Changes of Growth and Inflorescence Initiation by Exogenous Gibberellic Acid3 and 6-Benzylaminopurine Application in Phalaenopsis Orchids

This study was conducted to observe the effects of exogenous gibberellic acid(3) (GA(3)) and 6-benzylaminopurine (BAP) treatments on the growth and inflorescence initiation of Phalaenopsis and to determine whether hormonal applications can substitute for low-temperature exposure for floral transition. Phalaenopsis Queen Beer 'Mantefon' clones were treated with no hormones (control), GA(3) 100 mg/L, GA(3) 200 mg/L, BAP 100 mg/L, and GA(3) 100 mg/L + BAP 100 mg/L by foliar spray. The treatments were carried at 28 degrees C for vegetative growth and 20 degrees C for forcing, respectively. At 28 degrees C of vegetative temperature, all exogenous hormonal treatments did not induce inflorescence initiation, but lateral shoots were observed in BAP-treated plants even though this plant is a monopodial orchid. GA(3) significantly increased leaf length and decreased leaf width, and consequently increased length:width (L:W) ratio compared with the control and BAP alone. The trend grew as GA(3) concentration increased. Also, the GA(3) increased stem length and decreased stem diameter. At 20 degrees C of forcing temperature, L:W ratio responded similarly to 28 degrees C in GA(3) treatments, but leaf size was smaller than for the control or BAP alone. BAP accelerated inflorescence emergence and significantly increased inflorescence numbers, whereas GA(3) and GA(3) + BAP slightly delayed inflorescence emergence. GA(3) significantly promoted new leaf development at 20 degrees C of forcing condition. These results indicated that cytokinin was associated with the break of axillary vegetative and inflorescence meristems and exogenous GA(3) spray did not improve inflorescence initiation in Phalaenopsis. Although exogenous hormonal application did not substitute for low-temperature exposure, it showed a possibility in promoting the growth and inflorescence initiation.