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

Abstract

This study was conducted to observe the effects of exogenous gibberellic acid3 (GA3) 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), GA3 100 mg/L, GA3 200 mg/L, BAP 100 mg/L, and GA3 100 mg/L + BAP 100 mg/L by foliar spray. The treatments were carried at 28 °C for vegetative growth and 20 °C for forcing, respectively. At 28 °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. GA3 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 GA3 concentration increased. Also, the GA3 increased stem length and decreased stem diameter. At 20 °C of forcing temperature, L:W ratio responded similarly to 28 °C in GA3 treatments, but leaf size was smaller than for the control or BAP alone. BAP accelerated inflorescence emergence and significantly increased inflorescence numbers, whereas GA3 and GA3 + BAP slightly delayed inflorescence emergence. GA3 significantly promoted new leaf development at 20 °C of forcing condition. These results indicated that cytokinin was associated with the break of axillary vegetative and inflorescence meristems and exogenous GA3 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.

Exogenously applied gibberellic acid and benzylamine modulate growth and chemical constituents of dwarf schefflera: a stepwise regression analysis

“…Plant growth regulators will not be completely mobile if they are not sprayed directly on the leaf attached to the plant 73 . If only a single treated leaf remains green while other leaves abscise, assimilates will preferably translocate to the tissues treated with plant growth regulators and accumulate 74 . It is hypothesized that the hormone leads to assimilate translocation by establishing a new source-sink relationship 41 .…”

Exogenous GA3 promotes flowering in Paphiopedilum callosum (Orchidaceae) through bolting and lateral flower development regulation

“…Monopodial orchids, such as Phalaenopsis , have an apical meristem that remains active indefinitely while the bud primordia, which are capable of developing inflorescences, are formed in the axil of each leaf. Two or three inflorescences can be expected from the leaf axil under a 6-benzylaminopurine (6-BA) hormone treatment [ 25 ]. In sympodial orchids, such as Paphiopedilum , a new shoot may arise from the base of the previous shoot and differentiation of the flower bud primordium is directly associated with every new shoot [ 2 ].…”

“…For orchid plants, the impact of GA 3 varies among species. For example, applied alone, exogenous GA 3 negligibly affected flower induction in Phalaenopsis [ 25 ]. Nevertheless, an injection of optimum levels of GA 3 can break flower bud dormancy under high temperature and promote the continuous development of inflorescences [ 30 , 31 ].…”

Effect of Benzyl Amino Purine (BAP) on the Leaf Growth of Vanda limbata Blume Orchid In Vivo

“…Burhan (2017) reported that spraying BAP 100 and 200 mg l -1 produced the largest pseudo-stem diameter, more new leaves and induced flowering in hybrid Dendrobium orchids. Lee et al (2021) showed that spraying BAP 100 mg l -1 on Phalaenopsis orchids increased leaf width, stem diameter, accelerated flowering and emergence of lateral bud growth. The three studies used high concentrations of BAP on various types of orchids.…”