Effects of Plant Growth Regulators Ethephon and Protone on Flowering of Bougainvillea x buttiana 'Afterglow'

Bougainvillea cultivars are widely used ornamentals valued for their ability to bloom profusely while tolerating poor growing conditions such as pollution, compaction, and drought stress. Bougainvillea x buttiana cultivars are mostly considered qualitative short-day plants that flower more readily and profusely under short day lengths. Water stress has been shown to partially substitute for short-day induction. Ethylene and abscisic acid (ABA) are two drought-stress-related plant hormones that may have an important role to plant in drought-stress-induced flowering in bougainvillea. The plant growth regulators Ethephon (2-Chloroethylphosphonic acid) and ProTone® (s-ABA) were applied to B. x buttiana ‘Afterglow’ to investigate the effects of exogenous applications of ethylene and ABA on the flowering response of this cultivar, under 14 hour photoperiod. Both Ethephon and ProTone® applied as a “sprench” at 75ppm concentration did not result in significant increase in flowering. However, Ethephon treatment corresponded with a slight increase in flowering, while ProTone® treatment did not. ProTone® treatment appeared to cancel out the effect of Ethephon when applied simultaneously at 75ppm concentration. Further research into relationship between ethylene and ABA in flowering response of Bougainvillea, as well as the application rates of ethylene and ABA growth regulators, is warranted.