Effects of plant growth regulators and polyamines on bract longevity in Bougainvillea buttiana

There are no reports on plant growth regulators (PGR) or polyamines being used to stimulate bract longevity in bougainvillea species, yet understanding how PGR and polyamines influence bougainvillea bract phenology is important for flower profitability. Potted bougainvillea plants in four different bract development stages based on bract diameter were pre-treated with salicylic acid (SA) at a concentration of 0.5 mM combined with 1-naphthaleneacetic acid (NAA, 0.13 mM), gibberellic acid (GA, 0.29 mM), and 6-benzylaminopurine (BA, 0.22 mM) in 100 mL mixtures. Three 100 mL polyamine treatments [diamine putrescine (Put), triamine spermidine (Spd), and tetraamine spermine (Spm)] at 1 mM were also individually sprayed on bougainvillea bracts. Control bracts were sprayed only with water. Different PGR combinations and single polyamine treatments acted differently on bract longevity and endogenous 1-aminocylopropane-1-carboxylic acid (ACC) content, and each combination and single polyamine was not equally significant in regard to coordinating a response to ACC regulation. In combined chemical treatments, maximum and significantly prolonged bract longevity in all stages were detected in the SA + NAA + GA + BA treatment compared to controls and other combinations, and longevity increased as bract stage progressed. A strong synergistic interaction was observed between SA and NAA regarding bract longevity and ACC levels. Moreover, Put also significantly prolonged bract longevity and remarkably reduced endogenous ACC content at all stages, this effect increasing as bract stage progressed compared to Spd, Spm, and controls. Therefore, the effects of SA + NAA + GA + BA and single Put (1 mM) applied to bougainvillea bracts for increasing longevity in the nursery offers insight into re-vegetation, landscaping programs, and cultivation in gardens.