Use of paclobutrazol as a growth reduction strategy for ‘Vincent’s Choice’ ornamental sunflower

Abstract Floriculture has experienced exponential growth in Brazil, generating substantial revenue in the ornamental sector through the use of decorative flowers. Specific morphological traits are required to meet market standards for potted ornamental plants, such as compact architecture and restricted growth. Although ‘Vincent’s Choice’ sunflower is widely accepted by growers, its large size limits its commercialization in pots. This study aimed to evaluate different doses of paclobutrazol (PBZ), a plant growth regulator that inhibits the gibberellin biosynthesis pathway, the primary hormonal route for shoot elongation. PBZ was applied at 0, 100, 200, 300, 400, and 500 mg L-1, with five replicates per treatment. The variables analyzed included plant height, number of leaves, stem diameter, leaf area, fresh and dry biomass, and postharvest traits such as inflorescence diameter, colorimetric parameters (L*, a*, and b*), visual quality (graded scale), and anatomical traits (transverse leaf blade thickness). The concentration of 500 mg L-1 applied to the substrate demonstrated the most effective growth regulation without inducing phytotoxicity. This dose significantly reduced plant height and maintained postharvest quality, resulting in compact plants suitable for the producer and consumer markets of potted ornamental sunflower.