Paclobutrazol or uniconazole effects on ethylene sensitivity of potted ornamental plants and plugs

• PBZ or uniconazole effectively controlled excessive growth of tested species.
• PGRs did not lower postharvest ethylene sensitivity of plants exposed to ethylene.
• Both PGRs reduced postharvest flower abscission when not treated with ethylene.
• PGRs maintained darker foliage during simulated shipping and marketing.
• PGRs produced compact plants and extended postharvest longevity and quality.

Effects of paclobutrazol on postharvest ethylene sensitivity of potted cuphea (Cuphea hyssopifolia Kunth) and petunia (Petunia × hybrida Vilm.) plants, and uniconazole on portulaca (Portulaca oleracea L.) plugs were evaluated. Paclobutrazol was applied as a drench at 0, 1, 2, or 4 mg L−1 per 12.5 cm pot for cuphea, or 0, 2, 4, or 8 mg L−1 per 15.2 cm pot for petunia, while uniconazole was applied at 0, 2.0, 4.0, or 8.0 mg L−1 with a volume of 0.21 L m−2 as a foliar spray for portulaca plugs. With an increase in paclobutrazol dose or uniconazole concentration, plant growth [plant height and diameter (potted plants only), shoot fresh weight, or dry weight] was controlled for all species tested. While use of paclobutrazol or uniconazole controlled excessive plant growth of all three species, the plant growth retardants had no effect on postharvest ethylene sensitivity as most flowers abscised from all plants exposed to exogenous ethylene. However, both paclobutrazol and uniconazole reduced postharvest flower abscission of plants not treated with exogenous ethylene. During simulated shipping and marketing, paclobutrazol and uniconazole maintained darker foliage and controlled height. Drench applications of 2–4 mg L−1 paclobutrazol for cuphea and 4–8 mg L−1 for petunia potted plants and spray applications of 4–8 mg L−1 uniconazole for portulaca plugs produced compact, high quality plants while also extending postharvest longevity and quality.