Application of Calcium Chloride, Cytokinin and Abscisic Acid Increases the Postharvest Quality of Rose Cut-flower (<i>Rosa </i><i>hybrida</i>)

Postharvest quality deterioration remains a major limitation in the cut rose industry due to accelerated senescence driven by physiological and biochemical processes such as ethylene production, respiration, microbial contamination, and water imbalance. This study evaluated the effects of calcium chloride (CaCl₂), cytokinin, and abscisic acid (ABA), applied at different concentrations and application timings, on postharvest quality of tea hybrid rose (Rosa hybrida L.) cv. Rhodos. The experiment was conducted at Redlands Roses PLC, Ruiru, Kiambu County, Kenya, during two production flushes: November–December 2024 and January–February 2025. Treatments comprised CaCl₂ at 250, 500, and 750 mg L<sup>-1</sup>, cytokinin at 150, 250, and 350 mg L<sup>-1</sup>, and ABA at 5, 10, and 15 mg L<sup>-1</sup>, applied as preharvest-only, postharvest-only, or combined preharvest and postharvest applications, alongside an untreated control. Postharvest quality parameters assessed at two-day intervals included chlorophyll content (SPAD values), petal colour (CIE L*, a*, b*), percentage weight loss, and vase life. Data were analyzed using analysis of variance in SAS version 9.4, with mean separation at P ≤ 0.05. Postharvest application of CaCl₂ significantly enhanced chlorophyll retention in a concentration-dependent manner, increasing SPAD values from 55.33 and 51.77 in the control to 64.53 and 58.73 at 750 mg L<sup>-1</sup> in the first and second flushes, respectively. Preharvest application of cytokinin produced the highest chlorophyll content, reaching SPAD values of 69.23 and 62.50 at 350 mg L<sup>-1</sup>, while postharvest cytokinin application was not significant. ABA consistently reduced chlorophyll content, particularly under preharvest application. Calcium chloride significantly improved petal brightness and colour intensity, with the highest L*, a*, and b* values recorded at 750 mg L<sup>-1</sup> under combined application. Cytokinin enhanced petal redness, achieving maximum a* values of 57.83 and 62.44 at 350 mg L<sup>-1</sup> across both flushes, whereas ABA suppressed colour development. Weight loss was lowest under postharvest CaCl₂ application at 750 mg L<sup>-1</sup> and preharvest ABA at 10 mg L<sup>-1</sup>. Vase life was significantly extended by preharvest CaCl₂ and cytokinin, reaching 14.67 and 13.67 days, respectively, compared with 11.61 days in the control. The study demonstrates that preharvest application of calcium chloride and cytokinin is an effective strategy for improving postharvest quality, extending vase life, and enhancing marketability of cut roses under commercial production conditions.