Effect of calcium chloride, cytokinin and abscisic acid on growth and postharvest quality of rose cut-flower (Rosa hybrida)

Abstract

The global floriculture industry has grown steadily over the last few years and is predicted to do so in the coming years. However, there has been an increase in losses both in quantity and quality which has significantly affected the production and return on investment for rose flowers. The highest loss reported has been at the retail level (39.82%), wholesalers (27.52%), producers (18.87%) and local traders (13.78%). These losses have been attributed to high respiration and rapid cell disintegration leading to accelerated aging and loss of aesthetic value of cut rose. Efforts to minimize these losses have been focused on manipulating the growing environment, using preservatives and cold treatment. Application of growth regulators can reduce preharvest and postharvest losses. Much as there is potential to reduce losses through growth regulators, there is limited knowledge on the effect of calcium chloride, cytokinin and abscisic acid on growth and postharvest quality of rose flower. This study therefore investigated the effect of calcium chloride, cytokinin, and abscisic acid on the growth and postharvest quality of tea hybrid rose, Rhodos variety. The study was cultivated over two flushes, August 2023- November 2023 and November 2023January 2024 in Redlands Roses PLC, in Ruiru, Kiambu County. The field and the postharvest experiments were laid out in RCBD and CRD, respectively. The field experiment had 10 treatments including non-application (control); CaCl2 (250 mg/L, 500 mg/L and 750 mg/L), CKs (150 mg/L, 250 mg/L and 350 mg/L), and ABA (5 mg/L, 10 mg/L and 15 mg/L). The postharvest experiment comprised of different sets of treatment. There were 28 treatments; the first set of ten treatments comprised of control (0); CaCl2 (250 mg/L, 500 mg/L and 750 mg/L), CKs (150 mg/L, 250 mg/L and 350 mg/L), and ABA (5 mg/L, 10 mg/L and 15 mg/L). In the second set the cut flowers were subjected to the treatments in the field and during postharvest. The third set cut flowers were treated only at postharvest stage. Data was collected at seven days’ interval throughout the growth period, starting from 3 weeks after initial bending in flush 1 and after pruning in flush 2. At postharvest, data was collected at two days’ interval from the day of vasing until the termination of vase life of individual stem. Data obtained was analyzed using SAS version 9.4 and significant means were separated using the Least Significant Difference at =0.05. The analysis of variance for flush 1 and 2 respectively, showed that CKs significantly (p<0.05) increased the number of shoots produced per plant (4.22 and 2.78 shoots), stem length (83.22 cm and 82.56 cm), leaf area (76.67 and 72.44 cm2), number of suckers (17.83 and 15.67), flush days (51.72 and 53.67 days), and chlorophyll content (72.95 and 70.77 SPADS) in cut flowers. On the other hand, the shortest stem length was recorded on plots treated with ABA (68.56 and 68.78 cm), flush days (49.06 and 50.67 days), chlorophyll content (64.74 and 65.13 SPADS) and leaf area (61 and 54.11 cm2). CaCl2 reduced incidences of bent peduncles in flushes one and two (2.07 and 1.13). At postharvest in flush 1 and 2 respectively, CaCl2 and CKs significantly (p<0.05) increased chlorophyll contents, improved the petal color, vase life (14.67 and 13 days; 14.33 and 12.67 days) and reduced weight loss. To improve on the growth qualities (number of shoots produced per plant, stem length, leaf area, flush days, and chlorophyll content) the growers should consider application of cytokinin at high concentrations (250 mg/L and 350 mg/L). However, application of cytokinin comes with a risk of increased number of suckers. To reduce incidences of bent peduncles, growers should always apply 750 mg/L of CaCl2 before the formation of the flower bud. In order to improve cut flower quality after harvesting (chlorophyll contents, petal colour, vase life and reduced weight loss) growers should apply cytokinin and calcium chloride at preharvest or at preharvest and postharvest. To reduce the number of flush days in target of a specific market, growers can apply ABA (15 mg/L) at prebloom stage.