Stem bending in cut Gerbera jamesonii flowers : Effects of a pulse treatment with sucrose and calcium ions

The vase life of cut Gerbera flowers (Gerbera jamesonii cv. Tamara) is often short due to stem bending. The purpose of this study was to find a pulse treatment, to be applied directly after harvest, which would delay this bending. Bending was hypothesized to be due, at least in part, to a xylem blockage by bacteria (leading to early turgor loss), to lack of osmotic pressure, and to lack of cell wall stiffness. Chemicals tested included antimicrobial compounds, surfactants (to bypass xylem occlusion), sugars, inorganic ions, and chemicals affecting cell wall rigidity. When used as a pulse treatment, antimicrobial compounds such as chlorine and silver ions had no effect. Only a buffer at pH 3.0–3.5, which inhibits bacterial growth, delayed bending. A range of surfactants tested, many of which had antimicrobial activity, had no effect. Sugars delayed the time to bending, if accompanied by an efficient antimicrobial compound. Cell wall rigidity can be affected by calcium ions and H+ concentration. Treatment with calcium chloride delayed bending. Vanadate, an inhibitor of H+ transport to the cell wall, almost completely prevented stem bending, but resulted in unwanted petal discoloration. By contrast, fusicoccin, a promoter of H+ transport to cell walls, drastically hastened bending. A mixture of chemicals (50 mM calcium chloride, 25 g L−1 sucrose, buffered at pH 3.5 by citric acid and K2HPO4) was satisfactory as a 24 h pulse treatment, prior to 24 h of dry storage at 20 °C and vase life at 20 °C. It delayed the time to bending during vase life in cv. Tamara and six other cultivars tested which are prone to stem bending.