| Shipping potted flowering Hibiscus rosa-sinensis is a commercial problem due to abscission of flowers and flower buds. Several experiments were conducted to evaluate factors affecting bud abscission during shipping and the role of ethylene in this process. Plants were established in a greenhouse maintained between 26--30°C day and 21--24°C night under prevailing natural days. Flower buds were divided into six developmental stages: Stage 1 being the smallest (<1 cm) and Stage 6 an open flower. At the beginning of each experiment, two flower buds of each stage were randomly chosen and tagged per plant before applying treatments. This was considered to be day 0 of the experiment.;To determine the effect of ethylene on flower bud abscission, two experiments were conducted. H. rosa-sinensis was very sensitive to exogenous ethylene, as flower bud abscission occurred when plants were exposed to 0.2--0.3 muL.l -1. Larger buds were more sensitive to ethylene than the smaller ones. At low concentrations only the smaller buds (Stage 1 and 2) abscised prematurely while the remaining buds developed and senesced normally. Shipping temperatures and durations were also studied. High temperatures (25°C) and longer shipping durations (4 and 6 days) caused greater bud abscission compared to lower temperatures (13 and 18°C) and shorter durations (2 days). During shipping, the smaller buds (Stage 1 and 2) abscised, while the larger buds developed and senesced normally.;A series of experiments were conducted using three ethylene inhibitors, Silver thiosulphate (STS), Aminoethoxyvinyl glycine (AVG) and 1-Methylcyclopropene (1-MCP), to determine the role of ethylene in bud abscission. Neither STS nor 1-MCP protected the plants from shipping damage, while AVG reduced bud abscission but did not prevent it. When shipping at lower temperature (20°C), regardless of duration, both STS and AVG prevented bud abscission. 1-Methylcyclopropene showed no transient effect on the plant; therefore once new receptor sites developed they were not protected from ethylene.;Experiments were conducted to study the anatomical mechanism of calyx and peduncle abscission zones. Observations showed the calyx abscission zone to be preformed, while the peduncle abscission zone only formed following induction. Removing the bud below the calyx abscission zone induced peduncle abscission zone formation, while removing the bud above the calyx abscission zone showed no effect. The peduncle abscission zone was not induced by ethylene. Results showed a dependent relationship between the calyx and the peduncle abscission zones. |
