Regulation of Petal Abscission in Pelargonium × domesticum

The postharvest quality of regal pelargoniums [Pelargonium × domesticum L. H. Bailey] is limited by petal abscission. Cultivars that have diverse postharvest longevities were selected to study ethylene sensitivity and endogenous ethylene production. Petals of both intact and detached inflorescences abscised in response to low dosages of exogenous ethylene (0.5 μl·liter -1 for 1 hour). Ethylene sensitivity varied among cultivars and increased with floret age. Silver thiosulfate reduced ethylene sensitivity and often extended floret longevity beyond that of the controls. A climacteric-like rise in endogenous ethylene production occurred in excised gynoecia (including the receptacle) as floret age increased from 1 to 12 days postanthesis. Ethylene production increased a few days earlier and achieved a higher maximum rate in `Parisienne' than in `Virginia'; `Parisienne' also abscised petals earlier. Relatively low levels of endogenous ethylene may regulate petal abscission, since inflorescences were very sensitive to exogenous ethylene, and increased endogenous ethylene production preceded petal abscission.