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Abscission is an active developmental process occurring at the abscission zone of the fruit peduncle. The target cells in the abscission zone, which are involved in the process of separation, are located in the separation layer, which is organized in a few cellular layers. In general, it is accepted that the increase in ethylene production in the fruit is followed by increased sensitivity of these cells to ethylene, which would lead to abscission. The abscission process is divided into two phases with respect to sensitivity to auxin and ethylene. The auxin, 2,4-D (2,4-dichlorophenoxy acetic acid), has been used as a postharvest packhouse treatment to retard calyx abscission (to repress postharvest decay). Commercially the sodium salt 2,4-D (Deccomone ® ) is applied to the fruit in a dip treatment at 500 ppm. The aim of this experiment was to test three agrochemicals (aminoethoxyvinylglycine (AVG), 1-naphthylacetic acid (NAA) and 1-methylcyclopropene (1-MCP)) that could possibly replace the postharvest application of the auxin 2,4-D. AVG had a fruit firming effect but no significant effect on calyx retention. NAA resulted in a high percentage of abscission, probably due to auxin overdose. The 1-MCP at low concentrations of 100 ppb and 250 ppb resulted in calyx retention but had a desiccating effect on the calyx whereas at a high concentration of 500 ppb there was a significant increase in calyx abscission. There was no loss of internal quality or colour. To conclude, according to what is known about the role of ethylene in abscission, 1-MCP and AVG should have prevented abscission of the calyx. Unfortunately, the results show that this complex plant mechanism is not so readily manipulated and 2,4-D remains the best product to inhibit calyx abscission of citrus fruit.

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