Postharvest application of a new growth regulator reduces calyx alterations of citrus fruit induced by degreening treatment

Synthetic auxins, specially 2,4-dichlorophenoxyacetic acid (2,4-D), have been used as a postharvest treatment to retard calyx abscission, drying and browning, which occur as the result of degreening processes. Nevertheless, the use of 2,4-D is restricted by European Union (EU) legislation, which means that finding an alternative to this auxin in controlling calyx senescence is necessary. In the present research, the effect of postharvest application of a new growth regulator, S-ethyl-4-chloro-O-tolilooxytioacetate (HF-Calibra^®), currently registered for preharvest use, was used to investigate calyx senescence of early-season citrus varieties (‘Oronules’, ‘Clemenrubi’ and ‘Clemenules’ mandarins and ‘Navelina’ oranges) submitted to a commercial degreening treatment. After shelf-life, application of HF-Calibra^® treatment at different concentrations significantly reduced calyx changes. Although auxin treatments can retard color change, this delay had no negative effect from a commercial viewpoint since all the studied varieties reached a commercially acceptable color. The application of HF-Calibra^® at 10, 20, 40 or 60 mL/L affected neither weight loss nor sensory quality of the fruit (firmness, total soluble solids, titratable acidity, acetaldehyde and ethanol content and flavor). Postharvest application of HF-Calibra^® could be an alternative to 2,4-D to avoid calyx senescence of citrus fruit induced by a degreening treatment and to maintain fruit quality.