The Use of Auxins to Maintain Postharvest Quality of Citrus Fruit

The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) as a postharvest treatment, has been reported to retard calyx abscission occurring during the degreening process. The application of 2,4-D has also been used to maintain the quality during cold storage of citrus fruit. Nevertheless at the present, European Union legislation has restricted the postharvest use of 2,4-D in citrus crops. The effect of 3,5,6-trichloro-2-pyridyloxyacetic acid (3,5,6-TPA) on the incidence of calyx senescence during degreening treatment in the early Clementine cultivar was studied. 3,5,6-TPA treatments showed a positive effect on the control of calyx alterations symptoms when fruit where dipped in different solution concentrations prior to the degreening process. For 3,5,6-TPA treatments, in general, the higher the concentration, the lower percentage of affected fruit with calyx alterations symptoms is observed. In 'Oronules' mandarins, the delay in colour evolution, observed when using auxin treatments, had no negative effect from a commercial point of view. Therefore, no sensory alteration was observed in any treatment. The effect of 3,5,6-TPA treatment on physiological disorders of cold stored oranges were also studied. Different types of 3,5,6-TPA application prior to cold storage were carried out either by application of low volume spraying in the handling line, the application in combination with wax in the packing line or by dipping in a solution for 2 min. Despite the positive effects on maintaining the calyx, 3,5,6-TPA treatments did not significantly affect fruit quality parameters of the studied oranges cultivars.