Gibberellic acid and norflurazon affecting the time-course of flavedo pigment and abscisic acid content in Valencia sweet orange

Abstract

In Citrus, colour break has been positively related to ethylene, abscisic acid (ABA) and carbohydrates, and negatively related to gibberellins and nitrogen. However, the mechanisms by which these substances affect the process are not well understood. This study analyses the role of gibberellins and ABA, through gibberellic acid (GA(3)) and norflurazon (NFZ) applications, on the evolution of flavedo pigments in on-tree degreening and regreening 'Valencia' sweet orange fruit. In two experiments, 180 fruits were tagged previous to colour break, 60 were treated with NFZ, another 60 with GA(3), and the remaining 60 were used as control. In control fruit, flayed ABA concentration increased as did colour development, declining just before full colour developed. NFZ did not affect chlorophyll degradation, but provoked a partial blockage of the carotenoid biosynthesis pathway increasing phytoene and phytofluene concentrations in the flavedo. As a consequence, flavedo ABA concentration temporarily reduced as did fruit colour intensity, but it did not delay the onset of colour break. Conversely, GA(3) delayed flavedo chlorophyll degradation and reduced beta-cryptoxanthin and beta-citraurin biosynthesis, and, thus, delayed fruit colour break. GA(3)-treated fruit also accumulated higher lutein and beta-carotene concentrations, but remained greener than control fruit, and reduced flavedo ABA concentration, but not significantly. Ethylene was not detected, in any treatment. Our results confirm that ABA concentration paralleled colour development, but it did not trigger the process. (C) 2014 Elsevier B.V. All rights reserved.