Histological and Physiological Characterization of Rind Breakdown of 'Navelate' Sweet Orange

Rind breakdown of ‘Navelate’ sweet orange is characterized by sunken colourless areas of the peel which develop into reddish-brown, dry areas partially covering the exposed portion of the mature fruit. Sudden changes in relative humidity at fruit colour break seem to be responsible for the natural development of this disorder, which begins at the transitional zone of the flavedo-albedo and advances across the flavedo reaching the epidermis. Affected cells have reduced amounts of cytoplasm located in a central position and have twisted and squashed walls, forming areas of collapsed cells amongst the healthy cells of the flavedo and albedo. Comparisons of healthy and damaged areas of affected fruits showed no significant differences in wax morphology and cuticular thickness or permeability. Our results suggest that an excessive loss of water from hypodermal and albedo cells is responsible for the disorder.