RIND STRUCTURE, EPICUTICULAR WAX MORPHOLOGY AND WATER PERMEABILITY OF FORTUNE MANDARINE FRUITS AFFECTED BY PEEL FITTING

Rind structure and surface wax morphology of 'Fortune' mandarins affected by pre-harvest peel pitting were examined as related to the severity of this disorder. In fruits with slight symptoms of pitting (< 10% surface area pitted) a discrete number of epidermal cells were injured with signs of cellular breakdown. in fruits with moderate symptoms of pitting (10-50% surface area pitied) the injured zones also involved hypodermal cells. The surface of rind had an undulating appearance in fruits with severe symptoms of pitting (> 50% surface area pitted). The depressed areas in these fruits were devoid of crystalline wax structures and had a rough morphology. Broad regions of rind had crushed epidermal and hypodermal cells with infolded walls. These cells were either empty or filled with reduced cytoplasm amounts located in central positions of the cell. No signs of disruption in the cuticle were observed. Under field conditions, pitting occurrence coincided with higher permeability values of isolated cuticles. Furthermore, length of cold treatments required to show post-harvest pitting symptoms was shorter in fruits sampled at this stage than in those collected earlier or later. Our results indicate that the low temperatures induce the breakdown of the more external cellular strata of the rind. Thus, the physiological function of cuticle is highly impaired which, in turn, increases water permeability considerably.