Effect of gibberellin on cell-wall components of creasing peel in mature ‘Valencia’ orange

Abstract “Creasing”, a disorder of some orange cultivars causing cracks in the internal white tissue (albedo) of the peel, has not been satisfactorily explained, and has therefore been studied in orange cultivar ‘Valencia’ ( Citrus sinensis L. Osbeck) fruits from October to April by means of microscopic investigation and histochemical analyses of cell-wall polysaccharides. The microscopic examination revealed some morphological differences after the autumn, and a significant decrease in the pectic contents of cell walls. A visual detection of the disorder was possible only late in April, and was accompanied by a decrease in the amount of pectins and hemicellulose to less than 70% of cell-wall polysaccharides. When the combined level of these two polysaccharides amounted to more than 80% of total polysaccharides, the fruit was healthy; when it was 70–80% microscopic symptoms of creasing occurred. The histochemical studies showed that spraying the trees with GA in the summer (July), successfully prevented the appearance of external and internal creasing symptoms in the peel of mature ‘Valencia’ fruit next April. Microscopic and histochemical analyses made it possible to detect the disorder at a very early stage of fruit development.