Creasing of orange fruit

Several factors associated with creasing of oranges were observed and measured in a number of California field studies for more than a decade. Severity of creasing was found to be highly correlated with incidence. Creasing was highly variable among trees in a given orchard; occurred more frequently on the south half of the tree than on the north half; developed first on the side of the fruit facing the trunk; and became progressively more severe as the fruit aged. It was also associated with greater crop loads. Peel and juice composition were significantly different between creased and noncreased fruit from the same tree. Split or summer applications of nitrogen resulted in less creasing than spring applications; the effects of nitrogen rate were not consistent. Trees deficient in phosphorus in respect to volume yield produced fruit that had less creasing than phosphorus-sufficient trees, but the nutrient had no effect when applied beyond correction of the deficiency. Soil applications of potassium reduced creasing; potassium nitrate sprayed on foliage even after creasing was evident reduced creasing at harvest time. Over a ten-year period in one experiment, creasing was associated positively with the range between the mean minimum temperature for June and the mean maximum for July, also with the range between the mean minimum for December 15 to January 15 and the mean maximum for January 15 to February 15. Certain trees were consistently high in fruit yield and low in incidence of creasing. This suggests that a genetic factor might be influential.