EFFECTS OF GIBBERELLIN AND GIRDLING ON THE YIELD OF “NOVA” (CLEMANTINE × ORLANDO TANGELO) AND “NIVA” (VALENCIA × WILKING)

Abstract

GA3 and/or girdling half of the main branches significantly increased both fruit set and yield, but caused the highest rate of fruitlet drop. Spraying GA3 at mid-anthesis is the best treatment to improve fruit set and yield. Yield loss of up to 48% was due to rind-splitting-induced fruit abscission in August and mid-October. Morphological study of splitting revealed that this phenomenon occurred at the stylar end starting at the flavedo, progressing into the albedo and leaving the vascular bundles intact, although they separated later. Spraying Nova trees with different growth regulators in July, failed to reduce splitting. Reducing water supply by 35 or 50% from August onward, reduced rind splitting by up to 35% accompanied by a decrease in fruit size and yields. Internal quality was not affected when water supply was reduced by 35%. Reducing water supply by up to 50% decreased TSS/acid ratio and percent of juice. It is therefore, questionable whether reduced water supply is an effective treatment for limiting rind splitting and premature fruit drop.