Effect of Foliar Sprays of Some Growth Regulators on Prolonging Storage Season of Navel Orange Fruits on Trees and Reducing Pre-Harvest Drop

Due to some sudden price fluctuations, whether in the local market or export of navel orange fruits the producer may be forced to store the fruits on the trees to avoid low prices that cause economic losses and may push him to refrain from expanding citrus cultivation. This study was conducted for two seasons (2021 and 2022) to study the effect of foliar spraying with some growth regulators i.e.  Gibberellic acid (GA₃) and Isopropyl Ester(2, 4-D) at fruit color break in mid- September on extending the storage season of Washington navel orange fruits on trees and reducing pre- harvest drop. Isopropyl Ester (2, 4-D) at 20 ppm was the best treatment to reduce the average fruit drop rate (%) and achieve the highest fruit weight, juice weight percentage, TSS /acid and make the fruit peel thicker. Gibberellic acid at 20 ppm increased the peel firmness and the fruit content of vitamin C. Also, storing fruits on trees until mid-February (fourth harvest) was the best period for maintaining fruit quality. On the other hand, storing fruits on the trees did not affect the density of leaf inflorescences which considered one of the important things to increase the final yield. The anatomical study clearly showed that no cell division was noted during abscission layer formation. It can be recommended in order to extend the storage period of navel orange fruits on trees while maintaining fruit quality until mid-February, trees should be sprayed with 2,4-D at 20 ppm to achieve an economic return for the grower.