Effect of Gibberellic Acid Spraying on Alternate Bearing of Olive Trees

The present study was carried out for three successive seasons 2008/2009, 2009/2010 and 2010/2011 on fifteen years old of olive trees cv. Picual to reduce the degree of alternate bearing of olive through spraying gibberellic acid (GA3) on first or mid of December or on first or mid of January at concentrations, 0, 25, 50 and 75 ppm. The results showed that, spraying the olive trees with GA3 at 75 ppm on first December impact on reducing the density of flowering, fruit set, decreased the yield of 2009 season as compared with most GA3 concentrations, while control gave the highest yield. On the contrary, in 2010 season GA3 at 75 ppm on first December gave the highest yield, while control gave the lowest yield. In 2011 season, the control gave the highest yield while the lowest yield was observed when trees were sprayed with GA3 at 75 ppm at mid January. Spraying the olive trees with GA3 at 75 ppm on first December reduced the alternate bearing index (ABI) in comparison with other GA3 concentrations in different times. Spraying the olive trees with GA3 at 75 ppm on first December led to an increase in vegetative growth and to improve in fruit characteristics and increase the oil percentage.