Effect of gibberellic acid, glutamic acid and pollen grains extract on yield, quality and marketability of 'Khalas' date palm fruits

This study was done at Dibba Experiment Station, Eastern Region, Ministry of Environment & Water, UAE, during two successive seasons (2010 and 2011) on 'Khalas' date palm to improve fruit quality and yield. After fruit set, bunches were labeled and six bunches only were left on each tree. In 2010, on each tree (five trees were used; replicates), four treatments (control, gibberellic acid (GA3), glutamic acid (Glu) and a mixture of GA3 + Glu) were applied (one treatment per bunch). In 2011, an extra treatment (pollen grains extract) was added to the previous four treatments. Bunches were sprayed with the different treatments three times (at three-week intervals starting when the fruits were 1.6-1.7 cm in diameter) in both seasons. Gibberellic acid delayed fruit ripening (in both seasons) by about 4-5 weeks which can help in increasing marketability duration. In addition, in 2010, GA3 and GA3 + Glu increased yield, fruit bunch weight, fruit height, fruit thickness, fruit volume and average fruit weight significantly in comparison with the other treatments. Also, in the first season, GA3 and GA3 + Glu significantly increased fruit pulp (%) over that of the control and the Glu treatments. Besides, Glu, GA3 and GA3 + Glu increased TSS significantly over that of the control while the differences between the Glu, GA3 and GA3 + Glu treatments were not significant. However, no significant differences were noticed in fruit total sugars as affected by the different treatments. In the second season, Glu and GA3 significantly increased fruit yield over that of the control and the pollen grains extract. However, no significant differences were obtained in yield between Glu, GA3 and GA3 + Glu treatments. For bunches, Glu and GA3 increased weight significantly over that of the pollen grains extract and the control treatments. The mixture of GA3 + Glu increased bunch weight over the control and the pollen grains extract treatments, but data failed to show any significant differences. Similarly, GA3 and GA3 + Glu increased fruit height and thickness over that of the control. At the same trends, GA3, GA3 + Glu and pollen grains extract treatments resulted in increasing fruit weight and volume over the rest of the treatments without any significant differences between the treatments. Fruit pulp (%) was increased significantly by GA3 + Glu and pollen grains extract over the rest of the treatments. No significant differences were noticed in fruit pulp (%) as a result of Glu, GA3 and the control treatments. Gibberellic acid treatment, in the second season, resulted in a reduction of TSS in comparison with the rest of the treatments with no significant differences between the control, Glu, GA3 + Glu and pollen extract treatments. Pollen grains extract spray can be used instead of Glu and mixed with GA3 for future studies, since pollen grains contain Glu. It can be recommended to spray GA3 and GA3 + Glu/or pollen grains extract on the fruit after setting to get a positive effect of improving fruit weight, size and yield. Besides, GA3 can extend fruit marketability season by delaying ripening.