Zeinab Arefnezhad, Mehdi Khayyat, Mohammad Hassan Sayyari Zahan and Gholamreza Zamani

Background: The time of gibberellic acid application in the non-bearing year (OFF year) makes the different responses on seedless barberry plants in it (OFF year) and next year (ON year).
Objective: The present research was conducted to evaluate the effects of gibberellin sprays applied at different times on barberry plants.
Methods: The experiment was performed in three consecutive years (2016 to 2018) in Amirabad, Birjand, Iran. The treatments included: 1) Gibberellic acid (GA3 at 200 ppm), and 2) control (0 ppm), applied six times as foliar spraying on non-bearing trees, between April and September. The foliar sprays and measuring of vegetative traits were done on non-bearing trees in 2016 and 2017. Reproductive traits evaluated on bearing trees in 2017 and 2018.
Results: Leaf number, width and length and internode length of current barberry shoots increased significantly. GA3 application significantly decreased by flower and fruit number, TSS/TA and anthocyanin content of fruit juice. Data showed that September might be a very important time for flower induction and differentiation. GA3 application increased the carbohydrate and phenol content of leaves and shoots.
Conclusion: It can be concluded that spraying gibberellic acid influences all physiological and reproductive traits of barberry plants.

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