Boron deficiency can be a limiting factor for flowers and fruits formation in some olive orchards. The appropriate time of boron foliar application in different areas and cultivars needs more investigations. This study was conducted to investigate the effects of spraying with an optimum concentration of boron (350 mg/l) at different phenological stages: after fruit harvest in autumn (first stage), the onset of flower bud formation in winter (second stage), during anthesis in spring (third stage), alone or in combination, on flowering  and fruit formation in three olive cultivars (Bella di, Mission and Koroneiki). The characteristics such as inflorescences number, total flowers number, complete and incomplete flowers percent, final fruit-set, percentage of pollen germination, and leaf and inflorescence boron content were evaluated. Boron spraying increased the percentage of pollen germination in all three cultivars compared to control. Spraying  in first stage and in combination of the first and the second stages increased the total number of flowers and inflorescences in Koroneiki and in combination of all three stages increased these characteristics in Mission. Bella di with spraying in second stage and in combination of second and third stages, and Koroneiki in third stage had the highest percent of complete flowers. The highest percent of fruit-set was observed in combination of the first and the third stages, and in combination of the second and the third stages in Koroneiki and then in combination of all three stages in Mission. Spraying in combination of the second and the third stages increased leaf and inflorescence boron contend in all three cultivars.

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