We investigated the effect of gibberellic acid (GA3) in the fertilization of Clementine mandarin cv. 'Clemenules' (Citrus clementina Hort. ex Tan.), a parthenocarpic variety that produces seedless fruit due to its self-incompatible nature, but yields seedy fruits when grown under cross-pollination conditions. Experiments were conducted with on-tree 'Clemenules' flowers and 'Fortune' mandarin pollen (C. clementina Hort. ex Tan. × C. reticulata Blanco), which is sexually compatible with the former. Preanthesis treatment at -2 days after anthesis (-2 DAA) enhanced ovule abortion in both unpollinated and cross-pollinated (at +2 DAA) flowers. In the latter, the number of pollen tubes reaching the ovules was significantly reduced although pollen grains were not treated; thus, fertilization was partially avoided and seed set was reduced. When GA3was applied at anthesis (0 DAA) at the time of pollination, ovule abortion was again enhanced, and pollen tube growth was completely arrested; thus, fertilization was prevented and seed set was impeded. When GA3was applied 24 h after pollination (+1 DAA in flowers pollinated at anthesis), pollen tube growth was impaired but not arrested and ovule abortion was enhanced; therefore, fertilization was not prevented but impaired. We conclude that, when applied the days around anthesis, GA3(10 mg l-1) impairs fertilization by either enhancing ovule abortion or reducing pollen tube growth, in 'Clemenules' flowers under cross-pollination conditions. The intensity of the response depends on the physiological flower state at the moment of treatment. © 2008 Elsevier Ireland Ltd. All rights reserved.
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