Relationship of Seasonal Changes in Endogenous Plant Hormones and Alternate Bearing of Olive Trees

Changes in hormone concentrations in leaf, node, shoot tip, and fruit samples of three Turkish olive ( Olea europaea L.) cultivars (`Gemlik', `Memecik', and `Tavsan Yuregi') were monitored at monthly intervals over two successive years of the alternate-bearing cycle. Concentrations of abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid-like substances (GA), and kinetin-like cytokinin were determined and their relationship to flower bud formation were examined during “on” and “off” years. Results showed significant differences in IAA, ABA, GA 3 -like, and kinetin-like cytokinins between “on” and “off” cropping years in various tissues of olive trees. Relative balances between GA 3 -like and ABA concentrations of tissues appears to exhibit evidence of being a key regulator of floral development and alternate bearing.