Changes in the Morphology of the Apical Meristem and the Levels of Endogenous Hormones During Flower Bud Development of Different Lily (Lilium) Cultivars

The morphological and hormonal changes during flower bud differentiation and development in four important groups of modern lily ( Lilium ) cultivars (Oriental, Longiflorum, Asiatic and Oriental × Trumpet hybrids) were determined. The stem apices of eight lily hybrids (‘Loreto’, ‘Tresor’, ‘Siberia’, ‘Sorbonne’, ‘Dolcetto’, ‘White Heaven’, ‘Candy Club’ and ‘Bonbini’) were morphologically examined using a stereomicroscope. The levels of the endogenous hormones abscisic acid (ABA), indole-3-acetic acid (IAA), zeatin riboside (ZR) and gibberellic acid (GA3) were analyzed in a representative hybrid, the Oriental lily ‘Sorbonne’. The morphological progress of flower bud differentiation varied considerably among the eight lily hybrids, particularly in terms of the onset of flower bud initiation. The earlier the flower bud initiation, the earlier the flowering. Data on the timing of flower bud initiation and development suggest the possible control of the processes by plant hormones. IAA and ZR may work synergistically during flower bud initiation while GA3 may enhance flower bud development. A decrease in the IAA and ZR levels before flower bud differentiation and an increase in the ABA and GA3 levels of the stem apices after flower bud differentiation may promote flower bud formation. Key Words: ABA, GA3, flower bud differentiation, lily