FLOWER BUD INITIATION AND DEVELOPMENT OF JACARANDA MIMOSIFOLIA (BIGNONIACEAE) IN JAPAN

Jacaranda mimosifolia has attractive lilac-colored flowers and is deemed one of the most beautiful flowering trees in the world. This species is principally found in parks and along streets of cities in subtropical regions of the Americas, Africa and Australia. Under natural conditions, the flowering season is early summer (middle to late June in the southern part of Japan). We are conducting a breeding program for jacaranda with dwarf and juvenile flowering characteristics that are suitable for potted plants. However, there is no information on the timing of flower bud initiation and differentiation in J. mimosifolia. We observed flower bud development anatomically and investigated the effect of low temperature on flower bud differentiation. The apical meristem remained in the vegetative phase from November to late March of the following year. Enlargement of the apical meristem was observed in early April and formation of floral primordia was confirmed from mid-April through early May. The differentiation of apical and lateral flower bud primordial progressed rapidly and flower clusters were observable in mid-May. Flower bud differentiation was not observed under conditions of a continuous temperature of 25°C. More than 3 months of low temperature (15°C) seemed to be required for normal anthesis, although at least 1 month of low temperature was needed for flower bud differentiation.