Flowering Response of Bougainvillea to Drought Stress

Bougainvillea cultivars are widely used ornamentals valued for their ability to bloom profusely while tolerating poor growing conditions such as pollution, compaction, and drought stress. However, flowering is often inconsistent, with short-day photoperiod being the apparent trigger in the subtropics, and drought stress being the apparent trigger in the tropics. Established cultivation practices include subjecting them to drought stress to induce greater flowering, but little published research has been made into the mechanisms by which Bougainvillea are induced flower. This experiment seeks to show that drought stress has a significant effect in regulating the flowering response of Bougainvillea and is key to understanding how to induce and prolong the flowering period of Bougainvillea. Thirty-five rooted cuttings of Bougainvillea x glabra ‘Afterglow’ were pruned to the same height and grown under long-day conditions in a growth chamber with temperature regulated at 25 degrees Celsius. Cuttings were subjected to seven levels of water stress (1=50mL upon wilting, 2=25mL/3days, 3=25mL/2days, 4=50mL/2days, 5=50mL/day, 6=100mL/day, 7=permanently saturated) where 1=very high, 2= high, 3 and 4=medium, 5=low, 6=very low, and 7=saturation. Stomatal conductance was measured using a leaf porometer as a proxy of water stress. The number of flower buds on each plant was counted at the end of 6 weeks. Plants grown under saturation were the earliest to flower, and produced more flowers than plants grown under all the other treatments. Plants under very high and very low water stress flowered later and had fewer flowers than those under low, medium and high water stress. Plants grown under medium water stress produced more flowers than those grown under low or high water stress. These preliminary results support published findings that watering in between periods of medium water stress induces flowering in spite of long-day conditions. Additionally, these results also suggest that water stress at both high and low levels influences the initiation and number of flowers in Bougainvillea.