Abscisic Acid Improves the Drought Stress Tolerance of Chrysanthemum and Aster

Abscisic acid (ABA) is a plant hormone produced in roots in response to drought conditions.  ABA is translocated to the leaves where it stimulates the closure of stomata, reducing transpiration and water loss. We investigated the effect of various ABA spray concentrations on drought stress tolerance of three cultivars each of finished potted chrysanthemum (Chrysanthemum ×morifolium Ramat.) and aster (Aster novi-belgii L.)  Chrysanthemums were held in two postharvest greenhouse environments: one at 23/20 °C (9-h day/15-h night) and the other at 32/23 °C.  Asters were held at 23/20 °C only.  After all plants were well watered, 500, 1,000, or 2,000 mg·L^-1 of ABA were applied as a foliar spray at 0.2 L·m^-2 with the addition of a surfactant to improve ABA uptake into the leaves.  Some plants were provided with a simulated shipping period (5 °C in darkness for 48 h) then returned to postharvest greenhouse conditions.  Plants were subjectively scored at 0800 hr and again at 1600 hr based on their turgidity and overall appearance, where 3 = fully turgid and 0 = all leaves and flower buds had wilted.  At 23/20 °C, the 500 and 1,000 mg·L^-1 ABA applications to chrysanthemum increased the time to stage 2 (by 0.8 to 1.7 d) and stage 1 (by 1.7 to 3.1 d) for all three cultivars.  ABA did not increase the time to wilting in any cultivar at 32/23 °C.  The 500 and 1,000 mg·L^-1 ABA applications to aster at 23/20 °C increased the number of days to stage 2 (by 0.7 to 1.5 d) and stage 0 (by 0.9 to 5.8 d) for all three cultivars studied.  These results indicate that exogenous spray applications of ABA can be used to increase the postharvest drought stress tolerance of chrysanthemum and aster.