ABA and ABA Analog Foliar Sprays Reduce Evapotranspiration in Pansies

Spray applications of abscisic acid (ABA) and synthetic analogs of ABA are effective means of reducing evapotranspiration (ET), and have the potential to extend the shelf-life of bedding plants by reducing water loss and limiting growth. However, high concentrations or high volumes of spray of these compounds may produce undesirable phytotoxic side effects.  To determine the effect of different doses, we quantified the effects of spray applications of ABA and an ABA analog (8’-acetelyne ABA methyl ester, PBI- 429) on evapotranspiration of pansy (Viola × wittrockiana). Pansies were grown in a greenhouse to marketable size. Well- watered plants were transferred to growth chambers after foliar spray treatment with one of six concentrations of each compound (0 – 2000 ppm ABA and 0 – 200 ppm PBI-429, with surfactant).  Each plant was treated with approximately 1.5 mL of solution and water was withheld for the duration of the study. Load cells in the growth chambers were used to measure the cumulative ET of each plant. All ABA and PBI-429 treatments effectively reduced ET during the first few days after spray application. The highest concentration spray of each compound resulted in the greatest reduction in ET. The greatest reduction in ET was associated with the highest concentration of ABA, and ABA reduced ET more effectively than PBI-429 at equal concentrations. Control plants wilted after 1 or 2 d, while sprays with ABA or PBI-429 (at a concentration of 20 ppm or higher) extended the shelf life by up to 2 d, with ABA generally appearing to be more effective than PBI-429. However, ABA sprays induced leaf- yellowing at the three highest concentrations (500 ppm and greater), while no phytotoxic symptoms were observed in any plants treated with PBI- 429.