Reducing Evapotranspiration of Pansies: Efficacy and Duration of ABA and ABA-analog Spray Applications

Abscisic acid (ABA) and synthetic analogs of ABA have the potential for use as holding agents for ornamental plants. Foliar applications of these compounds induce stomatal closure, preventing water loss through transpiration, and thereby extending the shelf life of treated plants. The purpose of this study was to compare the efficacy of ABA and a synthetic ABA-analog, 8’ acetylene-methyl ester-ABA (PBI 429), on water and CO₂ exchange of pansies (Viola x wittrockiana) and to determine the duration of the effects of each compound. Plants were grown in a greenhouse and were well-watered and fertilized throughout the duration of the study. Spray treatments of a range of concentrations of ABA (0–2000 ppm) and PBI 429 (0–200 ppm) were applied to healthy mature pansies. Gas exchange parameters were measured using a CIRAS- 2 portable photosynthesis meter and leaf chlorophyll content was quantified using a Minolta SPAD meter. Spray applications of ABA significantly reduced net photosynthesis for 20 d and stomatal conductance for 12 d after application in a rate-dependent manner. PBI 429 sprays also reduced stomatal conductance and net photosynthesis, but to a lesser extent than ABA. Plants treated with ABA had a rate-dependent decline in leaf chlorophyll, while PBI 429 did not affect leaf chlorophyll. In summary, ABA was more effective than PBI 429 at reducing stomatal conductance and net photosynthesis, but had the negative side effect of inducing chlorosis.