Effects of exogenous abscisic acid (ABA) applications on water use and cropping of 'Thompson Seedless' grapevines

An experiment was conducted in 2011 to determine whether weekly applications of abscisic acid (ABA; ProTone, Valent BioSciences, Libertyville, IL) could mitigate water stress in deficit irrigated 'Thompson Seedless' grapevines (Vitis vinifera L.). The vineyard was divided into four main plots, each containing two vine rows assigned to different irrigation treatments; applied water at 70 or 35% crop evapotranspiration (ETc). Vine rows were further divided into four-vine subplots that were treated with solutions containing no ABA, or 100, 300, or 1000 mg L-1 ABA. Irrigation treatments commenced on July 5, and vines were first treated with ABA on July 6. The last ABA treatment was applied on August 31 and harvest occurred on September 7. Midday leaf water potential steadily declined from about July 14 through harvest, but the water potential of vines subjected to the 35% ETc treatment declined more rapidly than that for vines irrigated at 70% ETc. Most ABA treatments increased water potential of vines subjected to 35% ETc, but only the 1000 mg L-1 ABA treatment routinely increased water potential of vines irrigated at 70% ETc. Transpiration of vines in a weighing lysimeter was reduced by 50 to 60% in the days following application of 1000 mg L-1 ABA, and 30% over the course of a week. Soil water depletion in the 35% ETc plots was not affected by ABA treatments, but vines treated with 1000 ppm ABA depleted 29% less soil water than the non-treated vines in the 75% ETc plots. However, when applied water is added to the water budget, ABA-treated vines used only 9% less water than non-treated vines. Treatments had little or no effect on grape yield components or composition other than the 35% ETc treatment hastening maturity.