APPLICATION, TIMING AND CONCENTRATION OF ABSCISIC ACID OR ETHEPHON AND THEIR EFFECTS ON COLOR OF 'CRIMSON SEEDLESS' TABLE GRAPES

‘Crimson Seedless’ is the most important late-season red-fruited table grape cultivar in California. Unfortunately, its fruits do not develop adequate color in some years, even after ethephon is applied to them. Others found previously that application of abscisic acid (ABA) to grapes can enhance the anthocyanin concentrations of their skins, but synthetic ABA was so costly that commercial treatments were impractical and the technology was never refined. Recently, a relatively low-cost ABA production method was developed that may make the use of ABA on grapes economically feasible. Thus, in 2005, we tested the effect ABA (0, 75, 150, or 300 mg/L) and ethephon (250 mg/L) and different times of application (veraison, one month post-veraison, or two months post veraison) may have on fruits harvested monthly between August and October. Application time and plant growth regulator (PGR) treatments affected anthocyanins, color, and firmness, but had little effect on the soluble solids or titratable acidity of the fruits. The best time of application in terms of anthocyanins and color was between veraison and one month after veraison. Anthocyanin content was increased by ABA and ethephon, but higher values were observed in ABA treated fruit. Similar results were observed in color measurements; L^*, C^* and h° were affected by ABA and ethephon but the darkest and most red-colored fruit was obtained with 300 mg/L ABA.