Timing and Concentration of Abscisic Acid Applications Affect the Quality of 'Crimson Seedless' Grapes

'Crimson Seedless' is a table grape (Vitis vinifera) cultivar that often fails to develop adequate color, particularly in warm climate regions such as the San Joaquin Valley, California. Growers generally apply ethephon to 'Crimson Seedless' grapes to improve their color, but results are erratic. The plant hormone abscisic acid (ABA) stimulates anthocyanin production in some other varieties of grape, so applications of ABA might help improve the color of 'Crimson Seedless'. Application of ABA at veraison maximized anthocyanin accumulation, but later applications also increased pigmentation and, at the same time, reduced ABA's negative effect on berry puncture resistance. Concentrations of 150 and 300 mg center dot L-1 ABA increased anthocyanin levels more than did 75 mg center dot L-1 ABA. The relationships between anthocyanin content of the berry skins and the color characteristics lightness (L*), and hue angle (h degrees), were well described by the functions L*= 22.56x(-0.0865), and h degrees = 3.356x(-0.513), where x=skin anthocyanin content. Thus, at skin anthocyanin contents >= 0.03 mg center dot cm(-2), relatively large increases in anthocyanin content have relatively small effects on L* and h degrees of 'Crimson Seedless' grapes. Similar results have been obtained with other cultivars of grape. For this reason, we suggest to include direct color measurements, rather than relying only on anthocyanin content when evaluating color on grapes.