Abscisic acid improves colour development in 'Crimson Seedless' grapes in the vineyard and on detached berries

'Crimson Seedless' is a high quality, red, table grape (Vitis vinifera) cultivar, which may fail to develop adequate red colour in warm climates. In addition, most bunches contain some green berries when the rest of the bunch has become red. Abscisic acid (ABA) is a plant hormone which increases in grape berry skin at the onset of maturation and is involved in the regulation of anthocyanin accumulation. A commercial formulation, S-ABA (ProTone (R)), was sprayed at 400 mg l(-1) or 800 mg l(-1) in a vineyard at the beginning of veraison, or 200 mg l(-1), 400 mg l(-1), or 600 mg l(-1) S-ABA was applied to detached berries or to small bunches (five-to-six berries) in the laboratory by spraying or by allowing uptake through the pedicel. In the vineyard, the application of S-ABA affected berry colour, changing the red berry colour of the control [hue angle (h degrees) = 3.6] to black for S-ABA-treated clusters (h degrees = -45 degrees). Ripeness parameters (soluble solids content, titratable acidity, and berry size) were not affected by S-ABA treatment, but treated berries were less firm (250 g mm(-1)) than untreated control fruit (335 g mm(-1)) using a compression durometer. Anthocyanin accumulation in berries treated with 400 mg l(-1) S-ABA was almost double that of control berries, although the anthocyanin compositions were similar. Storage of grapes at 0 degrees C for 3 weeks, with no protection from decay, indicated that S-ABA did not increase their sensitivity to fungal infection. Green or breaker-stage detached berries, or bunches, developed a red colour by spraying with S-ABA or by uptake through the pedicel. Detached berries may therefore serve as an efficient system with which to test the effects of S-ABA and its interactions with other factors which influence colour development.