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  • Author or Editor: M. Cecilia Peppi x
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Forchlorfenuron (CPPU), a synthetic cytokinin, applied after fruit set increases the size and firmness of table grapes (Vitis vinifera L.) beyond what is possible without CPPU treatment. However, treatment with CPPU may inhibit coloring of ‘Flame Seedless’ grapes, limiting its use in growing areas where color has been consistently poor. In contrast, application of abscisic acid (ABA) to ‘Flame Seedless’ grapes may cause fruit softening, which is undesirable, but its primary effect is to increase anthocyanin content and fruit color. Thus, we hypothesized that application of CPPU followed by ABA might increase the size and firmness of ‘Flame Seedless’ grapes without excessively inhibiting coloring. Grapes were treated with 0 or 20 g·ha−1 CPPU (applied at fruit set) and 0, 300, or 600 mg·L−1 ABA (applied at veraison) in 2005 and with 0, 5, 10, 15, or 20 g·ha−1 CPPU and 0, 200, 400, or 600 mg·L−1 ABA in 2006. Both plant growth regulators (PGRs) increased berry mass, but grapes treated with CPPU were as firm, or firmer, than nontreated grapes, whereas those treated with ABA were of similar or lesser firmness. Treatment with CPPU generally reduced soluble solids and red berry color, whereas treatment with ABA reduced titratable acidity and increased red color. The PGRs did not interact to affect any of the fruit quality variables measured, so beneficial effects of CPPU or ABA were apparent whether the grapes were treated with either or both PGRs. Thus, the combined use of CPPU and ABA may be a desirable cultural practice for ‘Flame Seedless’.

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Poor coloration of red grapes grown in warm regions is a frequent problem that decreases production efficiency. Most table grape growers use ethephon to improve color, but its influence on color development is erratic, and it may reduce berry firmness. Application of S-abscisic acid (ABA) to grapes can increase the anthocyanins in their skins, but no protocols have been established regarding its potential commercial use. Therefore, we evaluated the effects of ABA and ethephon treatments on fruit quality characteristics, including those related to firmness and color, on `Flame Seedless' grapes (Vitis vinifera L.) in several experiments over three consecutive seasons. Abscisic acid had few effects on berry weight or juice composition, but it increased berry softening and skin anthocyanin concentrations. The effect of ABA on berry firmness was similar to ethephon. With respect to skin anthocyanin concentration and fruit color characteristics, 300 mg·L–1 ABA applied at veraison was superior to the other ABA concentrations and to ethephon applied at any of the times tested. Moreover, any concentration of ABA between 75 and 300 mg·L–1 applied after veraison improved color better than ethephon applied at the same time. There was a highly significant inverse curvilinear relationship between skin anthocyanin concentration and the lightness and hue of the berries. Anthocyanin concentrations between 0.01 and 0.04 mg·cm–2 had little effect on berry lightness and hue, so researchers should consider measuring color, not just anthocyanins, when evaluating the quality of red table grapes.

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