Abstract

Forchlorfenuron (CPPU), a synthetic cytokinin, applied after fruit set increasesthe size and firmness of table grapes (Vitis vinifera L.) beyond what is possible withoutCPPU treatment. However, treatment with CPPU may inhibit coloring of ‘FlameSeedless’ grapes, limiting its use in growing areas where color has been consistentlypoor. In contrast, application of abscisic acid (ABA) to ‘Flame Seedless’ grapes maycause fruit softening, which is undesirable, but its primary effect is to increaseanthocyanin content and fruit color. Thus, we hypothesized that application of CPPUfollowed by ABA might increase the size and firmness of ‘Flame Seedless’ grapes withoutexcessively inhibiting coloring. Grapes were treated with 0 or 20 gha–1 CPPU (applied atfruit set) and 0, 300, or 600 mgL–1 ABA (applied at veraison) in 2005 and with 0, 5, 10, 15,or 20 gha–1 CPPU and 0, 200, 400, or 600 mgL–1 ABA in 2006. Both plant growthregulators (PGRs) increased berry mass, but grapes treated with CPPU were as firm, orfirmer, than nontreated grapes, whereas those treated with ABA were of similar or lesserfirmness. Treatment with CPPU generally reduced soluble solids and red berry color,whereas treatment with ABA reduced titratable acidity and increased red color. ThePGRs did not interact to affect any of the fruit quality variables measured, so beneficialeffects of CPPU or ABA were apparent whether the grapes were treated with either orboth PGRs. Thus, the combined use of CPPU and ABA may be a desirable culturalpractice for ‘Flame Seedless’.