Effects of the Combination of Gibberellic Acid and Ammonium Nitrate on the Growth and Quality of Seedless Berries in 'Delaware' Grape

Abstract

The efficacy of ammonium nitrate (AMN), NH₄NO₃, as an additive to gibberellic acid (GA₃) solutions on berry growth and quality of seedless 'Delaware' grape was tested in 1995 (Expt. 1) and 1996 (Expt. 2). Clusters were dipped twice in GA₃ ± AMN solutions before and after full bloom in both years. Treatments with GA₃ alone are considered the control. The addition of AMN to 50 and 100 ppm GA₃ induced significantly larger growth rates than those of GA₃ alone during the early growth stage. At 12 days after full bloom (DAFB) cell sizes of berries that received the combined treatments were significantly larger than those that were treated with 50 ppm GA₃. At harvest, there were no significant differences in seedlessness and titratable acidity between treatments with or without AMN. However, in Expt. 1, the total soluble solids content (TSS) in berries from the combined treatments tended to be slightly lower than that in berries treated with GA₃ alone; in Expt. 2, no difference was observed, except with the treatment of 100 ppm GA₃ + 25 mM AMN. AMN, when combined with 50 ppm GA₃, produced more larger berries than did the 100 ppm GA₃ treatment. These results indicate that treatment with 50 ppm GA₃ + 25 mM AMN has the potential to produce larger berries with slightly lower TSS than do treatments without AMN or with 100 ppm GA₃ alone.