Effects of plant growth regulators and high temperature on colour development in ‘Crimson Seedless’ grapes

Abstract

Summary‘Crimson Seedless’ is a red, seedless table grape (Vitis vinifera) variety which may not develop adequate colour during hot weather. This problem can be alleviated, in part, by applying abscisic acid (ABA). We were interested to determine whether a gibberellin (GA3), which is used to improve the size of grape berries, might interfere with this response. We were also interested in examining whether short periods of high temperature would affect the response to ABA. In addition, we assessed the optimum time at which to apply ABA, and the role of ethylene in berry colour development. These experiments were conducted in commercial vineyards in Israel, and on detached berries held under controlled conditions. GA3 had no effect on the response to ABA. There was a mixed response to ethylene, and to the application of ethylene inhibitors in the vineyard or in controlled studies in growth chambers. The best response in terms of colour development (i.e., anthocyanin levels) on detached berries occurred when 200 mg l–1 ABA was applied in early August. A short period of high temperature did not affect the response to ABA, with similar accumulations of anthocyanins at 18ºC, 25ºC, or 38ºC for 24 h after ABA was applied. These results indicate that: (i) the practice of applying a GA3 spray to increase berry size did not affect the berry response to ABA; (ii) the responsiveness of grape berries to ABA was maintained for an extended time after the initiation of veraison; (iii) a period of high temperature after the application of ABA did not compromise the response of detached berries to ABA; and (iv) the response of berries to ethylene was not maintained after harvest. The best treatment to enhance colour in ‘Crimson Seedless’ grapes was therefore 200 – 400 mg l–1 ABA applied 2 – 3 weeks after veraison.