The Use of S-Abscisic Acid for the Enhancement of Grape Coloration

Worldwide, premium table grape production tends to be from warmer growing regions that are generally considered difficult coloring areas for quality red varieties.  Fruit color development can be influenced by a number of factors including the cultivar, rootstock, plant vigor, climate, canopy management, light exposure, crop load, irrigation, fertilization, and plant growth regulators.  Consequently, achieving optimal fruit color requires a programmatic approach rather than the use of a single tool or practice. The plant growth regulator ethephon is one tool that can be used to help improve color development; however, ethephon can be inconsistent and can cause berry softening.  Research has demonstrated that application of the plant hormone abscisic acid (S-ABA) to grape clusters increases fruit color in table grape varieties. Since 2008, nine international registrations have been granted to Valent BioSciences Corporation (VBC) for the commercial use of S-ABA for the acceleration of color development of red table grapes.  Formulations of S-ABA for use on table grapes have been commercialized under the trade name of ProTone^®.   Commercial table grape vineyards were selected for field trials in multiple regions.  Application timing was keyed to veraison, which is defined as the point at which 50% of the harvestable fruit has softened.  Split rate and sequential timing treatments were also incorporated into field evaluations.  Plot sizes varied from one to several acres (or hectares).  An equivalent size area treated with the grower standard coloring program was evaluated from adjacent rows.  At commercial harvest all fruit in the blocks of each treatment were evaluated.  The data was then transformed into boxes per unit area based on vine spacing within each site.  Financial analysis showing the increased returns following ProTone^® treatment will be shown. Large scale grower trials conducted in numerous table grape growing regions around the world, using conventional vineyard application equipment, have been conducted since 2009.  These trials were successful in demonstrating the commercial feasibility of using S-ABA (ProTone^®) as a color enhancing product for red table grapes.  The field data confirmed a wide application window in which S-ABA can be used from veraison to late in the harvest season to increase harvestable yields.