Abscisic Acid Impacts Tomato Fruit Quality by Increasing Carotenoids and Soluble Sugars and Decreasing Organic Acids

Plant growth regulators (PGRs) are chemicals used on a wide range of horticultural crops.  Similar to endogenous plant hormones, these exogenous chemicals regulate plant development and stimulate growth.  Research in recent years has focused on using PGRs to improve fruit quality parameters such as soluble sugars, fruit color, and phytonutrients. One such PGR is abscisic acid (ABA), which has been used effectively to improve fruit quality, specifically sugars and phytonutrients. The purpose of this study was to examine the effects of exogenous applications of ABA on tomato (Solanum lycopersicum) fruit carotenoids, soluble sugars and organic acids.  ABA treatments were applied foliarly or through the irrigation to the roots.  This study also compared how ABA and calcium (Ca) treatments together affect fruit quality and whether there are added benefits to treating plants with both simultaneously. Seeds of ‘Mt. Fresh Plus’ tomato were grown in the greenhouse at 25/20 °C (day/night) under a 16 h photoperiod. Plants were treated with ABA applications weekly.  Ca treatments were applied at three different treatment levels of 60, 90, and 180 mg×L^-1.  Ca treatments were applied to the plants via the irrigation lines.  ABA treatments were applied as a combination of foliar sprays and root applications.  For foliar ABA applications treatments consisted of a DI water control (0.0 mg ABA·L^-1) or 500 mg ABA·L^-1.  For ABA root applications, treatments consisted of a DI water control (0.0 mg ABA·L^-1) or 50 mg ABA·L^-1 applied via the irrigation lines.  ABA spray treatments were applied once weekly till dripping from the foliage, while root applications were applied four times per day with the irrigation cycle. Fruit tissue was harvested at red ripe maturity and evaluated for carotenoids, soluble sugars and organic acids. The application of ABA had a significant impact on tomato fruit lutein, β-carotene, and lycopene.  Glucose and fructose concentrations increased with ABA applications in the fruit tissue.  Furthermore, ABA applications increased malic and citric acids concentrations.  Therefore, ABA treatments did prove effective in increasing tomato fruit carotenoids, soluble sugars and organic acid concentrations. This study demonstrated that ABA is a viable PGR to significantly improve tomato fruit quality.