Exogenous Foliar and Root Applied Abscisic Acid Increases the Influx of Calcium into Tomato Fruit Tissue and Decreases the Incidence of Blossom-end Rot

There are various environmental stress factors that can potentially impact plant performance and quality parameters. Adequate levels of calcium (Ca) in tomato (Solanum lycopersicum) fruit have positive impacts on fruit quality, specifically firmness. One of the results of insufficient Ca uptake and movement in tomato is the physiological disorder blossom-end rot (BER), which is associated with a Ca deficiency in the distal fruit tissue. Previous research has demonstrated that foliar abscisic acid (ABA) applications decreased the incidence of BER and increased the uptake of Ca into fruit tissue. This study examined how foliar spray and root ABA applications, individually and in combination, affected the partitioning of Ca between the leaves and fruit of tomato plants, especially in the distal tissue, and how ABA affects the incidence of BER in the distal tissue of tomato fruit. 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 different Ca concentrations applied via the irrigation lines at 60, 90, or 180 mg Ca×L^-1.  ABA treatments were applied as a combination of foliar sprays and root applications.  Foliar ABA applications 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 (tops of pots were covered to prevent spray drip into the media), while root applications were applied four times per day through the irrigation system.  Fruit tissues were harvested 84-90 d after seeding.  Fruit tissue was harvested at red ripe maturity and evaluated for yield, BER and Ca concentrations.  Leaves were harvested at time of fruit harvest and were analyzed for Ca concentrations. The results indicate that a combination of the spray and root-appied ABA resulted in the greatest decrease in BER.  The foliar spray application of ABA combined with the Ca treatment of 180 mg×L^-1 decreased the incidence of BER even under stress conditions.  Results also demonstrate that ABA treatments are very effective in increasing fruit Ca and preventing BER in the early stages of plant development, but are less effective in preventing Ca deficiency in the later stages of plant growth.