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Plants encounter various environmental stress factors that can potentially impact nutritional requirements and fruit quality. Adequate levels of calcium (Ca) in tomato (Solanum lycopersicum) fruit have positive effects 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 root and foliar spray ABA applications, individually and in combination, affect 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. ‘Mt. Fresh Plus’ tomato were grown in the greenhouse at 25/20 8C (day/night) under a 16-hour photoperiod. Plants were treated with different Ca concentrations in the fertilizer solution. Plants were also treated with foliar spray ABA applications weekly. Calcium was applied through the irrigation lines at 60, 90, or 180 mg·L. ABA treatments were applied as a combination of foliar sprays and root applications. Foliar ABA applications, treatments consisted of deionized (DI) water control (0.0 mg ABA/L) or 500 mg ABA/L. For ABA root applications, treatments consisted of a DI water control (0.0 mg ABA/L) or 50 mg ABA/L applied through the irrigation lines. ABA spray treatments were applied once weekly until dripping from the foliage (tops of pots were covered to prevent spray drip into the pot), whereas root applications were applied four times per day through the irrigation system. Fruit tissues were harvested 84 to 90 days after seeding. Fruit tissue was harvested at red ripe maturity and evaluated for yield, BER, and Ca concentrations. Leaves were harvested at the time of fruit and were analyzed for Ca concentrations. The results indicate that a combination of the spray and root applications of ABA resulted in the greatest decrease in BER. The foliar spray application of ABA combined with the Ca treatment of 180 mg·L decreased the incidence of BER. Results also demonstrate that ABA treatments are 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 growth. Plants encounter various environmental stresses that can potentially impact nutritional requirements and fruit quality. Environmental stress factors frequently influence vegetative development by inhibiting plant growth. Studies have demonstrated that the plant hormone ABA helps plants acclimate to environmental stresses such as drought, extreme temperatures, and excess light (Hirayama and Shinozaki, 2007; Thompson et al., 2000). ABA affects gas exchange by closing stomatas, thereby decreasing photosynthesis, which has a negative effect on vegetative growth. However, ABA can have a positive effect on nutritional fluxes in the plant. For example, ABA can enhance potassium (K) absorption in cucumber (Cucumis sativus) under high-temperature conditions (Du and Tachibana, 1995), and it can promote Ca uptake in tomato (Solanum lycopersicum) fruit (Barickman et al., 2014a; de Freitas et al., 2011). Studies have demonstrated that adequate levels of Ca in tomato fruit have positive effects on fruit quality, specifically firmness (Vaz and Richardson, 1984). Cell wall integrity is maintained through the roles Ca plays in interconnections of pectinacious material (Willats et al., 2001). Research on ABA and Ca has predominantly focused on examining ABA as an environmental stress signal and its impact on signal transduction on a cellular level (Batistic et al., 2012; Chen et al., 2012). These studies examined how endogenous ABA increases as a result of environment stress such as drought and affects Ca levels (Du et al., 2010). For example, Guo et al. (2002) indicated that ABA triggers an oscillation in the cytosolic Ca concentrations initiating a series of signaling cascades that control physiological processes, including adaptation to environmental stress. This study focused on how exogenous application of ABA could affect Ca transport and partitioning between the leaves and fruit of tomato in protected culture environments. Calcium movement through the plant is regulated by source–sink relationships. Calcium moves to tissues that have the lowest water potential (Marschner, 1995). Calcium movement, which is passive and through the xylem, increases to tissues such as leaves because they are rapidly growing and have a lower water potential compared with root tissues. Other parts of the plants such as fruit tissue have higher water potentials and lower distribution of stomata than leaf tissue (Blanke, 1986). Therefore, movement of Ca into these tissues is considerably lower. Movement of Ca into fruit tissue is greatest when cells are actively dividing and expanding in the early stages of growth. After this stage of rapid growth, Ca movement is lessened because strength of the sink for Ca decreases (Ehret and Ho, 1986). Thus, fruit have a limited time for critical Ca uptake for rapidly expanding fruit tissue. There are only a few examples in the literature of studies demonstrating that foliar application of ABA can increase Ca uptake into tomato fruit tissue (de Freitas et al., 2011), especially the distal tissue (Barickman et al., 2014b). Insufficient Ca uptake and movement in tomato fruit tissue can result in the physiological disorder BER, which is associated with a Ca deficiency in the distal fruit tissue (Ho and White, 2005). Research on greenhouse tomato production has demonstrated that insufficient Ca supplied to the plants in the fertilizer solution rarely causes BER. More often, BER occurs in plants with an adequate Ca supply when grown in environmental conditions such as low humidity, high light intensity, and high temperature, which inhibit transport of Ca to rapidly growing distal fruit tissue (Saure, 2001). In addition, incidences of BER may occur during increased demand of distal fruit tissue for Ca in early stages of fruit development (Ho et al., 1993). Previous research has demonstrated that foliar ABA applications decreased the incidence of BER and increased the uptake of Ca into the fruit tissue (de Freitas et al., 2011). Applications of ABA negatively affect stomatal conductance (gS), which decreased Ca influx into the vegetative tissue allowing more Ca to be moved into the fruit tissue. Exogenous ABA can be applied to the plant either through root or in the form of a spray to the vegetative tissue. When applied Received for publication 30 June 2014. Accepted for publication 13 Aug. 2014. This research was made possible through support from the University of Tennessee UTIA, Agriculture Experiment Station. Research Associate/Graduate Research Assistant. Professor. Current title and address: Assistant Research and Extension Professor; Mississippi State University, North Mississippi Research and Extension Center, Verona, MS. To whom reprint requests should be addressed; e-mail carlsams@utk.edu. HORTSCIENCE VOL. 49(11) NOVEMBER 2014 1397 GROWTH REGULATORS

hortscience

Exogenous Foliar and Root Applications of Abscisic Acid Increase the Influx of Calcium into Tomato Fruit Tissue and Decrease the Incidence of Blossom-end Rot