Expt. 1.

‘Festive Ursula’ chrysanthemums in 6-inch-diameter pots were obtained from Green Circle Growers (Oberlin, OH), and Expt. 1 was conducted in Wooster, OH, from 28 Sept. to 9 Oct. 2007. Average greenhouse temperatures were 26/21 ± 2/3 °C day/night with daytime (0700–1800 hr) average relative humidity of 59.7% ± 7.3%. Plants were irrigated daily with 15N–2.2P–12.5K fertilizer (Peters Excel® Cal-Mag 15–5–15; Scotts-Sierra Horticulture Products, Marysville, OH) at 200 mg·L⁻¹ nitrogen (N) and were grown under natural irradiance with supplemental lighting provided by high-pressure sodium and metal halide lamps (GLX/GLS e-systems GROW lights; PARsource, Petaluma, CA). An average photosynthetic photon flux (PPF) of 176 μmol·m⁻²·s⁻¹ (maximum PPF of 600 μmol·m⁻²·s⁻¹) was provided from 0700 to 1800 hr daily, with a mean daily light integral (DLI) of 7.6 mol·m⁻²·d⁻¹.

Chrysanthemums were treated with either a spray or drench application of s-ABA (ConTego) at the half open flower stage [stage 3 (Syngenta Flowers Inc., 2010)]. All chrysanthemums were irrigated 12 h before the application of s-ABA. s-ABA was applied as a drench at 0, 125, 250, or 500 mg·L⁻¹ (60 mL per container) or as a spray at 0, 500, or 1000 mg·L⁻¹ (≈22.3 mL per plant, until the leaves were wet) with the addition of 0.05% surfactant (CapSil; Aquatrols, Cherry Hill, NJ). Spray applications were performed with a backpack sprayer (Regulator Bak-Pak; H.D. Hudson, Chicago, IL). Half of the plants from each ABA treatment had water withheld (drought-stressed) and the other half were irrigated daily. After 6 d, the drought-stressed plants were rewatered to evaluate plant recovery. The initial rewatering was with clear reverse osmosis water and all subsequent irrigations were with 100 mg·L⁻¹ N. Rewatered plants were then irrigated for 3 d.

Stomatal conductance readings were taken using a steady-state porometer (LI-1600; LI-COR, Lincoln, NE). Three basal leaves per plant were tagged and the same leaves were used for g_S measurements at each time point. Stomatal conductance was measured 1 d before s-ABA treatment (−1 d) and 1, 3, and 9 d after treatment (for drought-stressed chrysanthemums, 9 d was equivalent to 6 d of withholding water followed by 3 d of rewatering). Readings were taken at the same time each day, and data are the average of three replications, with three leaves measured per replication (n = 3).

Expt. 2.

Finished 8-inch-diameter pots of chrysanthemum cultivars Brandi, Colina Red, Flashy Gretchen, Golden Cheryl, Regina, and Wilma were obtained from Green Valley Growers (Ashland, OH). Plants were grown under normal greenhouse conditions, as described earlier, in Wooster, OH, from 21 Sept. to 15 Oct. 2009. Average greenhouse temperatures were 23/16 ± 2/2 °C day/night with daytime (0600–1800 hr) average relative humidity of 49.8% ± 11.6%. The average PPF was 259 μmol·m⁻²·s⁻¹ (maximum PPF of 924 μmol·m⁻²·s⁻¹) from 0600 to 1800 hr daily (DLI of 12.9 mol·m⁻²·d⁻¹). Before s-ABA application, plants were irrigated daily at the same time each day with 100 mg·L⁻¹ N as described previously.

All plants were irrigated 12 h before an application of s-ABA. Spray applications of s-ABA were applied at 0 or 500 mg·L⁻¹ (≈33.3 mL per plant, until leaves were wet) with 0.05% surfactant (CapSil). Chrysanthemums were treated with s-ABA when they were at the marketable stage of a few open flowers per plant [stage 2 (Syngenta Flowers Inc., 2010)]. The application rate of 500 mg·L⁻¹ s-ABA was selected based on the results from Expt. 1. Half of the chrysanthemums were irrigated daily and the other half were severely drought-stressed by completely withholding water until the s-ABA-treated plants wilted. Irrigated plants were watered daily with 100 mg·L⁻¹ N. After all of the s-ABA-treated plants within a cultivar reached a wilt status rating of 3, the plants were rewatered. Rewatering occurred for 3 d as stated previously. Data are the average of four replications with one plant per replication (n = 4).

Evaluations of wilt status.

Visual observations were taken daily in Expts. 1 and 2. All visual observations were based on whole plant wilt status. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to the touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Plants with a rating of 3 or less were considered to be unmarketable.

Statistical analysis.

Experiments were conducted in a completely randomized block design, which was blocked by replication and watering treatment (irrigated daily vs. drought-stressed). Values obtained from g_S and visual observations were analyzed by Proc GLM (generalized linear model) with least significant difference means separation test at P ≤ 0.05 using SAS (version 9.1.3; SAS Institute, Cary, NC).

Expt. 1. Determining effective s-ABA concentration and application method.

All concentrations of s-ABA and both application methods were effective at delaying wilting in drought-stressed chrysanthemums ‘Festive Ursula’, with no apparent phytotoxicity (Figs. 1 and 2). s-ABA was more effective at higher concentrations, and the plants drenched with 500 mg·L⁻¹ or sprayed with 500 or 1000 mg·L⁻¹ s-ABA had the longest shelf life extension (Table 1). These plants remained turgid (above a wilt status rating of 3) for 5 to 6 d before visual wilting was observed (Fig. 2). Chrysanthemums that were drenched with 125 and 250 mg·L⁻¹ s-ABA had a shorter shelf life extension, but showed delayed wilting by at least 1 d compared with control (0 mg·L⁻¹ s-ABA) plants (Fig. 2, Table 1).

Table 1.

Days until the appearance of visual symptoms of wilting and shelf life extension of drought-stressed ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA).

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Visual observation of drought-stressed ‘Festive Ursula’ chrysanthemum after treatment with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ (ppm) or as a spray at 0, 500, or 1000 mg·L⁻¹. Images of plants are after 3 d of drought stress and s-ABA treatment; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Visual observation of drought-stressed ‘Festive Ursula’ chrysanthemum after treatment with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ (ppm) or as a spray at 0, 500, or 1000 mg·L⁻¹. Images of plants are after 3 d of drought stress and s-ABA treatment; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Visual observation of drought-stressed ‘Festive Ursula’ chrysanthemum after treatment with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ (ppm) or as a spray at 0, 500, or 1000 mg·L⁻¹. Images of plants are after 3 d of drought stress and s-ABA treatment; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Wilt status ratings of drought-stressed ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Chrysanthemums were drought-stressed for 6 d after s-ABA application. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily. Day −1 is 1 d before s-ABA application. Values are the means ± sd of three replications (n = 3); 1 mg·L⁻¹ = 1 ppm.

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Wilt status ratings of drought-stressed ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Chrysanthemums were drought-stressed for 6 d after s-ABA application. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily. Day −1 is 1 d before s-ABA application. Values are the means ± sd of three replications (n = 3); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Wilt status ratings of drought-stressed ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Chrysanthemums were drought-stressed for 6 d after s-ABA application. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily. Day −1 is 1 d before s-ABA application. Values are the means ± sd of three replications (n = 3); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Spray, drench, and sprench (spray to drench) applications of s-ABA have been shown to delay drought-induced wilting in bedding plants and woody ornamentals (Blanchard et al., 2007; Kim and van Iersel, 2008; van Iersel et al., 2009; Waterland et al., 2010a, 2010b). Unfortunately, s-ABA applications cause leaf chlorosis, necrosis, and abscission in some species (Blanchard et al., 2007; Kim and van Iersel, 2008; Waterland et al., 2010a, 2010b). Symptoms of phytotoxicity are the most severe following the application of high concentrations of ABA (500, 1000, or 2000 mg·L⁻¹ s-ABA) (Kim and van Iersel, 2008; Waterland et al., 2010a, 2010b). In chrysanthemums, s-ABA applications delayed wilting without causing any apparent damage to leaves or flowers. This product may therefore be useful for extending the postproduction shelf life of chrysanthemums that encounter drought stress during shipping and/or retailing.

Stomatal conductance decreased at 1 d after s-ABA treatment, indicating that both spray and drench applications effectively induced stomatal closure in treated chrysanthemums. Drought-stressed chrysanthemums treated with s-ABA had a more rapid decrease in g_S than non–ABA-treated plants (0 mg·L⁻¹ s-ABA), and the largest differences were measured at 1 d after application (Fig. 3A). By Day 3, g_S was the same in all drought-stressed plants, regardless of s-ABA treatment (Fig. 3A). Both spray and drench applications of s-ABA also resulted in a decrease in g_S in all irrigated plants (Fig. 3B). In contrast to the drought-stressed plants, g_S in s-ABA-treated plants that were irrigated remained lower than the controls on Day 3.

Stomatal conductance readings of ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Drought-stressed chrysanthemums had water withheld for 6 d and were then rewatered for 3 d (A). Stomatal conductance was measured on drought-stressed and subsequently rewatered chrysanthemums (A) and irrigated (B) chrysanthemums after spray or drench applications of s-ABA. Stomatal conductance was measured at Day −1 (1 d before the application of s-ABA) and 1, 3, and 9 d after s-ABA treatment. Irrigated chrysanthemums were watered daily with 200 mg·L⁻¹ nitrogen. Values are the mean ± sd of three replications with three leaves per replication (n = 3); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Stomatal conductance readings of ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Drought-stressed chrysanthemums had water withheld for 6 d and were then rewatered for 3 d (A). Stomatal conductance was measured on drought-stressed and subsequently rewatered chrysanthemums (A) and irrigated (B) chrysanthemums after spray or drench applications of s-ABA. Stomatal conductance was measured at Day −1 (1 d before the application of s-ABA) and 1, 3, and 9 d after s-ABA treatment. Irrigated chrysanthemums were watered daily with 200 mg·L⁻¹ nitrogen. Values are the mean ± sd of three replications with three leaves per replication (n = 3); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Stomatal conductance readings of ‘Festive Ursula’ chrysanthemum treated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg·L⁻¹ or as a spray at 0, 500, or 1000 mg·L⁻¹. Drought-stressed chrysanthemums had water withheld for 6 d and were then rewatered for 3 d (A). Stomatal conductance was measured on drought-stressed and subsequently rewatered chrysanthemums (A) and irrigated (B) chrysanthemums after spray or drench applications of s-ABA. Stomatal conductance was measured at Day −1 (1 d before the application of s-ABA) and 1, 3, and 9 d after s-ABA treatment. Irrigated chrysanthemums were watered daily with 200 mg·L⁻¹ nitrogen. Values are the mean ± sd of three replications with three leaves per replication (n = 3); 1 mg·L⁻¹ = 1 ppm.

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In salvia (Salvia splendens), drench applications of s-ABA resulted in rapid stomatal closure, and g_S decreased within 3 h of application (Kim and van Iersel, 2008). Stomatal conductance in chrysanthemums may have decreased as rapidly, but our earliest measurement was taken at 1 d after application. Although shelf life extension was clearly rate-dependent, rate-dependent differences in g_S at 1 and 3 d after treatment were not observed (Table 1, Figs. 2 and 3). If chrysanthemum stomata responded within hours of the s-ABA application, these differences may have allowed the plants receiving higher concentrations of s-ABA to close their stomata faster and conserve more soil moisture earlier in the stress response than those treated with lower concentrations. This suggests that the timing of s-ABA application, immediately before any anticipated drought stress, may provide optimal protection.

After 6 d of drought stress, plants were rewatered to evaluate their recovery. s-ABA-treated plants were visually indistinguishable from the irrigated plants within 3 d of rewatering (Day 9), while the control plants (0 mg·L⁻¹ s-ABA drench and spray) developed necrosis on the margins of lower leaves (data not shown). Stomatal conductance increased on Day 9 in all rewatered plants, except those that were sprayed with 1000 mg·L⁻¹ s-ABA (Fig. 3A). On Day 9, the g_S of irrigated plants that had been drenched with s-ABA had returned to pre-ABA-treatment rates (Fig. 3B). In contrast, g_S was still lower in all irrigated plants that had been sprayed with s-ABA (Fig. 3B). This suggests that spray applications had a longer efficacy than drench applications. In chrysanthemums, the s-ABA may be absorbed and metabolized more quickly from the roots than from the leaves. It is also possible that daily irrigation may have leached some of the s-ABA from the soil before it was taken up by the plant. Previous experiments with bedding plants indicate that spray applications of s-ABA are more effective at delaying wilting in pansy (Viola ×wittrockiana), while drench applications are more effective in marigold (Tagetes patula) (Waterland et al., 2010a).

Expt. 2. Evaluating cultivar differences.

s-ABA delayed visual symptoms of wilting in all six chrysanthemum cultivars treated in Expt. 2. Drought-stressed chrysanthemums treated with 500 mg·L⁻¹ s-ABA remained turgid longer and maintained a higher wilt status rating than the control plants (0 mg·L⁻¹ s-ABA) (Fig. 4). The delay in wilting and subsequent shelf life extension was cultivar dependent. ABA treatment extended the shelf life of all drought-stressed chrysanthemums except ‘Brandi’ (Table 2). ABA was most effective in ‘Flashy Gretchen’ and ‘Wilma’ (3.8 d shelf life extension) and least effective in ‘Golden Cheryl’ (1.6 d shelf life extension) (Table 2). Cultivar variations could be associated with differential sensitivity to ABA or differences in growth habit, exposed media surface area, or water usage. ‘Brandi’ chrysanthemums were larger and had a more open growth habit than the other cultivars.

Table 2.

Days until the appearance of visual symptoms of wilting and shelf life extension of six cultivars of chrysanthemum treated with s-abscisic acid (s-ABA) at 0 or 500 mg·L⁻¹ (ppm) and drought-stressed.

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Wilt status ratings of six cultivars of chrysanthemum after s-abscisic acid (s-ABA) application and withholding water. Chrysanthemums were sprayed with 0 or 500 mg·L⁻¹ s-ABA. Water was withheld until the 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less). Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily with Day 0 just before the s-ABA application (1 to 2 h). Values are the means ± sd of four replications (n = 4); 1 mg·L⁻¹ = 1 ppm.

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Wilt status ratings of six cultivars of chrysanthemum after s-abscisic acid (s-ABA) application and withholding water. Chrysanthemums were sprayed with 0 or 500 mg·L⁻¹ s-ABA. Water was withheld until the 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less). Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily with Day 0 just before the s-ABA application (1 to 2 h). Values are the means ± sd of four replications (n = 4); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Wilt status ratings of six cultivars of chrysanthemum after s-abscisic acid (s-ABA) application and withholding water. Chrysanthemums were sprayed with 0 or 500 mg·L⁻¹ s-ABA. Water was withheld until the 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less). Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Visual ratings were taken daily with Day 0 just before the s-ABA application (1 to 2 h). Values are the means ± sd of four replications (n = 4); 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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All s-ABA-treated chrysanthemums recovered (regained turgor and a rating of 5) within 6 h (data not shown) and by 3 d after rewatering they were indistinguishable from the irrigated controls (Fig. 5). These plants were considered marketable and had no symptoms of leaf or flower damage. Drought-stressed chrysanthemums that received no s-ABA (0 mg·L⁻¹ s-ABA) had leaf chlorosis or necrosis and some of the plants did not regain turgor (Fig. 5). All non–ABA-treated chrysanthemums ‘Regina’, ‘Wilma’, and 50% of ‘Flashy Gretchen’ did not recover after rewatering and declined to a wilt status rating of 1. All flowers from these plants were wilted. Rewatered ‘Brandi’, ‘Colina Red’, and ‘Golden Cheryl’ that received no s-ABA regained turgor, but were less marketable than s-ABA-treated plants because they developed basal leaf chlorosis or necrosis on the leaf margins [Fig. 5 (data not shown)].

Visual observation of six cultivars of chrysanthemum after drought stress and subsequent rewatering. Plants were sprayed with 0 or 500 mg·L⁻¹ s-abscisic acid (s-ABA). Water was withheld until 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less), then plants were rewatered for 3 d to evaluate recovery. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Images are representative of all replications (n = 4) and were taken at 3 d after rewatering; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Visual observation of six cultivars of chrysanthemum after drought stress and subsequent rewatering. Plants were sprayed with 0 or 500 mg·L⁻¹ s-abscisic acid (s-ABA). Water was withheld until 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less), then plants were rewatered for 3 d to evaluate recovery. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Images are representative of all replications (n = 4) and were taken at 3 d after rewatering; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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Visual observation of six cultivars of chrysanthemum after drought stress and subsequent rewatering. Plants were sprayed with 0 or 500 mg·L⁻¹ s-abscisic acid (s-ABA). Water was withheld until 500 mg·L⁻¹ s-ABA-treated plants were visibly wilted (wilt status rating of 3 or less), then plants were rewatered for 3 d to evaluate recovery. Wilt status ratings were from 5 to 1, where 5 = completely turgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry and desiccated. Images are representative of all replications (n = 4) and were taken at 3 d after rewatering; 1 mg·L⁻¹ = 1 ppm.

Citation: HortTechnology hortte 20, 5; 10.21273/HORTTECH.20.5.896

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