Abscisic Acid Applications DecreaseStomatal Conductance and Delay Wiltingin Drought-stressed Chrysanthemums

Nicole L. Waterland1, John J. Finer, and Michelle L. Jones2

ADDITIONAL INDEX WORDS. ABA, antitranspirants, Chrysanthemum ·morifolium,floriculture, shelf life extension

SUMMARY. Drought stress during shipping and retailing reduces the postproductionquality and marketability of potted plants. Plants respond to drought stress byclosing their stomata and reducing transpirational water loss. This stress responseis mediated by the plant hormone abscisic acid (ABA). Exogenous applications ofs-abscisic acid (s-ABA), the biologically active form of the hormone, can enhancedrought tolerance and extend shelf life in a variety of bedding plants. However,little is known about the effectiveness of s-ABA at enhancing drought tolerancein perennial crops like chrysanthemum (Chrysanthemum ·morifolium). ‘FestiveUrsula’ chrysanthemum plants were drenched (0, 125, 250, or 500 mg�L–1) orsprayed (0, 500, or 1000 mg�L–1) with s-ABA. All applications containing s-ABAeffectively delayed wilting by reducing stomatal conductance (gS). Shelf life wasextended from 1.2 to 4.0 days depending on the concentration of s-ABA. Sprayapplications of 500 mg�L–1 s-ABA to six additional chrysanthemum cultivarsincreased shelf life from 1.6 to 3.8 days following drought stress. s-ABA treatmentalso allowed severely drought-stressed chrysanthemums to recover and remainmarketable after rewatering. Growers can treat chrysanthemums with s-ABA toreduce water use during shipping and to delay wilting if plants are not adequatelywatered during retailing.

Plants may be exposed to hightemperatures and irregular orinfrequent irrigation during ship-

ping and retailing. These poor post-production environments cause rapidsubstrate drying, plant wilting, andaccelerated senescence. Drought stressis a major cause of postproduction de-cline in greenhouse crops, and plantsquickly become unsalable (Armitage,1993; Barrett and Campbell, 2006;van Iersel et al., 2009). The ABA helps

plants survive drought stress by closingstomata to reduce transpirational waterloss and prevent wilting (Malladi andBurns, 2007).

Antitranspirants can be used byproducers to prevent wilting and ex-tend the postproduction shelf life andmarketability of floriculture crops(Goreta et al., 2007; Martin and Link,1973).Theseproductsenhancedroughttolerance by providing a physical bar-rier to water loss or by inducing sto-matal closure. Physical antitranspirantscontain resins, polymers, or waxes thatcoat the leaves and block the stomata.Physiological antitranspirants reducetranspiration rates by inducing theplants to close their stomata. Theseproducts may contain ABA or otherchemicals that cause the plant to pro-duce ABA. Prolonged stomatal closureand reduced transpiration can lead toheat stress under high temperatures,and antitranspirants may also causephytotoxicity (Blanchard et al., 2007;

Kim and van Iersel, 2008; Waterlandet al., 2010a, 2010b). Additional re-search is therefore needed to evaluateantitranspirants and determine howthey can be used to enhance the post-production quality of specific green-house and nursery crops.

Comparative research has shownthat antitranspirants containing ABAare more effective than physical anti-transpirants at reducing water lossand delaying drought-induced wilting(Goreta et al., 2007). A new commer-cial product containing s-ABA, thebiologically active form of ABA, Con-Tego (Valent BioSciences, Liberty-ville, IL), delays wilting in a variety ofbedding plants under severe droughtstress (Blanchard et al., 2007; Kim andvan Iersel, 2008; Waterland et al.,2010a, 2010b). Little is known aboutthe effectiveness or phytotoxicity ofs-ABA on potted crops like chrysan-themum. Chrysanthemums are animportant fall crop that accounts forabout 20% of the total potted peren-nial market in the United States (U.S.Department of Agriculture, 2009). En-hancing their postproduction droughttolerance would result in considerablesavings to retailers and producers.

The goal of this research was todetermine if s-ABA could be used toenhance the drought tolerance of gar-den chrysanthemums without anyphytotoxicity. Our objectives were 1) todetermine if exogenous application ofs-ABA delays wilting in finished chry-santhemums exposed to drought stressand 2) to identify any symptoms ofphytotoxicity that would negativelyaffect the marketability of treatedchrysanthemums.

Materials and methodsPlant materials and experimentaltreatments

EXPT. 1. ‘Festive Ursula’ chry-santhemums in 6-inch-diameter potswere obtained from Green CircleGrowers (Oberlin, OH), and Expt. 1was conducted in Wooster, OH, from28 Sept. to 9 Oct. 2007. Average green-housetemperatureswere26/21± 2/3�C

UnitsTo convert U.S. to SI,multiply by U.S. unit SI unit

To convert SI to U.S.,multiply by

29.5735 fl oz mL 0.03382.54 inch(es) cm 0.39371 ppm mg�L–1 1

(�F – 32) O 1.8 �F �C (1.8 · �C) + 32

Department of Horticulture and Crop Science, TheOhio Agricultural Research and Development Center,The Ohio State University, Wooster, OH 44691

The information in this publication is for educationalpurposes only. Mention of a trademark, proprietaryproduct, or vendor does not constitute a guaranteeor warranty of the product, nor does it imply approvalor disapproval to the exclusion of other products orvendors that may also be suitable.

This research was funded by the Ohio State UniversityD.C. Kiplinger Floriculture Endowment, the ValentBioSciences Corporation, and the Gladys WittmeyerKnox-Gene Wittmeyer Scholarship. Salaries and re-search support were provided in part by State andFederal funds appropriated to the Ohio AgriculturalResearch and Development Center, The Ohio StateUniversity.

Journal Article Number HCS 10-05.

We thank Green Circle Growers for their donation ofplant material and Valent BioSciences for donation ofchemicals.

1Current address: Division of Plant and Soil Sciences,West Virginia University, Morgantown, WV 26506.

2Corresponding author. E-mail: jones.1968@osu.edu.

896 • October 2010 20(5)

day/night with daytime (0700–1800 HR) average relative humidity of59.7% ± 7.3%. Plants were irrigateddaily 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 ni-trogen (N) and were grown undernatural irradiance with supplemen-tal lighting provided by high-pressuresodium and metal halide lamps(GLX/GLS e-systems GROW lights;PARsource, Petaluma, CA). An aver-age photosynthetic photon flux (PPF)of 176 mmol�m–2�s–1 (maximum PPFof 600 mmol�m–2�s–1) was providedfrom 0700 to 1800 HR daily, with amean daily light integral (DLI) of7.6 mol�m–2�d–1.

Chrysanthemums were treatedwith either a spray or drench applica-tion of s-ABA (ConTego) at the halfopen flower stage [stage 3 (SyngentaFlowers Inc., 2010)]. All chrysanthe-mums were irrigated 12 h before theapplication of s-ABA. s-ABA was ap-plied as a drench at 0, 125, 250, or500 mg�L–1 (60 mL per container) oras a spray at 0, 500, or 1000 mg�L–1

(�22.3 mL per plant, until the leaveswere wet) with the addition of 0.05%surfactant (CapSil; Aquatrols, CherryHill, NJ). Spray applications wereperformed with a backpack sprayer(Regulator Bak-Pak; H.D. Hudson,Chicago, IL). Half of the plants fromeach ABA treatment had water with-held (drought-stressed) and the otherhalf were irrigated daily. After 6 d, thedrought-stressed plants were rewa-tered to evaluate plant recovery. Theinitial rewatering was with clear reverseosmosis water and all subsequent irri-gations were with 100 mg�L–1 N. Rewa-tered plants were then irrigated for 3 d.

Stomatal conductance readingswere taken using a steady-state poro-meter (LI-1600; LI-COR, Lincoln,NE). Three basal leaves per plant weretagged and the same leaves were usedfor gS measurements at each time point.Stomatal conductance was measured1 d before s-ABA treatment (–1 d)and 1, 3, and 9 d after treatment (fordrought-stressed chrysanthemums, 9 dwas equivalent to 6 d of withholdingwater followed by 3 d of rewatering).Readings were taken at the same timeeach day, and data are the average ofthree replications, with three leavesmeasured per replication (n = 3).

EXPT. 2. Finished 8-inch-diameterpots of chrysanthemum cultivars Brandi,

Fig. 1. Visual observation of drought-stressed ‘Festive Ursula’ chrysanthemumafter treatment with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500mg�L21 (ppm) or as a spray at 0, 500, or 1000 mg�L21. Images of plants are after3 d of drought stress and s-ABA treatment; 1 mg�L21 = 1 ppm.

Table 1. Days until the appearance of visual symptoms of wilting and shelf lifeextension of drought-stressed ‘Festive Ursula’ chrysanthemum treated withs-abscisic acid (s-ABA).

Application methodand s-ABA concn (mg�L–1)z

Time until visuallywilted (d)y

Shelf lifeextension (d)x

Drench 0 1.7 cw

125 2.9 b 1.2250 2.9 b 1.2500 5.7 a 4.0

Spray 0 2.2 b500 5.3 a 3.1

1,000 6.0 a 3.8z1 mg�L–1 = 1 ppm.yValues are the average number of days from Day 0 that it took for each plant to show visible symptoms of wilting,which was a rating of 3 (wilted) on the wilt status rating scale of 5 to 1, where 5 = completely turgid, 4 = soft to thetouch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry anddesiccated. Values are means of three replications (n = 3).xShelf life extension refers to the number of additional days from the time the control plants wilted until the s-ABA-treated plants wilted.wMeans within the same treatment (spray or drench) followed by the same letter are not significantly different at P £0.05 as determined by the least significant difference test.

Fig. 2. Wilt status ratings of drought-stressed ‘Festive Ursula’ chrysanthemumtreated with s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg�L21 or asa spray at 0, 500, or 1000 mg�L21. Chrysanthemums were drought-stressed for 6d after s-ABA application. Wilt status ratings were from 5 to 1, where 5 = completelyturgid, 4 = soft to touch and starting to wilt, 3 = wilted, 2 = severely wilted, and1 = wilted to the point that leaves were dry and desiccated. Visual ratings weretaken daily. Day 21 is 1 d before s-ABA application. Values are the means ± SD

of three replications (n = 3); 1 mg�L21 = 1 ppm.

• October 2010 20(5) 897

Colina Red, Flashy Gretchen, GoldenCheryl, Regina, and Wilma wereobtained from Green Valley Growers(Ashland, OH). Plants were grownunder normal greenhouse conditions,as described earlier, in Wooster, OH,from 21 Sept. to 15 Oct. 2009. Aver-age greenhouse temperatures were23/16 ± 2/2 �C day/night with day-time (0600–1800 HR) average relativehumidity of 49.8% ± 11.6%. The aver-age PPF was 259 mmol�m–2�s–1 (maxi-mum PPF of 924 mmol�m–2�s–1) from0600 to 1800 HR daily (DLI of 12.9mol�m–2�d–1). Before s-ABA applica-tion, plants were irrigated daily at thesame time each day with 100 mg�L–1 Nas described previously.

All plants were irrigated 12 hbefore an application of s-ABA. Sprayapplications of s-ABA were applied at0 or 500 mg�L–1 (�33.3 mL per plant,until leaves were wet) with 0.05%surfactant (CapSil). Chrysanthemumswere treated with s-ABA when theywere at the marketable stage of a fewopen flowers per plant [stage 2(Syngenta Flowers Inc., 2010)]. Theapplication rate of 500 mg�L–1 s-ABAwas selected based on the results fromExpt. 1. Half of the chrysanthemumswere irrigated daily and the other halfwere severely drought-stressed bycompletely withholding water untilthe s-ABA-treated plants wilted. Irri-gated plants were watered daily with100 mg�L–1 N. After all of the s-ABA-treated plants within a cultivar reacheda wilt status rating of 3, the plants wererewatered. Rewatering occurred for3 d as stated previously. Data are theaverage of four replications with oneplant per replication (n = 4).

EVALUATIONS OF WILT STATUS.Visual observations were taken dailyin Expts. 1 and 2. All visual observa-tions were based on whole plant wiltstatus. Wilt status ratings were from5 to 1, where 5 = completely turgid,4 = soft to the touch and starting towilt, 3 = wilted, 2 = severely wilted, and1 = wilted to the point that leaves weredry and desiccated. Plants with a ratingof 3 or less were considered to beunmarketable.

STATISTICAL ANALYSIS. Experi-ments were conducted in a completelyrandomized block design, which wasblocked by replication and wateringtreatment (irrigated daily vs. drought-stressed). Values obtained from gS andvisual observations were analyzed byProc GLM (generalized linear model)

with least significant difference meansseparation test at P £ 0.05 using SAS(version 9.1.3; SAS Institute, Cary,NC).

Results and discussionEXPT. 1. DETERMINING EFFEC-

TIVE S-ABA CONCENTRATION AND

APPLICATION METHOD. All concentra-tions of s-ABA and both applicationmethods were effective at delayingwilting in drought-stressed chrysan-themums ‘Festive Ursula’, with noapparent phytotoxicity (Figs. 1 and2). s-ABA was more effective at higherconcentrations, and the plants drenchedwith 500 mg�L–1 or sprayed with 500 or1000 mg�L–1 s-ABA had the longestshelf life extension (Table 1). Theseplants remained turgid (above a wiltstatus rating of 3) for 5 to 6 d beforevisual wilting was observed (Fig. 2).Chrysanthemums that were drenchedwith 125 and 250 mg�L–1 s-ABA hada shorter shelf life extension, but showeddelayed wilting by at least 1 d comparedwith control (0 mg�L–1 s-ABA) plants(Fig. 2, Table 1).

Spray, drench, and sprench (sprayto drench) applications of s-ABA have

been shown to delay drought-inducedwilting in bedding plants and woodyornamentals (Blanchard et al., 2007;Kim and van Iersel, 2008; van Ierselet al., 2009; Waterland et al., 2010a,2010b). Unfortunately, s-ABA applica-tions cause leaf chlorosis, necrosis, andabscission in some species (Blanchardet al., 2007; Kim and van Iersel, 2008;Waterland et al., 2010a, 2010b). Symp-toms of phytotoxicity are the mostsevere following the application of highconcentrations of ABA (500, 1000, or2000 mg�L–1 s-ABA) (Kim and vanIersel, 2008; Waterland et al., 2010a,2010b). In chrysanthemums, s-ABAapplications delayed wilting withoutcausing any apparent damage toleaves or flowers. This product maytherefore be useful for extending thepostproduction shelf life of chrysan-themums that encounter droughtstress during shipping and/or retailing.

Stomatal conductance decreasedat 1 d after s-ABA treatment, indicat-ing that both spray and drench appli-cations effectively induced stomatalclosure in treated chrysanthemums.Drought-stressed chrysanthemumstreated with s-ABA had a more rapid

Fig. 3. Stomatal conductance readings of ‘Festive Ursula’ chrysanthemum treatedwith s-abscisic acid (s-ABA) as a drench at 0, 125, 250, or 500 mg�L21 or as a sprayat 0, 500, or 1000 mg�L21. Drought-stressed chrysanthemums had water withheldfor 6 d and were then rewatered for 3 d (A). Stomatal conductance was measured ondrought-stressed and subsequently rewatered chrysanthemums (A) and irrigated(B) chrysanthemums after spray or drench applications of s-ABA. Stomatalconductance was measured at Day 21 (1 d before the application of s-ABA) and 1,3, and 9 d after s-ABA treatment. Irrigated chrysanthemums were watered dailywith 200 mg�L21 nitrogen. Values are the mean ± SD of three replications with threeleaves per replication (n = 3); 1 mg�L21 = 1 ppm.

898 • October 2010 20(5)

RESEARCH REPORTS

decrease in gS than non–ABA-treatedplants (0 mg�L–1 s-ABA), and thelargest differences were measured at1 d after application (Fig. 3A). By Day3, gS was the same in all drought-stressed plants, regardless of s-ABAtreatment (Fig. 3A). Both spray anddrench applications of s-ABA alsoresulted in a decrease in gS in allirrigated plants (Fig. 3B). In contrastto the drought-stressed plants, gS ins-ABA-treated plants that were irri-gated remained lower than the con-trols on Day 3.

In salvia (Salvia splendens), drenchapplications of s-ABA resulted in rapidstomatal closure, and gS decreasedwithin 3 h of application (Kim andvan Iersel, 2008). Stomatal conduc-tance in chrysanthemums may havedecreased as rapidly, but our earliestmeasurement was taken at 1 d afterapplication. Although shelf life exten-sion was clearly rate-dependent, rate-dependent differences in gS at 1 and 3 dafter treatment were not observed(Table 1, Figs. 2 and 3). If chrysanthe-mum stomata responded within hoursof the s-ABA application, these dif-ferences may have allowed the plantsreceiving higher concentrations of s-ABA to close their stomata faster andconserve more soil moisture earlier inthe stress response than those treatedwith lower concentrations. This sug-gests that the timing of s-ABA appli-cation, immediately before anyanticipated drought stress, may pro-vide optimal protection.

After 6 d of drought stress, plantswere rewatered to evaluate their recov-ery. s-ABA-treated plants were visuallyindistinguishable from the irrigatedplants within 3 d of rewatering (Day9), while the control plants (0 mg�L–1

s-ABA drench and spray) developednecrosis on the margins of lower leaves(data not shown). Stomatal conduc-tance increased on Day 9 in all rewa-tered plants, except those that weresprayed with 1000 mg�L–1 s-ABA (Fig.3A). On Day 9, the gS of irrigatedplants that had been drenched withs-ABA had returned to pre-ABA-treatment rates (Fig. 3B). In contrast,gS was still lower in all irrigated plantsthat had been sprayed with s-ABA(Fig. 3B). This suggests that sprayapplications had a longer efficacy thandrench applications. In chrysanthe-mums, the s-ABA may be absorbedand metabolized more quickly fromthe roots than from the leaves. It is

also possible that daily irrigation mayhave leached some of the s-ABAfrom the soil before it was taken upby the plant. Previous experiments

with bedding plants indicate thatspray applications of s-ABA are moreeffective at delaying wilting in pansy(Viola ·wittrockiana), while drench

Fig. 4. Wilt status ratings of six cultivars of chrysanthemum after s-abscisic acid(s-ABA) application and withholding water. Chrysanthemums were sprayed with0 or 500 mg�L21 s-ABA. Water was withheld until the 500 mg�L21 s-ABA-treatedplants were visibly wilted (wilt status rating of 3 or less). Wilt status ratings were from5 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 to2 h). Values are the means ± SD of four replications (n = 4); 1 mg�L21 = 1 ppm.

Table 2. Days until the appearance of visual symptoms of wilting and shelf lifeextension of six cultivars of chrysanthemum treated with s-abscisic acid (s-ABA)at 0 or 500 mg�L–1 (ppm) and drought-stressed.

Cultivar

Time until visually wilted (d)zShelf life

extension (d)y0 mg�L–1 500 mg�L–1

Brandi 1.7 2.5 0.8Colina Red 3.8 5.5 1.8*Flashy Gretchen 5.5 9.3 3.8*Golden Cheryl 2.2 3.8 1.6*Regina 3.8 7.0 3.3*Wilma 4.8 8.5 3.8*zValues are the average number of days from Day 0 that it took each plant to show visible symptoms of wilting,which was a rating of 3 (wilted) on the wilt status rating scale of 5 to 1, where 5 = completely turgid, 4 = soft to thetouch and starting to wilt, 3 = wilted, 2 = severely wilted, and 1 = wilted to the point that leaves were dry anddesiccated.yShelf life extension refers to the number of additional days from the time the control plants wilted until the s-ABA-treated plants wilted. Values are means of four replications (n = 4).*Significant at P £ 0.05 as determined by the least significant difference test.

• October 2010 20(5) 899

applications are more effective inmarigold (Tagetes patula) (Water-land et al., 2010a).

EXPT. 2. EVALUATING CULTIVAR

DIFFERENCES. s-ABA delayed visualsymptoms of wilting in all six chrysan-themum cultivars treated in Expt.2. Drought-stressed chrysanthemumstreated with 500 mg�L–1 s-ABA re-mained turgid longer and maintaineda higher wilt status rating than thecontrol plants (0 mg�L–1 s-ABA) (Fig.4). The delay in wilting and subse-quent shelf life extension was cultivardependent. ABA treatment extendedthe shelf life of all drought-stressedchrysanthemums except ‘Brandi’ (Table2). ABA was most effective in ‘FlashyGretchen’ and ‘Wilma’ (3.8 d shelf life

extension) and least effective in ‘GoldenCheryl’ (1.6 d shelf life extension)(Table 2). Cultivar variations couldbe associated with differential sensi-tivity to ABA or differences in growthhabit, exposed media surface area, orwater usage. ‘Brandi’ chrysanthemumswere larger and had a more opengrowth habit than the other cultivars.

All s-ABA-treated chrysanthe-mums recovered (regained turgorand a rating of 5) within 6 h (datanot shown) and by 3 d after rewater-ing they were indistinguishable fromthe irrigated controls (Fig. 5). Theseplants were considered marketableand had no symptoms of leaf or flowerdamage. Drought-stressed chrysan-themums that received no s-ABA

(0 mg�L–1 s-ABA) had leaf chlorosisor necrosis and some of the plantsdid not regain turgor (Fig. 5). Allnon–ABA-treated chrysanthemums‘Regina’, ‘Wilma’, and 50% of ‘FlashyGretchen’ did not recover after rewa-tering and declined to a wilt statusrating of 1. All flowers from theseplants were wilted. Rewatered ‘Brandi’,‘Colina Red’, and ‘Golden Cheryl’ thatreceived no s-ABA regained turgor,but were less marketable than s-ABA-treated plants because they developedbasal leaf chlorosis or necrosis on theleaf margins [Fig. 5 (data not shown)].

ConclusionFoliar applications of s-ABA

delayed symptoms of drought stressin all seven chrysanthemum cultivarsevaluated. ABA-treated plants main-tained turgor by rapidly closing sto-mata and reducing transpirationalwater loss. Although s-ABA effectivelydelays drought-induced wilting ina variety of floriculture crops, applica-tions can result in leaf abscission andsenescence symptoms that reduce themarketability and overall quality ofthe plants (Blanchard et al., 2007; Kimand van Iersel, 2008; Waterland et al.,2010a, 2010b). In this research, nophytotoxicity was observed and shelflifewas extended in all drought-stressedchrysanthemums except the cultivar‘Brandi’. The greatest shelf life exten-sion and delay in wilting was observedwith higher concentrations (500 or1000 mg�L–1 sprays) of s-ABA. s-ABAis a very promising growth regulatorthat growers can use to protect chry-santhemums from drought stress dur-ing shipping and retailing. Decreasingpostproduction shrinkage will increaseproduct sell-through and increase prof-itability for both growers and retailers.

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Fig. 5. Visual observation of six cultivars of chrysanthemum after drought stressand subsequent rewatering. Plants were sprayed with 0 or 500 mg�L21 s-abscisicacid (s-ABA). Water was withheld until 500 mg�L21 s-ABA-treated plants werevisibly wilted (wilt status rating of 3 or less), then plants were rewatered for 3 d toevaluate 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 = wiltedto the point that leaves were dry and desiccated. Images are representative of allreplications (n = 4) and were taken at 3 d after rewatering; 1 mg�L21 = 1 ppm.

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