Growth Regulators Gene Blythe Section Editor and Moderator Growth Regulators Section 263
Determining the Effects of Exogenous Abscisic Acid on Evapotranspiration of Tomato (Solanum lycopersicon) Manuel G. Astacio and Marc W. van Iersel The University of Georgia, Department of Horticulture, Athens, GA 30602 dmc12@uga.edu Index Words: Transpiration, stomatal conductance, abscisic acid, drought stress, plant shelf life Significance to Industry: It is common for plants in the retail market to receive inadequate watering and lose aesthetic value within a short period of time. To help plants maintain their salability longer, the plant hormone abscisic acid (ABA) was applied as a drench to reduce transpiration by closing the stomata. This application was able to delay wilting by two (using 62.5 125 ppm) to five days (using 250 1000 ppm) as compared with nontreated control plants. Negative side effects of the ABA application were rate-dependent chlorosis on the lower leaves, followed by leaf abscission. Abscisic acid can be used to lengthen the shelf life of plants, but the lowest effective dose should be applied to minimize negative side effects. Nature of Work: Inadequate watering rapidly diminishes a plant s salability and drastically shortens its shelf life (1). In addition, the adoption of pay-by-scan systems has shifted much of the post-production care from retailers to growers, and the growers are only paid by the number of plants that are sold (7). These changes to the retail sector have shifted the burden of plant maintenance from retailers to growers. The hormone ABA has potential for extending the shelf life of plants during retail display. Normally, ABA is produced by the plant in response to drought conditions, accumulating in the leaves and causing the guard cells to respond by either closing stomata or preventing them from opening (4, 6), thus reducing transpiration (5). This effect can be profound and has commercial implications. Exogenous ABA applications can reduce water loss and enhance the shelf life of unwatered plants by several days to weeks depending on the rate of ABA application (3, 7). Studies have also examined the effect of an artificially high level of ABA on leaf physiology. Plants grown under these conditions exhibited smaller stomata in higher density than control treatments (2). The objectives of this study were to evaluate the effects of exogenous ABA applications on the evapotranspiration of tomato and how it affects the quality of the plants. Tomatoes were used as the model crop because they are sensitive to ABA applications and wilt rapidly. Super Sweet 100 tomatoes were seeded in 72-cell trays. Following germination, plants were transplanted into 10-cm round pots filled with soilless substrate (Fafard 2P; Conrad Fafard Inc., Agawam, MA) and grown on ebb and flow benches in a Growth Regulators Section 264
greenhouse. The ebb and flow benches watered the tomatoes daily with a fertilizer solution containing 100 ppm N (15-5-15 Cal-Mag, Scotts, Marysville, OH). An ABA stock solution (10% w/v s-aba, the biologically-active form of ABA, VBC- 30101; Valent BioSciences, Long Grove, IL) was diluted with deionized water to yield concentrations of 0, 62.5, 125, 250, 500, and 1000 ppm. This range of concentrations was chosen based on prior research that showed high efficacy at concentrations of 250 to 2000 ppm, although rates higher than 1000 ppm resulted in significant leaf abscission in annual salvia (Salvia splendens) (3). ABA applications were made on 13 Oct. 2009, and the tomatoes were watered to runoff prior to the ABA being applied. All applications were added as a drench, with each plant receiving 100 ml of ABA solution. After the ABA applications, water was withheld from half of the plants (unwatered), while the other half was rewatered as needed. Visual observations were taken daily for the duration of the study. In addition, pot weight was measured with 1- and 2-kg load cells (LSP-1 and LSP-2; Transducer Techniques, Temecula, CA) that were fastened to level sections of a metal frame and wired to a data logger (CR10; Campbell Scientific Inc., Logan, UT). The weight measurements were taken every 10 minutes, and cumulative weight loss over the course of the study was calculated as a measure of evapotranspiration. Daily weight changes were used to determine daily water use of the plants and, for rewatered plants, data were corrected for the amount of water applied. The experiment was designed as a randomized complete block with a split plot, with the rewatered/unwatered factor as the subplot factor. There were two blocks and the experimental unit was an individual plant. ABA treatments were analyzed separately for the rewatered versus the unwatered treatments using regression analysis. Since hormonal effects on plant physiology are generally not directly proportional to the hormonal concentration, ABA concentration were transformed using log([aba]+50) before testing for linear effects of ABA on cumulative evapotranspiration. Results and Discussion: Within 3-4 hours following ABA application, there was a clear reduction in evapotranspiration of the ABA-treated plants as compared with the control plants among the unwatered treatments (Fig. 1), and a similar trend was present in the rewatered plants (Fig. 2). Statistical analysis showed a P-value of 0.006752 for the unwatered treatments 1.5 hours following ABA application, although the rewatered treatments did not show a significant difference until 4.5 hours after ABA application (with a P-value of 0.03005). By the end of the second day following ABA application, the control plants had transpired 82 ml of water, whereas the plants treated with 62.5 ppm ABA had transpired 66 ml (Fig. 1). The plants treated with 125 1000 ppm ABA had only transpired 48.9 to 41.2 ml, respectively, at this time. By day 8, the control plants had used most of the available water (301 ml) and had begun to wilt, while the treated plants were still transpiring due to remaining water availability in the substrate (Fig. 1). By day 9, the plants treated with 62.5 ppm ABA had wilted, while those treated with 125 or 250 ppm ABA wilted by day 10. Plants treated with 500 and 1000 ppm ABA wilted by day 13 (Fig. 3). The time to wilting was prolonged by overcast weather on days 1-3, directly after ABA application. Growth Regulators Section 265
The ABA concentration had a direct effect on daily water use, with the control plants using 35 ml on the first full day following ABA application, and the 62.5 ppm-treated plants only using 25 ml (Fig. 4). By day 3, the daily water use for the control plants was 45 ml, whereas the ABA-treated plants used from 27 ml (1000 ppm) to 28 ml (62.5 ppm). During day 6, daily water use for the controls dropped sharply, and the plants started to wilt. A small drop was observed with the 62.5 ppm treatment on day 7, and on day 8 with the 125 and 250 ppm treatments (Fig. 4). In the rewatered treatments, control plants had the highest daily water use during the first four days, and the 500 and 1000 ppm-treated plants had distinctly lower water use than plants receiving the other treatments through day 10 (Fig. 5). Water use was similar in all treatments on days 11 and 12, indicating that the ABA might have lost its effectiveness by this time. Chlorosis of the leaves, which might have led to leaf abscission, was a negative side effect of the ABA treatments, with a correlation between ABA concentration and the presence of these symptoms. Chlorosis was first noted on lower leaves of treated plants two days following ABA applications, and leaf abscission occurred by days 4 and 5, after which leaf abscission tapered off. The prolonged time to wilting of the ABA-treated plants shows that ABA effectively reduced transpiration and extended the shelf life of the plants. Negative side effects, chlorosis and leaf abscission, were seen, emphasizing the need for further studies to determine the concentration that will reduce transpiration without detrimental side effects. Literature Cited: 1. Armitage, A.M. 1983. Keeping Quality of Bedding Plants. Florists' Rev. 171(4461):63-66. 2. Franks, P.J., G.D. Farquhar. 2001. The effect of exogenous abscisic acid on stomatal development, stomatal mechanics, and leaf gas exchange in Tradescantia virginiana. J. Plant Physiol. 125:935-942. 3. Kim, J. and M.W. van Iersel. 2008. ABA drenches induce stomatal closure and prolong shelf life of Salvia splendens. Proc. SNA Res. Conf. 53:107-111. 4. Jiang, F. and W. Hartung. 2008. Long-distance signaling of abscisic acid (ABA): The factors regulating the intensity of the ABA signal. J. Exp. Bot. 59:37-43. 5. Mahdieh, M., and A. Mostajeran. 2009. Abscisic acid regulates root hydraulic conductance via aquaporin expression modulation in Nicotiana tabacum. J. Plant Physiol. Doi: <http://dx.doi.org/10:1016/j.jplph.2009.06.001>. 6. Tallman, G. 2004. Are diurnal patterns of stomatal movement the result of alternating metabolism of endogenous guard cell ABA and accumulation of ABA delivered to the apoplast around guard cells by transpiration? J. Exp. Bot. 55:1963 1976. 7. Van Iersel, M.W., K. Seader, and S. Dove. 2008. Exogenous abscisic acid application effects on stomatal closure, water use, and shelf life of hydrangea (Hydrangea macrophylla). J. Environ. Hort. (in press). Growth Regulators Section 266
400 Cumulative Evapotranspiration (ml) 300 200 100 0 ppm 62.5 ppm 125 ppm 250 ppm 500 ppm 1000 ppm 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Time (days) Fig. 1. Cumulative evapotranspiration of tomato during a 13-day period as affected by drenches with different concentrations of ABA. Plants were not rewatered throughout the study. Data represent the mean ± standard error. Significant differences were noted 1.5 hours after ABA application, with a P-value of 0.006752. Growth Regulators Section 267
Cumulative Evapotranspiration (ml) 700 600 500 400 300 200 100 0 ppm 62.5 ppm 125 ppm 250 ppm 500 ppm 1000 ppm 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Time (Days) Fig. 2. Cumulative evapotranspiration of tomato during a 13-day period as affected by drenches with solutions with different concentrations of ABA. Plants were rewatered as needed during the course of the study. Data represent the mean ± standard error. Significant differences were noted 4.5 hours after ABA application, with a P-value of 0.03005. Growth Regulators Section 268
16 14 Time to Wilting (days) 12 10 8 6 4 0 63 125 250 500 1000 ABA concentration (ppm) Fig. 3. The effect of drenches with ABA solutions of different concentrations on time to wilting of tomato plants. R 2 = 0.90, P < 0.0001. Growth Regulators Section 269
70 Daily Evapotranspiration (ml/plant) 60 50 40 30 20 10 0 ppm 62.5 ppm 125 ppm 250 ppm 500 ppm 1000 ppm 0 0 2 4 6 8 10 12 14 Time (days) Fig. 4. Daily water use of tomato during a 13-day period as affected by drenches with solutions with different concentrations of ABA. Plants were not rewatered during the study. Growth Regulators Section 270
Daily Evapotranspiration (ml/plant) 100 80 60 40 20 0 ppm 62.5 ppm 125 ppm 250 ppm 500 ppm 1000 ppm 0 0 2 4 6 8 10 12 14 Time (days) Fig. 5. Daily water use of tomato during a 13-day period as affected by drenches with solutions with different concentrations of ABA. Plants were rewatered as needed during the course of the study. Growth Regulators Section 271
Effect of ABA, BA, and GA on Post-production Quality of Ivy Geraniums Yan Chen, Regina Bracy, and Allen Owings LSU AgCenter Hammond Research Station 21549 Old Covington Highway, Hammond, LA 70403 yachen@agcenter.lsu.edu Index Words: Postharvest quality, abscisic acid, gibberellic acid, 6-benzyladenine, Pelargonium peltatum L. Significance to Industry: Ivy geraniums (Pelargonium peltatum L.) in pots and hanging baskets are popular flowering plants for holiday and spring markets. Postharvest quality of geraniums in pots can be adversely affected by conditions such as extended darkness and exposure to ethylene during shipping and possible drought stress during retail display. Treatment with plant growth regulators (PGRs) prior to shipping may improve plant quality and extend the shelf life of geranium plants. In this study, GA plus BA, BA, GA, and ABA were evaluated for phytotoxicity on Maverick Pink and Ringo Salmon ivy geraniums and their effects on postharvest quality of these varieties. Nature of Work: Most geranium cultivars exhibit signs of senescence, such as abscission of flower petals and yellow leaves, when exposed to ethylene gas or subjected to other environmental stresses (3). Although 1-methylcyclopropene (1-MCP) treatment can reduce petal shattering (1), effects may vary or are transient in some varieties (2). Gibberellic acid (GA) and 6-benzyladenine (BA) were reported to increase vast life of carnation cut flowers at low rates of 1 to 10 ppm (4, 5) and the action of BA was initiated in the leaves (5). Products containing GA 4+7 plus BA were also reported to reduce leaf chlorosis and improve postharvest quality of various potted ornamentals. Recently, abscisic acid was reported to enhance the drought tolerance of several bedding plants (6). The objective of this study was to determine whether GA 4, BA, GA 4+7 +BA, or ABA could improve the quality of ivy geraniums during simulated shipping and retail shelf display. Two experiments were conducted to evaluate (1) phytotoxicity and (2) efficacy of the PGRs at different rates. In both experiments, rooted cuttings of ivy geraniums were potted into 6-inch azalea pots in Metro-Mix 300 growing medium (Sun Gro Horticulture, Bellevue, WA). Plants were grown in a greenhouse with temperature set at 85 F day/75 F night. Plants were fertilized at every other irrigation with Peters 20-10-20 at 120 ppm N rate and received a soft pinch two weeks after potting. In the phytotoxicity experiment, plants were potted on 23 May and treated on 22 July 2008. Plants in the efficacy experiment were potted on 4 June and treated on 25 July 2008. In both experiments, treatments were applied when 80% plants had 1 to 3 open florets. Growth Regulators Section 272
In the phytotoxicity experiment, GA 4+7 plus BA (Fascination, Valent U.S.A. Corp., Walnut Creek, CA; and Fresco, Fine Americas Inc., Walnut Creek, CA), BA (ExilisPlus, Fine Americas Inc., and MaxCel, Valent), GA 4 (NovaGib, Fine Americas), each at 5, 10, 50, and 100 ppm, were applied as a foliar spray. In the efficacy experiment, GA 4+7 plus BA (Fascination, Valent), BA (ExilisPlus, Fine Americas) and GA 4 (NovaGib, Fine Americas) were each applied as a foliar spray at 10 and 25 ppm. In addition, ABA (Valent) was applied as a drench at 125, 250, and 500 ppm, and as a foliar spray at 250, 500, and 1000 ppm. In both experiments, deionized water (city water filtered through a two-column B-Pure filtration system) was applied as a control treatment. A completely randomized design was used in both experiments with three and six replications in the phytotoxicity and efficacy experiments, respectively. In both experiments, plants were left on benches after a single application made on day 2 to simulate a waiting period before shipping. On day 3, plants were placed in cardboard boxes and moved to a walk-in cooler with temperature set at 46 F for a period of 48 hours in darkness to simulate shipping. On day 5, plants were placed on tables in a laboratory room for postproduction evaluation. Temperature and relative humidity in the room were set at 72 F and 55%, respectively, and recorded with a HOBO sensor (Onset Computer Inc.). Plants were watered once a week. In the phytotoxicity experiment, phytotoxicity ratings based on a scale of 0 (no injury) to 10 (plant death) were assigned to individual plants on days 3 (before simulated shipping), 7, and 14. In the efficacy experiment, open florets were counted on days 3, 7, 14, and 21. In addition, phytotoxicity ratings and number of chlorotic leaves were recorded. In both experiments, plants were rated for visual quality on a scale of 1 to 10 with 1 to 4 being unsalable, 5 to 8 being marketable at a discounted price, and 9 to 10 being highly attractive and marketable at a premium price. Data were analyzed with analysis of variance (ANOVA) using the GLM procedure SAS. Differences between treatment means were compared using Fisher s LSD. Results and Discussion: In the phytotoxicity experiment, Maverick Pink and Ringo Salmon had similar responses to PGR treatments (Table 1). GA 4+7 plus BA, as Fascination or Fresco, damaged young leaves and flower buds as burning and marginal browning at 50 and 100 ppm (Fig. 1). BA as Exilis Plus or MaxCel at 50 and 100 ppm caused similar injuries as Fascination and Fresco with symptoms being noticeable by day 7 and less severe than with the latter two products. GA as NovaGib did not cause injury. Based on these results, BA or products containing BA should be applied at lower rates to avoid injury. In the efficacy study, generally all plants had more flowers by 7 days after treatment, and the number of open florets decreased to very low numbers by day 14 (Table 2 and 3). GA 4+7 plus BA as Fascination at 10 ppm and ABA drench at 125 and 250 ppm resulted in more open florets than control plants in Maverick Pink, and only Ringo Salmon plants treated with ABA drench at 1000 ppm had more open florets than control plants. GA plus BA (Fascination) at 25 ppm and BA at 10 and 25 ppm caused leaf injury (data not shown). In both varieties, fewer chlorotic leaves were found with treatments containing BA compared with control plants on day 7 (Table 4). ABA as a foliar spray resulted in similar or greater numbers of chlorotic leaves. The overall plant visual quality on day 7 was rated considering phytotoxicity, leaf color, and flowering Growth Regulators Section 273
performance (Table 4). Only ABA foliar spray at 250 resulted in higher plant quality than control plants in Maverick Pink. Based on these results, the various PGRs tested in this study provided no or little improvement in the postharvest quality of ivy geraniums. Literature Cited 1. Blankenship S.M. and J.M. Dole. 2003. 1-Methylcyclopropene: A review. Postharvest Bio. Technol. 28:1-25. 2. Cameron, A.C. and M.S. Reid. 2001. 1-MCP blocks ethylene-induced petal abscission of Pelargonium peltatum but the effect is transient. Postharvest Bio. Technol. 22:169-177. 3. Jones, M.L., E.S. Kim, and S.E. Newman. 2001. Role of ethylene and 1-MCP in flower development and petal abscission in zonal geraniums. HortScience 36:1305-1309. 4. Paulin, A. and K. Muloway. Effects of 6 BA on the senescence of cut carnation. Acta Hort. 167: II Symposium on Growth Regulators in Floriculture. 5. Saks, Y., J. Van Staden and M.T. Smith. 1992. Effect of gibberellic acid on carnation flower senescence: Evidence that the delay of carnation flower senescence by gibberellic acid depends on the stage of flower development. Plant Growth Regul. 11(1):45-52. 6. Blanchard, M.G., L.A. Newton, E.S. Runkle, D. Woolard, C.A. Campbell, S. Kanlayanarat, T.A. Nell, and J. Eason. 2007. Exogenous applications of abscisic acid improved the postharvest drought tolerance of several annual bedding plants. Acta Hort. 127-132. Growth Regulators Section 274
Fig. 1. Ivy geranium leaves and florets treated with water (A and B, Maverick Pink ) and 100 ppm GA 4+7 plus BA (Fascination) on day 7 after treatment (C: leaves of Maverick Pink with burning. D: florets of Ringo Salmon showing faded color. E: Florets of Maverick Pink showing burning, faded color, and failure to open by day 21 after treatment). Growth Regulators Section 275
Table 1. Phytotoxicity ratings of Maverick Pink and Ringo Salmon ivy geranium plants on days 3, 7 and 14 after a single application of GA 4+7 plus BA, BA, and GA 4 products at increasing rates. PGR Fascination (GA 4+7 + BA) Rate (ppm) Maverick Pink Ringo Salmon Day 3 Day 7 Day 14 Day 3 Day 7 Day 14 5 0.17 ed 0.33 e 0.33 e 0.33 d 0.50 c 0.50 f 10 0.67 d 0.33 e 0.33 e 0.67 cd 0.33 c 0.50 f 50 3.00 b 2.33 c 5.00 c 1.17 c 2.33 b 4.33 cd 100 3.67 a 4.00 ab 6.33 b 3.67 a 4.00 a 7.00 ab Fresco (GA 4+7 + BA) ExilisPlus (BA) MaxCel (BA) NovaGib (GA 4 ) 5 0.17 ed 0.17 e 0.17 e 0 d 0 c 0 f 10 1.67 c 1.00 d 3.67 d 0.50 cd 0.50 c 1.67 e 50 3.00 b 3.67 b 5.00 c 2.67 b 4.00 a 6.33 b 100 4.00 a 4.50 a 7.33 ab 3.00 ab 3.67 a 7.00 ab 5 0 e 0 e 0 e 0 d 0 c 0.17 f 10 0 e 0 e 0 e 0 d 0.33 c 0.33 f 50 0 e 3.83 b 7.00 ab 0 d 2.33 b 4.67 c 100 0 e 4.00 ab 7.67 a 0 d 2.67 b 8.00 a 5 0 e 0.17 e 0 e 0 d 0 c 0 f 10 0 e 0 e 0.17 e 0.17 d 0.33 c 0.50 f 50 0.50 ed 2.33 c 6.67 ab 0.50 cd 0.50 c 3.33 d 100 0.50 ed 3.67 b 7.67 a 0.50 cd 2.33 b 4.33 cd 5 0 e 0 e 0 e 0 d 0 c 0 f 10 0 e 0 e 0 e 0 d 0 c 0 f 50 0 e 0 e 0 e 0 d 0 c 0 f 100 0 e 0 e 0 e 0 d 0 c 0 f Control Deionized water 0 e 0.17 e 0 e 0 d 0 c 0 f LSD 0.05 0.63 0.57 1.05 0.65 0.68 1.06 Growth Regulators Section 276
Table 2. Number of open florets on Maverick Pink ivy geranium plants on days 3, 7 and 14 after a single application of GA 4+7 plus BA, BA, and GA 4 products at increasing rates. PGR Rate Maverick Pink (ppm) Day 3 Day 7 Day 14 Day 21 Fascination (GA 4+7 + BA) 10 6.5 12.5 a 1.3 abcde 3.2 a 25 8.2 5.2 de 2.2 ab 2.2 abc ExilisPlus (BA) NovaGib (GA 4 ) ABA drench ABA foliar 10 5.2 7.5 bcde 2.5 a 2.5 ab 25 5.3 6.2 cde 0.8 bcde 0.5 cd 10 7.2 8.8 abcd 1.3 bcde 1.0 bcd 25 4.7 4.5 e 0.2 e 1.0 bcd 50 5.0 6.0 cde 0.8 bcde 1.2 bcd 100 5.2 3.8 e 0.3 de 0 d 125 11 9.7 abc 2.0 abc 2.3 abc 250 5.3 10.5 ab 1.6 abcd 2.2 abc 500 6.8 9.0 abcd 1.7 abcd 0.2 d 250 2.5 4.7 e 0.5 de 0 d 500 7.2 3.7 e 0.7 cde 0 d 1000 4.2 5.5 de 0.2 e 0 d Control Deionized water 4.2 6.7 cde 1.0 bcde 2.2 abc LSD 0.05 NS* 4.0 5.9 2.0 *No significant difference was found between treatments. Growth Regulators Section 277
Table 3. Number of open florets on Ringo Salmon ivy geranium plants on days 3, 7 and 14 after a single application of GA 4+7 plus BA, BA, and GA 4 products at increasing rates. PGR Rate (ppm) Ringo Salmon Fascination (GA 4+7 + BA) Day 3 Day 7 Day 14 Day 21 10 4.2 7.5 abc 1.2 bcdef 1.2 bcd 25 7.3 5.6 bcd 0.7 def 1.3 bcd Exilis Plus (BA) 10 7.3 7.0 bc 2.5 2.5 ab abcde 25 4.0 6.0 bcd 0.2 f 0 d NovaGib (GA 4 ) 10 6.0 6.3 bcd 0.5 f 0.7 cd 25 7.3 6.2 bcd 1.5 bcdef 0 d 50 5.7 2.5 d 1.0 cdef 0.2 d 100 7.8 7.0 bc 0.8 cdef 1.8 bc ABA drench 125 4.8 6.7 bc 3.2 ab 0.4 cd 250 5.3 7.6 abc 1.0 cdef 3.5 a 500 7.6 11.0 a 2.3 abcde 0.3 cd ABA foliar 250 4.8 5.2 cd 3.2 ab 1.3 bcd 500 3.8 9.3 ab 2.8 abc 1.2 bcd 1000 5.2 7.7 abc 2.7 abcd 0.2 d Control Deionized water 4.8 6.7 bc 3.3 a 0.5 cd LSD 0.05 NS 5.9 5.9 1.6 Growth Regulators Section 278
Table 4. Number of chlorotic leaves on Maverick Pink and Ringo Salmon ivy geraniums 7days after a single application of GA 4+7 plus BA, BA, and GA 4 products at increasing rates. Maverick Pink Ringo Salmon Rate Chlorotic leaves Visual Chlorotic leaves Visual quality z PGR ppm (no.) quality z (no.) Fascination 10 4.8 efg 7.9 ab 4.3 fgh 6.3 bcd (GA 4+7 + BA) 25 4.3 fg 5.0 ef 3.2 h 5.0 de ExilisPlus 10 3.8 g 6.4 cd 4.2 gh 5.6 cde (BA) 25 2.7 g 5.6 de 4.5 fgh 5.3 cde NovaGib (GA 4 ) ABA drench ABA foliar 10 6.3 def 7.3 abc 7.7 ef 7.0 b 25 7.2 de 4.3 fg 8.0 e 5.2 de 50 5.0 efg 5.0 ef 9.8 cde 4.7 e 100 6.3 def 3.5 g 6.8 efg 2.8 f 125 8.0 cd 7.8 ab 8.8 de 6.3 bcd 250 9.7 bc 5.8 de 11.4 bcd 6.6 bc 500 9.7 bc 5.8 de 15.3 a 5.7 bcde 250 8.2 cd 8.4 a 8.2 de 8.8 a 500 12.8 a 5.0 ef 13.7 ab 4.8 e 1000 11.3 ab 4.7 efg 12.7 abc 6.0 bcde Control Deionize d water 8.2 cd 7.1 bc 9.7 cde 8.4 a LSD 0.05 2.4 1.2 5.9 5.9 z Plant visual quality was rated by a scale of 1 to 10 where 1 to 4 being unsalable, 5 to 8 being marketable at a discounted price, and 9 to 10 being highly attractive and marketable at a premium price. Growth Regulators Section 279
Osteospermum Growth Control with Paclobutrazol Substrate Drenches Jared Barnes, Brian Whipker, Wayne Buhler, and Ingram McCall Department of Horticultural Science, 7609 Kilgore Hall North Carolina State University Raleigh, North Carolina, 27695 esculentus@gmail.com Index Words: Plant growth regulators, Cape daisy, South African daisy, cool-season crop; gibberellin biosynthesis inhibitors Significance to Industry: Osteospermum ecklonis is a tender perennial that is treated as an annual in the trade (3). It is typically grown and sold during cooler conditions because it initiates flowers between 50 F and 60 F (1). Excessive plant stretch can be a production challenge for greenhouse growers. Paclobutrazol (Bonzi; Syngenta, Greensboro, NC) is a triazole compound that inhibits gibberellin biosynthesis (2). Plants absorb paclobutrazol primarily through the leaves and less through the roots and stem (6), and once in the plant the compound acts to reduce internode elongation (2). Paclobutrazol has been used on Osteospermum with varying effects. When applied as a spray, Gibson and Whipker (5) found that 10 to 80 ppm were ineffective. Fischer (4) recommended a 1 to 2 ppm substrate drench, but drenches of 6 to 12 ppm were found to be ineffective during spring trials in the Midwest (A. Hammer, personal communication). The variation in results with sprays may be attributed to differences in the growing conditions in which the trials were conducted (California vs. West Virginia). Growers are without appropriate rate recommendations when it comes to paclobutrazol drenches. Therefore, this experiment was performed to evaluate which rates of paclobutrazol would be effective in controlling Osteospermum growth to make plants more suitable for retail sales. Nature of Work: Osteospermum ecklonis Pink Charme and Yellow 09 were transplanted into 4.5-inch pots containing Berger BM1 mix (Berger Peat Moss, Saint- Modeste, Quebec, Canada) on 18 Dec. 2008. This experiment was conducted in a polyfilm greenhouse in Raleigh, NC at 35 N latitude. The experiment was randomized with six replications of each of five treatments. Plants were fertilized with 150 ppm N from 13-2-13 Cal-Mag (SQM North America, Atlanta, Georgia) for the duration of the experiment. The initial temperature regime was 70 F days and 60 F nights. On 28 Dec. plants were pinched back to 4 to 6 nodes. The first paclobutrazol drench was applied on 16 Jan. 2009 at 2 oz/pot. A portion of the plants were treated with 25 ppm and another portion was treated with 50 ppm. On 22 Jan. temperatures were dropped to 60 C days and 50 C nights to synchronize flowering. Temperatures were raised to their previous levels on 26 Feb., and data were collected on plant height and diameter at the end of this cold treatment. On 26 Feb. a second 1 ppm paclobutrazol application was applied to one-half of the plants that received the initial 25 ppm and 50 ppm drenches; Growth Regulators Section 280
those plants that received the second application will be designated 25+1 and 50+1, respectively. When plants flowered, data on flowering date, height at flowering, and plant diameter (average of widest diameter and diameter perpendicular to this measurement) were collected. Photographs were taken to compare the treatments. All the data were subjected to PROC GLM (SAS Inst., Cary, NC). Where the F test indicated evidence of significant difference among the means, LSD (P 0.05) was used to establish differences between means. Results and Discussion: At the end of the cold period it was evident that paclobutrazol had controlled growth. Heights were significantly different between the two cultivars. Heights of Pink Charme control, 25 ppm-treated, and 50 ppm-treated plants were 4.5 inches, 2.8 inches, and 2.9 inches, respectively. Heights of Yellow 09 control, 25 ppm-treated, and 50 ppm-treated plants were 7.1 inches, 7.8 inches, 3.1 inches, respectively. At the end of the cold period, differences between diameters of the two cultivars were not significantly different. However, there was a significant difference between the nontreated control (13.1 inches), 25 ppm-treated (10.9 inches), and 50 ppm-treated (10.6 inches) plants. Once the plants flowered there was a significant difference between the flowering delay of the treatments, but no difference between cultivars. Control plants flowered after 85.5 days, and with the use of paclobutrazol drenches flowering was delayed by 5 to 7 days (Fig. 1). There was a significant difference between the heights of the two cultivars. Nontreated Pink Charme plants had an average height of 7.7 inches. All of the Pink Charme plants treated with paclobutrazol were shorter (Fig. 2). The average heights of the 25 and 50 ppm-treated plants were 5.7 and 5.9 inches, respectively, and for the 25+1 and 50+1 ppm-treated plants heights were 5.1 and 5.1 inches, respectively. Yellow 09 was the more vigorous cultivar and attained a height of 11.2 inches (Fig. 2). Plants receiving 25 and 50 ppm were 6.5 and 6.8 inches, respectively, and the 25+1 and 50+1 ppmtreated plants were 5.8 and 5.5 inches tall. For both cultivars, the extra 1 ppm paclobutrazol drench application resulted in additional growth control (Fig. 2). At flowering there was a significant difference between the average diameter of plants treated with paclobutrazol drenches, but no difference between cultivars. Control plants and plants that received only one application of paclobutrazol had similar diameters (Fig. 3). Control, 25 ppm-treated, and 50 ppm-treated plant diameters were 7.2 inches, 7.1 inches, and 7.0 inches, respectively. Both the 25+1 and 50+1 ppm-treated plants had diameters averaging 6.1 inches. The significance of having a smaller diameter is that it reduces greenhouse growing area required. There was a 25.6% reduction in the area between the control and 25+1 ppm-treated Pink Charme plants, and there was a 32.2% reduction in area between the control and 25+1 ppm-treated Yellow 09 plants. Plants that are treated with the extra 1 ppm will take up less space on the growing bench, and growers will realize the added benefit of better spacing efficacies. Growth Regulators Section 281
Based on the results, 25 ppm paclobutrazol drenches applied before the start of the cold period gave adequate control of plant height, and the extra cost of the 50 ppm drench was not justified. If growers desire to have a closer-spaced crop, then applying the additional 1 ppm paclobutrazol drench at the end of the cold period will enable them to fit more plants on a bench. Literature Cited 1. Armitage, A.M. 2001. Armitage s Manual of Annuals, Biennials, and Half-hardy Perennials. Timber Press; Portland, Oregon. 2. Davis, T.D. and E.A. Curry. 1991. Chemical regulation of vegetative growth. Critical Reviews in Plant Sciences 10(2):151-188. 3. Dole, J.M. and H.F. Wilkins. 2005. Floriculture Principles and Species, 2nd ed., Pearson-Prentice Hall, Upper Saddle River, New Jersey. 4. Fischer. No date. Tradewinds Osteospermum Culture Information. 5. Gibson, J.L. and B.E. Whipker. 2003. Efficacy of plant growth regulators on the growth of vigorous Osteospermum cultivars. HortTechnology 13:132-135. 6. Whipker, B.E., J.L. Gibson, T. J. Cavins, I. McCall, and P. Konjoian. 2003. Growth regulators. In: D. Hamrick (ed.). Ball Red Book, 17th. Edition. Ball Publishing, St. Charles, I Growth Regulators Section 282
94 92 90 Days 88 86 84 82 Untreated 25 mg/l 50 mg/l 25+1 mg/l 50+1 mg/l Paclobutrazol rate Fig. 1. Days to flowers for Osteospermum ecklonis using five different paclobutrazol treatments. The initial application of paclobutrazol was made on 16 Jan. 2009. The 25 and 50 ppm (mg/l) treatments that are marked with a +1 ppm received an additional 1 ppm application of paclobutrazol on 26 Feb. Data was collected for the treatments between 51 and 70 days after the initial application. Growth Regulators Section 283
30 25 'Pink Charme' 'Yellow 09' Height (cm) 20 15 10 5 0 Untreated 25 mg/l 50 mg/l 25+1 mg/l 50+1 mg/l Paclobutrazol rate Fig. 2. Plant heights for Osteospermum ecklonis Pink Charme and Yellow 09 using five different paclobutrazol treatments. The initial application of paclobutrazol was made on 16 Jan. 2009. The 25 and 50 ppm (mg/l) treatments that are marked with a +1 ppm received an additional 1 ppm application of paclobutrazol on 26 Feb. Data was collected for the treatments between 51 and 70 days after the initial application. Growth Regulators Section 284
Diameter (cm) 19 18.5 18 17.5 17 16.5 16 15.5 15 14.5 14 Untreated 25 mg/l 50 mg/l 25+1 mg/l 50+1 mg/l Paclobutrazol rate Fig. 3. Plant diameters for Osteospermum ecklonis using five paclobutrazol treatments. The initial application of paclobutrazol was made on 16 Jan. 2009. The 25 and 50 ppm (mg/l) treatments that are marked with a +1 ppm received an additional 1 ppm application of paclobutrazol on 26 Feb. Data was collected for the treatments between 51 and 70 days after the initial application. Growth Regulators Section 285
Effect of BA, GA and MCP on Post-production Quality of New Guinea Impatiens Yan Chen, Regina Bracy, and Allen Owings LSU AgCenter Hammond Research Station 21549 Old Covington Highway, Hammond, LA 70403 yachen@agcenter.lsu.edu Index Words: Impatiens hawkeri, gibberellin A 4 and A 7, 6-benzyladenine, 1- Methylcyclopropene (1-MCP) Significance to Industry: New Guinea impatiens (Impatiens hawkeri) are popular annual plants for containers and landscape plantings. Postharvest quality of impatiens can be adversely affected by environmental conditions during shipping and retail shelf display. In this study, GA 4+7 plus BA, BA, GA 4, and 1-MCP were evaluated for their effects on the post-production quality of New Guinea impatiens during simulated shipping and retail display. GA 4 at 100 ppm increased number of open flowers on Electric Orange and 1-MCP increased flower number on Harmony Red by 21 days after treatments. Negative side effects was observed as stretching of Electric Orange plants (with the most prominent symptoms found with GA 4+7 plus BA-treated plants) and stretching and leaf puckering of Harmony Red plants treated with GA 4, BA, and 1- MCP. Nature of Work: New Guinea impatiens is an annual bedding plant with increasing popularity for containers and landscape use due to the many new varieties introduced in recent years. Post-production quality of New Guinea impatiens is adversely affected by certain conditions such as darkness during shipping and low light and drought during retail display. Previous studies have suggested that 1-MCP prevents the petal abscission and leaf chlorosis induced by ethylene during shipping (1). Application of GA 3 helps impatiens plants overcome water deficit (4). In addition, GA 4+7 and BA were also reported to reduce leaf chlorosis and improve postharvest quality of various potted ornamentals (2, 3, 5). The objective of this study was to determine whether GA 4+7 plus BA, BA, GA 4, or 1-MCP could enhance the postharvest quality of New Guinea impatiens. Rooted cuttings of Harmony Red and Electric Orange New Guinea impatiens were potted into 4-inch pots in Metro-Mix 300 growing medium (Sun Gro Horticulture, Bellevue, WA) on 18 April 2008. Plants were grown in a greenhouse with temperature set at 75 F day/65 F night and covered with 34% Aluminet shade cloth (Polysack, Inc., Negev, Israel). Plants were fertilized at every other irrigation with Peters 20-10-20 at 100 ppm N. A soft pinch was made on all plants at 3 weeks after planting. After 7 weeks of production, a total of 48 plants with 1 to 3 open flowers were selected and treated with selected plant growth regulators (PGRs) on 13 June (day 1). A foliar spray using 3 quarts per 100 ft 2 of the following solutions were applied as treatments: 100 ppm GA 4+7 Growth Regulators Section 286
plus BA (Fascination, Valent U.S.A. Corp., Walnut Creek, CA), 100 ppm BA (Exilis Plus, Fine Americas Inc., Walnut Creek, CA), 100 ppm BA (MaxCel, Valent), 100 ppm GA 4 (NovaGib, Fine Americas Inc.), 1 ppm 1-MCP (EthylBlock, Floralife, Walterboro, South Carolina), and deionized water (city water filtered through a two-column B-Pure filtration system). Each treatment had eight plants (replications) arranged as a randomized complete block design with four blocks (benches) and two plants as subsamples per block. For the 1-MCP treatment, plants were placed in a plastic tub and EthylBloc powder was placed in a weighing boat in the center of the container. The container was sealed after the buffer solution was added to the powder and then kept under lab condition with temperature set at 72 F for 12 hours. Plants were then placed back onto greenhouse benches and were held with other plants during day 2 to simulate a waiting period before shipping. On day 3, all plants were placed in cardboard boxes and moved to a walk-in cooler with temperature set at 46 F for a period of 48 hours in darkness to simulate shipping. On day 5, all plants were placed on tables in a laboratory room for post-production evaluation. Temperature and relative humidity in the room were set at 72 F and 55%, respectively, and recorded with a HOBO sensor (Onset Computer Corp., Pocasset, MA). Plants were watered once a week. Plant height and diameter were measured on days 1 and 28. Open flowers were counted on days 1, 7, 14, 21, and 28. Visual quality (on a scale of 1 to 10, with 1 to 4 being unsalable, 5 to 8 being marketable at a discounted price, and 9 to 10 being highly attractive and marketable at a premium price) and phytotoxicity (with 0 being no phytotoxicity and 10 being plant death) were assessed at the same time. Data were analyzed with analysis of variance (ANOVA) by using the GLM procedure of SAS. Differences between treatment means were compared using Fisher s LSD. Results and Discussion: Overall, plants of Harmony Red had fewer open flowers than Electric Orange (Fig.1 A and B). Plants in two BA treatments had similar or fewer flowers than did control plants. By day 21, GA 4 at 100 ppm had resulted in an increased number of open flowers on Electric Orange, while1-mcp increased flower number on Harmony Red. One negative effect was observed as stem stretching (longer internodes; data not shown) in Electric Orange, with the GA 4+7 plus BA treatment causing the most severe stretching (Fig. 2). Harmony Red treated with GA 4+7 plus BA exhibited some stretching, but not as noticeably with Electric Orange. Foliar distortion was noted on Harmony Red as leaf puckering in GA 4 -, BA-, and 1-MCP-treated plants. By 28 days after treatment, Electric Orange maintained marketable visual quality regardless of PGR treatments, and Harmony Red treated with deionized water or GA 4+7 plus BA had better visual quality (Fig. 3). Based on these results, application of GA 4 or 1-MCP temporarily increased number of flowers, but none of the PGR treatments enhanced post-production quality as reflected by the visual plant quality ratings. Growth Regulators Section 287
Literature Cited 1. Blankenship S.M. and J.M. Dole. 2003. 1-Methylcyclopropene: a review. Postharvest Biol. and Technol. 28:1-25 2. Funnell, K.A. and R.D. Heins. 1998. Plant growth regulators reduce postproduction leaf yellowing of potted Asiflorum lilies. HortScience 33:1036-1037 3. Kim, H.J. and W.B. Miller. 2008. Effects of GA 4+7 and benzyladenine application on postproduction quality of 'Seadov' pot tulip flowers. Postharvest Biol. and Technol. 47:416-421 4. Lukaszewska, A, K. Kutnik, and W. Chylinski. 2007. Effect of calcium chloride and Arbolin 038 on response of Impatiens walleriana to soil water deficit. Ann. of Warsaw Univ. of Life Sci. Hort. and Landscape Architecture 28:87-94 5. Saks, Y., J. van Staden, and M.T. Smith. 1992. Effect of gibberellic acid on carnation flower senescence: evidence that the delay of carnation flower senescence by gibberellic acid depends on the stage of flower development. Plant Growth Regul. 11:45-52 Growth Regulators Section 288
Fig 1. Numbers of open flowers on (A) Harmony Red and (B) Electric Orange New Guinea impatiens at 1, 7, 14, 21, and 28 days after treatment with selected plant growth regulators. All florets with petals separated from each other were counted as open flowers. Error bars represent one standard deviation (n = 4). Growth Regulators Section 289
Fig 2. Phytotoxicity injury ratings of (A) Harmony Red and (B) Electric Orange New Guinea impatiens at 1, 7, 14, 21, and 28 days after treatment with selected plant growth regulators. The injury ratings used a scale of 0 to 10, with 0 being no injury and 10 being completely dead. Error bars represent one standard deviation (n = 4). Growth Regulators Section 290
Fig 3. Plant visual quality ratings of (A) Harmony Red and (B) Electric Orange New Guinea impatiens at 1, 7, 14, 21, and 28 days after treatment with selected plant growth regulators. Visual quality ratings used a scale of 1 to 10 where 9 to 10 represents premium market quality, 7 to 8 represents marketable quality, 5 to 6 represent acceptable but discounted quality, 3 to 4 represent poor quality, and 1 to 2 represent unsalable quality. Error bars represent one standard deviation (n = 4). Growth Regulators Section 291