Effect of Daminozide, Paclobutrazol and Chlormequat on Development and Quality of Potted Persian Carpet Zinnia

Transcription

1 Effect of Daminozide, Paclobutrazol and Chlormequat on Development and Quality of Potted Persian Carpet Zinnia A.C.R. Pinto 1, T.J.D. Rodrigues 1, I.C. Leite 1 and J.C. Barbosa 2 1 FCAV-UNESP, Departamento de Biologia Aplicada à Agropecuária, Via de Acesso Prof. Paulo Donato Castellane, Km 5, s/n, CEP , Jaboticabal, SP, Brazil 2 FCAV-UNESP, Departamento de Ciências Exatas, Jaboticabal, SP, Brazil Keywords: growth regulators, pot plant, Zinnia haageana Abstract In Brazil zinnias have good prospect for the flowering potted plant market, once consumers demand for new forms of products is stimulated by novelty. Persian Carpet is a highly ornamental plant, with fast growth, minimal labor requirements and low cost seeds. The present study evaluated the effect of growth regulators on development and quality of Persian Carpet grown as a potted plant. Growth regulators are commonly used to control growth and produce short and compact plants. Paclobutrazol (0.5, 0.75 and 1.0 mg a.i./pot) and chlormequat (1.0, 2.0 and 3.0 g.l -1 ) were applied as a single drench, and daminozide (2.5, 3.75 and 5.0 g.l -1 ) as a single foliar spray to runoff. Regulators were applied at apical flower bud stage. Daminozide (5.0 g.l -1 ), paclobutrazol (0.5, 0.75 and 1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) significantly reduced plant height and side branches length compared to the control. Plant height showed a negative linear response to the increasing concentration of daminozide or paclobutrazol. Paclobutrazol (1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) increased foliage and flowers harvest index. Plant spread diameter and canopy shape were improved with paclobutrazol (0.75 mg a.i./pot). Chlormequat (2.0 and 3.0 g.l -1 ) caused phytotoxicity symptoms, turning plants unsuitable for commercialization. Studied regulators concentrations did not affect flower diameter and production cycle. Although regulators controlled height and side branches growth significantly, plants were not short and compact enough to attend market quality. INTRODUCTION Zinnias are cultivated as garden plants and cut flowers in Brazil, showing a good potential for the flowering potted plant market. In Brazil there is an increasing need for new species and cultivars, and new forms of products to attend consumer's demand, which is stimulated by novelty, curiosity and also, by frequently changes in consumer's preferences. Persian Carpet is a highly ornamental garden annual. It has striking flowers colour, long bloom period and a well-branched plant form, with fast growth, minimal labor requirements, and low cost seeds, showing a potential as a flowering potted plant. In studies about production of zinnias as potted plants, 'Persian Carpet' was not short and compact enough to produce high-quality marketable plants (Pinto, 2003). Growth regulators may be useful in controlling growth and manipulating plants shape and size, producing short and attractive compact plants (Davis and Andersen, 1989; Andersen and Andersen, 2000). The effect of growth regulators on Zinnia haageana Regel have not been previously studied at Brazil, and differences in responsiveness to growth regulators may be found among species, cultivars and growing conditions. The objective of this study was to evaluate the effect of growth regulators on development and quality of Persian Carpet grown as a flowering potted plant. MATERIALS AND METHODS Persian Carpet was sown on polystyrene plug trays (model CM ), containing commercial media and transplanted to 0.60 L black plastic pots (9.4 cm deep and 13.0 cm wide), when the second nodal leaves were fully expanded. Each pot was Proc. V th IS on New Flor. Crops Eds.: A.F.C. Tombolato and G.M. Dias-Tagliacozzo Acta Hort. 683, ISHS

2 filled with commercial growing media, a mixture of composted pine and eucalyptus bark, composted tree fern fiber dust, washed coconut dust, sterilized rice shell, turf, crushed vegetal charcoal, vermiculite and clay (ph water of 6.12 and E.C. of 0.75) and fertilized with Osmocote Sierra Scotts micro (1.08 g/pot). Plants were grown during the fall season, at Jaboticabal, São Paulo State, Brazil, in greenhouse under natural photoperiod (11h56' to 11h), and at minimum, maximum and mean temperature of 8.0, 40.0 and 26.0 ± 1 C. Daily relative humidity varied from 36 to 99%. Weekly evaluation carried with a steady state porometer during the production cycle pointed a μmol m -2 s -1 PPF inside greenhouse. Plants were irrigated and each pot received the same amount of water. The experimental design was a complete randomized blocks, with ten treatments (control and three concentrations of daminozide, paclobutrazol and chlormequat) and four replications (two pots per experimental unit, with one plant per pot). Paclobutrazol (0.5, 0.75 and 1.0 mg a.i./pot) and chlormequat (1.0, 2.0 and 3.0 g.l -1 ) were applied as a single drench (40ml/pot), and daminozide (2.5, 3.75 and 5.0 g.l -1 ) as a single uniform foliar spray to runoff (10ml/pot). Control plants were sprayed with deionized water (10ml/pot). Regulators were applied at late afternoon (16:30h), when relative humidity and temperature inside greenhouse varied from 35% and 31.0 C ± 1 C (beginning of the application) to 45% and 27.0 C ± 1 C (one hour and half after the beginning of the application). Freshly preparated aqueous solutions of the regulators were applied when apical flower bud presented between 3-5 mm in length. Main stem height (from main stem base to flower receptacle insertion), internode length and number of nodes, side branches length and total leaf area were measured at the end of the production cycle (ten to eleven open flowers per plant). Total leaf area was estimated by taking a sample of 20 leaves from each experimental unit, measured with a Digital Image Analysis System, Delta T Devices. Total leaf area value was determined, by proportion, using the dry mass value of measured leaves. Plants were separated into leaves, main stem, side branches, flowers, floral buds and roots, dried at 75 C in a forced-air oven, for plant parts dry mass (g) and dry mass percentage analysis. Foliage and flowers harvest index was determined (Daie, 1985). Production cycle was established considering the number of days, from sowing, to ten or eleven opened flowers (once sometimes two flowers opened at the same time). It was considered an opened flower only when ray florets petals were fully expanded and tubular florets opened. To evaluate plant quality were measured flower diameter, plant height (from media surface to plant highest point) and spread diameter (major width from one tip to the other of foliage canopy), and canopy visual shape quality, rating of 0 (regular and rounded) to 1 (irregular and not rounded). Considering the pot size used for 'Persian Carpet' production, a plant height pattern between cm would be appropriated for selection of plants with a pleasant and compact aspect. Data were subjected to analysis of variance (ANOVA) and to Tukey's multiple range test. Regression analysis was determined to establish the concentration response curves of growth regulators (control data included in regression analysis). RESULTS AND DISCUSSION Chlormequat (2.0 and 3.0g.L -1 ) caused phytotoxicity symptoms 24 hours after application, damaging leaves severely (leaf burning, browning, necrosis and dryness), turning plants unmarketable or killing the plants. These symptoms were similar to the ones observed on Z. elegans 'Lilliput' treated with the same concentrations, method of application, and under the same ambiental conditions (Pinto, 2003). Plants from these chlormequat treatments were not included for statistical analysis. Daminozide at 5.0 g.l -1 caused smaller and transient foliar lesions. The higher ambient temperature and lower relative humidity during the time of application may have been the cause of the foliar lesions. There were no apparent phytotoxic effects of the other concentrations of growth 400

3 regulators on foliage and flowers colour. It was not observed malformed leaves or flowers. Regulators treated plants showed shorter internodes than control plants (Table 1). Daminozide and paclobutrazol decreased significantly internode length and main stem height with increase in concentration (Table 2). Main stem height suppression was related to internode elongation control and not to a decrease in the number of nodes (Table 1). The regression analysis for number of nodes and regulators concentrations was not significant (data not shown). Daminozide (5.0 g.l -1 ), paclobutrazol (0.5, 0.75 and 1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) significantly reduced side branches length and plant height compared to control (Table 1). Plant height decreased as the concentration of daminozide or paclobutrazol increased. Side branches length responded quadratically to paclobutrazol treatment but showed a negative linear response to the increasing concentration of daminozide (Table 2). Minimum side branches length of cm for 0.83 mg a.i./pot paclobutrazol is predicted from the model. The plant height reductions of Z. haageana 'Persian Carpet' by daminozide spray (5.0 g.l -1 ) and paclobutrazol drenches (0.5 and 1.0 mg a.i./pot) are in agreement, respectively, with the results found by Banko and Stefanis (1988), and Cox and Keever (1988) for Z. elegans cultivars. Also, Banko and Stefanis (1988) reported that zinnia growth suppression requires higher rates of paclobutrazol drench (up to 0.15 mg a.i./pot). As shown by our study, paclobutrazol drench at higher rates resulted in shorter plants. Plant spread diameter and canopy shape were improved with paclobutrazol (0.75 mg a.i./pot), as shown on Table 1. Canopy shape showed a negative linear response to the increasing concentration of daminozide or paclobutrazol, and spread diameter with paclobutrazol concentrations (Table 2). Although daminozide (5.0 g.l -1 ), paclobutrazol (all concentrations) and chlormequat (1.0 g.l -1 ) controlled internode, side branches and plant height growth, and paclobutrazol (0.75 mg a.i./pot) improved plant spread diameter and canopy shape, plants were not short and compact enough to attend market quality. Plants still too spread, probably leading to mechanical damaged during handling, packing, transport and marketing. The inadequated plant spread diameter was related to the insufficient growth control of side branches and main stem internodes. Probably, an early regulators application, when main stem internodes are yet shorter (plants with at least the third nodal leaves completely expanded), could lead to a major control of main stem internodes elongation, without retarding the transition from the vegetative to the reproductive stage. Kim et al. (1989) reported that under inductive flowering conditions, the two-leaf-pair stage may correspond to the transition from vegetative to reproductive stage in zinnia. A second application may be necessary to aid on the control of side branches elongation, which starts the major growth period, at the visible apical flower bud stage (bud between 3-5 mm in length) extending to one week after this stage (Pinto, 2003). This application may also contribute to the control of main stem internodes elongation up to the end of the production cycle. Holcomb (1992) reported that daminozide spray application to Z. elegans cultivars at an early stage of development would lead to better quality potted plants. The number of leaves and total leaf area were not affected by regulators applications, and the regression analysis for these parameters and regulators concentrations were not significant (data not shown). The number of leaves of zinnia is related to plant's number of nodes (usually, a maximum of two leaves develop at each node). When regulators suppress internode elongation without changing the number of nodes, no effect is observed in the number of leaves. Sachs and Hackett (1972) reports that leaf initiation may not be inhibited, when regulators reduce subapical meristematic activity without concomitant disruption of apical meristematic function. The paclobutrazol (1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) treated plants had significantly greater floral buds and flowers dry mass, respectively, compared to control plants. Paclobutrazol (1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) also showed a 401

4 significant decrease in side branches dry mass and in plant total dry mass (g) compared to control plants. Daminozide (5.0 g.l -1 ) and paclobutrazol (0.5 and 0.75 mg a.i./pot) reduced side branches dry mass compared to control, but did not reduce plant total dry mass (Table 3). Side branches dry mass responded quadratically to paclobutrazol treatment but showed a negative linear response to the increasing concentration of daminozide (Table 2). Minimum side branches dry mass of % for 0.86 mg a.i./pot paclobutrazol is predicted from the model. Leaves and roots dry mass showed a positive linear response to the increasing concentration of daminozide. Daminozide and paclobutrazol increased floral buds dry mass with increase in concentration. Paclobutrazol decreased plant total dry mass with increase in concentration (Table 2). Paclobutrazol and daminozide seemed to reduce sink activity in side branches and increased in floral buds (Table 2). However, only daminozide increased it in the roots and leaves, leading to an assimilate retention on leaves. Kim and Suzuki (1989) reported that branches translocation is more restricted compared to roots. Roots growth is less affected, or could also increase, by regulators application (Latimer, 1991). Paclobutrazol (1.0 mg a.i./pot) and chlormequat (1.0 g.l -1 ) increased foliage and flowers harvest index (Table 3), which showed a positive linear response to the increasing concentration of paclobutrazol (Table 2). For flowering potted plants the harvest products of economic importance are foliage and flowers. The regulators concentrations did not reduce flower diameter nor delayed production cycle (Table 3). Regression analysis for these parameters and regulators concentrations were not significant (data not shown). These results are in contrast to the ones obtained by Armitage et al. (1981), Latimer (1991), and Pinto (2003) where daminozide (5.0 g/l -1 ) delayed Z. elegans cultivars flowering time. Probably due to differences in species sensibility and number of applications. Growth regulators could decrease the synthesis of gibberellins that promotes internodes elongation and, simultaneously, promote or inhibit the active endogenous gibberellins, which may be flowering promoters (Koranski et al., 1979). Further studies should adjust suitable concentrations for regulators application on earlier developmental stages, and attempt to establish suitable number of applications for production of good quality potted plants. ACKNOWLEDGEMENTS To CNPq for granting A.C.R. Pinto, T.J.D. Rodrigues and J.C. Barbosa. Literature Cited Andersen, A.S. and Andersen, L Growth regulation as a necessary prerequisite for introduction of new plants. Acta Hort. 541: Armitage, A.M., Bass, R.E., Carlson, W.H. and Ewart, L.C Control of plant height and flowering of zinnia by photoperiod and growth retardants. HortScience, 6(2): Banko, T.J. and Stefani, M.A Growth response of selected container-grown bedding plants to paclobutrazol, uniconazole, and daminozide. J. Environ. Hort., 6(4): Cox, D.A. and Keever, G.J Paclobutrazol inhibits growth of zinnia and geranium. HortScience, 23(6): Daie, J Carbohydrate partitioning and metabolism in crops. Hort. Rev., 7: Davis, T.D. and Andersen, A.S Growth retardants as aids in adapting new floricultural crops to pot culture. Acta Hort. 252: Holcomb, E.J Flowering potted plants for fall with soil heating. Bulletin of Pennsylvania Flower Growers, n.339, p.1-5. Kim, H.Y., Abe, T., Watanabe, H. and Suzuki, Y Changes in flower bud development of Zinnia elegans as influenced by growth retardant S-07. J. Hort. Sci., 64(1): Koranski, D.A., McCown, B.H., Struckmeyer, B.E. and Beck, G.E Gibberellin- 402

5 growth interactions on the growth and flowering of Clerodendrum thomsoniae. Physiol. Plant., 45: Latimer, J.G Growth retardants affect landscape of Zinnia, Impatiens and Marigold. HortScience, 26(5): Pinto, A.C.R Efeitos de tamanho de vaso, sistemas de condução e reguladores vegetais no desenvolvimento e na qualidade de cultivares de zínia. Ph.D. thesis (Agronomy). FCAV, UNESP, Jaboticabal, 166p. Sachs, R.M. and Hackett, W.P Chemical inhibition of plant height. HortScience, 72(5):

6 Tables Table 1. Effects of growth regulators on main stem height, number of nodes and internode length, side branches length, plant height and spread diameter, and canopy shape of 'Persian Carpet' plants, at the end of the production cycle. Main stem Plant Treatment Height No. of Internode Side branches Height Spread diameter Canopy (cm) nodes length (cm) length (cm) (cm) (cm) shape Control a 6.88 a 5.93 a a a a 1.17 a 2.50 g.l -1 daminozide ab 6.75 a 4.76 b ab ab a 0.96 ab 3.75 g.l -1 daminozide ab 7.00 a 4.66 b bc ab ab 0.93 ab 5.00 g.l -1 daminozide ab 7.25 a 4.53 b bc b ab 0.98 ab 0.50 mg a.i. paclobutrazol ab 7.00 a 4.51 b bc b ab 0.98 ab 0.75 mg a.i. paclobutrazol ab 6.88 a 4.61 b c b b 0.85 b 1.00 mg a.i. paclobutrazol b 6.75 a 4.33 b c b ab 0.95 ab 1.00 g.l -1 chlormequat ab 6.75 a 4.72 b c b ab 0.86 ab Mean Ftest treatment 2.90 * 0.85 ns 4.07 ** ** 6.08 ** 3.76 ** 2.25 ns HSD (Tukey's test) Coefficient of variation Means separations within columns by Tukey's multiple range test, 5% level; HSD = honestly significant difference; ns nonsignificant at p>0.05; * significant at p<0.05; ** significant at p<0.01; data converted to x , for analysis and presentation; Canopy shape quality rating: 0=regular and rounded, 1=irregular and not rounded. 404

7 Table 2. Polynomial regression equations adjusted to evaluated parameters (Y) of 'Persian Carpet' plant as dependent variables of growth regulators concentrations (X). Evaluated parameter (Y) Growth regulators (X) Regression equation F test (model) R 2 Main stem height (cm) Daminozide Y = X * 0.74 Paclobutrazol Y = X ** 0.88 Internode length (cm) Daminozide Y = X ** 0.88 Paclobutrazol Y = X ** 0.84 Plant height (cm) Daminozide Y = X * 0.88 Paclobutrazol Y = X ** 0.91 Side branches length (cm) Daminozide Y = X ** 0.98 Paclobutrazol Y = X X ** 0.99 Canopy shape Daminozide Y = X * 0.68 Paclobutrazol Y = X * 0.72 Plant spread diameter (cm) Paclobutrazol Y = X * 0.68 Side branches dry mass Daminozide Y = X * 0.96 Paclobutrazol Y = X X * 0.99 Leaves dry mass Daminozide Y = 0.730X * 0.65 Floral buds dry mass Daminozide Y = 0.213X * 0.91 Paclobutrazol Y = 2.186X ** 0.81 Root dry mass Daminozide Y = 0.354X * 0.47 Plant total dry mass (g) Paclobutrazol Y = X * 0.67 Foliage and flowers harvest index Paclobutrazol Y = 0.092X ** 0.89 * significant at p<0.05; ** significant at p<0.01; R 2 - coefficient of determination. 405

8 Table 3. Effects of growth regulators on plant parts dry mass, total dry mass (g), foliage and flowers harvest index (FFHI), production cycle and flower diameter of 'Persian Carpet', at the end of the production cycle. Treatment Green leaves Main stem Side branches Flowers Floral buds Roots Total (g) FFHI (g/g) Production cycle (days) Flower diameter (cm) Control 21.8 a 14.4 a 37.7 a 17.9 bc 2.7 b 5.5 a 6.87 a 0.40 b 49.0 a 3.80 a 2.50 g.l -1 daminozide 24.2 a 13.5 a 32.6 ab 18.3 abc 3.5 ab 7.9 a 6.18 ab 0.43 ab 48.5 a 4.03 a 3.75 g.l -1 daminozide 26.5 a 13.7 a 32.1 ab 17.8 c 3.7 ab 6.2 a 6.41 ab 0.44 ab 50.3 a 3.73 a 5.00 g.l -1 daminozide 24.7 a 14.2 a 30.2 bc 19.5 abc 3.7 ab 7.7 a 6.57 ab 0.44 ab 51.8 a 3.70 a 0.50 mg a.i. paclobutrazol 26.0 a 14.6 a 26.6 bc 21.5 abc 4.5 ab 6.8 a 5.17 ab 0.48 ab 47.5 a 3.68 a 0.75 mg a.i. paclobutrazol 24.8 a 15.2 a 23.3 c 24.9 ab 4.0 ab 7.8 a 5.87 ab 0.48 ab 48.8 a 4.17 a 1.00 mg a.i. paclobutrazol 28.7 a 14.2 a 24.4 c 20.7 abc 5.2 a 6.8 a 5.06 b 0.49 a 50.4 a 3.90 a 1.00 g.l -1 chlormequat 25.8 a 15.0 a 23.7 c 25.0 a 4.2 ab 6.3 a 4.95 b 0.51 a 47.6 a 3.76 a Mean F test treatment 1.67 ns 0.46 ns ** 3.90 ** 2.21 ns 1.52 ns 4.22 ** 3.90 ** 1.87 ns 2.28 ns HSD (Tukey's test) C.V Means separations within columns by Tukey's multiple range test, 5% level; HSD = honestly significant difference; C.V = coefficient of variation; ns nonsignificant at p>0.05; ** significant at p<