- Email: [email protected]
Paclobutrazol retards vegetative growth in hydroponically-cultured Leonotis leonurus (L.) R.Br. Lamiaceae for a multipurpose flowering potted plant
South African Journal of Botany 106 (2016) 67–70
Contents lists available at ScienceDirect
South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb
Paclobutrazol retards vegetative growth in hydroponically-cultured Leonotis leonurus (L.) R.Br. Lamiaceae for a multipurpose flowering potted plant A.A. Teto, C.P. Laubscher, P.A. Ndakidemi, I. Matimati ⁎ Faculty of Applied Science, Cape Peninsula University of Technology, P.O. Box 1906, Bellville 7535, South Africa
a r t i c l e
i n f o
Article history: Received 5 February 2016 Received in revised form 13 April 2016 Accepted 13 May 2016 Available online xxxx Edited by L Sebastiani Keywords: Growth retardant Medicinal plant Leaf senescence Dry weight Plant height Potted plants
a b s t r a c t Leonotis leonurus (L.) R.Br.; Lamiaceae is an indigenous southern African plant of commercial interest, which grows up to 3 m tall and 1.5 m wide, thus making it difficult to cultivate for the potted flowering plant industry. We tested different rates of a growth retardant paclobutrazol for retarding vegetative growth of L. leonurus for use as a flowering potted plant. The aim of the study was to determine the ideal rate of paclobutrazol from treatments of 0 (control), 2, 4, 8 and 16 mg active ingredient (a.i.) per plant applied to rooted cuttings of 8 ± 0.5 cm in height. Plants which received 2 mg a.i. were marginally shorter than the untreated control, while those treated with 4, 8, and 16 mg a.i of paclobutrazol were greatly dwarfed. Plants treated with 4, 8 and 16 mg a.i of paclobutrazol were seriously stunted, rosette, with senescing leaves and low fresh and dry weights. The concentration of 4 mg a.i caused the largest dwarfing with plants in this treatment only weighing 32% of the total fresh weight of the control and 31% of the total dry weight of the control plants. We therefore recommend the application of as little as 2 mg a.i. of paclobutrazol as an alternative way of chemically inducing dwarfing in L. leonurus, for producing flowering potted plants. © 2016 SAAB. Published by Elsevier B.V. All rights reserved.
1. Introduction Leonotis leonurus (L.) R. Br. Lamiaceae, commonly known as wild dagga or lion's ear, is a robust ornamental shrub with multiple medicinal uses. It grows widely throughout South Africa, especially amongst rocks in grasslands (Agnihotri et al., 2009). L. leonurus has bright orange nectar-rich velvety flowers, which are displayed in whorls at the top of each stem (Riley, 1963; Joffe, 2003). This fast growing perennial is drought tolerant and contains long soft and hairy leaves with serrate edges. Amongst its multiple uses are several medicinal applications, such as treatment for snake, spider and scorpion bites as well as bee stings (Ascensão et al., 1995). An infusion and a decoction of the leaf and stem have been used internally for coughs, colds, influenza, bronchitis, high blood pressure and headaches (Bienvenu et al., 2002). In addition, it has traditionally been smoked for the relief of epilepsy. L. leonurus is a very beautiful garden ornamental, with great potential as a flowering potted plant. Despite its great potential as a potted flowering plant, it often grows up to 3 m tall and 1.5 m wide, thus making it difficult to grow as a potted flowering plant. There is a big demand worldwide for indigenous potted flowering plants (Barzilay et al., 1992). Growers make efforts to produce ⁎ Corresponding author. Tel.: +27 21 959 5893; fax: +27 21 959 6832. E-mail address: [email protected] (I. Matimati).
http://dx.doi.org/10.1016/j.sajb.2016.05.012 0254-6299/© 2016 SAAB. Published by Elsevier B.V. All rights reserved.
inexpensive attractive plants at desirable times (Hayashi et al., 2001). Hydroponic cultivation of ornamental plants has, however, allowed farmers to grow under controlled conditions some species that would otherwise naturally grow during certain seasons. As a result, the commercial production of ornamental plants is growing worldwide and its monetary value has significantly increased over the last two decades, with a great potential for continued further growth in both domestic and international markets (Rout et al., 2006). The current demand for potted ornamentals can be met through the use of growth retardants, which enable the dwarfing of many tall ornamental plants (Barzilay et al., 1992). The technique utilizes synthetic plant growth regulators, which alter the physiology and growth rate of plants by mimicking natural plant hormones. Paclobutrazol, for example, is a gibberellin biosynthesis inhibitor, which is known to result in growth retardation on a wide variety of crops (Huang et al., 1989). Recent studies show that paclobutrazol has been used successfully to control plant height, branching and flowering of many plants over the years (Hayashi et al., 2001). Successful dwarfing of an ornamental shrub determines whether it can be adapted for producing a flowering potted plant (Menhenett, 1984), with such plants having the added benefit of being enjoyed as they grow. When using growth retardants for dwarfing shrubs for flowering potted plants, leaf size and inflorescence height must be reduced without altering plant shape or flower size (Al-Khassawneh
68
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
2.3. Data collection and analysis
et al., 2006). Natural growth of L. leonurus, for example, produces a big shrub for growing a flowering potted plant, yet the application of paclobutrazol may induce economically viable results. Research into growth retardants like paclobutrazol could prove useful to the horticultural industry by enabling the production of previously available and/or unusual species such as L. leonurus. The aim of this study was to determine an effective rate of a growth retardant for paclobutrazol dwarfing L. leonurus for potted plant production. We therefore tested varying concentrations of paclobutrazol on L. leonurus, in a hydroponic experiment to determine an ideal rate that effectively reduces leaf size and flower height. These were then potted at the end of the study.
Stem length, number of leaves, crown and stem diameter were measured weekly in the morning and the data recorded. Weights of roots and shoots were measured at the end of the study after 63 days from spraying paclobutrazol. Stem length, stem diameter, crown diameter, leaf numbers, root and shoot weights were analyzed for statistical significance using one-way analysis of variance (ANOVA). Counts of leaf numbers were first log-transformed before a one-way ANOVA. Data were presented as mean values with predicted standard errors (S.E). These computations were done with the software program STATISTICA [Software Programme version 2009 (StatSoft Inc., Tulsa, OK, USA)]. The Fisher least significant difference was used to compare treatment means at P ≤ 0.05 level of significance (Steel and Torrie, 1980).
2. Materials and methods 2.1. Experimental set-up
3. Results and discussion A hydroponic experiment was set up in a glasshouse at the Cape Town campus of the Cape Peninsula University of Technology (CPUT). It comprised of five white plastic gutters connected to five water tanks for water supply to the gutters. Each tank had a pump which supplied water to the plants. The set-up was mounted onto a steel table, for support, and placed in a greenhouse. The five gutters were all filled with leca clay pebbles as medium for anchoring the plant cuttings. Ten rooted cuttings of L. leonurus of the same height were planted in each of the plastic gutters. Plants in each of the four gutters were treated with one of the different levels of paclobutrazol whilst plants in the fifth gutter were treated with dH2O to act as an untreated control. To induce flowering during the winter period in L. leonurus, which is a long day plant, an incandescent lamp was placed a meter above the steel table and lit daily from 18H00 until 24H00. The nutrient solution comprised of distilled water and Chemicult® [Chemicult Products (Pty) Ltd., Camps Bay, South Africa, 8040] (2 g L− 1) and maintained at a pH of 5.8. The greenhouse was fitted with Alunet (40% shade screen), where temperature and humidity were monitored on a weekly basis. Midday temperatures fluctuated between 16–20 °C and relative humidity between 39–86%. The water of the hydroponic system was constantly flowing.
3.1. Shoot and root weights following paclobutrazol treatment Both fresh and dry weights of Leonotis leonurus plants that were treated with varying rates of paclobutrazol were significantly (P ≤ 0.001) lower than the weights of control plants, which were sprayed with dH2O (Table 1), indicating that growth was retarded by paclobutrazol. Despite the marginal differences in fresh weights of shoots (P ≤ 0.05) and roots (P ≤ 0.01) across the plants treated with paclobutrazol, these weight differences became statistically indistinguishable after drying (Table 1). 3.2. Growth response of plants following paclobutrazol treatment All plants significantly (P b 0.001) increased in height, number of leaves, crown and stem diameter (Fig. 1a) over the duration of the study (63 days). Although all experimental plants started at the same height of ca. 10 ± 0.6 cm (measured at 7 days after spraying), the plants that were treated with paclobutrazol became significantly (P b 0.001) retarded at 63 days when compared to control plants that were sprayed with dH2O. A growth trend in height of control plants had a steeper slope (ANCOVA interaction term: t = − 2.495; P = 0.014) than the slope of the trend in plants treated with paclobutrazol (Fig. 1a), indicating that overall height of control plants was ca. 4-times taller than at 7 days, which is the highest rate compared to plants treated with paclobutrazol, which ranged between ca. 1.3–1.6 times taller than at 7 days (Table 2). The growth of stem height varied with the applied concentration of paclobutrazol and these height variations were noticeable from 7 days after treatment until the termination of the experiment at 63 days. Compared with the control plants, supplying 16 mg a.i. of paclobutrazol significantly (P b 0.001) reduced the height by 7 days, whereas plants that received 2, 4, and 8 mg a.i. showed no significant change. From between 21 days to 28 days, however, all paclobutrazol-treated plants were significantly (P b 0.001) shorter than the control plants, with the 16 mg a.i. treatment having the shortest stems. Likewise, the control plants were
2.2. Foliar spray L. leonurus grows up to 3 m, therefore maximum dwarfing is required for producing flowering potted plants. Rooted stem cuttings were planted when they had attained 8 ± 0.5 cm in height. Paclobutrazol (Cultar®), Syngenta Ltd., Brackenfell, South Africa) was applied as foliar spray 7 days after planting. Five treatment levels were applied thrice at weekly intervals supplying 0, 2, 4, 8 or 16 mg a.i. paclobutrazol plant−1. To supply these paclobutrazol levels we sprayed different quantities of Cultar® (250 g L−1 paclobutrazol active ingredient), which amounted to 0, 8, 16, 32 and 64 ml Cultar® plant−1. To ensure absorption of Cultar®, the amounts sprayed were split equally over the three weeks, commencing 7 days after planting. The 0 mg a.i. treatment comprised of dH2O, which acted as the untreated control.
Table 1 Root and shoot weight (g) of Leonotis leonurus grown in the glasshouse and treated with varying rates of paclobutrazol. Values (Mean ± SE, n = 10) followed by dissimilar letters in a column are significantly different at *: P ≤ 0.05; ***: P ≤ 0.001 according to Fischer least significance difference. WK = Week; SE = Standard error). Paclobutrazol (mg a.i.) 0 2 4 8 16 One-way (F-statistic)
Fresh weight (g)
Dry weight (g)
Root
Shoot
Total
Root
Shoot
Total
10.3 ± 1.6a 10.0 ± 0.7ab 5.8 ± 0.8c 6.4 ± 0.8bc 6.8 ± 0.8bc 3.5*
17.5 ± 2.0a 10.0 ± 0.9b 5.5 ± 0.9c 5.9 ± 0.8bc 6.4 ± 0.6bc 17.5***
34.7 ± 6.5a 19.9 ± 1.4b 11.2 ± 1.6b 12.2 ± 1.6b 13.2 ± 1.2b 9.1***
1.0 ± 0.1a 0.7 ± 0.1b 0.5 ± 0.1b 0.5 ± 0.1b 0.6 ± 0.1b 5.9***
3.5 ± 0.4a 1.8 ± 0.1b 1.0 ± 0.2b 1.1 ± 0.1b 1.3 ± 0.1b 18.6***
4.5 ± 0.6a 2.5 ± 0.2b 1.4 ± 0.2b 1.6 ± 0.2b 1.9 ± 0.2b 14.8***
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
69
Fig. 1. a) Stem length (cm) and b) diameter (cm), c) crown diameter (cm) and d) number of leaves of glasshouse grown Leonotis leonurus following treatment with varying levels of paclobutrazol at 0 (control), 2, 4 6, 8, 16 mg a.i. Each circle and bar represents a mean ± SE (n = 6); significantly different means (after a one-way ANOVA with post-hoc Fischer's LSD, P b 0.001) have different letters.
tallest at 63 days, followed by plants that received the lowest dose of 2 mg a.i. treatment. The shorter stems observed in the paclobutrazoltreated plants are most likely due to the systematic inhibition of biosynthesis of gibberellins (GA), which are plant growth regulators effective in shoot elongation (Rai and Bist, 1992). Paclobutrazol is a potent inhibitor of biosynthesis of gibberellins (Huang et al., 1989). The effect of paclobutrazol on stem diameter of Leonotis leonurus (Fig. 1b) from 28 days to 54 days suggests that stem diameter was significantly (p b 0.05) reduced by the application of paclobutrazol. All paclobutrazol-treated plants showed the same trend, which was lower than of the control plants (Table 2). The observed decrease in stem diameter relative to control plants suggests that paclobutrazol retarded their stem growth. Our results are similar to those of Wieland and Wample (1985), who showed that paclobutrazol applications reduced the stem diameter growth of Malus domestica ‘delicious’ apple trees. Similar to our data, growth of stems in greenhouse-grown banana plants was induced by paclobutrazol (EI-Otmani et al., 1992). The crown diameter of Leonotis leonurus was significantly (P b 0.001) reduced after the application of paclobutrazol (Fig. 1c). With the exception of 7 days and 28 days, the greater crown diameter was observed with the control treatment (Table 2). The lowest crown
Table 2 Overall change in stem length (cm), stem diameter (cm), crown diameter (cm) and number of leaves of glasshouse grown Leonotis leonurus following weekly sprays with varying levels of paclobutrazol at 0 mg a.i. (control), 2 mg a.i., 4 mg a.i., 6 mg a.i., 8 mg a.i., 16 mg a.i. Values show how many times greater the final values were (e.g. 2.0 = two-fold increase). Rate of paclobutrazol (mg a.i.)
Increase in height/ stem length (−fold)
Increase in stem diameter (−fold)
Increase in crown diameter (−fold)
Increase in leaf number (−fold)
0 2 4 8 16
3.9 1.6 1.3 1.3 1.6
1.3 1.0 1.0 1.0 1.0
3.4 1.8 1.4 1.6 1.3
3.0 2.1 2.0 2.0 1.8
diameter was, however, observed from 35 days in plants treated with more than 4 mg a.i. with the exception of 8 mg a.i., which had an unexpected slight rise after 49 days. These results suggest that application of paclobutrazol probably inhibited the formation of leaves thereby affecting the crown diameter. In a similar study involving paclobutrazol, high concentrations of 10 mg a.i. resulted in decreased shoot length of Hebe × franciscana ‘Variegata’ (Kristensen and Adriansen, 1988). Although leaf numbers generally increased over time (Fig. 1d), there was a significant decrease in the number of Leonotis leonurus leaves with higher levels of paclobutrazol treatments (Table 2). Generally, the highest number of leaves was observed with the control treatment whereas the lowest number of leaves was observed when the highest rate of 16 mg a.i. of paclobutrazol was applied. The number of leaves after 16 mg a.i. of paclobutrazol was, however, the same as those for 4 and 8 mg a.i. at 21 days (Table 2). The observed results were probably due to leaf senescence as a result of paclobutrazol on L. leonurus. Some studies have also showed that foliar application of paclobutrazol inhibited the growth of leaves in strawberry, thus, reducing the plant yields (Jiao et al., 1986; Nishizawa, 1993). In conclusion, paclobutrazol can provide an alternative way of chemically inducing dwarfing in L. leonurus, for producing potted flowering plants. Indeed, height, stem diameter, crown diameter and number of leaves were reduced within 7 days by as little as 2 mg a.i. supplied to rooted cuttings. Although higher rates of paclobutrazol of 4, 6, 8 and 16 mg a.i. reduced the size of the plants, they resulted in defoliation and rosette plants. We therefore recommend 2 mg a.i. as it produced plants with desired characteristics for container production. Further studies are, however, required to combine paclobutrazol with other plant growth regulators used in flower production. Paclobutrazol is hazardous to health, therefore individuals mixing or spraying it must wear protective clothing to avoid all personal contact, including inhalation. Acknowledgements This study was funded by the Department of Horticulture, Faculty of Applied Sciences at Cape Peninsula University of Technology (Grant Number E280).
70
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
Author contribution statement AAT, CPL and PAN contributed to the conception or design of the study, including data acquisition and preliminary analyses. IM participated in analysis and interpretation of data, revising the work critically for important intellectual content and manuscript preparation. References Agnihotri, V.K., Hala, N.E., Troy, J.S., Ikhlas, A.K., Larry, A.W., 2009. Constituents of Leonotis leonurus flowering tops. Phytochemistry 2, 103–105. Al-Khassawneh, N.M., Karam, N.S., Shibli, R.A., 2006. Growth and flowering of black iris (Iris nigricans) following treatment with plant growth regulators. Scientia Horticulturae 107, 187–193. Ascensão, L., Marques, N., Pais, M.S., 1995. Glandular trichomes on vegetative and reproductive organs of Leonotis leonurus (Lamiaceae). Annals of Botany 75, 619–626. Barzilay, A., Ben-Jaacov, J., Cohen, A., Ion, A., Halevy, A.H., 1992. Minigladiolus as a flowering pot plant. Scientia Horticulturae 49, 117–124. Bienvenu, E., Amabeoku, G.J., Eagles, P.K., Scott, G., Springfield, E.P., 2002. Anticonvulsant activity of aqueous extract of Leonotis leonurus. Phytomedicine 9, 217–223. EI-Otmani, M., Cheikh, N., Sedki, M., 1992. Effects of paclobutrazol on greenhouse-grown bananas in Morocco. Scientia Horticulturae 49, 255–266. Hayashi, T., Heins, R.D., Cameron, A.C., Carlson, W.H., 2001. Etherphon influences flowering, height, branching of several herbaceous perennials. Scientia Horticulturae 91, 305–323.
Huang, H., Yin, W.S., Zheng, G.F., 1989. The effect of paclobutrazol on watermelon growth. Scientia Horticulturae 39, 9–14. Jiao, J., Tsujita, M.J., Murr, D.P., 1986. Effects of paclobutrazol and a-rest on growth, flowering and leaf carbohydrate and leaf senescence 'Nellie White' Easter Lily (Lilium longiflorum). Scientia Horticulturae 30 (135–14). Joffe, P., 2003. Easy Guide to Indigenous Shrubs. Briza Publications, South Africa. Kristensen, L.N., Adriansen, E., 1988. Growth and flowering in Hebe × franciscana ‘Variegata’ treated with plant growth regulators. Scientia Horticulturae 36, 139–149. Menhenett, R., 1984. Comparison of a new triazole retardant paclobutrazol (PP 333) with ancymidol, chlorphonium chloride, daminozide and piproctanyl bromide, on stem extension and inflorescence development in Chrsanthemum morifolium Ramat. Scientia Horticulturae 24, 349–358. Nishizawa, T., 1993. The effect of paclobutrazol on growth and yield during first year greenhouse strawberry production. Scientia Horticulturae 54, 267–274. Rai, N., Bist, L.D., 1992. Effect of soil- and foliar-applied paclobutrazol on vegetative growth flowering, fruit set and yield of oriental pear (Pyrus pyrifolia (Burm.) Nakai). Scientia Horticulturae 50, 153–158. Riley, H.P., 1963. Families of Flowering Plants of Southern Africa. University of Kentacky Press, USA. Rout, G.R., Mohapatra, A., Mohan Jain, S., 2006. Tissue culture of ornamental pot plants: a critical review on present scenario and future prospects. Biotechnology Advances 24, 531–560. Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics: a Biometrical Approach. second ed. McGraw Hill, New York. Wieland, W.F., Wample, R.L., 1985. Effects of paclobutrazol on growth, photosynthesis and carbohydrate content of ‘delicious’ apples. Scientia Horticulturae 26, 139–147.
Contents lists available at ScienceDirect
South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb
Paclobutrazol retards vegetative growth in hydroponically-cultured Leonotis leonurus (L.) R.Br. Lamiaceae for a multipurpose flowering potted plant A.A. Teto, C.P. Laubscher, P.A. Ndakidemi, I. Matimati ⁎ Faculty of Applied Science, Cape Peninsula University of Technology, P.O. Box 1906, Bellville 7535, South Africa
a r t i c l e
i n f o
Article history: Received 5 February 2016 Received in revised form 13 April 2016 Accepted 13 May 2016 Available online xxxx Edited by L Sebastiani Keywords: Growth retardant Medicinal plant Leaf senescence Dry weight Plant height Potted plants
a b s t r a c t Leonotis leonurus (L.) R.Br.; Lamiaceae is an indigenous southern African plant of commercial interest, which grows up to 3 m tall and 1.5 m wide, thus making it difficult to cultivate for the potted flowering plant industry. We tested different rates of a growth retardant paclobutrazol for retarding vegetative growth of L. leonurus for use as a flowering potted plant. The aim of the study was to determine the ideal rate of paclobutrazol from treatments of 0 (control), 2, 4, 8 and 16 mg active ingredient (a.i.) per plant applied to rooted cuttings of 8 ± 0.5 cm in height. Plants which received 2 mg a.i. were marginally shorter than the untreated control, while those treated with 4, 8, and 16 mg a.i of paclobutrazol were greatly dwarfed. Plants treated with 4, 8 and 16 mg a.i of paclobutrazol were seriously stunted, rosette, with senescing leaves and low fresh and dry weights. The concentration of 4 mg a.i caused the largest dwarfing with plants in this treatment only weighing 32% of the total fresh weight of the control and 31% of the total dry weight of the control plants. We therefore recommend the application of as little as 2 mg a.i. of paclobutrazol as an alternative way of chemically inducing dwarfing in L. leonurus, for producing flowering potted plants. © 2016 SAAB. Published by Elsevier B.V. All rights reserved.
1. Introduction Leonotis leonurus (L.) R. Br. Lamiaceae, commonly known as wild dagga or lion's ear, is a robust ornamental shrub with multiple medicinal uses. It grows widely throughout South Africa, especially amongst rocks in grasslands (Agnihotri et al., 2009). L. leonurus has bright orange nectar-rich velvety flowers, which are displayed in whorls at the top of each stem (Riley, 1963; Joffe, 2003). This fast growing perennial is drought tolerant and contains long soft and hairy leaves with serrate edges. Amongst its multiple uses are several medicinal applications, such as treatment for snake, spider and scorpion bites as well as bee stings (Ascensão et al., 1995). An infusion and a decoction of the leaf and stem have been used internally for coughs, colds, influenza, bronchitis, high blood pressure and headaches (Bienvenu et al., 2002). In addition, it has traditionally been smoked for the relief of epilepsy. L. leonurus is a very beautiful garden ornamental, with great potential as a flowering potted plant. Despite its great potential as a potted flowering plant, it often grows up to 3 m tall and 1.5 m wide, thus making it difficult to grow as a potted flowering plant. There is a big demand worldwide for indigenous potted flowering plants (Barzilay et al., 1992). Growers make efforts to produce ⁎ Corresponding author. Tel.: +27 21 959 5893; fax: +27 21 959 6832. E-mail address: [email protected] (I. Matimati).
http://dx.doi.org/10.1016/j.sajb.2016.05.012 0254-6299/© 2016 SAAB. Published by Elsevier B.V. All rights reserved.
inexpensive attractive plants at desirable times (Hayashi et al., 2001). Hydroponic cultivation of ornamental plants has, however, allowed farmers to grow under controlled conditions some species that would otherwise naturally grow during certain seasons. As a result, the commercial production of ornamental plants is growing worldwide and its monetary value has significantly increased over the last two decades, with a great potential for continued further growth in both domestic and international markets (Rout et al., 2006). The current demand for potted ornamentals can be met through the use of growth retardants, which enable the dwarfing of many tall ornamental plants (Barzilay et al., 1992). The technique utilizes synthetic plant growth regulators, which alter the physiology and growth rate of plants by mimicking natural plant hormones. Paclobutrazol, for example, is a gibberellin biosynthesis inhibitor, which is known to result in growth retardation on a wide variety of crops (Huang et al., 1989). Recent studies show that paclobutrazol has been used successfully to control plant height, branching and flowering of many plants over the years (Hayashi et al., 2001). Successful dwarfing of an ornamental shrub determines whether it can be adapted for producing a flowering potted plant (Menhenett, 1984), with such plants having the added benefit of being enjoyed as they grow. When using growth retardants for dwarfing shrubs for flowering potted plants, leaf size and inflorescence height must be reduced without altering plant shape or flower size (Al-Khassawneh
68
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
2.3. Data collection and analysis
et al., 2006). Natural growth of L. leonurus, for example, produces a big shrub for growing a flowering potted plant, yet the application of paclobutrazol may induce economically viable results. Research into growth retardants like paclobutrazol could prove useful to the horticultural industry by enabling the production of previously available and/or unusual species such as L. leonurus. The aim of this study was to determine an effective rate of a growth retardant for paclobutrazol dwarfing L. leonurus for potted plant production. We therefore tested varying concentrations of paclobutrazol on L. leonurus, in a hydroponic experiment to determine an ideal rate that effectively reduces leaf size and flower height. These were then potted at the end of the study.
Stem length, number of leaves, crown and stem diameter were measured weekly in the morning and the data recorded. Weights of roots and shoots were measured at the end of the study after 63 days from spraying paclobutrazol. Stem length, stem diameter, crown diameter, leaf numbers, root and shoot weights were analyzed for statistical significance using one-way analysis of variance (ANOVA). Counts of leaf numbers were first log-transformed before a one-way ANOVA. Data were presented as mean values with predicted standard errors (S.E). These computations were done with the software program STATISTICA [Software Programme version 2009 (StatSoft Inc., Tulsa, OK, USA)]. The Fisher least significant difference was used to compare treatment means at P ≤ 0.05 level of significance (Steel and Torrie, 1980).
2. Materials and methods 2.1. Experimental set-up
3. Results and discussion A hydroponic experiment was set up in a glasshouse at the Cape Town campus of the Cape Peninsula University of Technology (CPUT). It comprised of five white plastic gutters connected to five water tanks for water supply to the gutters. Each tank had a pump which supplied water to the plants. The set-up was mounted onto a steel table, for support, and placed in a greenhouse. The five gutters were all filled with leca clay pebbles as medium for anchoring the plant cuttings. Ten rooted cuttings of L. leonurus of the same height were planted in each of the plastic gutters. Plants in each of the four gutters were treated with one of the different levels of paclobutrazol whilst plants in the fifth gutter were treated with dH2O to act as an untreated control. To induce flowering during the winter period in L. leonurus, which is a long day plant, an incandescent lamp was placed a meter above the steel table and lit daily from 18H00 until 24H00. The nutrient solution comprised of distilled water and Chemicult® [Chemicult Products (Pty) Ltd., Camps Bay, South Africa, 8040] (2 g L− 1) and maintained at a pH of 5.8. The greenhouse was fitted with Alunet (40% shade screen), where temperature and humidity were monitored on a weekly basis. Midday temperatures fluctuated between 16–20 °C and relative humidity between 39–86%. The water of the hydroponic system was constantly flowing.
3.1. Shoot and root weights following paclobutrazol treatment Both fresh and dry weights of Leonotis leonurus plants that were treated with varying rates of paclobutrazol were significantly (P ≤ 0.001) lower than the weights of control plants, which were sprayed with dH2O (Table 1), indicating that growth was retarded by paclobutrazol. Despite the marginal differences in fresh weights of shoots (P ≤ 0.05) and roots (P ≤ 0.01) across the plants treated with paclobutrazol, these weight differences became statistically indistinguishable after drying (Table 1). 3.2. Growth response of plants following paclobutrazol treatment All plants significantly (P b 0.001) increased in height, number of leaves, crown and stem diameter (Fig. 1a) over the duration of the study (63 days). Although all experimental plants started at the same height of ca. 10 ± 0.6 cm (measured at 7 days after spraying), the plants that were treated with paclobutrazol became significantly (P b 0.001) retarded at 63 days when compared to control plants that were sprayed with dH2O. A growth trend in height of control plants had a steeper slope (ANCOVA interaction term: t = − 2.495; P = 0.014) than the slope of the trend in plants treated with paclobutrazol (Fig. 1a), indicating that overall height of control plants was ca. 4-times taller than at 7 days, which is the highest rate compared to plants treated with paclobutrazol, which ranged between ca. 1.3–1.6 times taller than at 7 days (Table 2). The growth of stem height varied with the applied concentration of paclobutrazol and these height variations were noticeable from 7 days after treatment until the termination of the experiment at 63 days. Compared with the control plants, supplying 16 mg a.i. of paclobutrazol significantly (P b 0.001) reduced the height by 7 days, whereas plants that received 2, 4, and 8 mg a.i. showed no significant change. From between 21 days to 28 days, however, all paclobutrazol-treated plants were significantly (P b 0.001) shorter than the control plants, with the 16 mg a.i. treatment having the shortest stems. Likewise, the control plants were
2.2. Foliar spray L. leonurus grows up to 3 m, therefore maximum dwarfing is required for producing flowering potted plants. Rooted stem cuttings were planted when they had attained 8 ± 0.5 cm in height. Paclobutrazol (Cultar®), Syngenta Ltd., Brackenfell, South Africa) was applied as foliar spray 7 days after planting. Five treatment levels were applied thrice at weekly intervals supplying 0, 2, 4, 8 or 16 mg a.i. paclobutrazol plant−1. To supply these paclobutrazol levels we sprayed different quantities of Cultar® (250 g L−1 paclobutrazol active ingredient), which amounted to 0, 8, 16, 32 and 64 ml Cultar® plant−1. To ensure absorption of Cultar®, the amounts sprayed were split equally over the three weeks, commencing 7 days after planting. The 0 mg a.i. treatment comprised of dH2O, which acted as the untreated control.
Table 1 Root and shoot weight (g) of Leonotis leonurus grown in the glasshouse and treated with varying rates of paclobutrazol. Values (Mean ± SE, n = 10) followed by dissimilar letters in a column are significantly different at *: P ≤ 0.05; ***: P ≤ 0.001 according to Fischer least significance difference. WK = Week; SE = Standard error). Paclobutrazol (mg a.i.) 0 2 4 8 16 One-way (F-statistic)
Fresh weight (g)
Dry weight (g)
Root
Shoot
Total
Root
Shoot
Total
10.3 ± 1.6a 10.0 ± 0.7ab 5.8 ± 0.8c 6.4 ± 0.8bc 6.8 ± 0.8bc 3.5*
17.5 ± 2.0a 10.0 ± 0.9b 5.5 ± 0.9c 5.9 ± 0.8bc 6.4 ± 0.6bc 17.5***
34.7 ± 6.5a 19.9 ± 1.4b 11.2 ± 1.6b 12.2 ± 1.6b 13.2 ± 1.2b 9.1***
1.0 ± 0.1a 0.7 ± 0.1b 0.5 ± 0.1b 0.5 ± 0.1b 0.6 ± 0.1b 5.9***
3.5 ± 0.4a 1.8 ± 0.1b 1.0 ± 0.2b 1.1 ± 0.1b 1.3 ± 0.1b 18.6***
4.5 ± 0.6a 2.5 ± 0.2b 1.4 ± 0.2b 1.6 ± 0.2b 1.9 ± 0.2b 14.8***
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
69
Fig. 1. a) Stem length (cm) and b) diameter (cm), c) crown diameter (cm) and d) number of leaves of glasshouse grown Leonotis leonurus following treatment with varying levels of paclobutrazol at 0 (control), 2, 4 6, 8, 16 mg a.i. Each circle and bar represents a mean ± SE (n = 6); significantly different means (after a one-way ANOVA with post-hoc Fischer's LSD, P b 0.001) have different letters.
tallest at 63 days, followed by plants that received the lowest dose of 2 mg a.i. treatment. The shorter stems observed in the paclobutrazoltreated plants are most likely due to the systematic inhibition of biosynthesis of gibberellins (GA), which are plant growth regulators effective in shoot elongation (Rai and Bist, 1992). Paclobutrazol is a potent inhibitor of biosynthesis of gibberellins (Huang et al., 1989). The effect of paclobutrazol on stem diameter of Leonotis leonurus (Fig. 1b) from 28 days to 54 days suggests that stem diameter was significantly (p b 0.05) reduced by the application of paclobutrazol. All paclobutrazol-treated plants showed the same trend, which was lower than of the control plants (Table 2). The observed decrease in stem diameter relative to control plants suggests that paclobutrazol retarded their stem growth. Our results are similar to those of Wieland and Wample (1985), who showed that paclobutrazol applications reduced the stem diameter growth of Malus domestica ‘delicious’ apple trees. Similar to our data, growth of stems in greenhouse-grown banana plants was induced by paclobutrazol (EI-Otmani et al., 1992). The crown diameter of Leonotis leonurus was significantly (P b 0.001) reduced after the application of paclobutrazol (Fig. 1c). With the exception of 7 days and 28 days, the greater crown diameter was observed with the control treatment (Table 2). The lowest crown
Table 2 Overall change in stem length (cm), stem diameter (cm), crown diameter (cm) and number of leaves of glasshouse grown Leonotis leonurus following weekly sprays with varying levels of paclobutrazol at 0 mg a.i. (control), 2 mg a.i., 4 mg a.i., 6 mg a.i., 8 mg a.i., 16 mg a.i. Values show how many times greater the final values were (e.g. 2.0 = two-fold increase). Rate of paclobutrazol (mg a.i.)
Increase in height/ stem length (−fold)
Increase in stem diameter (−fold)
Increase in crown diameter (−fold)
Increase in leaf number (−fold)
0 2 4 8 16
3.9 1.6 1.3 1.3 1.6
1.3 1.0 1.0 1.0 1.0
3.4 1.8 1.4 1.6 1.3
3.0 2.1 2.0 2.0 1.8
diameter was, however, observed from 35 days in plants treated with more than 4 mg a.i. with the exception of 8 mg a.i., which had an unexpected slight rise after 49 days. These results suggest that application of paclobutrazol probably inhibited the formation of leaves thereby affecting the crown diameter. In a similar study involving paclobutrazol, high concentrations of 10 mg a.i. resulted in decreased shoot length of Hebe × franciscana ‘Variegata’ (Kristensen and Adriansen, 1988). Although leaf numbers generally increased over time (Fig. 1d), there was a significant decrease in the number of Leonotis leonurus leaves with higher levels of paclobutrazol treatments (Table 2). Generally, the highest number of leaves was observed with the control treatment whereas the lowest number of leaves was observed when the highest rate of 16 mg a.i. of paclobutrazol was applied. The number of leaves after 16 mg a.i. of paclobutrazol was, however, the same as those for 4 and 8 mg a.i. at 21 days (Table 2). The observed results were probably due to leaf senescence as a result of paclobutrazol on L. leonurus. Some studies have also showed that foliar application of paclobutrazol inhibited the growth of leaves in strawberry, thus, reducing the plant yields (Jiao et al., 1986; Nishizawa, 1993). In conclusion, paclobutrazol can provide an alternative way of chemically inducing dwarfing in L. leonurus, for producing potted flowering plants. Indeed, height, stem diameter, crown diameter and number of leaves were reduced within 7 days by as little as 2 mg a.i. supplied to rooted cuttings. Although higher rates of paclobutrazol of 4, 6, 8 and 16 mg a.i. reduced the size of the plants, they resulted in defoliation and rosette plants. We therefore recommend 2 mg a.i. as it produced plants with desired characteristics for container production. Further studies are, however, required to combine paclobutrazol with other plant growth regulators used in flower production. Paclobutrazol is hazardous to health, therefore individuals mixing or spraying it must wear protective clothing to avoid all personal contact, including inhalation. Acknowledgements This study was funded by the Department of Horticulture, Faculty of Applied Sciences at Cape Peninsula University of Technology (Grant Number E280).
70
A.A. Teto et al. / South African Journal of Botany 106 (2016) 67–70
Author contribution statement AAT, CPL and PAN contributed to the conception or design of the study, including data acquisition and preliminary analyses. IM participated in analysis and interpretation of data, revising the work critically for important intellectual content and manuscript preparation. References Agnihotri, V.K., Hala, N.E., Troy, J.S., Ikhlas, A.K., Larry, A.W., 2009. Constituents of Leonotis leonurus flowering tops. Phytochemistry 2, 103–105. Al-Khassawneh, N.M., Karam, N.S., Shibli, R.A., 2006. Growth and flowering of black iris (Iris nigricans) following treatment with plant growth regulators. Scientia Horticulturae 107, 187–193. Ascensão, L., Marques, N., Pais, M.S., 1995. Glandular trichomes on vegetative and reproductive organs of Leonotis leonurus (Lamiaceae). Annals of Botany 75, 619–626. Barzilay, A., Ben-Jaacov, J., Cohen, A., Ion, A., Halevy, A.H., 1992. Minigladiolus as a flowering pot plant. Scientia Horticulturae 49, 117–124. Bienvenu, E., Amabeoku, G.J., Eagles, P.K., Scott, G., Springfield, E.P., 2002. Anticonvulsant activity of aqueous extract of Leonotis leonurus. Phytomedicine 9, 217–223. EI-Otmani, M., Cheikh, N., Sedki, M., 1992. Effects of paclobutrazol on greenhouse-grown bananas in Morocco. Scientia Horticulturae 49, 255–266. Hayashi, T., Heins, R.D., Cameron, A.C., Carlson, W.H., 2001. Etherphon influences flowering, height, branching of several herbaceous perennials. Scientia Horticulturae 91, 305–323.
Huang, H., Yin, W.S., Zheng, G.F., 1989. The effect of paclobutrazol on watermelon growth. Scientia Horticulturae 39, 9–14. Jiao, J., Tsujita, M.J., Murr, D.P., 1986. Effects of paclobutrazol and a-rest on growth, flowering and leaf carbohydrate and leaf senescence 'Nellie White' Easter Lily (Lilium longiflorum). Scientia Horticulturae 30 (135–14). Joffe, P., 2003. Easy Guide to Indigenous Shrubs. Briza Publications, South Africa. Kristensen, L.N., Adriansen, E., 1988. Growth and flowering in Hebe × franciscana ‘Variegata’ treated with plant growth regulators. Scientia Horticulturae 36, 139–149. Menhenett, R., 1984. Comparison of a new triazole retardant paclobutrazol (PP 333) with ancymidol, chlorphonium chloride, daminozide and piproctanyl bromide, on stem extension and inflorescence development in Chrsanthemum morifolium Ramat. Scientia Horticulturae 24, 349–358. Nishizawa, T., 1993. The effect of paclobutrazol on growth and yield during first year greenhouse strawberry production. Scientia Horticulturae 54, 267–274. Rai, N., Bist, L.D., 1992. Effect of soil- and foliar-applied paclobutrazol on vegetative growth flowering, fruit set and yield of oriental pear (Pyrus pyrifolia (Burm.) Nakai). Scientia Horticulturae 50, 153–158. Riley, H.P., 1963. Families of Flowering Plants of Southern Africa. University of Kentacky Press, USA. Rout, G.R., Mohapatra, A., Mohan Jain, S., 2006. Tissue culture of ornamental pot plants: a critical review on present scenario and future prospects. Biotechnology Advances 24, 531–560. Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics: a Biometrical Approach. second ed. McGraw Hill, New York. Wieland, W.F., Wample, R.L., 1985. Effects of paclobutrazol on growth, photosynthesis and carbohydrate content of ‘delicious’ apples. Scientia Horticulturae 26, 139–147.