Growth of chrysanthemum under coloured plastic films with different light qualities and quantities

Scientia Horticulturae 79 (1999) 195±205

Growth of chrysanthemum under coloured plastic films with different light qualities and quantities E. Oyaerta,*, E. Volckaertb, P.C. Debergha a

Department of Plant Production - Horticulture, Faculty of Agricultural and Applied Biological Sciences, University of Gent, Coupure links 653, 9000 Gent, Belgium b Research Centre for Ornamental Plants, Schaessestraat 18, 9070 Destelbergen, Belgium Accepted 12 August 1998

Abstract Several spectral filters were tested on Dendranthema  grandiflorum `White Reagan' (Chrysanthemum morifolium), as an alternative for chemical growth regulators. Three blue polyethylene (PE) films and one vaporised interference film were compared to four neutral filters with corresponding PPFD transmittances (differing from 25% to 73%). The blue PE films had blue : red ratios (B : R) from 6.2 to 85.5 with increasing pigment concentration, and red : far red ratios (R : FRn) between 0.43 and 1.45. The vaporised film had a relative low B : R (1.41) and a high R : FRn (2.06). B : R and R : FRn of the control filters were 1. All coloured filters altered plant habit drastically. The inhibition of stem elongation increased with increasing pigment concentration under the blue PE films, with a maximum of 22% growth reduction compared to the control. Although fewer leaves were developed, internode length was significantly shorter under all coloured filters compared to the corresponding controls. The blue filters resulted in a lower number of axillary shoots, a smaller leaf area and a lower total dry weight than the control filters. Furthermore, dry weight was translocated from stem to leaves. The vaporised film, which was characterised by the highest light transmission percentage, resulted in a relative small growth reduction compared to the corresponding control. Since this film had no significant effect on branching rate, leaf area and dry weight, plant quality remained intact. If the vaporising technique could be improved, more extreme B : R and R : FR ratios could be obtained, which would result in larger growth reductions. Such a spectral filter would provide growers with an environment-friendly tool for growth regulation of ornamental crops. # 1999 Elsevier Science B.V. All rights reserved.

Abbreviations: PE, polyethylene; B, blue light; R, red light; FR, far red light; PPFD, photosynthetic photon flux density; , phytochrome photo-equilibrium; CuSO4, copper sulphate; SDW, stem dry weight; LWR, leaf weight ratio; SWR, stem weight ratio; ILA, individual leaf area * Corresponding author. Tel.: +32-9-2646077; fax: +32-9-2646225; e-mail: [email protected] 0304-4238/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 2 3 8 ( 9 8 ) 0 0 2 0 7 - 6

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Keywords: Dendranthema  grandi¯orum; Chrysanthemum morifolium; Light; Spectral ®lters; Growth inhibition

1. Introduction A wide range of ornamental plants is treated with chemical growth regulators to obtain compact, high quality plants. Several alternatives for these chemical products have been tested. Among these, negative DIF (Myster and Moe, 1995) and spectral filters (Mortensen and Strùmme, 1987) are most promising. The success of DIF depends on plant species (Myster and Moe, 1995) and geographic location or season (Kulack, 1990a). Although the physiology behind DIF is still not completely understood (Langton and Cockshull, 1997), DIF is applied by many growers (Kulack, 1990b). Spectral filters, which selectively transmit certain wave length bands, have also resulted in growth inhibition and other morphological adaptations of several plant species. Plant dry weight, percentage dry matter, number of leaves, branching rate and total leaf area were altered under different light qualities for chrysanthemum and poinsettia (Mortensen and Strùmme, 1987). The interpretation of these photomorphogenic responses is generally related to the photon ratios B : R and R : FR and to the phytochrome photo-equilibrium  (Rajapakse et al., 1992). Morgan and Smith (1976) found a linear relationship between  and the logarithmic stem extension rate of Chenopodium album. Nevertheless, in experiments with CuSO4 solutions, the commonly used phytochrome parameters like R : FR or  estimates do not correlate well with plant responses (Venkat et al., 1996). Rajapakse and Kelly (1994) also reported that the interpretation of photon ratios, in order to explain photomorphogenic plant responses, needs to be done with caution, especially with filters that remove R and FR. Moreover, presenting the graphical spectral data seems indispensable in correlating plant morphogenic reactions to the light environment (Rajapakse et al., 1992). The spectrum obtained by growing plants under double layer polycarbonate plates filled with aqueous solutions of CuSO4, has proved to be an efficient light quality to inhibit elongation of internodes of chrysanthemum (Rajapakse and Kelly, 1992). Since such a fluid roof system cannot be extrapolated to a large scale use in greenhouses, selective plastic filters seem to guarantee practical use for growers (Murakami et al., 1997). The objective of our research was to evaluate plastic filters which are suitable for greenhouse application. Such a film could be used in tunnel cultures or as a screen in greenhouses and would provide growers with a practical tool for growth regulation of ornamental crops.

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2. Materials and methods 2.1. Plant material Rooted cuttings of Dendranthema  grandiflorum `White Reagan' (Chrysanthemum morifolium) were planted in 17 cm pots in standard peat mixture and were grown in a greenhouse as single-stem cut flowers. Fertigation was provided by drip-to-drip irrigation as a standard chrysanthemum nutrient solution of 2 ms/ cm from liquid fertilisers (Biofeed, Zwijndrecht, Netherlands) based on light sum. Day/night temperature was set to 21/198C. The experiment started on 16 September and ended on 23 October. Vegetative growth was only investigated. 2.2. Light quality and quantity In the experiment four coloured filters were tested. Three of them were polyethylene (PE) films containing a blue absorption pigment (code 4020, Hyplast N.V., Hoogstraten, Belgium) in different concentrations (1±3%). A fourth coloured filter consisted of a mica film with a vaporised coating of several metaloxide layers, resulting in a transparent film with interference effect (Hyplast, Hoogstraten, Belgium, in co-operation with Fraunhofer Institute, Dresden, Germany). As the light transmittance was different for each coloured filter, four different control filters were provided. These control filters consisted of several layers of neutral shading cloths (white shading cloths of 20% transmission reduction, AMEVO±UBINK, Bavikhove, Belgium), to ensure equal photosynthetic photon flux densities (PPFD) as under the corresponding coloured film. Transmission spectra (Fig. 1) were determined with a LI1800 spectroradiometer (LI-COR, Lincoln, NE) under standard conditions in a dark room with a white fluorescent lamp (OSRAM L36W/31).  was estimated according to Sager et al. (1988). Transmission percentages, B : R and R : FR ratios (narrow band and broad band) and  are presented in Table 1. A long-day photoperiod of 16 h was provided by high pressure sodium lamps (PHILIPS HPS 400 W), which resulted in average PAR-values under the filters of 50±200 mmol/m2 s depending on their transmission percentage. 2.3. Data collection Each experimental unit consisted of 40 plants, of which 15 plants were measured on a regular basis. Plant height, number of leaves and number of axillary shoots were measured. Average internode length was calculated. At the end of the experiment, fresh and dry weights of stem, leaves and axillary shoots were determined. Plant material was dried at 808C for 24 h. The areas of the leaves of the main stem and axillary shoots were determined with an image

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Fig. 1. Spectral distribution of the transmission spectra of three blue PE films and a vaporised mica film, measured under standard circumstances.

Table 1 Spectral characterisation under standardised conditions of three blue PE films with different pigment concentrations and a vaporised mica film: transmission percentage in PPFD region (400± 700 nm), photon flux ratio between different wavelength regions and  Filter Control Control Control Control

Transmission % 1 2 3 4

Blue 1% Blue 2% Blue 3% Vaporised film

B : Ra

R : FRba

R : FRna



40 33 25 73

0.98 0.98 0.98 0.98

1.01 1.01 1.01 1.01

1.02 1.02 1.02 1.02

0.71 0.71 0.71 0.71

40 33 25 73

6.20 14.83 85.53 1.41

0.31 0.15 0.03 2.08

1.45 1.03 0.43 2.06

0.64 0.61 0.57 0.77

a

B : R ˆ 400±500/600±700 nm; R : FR b ˆ 600±700/700±800 nm; R : FR n ˆ 655±665/725± 735 nm.

analysis system (Delta-T Devices, Cambridge, UK). Petiole length, leaf blade length and individual leaf area were determined from six fully grown leaves per plant. From these data, percentage dry weight and stem dry weight (SDW) per unit length were calculated, as well as leaf weight ratio (LWR), stem weight ratio (SWR) and individual leaf area (ILA) as the average area of six fully grown leaves. For LWR, main stem leaves as well as axillary shoots were taken into account.

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2.4. Experimental design In the analysis of variance each treatment was compared to its individual control with equal transmission percentage, in a two block design. Differences among treatment means were tested using an LSD-test (P ˆ 0.95). 3. Results 3.1. Spectral distribution The filters containing blue absorption pigments were characterised by a lower R : FR than the control when measured in the broad band and a higher R : FR when measured in the narrow band (Table 1). This is related to an increased absorption of FR as the concentration of blue pigment increased from 1% to 3% (Fig. 1). The vaporised filter is characterised by a transmission drop in the FR region to about 40%. 3.2. Growth parameters All plastic films tested reduced plant height significantly compared to their corresponding control treatments. Growth inhibition was largest under the 3% blue film (22%) and diminished with blue pigment concentration to 14% and 11%, respectively, and was smallest under the vaporised mica film (9%) (Fig. 2). Growth under the blue films was already significantly smaller than under the control filter after 10 days, while under the vaporised film the effect was significant only after 28 days. Number of leaves was significantly reduced under all coloured films (differing from two leaves less under the 1% blue film to three leaves less under the 3% blue film compared to the respective control treatment), except for the vaporised film (Table 2). Nevertheless, average internode length was reduced significantly under the four coloured filters. As the concentration of blue pigment increased, the number of axillary shoots decreased. Only the vaporised film did not influence the development of axillary shoots. 3.3. Leaf area and pigmentation Total leaf area of the main stem, as well as of the axillary shoots, was significantly lower under the plastic films than the respective control treatments. Leaf area of the axillary shoots under the 2% and 3% blue films was reduced to approximately 50% of that of their controls (Fig. 3). The area of an individual adult leaf of the main stem was significantly smaller under the blue films than for

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Fig. 2. Growth curves of Dendranthema  grandiflorum `White Reagan' under four pigmented films and corresponding controls with equal transmission percentages.

the control treatments, except for the vaporised film (Table 2). Petiole length was not influenced by any of the coloured filters (data not presented). 3.4. Dry matter partitioning All blue films reduced total plant dry weight and percentage dry weight, while this was not the case under the vaporised film (Table 3). All control films were characterised by a ratio between stem and leaf dry weight of approximately 1 : 1 (Fig. 4), while under all coloured films relatively more dry weight was stored in the leaves and less in the stems. This effect is reflected in a significantly lower SDW per unit length and a higher LWR and a lower SWR under the coloured films (Table 3). The development of axillary shoots decreased as the PPFD level

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Table 2 Number of leaves and axillary shoots, average internode length of chrysanthemums grown under four coloured filters and four corresponding control filters Filter

Number of leaves

Internode length (cm)

Number of axillary shoots

Control 1 Blue 1%

30.4 b 28.8 a

2.58 b 2.43 a

26.3 b 23.6 a

Control 2 Blue 2%

29.9 a 26.7 a

2.45 b 2.36 a

24.4 b 18.2 a

Control 3 Blue 3%

30.9 b 26.6 a

2.55 b 2.31 a

26.0 b 18.3 a

Control 4 Vaporised film

31.6 a 32.1 a

2.41 b 2.16 a

28.3 a 28.5 a

a

Different letters are significant differences at 0.95 level (LSD-test).

Table 3 Percentage dry to fresh weight, SDW/cm, LWR, SWR and ILA of chrysanthemum grown under three blue films and a vaporised mica film and their corresponding controls Filter

Dry weight (%)

SDW/cm (g/cm)

LWR (g (leaves)/g (plant))

SWR ILA (g (stem)/g (plant)) (cm2)

Control 1 Blue 1%

10.7 a* 10.2 a

0.036 b 0.026 a

0.64 a 0.67 a

0.36 a 0.33 a

42.07 b 38.9 a

Control 2 Blue 2%

10.2 b 9.4 a

0.032 b 0.022 a

0.64 a 0.67 b

0.36 b 0.33 a

45.08 b 38.25 a

Control 3 Blue 3%

10.3 b 9.5 a

0.034 b 0.020 a

0.63 a 0.67 b

0.37 b 0.33 a

45.42 b 35.58 a

Control 4 Vaporised film

10.9 a 10.8 a

0.044 a 0.046 a

0.66 a 0.71 b

0.34 b 0.29 a

42.84 a 41.97 a

a

Different letters are significant differences at 0.95 level (LSD-test).

under the film decreased, which is reflected in dry weight and in leaf area (Figs. 3 and 4). 4. Discussion The growth reduction of chrysanthemum plants under the blue PE films increased with increasing pigmentation and with increasing B : R and R : FRn ratio (Table 1 and Fig. 2). It is well known that light with a high R : FR and B : R

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Fig. 3. Effect of four spectral filters on leaf area of Dendranthema  grandiflorum `White Reagan' compared to their controls.

results in reduced shoot elongation (Rajapakse and Kelly, 1992; McMahon et al., 1991). The relatively poor growth reduction of 9% under the vaporised film, which is nevertheless characterised by the highest  values and the highest R : FR (narrow and broad band), could be caused by its low B : R ratio. Mortensen and Strùmme (1987) stated that a small change in R : FR gives the same effect as a large change in B : R. This suggests that the R : FR ratio under the vaporised mica film, which was twice as high as under the control filter, caused inhibition of stem elongation. This growth reduction would probably be more extreme if the vaporised filter had a lower transmission capacity in the far red wave length region. In contrast, Venkat et al. (1996) found that the absence of FR and the

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Fig. 4. Effect of four spectral filters on dry weight partitioning of Dendranthema  grandiflorum `White Reagan' compared to their corresponding controls.

presence of R were critical factors for height reduction of chrysanthemum whereas the effect of B depended on the presence or absence of FR. Murakami et al. (1997) reported growth reduction in FR-deficient light and elongation in R-deficient light. The results of Venkat et al. (1996) indicated that the CuSO4 effects were controlled by phytochrome. Our results on the contrary imply that probably phytochrome as well as the blue absorbing pigment (BAP) were active in determining plant responses. We have repeatedly achieved growth inhibitions with these blue PE films on different chrysanthemum cultivars, in different

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seasons, with natural light and with supplementary assimilation light and with sunflower (data not published). The decreased plant dry weight under the blue filters is probably a result of a decreased CO2-assimilation rate. This will most likely also affect the shoot elongation and the ILA (Table 3). This is also in correspondence with previous results by Mortensen and Strùmme (1987). Blue filters reduce the concentration of soluble sugars (sucrose, glucose and fructose) and starch in leaf and stem for chrysanthemum and rose (Decoteau et al., 1993; Rajapakse and Kelly, 1995). The changes in LWR and SWR of the chrysanthemums reflect a translocation of dry matter from stem to leaves under the blue pigmented films as well as under the vaporised film (Table 3). Casal et al. (1995) reported that low R : FR increases the amount of reducing sugars in internodes, as a result of carbon repartitioning from leaves to stem in Sinapis alba. This agrees with the effects of CuSO4 filters (high R : FR) which reduced the percentage dry matter accumulation of Dendranthema  grandiflorum in stems and increased it in leaves (Rajapakse et al., 1992). B-treatments increased the dry weight/cm shoot in several plant species (Mortensen and Strùmme, 1987). Our results show that in the presence of FR light this is not the case. The main consequence of low PAR values under a filter seems to be a low branching rate. According to Assmann (1992) reduced branching and stem elongation are common morphological responses to reduced light intensities in both neutral and canopy shade treatments. On the other hand, B-stimulated formation of lateral breaks in Chrysanthemum  morifolium Ramat. and in other plant species (Mortensen and Strùmme, 1987). 5. Conclusions In this study the vaporised mica film is most promising for greenhouse production, provided that a higher transmission capacity in the blue wave lengths can be achieved by further optimisation of the spectral characteristics of this film. Despite the rather small rate of growth reduction, the most interesting effect of the vaporised film is a reduced stem elongation without any effect on branching rate, leaf area and dry weight, which leaves plant quality intact. The positive effects on plant quality are most probably due to the high transmission capacity of this vaporised film, compared to the blue PE films. These blue films were characterised by more extreme B : R and R : FR ratios but lacked the reflection of the FR wavelength region as in CuSO4 filters. Acknowledgements This work was supported by the EC (AIR3-CT94-0974). We thank Hyplast N.V. for providing the filter materials.

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