Directory UMM :Data Elmu:jurnal:S:Scientia Horticulturae:Vol84.Issue3-4.June2000:
Scientia Horticulturae 84 (2000) 215±225
Growth responses of chrysanthemum and bell pepper
transplants to photoselective plastic ®lms$
Shumin Lia, Nihal C. Rajapaksea,*, Roy E. Youngb,1, Ryu Oic
a
b
Department of Horticulture, Clemson University, Clemson, SC 29634, USA
Department of Agricultural and Biological Engineering, Clemson University,
Clemson, SC 29634, USA
c
Organic Performance Materials Laboratory, Mitsui Chemicals,
1190 Kasama-cho, Sakae-ku, Yokohama 247, Japan
Accepted 8 November 1999
Abstract
Plant response to photoselective plastic ®lms with three concentrations of a far-red (FR) light
absorbing dye (named as YCE-1 #80, YCE-1 #75 and YCE-1 #65) was tested using chrysanthemum
(Dendranthema grandi¯orum (Ramat.) Kitamura) and bell pepper (Capsicum annuum L.) as
model plants. The dye in ®lms intercepted FR wavelengths of sunlight with maximum interception
at 760 nm. FR light interception increased and transmission of photosynthetic photon ¯ux (PPF)
decreased as the dye concentration increased. The R:FR ratio and estimated phytochrome
photoequilibrium (fc) of transmitted light increased from 1.1 to 3.7 and from 0.72 to 0.81,
respectively, with increase in dye concentration. Light transmitted through photoselective ®lms
reduced plant height and internode length by 10±35% depending on the crop and dye concentration
in the ®lm. Photoselective ®lms reduced the leaf area and shoot dry weight of plants. Speci®c leaf
dry weight (dry weight per unit leaf area) and speci®c stem dry weight (dry weight per unit length
of stem) were also slightly reduced in plants grown inside photoselective ®lm chambers suggesting
that both small plants and reduced dry matter assimilation may have contributed to the reduction in
shoot dry weight. Reduction in plant height was apparent within 2 weeks after initiation of the
treatment. Plant height progressively decreased as the dye concentration increased. Although ®lms
with higher dye concentrations are more effective in height reduction, the reduction in PPF with
$
Technical contribution No. 4559 of the South Carolina Agricultural Experiment Station,
Clemson University.
*
Corresponding author. Tel.: 1-864-656-4970; fax: 1-864-656-4960.
E-mail address: nrjpks@clemson.edu (N.C. Rajapakse).
1
Present address: Department of Agricultural and Biological Engineering, Pennsylvania State
University, University Park, PA 16802-1909, USA.
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 3 6 - 3
216
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
increasing dye concentration can adversely affect plant growth and development, and this fact
should be considered in commercial production of photoselective ®lms. Our results indicate that a
photoselective ®lm with a R:FR ratio of 2.2 (or fc of 0.78, which corresponds to 75% light
transmission) caused about 20% height reduction in chrysanthemum and 30% height reduction in
bell pepper after 4 weeks of treatment. This initial work demonstrates that the use of greenhouse
®lms with FR light absorbing dyes to control plant height is as effective as chemical growth
regulators or CuSO4 ®lters. With the commercial development of photoselective greenhouse covers
or shade material, nursery and greenhouse industry could reduce costs for growth regulating
chemicals, reduce health risks to their workers and consumers, and reduce potential environmental
pollution. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Spectral ®lters; Greenhouse covers; Photomorphogenesis; Height control
1. Introduction
Plants can perceive subtle changes in red (R) and far-red (FR) light
composition in their environment and make physiological and morphological
adjustment through phytochrome. Upon prolonged exposure to a given light
environment, a photoequilibrium (f) develops between active Pfr level relative to
total phytochrome. In general, an environment with high R light relative to FR
light results in establishing a high f. Morgan and Smith (1976, 1979) reported
that stem elongation rate of herbaceous plants were inversely proportioned to the
f. Therefore, plants grown in an environment with high R light can be shorter
than those produced in high FR light.
In greenhouse industry, growers often place plants close together and hang
baskets over the benches to increase production capacity. This results in a relative
increase in FR light in lower canopy due to the absorption of R light by the upper
canopy. Therefore, a low f can be established in the plant under overcrowded
conditions, resulting in spindly and tall plants. Growers often control this
undesirable growth by chemical growth retardants. Because of the human safety
issues, the use of growth regulating chemicals has been subjected to strict
regulations on ornamental crops and banned on food crops. Currently, there are
no chemicals available for height control of vegetable transplants in the USA.
Growers in other countries are facing similar restrictions on using chemical
growth regulators on food crops. This has led to increased interest in nonchemical alternatives. Manipulation of greenhouse light quality to establish a
high f offers a non-chemical alternative for height control of greenhouse crops.
Relative amount of R light in a greenhouse can be increased to establish a high
f by using electric light sources that are high in R wavelengths and low in FR
wavelengths. Although there is a growing demand for arti®cial lighting for plant
growth, the initial cost of establishing such a system could be high and some
arti®cial lighting sources may lead to irregular plant growth due to uneven
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
217
spectral distribution (spectral gaps) of the lighting source (Protasova et al., 1990).
Spectral ®lters that can ®lter out FR light can be used to alter greenhouse light
quality relatively inexpensively. In earlier work, it was shown that liquid copper
sulfate (4% CuSO45H2O) ®lters were effective in removing FR light and
establishing a high phytochrome photoequilibrium (fc) within plants (Mortensen
and Strùmme, 1987). FR light ®ltering by CuSO4 ®lters was effective in
controlling height of a wide range of greenhouse crops (Mortensen and Strùmme,
1987; McMahon et al., 1991; Rajapakse and Kelly, 1992). Although effective,
liquid ®lters have limited value to commercial growers because of its high initial
cost, dif®culty in liquid handling and phytotoxicity in the event of spill.
The development of plastic photoselective greenhouse covering with FR light
absorbing dyes could facilitate the commercialization of spectral ®lters as a nonchemical alternative for greenhouse crop height control. To the knowledge of the
authors, such greenhouse ®lms are not commercially available. In this paper, we
report the effectiveness of plastic greenhouse covers with varying concentrations
of a FR light absorbing dye in controlling height of chrysanthemum and bell
pepper plants. The objectives of this work were to test the effectiveness of
photoselective ®lms and select a dye concentration that gives an optimum height
control while minimizing the reduction in radiation entering the greenhouse.
2. Materials and methods
2.1. Photoselective ®lms
Polyethylene (PE) ®lms with varying concentrations of a FR light absorbing
dye were produced by Mitsui Chemicals, Tokyo, Japan. These ®lms are identi®ed
by the following code names: BCE-1 (control, dye at 0 g mÿ2), YCE-1 #80 (dye
at 0.08 g mÿ2), YCE-1 #75 (dye at 0.13 g mÿ2) and YCE-1 #65 (dye at
0.22 g mÿ2). The photosynthetic photon ¯ux (PPF) transmission of BCE-1
(control), YCE-1 #80, #75, and #65 ®lms were about 90, 80, 75 and 65%,
respectively. Four PVC framed growth chambers (1.2 1.2 1.3 m3; one for
each ®lm) were covered with the above experimental ®lms. Another chamber
with the same dimension as above was covered with sealed double-layered
polycarbonate panels ®lled with liquid CuSO4 (4%) to compare the effectiveness
of the ®lms. The PPF transmission of CuSO4 ®lter was about 75%. All growth
chambers were placed inside a glasshouse.
PPF inside growth chambers were measured (at ®ve locations within each
chamber) between 12:00 and 14:00 hours on clear days at 2-week intervals with
an LI-185 quantum meter ®tted with an LI-190SA quantum sensor (LI-COR,
Lincoln, NE). The PPF was adjusted to be the same among all chambers with
cheesecloth before the placement of plant in the chambers. The average
218
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
instantaneous PPF inside chambers was 620 120 mmol mÿ2 sÿ1. Daily PPF
integral was recorded with LI-1000 data logger ®tted with an LI-190SB quantum
sensor. Plants in the chambers received an average daily PPF integral of
16 2 mol mÿ2 on a clear day.
Spectral distribution in 10 nm increments from 330 to 1100 nm was measured
at the middle of each chamber with a LI-1800 spectroradiometer ®tted with a LI1800-10 remote cosine sensor at the beginning and end of the experiments. The
cheesecloth did not alter the quality of light transmitted. Multiple light scans
within a chamber indicated that the spectral distribution was uniform inside the
chamber. The R:FR ratio was determined as the ratio of photon ¯ux density
between 600 and 700 nm (R) and 700 and 800 nm (FR). fc was estimated as
described by Sager et al. (1988).
2.2. Plant material and culture
Fifty uniformly rooted `Bright Golden Anne' chrysanthemum shoot cuttings
with six to seven leaves were planted individually in 0.6 l square pots containing
a commercial potting mix (Metro Mix-360, Scotts-Sierra Horticultural Products,
Marysville, OH). Plants were allowed to establish as single stem plants in the
greenhouse for 1 week before transferring to the experimental chambers. Bell
pepper `Capistrano' seeds were sown in 98-cell plug trays containing the same
potting mix and germinated under an intermittent mist. When cotyledons were
fully expanded, 50 seedlings were transplanted individually in 0.6 l square pots
and allowed to establish for 1 week. After 1 week establishment, chrysanthemum
and bell pepper plants (10 plants of each experiment per treatment) were
transferred to experimental chambers and were grown for 4 weeks. When
treatment was initiated, chrysanthemum and bell pepper plants were 7.0 and
1.5 cm tall, respectively. All plants were irrigated with 200 mg lÿ1 N from 20 N±
4.4 P±16.7 K fertilizer (Peter's 20-10-20 Peat-lite special, Scotts-Sierra Horticultural Products) as needed. Daily maximum and minimum air temperatures
inside chambers were recorded during the experiment. Average daily maximum
or minimum temperatures during experimental period was not different among
chambers and were 28 2 and 22 28C, respectively.
2.3. Experimental design, data collection and analyses
Experimental chambers were randomly placed inside the glasshouse. Because
of the limited number of chambers, experiments were repeated to replicate
(September±November 1997). In each replicate, 10 plants were grown for each
crop. Plants were randomly placed with approximate spacing of 18 18 cm.
Plant height (height from soil level to apex) and the number of fully expanded
leaves were recorded weekly. Average internode length was calculated as plant
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
219
height divided by number of leaves. Total leaf area (LI-3100 Area Meter, Lincoln,
NE) and dry weights of stems and leaves were measured at the end of the 4-weektreatment. For dry weight measurements, tissue was oven dried at 858C for 48±
72 h. Data were analyzed using analysis of variance procedure (SAS institute,
Cary, NC) and differences among treatment means were tested by Duncan's
multiple range test at P 0.05.
3. Results and discussion
3.1. Light quality
Spectral distribution curves of light transmitted through unshaded photoselective ®lms are shown in Fig. 1. The dye in YCE-1 photoselective ®lms
intercepted FR wavelengths of sunlight with maximum interception at 760 nm.
The interception of FR wavelengths increased as the dye concentration increased.
In contrast, CuSO4 ®lter intercepted almost all wavelengths beyond 700 nm
Fig. 1. Photon distribution of light transmitted through photoselective ®lms. BCE-1 is the control
®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light absorbing dye at 0.08,
0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels ®lled with 4%
CuSO45H2O liquid.
220
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
Table 1
R:FR ratios and estimated fc of light transmitted through photoselective ®lms and liquid CuSO4
®ltera
Treatmentb
R:FR ratio
fc
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
4% CuSO4
1.1
1.6
2.3
3.7
3.6
0.72
0.75
0.78
0.81
0.80
a
R 600±700 nm; FR 700±800 nm.
BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light
absorbing dye at 0.08, 0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels
®lled with 4% CuSO45H2O liquid.
b
(capacity of the spectroradiometer was 330±1100 nm). The CuSO4 chamber had
more blue and less R light than photoselective ®lm chambers. The R:FR ratio
increased from 1.1 to 3.7 and estimated fc increased from 0.72 to 0.81 as the dye
concentration in ®lms increased (Table 1). The R:FR ratio and fc of transmitted
light did not change during the experiment (data not shown).
3.2. Plant growth under photoselective ®lms
Photoselective ®lms reduced height of chrysanthemum plants and bell pepper
seedlings (Fig. 2). The height reduction by ®lms increased as the dye
concentration increased. For example, the ®nal height of chrysanthemum plants
was reduced to 11, 19 and 22% inside YCE-1 #80, #75, and #65 chambers (lowest
to highest R:FR ratio or fc), respectively, compared to control plants. A similar
trend was observed in bell pepper height reduction. Both chrysanthemum and bell
pepper plants grown in CuSO4 chamber were the shortest, but they were not
signi®cantly different from plants grown in YCE-1 #65 chamber, indicating that
®lms with highest dye concentration (tested here) were as effective as CuSO4
®lter. Our results are in agreement with Murakami et al. (1995, 1996a,b) who
reported a reduction of plant height of cucumber (Cucumis sativus L.), tomato
(Lycopersicon esculentum Mill.), and sun¯ower (Helianthus annuus L.) under FR
light intercepting ®lters. Similar to ®ndings of Morgan and Smith (1976), height
of chrysanthemum and pepper plants were inversely proportional to the fc.
Although the R:FR ratio and fc were similar in YCE-1 #65 and CuSO4 chambers,
plants grown in CuSO4 chamber were slightly shorter than those grown in YCE-1
#65 chamber (Fig. 2). This may be explained by the fact that CuSO4 chamber had
more blue wavelengths compared to photoselective ®lms. Blue light has been
shown to reduce plant height (Adamse et al., 1988; Warpeha and Kaufman,
1989). In addition to the blue light, CuSO4 ®lters also removed almost all of FR
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
221
Fig. 2. Weekly height increase of chrysanthemum and bell pepper seedlings grown in different
photoselective ®lm chambers. Vertical bars indicate standard error. Each point is the mean of 20
plants. BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR
absorbing dye at 0.08, 0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels
®lled with 4% CuSO45H2O liquid. Plants in all treatment chambers received the same amount of
PPF.
wavelengths whereas photoselective ®lm let some FR wavelengths into the
chamber. Therefore, it is dif®cult to compare the role of each wavelength band on
height control by ®lms and CuSO4 ®lters.
The effectiveness of ®lms also varied with species. Final height of
chrysanthemum was reduced 22% by YCE-1 #65 ®lm whereas that of bell
peppers was reduced 35% by the YCE-1 #65 ®lm, suggesting that bell pepper
seedlings were more responsive to ®ltered light than the chrysanthemum plants.
222
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
The difference in responsiveness could be due to the stage of development of
plants when they were exposed to photoselective ®lms. Bell pepper seedlings
only had one or two true leaves when they were placed in photoselective ®lm
chambers whereas chrysanthemum cuttings had six to seven leaves when they
were placed in the chambers.
The dye concentration in ®lms in¯uenced the time it takes for plants to respond
to altered light environment (Fig. 2). Height reduction in chrysanthemum was
observed after 1 week exposure to YCE-1 #65 compared to 2 weeks in YCE-1
#75 and 3 weeks in YCE-1 #80 chambers. A similar pattern was observed for bell
pepper seedlings, but they responded sooner; height reduction was achieved
under YCE-1 #80 ®lm after 2 weeks of exposure. Average internode length
followed a pattern similar to height reduction (data not shown). Number of leaves
was not signi®cantly affected by the photoselective ®lms (data not shown),
indicating that height reduction was a result of internode length reduction, but not
due to the delay in stage of development.
Photoselective ®lms and CuSO4 ®lter reduced total leaf area and leaf size in
both chrysanthemums and bell peppers (Table 2). Chrysanthemums grown in
YCE-1 #65 and CuSO4 had smallest individual leaves and total leaf area. In
chrysanthemum, total leaf area or leaf size was not different between YCE-1 #80
or #75 chambers and the control chamber. However, in bell peppers total leaf area
of control plants was greater than plants grown in YCE-1 chambers. Reduction in
leaf size gives a compact appearance to the plant but can result in reduction of
photosynthetic area which further results in a reduction in dry matter
accumulation.
Total shoot dry weight of chrysanthemums and bell pepper seedlings decreased
progressively as the dye concentration in ®lms (R:FR ratio or fc) increased. Total
shoot dry weight of chrysanthemums and peppers grown in the CuSO4 and YCE1 #65 chamber was reduced over 40% (Table 2). Photoselective ®lms reduced leaf
and stem dry weights of chrysanthemum and bell pepper, but the stem dry weight
reduction was greater than the leaf dry weight reduction. Speci®c leaf dry weight
(SLDW, dry weight per unit leaf area) and speci®c stem dry weight (SSDW, dry
weight per unit length of stem) were reduced in plants grown inside
photoselective ®lms. Speci®c dry weight reduction increased as the dye
concentration increased. Reduction in speci®c dry weights indicates that dry
matter assimilation was affected by photoselective ®lms and that both small
plants and the reduction in dry matter assimilation may have contributed to the
reduction in total shoot dry weight.
The photoselective ®lms affected dry matter partitioning into leaves and stems
(Table 2). In chrysanthemums, plants grown in the control chamber had 66% of
total shoot dry matter in leaves and 34% in stems. Photoselective ®lms reduced
percentage dry matter accumulation in stems from 34 to 24% and increased dry
matter accumulation in leaves from 66 to 76%. Percentage dry matter
Table 2
In¯uence of photoselective ®lms on total leaf area (LA), average leaf size (LS), leaf dry weight (LDW), speci®c leaf dry weight (SLDW), stem dry
weight (SDW), speci®c stem dry weight (SSDW), and total shoot dry weight (TDW) of chrysanthemum and bell pepper seedlings
LA (cm2)
LS (cm2)
LDW (g)
SLDW
(g cmÿ2)
SDW (g)
SSDW
(g cmÿ1)
TDW (g)
Chrysanthemum
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
CuSO4
681ab
649a
630a
561b
522b
28a
28a
27a
24b
23b
2.96a (66)c
2.53b (71)
2.16c (73)
1.78d (76)
1.63d (79)
0.0044a
0.0039b
0.0034c
0.0032c
0.0031c
1.55a (34)
1.06b (29)
0.79c (27)
0.56d (24)
0.44e (21)
0.0431a
0.0332a
0.0271b
0.0213bc
0.0178c
4.51a
3.59b
2.95c
2.34cd
2.07d
Bell pepper
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
CuSO4
555a
485b
430bc
417cd
378d
50a
49a
43b
42b
38c
1.96a (70)
1.76ab (72)
1.34bc (72)
1.20bc (73)
1.18c (77)
0.0034a
0.0036a
0.0031ab
0.0029b
0.0031ab
0.82a (30)
0.69b (28)
0.51c (28)
0.44cd (27)
0.35d (23)
0.0703a
0.0707a
0.0617b
0.0584bc
0.0497c
2.78a
2.45b
1.85c
1.64cd
1.53d
a
BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light absorbing dye at 0.08, 0.13 and 0.22 g mÿ2,
respectively. CuSO4 is the chamber covered with panels ®lled with 4% CuSO45H2O liquid.
b
Each number is the mean of 20 plants. Mean comparison within a column by Duncan's multiple range test at P 0.05. Means with the same letter
are not signi®cantly different.
c
Numbers in parentheses are % dry weight.
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
Treatmenta
223
224
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
accumulation in leaves increased as the R:FR ratio increased. In peppers, plants
grown in the control chamber had 70% of total shoot dry matter in leaves and
30% in stems. Photoselective ®lms reduced percentage dry matter accumulation
in stems from 30 to 27% and increased dry matter accumulation in leaves from 70
to 73%. In both chrysanthemum and peppers, the greatest change in dry matter
partitioning was found in CuSO4 ®lter-grown-plants. Quality of light can
in¯uence the translocation of photosynthates. Hurd (1974) reported that light low
in R:FR ratio increased stem dry weight of tomato plants. Kasperbauer (1987)
reported that lowering R:FR ratio increased photosynthate partitioning into shoots
and developing seeds. The greater dry matter accumulation into leaves under
photoselective ®lms may be because of the relatively high R and low FR light in
these treatments. Britz and Sager (1990) reported that plants grown under blue
light de®cient sources had less translocation of photosynthate out of leaves, thus
increasing leaf dry matter content.
4. Conclusions
In summary, photoselective plastic ®lms with FR light intercepting dyes were
effective in regulating plant height of chrysanthemum and bell pepper plants
without the use of chemical growth regulators. The ®lm with the highest dye
concentration (used in this study) was as effective as 4% CuSO4 ®lters in
controlling plant height. Although ®lms with higher dye concentration are more
effective in height reduction, the reduction in PPF transmission with increased
dye concentration may adversely affect plant growth and development, and this
fact should be considered in commercial development of photoselective ®lms.
Our results indicate that a photoselective ®lm with a R:FR ratio of 2.2 (which
corresponds to 75% light transmission) caused about 20% height reduction in
chrysanthemum and 30% height reduction in bell pepper after 4 weeks of
treatment. This initial work demonstrates that the use of greenhouse ®lms with
FR light absorbing dyes is as effective as chemical growth regulators or CuSO4
®lters in controlling plant height of chrysanthemums and bell pepper seedlings.
With the commercial development of photoselective greenhouse covers or shade
material, nursery and greenhouse industry could reduce costs for growth
regulating chemicals, reduce health risks to their workers and consumers, and
reduce potential environmental pollution.
References
Adamse, P., Jaspers, P.A.P.M., Bakker, J.A., Wesselius, J.C., Heeringa, G.H., Kendrick, R.E.,
Koornneef, M., 1988. Photophysiology of tomato mutant de®cient in labile phytochrome. J. Plant
Physiol. 133, 436±440.
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
225
Britz, S.J., Sager, J.C., 1990. Photomorphogenesis and photoassimilation in soybean and sorghum
grown under broad spectrum or blue-de®cient light sources. Plant Physiol. 94, 448±454.
Hurd, R.G., 1974. The effect of an incandescent supplement on the growth of tomato plants in low
light. Ann. Bot. 38, 613±623.
Kasperbauer, M.J., 1987. Far-red light re¯ection from green leaves and effects on phytochromemediated assimilate partitioning under ®eld conditions. Plant Physiol. 85, 350±354.
McMahon, M.J., Kelly, J.W., Decoteau, D.R., Young, R.E., Pollock, R.K., 1991. Growth of
Dendranthema grandi¯orum (Ramat.) Kitamura under various spectral ®lters. J. Am. Soc.
Hort. Sci. 116, 950±954.
Morgan, D.C., Smith, H., 1976. Linear relationship between phytochrome photoequilibrium and
growth in plants under simulated natural radiation. Nature 262, 210±212.
Morgan, D.C., Smith, H., 1979. A systematic relationship between phytochrome-controlled
development and species habit, for plants grown in simulated natural radiation. Planta 145, 253±
258.
Mortensen, L.M., Strùmme, E., 1987. Effect of light quality on some greenhouse crops. Sci. Hort.
33, 27±36.
Murakami, K., Cui, H., Kiyota, M., Aiga, I., 1995. The design of special covering materials for
greenhouses to control plant elongation by changing spectral distribution of daylight. Acta Hort.
399, 135±142.
Murakami, K., Cui, H., Kiyota, M., Yamane, T., Aiga, I., 1996a. The effects of covering materials
for greenhouses to control plant growth by changing spectral distribution of daylight. Acta Hort.
435, 123±130.
Murakami, K., Cui, H., Kiyota, M., Takemura, Y., Oi, R., Aiga, I., 1996b. Covering materials to
control plant growth by modifying the spectral balance of daylight. Plasticulture 110, 2±14.
Protasova, N.N., Welles, J.M., Dobrovolskii, M.W., Tsoglin, L.N., 1990. Spectral characteristics of
light sources and plant growth peculiarities under arti®cial illumination. Soviet Plant Physiol.
37, 293±303.
Rajapakse, N.C., Kelly, J.W., 1992. Regulation of chrysanthemum growth by spectral ®lters. J. Am.
Soc. Hort. Sci. 117, 481±485.
Sager, J.C., Smith, W.O., Edwards, J.C., Cyr, K.L., 1988. Photosynthetic ef®ciency and
phytochrome photoequilibria determination using spectral data. Trans. ASAE 31, 1882±1887.
Warpeha, K.M., Kaufman, L.S., 1989. Blue-light regulation of epicotyl elongation in Pisum sativus.
Plant Physiol. 89, 544±548.
Growth responses of chrysanthemum and bell pepper
transplants to photoselective plastic ®lms$
Shumin Lia, Nihal C. Rajapaksea,*, Roy E. Youngb,1, Ryu Oic
a
b
Department of Horticulture, Clemson University, Clemson, SC 29634, USA
Department of Agricultural and Biological Engineering, Clemson University,
Clemson, SC 29634, USA
c
Organic Performance Materials Laboratory, Mitsui Chemicals,
1190 Kasama-cho, Sakae-ku, Yokohama 247, Japan
Accepted 8 November 1999
Abstract
Plant response to photoselective plastic ®lms with three concentrations of a far-red (FR) light
absorbing dye (named as YCE-1 #80, YCE-1 #75 and YCE-1 #65) was tested using chrysanthemum
(Dendranthema grandi¯orum (Ramat.) Kitamura) and bell pepper (Capsicum annuum L.) as
model plants. The dye in ®lms intercepted FR wavelengths of sunlight with maximum interception
at 760 nm. FR light interception increased and transmission of photosynthetic photon ¯ux (PPF)
decreased as the dye concentration increased. The R:FR ratio and estimated phytochrome
photoequilibrium (fc) of transmitted light increased from 1.1 to 3.7 and from 0.72 to 0.81,
respectively, with increase in dye concentration. Light transmitted through photoselective ®lms
reduced plant height and internode length by 10±35% depending on the crop and dye concentration
in the ®lm. Photoselective ®lms reduced the leaf area and shoot dry weight of plants. Speci®c leaf
dry weight (dry weight per unit leaf area) and speci®c stem dry weight (dry weight per unit length
of stem) were also slightly reduced in plants grown inside photoselective ®lm chambers suggesting
that both small plants and reduced dry matter assimilation may have contributed to the reduction in
shoot dry weight. Reduction in plant height was apparent within 2 weeks after initiation of the
treatment. Plant height progressively decreased as the dye concentration increased. Although ®lms
with higher dye concentrations are more effective in height reduction, the reduction in PPF with
$
Technical contribution No. 4559 of the South Carolina Agricultural Experiment Station,
Clemson University.
*
Corresponding author. Tel.: 1-864-656-4970; fax: 1-864-656-4960.
E-mail address: nrjpks@clemson.edu (N.C. Rajapakse).
1
Present address: Department of Agricultural and Biological Engineering, Pennsylvania State
University, University Park, PA 16802-1909, USA.
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 3 6 - 3
216
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
increasing dye concentration can adversely affect plant growth and development, and this fact
should be considered in commercial production of photoselective ®lms. Our results indicate that a
photoselective ®lm with a R:FR ratio of 2.2 (or fc of 0.78, which corresponds to 75% light
transmission) caused about 20% height reduction in chrysanthemum and 30% height reduction in
bell pepper after 4 weeks of treatment. This initial work demonstrates that the use of greenhouse
®lms with FR light absorbing dyes to control plant height is as effective as chemical growth
regulators or CuSO4 ®lters. With the commercial development of photoselective greenhouse covers
or shade material, nursery and greenhouse industry could reduce costs for growth regulating
chemicals, reduce health risks to their workers and consumers, and reduce potential environmental
pollution. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Spectral ®lters; Greenhouse covers; Photomorphogenesis; Height control
1. Introduction
Plants can perceive subtle changes in red (R) and far-red (FR) light
composition in their environment and make physiological and morphological
adjustment through phytochrome. Upon prolonged exposure to a given light
environment, a photoequilibrium (f) develops between active Pfr level relative to
total phytochrome. In general, an environment with high R light relative to FR
light results in establishing a high f. Morgan and Smith (1976, 1979) reported
that stem elongation rate of herbaceous plants were inversely proportioned to the
f. Therefore, plants grown in an environment with high R light can be shorter
than those produced in high FR light.
In greenhouse industry, growers often place plants close together and hang
baskets over the benches to increase production capacity. This results in a relative
increase in FR light in lower canopy due to the absorption of R light by the upper
canopy. Therefore, a low f can be established in the plant under overcrowded
conditions, resulting in spindly and tall plants. Growers often control this
undesirable growth by chemical growth retardants. Because of the human safety
issues, the use of growth regulating chemicals has been subjected to strict
regulations on ornamental crops and banned on food crops. Currently, there are
no chemicals available for height control of vegetable transplants in the USA.
Growers in other countries are facing similar restrictions on using chemical
growth regulators on food crops. This has led to increased interest in nonchemical alternatives. Manipulation of greenhouse light quality to establish a
high f offers a non-chemical alternative for height control of greenhouse crops.
Relative amount of R light in a greenhouse can be increased to establish a high
f by using electric light sources that are high in R wavelengths and low in FR
wavelengths. Although there is a growing demand for arti®cial lighting for plant
growth, the initial cost of establishing such a system could be high and some
arti®cial lighting sources may lead to irregular plant growth due to uneven
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
217
spectral distribution (spectral gaps) of the lighting source (Protasova et al., 1990).
Spectral ®lters that can ®lter out FR light can be used to alter greenhouse light
quality relatively inexpensively. In earlier work, it was shown that liquid copper
sulfate (4% CuSO45H2O) ®lters were effective in removing FR light and
establishing a high phytochrome photoequilibrium (fc) within plants (Mortensen
and Strùmme, 1987). FR light ®ltering by CuSO4 ®lters was effective in
controlling height of a wide range of greenhouse crops (Mortensen and Strùmme,
1987; McMahon et al., 1991; Rajapakse and Kelly, 1992). Although effective,
liquid ®lters have limited value to commercial growers because of its high initial
cost, dif®culty in liquid handling and phytotoxicity in the event of spill.
The development of plastic photoselective greenhouse covering with FR light
absorbing dyes could facilitate the commercialization of spectral ®lters as a nonchemical alternative for greenhouse crop height control. To the knowledge of the
authors, such greenhouse ®lms are not commercially available. In this paper, we
report the effectiveness of plastic greenhouse covers with varying concentrations
of a FR light absorbing dye in controlling height of chrysanthemum and bell
pepper plants. The objectives of this work were to test the effectiveness of
photoselective ®lms and select a dye concentration that gives an optimum height
control while minimizing the reduction in radiation entering the greenhouse.
2. Materials and methods
2.1. Photoselective ®lms
Polyethylene (PE) ®lms with varying concentrations of a FR light absorbing
dye were produced by Mitsui Chemicals, Tokyo, Japan. These ®lms are identi®ed
by the following code names: BCE-1 (control, dye at 0 g mÿ2), YCE-1 #80 (dye
at 0.08 g mÿ2), YCE-1 #75 (dye at 0.13 g mÿ2) and YCE-1 #65 (dye at
0.22 g mÿ2). The photosynthetic photon ¯ux (PPF) transmission of BCE-1
(control), YCE-1 #80, #75, and #65 ®lms were about 90, 80, 75 and 65%,
respectively. Four PVC framed growth chambers (1.2 1.2 1.3 m3; one for
each ®lm) were covered with the above experimental ®lms. Another chamber
with the same dimension as above was covered with sealed double-layered
polycarbonate panels ®lled with liquid CuSO4 (4%) to compare the effectiveness
of the ®lms. The PPF transmission of CuSO4 ®lter was about 75%. All growth
chambers were placed inside a glasshouse.
PPF inside growth chambers were measured (at ®ve locations within each
chamber) between 12:00 and 14:00 hours on clear days at 2-week intervals with
an LI-185 quantum meter ®tted with an LI-190SA quantum sensor (LI-COR,
Lincoln, NE). The PPF was adjusted to be the same among all chambers with
cheesecloth before the placement of plant in the chambers. The average
218
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
instantaneous PPF inside chambers was 620 120 mmol mÿ2 sÿ1. Daily PPF
integral was recorded with LI-1000 data logger ®tted with an LI-190SB quantum
sensor. Plants in the chambers received an average daily PPF integral of
16 2 mol mÿ2 on a clear day.
Spectral distribution in 10 nm increments from 330 to 1100 nm was measured
at the middle of each chamber with a LI-1800 spectroradiometer ®tted with a LI1800-10 remote cosine sensor at the beginning and end of the experiments. The
cheesecloth did not alter the quality of light transmitted. Multiple light scans
within a chamber indicated that the spectral distribution was uniform inside the
chamber. The R:FR ratio was determined as the ratio of photon ¯ux density
between 600 and 700 nm (R) and 700 and 800 nm (FR). fc was estimated as
described by Sager et al. (1988).
2.2. Plant material and culture
Fifty uniformly rooted `Bright Golden Anne' chrysanthemum shoot cuttings
with six to seven leaves were planted individually in 0.6 l square pots containing
a commercial potting mix (Metro Mix-360, Scotts-Sierra Horticultural Products,
Marysville, OH). Plants were allowed to establish as single stem plants in the
greenhouse for 1 week before transferring to the experimental chambers. Bell
pepper `Capistrano' seeds were sown in 98-cell plug trays containing the same
potting mix and germinated under an intermittent mist. When cotyledons were
fully expanded, 50 seedlings were transplanted individually in 0.6 l square pots
and allowed to establish for 1 week. After 1 week establishment, chrysanthemum
and bell pepper plants (10 plants of each experiment per treatment) were
transferred to experimental chambers and were grown for 4 weeks. When
treatment was initiated, chrysanthemum and bell pepper plants were 7.0 and
1.5 cm tall, respectively. All plants were irrigated with 200 mg lÿ1 N from 20 N±
4.4 P±16.7 K fertilizer (Peter's 20-10-20 Peat-lite special, Scotts-Sierra Horticultural Products) as needed. Daily maximum and minimum air temperatures
inside chambers were recorded during the experiment. Average daily maximum
or minimum temperatures during experimental period was not different among
chambers and were 28 2 and 22 28C, respectively.
2.3. Experimental design, data collection and analyses
Experimental chambers were randomly placed inside the glasshouse. Because
of the limited number of chambers, experiments were repeated to replicate
(September±November 1997). In each replicate, 10 plants were grown for each
crop. Plants were randomly placed with approximate spacing of 18 18 cm.
Plant height (height from soil level to apex) and the number of fully expanded
leaves were recorded weekly. Average internode length was calculated as plant
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
219
height divided by number of leaves. Total leaf area (LI-3100 Area Meter, Lincoln,
NE) and dry weights of stems and leaves were measured at the end of the 4-weektreatment. For dry weight measurements, tissue was oven dried at 858C for 48±
72 h. Data were analyzed using analysis of variance procedure (SAS institute,
Cary, NC) and differences among treatment means were tested by Duncan's
multiple range test at P 0.05.
3. Results and discussion
3.1. Light quality
Spectral distribution curves of light transmitted through unshaded photoselective ®lms are shown in Fig. 1. The dye in YCE-1 photoselective ®lms
intercepted FR wavelengths of sunlight with maximum interception at 760 nm.
The interception of FR wavelengths increased as the dye concentration increased.
In contrast, CuSO4 ®lter intercepted almost all wavelengths beyond 700 nm
Fig. 1. Photon distribution of light transmitted through photoselective ®lms. BCE-1 is the control
®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light absorbing dye at 0.08,
0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels ®lled with 4%
CuSO45H2O liquid.
220
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
Table 1
R:FR ratios and estimated fc of light transmitted through photoselective ®lms and liquid CuSO4
®ltera
Treatmentb
R:FR ratio
fc
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
4% CuSO4
1.1
1.6
2.3
3.7
3.6
0.72
0.75
0.78
0.81
0.80
a
R 600±700 nm; FR 700±800 nm.
BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light
absorbing dye at 0.08, 0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels
®lled with 4% CuSO45H2O liquid.
b
(capacity of the spectroradiometer was 330±1100 nm). The CuSO4 chamber had
more blue and less R light than photoselective ®lm chambers. The R:FR ratio
increased from 1.1 to 3.7 and estimated fc increased from 0.72 to 0.81 as the dye
concentration in ®lms increased (Table 1). The R:FR ratio and fc of transmitted
light did not change during the experiment (data not shown).
3.2. Plant growth under photoselective ®lms
Photoselective ®lms reduced height of chrysanthemum plants and bell pepper
seedlings (Fig. 2). The height reduction by ®lms increased as the dye
concentration increased. For example, the ®nal height of chrysanthemum plants
was reduced to 11, 19 and 22% inside YCE-1 #80, #75, and #65 chambers (lowest
to highest R:FR ratio or fc), respectively, compared to control plants. A similar
trend was observed in bell pepper height reduction. Both chrysanthemum and bell
pepper plants grown in CuSO4 chamber were the shortest, but they were not
signi®cantly different from plants grown in YCE-1 #65 chamber, indicating that
®lms with highest dye concentration (tested here) were as effective as CuSO4
®lter. Our results are in agreement with Murakami et al. (1995, 1996a,b) who
reported a reduction of plant height of cucumber (Cucumis sativus L.), tomato
(Lycopersicon esculentum Mill.), and sun¯ower (Helianthus annuus L.) under FR
light intercepting ®lters. Similar to ®ndings of Morgan and Smith (1976), height
of chrysanthemum and pepper plants were inversely proportional to the fc.
Although the R:FR ratio and fc were similar in YCE-1 #65 and CuSO4 chambers,
plants grown in CuSO4 chamber were slightly shorter than those grown in YCE-1
#65 chamber (Fig. 2). This may be explained by the fact that CuSO4 chamber had
more blue wavelengths compared to photoselective ®lms. Blue light has been
shown to reduce plant height (Adamse et al., 1988; Warpeha and Kaufman,
1989). In addition to the blue light, CuSO4 ®lters also removed almost all of FR
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
221
Fig. 2. Weekly height increase of chrysanthemum and bell pepper seedlings grown in different
photoselective ®lm chambers. Vertical bars indicate standard error. Each point is the mean of 20
plants. BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR
absorbing dye at 0.08, 0.13 and 0.22 g mÿ2, respectively. CuSO4 is the chamber covered with panels
®lled with 4% CuSO45H2O liquid. Plants in all treatment chambers received the same amount of
PPF.
wavelengths whereas photoselective ®lm let some FR wavelengths into the
chamber. Therefore, it is dif®cult to compare the role of each wavelength band on
height control by ®lms and CuSO4 ®lters.
The effectiveness of ®lms also varied with species. Final height of
chrysanthemum was reduced 22% by YCE-1 #65 ®lm whereas that of bell
peppers was reduced 35% by the YCE-1 #65 ®lm, suggesting that bell pepper
seedlings were more responsive to ®ltered light than the chrysanthemum plants.
222
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
The difference in responsiveness could be due to the stage of development of
plants when they were exposed to photoselective ®lms. Bell pepper seedlings
only had one or two true leaves when they were placed in photoselective ®lm
chambers whereas chrysanthemum cuttings had six to seven leaves when they
were placed in the chambers.
The dye concentration in ®lms in¯uenced the time it takes for plants to respond
to altered light environment (Fig. 2). Height reduction in chrysanthemum was
observed after 1 week exposure to YCE-1 #65 compared to 2 weeks in YCE-1
#75 and 3 weeks in YCE-1 #80 chambers. A similar pattern was observed for bell
pepper seedlings, but they responded sooner; height reduction was achieved
under YCE-1 #80 ®lm after 2 weeks of exposure. Average internode length
followed a pattern similar to height reduction (data not shown). Number of leaves
was not signi®cantly affected by the photoselective ®lms (data not shown),
indicating that height reduction was a result of internode length reduction, but not
due to the delay in stage of development.
Photoselective ®lms and CuSO4 ®lter reduced total leaf area and leaf size in
both chrysanthemums and bell peppers (Table 2). Chrysanthemums grown in
YCE-1 #65 and CuSO4 had smallest individual leaves and total leaf area. In
chrysanthemum, total leaf area or leaf size was not different between YCE-1 #80
or #75 chambers and the control chamber. However, in bell peppers total leaf area
of control plants was greater than plants grown in YCE-1 chambers. Reduction in
leaf size gives a compact appearance to the plant but can result in reduction of
photosynthetic area which further results in a reduction in dry matter
accumulation.
Total shoot dry weight of chrysanthemums and bell pepper seedlings decreased
progressively as the dye concentration in ®lms (R:FR ratio or fc) increased. Total
shoot dry weight of chrysanthemums and peppers grown in the CuSO4 and YCE1 #65 chamber was reduced over 40% (Table 2). Photoselective ®lms reduced leaf
and stem dry weights of chrysanthemum and bell pepper, but the stem dry weight
reduction was greater than the leaf dry weight reduction. Speci®c leaf dry weight
(SLDW, dry weight per unit leaf area) and speci®c stem dry weight (SSDW, dry
weight per unit length of stem) were reduced in plants grown inside
photoselective ®lms. Speci®c dry weight reduction increased as the dye
concentration increased. Reduction in speci®c dry weights indicates that dry
matter assimilation was affected by photoselective ®lms and that both small
plants and the reduction in dry matter assimilation may have contributed to the
reduction in total shoot dry weight.
The photoselective ®lms affected dry matter partitioning into leaves and stems
(Table 2). In chrysanthemums, plants grown in the control chamber had 66% of
total shoot dry matter in leaves and 34% in stems. Photoselective ®lms reduced
percentage dry matter accumulation in stems from 34 to 24% and increased dry
matter accumulation in leaves from 66 to 76%. Percentage dry matter
Table 2
In¯uence of photoselective ®lms on total leaf area (LA), average leaf size (LS), leaf dry weight (LDW), speci®c leaf dry weight (SLDW), stem dry
weight (SDW), speci®c stem dry weight (SSDW), and total shoot dry weight (TDW) of chrysanthemum and bell pepper seedlings
LA (cm2)
LS (cm2)
LDW (g)
SLDW
(g cmÿ2)
SDW (g)
SSDW
(g cmÿ1)
TDW (g)
Chrysanthemum
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
CuSO4
681ab
649a
630a
561b
522b
28a
28a
27a
24b
23b
2.96a (66)c
2.53b (71)
2.16c (73)
1.78d (76)
1.63d (79)
0.0044a
0.0039b
0.0034c
0.0032c
0.0031c
1.55a (34)
1.06b (29)
0.79c (27)
0.56d (24)
0.44e (21)
0.0431a
0.0332a
0.0271b
0.0213bc
0.0178c
4.51a
3.59b
2.95c
2.34cd
2.07d
Bell pepper
BCE-1
YCE-1 #80
YCE-1 #75
YCE-1 #65
CuSO4
555a
485b
430bc
417cd
378d
50a
49a
43b
42b
38c
1.96a (70)
1.76ab (72)
1.34bc (72)
1.20bc (73)
1.18c (77)
0.0034a
0.0036a
0.0031ab
0.0029b
0.0031ab
0.82a (30)
0.69b (28)
0.51c (28)
0.44cd (27)
0.35d (23)
0.0703a
0.0707a
0.0617b
0.0584bc
0.0497c
2.78a
2.45b
1.85c
1.64cd
1.53d
a
BCE-1 is the control ®lm. YCE-1 #80, #75, and #65 are photoselective ®lms with the FR light absorbing dye at 0.08, 0.13 and 0.22 g mÿ2,
respectively. CuSO4 is the chamber covered with panels ®lled with 4% CuSO45H2O liquid.
b
Each number is the mean of 20 plants. Mean comparison within a column by Duncan's multiple range test at P 0.05. Means with the same letter
are not signi®cantly different.
c
Numbers in parentheses are % dry weight.
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
Treatmenta
223
224
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
accumulation in leaves increased as the R:FR ratio increased. In peppers, plants
grown in the control chamber had 70% of total shoot dry matter in leaves and
30% in stems. Photoselective ®lms reduced percentage dry matter accumulation
in stems from 30 to 27% and increased dry matter accumulation in leaves from 70
to 73%. In both chrysanthemum and peppers, the greatest change in dry matter
partitioning was found in CuSO4 ®lter-grown-plants. Quality of light can
in¯uence the translocation of photosynthates. Hurd (1974) reported that light low
in R:FR ratio increased stem dry weight of tomato plants. Kasperbauer (1987)
reported that lowering R:FR ratio increased photosynthate partitioning into shoots
and developing seeds. The greater dry matter accumulation into leaves under
photoselective ®lms may be because of the relatively high R and low FR light in
these treatments. Britz and Sager (1990) reported that plants grown under blue
light de®cient sources had less translocation of photosynthate out of leaves, thus
increasing leaf dry matter content.
4. Conclusions
In summary, photoselective plastic ®lms with FR light intercepting dyes were
effective in regulating plant height of chrysanthemum and bell pepper plants
without the use of chemical growth regulators. The ®lm with the highest dye
concentration (used in this study) was as effective as 4% CuSO4 ®lters in
controlling plant height. Although ®lms with higher dye concentration are more
effective in height reduction, the reduction in PPF transmission with increased
dye concentration may adversely affect plant growth and development, and this
fact should be considered in commercial development of photoselective ®lms.
Our results indicate that a photoselective ®lm with a R:FR ratio of 2.2 (which
corresponds to 75% light transmission) caused about 20% height reduction in
chrysanthemum and 30% height reduction in bell pepper after 4 weeks of
treatment. This initial work demonstrates that the use of greenhouse ®lms with
FR light absorbing dyes is as effective as chemical growth regulators or CuSO4
®lters in controlling plant height of chrysanthemums and bell pepper seedlings.
With the commercial development of photoselective greenhouse covers or shade
material, nursery and greenhouse industry could reduce costs for growth
regulating chemicals, reduce health risks to their workers and consumers, and
reduce potential environmental pollution.
References
Adamse, P., Jaspers, P.A.P.M., Bakker, J.A., Wesselius, J.C., Heeringa, G.H., Kendrick, R.E.,
Koornneef, M., 1988. Photophysiology of tomato mutant de®cient in labile phytochrome. J. Plant
Physiol. 133, 436±440.
S. Li et al. / Scientia Horticulturae 84 (2000) 215±225
225
Britz, S.J., Sager, J.C., 1990. Photomorphogenesis and photoassimilation in soybean and sorghum
grown under broad spectrum or blue-de®cient light sources. Plant Physiol. 94, 448±454.
Hurd, R.G., 1974. The effect of an incandescent supplement on the growth of tomato plants in low
light. Ann. Bot. 38, 613±623.
Kasperbauer, M.J., 1987. Far-red light re¯ection from green leaves and effects on phytochromemediated assimilate partitioning under ®eld conditions. Plant Physiol. 85, 350±354.
McMahon, M.J., Kelly, J.W., Decoteau, D.R., Young, R.E., Pollock, R.K., 1991. Growth of
Dendranthema grandi¯orum (Ramat.) Kitamura under various spectral ®lters. J. Am. Soc.
Hort. Sci. 116, 950±954.
Morgan, D.C., Smith, H., 1976. Linear relationship between phytochrome photoequilibrium and
growth in plants under simulated natural radiation. Nature 262, 210±212.
Morgan, D.C., Smith, H., 1979. A systematic relationship between phytochrome-controlled
development and species habit, for plants grown in simulated natural radiation. Planta 145, 253±
258.
Mortensen, L.M., Strùmme, E., 1987. Effect of light quality on some greenhouse crops. Sci. Hort.
33, 27±36.
Murakami, K., Cui, H., Kiyota, M., Aiga, I., 1995. The design of special covering materials for
greenhouses to control plant elongation by changing spectral distribution of daylight. Acta Hort.
399, 135±142.
Murakami, K., Cui, H., Kiyota, M., Yamane, T., Aiga, I., 1996a. The effects of covering materials
for greenhouses to control plant growth by changing spectral distribution of daylight. Acta Hort.
435, 123±130.
Murakami, K., Cui, H., Kiyota, M., Takemura, Y., Oi, R., Aiga, I., 1996b. Covering materials to
control plant growth by modifying the spectral balance of daylight. Plasticulture 110, 2±14.
Protasova, N.N., Welles, J.M., Dobrovolskii, M.W., Tsoglin, L.N., 1990. Spectral characteristics of
light sources and plant growth peculiarities under arti®cial illumination. Soviet Plant Physiol.
37, 293±303.
Rajapakse, N.C., Kelly, J.W., 1992. Regulation of chrysanthemum growth by spectral ®lters. J. Am.
Soc. Hort. Sci. 117, 481±485.
Sager, J.C., Smith, W.O., Edwards, J.C., Cyr, K.L., 1988. Photosynthetic ef®ciency and
phytochrome photoequilibria determination using spectral data. Trans. ASAE 31, 1882±1887.
Warpeha, K.M., Kaufman, L.S., 1989. Blue-light regulation of epicotyl elongation in Pisum sativus.
Plant Physiol. 89, 544±548.