Glass & Kadir
Honors Project, 2005
EVALUATION OF ANTI-TRANSPIRATION ORGANIC MATERIALS ON
STRAWBERRY PLANTS UNDER HIGH TEMPERATURES
Ben Glass1 and Sorkel Kadir2
1
2
Agronomy Department
Horticulture, Forestry, and Recreation Resources Department
Kansas State University
Honors Project, 2005
ABSTRACT
Strawberry production is increasing in Kansas, but is limited by the high temperatures experienced during
the growing season. Heat stress disrupts photosystem II of photosynthesis by increasing plant metabolic
reaction rates and decreasing water availability. The use of Surround is common in many horticultural
crops to enhance fruit color and finishing and control pests. Surround, a kaolin clay, and Raynox, a
natural wax, block harmful radiation from disrupting the photosynthetic cycle. Two strawberry cultivars
(Fragaria x ananassa, Duch) ‘Chandler’ and ‘Sweet Charlie,’ were grown in 20/15 ºC ± 1, 30/25 ºC ± 1,
and 40/35 ºC ± 1 temperatures and 16/8 D/N photoperiods with three replications of each of the three
treatments. Fluorescence and photosynthetic measurements were taken weekly for six weeks. Flowering
and fruiting notes were taken as needed. Leaf area, leaf, shoot, and root dry weight were taken at the end
of the experiment. Cultivar differences were not significant except for the flowering and fruiting data.
Data from the 30/25 ºC chamber was not a significant influence on plant growth and development. Plant
biomass was greater in plants in 40/35 ºC chamber when treated with Raynox than with Surround or in
the control treatment. Raynox significantly protected photosynthesis in plants exposed to 40/35 ºC longer
than either Surround or the control treatment. Flower and fruit number were greater in the 20/15 ºC and
the fruit was larger. Raynox kept plants cooler allowing carbohydrate reserves to build for further plant
development.
INTRODUCTION
Traditionally, Kansas agriculture has been based on commodity crops such as wheat, corn,
sorghum, and soybeans. These crops are no longer providing enough income for many farmers so many
are seeking alternative crops, such as strawberries, to diversify their operation. Strawberry plants in
Kansas are annually subjected to high temperatures, which is one of the primary limiting factors to
strawberry production.
Heat stress causes irreversible damage to plant function and development. Heat stressed crops
exhibit decreased photosynthesis, increased fruit drop, loss of cell turgor pressure, metabolic disruption,
build up of toxins, canopy collapse and tissue death (Engelhard, 2002). High temperatures can increase
the rate of reproductive development, shortening the time for photosynthesis to contribute to fruit or seed
production (Hall, 2005). Wheat plants can be injured at seedling emergence, reproductive development,
stem elongation, heading, and flowering by high temperatures that exceed 90 °F for a specific period of
time. High temperatures cause a decline in photosynthesis and increase of plant respiration. During heat
stress and high respiration rates, carbohydrate reserves are consumed because the plant cannot supply the
necessary energy, which results in a loss of plant growth. Under controlled environmental conditions,
mean grain weight declined by 16% for each 5 °C increase in temperature in wheat (Asana, R.D. and
Williams, R.F., 1965).
Heat stress causes water loss resulting in a reduction in photosynthetic rate, leaf area and delay of
leaf growth and development (McCarthy, 2005). Increase in temperature increases plant metabolic
reaction rates and decreases water availability, which is essential for photosynthetic reactions. Heat stress
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Honors Project, 2005
is often associated with decreased membrane and protein integrity, and an increase in the root to shoot
ratio. Stomatal conductance is reduced causing an increase in leaf temperature due to a decrease in water
vapor exchange.
Photosystem II is the most sensitive process to high temperatures, especially the water splitting
complex which affects the electron transport system (Hopkins, 1999). Chlorophyll fluorescence increases
under high temperature due to damage to photosystem II and deactivation of important enzymes.
Heat stress can be alleviated through several cultural practices. Plants should be kept well watered,
encourage the development of the crop earlier in the season before temperatures rise, enhance deep
rooting, selecting more heat resistant cultivars, and use growth regulators (Xiaozhong Liu and Bingru
Huang, 2005). In addition, the use of high tunnels for shade and protection from drying winds may be
beneficial as well as evaporative cooling systems. Recently, ‘Surround WP’ and ‘Raynox’ have been
reported to alleviate heat stress on fruit crops.
Surround, an organic product composed of modified kaolin clay (Engelhard Corporation of Iselin,
New Jersey) has widespread use in horticultural production. It is has been widely used in apples and
pears to enhance fruit color and finishing, control pests like pear psylla, leafhoppers/sharpshooters, thrips,
rose chafer, Japanese beetle, and apple and blueberry maggot. Surround, an inert, wettable powder, can
be applied with standard commercial sprayers, hand-held sprayers, and backpack sprayers. The particles
form a barrier film that can reflect radiation and cool the canopy. This barrier allows photosynthetically
active radiation (PAR) through the film while largely blocking or reflecting harmful infrared and
ultraviolet radiation that can cause sunburn damage and heat stress. Surround must be applied prior to
high temperatures and thorough coverage of the plant must be maintained for optimum efficacy. Spray
intervals are generally from 5 to 14 days.
Raynox is another organic material made from a waxy emulsion (natural wax) containing an
organically modified clay. Raynox blocks part of the damaging UV-B radiation and reduces fruit surface
temperatures too.
This experiment was conducted to evaluate the efficacy of Surround and Raynox for alleviation
of heat stressed strawberry cultivars under controlled environmental conditions.
MATERIALS AND METHODS
Plant Materials
The experiments were conducted during 2004 and 2005 at the Department of Horticulture,
Forestry, and Recreation Resources, Kansas State University, Manhattan, Kansas. Two strawberries
(Fragaria x ananassa, Duch) ‘Chandler’ and ‘Sweet Charlie,’ were selected for this study. Daughter
plants were taken from the mother plants already growing in the greenhouse under 23/18º (C) day/night
(D/N) temperatures with 10/14 h photoperiod (200 µmole m-2 s-1). Plants were grown individually in
1:1:1 (by volume) of sand:peat:soil mix in polyethylene pots (16.25 x 16.25 x 12.5 cm). Plants were
irrigated as needed and fertilized weekly with a commercial fertilizer containing 300 µgL-1 nitrogen, 250
µgL-1 phosphorus, and 220 µgL-1 potassium. After growing 5 weeks in the greenhouse plants were
sprayed with Surround at the rate of 1 pound/2 gallons and Raynox at the rate of 2.5 gallons/acre plus a
softener at 7 ounces/50 gallons until the material dripped off the leaves. Plants were allowed to dry for
twenty four hours before transferring to three growth chambers (Control Environments LTD Conviron
CMP 3244 growth chambers, Winnipeg, Manitoba Canada) set at 20/15 ºC ± 1, 30/25 ºC ± 1, and
40/35 ºC ± 1 temperatures and 16/8 D/N photoperiods. Light intensity was 450 µmolm-2 s-1 PAR
measured with LI-188 B Integrating Quantum/Radiometer/Photometer and LI-1905 sensor, Li-Cor, Inc,
Lincoln, Nebraska, USA. Humidity was not controlled but was monitored to be in the range of 40% ± 10
during the day and 70% ± 10 relative humidity during the night. All plants were checked daily and
watered as needed to prevent secondary injury due to desiccation.
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Honors Project, 2005
Plant Measurements
Chlorophyll fluorescence was measured weekly using the Hansatech Instruments LTD
Fluorescence Monitoring System, Kings Lynn, England. Data expressed as initial fluorescence (Fo),
variable fluorescence (Fv), and maximum quantum efficiency of photosystem II (Fv/Fm). Photosynthesis
was measured weekly with the Li-Cor Inc. LI 6400 Portable Photosynthesis System Lincoln, Nebraska,
USA. Data expressed as photosynthetic rate (Pn), stomata conductance (gs) and transpiration (E). Leaf
area was measured; leaf, shoot, and root dry weight were determined at the end of the experiment after
drying the tissues for three days in Precision Scientific Thelco dryers at 60-70º C. Flower number, date of
flowering, fruit weight, and number of fruits were taken daily or as needed.
Experimental Design
The experiment was a completely randomized factorial arrangement with two cultivars x three
treatments x three temperatures with three replications. The study was conducted in September of 2004
and repeated in January of 2005. Data was analyzed using standard analysis of variance (ANOVA).
Differences among means were tested by Fisher’s protected least significant difference (LSD) (p=0.05)
(Snedcor and Cochran, 1967).
RESULTS AND DISCUSSION
Leaf Area (cm2)
There was not significant differences between the cultivars, except with the fruit and flowering
data since ‘Sweet Charlie’ produces earlier than ‘Chandler.’ Figures 1-4 show that plants treated with
Raynox had significantly more plant growth and mass than those with the other treatments. Plants not
treated with Raynox died in the 40/35 ºC. This is eflected by the leaf area and leaf dry weight data.
Although plants protected by Surround had significantly more shoot dry weight in the 40 ºC chamber,
Raynox provided appreciably better protection. Surround was not significantly better than control
treatment in either the 20 ºC or 30 ºC chamber. Root dry weight of Surround and Raynox were not
significantly different in the 20 ºC chamber, but was in the 40 ºC.
700
600
500
400
300
200
100
0
Raynox
Control
Surround
LSD=1.1
LSD=78
20
30
40
Temperature (C)
Figure 1. Effect of Raynox and Surround compared to the control on total leaf area of strawberry plants
exposed to 20/15 ºC, 30/25º C, and 40/35º C for 6 weeks.
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Honors Project, 2005
5
Shoot Dry Weight (g)
Raynox
4
Control
Surround
LSD=1.1
3
LSD=1.07
2
1
0
20
30
40
Temperature (C)
Figure 2. Effect of Raynox and Surround compared to the control on total shoot dry weight of strawberry
plants exposed to 20/15 ºC, 30/25º C, and 40/35º C for 6 weeks.
6
Leaf Dry Weight (g)
Raynox
5
Control
4
Surround
LSD=1.1
3
2
LSD=1.5
1
0
20
30
40
Temperature (C)
Figure 3. Effect of Raynox and Surround compared to the control on total leaf dry weight of strawberry
plants exposed to 20/15 ºC, 30/25º C, and 40/35º C for 6 weeks.
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Honors Project, 2005
6
Root Dry Weight (g)
Raynox
5
Control
Surround
LSD=1.1
4
LSD=1.1
3
2
1
0
20
30
40
Temperature (C)
Figure 4. Comparison Effect of Raynox and Surround compared to the control on total root dry weight of
strawberry plants exposed to 20/15 ºC, 30/25º C, and 40/35º C for 6 weeks.
Surround might have blocked light for photosynthesis causing a lower photosynthetic rate in the
20 ºC chamber. There was significant difference between all three treatments in the 40 ºC by week three.
At week 5 the control was significantly higher than either Surround or Raynox probably due to the
cooling effect and decrease in transpiration caused by the two materials on the leaves. The control
treatment is good for 3 weeks, Surround 4 weeks, and Raynox 5 weeks for the protection of the
photosynthetic cycle. By the end of 6 weeks Raynox treated plants were the only plants still continuing
photosynthesis.
Photosynthesis
(umole CO2 m-2 s-1)
Photosynthesis
(umole CO2 m-2 s-1)
20
LSD=1.1
18
16
14
12
10
Surround
8
Raynox
6
Control
LSD=1.1
4
2
0
1
2
3
4
10
8
6
4
2
0
1
5
2
3
4
5
Week
Week
Figure 5. Effect of Raynox and Surround compared to the control on the photosynthetic rate of
strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.
When PSII is disrupted, a plants water efficiency (WUE) decreases. In the 20 ºC Surround and
Raynox may have interfered with optimum WUE by decreasing transpiration, but it is significant in the
40 º(C) that Raynox improved water efficiency. Raynox kept the plants from desiccating allowing
photosynthesis to continue.
5
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Water Use Efficiency
(mole CO2/mole H2O)
Water Use Efficiency
(mole CO2/mole H2O)
Glass & Kadir
Honors Project, 2005
Raynox
Surround
Control
LSD=0.1
LSD=0.1
1
2
3
4
0.3
0.25
0.2
0.15
0.1
0.05
0
1
5
2
3
4
5
Week
Week
Figure 6. Effect of Raynox and Surround compared to the control on the water use efficiency of
strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.(WUE= PS/E)
0.84
0.82
0.8
0.78
0.76
0.74
0.72
0.7
0.68
0.66
Control
1
Raynox
0.8
Surround
LSD=0.06
Fv/Fm
Fv/Fm
The damage to PSII causes initial fluorescence to increase. The significance of treatment with
Raynox is evident in the 40 ºC where Raynox protected the plant photosynthetic system the most over the
experiment. Both Surround and Raynox kept the plants cooler, but Raynox kept them significantly cooler
for four weeks longer than Surround. The plants in the 40 ºC remained green indicating PSII was less
disrupted than in the other treatments and corresponds with photosynthesis (Figure 5).
0.6
0.4
0.2
LSD=0.06
0
1
2
3
Week
4
5
0
0
6
1
2
3
4
5
6
Week
Figure 7. Effect of Raynox and Surround compared to the control on photosystem II (Fv/Fm) of
strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.
Significance between cultivars occurs in flower number, fruit number, and weight of fruit
collected. The 20 º(C) seemed more conducive towards flower development. Raynox protects the
vegetation allowing enough carbohydrate reserves to form flowers even under heat stress. ‘Sweet
Charlie’ produced earlier than ‘Chandler’ due to cultivar differences. By producing earlier it also escaped
some heat stress that may have inhibited ‘Chandler.’ More flowers were produced than formed fruit. The
number of fruit produced by Raynox treated ‘Sweet Charlie’ growing in the 20 ºC chamber was
significantly higher than either Surround or control treated plants in the same temperature.
6
Chandler
Sweet Charlie
Chandler
Treatment
Surround
Raynox
Control
Surround
Raynox
18
16
14
12
10
8
6
4
2
0
Control
Surround
Raynox
Control
Surround
Raynox
LSD=1.5
Control
Number of Flowers
18
16
14
12
10
8
6
4
2
0
Number of Flowers
Glass & Kadir
Honors Project, 2005
Sweet Charlie
Treatment
Chandler
Sweet Charlie
Chandler
Treatment
Surround
Raynox
Control
Control
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Surround
Number of Fruit
Surround
Raynox
Control
Surround
Raynox
LSD=2.3
Raynox
14
12
10
8
6
4
2
0
Control
Number of Fruit
Figure 9. Effect of Raynox and Surround compared to the control on flower number of
‘Chandler’ and ‘Sweet Charlie’ strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.
Sweet Charlie
Treatment
Figure 10. Effect of Raynox and Surround compared to the control on fruit number of
‘Chandler’ and ‘Sweet Charlie’ strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.
6
6
5
4
3
2
1
0
LSD=0.7
5
Surround
Weight (g)
Chandler
Raynox
Control
Surround
Raynox
Control
Weight (g)
Larger fruit were produced in the 20 ºC. The plants in 30 ºC started fruiting first, producing
smaller fruit. The fruit in the 40 ºC was produced early in the experiment, however they desiccated
before they ripened. ‘Sweet Charlie’ is an earlier producer, so it produced before being exposed to as
much stress as ‘Chandler,’ however, the berry that was picked is not within significance.
4
3
2
1
0
Control Raynox Surround Control Raynox Surround
Chandler
Sweet Charlie
Treatment
Sweet Charlie
Treatment
Figure 11. Effect of Raynox and Surround compared to the control on fruit weight of
‘Chandler’ and ‘Sweet Charlie’ strawberry plants exposed to 20/15 ºC and 40/35 ºC for 6 weeks.
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Honors Project, 2005
The data is an average between the two cultivars (Figures 1-10). Data for the 30/25 ºC is not
because it is not a significant influence on plant growth and development. Raynox provides protection to
strawberry plants exposed to high temperatures. Photosynthesis (Figure 5) remains active and PSII
(Fv/Fm) (Figure 8) is more efficient with less disruption than in the control or Surround treatments. Use
of Raynox results in higher shoot biomass (Figure 2) and root biomass (Figure 4) than either the control
or the Surround treatments. Raynox or Surround would be an option to use when a short period of high
temperature is predicted.
References
Agriculture Notes. 2001. ‘Clay instead of pesticides?’ U.S. Environmental Protection Agency. Issue 65.
<http://notes.tetratechffx.com/newsnotes.nsf/0/aa1073157a18c6e985256a700058af19?OpenDocument>
Asana, R.D. and Williams, R.F. 1965. The effect of temperature stress on grain development in wheat.
Aust. J. Agric. Res. 16: 1-13
Engelhard Corporation. 2002. Surround product information. 2002. <www.engelhard.com/surround>
Hall, A. E. 2005. ‘Heat stress and its impact.’ University of California. Plantstress.com.
<http://www.plantstress.com/Articles/heat_i/heat_i.htm>
Hopkins, W.G. 1999. Introduction to plant physiology. 2nd Ed. John Wiley & Sons Ltd. West Sussex,
England.
Liu, X. and Huang, B. 2002. ‘Cytokinin effects on creeping bentgrass response to heat stress.’
Crop Science 42:466-472. <http://crop.scijournals.org/cgi/content/full/42/2/466>
McCarthy, H. ‘Environmental stress.’ Duke University: Nicholas School of the Environment
and Earth Sciences. <http://www.biology.duke.edu/bio265/hrm/growth.html>
Snedecor and Cochran. Statistical Methods. 6th ed. 1967. Iowa State University Press. Ames, Iowa.
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