Interaction effects of paclobutrazol and salinity on
photosynthesis and vegetative growth of strawberry
plants
S. Jamalian¹, A. Tehranifar¹, E. Tafazoli², G. H. Davarynejad¹,
S.Eshghi²
¹Horticulture Department, College of Agriculture, Ferdowsi University of Mashad,Mashad, Iran
²Horticulture Department, College of Agriculture, Shiraz University, Shiraz, Iran
Abstract
Strawberry plants (Fragaria × ananassa Duch) are very susceptible to
salinity. To investigate the interaction effects of paclobutrazol (PP333) and
salinity on gas exchange parameters and growth factors of the plant, 3
levels of NaCl [0,5,10 mM], incorporated into the nutrient solution and 4
levels of PP333 [0,10,20,30 mg/L], were applied by spraying. Both salinity
and PP333 reduced leaf area. Highest level of PP333 reduced shoot dry
weight. 20 mg/L of PP333 could overcome the detrimental effect of salinity
in root dry weight and total dry weight. PP333 also could mitigate some
reducing effects of high salinity in photosynthetic rate (A), water use
efficiency, relative water content and chlorophyll content. Both salinity
and PP333
have caused reduction in stomatal conductance (gs),
transpiration rate (E), number of runners and petiole length. Specific leaf
weight was increased by both salinity and PP333.
1
Keywords: Paclobutrazol; Salinity; Strawberry; Growth; Photosynthetic
rate
1. Introduction
Since strawberry plants are very sensitive to saline conditions, therefore
the reduction of salt stress in the greenhouse using hydroponic systems, is
needed. The most common practice is to increase leaching, however this
method sometimes is expensive and impractical. Few studies have focused
on application of growth regulators to induce tolerance. There is a report
that paclobutrazol (PP333), a gibberelline biosynthesis inhibitor, promoted
salt stress avoidance in peach (Prunus persica L.)(Abou El-Khashab et al.,
1997). PP333 has also been shown to reduce the symptoms and mortality
due to salt stress in Rhamnus alternus seedlings (Banon et al., 2003). PP333
also modulated salt induced alternations in pigment content, proline level,
lipid peroxidation and antioxidant activity in leaves of zuzuba seedlings
(Fletcher et al., 2000). Studies have also been undertaken to investigate
the effect of paclobutrazol and uniconazol (Another gibberelline
biosynthesis inhibitor), on cold hardiness and endogenous ABA levels in
Actinidia arguta during a dormancy cycle (Tafazoli and Beyl, 1993).
Similarly paclobutrazol treatments has reduced chilling injury and
responses to the cold stress in tomato seedlings(Lycopersicum esculentum
2
L.)(Jaafari et al., 2006). These results imply that using growth regulators
such as triazols may be an effective way of improving plant stress
tolerance. The aim of this study was to determine the effect of PP333 on
salt tolerance in strawberry plants under hydroponic conditions.
2. Materials and Methods
2.1. Plant material and growing conditions
Cold stored rooted runner strawberry plants (Fragaria × ananassa
Duch.) of ‘Selva’cultivar were planted in 2 L containers filled with a
mixture of perlite and peatmoss. Plants were fed continuously from the
start of the experiment with nutrient solution (Melspray). Sodium Chloride
(NaCl) was incorporated into the nutrient solution. Three levels of Nacl [
0, 5, 10 mM ] and four levels of PP333 [0, 10, 20, 30 mg/L] were imposed
at the beggining of the experiment.A hand sprayer was used to apply
PP333 to the point of runoff.The design of the experiment was a complete
randomized with five replications and twelve treatments.
2.2. Gas exchange parameters
Photosynthetic rate (A), transpiration rate (E) and stomatal conductance
(gs) were measured two times (two and ten weeks after the start of the
3
experiment), using LCi portable photosynthesis meter. (INSTRUCTION
MANUAL , L . MAN-LCI). Water use efficiency (WUE) was calculated
as A/E. The youngest fully expanded middle leaflet was selected for
measurment on each occasion.
2.3. Relative water content (RWC)
For each replication four discs of leaf tissue (1 cm in diameter) were
weighed, floated on distilled water for four hours to become fully turgid,
weighed, dried at 70°C and then weighed again.The relative water content
was calculated as:
% RWC = [(Fresh mass-Dry mass)/Turgid mass-Dry mass)] ×100
2.4. Vegetative Growth Parameters
Leaf samples were randomly collected and mean leaf area was measured
using a leaf area meter (Delta-T Devices , England).Shoot and root dry
weight was recorded after gently washing and ovendrying at 70°C for 72
hours.To determine specific leaf weight (SLW), ten leaf discs from each
replication were prepared, then oven dried for 48 hours. After which, dry
weight of discs was calculated. Dry weight/area was determined as SLW .
4
Chlorophyll content was measured by a chlorophyll meter. (SPAD-502.
Minolta Co.Ltd). Number of runners and petiole length were also counted
and measured throughout the period of experiment.
2.5. Statistical analyses
Data were analyzed using MSTATC software and means were compared
by Duncan’s test. The 5% probability level was accepted to indicate
significance.
3. Results and Discussion
3.1. Growth analysis
Leaf area was reduced by both salinity and PP333. The interaction of the
highest level of salinity and PP333 resulted in lowest leaf area (Table 1).
Reduced leaf area in sweet orange by PP333 (Joseph and Yelenosky, 1992)
and in strawberry cultivars ‘Elsanta’ and ‘Korona’ (Saied et al., 2005),
two pepper cultivars (Chartzoulakis and Klapaki, 2000), tomatoes and
melons (del Amor, 2000), greenhouse cucumber (Chartzoulakis, 1992), by
salinity has also been reported. Shoot dry weight was increased with
increased salinity and PP333 up to 5 mM and 20 mg/lit respectively.
However higher level of PP333 (30mg/L), reduced it (Table 2). But it has
5
been reported that high salinity reduced shoot dry weight of celery (De
Pascale, 2003) Highest level of salinity reduced root dry weight. Similar
result was shown in two pepper cultivars (Chartzoulakis, 2000).
Interaction of these two factors reveals that 20mg/L PP333 could overcome
partially the reduced effect of salinity (Table 3). Similar trend can be seen
in total dry weight (Data not shown). Also decrease in plant dry weight by
salinity has been shown in some other strawberry cultivars (Kepenek and
Koyuncu, 2002a).
3.2. Gas exchange parameters
Photosynthetic rate (A) was significantly reduced by salinity.Similar
result was observed in ‘Korona’ cultivar of strawberry (Saied et al., 2003).
However PP333 increased it especially at highest level of salinity (Table 4).
Increased of A by PP333 on apple has been reported by Huang et al.
(1995). Salinity stress in reducing A in tomato and potato is documented
(del Amor., 2000). PP333 has been reported to increase A in peach cuttings
treated with NaCl (Abou El-Khashab., 1996). Both PP333 and salinity have
caused reduction in stomatal conductance (gs) (Table 5). Transpiration
rate (E) was also not to be reduced significantly with increased
concentration of PP333 in saline treated plant. Lowest E was associated
with highest level of PP333 and NaCl (Table6).
6
3.3. Water use efficiency and relative water content
Salinity reduced WUE and RWC. However PP333 could overcome these
reductions (Table 7 and 8). It has also been reported that increasing
salinity adversely affected WUE in tomato (Al-Karaki, 2000). Salinity did
not affect RWC in peach, although PP333 application increased RWC in
high salinity (Abou El-Khashab et al., 1997). But in Rhamnus alternus
seedlings, salinity reduced RWC (Banon et al., 2003).
3.4. Specific leaf weight and chlorophyll content
Specific leaf weight was increased by both salinity and PP333 and the
interaction was significant (Table 9). Though salinity reduced chlorophyll
content of the leaves, however PP333 reduced this reduction rate(Table 10).
Reduced chlorophyll content due to salinity has been reported in pepper
(Gunes et al., 1996) and strawberry cultivars, ‘Oso Grande’ and
‘Camarosa’ (Kaya et al., 2002) and in Althernanthera Philoxerioides
(Longstrethetal., 1984).
3.5. Number of runners and petiole length
7
Both PP333 and salinity reduced the number of runners and petiole length
(Table 11 and 12). Similar results about number of runners has been
reported by Kepenek and Koyuncu (2002b) and Beech et al., (1988).
4. Conclusion
In general, it can be concluded that PP333 reduced the stress effect of
salinity. Probably through production of some special organic compounds
in the cells. To some extent plants are naturaly capable of withstanding
stresses and PP333 increases the potentials. Moreover PP333 reduces
membrane permeability and increase antioxidant enzyme activity, which
is defence mechanism (Banon et al., 2003). Reduction in undesirable ions
in the cell due to use of PP333 will result in better growth and development
of the plant (Abou-El Khashab, 1997).It might be possible that PP333
caused changes in the photosynthetic activity of chloroplasts. The
reduction in leaf area was corrected by the thicker leaves and the increase
of their photosynthetic capacity (Christov et al., 1995).
References
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Rieger,
M.,1997.
Paclobutrazol
8
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263-268.
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Christv, Ch., Tsvetkov, I., Kovachev, V., 1995. Use of paclobutrazol to
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growth and yield of greenhouse cucumber. J. Hort. Sci. 67 (1) 115-119.
Chartzoulakis, K.S., Klapaki,G., 2000. Effects of NaCl salinity on growth
and yield of two pePPer cultivars. Acta. Hort.511, 143-149.
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graveolens L.var dulce (Mill.) Pers] under saline irrigation. J. Amer.
Soc. Hort. Sci. 128 (1), 136-143.
9
del Amor, F.M., Martinez V., Gerda, A., 2000.Gas exchange,water
relations and ion concentrations of salt stressed tomato and melon
plants. J. Plant Nut. 23 (4), 1315-1325.
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resistance, proline and mineral composition of pepper. J. Plant Nut. 19
(2), 384-396.
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paclobutrazol on photosynthesis rate and dry matter partitioning in the
aPPle tree. J. Plant Nut. 18 (5), 901-910.
Joseph, C.V., Yelenosky, G., 1992. Growth and photosynthesis of sweet
orange plants treated with paclobutrazol. J. Plant Growth Regul. 11, 8589.
Kaya, C., Kirnak, H., Higgs, D., Saltali, K., 2002. Supplementary calcium
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high (NaCl) salinity. Sci. Hort. 93, 65-74.
Kepenek, K., Koyuncu, F., 2002a. Studies on salt tolerance of some
strawberry cultivars under glasshouse. Acta. Hort. 573, 297-301.
Kepenek, K., Koyuncu, F., 2002b. Effects of salt on expression of
resistance in some domestic and foreign strawberry cultivars. Acta Hort.
573, 289-303.
10
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photosynthesis and growth in [Alternanthera philoxeroides (Mart.)
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growth, photosynthesis and ionic contents of strawberry cultivars
‘Elsanta’ and ‘Korona’. Acta Hort. 609, 67-73.
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on growth, yield and fruit quality of strawberry cultivars ‘Elsanta’ and
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11
Table 1
The effect of NaCl and PP333 treatments on strawberry leaf area (cm²)
Salinity (mM)
PP333 (mg/L)
0
5
10
53.03 b
50.33 b
Mean
0
59.27 a*
54.21 A
10
44.47 c
42.22 cd
43.17 c
43.29 B
20
43.70 c
40.39 cd
36.25 e
4 0.11 C
30
41.98 cd
38.66 de
31.96 f
37.53 D
Mean
47.35 A
43.58 B
40.43 C
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
12
Table 2
The effect of NaCl and PP333 treatments on shoot dry weight of strawberry plants (g/plant)
Salinity (mM)
PP333 (mg/L)
0
5
10
17.80 de
14.82 e
Mean
0
38.11 a *
23.58 A
10
25.27 c
24.43 c
26.45 c
25.38 A
20
18.96 d
30.02 b
23.39 c
24.12 A
30
16.09 de
17.04 de
17.08 de
16.74 B
Mean
24.61 A
22.32 B
20.43 C
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
13
Table 3
The effect of NaCl and PP333 treatments on root dry weight of strawberry plants (g/plant)
Salinity (mM)
PP333 (mg/L)
0
5
10
Mean
0
21.37 b*
11.14 f
9.84 f
14.12 C
10
20.36 bc
18.40 cd
16.02 de
18.26 A
20
10.71 f
24.20 a
14.47 e
16.46 B
30
20.64 bc
16.41 de
13.96 e
17.02 AB
Mean
18.28 A
17.54 A
13.57 B
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
14
Table 4
The effect of NaCl and PP333 treatments on photosynthetic rate (A) (µmolmˉ²sˉ¹) in strawberries
Salinity (mM)
PP333 (mg/L)
0
5
10
Mean
0
7.59 ef *
6.58 f
4.46 g
6.21 B
10
9.05 cde
8.26 def
10.14 bc
9.15 A
20
11.25 ab
8.85 cde
8.94 cde
9.68 A
30
12.12 a
9.46 cd
7.70 def
9.76 A
Mean
10.0 A
8.26 B
7.81 B
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
15
Table 5
The effect of NaCl and PP333 treatments on leaf stomatal conductance (gs) (µmolmˉ²sˉ¹) of
strawberry plants
Salinity (mM)
PP333 (mg/L)
0
5
10
0
202.5 a*
170.0 b
10
160.0 bc
150.0 bcd
122.5 def
144.2 B
20
137.5 cde
145.0 bcde
120.0 ef
134.2 BC
30
130.0 def
132.5 cdef
107.5 f
123.3 C
157.5 A
149.4 A
122.5 B
Mean
140.0 cde
Mean
170.8 A
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
16
Table 6
The effect of NaCl and PP333 treatments on strawberry transoiration rate (E) (mmolmˉ²sˉ¹).
Salinity (mM)
PP333 (mg/L)
0
5
10
0
7.92 a*
10
6.11 cde
6.75 bc
6.40 bcd
6.42 B
20
5.39 de
6.01 cde
6.82 bc
6.07 B
30
5.28 de
5.39 de
4.98 e
5.21 C
6.17 A
6.35 A
6.19 A
Mean
7.26 ab
6.54 bc
Mean
7.24 A
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
17
Table 7
The effect of NaCl and PP333 treatments on water use efficiency (A/E) in strawberry
Salinity (mM)
PP333 (mg/L)
0
5
10
0.90 ef
0.67 ef
Mean
0
0.95 ed*
0.84 C
10
1.48 cd
1.23 de
1.59 cd
1.43 B
20
2.12 ab
1.52 cd
1.31 de
1.65 B
30
2.30 a
1.83 bc
1.54 cd
1.89 A
Mean
1.71 A
1.37 B
1.28 B
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
18
Table 8
The effect of NaCl and PP333 treatments on relative water content of strawberry leaves (%)
Salinity (mM)
PP333 (mg/L)
0
5
10
65.43 cde
72.64 ab
Mean
0
70.89 abc*
69.69 A
10
69.55 abcd
75 .19 a
70.40 abc
71.71 A
20
67.86 bcd
64.28 de
59.71 e
63.96 B
30
74.24 a
72.30 ab
61.96 e
69.50 A
Mean
70.64 A
69.30 A
66.18 B
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
19
Table 9
The effect of NaCl and PP333 treatments on strawberry specific leaf weight (SLW) (g/dm²)
Salinity (mM)
PP333 (mg/L)
0
5
66.75 de
10
Mean
66.63 g
64.89 D
0
64.30 fg*
10
71.65 c
65.98 ef
71.68 c
69.77 B
20
63 g
66.53 def
72.85 bc
67.47 C
30
76.43 a
74.30 ab
68.80 d
73.18 A
Mean
68.84 A
68.39 A
69.24 A
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
20
Table 10
The effect of NaCl and PP333 treatments on
(mg/g fresh weight).
chlorophyll content in strawberry
Salinity (mM)
PP333 (mg/L)
0
5
10
1.08 e
Mean
0
1.25 d*
1.10 e
1.14 C
10
1.44 bc
1.45 bc
1.41 c
1.43 B
20
1.50 abc
1.43 bc
1.51 abc
1.48 B
30
1.58 a
1.59 a
1.53 ab
1.57 A
Mean
1.44 A
1.39 B
1.38 B
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
21
Table 11
The effect of NaCl and PP333 treatments on runner number of strawberry
Salinity (mM)
PP333 (mg/L)
0
5
10
3.8 d
Mean
0
7.8 a*
6.4 b
10
4.4 cd
4.4 cd
4.8 c
4.53 B
20
2.6 e
2.2 ef
2.0 ef
2.26 C
30
1.6 f
1.6 f
1.4 f
1.53 D
4.10 A
3.65 B
3.0 C
Mean
6.00 A
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
22
Table 12
The effect of NaCl and PP333 treatments on strawberry petiole length (cm).
Salinity (mM)
PP333 (mg/L)
0
5
10
8.73 a
8.31 ab
Mean
0
7.82 ab*
8.29 A
10
6.67 cd
5.74 ef
7.44 bc
6.64 B
20
6.44 de
5.64 ef
4.99 fg
5.69 C
30
4.37 g
4.24 g
5.64 ef
4.75 D
Mean
5.75 B
6.32 A
6.09 AB
*Mean followed by the same letter (small letters for means and capital letters for means of rows
and columns) are not significantly different at 5 % level of probability using DMRT.
23