International Research Journal of Plant Science (ISSN: 2141-5447) Vol. 4(8) pp. 222-235, September, 2013
DOI: http:/dx.doi.org/10.14303/irjps.2013.051
Available online http://www.interesjournals.org/IRJPS
Copyright © 2013 International Research Journals
Full Length Research Paper
To compare the allelopathic potentiality of two
Heliotropium species on the growth of Calotropis
procera and Lycopersicon esculentum
Hussein F. Farrag 1&2*, Abdallah M. Sliai 2 and Tha´ar F. Mhmas 2
1
Botany Department, Faculty of Science, Cairo University, Egypt.
Biology Department, Faculty of Science, Taif University, Saudi Arabia.
2
*Corresponding Authors E-mail: hfarrag2012@hotmail.com; Tel: +966550791544
Abstract
In this paper we compare the allelopathic potentiality of two invasive species; Heliotropium
curassavicum and H. bacciferum. The shoot height, root depth and root/shoot ratio for Calotropis
procera and Faba sativa plants were generally reduced under mulching of the two invasive plants
during different growth stages. Numbers of recorded flowers were 6.66, 2.33, 1.66 and 1 for control, T1,
T 2 and T3; respectively, for the treated plants by H. curassavicum, while these values increased to 7.66,
3.54, 2.56 and 0.33 for the same treatments but to plants treated with H. bacciferum. The RGRs of the
tow test species generally decreased with age as a result of decreased age-specific LAR and slow
NAR. Correlation between RGR and other growth variables demonstrated that RGR positively
correlated with NAR, LAR and SLA for all treatments of C. procera, while the test species F. sativa,
showed negative correlation between RGR and NAR values and positive correlation with LAR and SLA.
On the basis of these results, it was concluded that the mulch treatments using H. curassavicum had
much inhibitory effect than that of H. bacciferum for both test species. The present study recommend
the use of the two Heliotropium species for the biocontrol of harmful weeds like C. procera and in the
same time alert for the inhibitory effect of these species on the growth of economic plants like F.
sativa.
Keywords: Allelopathy, Heliotropium curassavicum, Heliotropium bacciferum, Relative growth rate, Net
assimilation rate, Specific leaf area, Specific leaf weight.
INTRODUCTION
Allelopathy involves any direct or indirect harmful effect of
one plant through release of chemical compounds on the
other. These allelopathic chemicals inhibit seed
germination or reduce growth of the other plant species.
Moreover, allelochemicals affect cell division, production
of plant hormones, membrane permeability, germination
of pollen grains, mineral uptake, movement of stomata,
pigment synthesis, photosynthesis, respiration, protein
synthesis, nitrogen fixation, specific enzyme activities and
development of conductive tissue (Rice, 1984; Rizvi et al.
1992; Hegazy et al. 1995; Wink et al. 1998; Hegazy et al.
2001; El-Khatib et al. 2004; Florentine et al. 2005; Rafael
et al. 2005; Jamali et al. 2006; Farrag 2007; Inderjit et al.
2008; Pisula and Meiners 2010; Kim and Lee 2011;
Djurdjević et al. 2012; Mansour 2013; Farrag et al.,
2013). Allelochemicals include phenolic acids, coumarins,
terpenoids and flavonoides. These compounds are
released from the plants as vapour, as leachings from the
foliage, as exudates from the roots, or in the course of
breakdown or decomposition of dead plant residues.
Allelopathy is existent in the natural and agricultural
ecosystems. It is a mechanism by which weeds affect
crop growth and yield. Allelopathy is possibly a significant
factor in maintaining the present balance among the
various plant species (Rao 1983; Florentine et al. 2006;
Kim and Lee 2011). There is increasing evidence that
many plant invaders interfere with native plants through
allelopathy. This allelopathic interference may be a key
mechanism of plant invasiveness (Bousquet-Mélou et al.,
2005; Dorning and Cipollini, 2006; Callaway and Maron,
Farrag et al. 223
2006; Farrag 2007; Inderjit et al., 2008; Thorpe et al.,
2009; Pisula and Meiners, 2010; Kim and Lee, 2011;
Djurdjević et al. 2012 ). Several studies demonstrated the
negative relationship between native and exotic species
(Fox and Fox 1986; Rejmanek 1989; Woods 1993; Pysek
and Pysek 1995; Tilman 1997; Florentine et al., 2005;
Callaway and Maron, 2006; Farrag 2007; Inderjit et al.,
2008; Thorpe et al., 2009; Pisula and Meiners, 2010; Kim
and Lee, 2011; Djurdjević et al. 2012). There is much
evidence that allelochemicals from weeds inhibit crop
growth (Florentine et al. 2005). Farrag (2007) studied the
allelopathic effects of three weeds; namely, Heliotropium
curassavicum, Bassia indica and Chenopodium
ambrosioides on the associated weeds and crops in the
Nile Delta region, Egypt.
In Saudi Arabia, Heliotropium curassavicum L. and
Heliotropium bacciferum (Boraginaceae) have become
two of the most common polycarpic weeds infesting
many Wadis and newly reclaimed fields at many areas of
Taif regions (Farrag 2012 and Farrag et al., 2013).
Because of their vigorous growth and natural ability to
colonize the disturbed salt affected sand flats, the
species spreads rapidly invading the newly reclaimed
lands and the surrounding fields as a troublesome weed
(Hegazy 1994; Hegazy et al. 1994; Farrag 2007). The
success of different Heliotropium species as weeds can
be attributed to a large extent to their ability to produce
adventitious root buds which allow for the plant’s
perennation and spread (Hegazy et al. 1994; Farrag
2007; Farrag et al., 2013).
The aim of the current work is to compare the
allelopathic potentiality of two invasive species belongs to
the genus Heliotropium (Boraginaceae); namely,
Heliotropium curassavicum L. and Heliotropium
bacciferum Forssk., on the growth of one important
economic crop; Faba sativa (Fabaceae) and one
common
toxic
weed;
Calotropis
procera
(Asclepiadaceae) in Taif.
MATERIALS AND METHODS
Materials
The seeds of the crop; Faba sativa
was obtained
commercially from Panda store –Taif, while seeds of the
weed; Calotropis procera was collected from naturally
growing populations at Wadi Al-Argy, Seesed, about 5
km east of Taif (210 17/ N and 400 29/ E and altitude of
1595m). Plastic pots (18 cm diameter and 25 cm depth)
were used. The soil was obtained from the field study
site. The soil samples were air-dried and passed through
2-mm sieve to separate litter and gravel. The air-dried
sieved soil was filled into the experimental pots (8 kg
soil/pot). H.curassavicum and H.bacciferum plant
materials for the purpose of mulching experiment were
collected from naturally growing plants at Wadi Al-Argy,
Seesed- Taif.
Experimental design
The experiment was conducted in an open greenhouse
(protected area) at Wadi Argy, under the external natural
environmental conditions during the period 4 April 2012
to 24 November 2012. The prevailing climatic conditions
during the experimental period includes temperature
which ranged between a minimum of 12.8 oC in
November to a maximum value of 34.4 oC in July.
Relative humidity ranged between minimum of 23% in
June to a maximum value of 55% in November (Farrag,
2012). Ten seeds were sown in every pot at depth of
1cm. Ground powder with three application rates of 2.5, 5
and 10 g per 8 kg soil for each invasive species treatment
referred as T1, T2 and T3; respectively, were evenly
mulched on the soil surface of the corresponding pot. In
control treatment the seeds were sown in soils without
mulching. Total of twelve pots were used for each
treatment, three of which were harvested for each of the
four growth stages; seedling, juvenile, mature and
flowering. Seedling emergence was monitored daily. After
the seedling emergence ceased, seedlings were thinned
to the most similar healthy five individuals per pot. The
pots were watered regularly and equally at the same time
for all treatments when needed. The amount of water per
pot was adjusted to avoid leaching of the soil water out of
pots.
Harvest and measurements
Plant materials were harvested and data gathered at the
four growth stages; seedling, juvenile, mature and
flowering stages for all target plants. At each harvest
stage, whole pot of each treatment was gently inverted
and whole plants harvested individually by carefully
clearing the soil with pressurized tap water. The growth
criteria measurements included root depth, shoot height,
leaf area, number of leaves and flowers. The whole plant
then divided into separate organs; roots, stems, leaves,
and reproductive organs (flowers), which then oven dried
at 75 0C until constant weight. Dry phytomass was
recorded for each plant organ. Five replicates were used
for every measurement.
Root/shoot ratios, percent dry matter allocation and
growth parameters including Relative Growth Rate
(RGR), Net Assimilation Rate (NAR), Leaf Area Ratio
(LAR), Specific Leaf Area (SLA) and Specific Leaf Weight
(SLW) were calculated according to Hunt (1978) by using
the following equations: The RGR was calculated as mg
-1
-1
mg day over the time interval as: RGR = (ln W 2 – ln W 1)
/ (t2 –t1) Where, W 1 and W 2 are weights at time t1 and t2,
-2
-1
respectively. The NAR was calculated as mg mm day
over the time interval as: NAR = {(ln A2 – ln A1) / (A2 –
224 Int. Res. J. Plant Sci.
2
A1)} X {(W 2 – W 1) / (t2 –t1)}, and LAR calculated as mm
-1
mg as follow: LAR= {(ln W 2 – ln W 1) / (lnA2 – lnA1)} X
{(A2 –A1)/ (W 2 – W 1)} where, W 1, W 2 are weights and A1,
A2 are leaf areas at time t1 and t2, respectively. The SLA
was calculated as mm2 mg-1 as: SLA = Leaf area / Leaf
weight. The SLW was calculated as mg mm-2 as: SLW =
Leaf weight / Leaf area
Statistical analysis
Data were analyzed by ANOVA test to determine the
significant differences among the mean values at P< 0.05
and P < 0.01 probability levels using a “general linear
model” procedure of the Statistical Analysis System
(SAS) program (SAS Institute, 1985). The correlation
between RGR and other growth parameters was
undertaken by using SPSS program version 10.
RESULTS
Vegetative attributes
The effect of mulching on the root depth and shoot height
of C. procera and F. sativa demonstrated significant
inhibitory effects on both root and shoot lengths in the
different growth stages. The inhibitory effect of H.
curassavicum was generally more than that of H.
bacciferum as follow:
In case of C. procera treated with H. curassavicum the
root depths were 12.6, 6.3, 5, 3.3cm (p< 0.01) at the
juvenile stage for the treatments of control, T1, T2 and T3;
respectively, while these values were relatively higher
and recorded 12.6, 10.1, 6.4 and 6.7cm for plants treated
with H. bacciferum and there is no significant difference
between treatments. Shoot heights on the other hand,
obeyed the same trend of root depths; the shoot heights
of C. procera plants treated with H. curassavicum at the
mature growth stage were 45.3, 31.6, 23.2 and 15.2cm
(p< 0.05) for treatments control, T1, T2 and T3;
respectively, and theses values were amounting to 45.3,
38.2, 26.3 and 16.9cm (p< 0.05) for the same treatments
and growth stage of plants treated H. bacciferum (Figure
1).
In case of F. sativa treated with H. curassavicum the
root depths were 49, 46, 25 and 16.3cm (p< 0.05) at the
flowering stage for the treatments of control, T1, T2 and
T3; respectively, and in parallel these values were
relatively higher and recorded 49, 48, 27 and 19cm (p<
0.01) for plants treated with H. bacciferum at the same
growth stage. The same occurred considering shoot
heights of plants treated with H. curassavicum at the
flowering growth stage were 32.7, 25.7, 20.3 and 17.3cm
for treatments control, T1, T2 and T3; respectively, and the
recorded values were 32.7, 29.3, 23.6 and 19cm (p<
0.05) for the same treatments and growth stage of plants
treated H. bacciferum (Figure 1).
The root-shoot (R:S) ratio for all test plants, in almost
all growth stages except seedling stage, was almost
lower than unity (Figure 2). For C. procera, the R:S ratio
decreased from 2.15 in control plants to 1.01, 1.93 and
1.07 in plants mulched by H. curassavicum under the
three treatments T1, T2 and T3; respectively, during the
seedling growth stage. In the same way, the R:S ratios
were 2.15, 1.4, 1.46 and 0.85 for treated plants by H.
bacciferum of control, T1, T2 and T3; respectively.
Alternatively, the R:S ratio of the control plants
demonstrated lower values than that of treated plants as
it was 0.59 in control plants during mature growth stage,
while increased to 0.67, 0.75 and 0.88 in plants treated
by H. curassavicum under the treatments T1, T2 and T3;
respectively. The R:S ratio of control and treated plants of
C. procera by H. curassavicum was generally higher than
that of plants treated by H. bacciferum in the seedling,
mature and flowering growth stages with non significant
difference (Figure 2).
Considering F. sativa, the root-shoot (R:S) ratio for all
test plants in most all growth stages was almost more
than unity (Figure 2). The R:S ratio decreased from 1.83
in control plants to 1.85, 1.16 and 1 in plants mulched by
H. curassavicum under the three treatments T1, T2 and
T3; respectively, during the juvenile growth stage. In the
same way, the R:S ratios were 1.83, 1.83,1.04and 1.01
for treated plants by H. bacciferum of control, T1, T2 and
T3; respectively. On contrary, the R:S ratio of the control
plants demonstrated lower values than that of treated
plants as it was 0.54 in control plants during seedling
growth stage, and increased to 0.97, 0.88 and 1.09 in
plants treated by H. curassavicum under the treatments
T1, T2 and T3; respectively. In addition, and in opposite to
case of C. procera, the R:S ratio of control and treated
plants of F.sativa by H. curassavicum was generally
higher than that of plants treated by H. bacciferum in the
juvenile, mature and flowering growth stages with non
significant difference (Figure 2).
Reproductive attributes
Less number of flowers per individual was recorded in the
treated plants than in the control of all test species.
Considering C. procera, fewer numbers of flowers
obtained in case of plants treated with H. curassavicum
as compared to those treated with H. bacciferum.
Numbers of recorded flowers were 10.33, 9.66, 9.33 and
8.33 for control, T1, T2 and T3; respectively, for the treated
plants by H. curassavicum, while these values relatively
increased to 11.66, 10.33, 9.66 and 8.66 for the same
treatments of plants treated with H. bacciferum.
Considering F. sativa, the same trend of results occurred.
Less number of flowers obtained in case of plants treated
with H. curassavicum as compared to those treated with
H. bacciferum. Numbers of recorded flowers were 6.66,
2.33, 1.66 and 1 for control, T1, T2 and T3; respectively,
for the treated plants by H. curassavicum, while these
Farrag et al. 225
Calotropis procera
Faba sativa
Figure 1. Mean and standard deviation of Root depth and shoot height of C.procera and F.sativa
growing under mulching treatment of H.curassavicum (a) and H.bacciferum (b) at different growth
stages;1= Seedling, 2 = Juvenile, 3 = Mature and 4= Flowering. Vertical bar around the mean is the
standard deviation.
values relatively generally increased to 7.66, 3.54, 2.56
and 0.33 for the same treatments of plants treated with H.
bacciferum (Table 1). Generally, the allelopathic effect of
both H. curassavicum and H. bacciferum concerning
number of flowers showed more inhibitory effect towards
F. sativa than C. procera.
Dry matter allocation
Allocation of dry matter among different plant organs in
the two test species; C. procera and F. sativa, is
illustrated in Figure 3.
Considering C. procera plants treated by H.
curassavicum, the allocation to leaves was higher than
the other plant organs in all growth stages except the
juvenile stage for both control and treated plants
cultivated under different mulches (Figure 3, a).
Comparing the dry matter allocation of plant organs of the
control with the treated plants under different mulches
indicated that there was general reduction in dry matter of
treated plants. Percent of dry matter allocated to leaves
was found to be 57.64 % in control plants during the
flowering growth stage and this value significantly
reduced (p < 0.01) into 49.02, 32.48 and 17.33% in the
treated plants; T1, T2 and T3, respectively. On the other
hand, percent dry matter of stem, root and reproductive
organs of controls during the same growth stage and
mulch treatment were 30.64 and 11.53% and increased
to 42.07 and 24.57% in T3 treated plants. Reproductive
organs (flowers) follow the same trend of the leaves as it
recorded 0.57% and this value reduced into 0.28, 0.21
and 0.09% for plants in the flowering growth stage with
no significant difference (Figure 3, a ).
Dry matter allocation of C. procera plants treated with
H. bacciferum was illustrated in Figure 3(b). It is to be
noted that, dry matter allocation for control plants at
different growth stages gave relatively higher values than
those of treated plants. For example, dry matter
allocation for leaves, stem , root and reproductive organs
of control plants at the flowering stage were 57.64, 30.64,
11.53 and 0.58%; respectively, and these values
significantly reduced into 33.28, 41.37, 25.18 and 0.17%
for the treated plants (T3) at the same growth stage. In
addition, comparing dry matter allocation of the different
226 Int. Res. J. Plant Sci.
Calotropis procera
c
T1
T2
T3
2.5
Root/shoot ratio
2
1.5
1
0.5
0
1
2
3
4
1
2
a
3
4
3
4
b
Growth stages
Faba sativa
c
T1
T2
T3
2
1.8
Root/shoot ratio
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1
2
3
4
1
a
2
b
Growth stages
Figure 2. Mean and standard deviation of root/shoot ratio of C.procera and
F.sativa, growing under mulching treatment of H.curassavicum (a) and
H.bacciferum (b) at different growth stages;1= Seedling, 2 = Juvenile, 3 =
Mature and 4= Flowering. Vertical bar around the mean is the standard
deviation.
Farrag et al. 227
Table 1. Number of Flowers of C.procera and F.sativa subjected to the mulching treatment
of (a) = H. curassavicum and (b) = H.bacciferum in the flowering stage. Mean values are
given and values between bracts are the standard deviations.
C.procera
Treatment
Control
T1
T2
T3
(a)
10.33(1.88)
9.66(0.94)
9.33(0.47)
8.33(0.47)
F.sativa
(b)
11.66(1.24)
(a)
6.66(1.69)
(b)
7.66(0.59)
10.33(0.48)
9.66(0.48)
8.66(0.45)
2.33(0.47)
1.66(0.47)
1.00(0.01)
3.54(0.12)
2.56(0.08)
0.33(0.01)
C.procera
F.sativa
Figure 3. Dry matter allocation of C.procera and F.sativa subjected to the mulching treatment
of (a) =H.curassavicum and (b)=H.bacciferum at different growth intervals;1=SeedlingJuvenile, 2=Juvenile-Mature and 3= Mature-Flowering. Vertical bar around the mean is the
standard deviation.
plant organs in most growth stages demonstrated that,
percent allocation of leaves > stem > root > flowers.
Comparing the obtained data, one may concluded
that, dry matter allocation of C. procera plants treated
with H. bacciferum is more negatively affected by the
allelochemicals as compared to those treated by H.
curassavicum in the early growth stages (seedling and
juvenile) while the opposite occurred in the late growth
stages (mature and flowering). For instance, the dry
matter allocation of C. procera plants treated with H.
curassavicum (T1) was 57.77, 26.67, and 15.56% for
leaves, stem and root; respectively, at the seedling
growth stage and these values were comparatively
reduced into 37.41, 8.63 and 13.51% for the same
organs but to plants treated with H. bacciferum at the
same growth stage. On contrary, the dry matter allocation
of C. procera plants treated with H. curassavicum (T1)
was 41.14, 26.15 and 32.71% for leaves, stem and root;
respectively, at the mature growth stage and these
values were comparatively increased to 42.57, 32.71 and
24.72% for the same organs but to plants treated with H.
bacciferum at the same growth stage (Figure 3, a and b).
Considering the test plant F. sativa treated with either
H. curassavicum, dry matter allocation for control plants
at early growth stages gave relatively higher values than
those of treated plants while the opposite occurred at the
228 Int. Res. J. Plant Sci.
Table 2. Correlations (r) between the relative growth rate (RGR) and other growth parameters; net assimilation
rate (NAR), leaf area ratio (LAR), specific leaf area (SLA) and specific leaf weight (SLW) of the test species as
affected by mulching treatment of (a) = H. curassavicum and (b) = H. bacciferum, using Pearson correlation
coefficient (Two-tailed test). *P<0.05, **P<0.01.
NAR
Test species
C. procera
Control
T1
T2
T3
F. sativa
Control
T1
T2
T3
LAR
(a)
(b)
(a)
P
r
P
r
P
r
P
0.993**
0.896
0.457
0.465
0.006
0.144
0.674
0.451
0.350
0.448
0.349
0.279
0.560
0.632
0.563
0.731
0.775
0.546
0.864
0.893
0.235
0.264
0.279
0.220
0.975*
0.981*
0.866
0.909
0.018
0.019
0.146
0.091
-0.993
-0.870
-0.786
-0.151
0.077
0.253
0.335
0.860
-0.549
-0.275
0.517
0.531
0.825
0.975
0.654
0.643
0.836
1.000**
1.000**
0.798
0.370
0.008
0.006
0.412
0.917
0.961*
0.994
.953*
0.347
0.078
0.070
0.050
SLA
C. procera
Control
T1
T2
T3
F. sativa
Control
T1
T2
T3
(b)
r
SLW
0.639
0.607
0.998*
0.738
0.361
0.393
0.062
0.282
0.993**
0.858
0.636
0.851
0.007
0.142
0.364
0.149
-0.929
-0.809
-0.718
-0.452
0.071
0.191
0.282
0.548
-0.914
-0.915
-0.837
-0.961*
0.086
0.085
0.163
0.039
0.985*
0.954
0.971
1.000**
0.018
0.194
0.155
0.006
0.972
0.982
0.987
0.997*
0.082
0.079
0.103
0.046
-0.982
-0.956
-0.959
-0.853
0.082
0.187
0.183
0.051
-0.947
-0.974
-0.987
-0.994
0.209
0.134
0.105
0.069
late growth stages. For example, dry matter allocation for
leaves and root of control plants at the seedling stage
were 26.86 and 44.67%; respectively, and these values
significantly reduced into 24.24 and 37.11% for the
treated plants (T1) at the same growth stage.
Alternatively, dry matter allocation for control plants at the
mature growth stage was 39.9 and 14.21% for leaves
and stem; respectively, and these values increased to
42.97 and 18.47 for the same organs of plants treated by
T1. The present data revealed that, the allocation of dry
matter towards root> leaves> stem > flowers, which is not
in same as the above mentioned test species (F. sativa).
In addition, there were significant differences in the dry
matter allocation between control and different mulch
treatments in most growth stages and for most plant
organs. For example, there was significant difference (p<
0.01) between the values of dry matter allocation for stem
in the seedling stage and for flowers in the flowering
growth stage. It is to be mentioned that there was no
significant differences between dry matter allocations of
some plant organs in some growth stages, e.g. root in the
seedling and flowering growth stages.
The present data for the dry matter allocation of F.
sativa treated with H. bacciferum, generally gave similar
trend as that of plants treated with H. curassavicum
considering control and treated plants but the inhibitory
effect of H. bacciferum was relatively more stronger than
that in plants treated by H. curassavicum. For example,
dry matter allocation for leaves of F. sativa treated by H.
curassavicum in the seedling stage were 26.86, 24.24,
38.84 and 19.13% for control, T1, T2 and T3 plants;
respectively, and these values generally reduced into
26.86, 26.69, 30.10 and 13.33% for the same plant
treatments respectively, but plants treated with H.
bacciferum (Figure 3, a and b).
Growth analysis
Growth analysis of the test species and the variation in
growth parameters in response to the effect of mulching
treatment including relative growth rate (RGR), net
assimilation rate (NAR), leaf area ratio (LAR), specific
leaf area (SLA) and specific leaf weight (SLW) of the two
test species are illustrated in Figures (4-7). The
correlation between RGR and other growth parameters is
given in Table 2.
Farrag et al. 229
C.procera
F.sativa
Figure 4. Relative growth rate (RGR) of C.procera and F.sativa subjected to the mulching treatment of
(a)= H.curassavicum and (b)= H.bacciferum at different growth intervals;1=Seedling-Juvenile, 2=
Juvenile-Mature and 3= Mature-Flowering. Vertical bar around the mean is the standard deviation.
Relative growth rate
The RGRs of the two test species generally decreased
with time. Considering C.procera, the RGR of control
plants during the late growth stages (mature and
flowering) is generally higher than that of treated plants
especially in case of C. procera plants treated with H.
bacciferum. The RGR of C.procera control plant during
the juvenile –mature growth interval and using H.
bacciferum as a mulch treatment was (0.082 mg mg-1
-1
day ) and this value significantly reduced into (0.078 and
0.079 mg mg-1 day-1) in plants of treatments T1 and T2,
respectively (figure 4, b). On the contrary, the RGRs of C.
procera treated by H. curassavicum took opposite trend
than the above mentioned case in most growth stages.
For example, the recorded RGRs for C. procera were
(0.017, 0.022, 0.023 and 0.025 mg mg-1 day-1) for plants
treated by H. curassavicum by the rates control, T1, T2
and T3; respectively.
The RGRs for the treated plants of F. sativa showed
similar way to the above mentioned test species, C.
procera, but with one exception that in most growth
stages increase in mulch treatment, increase RGRs using
either H. curassavicum or H. bacciferum. The recorded
RGRs for F. sativa treated by H. curassavicum were
0.169, 0.190, 0.238 and 0.243 mg mg-1 day-1 for plants
treated by the rates; control, T1, T2 and T3, respectively,
during the seedling-juvenile growth stage. In the same
way, the recorded RGRs for F. sativa treated by H.
bacciferum were 0.169, 0.164, 0.173 and 0.270 mg mg-1
day-1 for plants treated by the rates; control, T1, T2 and
T3, respectively, during the same growth stage (figure 4,
a).
Net assimilation rate
The variation of NAR among the test species was
dependent on both type of test species and growth stage.
NAR increased (in the control and treated plants) in the
first growth interval (seedling- juvenile) than second
(juvenile- mature) and third (mature-flowering) growth
interval as test plant treated with H.curassavicum. For
-2
example, the NAR were 0.104, 0.077 and 0.022 mg mm
-1
day for T1 C.procera plants treated with H.curassavicum
and during the three growth intervals. On the contrary,
the NAR increased in the third growth interval in most
cases when test plant treated with H.bacciferum. For
instance, the recorded NAR were 0.000161, 1.72 and
3.97 mg mm-2 day-1 for T3 F.sativa plants treated by H.
bacciferum (Figure 5 a and b).
230 Int. Res. J. Plant Sci.
C.procera
F.sativa
Figure 5. Net assimilation rate (NAR) of C.procera and F.sativa subjected to the mulching
treatment of (a)=H.curassavicum and (b)=H.bacciferum at different growth intervals;1=
Seedling-Juvenile,2=Juvenile-Mature and 3= Mature-Flowering. Vertical bar around the
mean is the standard deviation.
Leaf area ratio
Both C. procera and F. sativa, attained the highest LAR
values in the first growth interval, the seedling stage and
then the values decreased in the subsequent growth
intervals recording the minimum values in the flowering
stage(Figures 6). C. procera plants treated by H.
bacciferum, recorded the maximum LAR values among
the different test species as it recorded 10086.75,
2
-1
14303.54, 5790.18 and 6943.79 mm mg in control, T1,
T2 and T3 treated plants, respectively,
during the
seedling- juvenile growth (Figure 6, a).
It is to be noted that throughout nearly the whole
growth intervals and for both two test species, higher
LAR values attained in plants treated by H. curassavicum
as compared with those of plants treated with H.
bacciferum. For example, LAR of C. procera significantly
(p< 0.05) recorded 1141.36, 912.12 and 977.6 mm2 mg-1
for T1, T2 and T3 treated plants by H. curassavicum during
the juvenile- mature growth stage. These values were
comparatively small, recording 640.77, 411.98 and
693.42 mm2 mg-1 for the same concentrations and growth
interval but using H. bacciferum as a mulch treatment
(Figure 6a and b).
LAR for F. sativa plants showed increase in values in
the second growth interval (juvenile- mature) followed by
sharp decrease in these values in the last growth interval
(mature- flowering) using either of the two mulch
treatments. For instance, LARs for F. sativa treated by
(T1) H. curassavicum were 1384.08, 1629.5 and 890.18
mm2 mg-1 in the seedling-juvenile, juvenile-mature and
mature-flowering growth intervals; respectively.
Specific leaf area
There was general trend of decrease of the SLA values
as the plant mulch treatment increase and as plants age
(Figure 7). Plants of C. procera treated with H.
curassavicum recorded SLA values amounted to
2
-1
55287.95, 33589.76, 8644.06 and 2960.21 mm mg in
control, T1, T2 and T3 plants, respectively in the seedling
growth stage. These values are reduced gradually in the
Farrag et al. 231
C.procera
F.sativa
Figure 6. Leaf area ratio (LAR) of C.procera and F.sativa subjected to the mulching treatment of
(a) =H.curassavicum and (b)=H.bacciferum at different growth intervals;1=SeedlingJuvenile,2=Juvenile-Mature and 3=Mature-Flowering. Vertical bar around the mean is the
standard deviation.
subsequent growth stages recording minimum values
amounted to 265.23, 401.04, 544.81 and 545.29 mm2
mg-1, respectively, for the same treatments during the
flowering growth stage of the same plant. In addition, the
SLA values of control plants were relatively higher than
that of treated plants using either one of the two mulch
powders. For example, SLA in the mature growth stage
of C. procera treated by H. bacciferum was 1010.52 mm2
mg-1 and this value greatly reduced to about its half
(594.67 mm2 mg-1) using the first mulch treatment (T1).
The data revealed greater SLA values using either C.
procera or F. sativa plants treated with H. bacciferum,
than the test plant treatments by H. bacciferum. The
recorded SLA values were 906.72 and 3731.01 mm2 mg-1
for C. procera and F. sativa plants; respectively, and
treated by (T2) H. curassavicum during the mature growth
interval. These values greatly reduced into 515.71 and
2
-1
3218.42 mm mg for the same plants and treatment but
using H. bacciferum.
Specific leaf weight
SLW values gradually increase as plants age. Plants of
C. procera treated with H. curassavicum recorded SLW
values amounted to 0.0006, 0.0001, 0.0001 and
-2
0.0003mg mm in control, T1, T2 and T3 plants,
respectively and during the seedling growth stage. These
values increased gradually in the subsequent growth
stages recording maximum of 0.003, 0.002, 0.001 and
0.001 mg mm-2, respectively, for the same treatments
during the flowering growth stage of the same plant
(Figure 7). In addition, there is no clear trend on
comparing the SLW values of control and treated plants
using different mulch treatment among the different test
species.
Correlation between RGR and other growth variables
demonstrated that RGR positively correlated with NAR,
LAR and SLA for all treatments of C. procera, while the
test species F. sativa, showed negative correlation
between RGR and NAR values and positive correlation
with LAR and SLA. There were negative correlations
between RGR values and that of SLW for the two test
species under different mulch treatments. For C. procera
treated with H. curassavicum, RGR values are highly and
positively correlated with NAR values (r=0.993, P<0.01)
in control plants, compared to relatively weaker but
positive correlations in the treated plants by H.
bacciferum (Table 2). On the contrary, RGR values are
negatively correlated with NAR values in case of F. sativa
treated with either H. curassavicum or H. bacciferum
recording (r=-0.993, P=0.077) in control plants, compared
to relatively stronger but still negative correlations in the
232 Int. Res. J. Plant Sci.
C.procera
c
T1
T2
F.sativa
T3
c
70000
6000
60000
5000
T2
T3
4000
40000
SLA
SLA
50000
T1
30000
3000
2000
20000
1000
10000
0
0
1
2
3
4
1
2
a
3
4
1
2
3
b
4
T1
T2
2
3
4
3
4
b
Growth stages
c
1
a
Growth stages
T3
c
T1
T2
T3
0.0006
0.0045
0.004
0.0005
0.0035
0.003
0.0004
SLW
SLW
0.0025
0.002
0.0015
0.0003
0.0002
0.001
0.0005
0.0001
0
-0.0005
1
2
3
4
1
a
2
3
4
b
0
1
2
3
4
1
a
Growth stages
2
b
Growth stages
Figure 7. Specific leaf area (SLA) and specific leaf weight (SLW) of C.procera and F.sativa
subjected to the mulching treatment of (a) =H.curassavicum and (b) =H.bacciferum at
different growth stages; 1= Seedling, 2= Juvenile, 3= Mature and 4-Flowering. Vertical bar
around the mean is the standard deviation.
treated plants amounted to -0.870, -0.786 and -0.151 at
P= 0.253, 0.335 and 0.860 for treated plants T1, T2 and
T3 mulched by H. curassavicum powder, respectively.
The RGR values were positively and strongly correlated
with NAR in both test plants using either mulch. Another
point is that mulch treatments increase the correlation
between RGR and SLA in case of F. sativa and decrease
the same correlation in the rest of test species.
DISCUSSION
Vegetative attributes
Root length is found to be statistically more accurate than
seed germination in assessing the response of test plants
to allelochemicals (Cope, 1982). In accordance with
inhibitory effects of mulching on the shoot height and root
depth of the two test species in the present study,
decrease in plant growth as influenced by allelochemicals
was reported by several investigators (e.g. Heisey and
Delwiche 1985; Hegazy et al. 1990, 1994 and 2001;
Mahall and Callaway 1991 and 1992; Inderjit and Jacob
Weiner 2001; Ridenour and Callaway 2001; Elkhatib et
al. 2004; Setia et al. 2007; Jabeen et al. 2011 ;Raoof and
Siddiqui 2012 and Farrag et al., 2013).
Allellochemicals of H. curassavicum had much
inhibitory effect than that of H. bacciferum for both test
species; C. procera and F. sativa, in the early growth
stages like the seedling and juvenile growth stages than
the late growth stages. That may explained by Farrag et
al., 2013, who mentioned that, the inhibitory effect of
allelochemicals released by different invasive plant
powder on shoot height and root depth of the other test
species was observed in the late growth stages.
Moreover, the accumulation of allelochemicals in the
body of this test species may explain this behavior. In
addition, soil microbes play an important role in the
qualitative and quantitative availability of allelochemicals
(Turner and Rice 1975; Chapman and Lynch 1983; Blum
et al. 1987; Nair et al. 1990; Chase et al. 1991b, Jabeen
et al., 2011; Raoof and Siddiqui 2012). Many microbes
utilize phenolic acids and flavonoids as a carbon source
and deplete phenolics from the medium (Westlake et al.
1959; Vaughan et al. 1984; Blum et al. 1987). Norstadt
and McCalla (1963) suggested that the toxins from plant
Farrag et al. 233
residues and microorganisms are jointly responsible for
the inhibitory effect of the plant residues. DeFrank and
Putnam (1985) reported that soil-borne actinomycetes
could enhance allelopathic effects. This may explain that
the root depth of the test species of the present study
was more affected by the inhibitory effect of
allellochemicals than that of shoot length.
The root/shoot ratio of control plants of the present
study test species were generally reduced under the
effect of using different allelochemicals during different
growth stages and this reduction reached its maximum in
the late growth stages and that can be interpreted as
explained by Nilsson (1994) who suggested that the
decrease in root/shoot ratio as a response to nutrient
deficiency appears to be applied for plants subjected to
allelopathic interactions.
Reproductive attributes and dry matter allocation
Less number of flowers per individual was recorded in the
treated plants as compared with control plants of the
present study. In this regard, many authors (Einhellig and
Rasmussen 1993; Hejl et al. 1993; Inderjit and Dakshini
1995; El-khatib and Abd-Elaah 1998; Hegazy et al. 1999
and 2001; El-khatib et al. 2004; Farrag 2007; El-Darier et
al., 2011 and Bich and Noguchi 2012) have reported the
inhibitory effects of allelochemicals on the chlorophyll
content and net photosynthetic rate of their test species
which intern affect the reproductive opportunity of the test
species and as a result suppression in reproductive
organs was shown by plants mulched by invasive plant
powders. This feature is considered as a plastic response
of the allelopathically stressed plants which enables them
to live but with a diminished reproductive growth (Raynal
and Bazzaz 1975).
Growth analysis
The relative growth rate of plants is determined by their
genetic background and by environmental conditions
(Rafael et al. 2005). The RGRs of most test species of
the present work generally decreased with plant’s age.
This is in agreement with slow RGR that was observed
by Hegazy and Ismail (1992) as a result of decreased
age-specific LAR and slow NAR that reflect the
decreased amount of leaf production with age resulting in
slower growth. On the other hand, RGRs of controls of
the present work are generally higher than that of treated
plants especially in case of C. procera. The slow RGR of
treated plants may be implied by the toxic allelochemicals
released from different invasive plant powders. In
addition, the higher RGR of controls as compared to
treated plants may be explained by the increment of dry
matter allocated to the leaves. This means that better
RGR in controls and mild treated plants (T2) as compared
to high mulch treated plants (T3). Similarly, Sayed and
Hegazy (1994), found that the pattern of RGR increment
followed that of dry matter allocated into vegetative parts
(stem and leaves) and a decrease in RGR resulted from
an increased dry matter allocated to sexual structures
(flowers and fruits) at the expense of vegetative parts. In
addition, the reduced dry mass and RGR of rice with
increased density of lotus rhizomes indicates a possible
response to allelopathic interference (Hegazy et al.
2001). RGR may increase in the seedling-juvenile growth
interval and then decrease in the proceeding growth
intervals as shown in F.sativa. This may be explained by
the fact that growth rate in the seedling- juvenile growth
interval is normally the most rapid in the life of desert
plants compared to the subsequent growth intervals
(Burdon and Harper 1980).
The wide variation in RGR among species was
explained mainly by the variation in the plant
morphological variables, such as LAR and in particular
the SLA. This finding is in agreement with many other
studies supporting SLA as a major factor associated with
variation in the RGR (e.g. Poorter and Remkes 1990;
Garnier 1992; Maranon and Grubb 1993; Atkin et al.
1996; Cornelissen et al. 1996; Van der Boogaard et al.
1996; Lambers et al. 1998; Pooter and Van der Werf
1998; Isabel Antunez et al. 2001; Rafael et al. 2005;
Farrag 2007; Chengxu et al., 2011; Farrag et al., 2013).
In accordance with findings of Farrag 2007, the
variation of NAR between the two test species and within
control and treated plants of the same test species was
very dynamic with age. Variability of NAR values among
different species was parallel to the fluctuations in the
RGR values of most species. All test species attained the
highest LAR values in the first growth interval,
emergence-seedling, and then values decreased in the
subsequent growth intervals and this can be explained by
the general trend of the decrease of the SLA values as
the plants age. The positive correlation between RGR
and other growth variables is in agreement with findings
of many authors (e.g. Lambers et al. 1998; Loveys et al.
2002; Shipley 2002 and Rafael et al. 2005; Farrag 2007;
Raoof and Siddiqui 2012; Farrag 2013). In addition,
environmental conditions determine both the realized
RGR and the relative importance of the other growth
components. Two studies have challenged the general
view of SLA as a major determinant of RGR. Shipley
(2002) argued that the commonly reported result that “the
interspecific variation in RGR is determined primarily by
SLA”, is partly due to low irradiance used in most
experiments. Therefore, the relative importance of SLA
and NAR would change depending on the irradiance
perceived by plant. In another study, Loveys et al. (2002)
found that RGR was significantly and positively correlated
with NAR, when plants were cultivated at 18 oC.
However, when growth temperature was increased to 23
or 28 oC the RGR pattern switched, and correlated
positively with SLA, which is in agreement of results of
the present work.
234 Int. Res. J. Plant Sci.
CONCLUSION
In conclusion, the present study revealed that mulch
treatments with H. curassavicum and/or H.bacciferum
invasive plant powders greatly suppressed the vegetative
and dry matter allocation of the two test species.
Moreover, the allelopathic effect of both H. curassavicum
and H. bacciferum concerning number of flowers showed
more inhibitory effect towards F. sativa than C. procera.
Root/shoot ratio of control plants were generally reduced
under the mulch effect and this reduction reaches its
maximum in the late growth stages. The RGRs of most
test species generally decreased with age as a result of
decreased age-specific LAR and slow NAR. Variability of
NAR values among different species may be explained
by the fluctuations in the RGR values of this species.
Correlation between RGR and other growth variables
demonstrated that RGR positively correlated with NAR,
LAR and SLA for all treatments of C. procera, while the
test species F. sativa, showed negative correlation
between RGR and NAR values and positive correlation
with LAR and SLA. The present study recommend the
use of the two Heliotropium species for the biocontrol of
harmful weeds like C. procera and in the same time alert
for the inhibitory effect of these species on the growth of
economic plants like F. sativa.
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How to cite this article: Farrag HF, Sliai AM and Mhmas TF (2013).
To compare the allelopathic potentiality of two Heliotropium species
on the growth of Calotropis procera and Lycopersicon esculentum.
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