American Journal of Plant Sciences, 2013, 4, 2138-2147
Published Online November 2013 (http://www.scirp.org/journal/ajps)
http://dx.doi.org/10.4236/ajps.2013.411266
Open Access AJPS
Allelopathic Effect of Aqueous Extract of Argemone
mexicana L on Germination and Growth of Brachiaria
dictyoneura L and Clitoria ternatea L
Hassan S. Namkeleja, Mokiti T. Tarimo, Patrick A. Ndakidemi
School of Life Sciences and Bioengineering, The Nelson Mandela African Institution of Science and Technology, Arusha, Tanzania.
Received August 11th, 2013; revised September 11th, 2013; accepted October 11th, 2013
Copyright © 2013 Hassan S. Namkeleja et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The present study was conducted in the laboratory to investigate the allelopathic effect of Mexican poppy (Argemone
mexicana L.) to the germination and growth parameters of two native species Brachiaria dictyoneura L and Clitoria
ternatea L. Different concentrations of leaf and seed aqueous extracts from Argemone mexicana (0%, 25%, 50%, 75%
and 100%) were evaluated. Results showed that seed germination, root length, shoot length, seedling length, fresh
weight and dry weight of B. dictyoneura and C. ternatea seedlings were significantly reduced by leaf and seed extracts
compared with control treatments. Roots were more affected than shoots; and leaf extract was more suppressive than
seed extracts. From the results, it is concluded that leaf and seed extracts have some allelochemicals with inhibitory
effect on germination and growth of the tested plant species.
Keywords: Allelochemicals; Root Length; Shoot Length
1. Introduction
Invasive alien plants are among the important factors that
influence plants growth parameters in and among farm-
ing systems and wildlife ecosystems. Integrity of farming
system and natural ecosystems are threatened by alien
invasive species which displace some of the native spe-
cies and establishing mono-species in new habitat [1-3].
Production and release of allelopathic compounds (al-
lelochemicals) by invasive species are factors that en-
hance its competitive ability over native species [4].
Plants can affect neighboring plants by releasing chemi-
cals into the environment [5]. The Austrian plant physi-
ologist Hans Molisch named this phenomenon “allelo-
pathy” in 1937 [6]. Allelopathy refers to the effects of
one plant on another plant or organisms through the re-
lease of chemicals into the environment [2,7]. Al-
lelochemicals released from plants, imposing allelopathic
influences are classified as secondary metabolites and are
produced as offshoots of the primary metabolic pathways
in plants [8]. Allelopathic effect of some invasive species
over other species is stronger in introduced habitats than
in native lands because in new habitat native species may
not be as adapted to specific allelochemicals of invaders
as species do in the native range [4]. Mechanistically,
allelochemicals have a role in the determination of nutrient
dynamics, mycorrhizae, soil chemical characteristics and
microbial ecology [9,10]. Allelochemicals released by
invasive species also affect native species through dif-
ferent pathways that includes interruption of plants nu-
trients uptake, change in membrane permeability [11],
interference in cell division and elongation process in
roots and shoots [12-14], interference in chlorophyll
formation [15] protein synthesis inhibition [11,16] and
change or inactivate the activity and functions of certain
hormones and enzymes [17]. Hence, allelopathy has been
considered as among of key factor to the success of inva-
sive plant species over native species [2-4,18]. Argemone
mexicana (Mexican poppy) is amongst the ecologically
and economically destructive exotic invasive plant spe-
cies in Tanzania affecting both natural and agricultural
ecosystems [19]. A. mexicana is a herb plant with branches,
which has naturalized widely in many tropical and sub-
tropical regions although it is a native of tropical Ameri-
can [20]. It is a widespread annual weed primarily asso-
ciated with agricultural crops and wastelands. It is a ma-
jor weed of a number of crops in the tropics and warm

Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
2139
temperate regions and is persistent as it produces a seed
bank. A. mexicana is amongst invasive weeds reported to
release allelochemicals which affect some other species
within its vicinity especially crops in agricultural fields.
Burhan and Shaukat [21] reported the inhibition effect of
A. Mexicana extracts in seed germination, root and shoot
growth of pearl-millet, mustard, wheat, carrot, corn and
turnip caused by allelopathic compounds dissolved in
extracts. Another study by Paul and Begum [22] indi-
cated that seed germination percentage, root length, shoot
length and seedling dry weight of blackgram (Vigna
mungo) and rapeseed (Brassica napus) were significantly
decreased with the increase of both root and leaf extracts
of A. mexicana. Alagesaboopathi [23] also reported that
there was decrease in seed germination and inhibition of
plumule and radicle length of Sorghum bicolor seedlings
with increase in A. mexicana leaf extracts concentration
due to allelopathic potentialities. Paul and Begum [24]
reported allelopathic effect of A. mexicana on germina-
tion and seedling growth of Lentil (Lens culinaris). Al-
lelopathic effect of A. mexicana retarded the growth of
tomato plants at higher concentration [25].
All these researches have reported inhibitory effect in
seed germination, root length and shoot length and other
primary growth parameters caused by allelochemicals
present in aqueous extracts. Although allelopathic effect
of A. mexicana on crops (such as beans and maize) has
been reported, little information is available on their
influence on wild plant species. Therefore this study was
conducted to investigate the allelopathic effect of leaf
and seed aqueous extracts of A. mexicana on germination
and seedling growth of B. dictyoneura and C. ternatea
which are important pasture for wildlife and livestock.
The data from this study will help in current efforts to
eradicate alien invasive species (A. mexicana) in wildlife
protected areas in Tanzania.
2. Material and Methods
2.1. Preparation of the Aqueous Extract Solution
Seeds and leaves of A. mexicana plants were collected at
Ngorongoro Conservation Area (NCA). NCA is one of
wildlife protected areas in Serengeti Ecosystem which
has been invaded by A. mexicana. The Seeds and leaves
were separately washed thoroughly with distilled water
and air dried at room temperature for eight days. Seeds
and leaves were separately crushed in a blander into
powdery form and 100 g of these crushed materials were
soaked separately in a corked, conical flask containing
1000 mL (1 Liter) of distilled water for 72 hours
and filtered through Whatman filter paper No. 1. The
extract was diluted to obtain the concentrations of 25
g·L−1 (25%), 50 g·L−1 (50%), 75 g·L−1 (75%), and 100
g·L−1 (100%) while the distilled water was used in the
control treatment.
2.2. Determination of Germination Percentage,
Root Length, and Shoot Length
The seeds of Brachiaria dictyoneura were collected from
Ngorongoro Conservation Area and that of Clitoria ter-
natea were obtained from the National Plant Genetic
Resources Centre of Tanzania at Tropical Pesticides Re-
search Institute (TPRI)—Arusha Tanzania. The seeds
were washed three times in running tap water to remove
any impurities and afterwards surface sterilized with 5%
of sodium hypochlorite for two minutes then rinsed four
times with distilled water. Toxicity of aqueous extract of
A. mexicana was tested against Brachiaria dictyoneura
and Clitoria ternatea whereby 10 seeds of each target
species were placed in 9 cm autoclave petri dishes lined
up with double layer of whatman No. 1 filter paper and
10 mL of test extract for each concentration (25%, 50%,
75%, and 100%) of leaves and seeds. The seeds treated
with distilled water were taken as a control (T0) while
seeds in petri dishes with four different concentrations
(T1 = 25%, T2 = 50%, T3 = 75%, T4 = 100%) of Argemone
mexicana extract constituted a four sets of treated seeds
for each species (Brachiaria dictyoneura and Clitoria
ternate). The petri dishes were covered by caps and kept
inside the cupboards at room temperature. The experi-
mental design was a randomized entire block with four
replications for each treatment. Extract/distilled water
were added to moisten the seeds when required.
Seeds were observed every day and number of germi-
nated seeds was recorded (germination count) whereas
the emergence of the radicle from the seed was consid-
ered as criterion for germination to be recorded. Germi-
nation was recorded every day (at 24 hours intervals)
over a 10-day period. On 15th day after germination the
root length, shoot length and seedling length were meas-
ured by using digital caliper while fresh weight and dry
weights of each seedling were measured by digital
weighing balance. The dry weight of each seedling was
measured after placing them in an oven maintained at
55˚C for 5 days.
2.3. Statistical Analysis
Percentage of inhibition/stimulation effect on germina-
tion and root and shoot elongation over control (T0) was
calculated using the equation used by Signh and Chaud-
hary [26]:
Inhibition (−) or stimulation (+) = [(Germinated seeds
in extracts − Germinated seed in control)/Geminate seeds
in control] × 100.
The data from the experiment was analyzed using the
Open Access AJPS

Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
Open Access AJPS
2140
software of STATISTICA program 2013. When signifi-
cant differences were detected by the analysis of variance
(ANOVA), mean values of root length, shoot length,
fresh weight and dry weight of seedlings were used to
compare treatment means at p = 0.05 according to
Fisher’s Least Significant Difference (LSD).
3. Results
3.1. Effects of Aqueous Extracts of A. mexicana
on Seed Germination
Table 1 presents mean seed germination percentages of
B. dictyoneura and C. ternatea treated with different
concentrations of seed and leaf aqueous extracts of A.
mexicana. Seed and leaf aqueous extracts of A. mexicana
significantly (p ≤ 0.01) affected the germination of B.
dictyoneura and C. ternatea seeds. Mean seed germination
percentage of control treatments was high compared with
seeds treated with aqueous extracts. The mean seed
germination percentage was decreasing with increase in
aqueous extracts concentration (Table 1). The mean
germination percentage of B. dictyoneura seeds was 65%,
50%, 12.5% and 7.5% when treated with concentrations
of 25%, 50%, 75% and 100% leaf extracts respectively.
Therefore when compared with control, the leaf extracts
at the concentrations of 25%, 50%, 75% and 100%
significantly inhibited (p ≤ 0.001) germination of B.
dictyoneura by −31.6%, −47.4%, −86.8% and −92.1%
respectively. In seed extract, the percentage germination
of B. dictyoneura were also significantly reduced (p ≤
0.001) with increase in concentration whereby at the
concentration of 25%, 50%, 75% and 100% aqueous
seed extracts, the germination was 70%, 50%, 32.5% and
17.5% respectively. Relative to control treatment, the
germination percentages were significantly reduced with
increase in seed extracts concentration from 25%, 50%,
75% and 100% and this inhibited germination of B. dict-
yoneura by −24%, −45.9%, −64.8% and −81.1% res-
pectively. The similar trend was observed in seed ger-
mination of C. ternatea whereby at concentration of 25%,
50%, 75% and 100% of leaf extract, the percentage ger-
mination were 77.5%, 77.5%, 37% and 25% respectively.
At concentrations of 25, 50, 75 and 100%, the germi-
nation of C. ternatea was significantly (p ≤ 0.001) re-
duced by −20.5%, −20.5%, −62.1% and −74.4% respec-
tively. Variation in mean germination percentage of C.
ternatea was caused by inhibition effect that was in-
creasing with increase in concentrations of leaf extracts
when compared with the control treatment.
Mean germination percentages of C. ternate were also
significantly reduced (p ≤ 0.01) by −24.2%, −26.3%,
−36.8% and −44.7% when treated with concentrations of
25%, 50%, 75% and 100% seed extracts respectively.
Generally, germination inhibition was greater with 100%
extract than with the other concentrations.
3.2. Effects of Aqueous Extracts of Argemone
mexicana on Roots and Shoots Elongation
(mm)
Root and shoot lengths of 15 days old seedlings of C.
ternatea and B. dictyoneura treated with leaf and seed
aqueous extracts of Argemone mexicana were much
shorter in comparison with those of the control. The
length of roots and shoots of C. ternatea and B. dictyo
neura was decreasing with increase in concentrations of
seed and leaf extracts.
Table 1. Effect of seed and leaf extracts of A. mexicana on germination percentage of B. dictyoneura and C. ternatea.
B. dictyoneura C. ternatea
Extract Concentrations Seed Extracts Leaf Extracts Seed Extracts Leaf Extracts
T0 (Control) 92.5 ± 4.78d 95 ± 5c 95 ± 2.88c 97.5 ± 2.5c
T1 (25%) 70 ± 4.08c 65 ± 5b 72.5 ± 4.78b 77.5 ± 8.54b
(−24) (−31.6) (−24.2) (−20.5)
T2 (50%) 50 ± 5.77b 50 ± 5.77b 70 ± 7.07ab 77.5 ± 4.79b
(−45.9) (−47.4) (−26.3) (−20.5)
T3 (75%) 32.5 ± 4.78ab 12.5 ± 6.29a 60 ± 9.12ab 37 ± 2.5a
(−64.8) (−86.8) (−36.8) (−62.1)
T4 (100%) 17.5 ± 8.54a 7.5 ± 4.79a 52.5 ± 6.29a 25 ± 9.57a
(−81.1) (−92.1) (−44.7) (−74.4)
One way ANOVA (F Statistics) 26.2037*** 46.1357*** 6.35** 23.156***
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at p = 0.05 according to LSD. Values in the parenthesis indicates percent-
age of the inhibitory (−) effects in comparison with control (T0).

Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
2141
Roots length of B. dictyoneura treated with concentra-
tion of 25%, 50%, 75% and 100% seed extract were 20.4,
16.4, 10.7 and 8.3 mm long respectively (Table 2). Root
elongation inhibition percentages of seedlings treated
with 25%, 50%, 75% and 100% of seed extracts was
−29.4%, −43.3%, −63% and −71.3% respectively. Leaf
extracts also significantly (p ≤ 0.001) reduced roots
elongation in comparison with control by −36.1%,
−50.3%, −66%, and −64.6% when treated at concentra-
tions of 25%, 50%, 75% and 100% respectively.
In leaf extracts, the shortest roots were recorded at
higher concentrations whereas longest was recorded in
the control treatment. The shoot lengths of B. dictyo-
neura were significantly (p ≤ 0.001) reduced by −20.5%,
−54.2%, −67.3% and −68.6% at concentrations (seed
extracts) of 25%, 50%, 75% and 100% respectively. The
tallest shoot of 60.5 mm long was observed in control
treatment while at concentrations of 25%, 50%, 75% and
100%; shoot length was 48.1, 27.7, 19.8 and 19 mm re-
spectively. In leaf extracts, the tallest shoot of 60.1 mm
was measured in control treatment compared with 46.8,
25.5, 19.9 and 18.3 mm long, which was recorded in
concentrations of 25%, 50%, 75% and 100% respectively.
In comparison with control, shoot lengths were signifi-
cantly (p ≤ 0.001) reduced by −22.1%, −57.6%, −66.9%
and −69.6% in leaf extracts with concentration of 25%,
50%, 75% and 100% respectively.
The allelopathic effect of seed and leaf extract of A.
mexicana on root and shoot lengths of C. ternatea is
shown in Table 3. Root lengths of C. ternatea were re-
duced with increase in concentration of seed extracts.
The mean root length of C. ternatea treated with distilled
water (control) was 35 mm long while, the root length of
seedlings treated with 25%, 50%, 75% and 100% extract
concentrations was 31.3, 24.5, 24.3 and 16.9 mm long re-
spectively. Root length inhibition caused by seed extract
at concentrations of 25%, 50%, 75% and 100% was
−10.6%, −30%, −30.6% and −51.7% respectively. Root
elongation of C. ternatea was also significantly (p ≤
0.001) hindered by different concentration of leaf extract
whereby elongation inhibition was −26.5%, −49.9%,
−63.6% and −83.5% at the concentrations of 25%, 50%,
75% and 100% respectively. Mean root length in control
treatment was 39.3 mm while in concentrations of 25%,
50%, 75% and 100%, the mean root length was 28.9,
19.7, 14.3 and 6.5 mm respectively.
In comparison with control treatment, the allelopathic
effect of leaf extract of A. mexicana reduced significantly
(p ≤ 0.01) the shoot length of C. ternatea. At concentra-
tions of 25%, 50%, 75% and 100%, the shoot length was
81.4, 74.8, 94.5 and 13.6 mm respectively. Shoot length
inhibition caused by leaf extracts was −22.5%, −28.8%,
−10% and −87% in response to extract concentrations of
25%, 50%, 75% and 100% respectively. Seed extracts of
A. mexicana also reduced shoot length of C. ternatea but
it was not significant.
3.3. Effects of Aqueous Extracts of A. mexicana
on Seedling Length (mm)
Mean seedlings length of C. ternatea and B. dictyoneura
treated with different concentrations of leaf and seed
extracts of A. mexicana were much shorter in comparison
with those of the control treatment (Table 4). Different
concentrations of seed extracts significantly (p ≤ 0.05)
reduced seedling length of C. ternatea by −8.5, −10.5,
−23.6 and −31.8% in response to seed extract concentra-
tions of 25%, 50%, 75% and 100% respectively. Mean
Table 2. Effect of seed and leaf extracts of A. mexicana on root and shoot elongation and seedling growth of B. dictyoneura.
Seed Extracts Leaf Extracts
Extract Concentrations Root Length (mm) Shoot Length (mm) Root Length (mm) Shoot Length (mm)
T0 (Control) 28.9 ± 1.31d 60.5 ± 0.43d 28.8 ± 0.75d 60.1 ± 1.15d
T1 (25%) 20.4 ± 0.01c 48.1 ± 1.68c 18.4 ± 0.085c 46.8 ± 1.14c
(−29.4) (−20.5) (−36.1) (−22.1)
T2 (50%) 16.4 ± 0.9b 27.7 ± 1.41b 14.3 ± 0.59b 25.5 ± 1.13b
(−43.3) (−54.2) (−50.3) (−57.6)
T3 (75%) 10.7 ± 0.23a 19.8 ± 0.96a 9.80 ± 1.33a 19.9 ± 0.41a
(−63) (−67.3) (−66) (−66.9)
T4 (100%) 8.3 ± 0.31a 19.0 ± 0.25a 10.2 ± 0.51a 18.3 ± 1.29a
(−71.3) (−68.6) (−64.6) (−69.6)
One way ANOVA (F Statistics) 109.7704*** 254.767*** 82.252*** 269.857***
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at P = 0.05 according to LSD. Values in the parenthesis indicates percent-
age of the inhibitory (−) effects in comparison with control (T0).
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Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
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Table 3. Effect of seed and leaf extracts of A. mexicana on root and shoot elongation (mm) of C. ternatea.
Seed Extracts Leaf Extracts
Extract Concentrations Root Length (mm) Shoot Length (mm) Root Length (mm) Shoot Length (mm)
T0 (Control) 35.0 ± 1.75d 106.7 ± 1.78a 39.3 ± 2.18d 105.0 ± 1.88b
T1 (25%) 31.3 ± 3.0cd 98.4 ± 6.58ab 28.9 ± 1.51c 81.4 ± 8.44a
(−10.6) (−7.8) (−26.50) (−22.50)
T2 (50%) 24.5 ± 1.51b 102.3 ± 5.86b 19.7 ± 3.11b 74.8 ± 10.12a
(−30) (−4.1) (−49.9) (−28.8)
T3 (75%) 24.3 ± 4.24abc 83.9 ± 6.99ab 14.3 ± 0.88ab 94.5 ± 2.47ab
(−30.6) (−21.4) (−63.6) (−10)
T4 (100%) 16.9 ± 2.03a 79.7 ± 12.02b 6.5 ± 0.0a 13.6 ± 0.0c
(−51.70) (−25.30) (−83.5) (−87)
One way ANOVA (F Statistics) 9.8*** 2.3 NS 23.688*** 10.6397**
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at p = 0.05 according to LSD. Values in the parenthesis indicates percent-
age of the inhibitory (−) effects in comparison with control (T0).
Table 4. Effect of seed and leaf extracts of A. mexicana on seedling length (mm) of B. dictyoneura and C. ternatea.
C. ternatea B. dictyoneura
Extract Concentrations Seed Extracts Leaf Extracts Seed Extracts Leaf Extracts
T0 (Control) 141.7 ± 3.31b 144.2 ± 2.83c 89.4 ± 1.5d 88.8 ± 1.89d
T1 (25%) 129.6 ± 6.56ab 110.4 ± 8.33a 68.5 ± 1.67c 65.2 ± 1.54c
(−8.5) (−23.4) (−23.4) (−26.6)
T2 (50%) 126.8 ± 7.12ab 97.4 ± 13.79a 44.1 ± 2.25b 39.7 ± 1.65b
(−10.5) (−32.5) (−50.7) (−55.3)
T3 (75%) 108.2 ± 11.23ac 108.8 ± 1.59a 30.5 ± 1.14a 29.6 ± 1.48a
(−23.6) (−24.5) (−65.9) (−66.6)
T4 (100%) 96.6 ± 14.01c 20.2 ± 0.0b 27.3 ± 0.51a 28.5 ± 0.78a
(−31.8) (−86) (−69.5) (−67.9)
One way ANOVA (F Statistics) 4.07* 14.362*** 267.277*** 233.903***
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at p = 0.05 according to LSD. Values in the parenthesis indicates percent-
age of the inhibitory (−) effects (%) in comparison with control (T0).
seedling lengths of C. ternatea in control treatment was
141.7 mm long while at concentrations of 25%, 50%,
75% and 100% of seed extracts were 129.6, 126.8, 108.2
and 96.6 mm respectively. In leaf extracts, seedling
length of C. ternatea was significantly (p ≤ 0.001) re-
duced as extract concentrations was increasing. Inhibi-
tion percentages of seedling length caused by leaf extract
concentrations of 25%, 50%, 75% and 100% were
−23.4%, −32.5%, −24.5% and −86% respectively. Mean
seedling length of C. ternatea at concentrations of 25%,
50%, 75% and 100% leaf extract of A. mexicana was
110.4, 97.4, 108.8 and 20.2 mm respectively. Hence
seedling length was decreasing with increase in extract
concentration relative to the control treatment in which
the seedling length was 144.2 mm long. Mean seedlings
length of B. dictyoneura treated with seed extracts of A.
Mexicana were significantly (p ≤ 0.001) reduced com-
pared with control treatment by −23.4%, −50.7%,
−65.9% and −69.5% in response to the concentrations of
25%, 50%, 75% and 100% respectively (Table 4). In-
crease in inhibition percentages caused the decrease in
seedling lengths whereby in control treatment the mean
seedling length of 89.4 mm long was recorded while at
concentrations of 25%, 50%, 75% and 100% seedling
length was 68.5, 44.1, 30.5 and 27.3 mm respectively.
The similar trend was observed in seedlings treated with
leaf extracts whereby significant (p ≤ 0.001) reduction in
seedling lengths was observed with increasing concentra-
tions in the extracts. Mean seedling lengths of B. dictyo-
neura in the control treatment was 88.8 mm while those
Open Access AJPS

Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
2143
treated with concentrations of 25%, 50%, 75% and 100%
leaf extracts had length of 65.2, 39.7, 29.6 and 28.5 mm
respectively. Hence length inhibition impact caused by A.
Mexicana leaf extract at concentrations of 25%, 50%,
75% and 100% was −26.6%, −55.3%, −66.6% and
−67.7% respectively.
3.4. Effects of Aqueous Extracts of A. mexicana
on Fresh Weight and Dry Weight (mg)
Mean seedling fresh weight and dry weights of B. dic-
tyoneura are presented in Table 5. The fresh weight and
dry weight of B. dictyoneura seedlings were significantly
(p ≤ 0.001) affected upon treatment with different con-
centrations of leaf and seed extracts of A. mexicana. In
seed and leaf extract of A. mexicana the fresh weight and
dry weight of B. dictyoneura decreased with increasing
concentrations in the extracts.
The mean fresh weights of B. dictyoneura in the con-
trol treatment was 22.3 mg while at concentration of 25%,
50%, 75% and 100% seed extracts, fresh weight was
15.5, 12.1, 8.5 and 5.9 mg respectively. Hence, in com-
parison with mean fresh weight in the control treatment,
the fresh weight of B. dictyoneura at 25%, 50%, 75% and
100% seed extracts concentrations were reduced by
−30%, −45.7%, −61.9% and −73.5% respectively.
With leaf extracts of A. mexicana, the mean fresh
weights of B. dictyoneura decreased with increase in
extracts concentration. Mean fresh weight of seedling
treated with leaf extract at concentrations of 25%, 50%,
75% and 100% was 22.7, 12.9, 10.7, 10.1 and 7.5 mg
respectively. In comparison with mean fresh weight of
control treatment, the mean fresh weights at concentra-
tions of 25%, 50%, 75% and 100% leaf extracts was sig-
nificantly inhibited by −43%, −52.9%, −55.6% and
−67% respectively.
Phytotoxin of seed extract of A. mexicana also inhib-
ited dry weight of B. dictyoneura at different concentra
tion levels. The highest dry seedling weight of 1.97 mg
was acquired in control treatment while at concentrations
of 25%, 50%, 75% and 100% the mean dry weights were
1.4, 0.63, 0.29, and 0.17 mg respectively. The reduction
percentage of seedling dry weight in the seed extract at
concentrations of 25%, 50%, 75% and 100% were
−28.9%, −68%, −85% and −91% respectively.
Results in Table 5 illustrate that the leaf extracts also
significantly (p ≤ 0.001) decreased the seedling dry
weight as compared with control treatment. The seedling
dry weight of 1.8 mg was obtained in control treatment,
while dry weights of 0.5, 0.33, 0.27 and 0.25 mg were
recorded at concentrations of 25%, 50%, 75% and 100%
respectively. The inhibition effect in dry weights of seed-
lings treated with leaf extracts at concentration of 25%,
50%, 75% and 100% were −72.2%, −81.7%, −85%,
−86.1% respectively.
Mean fresh weight and dry weights in Table 6, dem-
onstrated that seed and leaf extracts of A. mexicana sig
nificantly decreased the seedling fresh and dry weight of
C. ternatea as compared with control treatment.
Mean fresh weight of C. ternatea treated with seed ex-
tracts significantly decreased by −5%, −17%, −22% and
−28% when treated with seed extract at concentrations of
25%, 50%, 75% and 100% respectively. Thereafter, the
mean fresh weight of C. ternatea in the control treatment
was 340 mg, while at concentrations of 25%, 50%, 75%
Table 5. Effect of seed and leaf extracts of A. mexicana on fresh and dry weight of Brachiaria dictyoneura.
Seed Extracts Leaf Extracts
Extract Concentrations Fresh Weight (mg) Dry Weight (mg) Fresh Weight (mg) Dry Weight (mg)
T0 (Control) 22.3 ± .29d 1.97 ± 0.25b 22.75 ± 1.89c 1.8 ± 0.11b
T1 (25%) 15.6 ± 0.71c 1.4 ± 0.37b 12.97 ± 0.58b 0.5 ± 0.18a
(−30) (−28.9) (−43) (−72.2)
T2 (50%) 12.1 ± 0.74b 0.63 ± 0.11a 10.71 ± 0.59ab 0.33 ± 0.19a
(−45.7) (−68) (−52.9) (−81.7)
T3 (75%) 8.5 ± 1.28a 0.29 ± 0.01a 10.1 ± 0.59ab 0.27 ± 0.17a
(−61.9) (−85.3) (−55.6) (−85)
T4 (100%) 5.9 ± 0.81a 0.17 ± 0.04a 7.5 ± 0.7a 0.25 ± 0.15a
(−73.5) (−91.4) (−67) (−86.1)
One way ANOVA (F Statistics) 37.8702*** 12.226*** 27.051*** 16.614***
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at p = 0.05 according to LSD. Values in the parenthesis indicates percent-
age of the inhibitory (−) effects in comparison with control (T0).
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Table 6. Effect of seed and leaf extracts of A. mexicana on fresh and dry weight of Clitoria ternatea.
Seed Extracts Leaf Extracts
Extract Concentrations Fresh Weight (mg) Dry Weight (mg) Fresh Weight (mg) Dry Weight (mg)
T0 (Control) 340 ± 15.31c 33.5 ± 2.08c 343 ± 7.9b 35.1 ± 1.64c
T1 (25%) 321.7 ± 17.77bc 25.4 ± 3.07b 240.9 ± 30.9a 18.2 ± 1.83ab
(−5) (−24) (−30) (−48)
T2 (50%) 282.5 ± 15.94ab 15.4.0 ± 2.26a 168.0 ± 29.9a 13.7 ± 1.71a
(−17) (−54) (−51) (−61)
T3 (75%) 263.9 ± 47.52ab 13.9 ± 1.25a 144.8 ± 45.46a 13.7 ± 4.13a
(−22) (−59) (−58) (−61)
T4 (100%) 243.4 ± 18.74a 11.9 ± 1.37a 134.5 ± 0.0a 10.2 ± 0.0a
(−28) (−64) (−61) (−71)
One way ANOVA (F Statistics) 4.305* 16.25*** 8.99** 65.87***
Values presented are means ± SE. *, **, *** = significance at p ≤ 0.05, p ≤ 0.01, p ≤ 0.001 respectively. NS = not significant, SE = Standard error of mean. Means
followed by similar letter in a column are not significantly different from each other at p = 0.05 according to LSD. Values in the parenthesis indicates the per-
centage of inhibitory (−)effects in comparison with control (T0).
and 100% fresh weight was 321.7, 282.5, 263.9 and
243.4 mg respectively. Similar trend was evident with
leaf extract whereby the mean fresh weight of C. ter-
natea decreased with increasing concentrations of A.
mexicana. Mean fresh weight at concentrations of 25%,
50%, 75% and 100% leaf extract was 240.9, 168, 144.8
and 134.5 mg respectively. Relative to the control treat-
ment, the mean fresh weight of C. ternatea treated with
concentration of 25%, 50%, 75% and 100% leaf extract
were significantly (p ≤ 0.01) reduced by −30%, −51%,
−58% and −61% respectively Dry weight of C. ternatea
was significantly (p ≤ 0.01) reduced by seed extracts
compared with the control treatment (Table 6). The de-
crease in seedling dry weight with seed extracts was
−24%, −54%, −59% and −64% in response to seed ex-
tracts concentrations of 25%, 50%, 75% and 100% re-
spectively. Hence, the highest dry weight of 33.5 mg was
acquired in the control treatment while at concentrations
of 25%, 50%, 75% and 100% seed extracts, the dry
weight were 25.4, 15.4, 13.9 and 11.9 mg respectively. In
leaf extracts of A. mexicana, the trend of dry weights was
similar to that of seed extracts whereby dry weight of C.
ternatea decreased with increasing concentration. Dry
weight of seedlings in the control treatment was higher
(35.1 mg) than seedlings that treated with leaf extracts of
different concentrations. Dry weights of C. ternatea
seedlings were 18.2, 13.7, 13.7, and 10.2 mg in response
to leaf extract concentrations of 25%, 50%, 75% and
100% respectively. Therefore, mean dry weights of C.
ternatea were inhibited by −48%, −61%, −61% and
−71% when treated with leaf extract at concentrations of
25%, 50%, 75% and 100% respectively.
4. Discussion
This study clearly shows that there is phototoxic effect of
aqueous extracts of leaves, and seeds of A. mexicana on
the germination and growth of C. ternatea and B. dic-
tyoneura. Higher concentrations of leaf and seed extracts
had a higher degree of germination inhibition. This might
have been caused by some of allelochemicals present in
leaf and seed aqueous extracts of A. mexicana. These
results correlates with studies conducted by Burhan and
Shaukat, [21] Paul and Begum [22] and Alagesaboopathi
[23] who reported seed germination inhibition of Sor-
ghum bicolor, carrot, wheat, mustard, turnip, pearl-millet,
blackgram, rapeseed wheat and corn with increase in A.
mexicana leaf and shoot extracts concentration. The
germination reductions in these studies were related to
the allelopathic potential of A. Mexican. In detailed stud-
ies, Rice, [27] revealed that some of allelochemicals in-
terrupted the mitotic activity of young cells, resulting in
the inhibition of seed germination. Similar to our study,
several researchers have reported germination inhibition
in some cultivated crop species. For instance, Chandra et
al. [28] and Esmaeili et al. [29] reported that salicylic
and vanillic inhibited seed germination of cowpea (Vigna
unguiculata) and Barnyard grass (Echinochlo a crus-galli
L) respectively.
In this study, shoot, root and seedling growth of C.
ternatea and B. dictyoneura treated with different con-
centrations of seed and leaf extracts of A. mexicana were
reduced with increasing concentrations. Reduction in
seedling growth might have been caused by some of al-
lelochemicals. According to studies by Cruz-Ortega et al.
[12] Colpas et al. [13] and Cruz et al. [14] some al-
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Allelopathic Effect of Aqueous Extract of Argemone mexicana L on Germination and
Growth of Brachiaria dictyoneura L and Clitoria ternatea L
2145
lelochemicals from A. mexicana were reported to inter-
rupt the process of cell division and elongation in roots
and shoots which in turn reduced the seedling growth.
Barkosky and Einhellig [30] also found that the growth
of soybean seedlings was reduced with high concentra-
tions of phydroxybenzoic acid. Chen et al. [31] postu-
lated that exudates of vanillin and cinnamic acid posed
allelopathic effect on egg plant seedling growth at high
level concentration. Elsewhere, other researchers found
that cinnamic acid was an allelochemical responsible for
allelopathy for root growth in cucumber [32] and shoot
and root length of cabbage seedlings [33]. Hence results
on seedling growth found in this study conforms to find-
ings reported by Alagesaboopathi [23]; Paul and Begum
[24]; Jilani et al. [25]; Burhan and Shaukat [21] who re-
ported allelopathic effect of A. mexicana on the growth
of tomato, sorghum, lentil, carrot, wheat, mustard, turnip,
pearlmillet, corn, blackgram and rapeseed.
In comparative analysis between control treatment and
aqueous extract treatments, the root lengths were greatly
inhibited than shoot lengths. The difference in the extents
to which roots and shoots were affected by aqueous ex-
tracts in this study may be due to the contact of the roots
with the filter paper, leading to constant absorption of the
extract solution [34]. Also Nishida et al. [35] postulated
that permeability of allelochemicals to root tissues is
greater than in shoots. Chon et al. [36] reported that root
length is good indicator of allelopathic effect of plant
extracts because it is more sensitive to phytotoxic com-
pounds than shoot growth. Keshavarzi et al. [37] also
concluded that extracts has more impact on radicle length,
because it has direct contact with radicle. Similar kind of
observation was also reported by Sarkar et al. [34] who
studied allelopathic effect of Cassia tora on seed germi-
nation and growth of mustard.
The present study also found that seed and leaf extract
of A. mexicana significantly reduced fresh and dry
weights of B. dictyoneura and C. ternatea with increas-
ing extracts concentration. Decrease in fresh and dry
weight might be attributed to allelochemicals inhibiting
protein and carbohydrate synthesis and hence reducing
seedling growth [11,16,38]. Similar to our study, Alage-
saboopathi [23] also reported the decrease in fresh and
dry weights of sorghum upon treatment with different
concentrations of A. mexicana leaf aqueous extracts.
Overall, leaf extracts were found to have more allelo-
pathic effect compared with seed extracts in most of pa-
rameters tested. Similar findings were also reported by
Paul and Begum [22]; Cipollini and Flint [39] in black-
gram, rapeseed, wheat and native woodland plants.
Moreover, in this study the allelopathic effects of leaf
and seed extracts of A. mexicana was stronger in grass
species (B. dictyoneura) than in the leguminous species
(C. ternatea). This observation might be due to the fact
that some leguminous species has allelopathic potentials.
Study done by Piyatida and Kato-Nunguchi [40] con-
cluded that C. ternatea has inhibitory effect on the
growth of lettuce (Lactuca sativa L), alfalfa (Medicago
sativa L) and timothy (Phleum pretence L).
5. Conclusion
From the present study, it is evident that, A. mexicana
has allelopathic effect on the germination, growth and
development of C. ternatea and B. dictyoneura. The al-
lelochemicals compounds in A. mexicana might have
inhibited the seed germination, seedling growth in the
tested plant species. However, the inhibition was dose
dependent as there was great inhibition at higher extract
concentrations. A. mexicana being allelopathic and inva-
sive alien species in Tanzania it should be controlled in
natural ecosystems and agricultural fields otherwise may
suppress crops and native plant species. However, further
research is needed to isolate and identify specific al-
lelochemicals presented in A. mexicana and mechanisms
which caused inhibition in the tested species.
6. Acknowledgements
Many thanks are due to Dr Margaret J Mollel from Na-
tional Plant Genetic Resources Centre of Tanzania at
TPRI for providing seeds used in this study and Labora-
tory scientists at the Nelson Mandela African Institute of
Science and Technology (NM-AIST Laboratory) for
their valuable assistance during the course of the research.
This study was funded by Tanzania Commission for
Science and Technology (COSTECH) through the Nel-
son Mandela African Institution of Science and Tech-
nology.
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