Allelopathic Effects of Aqueous Extracts of Eucalyptus occidentalis

Short Communication
Allelopathic Effects of Aqueous Extracts of Eucalyptus
occidentalis, Acacia ampliceps and Prosopis juliflora on the
Germination of Three Cultivated Species
Ezzeddine Saadaoui, Naziha Ghazel, Chokri Ben Romdhane, Station Régionale
de Gabès, Institut National des Recherches en Génie Rural, Eau et Forêt
(INRGREF), Université de Carthage, Tunis, Tunisia, Nizar Tlili, Faculté des
Sciences de Gafsa, Université de Gafsa, Tunisia, and Abdelhamid Khaldi,
INRGREF, Université de Carthage, Tunis, Tunisia
__________________________________________________________________________
ABSTRACT
Saadaoui, E., Ghazel, N., Ben Romdhane, Ch., Tlili, N., and Khaldi, A. 2014.
Allelopathic effects of aqueous extracts of Eucalyptus occidentalis, Acacia ampliceps and
Prosopis juliflora on the germination of three cultivated species. Tunisian Journal of
Plant Protection 9: 11-16.
This study concerns the effect of the aqueous extracts of Eucalyptus occidentalis, Acacia ampliceps and
Prosopis juliflora on the germination of three species frequently cultivated in the South of Tunisia:
Barley (Hordeum vulgare), annual lucerne (Medicago sativa) and jew's mallow (Corchorus olitorius).
Aqueous extracts were obtained after a maceration of the dry plant material in distilled water (90 g/l)
during 48 h at 60°C. The extraction was made from three vegetative organs (roots, twigs and leaves)
for each species. The results showed a variable behavior between the species according to the origin of
the extract. Barley is the most sensitive species, showing decrease of germination rate essentially with
the leaf extracts of P. juliflora (52.5 ± 15.86%), E. occidentalis (61.5 ± 7.89%) and A. ampliceps (65.5
± 5.7%). The annual lucerne showed a moderate tolerance; its germination rate was 76 ± 11.61, 81.5 ±
5.74 and 96 ± 2.82%, respectively, for the leaf extracts of A. ampliceps, E. occidentalis and P. juliflora.
C. olitorius was found to be the most tolerant species to all extracts; only leaf extracts of E.
occidentalis resulted in a lower germination than the control; it was 90 ± 4.32%. The extracts of the
studied species affected the root system length; a reduction of the length was essentially observed for
M. sativa and C. olitorius.
Keywords: Acacia ampliceps, allelopathy, aqueous extract, Eucalyptus occidentalis, germination,
Prosopis juliflora
__________________________________________________________________________
Allelopathy, from the latin words allelon
of each other and pathos to suffer refers
to the chemical inhibition of one
species by another. Although, the term
allelopathy is most commonly used to
describe the chemical interaction between
two plants, it has also been used to
describe microbe-microbe, plant-microbe
and plant-insect or plant-herbivore
chemical communication (9). The
chemical substances, collectively known
as allelochemicals, are usually secondary
Corresponding author: Ezzeddine Saadaoui
Email: [email protected]
Accepted for publication 11 May 2014
Tunisian Journal of Plant Protection
11
Vol. 9, No. 1, 2014
plant products or waste products of main
metabolic pathways of plants (10). In
plants, allelochemicals can be present in
leaves, bark, roots, root exudates, flowers
and fruits. The delivery of allechemicals
into the rhizosphere is often thought to
occur through leaching from leaves and
other aerial plant parts, through volatile
emissions by roots exudation and by the
breakdown of bark and leaf litter (12).
Indeed, plants use up to 30% of their
photosynthate in the production of root
exudates, which affect the local soil
environment, termed the rhizosphere.
Each of these processes may release
chemicals that mediate allelopathic
interactions between plants. Media
containing exudates inhibited the growth
and germination of several plant species,
suggesting the presence of phytotoxins
(3). Eucalyptus sp., Acacia sp., and
Prosopis sp. have an allelopathic effect
on seed germination of other species (4,
5, 6, 7). The purpose of this study is to
elucidate the effect of the aqueous
extraction of three species (Eucalyptus
occidentalis, Acacia ampliceps and
Prosopis juliflora) and three organs from
each species (leaves, twigs and roots) on
the germination of three other species
(Hordeum vulgare, Medicago sativa and
Corchorus olitorius) cultivated frequently
in the region of Gabes, in the south of
Tunisia.
The aqueous extracts were
prepared from dry plant material. A mass
of 90 g of each plant material was soaked
into 1 liter of distilled water and kept at
60°C for 48 h before filtration to prepare
extract of 90 g/l. The seeds were
thoroughly washed with distilled water
and surface sterilized with sodium
hypochlorite (12%) for 2-3 min. In each
Petri dish, 50 seeds were placed and 2 ml
of aqueous water were added (leaf, twig
and root), and then kept inside the
Tunisian Journal of Plant Protection
incubator at 28°C. The control was
treated with 2 ml of distilled water. Each
treatment had four replicates. Seeds
belong to three cultivated species in the
south of Tunisia (H. vulgare, M. sativa
and C. olitorius). Seed germination was
investigated every day and radicle length
was recorded. Data were analyzed by the
analysis of variance (ANOVA), using the
XLstat, 2012 software package and
differences were considered statistically
significant at P < 0.05.
The leaf extract of E. occidentalis
reduced significantly the germination for
the three studied species (P < 0.05).
However, the twig extract affected only
on the germination of H. vulgare seeds
(Fig. 1). The aqueous extract of the leaves
showed the lowest rate of germination for
the three studied species. The extracts of
all organs of E. occidentalis reduced only
the extension of M. sativa and C. olitorius
roots (Fig. 1). For A. ampliceps extracts,
the lowest germination percentage was
obtained for H. vulgare seeds treated with
root, twig and leaf extracts and with leaf
extract for M. sativa seeds. C. olitorius
showed a constant rate of germination for
all treatments. The leaf extract of A.
ampliceps affected negatively the
germinating potential of M. sativa and H.
vulgare seeds. A. ampliceps extracts had
also reduced the extension of M. sativa
and C. olitorius roots (Fig. 2). The
extracts of the roots, twigs and leaves of
P. juliflora decreased significantly the
germination percentage of H. vulgare (P
< 0.05). Indeed, the lowest rate of
germination was noted on barley seeds
treated with leaf extract (52.5 ± 15.86%)
as indicated by a decrease of about 40%
compared to the untreated control. The
inhibitory effect was not significant for
M. sativa and C. olitorius seeds. This
decrease was not observed for the root
extension (Fig. 3).
12
Vol. 9, No. 1, 2014
a a a
100
a a a
a a
a
10
b
80
Root length (mm)
Germination (%)
a
12
b b
b,c
60
40
20
8
b
6
b
a
b
b
b
a
a
M. sativa
b a
C. olitorius
4
H. vulgare
2
0
0
control
control
A
root
twig
leaf
root
twig
leaf
B
Fig. 1. Effects of aqueous extracts (root, twig and leaf) of Eucalyptus occidentalis on germination (A) and root
length (B) of Hordeum vulgare, Medicago sativa and Corchorus olitorius. For each cultivated species, bars affected
by the same letters are not significantly different at P < 0.05.
a a a
100
a a a
a a
a
10
b
80
Root length (mm)
Germination (%)
a
12
b b
b,c
60
40
20
8
b
6
a
b
b
b
b
a
a
M. sativa
b a
C. olitorius
4
H. vulgare
2
0
0
control
control
A
root
twig
leaf
root
twig
leaf
B
Fig. 2. Effects of aqueous extracts (root, twig and leaf) of Acacia ampliceps on germination (A) and root length (B)
of Hordeum vulgare, Medicago sativa and Corchorus olitorius. For each cultivated species, bars affected by the
same letters are not significantly different at P < 0.05.
a
a a
a a
b,c
80
Germination (%)
a a
a a
b,c
60
c
40
20
0
A
control
root
twig
leaf
Root length (mm)
100
12
10
8
6
4
2
0
B
a a
b
a
a
a
a
b b
b
b
b
C. olitorius
M. sativa
H. vulgare
control root
twig
leaf
Fig. 3. Effects of aqueous extracts (root, twig and leaf) of Prosopis juliflora on germination (A) and root length (B)
of Hordeum vulgare, Medicago sativa and Corchorus olitorius. For each cultivated species, bars affected by the
same letters are not significantly different at P < 0.05.
Tunisian Journal of Plant Protection
13
Vol. 9, No. 1, 2014
The aqueous extracts of the three
studied species (E. occidentalis, A.
ampliceps and P. juliflora) decreased the
germination rate of seeds of three plants
tested i.e H. vulgare, M. sativa and C.
olitorius. This decrease was more
significant for leaf extract for the three
species. These findings agreed with those
obtained by other authors (4, 5, 6). The
high inhibitory effect of Triticum
aestivum germination was recorded with
P. juliflora leaf extract (10). High
susceptibility of H. vulgare seeds to
Eucalyptus (8), Ocimum basilicum (12),
Armoracia rusticana (11), Salvia
officinalis and Juglans regia extracts (1,
2) was reported. The decrease of
germination also depended on the species
studied. H. vulgare was found to be the
most sensitive species to all extracts
tested while M. sativa and C. olitorius
exhibited a tolerance to the water extracts.
Indeed, tolerance of M. sativa seeds to
aqueous extracts from Eucalyptus leaves
was also reported by Yu (13). The
decrease of root system length was
highest for M. sativa and C. olitorius and
lowest for H. vulgare. No positive
correlation was observed between the
decrease in the percentage of germination
and that of the root length. This
phenomenon can be understandable by a
different specific physiological behavior.
The study of the allelopathic effect on the
germination and the production of the
cultivated species needs to be more
elucidated in arid regions.
__________________________________________________________________________
RESUME
Saadaoui E., Ghazel N., Ben Romdhane Ch., Tlili N. et Khaldi A. 2014. Effet
allélopathique des extraits aqueux d’Eucalyptus occidentalis, Acacia ampliceps et
Prosopis juliflora sur la germination de trois espèces cultivées. Tunisian Journal of
Plant Protection 9: 11-16.
Cette étude concerne l’effet des extraits aqueux d’Eucalyptus occidentalis, Acacia ampliceps et
Prosopis juliflora sur la germination de trois espèces fréquemment cultivées au sud tunisien: l’orge
(Hordeum vulgare), la luzerne annuelle (Medicago sativa) et la corète (Corchorus olitorius). Les
extraits aqueux ont été obtenus après une macération du matériel végétal sec (90 g/l) dans de l’eau
distillée pendant 48 h à 60°C. Pour chaque espèce étudiée, les extraits ont été obtenus à partir de trois
organes (racines, rameaux et feuilles). Les résultats ont montré un comportement variable entre les
espèces selon l’origine de l’extrait. L’orge est l’espèce la plus sensible, montrant une chute du taux de
germination et surtout avec les extraits des feuilles de P. juliflora (52,5 ± 15,86%), E. occidentalis
(61,5 ± 7,89%) et A. ampliceps (65,5 ± 5,7%). La luzerne annuelle a montré une tolérante modérée, son
pourcentage de germination a été de 76 ± 11,61, 81,5 ± 5,74 et 96 ± 2,82% avec les extraits de feuilles
d’A. ampliceps, E. occidentalis et P. juliflora, respectivement. La corète s’est montrée l’espèce la plus
tolérance à tous les extraits; seul l’extrait de feuilles d’E. occidentalis a induit une faible germination
comparé au témoin qui a été de 90 ± 4,32%. Les extraits des espèces étudiées ont affecté la longueur de
la racine principale; une réduction de la longueur a été observée surtout chez M. sativa et C. olitorius.
Mots clés : Acacia ampliceps, allélopathie, Eucalyptus occidentalis, extrait aqueux, germination,
Prosopis juliflora
__________________________________________________________________________
Tunisian Journal of Plant Protection
14
Vol. 9, No. 1, 2014
__________________________________________________________________________
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juliflora
___________________________________________________________________________
Prosopis ،Eucalyptus occidentalis ،Acacia ampliceps ،
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