The present study aimed to evaluate the phytotoxic potential of essential oils. For this purpose, 18 essential oil samples extracted from Korean plants and 64 commercial essential oils were screened for their phytotoxic potential against the seedling growth of
L. (rapeseed). Among the 82 samples, 11 commercial oils (cinnamon, citronella, clove, cumin seed, geranium, jasmine, lemongrass, palmarosa, pimento, rose otto and spearmint) strongly inhibited the seedling growth with GR
value <150 μg mL
. Major components from these effective essential oils were identified by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS). GC-MS analyses revealed that the effective samples mainly consist of benzyl benzoate, carvone, citral, citronellol, eugenol, geraniol, D-limonene and terpinene. Subsequently, bioactivity of these individual components was evaluated against the seedling growth of
. The components from different chemical groups exhibited different potency in inhibiting the seedling growth with varied GR
values ranged from 29 μg mL
to >1,000 μg mL
. In the greenhouse experiment, citral and geraniol completely suppressed the growth of all the tested 10 plants at 100 kg ha
. In conclusion, the individual essential oil components geraniol and citral could be used as natural herbicides for weed management.
Weeds are one of the most important pests causing economic losses in the world agriculture. In commercial crop cultivation, the competitions caused by the growth of weeds are influencing the reduction of crop yield and quality of their products. The weed control can be achieved by manual, herbicidal or biological control methods
. Manual control method using hand weeding is a good weed control strategy, but requires more number of workers and also consuming more time. The use of synthetic herbicides to control weeds is common and the most effective method. Although synthetic herbicides have showed promising results, the continuous use of synthetic herbicides produce negative impacts on human health and environment, and linked to increasing herbicidal resistance in weed species
Batish et al., 2007)
. Thus, there is an important to search for environmentally safer and novel compounds with more effective, more specic targets for the management of weeds. In this regard, allelopathy is one of the alternative methods to control weed species biologically through the production and release of phytotoxic chemicals from different parts of living or decomposing plant materials
Phytotoxic compounds may help to reduce the use of synthetic herbicides and environmentally friendly method to attain high quality agricultural products
(Singh et al., 2003
Khanh et al., 2006)
. Recently, many studies have investigated the phytotoxic potentials of plant extracts and individual compounds and their ability to control weeds in crop production. Among the various natural plant products, essential oils constitute an important group of that provide a versatile source of bioactive components. Essential oils are natural, volatile and complex mixtures of terpenes in addition to some other non-terpene components as phenylpropanoids
. A number of studies have reported that the essential oils and their components are potent inhibitors of seed germination and retard plant growth
(Batish et al., 2007
Kaur et al., 2010
Yun et al., 2013)
. In phytotoxic activity, plant cuticle is the first barrier for diffusing the active component into the leaf tissue. Essential oils are known to promote the penetration of the active component through solubilizing or disrupting the nature of the cuticular waxes
(Izadi-Darbandi et al., 2013)
The present study was undertaken to evaluate the phyotoxic potential of essential oils and their components. For this purpose, essential oils extracted from different plants in Korea and commercially available essential oils were screened through a seed bioassay of
(rapeseed). Further, major components of effective essential oil samples were identified by SPME/GC-MS analysis. In addition, a greenhouse experiment was carried out using effective individual essential oil components against different plant species.
Materials and Methods
- Essential oils and individual chemicals
A total of 64 commercially available essential oils were purchased from Aroma House, Seoul, Republic of Korea (
). Benzyl benzoate, carvone, citral, citronellol, eugenol, geraniol, D-limonene, and terpinene were purchased from Sigma-Aldrich (St. Louis, MO, USA).
- Extraction of essential oils
Fresh plant parts of 18 plants (
) were collected in June 2012 from different places in Republic of Korea. The essential oil was extracted from the samples by steam distillation for 60 min (1 kg sample) using a Clevenger-type apparatus. The collected essential oils were dried with anhydrous sodium sulfate and stored under refrigeration (4℃).
Inhibitory activity of essential oils extracted from Korean plants against the seedling growth ofBrassica napus.
|S. No. ||Plant names ||Family name ||Plant parts ||GR50 (μg mL−1)z |
|1 ||Abies holophylla Maxim ||Pinaceae ||Needles ||556 |
|2 ||Abies koreana E.H. Wilson ||Pinaceae ||Cones ||1,552 |
|3 ||Abies nephrolepis (Trautv.) Maxim. ||Pinaceae ||Needles ||3,042 |
|4 ||Picea koraiensis Nakai ||Pinaceae ||Needles ||3,632 |
|5 ||Pinus bungeana Zucc. ex Endl. ||Pinaceae ||Needles ||>5,000 |
|6 ||Pinus densiflora Siebold & Zucc. ||Pinaceae ||Needles ||>5,000 |
|7 ||Pinus koraiensis Siebold & Zucc. ||Pinaceae ||Needles ||1,582 |
|8 ||Pinus parviflora Siebold & Zucc. ||Pinaceae ||Needles ||898 |
|9 ||Cosmos bipinnatus Cav. ||Compositae ||Flowers ||2,718 |
|10 ||Dendranthema indicum (L.) DesMoul. ||Compositae ||Flowers ||318 |
|11 ||Ligularia fischeri ||Compositae ||Leaves ||1,657 |
|12 ||Ligularia stenocephala (Maxim.) Matsum. & Koidz. ||Compositae ||Leaves ||2,272 |
|13 ||Juniperus chinensis L. ||Cupressaceae ||Leaves ||>5,000 |
|14 ||Chamaecyparis obtuse Siebold & Zucc. ||Cupressaceae ||Leaves ||942 |
|15 ||Thuja orientalis L. ||Cupressaceae ||Leaves ||>5,000 |
|16 ||Aralia cordata var. continentalis (Kitag.) Y. C. Chu ||Araliaceae ||Roots ||1,134 |
|17 ||Glechoma grandis (A. Gray) Kuprian ||Labiatae ||Whole plant ||567 |
|18 ||Metasequoia glyptostroboides Hu & W. C. Cheng ||Taxodiaceae ||Cones ||1,225 |
zGR50 values were calculated from four replicates of each sample.
Inhibitory activity of commercial essential oils against the seedling growth ofBrassica napus.
|S. No. ||Essential oil ||GR50 (μg mL−1)z ||S. No. ||Essential oil ||GR50 (μg mL−1)z |
|1 ||Angelica ||2,832 ||33 ||Lemongrass ||64 |
|2 ||Basil ||484 ||34 ||Lime ||1,577 |
|3 ||Bergamot ||1,308 ||35 ||Magnolia ||275 |
|4 ||Black pepper ||1,156 ||36 ||Majoram ||399 |
|5 ||Cajaput ||241 ||37 ||Mandarin ||3,762 |
|6 ||Camphor ||763 ||38 ||Myrtle ||906 |
|7 ||Caraway ||223 ||39 ||Neroli ||337 |
|8 ||Cardamom ||1,748 ||40 ||Niaouli ||911 |
|9 ||Carrot seed ||2,374 ||41 ||Nutmeg ||1,401 |
|10 ||Cedar wood ||1,382 ||42 ||Orange ||2,007 |
|11 ||Chamomile German ||>5,000 ||43 ||Patchouli ||1,206 |
|12 ||Chamomile Roman ||1,561 ||44 ||Palmarosa ||26 |
|13 ||Cinnamon ||79 ||45 ||Peppermint ||209 |
|14 ||Citronella ||79 ||46 ||Petitgrain ||457 |
|15 ||Clary sage ||684 ||47 ||Pimento ||52 |
|16 ||Clove ||48 ||48 ||Pine ||1,338 |
|17 ||Coriander ||315 ||49 ||Rose absolute ||599 |
|18 ||Cumin seed ||149 ||50 ||Rosemary ||873 |
|19 ||Cypress ||>5,000 ||51 ||Rose otto ||70 |
|20 ||Eucalyptus ||>5,000 ||52 ||Rose wood ||1,349 |
|21 ||Fennel ||667 ||53 ||Sage ||537 |
|22 ||Fir ||1,019 ||54 ||Sandalwood ||>5,000 |
|23 ||Frankincense ||1,370 ||55 ||Savory ||208 |
|24 ||Galbanum ||1,458 ||56 ||Spearmint ||149 |
|25 ||Geranium ||81 ||57 ||Tagetes ||758 |
|26 ||Ginger ||2,443 ||58 ||Tangerin ||575 |
|27 ||Grapefruit ||1,351 ||59 ||Teatree ||425 |
|28 ||Hyssop ||180 ||60 ||Thyme ||218 |
|29 ||Jasmine ||107 ||61 ||Vanilla ||>5,000 |
|30 ||Juniper ||>5,000 ||62 ||Vetiver ||855 |
|31 ||Lavender ||492 ||63 ||Yarrow ||503 |
|32 ||Lemon ||>5,000 ||64 ||Ylang ylang ||705 |
zGR50 values were calculated from four replicates of each sample.
- Seed materials
The seeds of rapeseed (
L.), Indian jointvetch (
L.), velvet leaf (
Medik.), cotton (
L.), soybean (
L.), roundleaf morning-glory (
Lam.) barnyardgrass (
(Willd.) Honda), Southern crabgrass (
(Retz.) Koeler), green foxtail (
L.), annual bluegrass (
L.) and maize (
L.) were purchased from local market, Chuncheon, Republic of Korea. Undersized or damaged seeds were discarded.
- Seed bioassay
The seed bioassay of essential oils was evaluated on seeds of
(rapeseed). To accomplish this experiment, 1% agar in distilled water was used as growth medium. The rapeseeds were surface sterilized with 0.5% sodium hypochlorite for 3min then washed with sterile distilled water. Essential oils were prepared with series of concentrations from 0-5,000 μg mL
(diluted using 0.01% Tween 20 v/v). The seeds were placed in a 24-well cell culture plate contains 1% agar medium (5 seeds per well). Then, one mL of each test solution was added to respective wells with four replicates per treatment. The plates were covered with plastic bags to maintain humidity and allowed to germinate in the growth chamber at 25℃/ 23℃ (day/night), 60% relative humidity, and 250 μmol m
light intensity for 5 days.
After the incubation period, the effect of essential oils on seedling growth was determined by measuring the weight of the seedlings. Inhibitory activity of essential oils against rapeseed growth was calculated based on growth rate
) values (effective concentrations capable of inhibiting 50% of plant growth). Further studies were carried out with most effective essential oil samples.
- SPME conditions
One mL of essential oil was introduced into SPME vial. The SPME device coated (fused-silica fiber) with a 100 μm layer of polydimethylsiloxane (Supelco, Bellefonte, PA, USA) was used for extraction of the plant volatiles and the vial was sealed with a silicone septum. They were exposed in the SPME vial at 60℃ for 30min and immediately introduced in the gas chromatography injector.
- Gas chromatography/mass spectrometry (GC/MS) analysis
GC-MS analysis was performed with a Varian CP 3800 gas chromatography equipped with a VF-5 MS polydimethylsiloxane capillary column (30×0.25mm×0.25μm) and a Varian 1200 L mass detector (Varian, CA, USA). Helium was used as a carrier gas at the rate of 1 mL min
. Oven temperature was kept at 50℃ for 5min initially, and then raised with rate of 5℃ min
to 250℃ min
. The injector temperature was set at 250℃. The mass spectra were recorded in the electrospray ionization mode at 70 eV in a scan range of 50-600m z
. The major components of essential oils were identified by comparing the retention indices of the GC peaks obtained using homologous series of n-alkanes (C
) with those reported in literature
. The mass spectra of the peaks were also matched with standards reported in literature and National Institute of Standards and Technology (NIST, 3.0) library.
- Effect of major components on seedling growth
The individual major components, namely benzyl benzoate, carvone, citral, citronellol, eugenol, geraniol, D-limonene and terpinene were used to evaluate their inhibitory activity against the seedling growth of
. The effect of individual components on seedling growth was carried out by following the procedure as mentioned earlier in the seed bioassay section.
- Greenhouse experiment
For greenhouse experiment, eight pure compounds, namely benzyl benzoate, carvone, citral, citronellol, eugenol, geraniol, D-limonene and terpinene were used to evaluate their herbicidal potential. In this experiment, five dicot plants (
) and five monocot plants (
) were used. The nursery trays were filled with sandy soil.
Ten seeds of each species were sown separately in each tray (350 cm
). Five days after seed sowing, different concentrations (25, 50 and 100 kg ha
) of eight pure individual components were prepared separately (Tween-20 0.01% v/v) and sprayed (1000 L ha
) using CO
pressure belt-driven track sprayer (R & D sprayer, 8002 EVB nozzle, 40 psi, 40 cm height). The observation was made post spray treatment of the test materials and the data were recorded at 3, 7 and 14 days after treatment by visually counting the plants in each treatment.
- Statistical analysis
The seed bioassay was conducted with four replications and the statistical analysis was carried out by analysis of variance (ANOVA) followed by Duncan’s test, and values of P<0.05 were considered significantly different. The data were evaluated with SPSS 18.0 software package (SPSS Inc., Chicago, IL, USA).
Results and Discussion
- Phytotoxic effect of essential oils on seedling growth of rapeseed
It is well known that phytotoxic compounds from plants are considered to be safe and beneficial to the environment and human beings
(Khanh et al., 2006)
. A variety of plant species have phytotoxic effects on weed species. The growth inhibitory activity of essential oils has remarkably increased the interest in exploring essential oil from plants for potential weed management. Germination and seedling growth bioassays are important preliminary screening methods to determine phytotoxic potential of plant extracts and compounds. In the present study, herbicidal activity of 18 essential oil samples extracted from Korean plants and 64 commercial essential oil samples was evaluated by seed bioassay using rapeseed. The results are expressed as GR
that is an effective concentration capable of inhibiting the seedling growth of rapeseed by 50% (
). Among the 18 essential oil samples extracted from Korean plants,
showed higher inhibitory activity (GR
of 318 μg mL
) followed by
of 556 μg mL
of 567 μg mL
In the case of commercial oil samples, GR
values against rapeseed seedling growth were ranged between 26 and >5,000 μg mL
. Out of 64 commercial essential oil samples, 11 oils (cinnamon, citronella, clove, cumin seed, geranium, jasmine, lemongrass, palmarosa, pimento, rose otto and spearmint) showed remarkable inhibitory activity against rapeseed seedling growth with GR
values of below 150 μg mL-1. Among them, palmarosa oil showed the highest inhibitory activity on seedling growth (GR
of 26 μg mL
) followed by clove (GR
of 48 μg mL
) and pimento (GR
of 52 μg mL
) oils. Previously, many authors have investigated the inhibitory effect of essential oil from various aromatic plants. Essential oil from
Waldst. & Kit. reduced the emergence and seedling growth of weed species such as
(L.) P. Beauv. and
(Kaur et al., 2010)
. The essential oils from the aerial parts of catmint (
Benth.) effectively inhibited the seedling growth of weed species such as
L. by inducing oxidative stress
(Mutlu et al., 2011)
Poonpaiboonpipat et al. (2013)
reported that the essential oil from
Stapf remarkably inhibited germination and seedling growth of
and affecting α-amylase activity of seeds.
- Identification of major components using SPME/GC-MS
Further studies in relation to identification of chemical components were carried out with these 11 effective essential oil samples. In order to identify the major components from the effective 11 essential oil samples, SPME-GC/MS analyses were performed. Area percentage of major components identified from the essential oil samples is presented in
. Eugenol was detected as a major component in clove (92.27%), cinnamon (91.89%) and pimento (72.9%) oils. In citronella oil, the major components were citronellal (50.56%) and geraniol (24.52%). The main components of the essential oil from cumin seed oil were 2-mehtyl-3-phenyl-proponal (42.48%), safranal (15.88%), terpinene (12.48%) and cymene (10.30%). Citronellol was found to be a major component in geranium (38.41%) and rose otto (58.64%) oils. In jasmine oil, benzyl benzoate (35.88%) and benzyl acetate (30.80%) were found to be main components. Citral (52.59%) and β-citral (33.66%) were major ones in lemongrass oil. Geraniol (86.56%) and carvone (76.65%) are found to be main components in palmarosa and spearmint oils, respectively. The results revealed that the analyzed essential oil samples mainly composed of oxygenated monoterpenes.
Chemical composition of 11 effective essential oil samples.
|Sample ||Compound name ||Area % ||Component group |
|Cinnamon ||Eugenol ||91.89 ||Alcohol |
|Citronella ||Citronellal ||50.56 ||Aldehyde |
| ||Geraniol ||24.52 ||Alcohol |
|Clove ||Eugenol ||92.27 ||Alcohol |
|Cumin seed ||Cymene ||10.30 ||Hydrocarbon |
| ||Terpinene ||12.48 ||Hydrocarbon |
| ||2-Methyl-3-phenylpropanal ||42.48 ||Aldehyde |
| ||Safranal ||15.88 ||Aldehyde |
|Geranium ||Citronellol ||38.41 ||Alcohol |
| ||Geraniol ||31.73 ||Alcohol |
|Jasmine ||Benzyl acetate ||30.80 ||Acetate |
| ||Benzyl benzoate ||35.88 ||Acetate |
|Lemongrass ||Citral ||52.89 ||Aldehyde |
| ||β-Citral ||33.66 ||Aldehyde |
|Palmarosa ||Geraniol ||86.56 ||Alcohol |
| ||Geranyl acetate ||11.47 ||Aldehyde |
|Pimento ||Eugenol ||72.9 ||Alcohol |
| ||Caryophyllene ||6.3 ||Hydrocarbon |
|Rose otto ||Citronellol ||58.64 ||Alcohol |
| ||Geraniol ||15.48 ||Alcohol |
|Spearmint ||Limonene ||16.70 ||Hydrocarbon |
| ||Carvone ||76.65 ||Ketone |
- Phytotoxic effect of individual essential oil components
Based on the results of chemical composition, individual components namely, benzyl benzoate, carvone, citral, citronellol, eugenol, geraniol, D-limonene and terpinene were used to evaluate their inhibitory activity against the seedling growth of three different species. All the tested 8 components effectively inhibited the seedling growth of
). Among the three plants,
B. napus and E. crus-galli
are more susceptible than
. Citral showed significantly higher inhibitory activity (
of 34 μg mL
. In the case of
, geraniol exhibited significantly higher inhibitory activity (
<0.05) of seedling growth than other components with GR
of 29 μg mL
. Out of eight components, terpinene and D-limonene showed lower inhibitory activity. The herbicidal potential of tested compounds varied enormously against the three plant species. Four components of 8 (geraniol, citronellol, citral and carvoen) are coming under oxygenated monoterpene group, two components (terpinene and limonene) are monoterpene and eugenol is a phenylpropanoid and benzyl benzoate is esters of benzyl alcohol and benzoic acid.
Effect of individual essential oil components on seedling growth ofBrassica napus,Echinochloa crus-galliandAeschynomene indica.
|S. No. ||Compound Name ||GR50 (μg mL−1)z |
|Brassica napus ||Echinochloa crus-galli ||Aeschynomene indica |
|1 ||Benzyl benzoate ||205e ||>1,000e ||547f |
|2 ||Carvone ||88d ||50b ||259e |
|3 ||Citral ||34a ||283d ||163d |
|4 ||Citronellol ||66c ||67c ||135a |
|5 ||Eugenol ||43b ||72c ||155c |
|6 ||Geraniol ||82d ||29a ||144b |
|7 ||D-Limone ||574f ||>1,000e ||936h |
|8 ||Terpinene ||>1,000g ||280d ||891g |
zGR50 values were calculated from four replicates of each sample. Mean values followed by different superscripts in a column are significantly different (P< 0.05).
Previous studies have shown that essential oils and their individual components isolated from various plant species, exhibited potent herbicidal effects on weed germination and primary root growth of several other species.
Martino et al. (2010)
studied the anti-germinative potential of twenty seven monoterpenes, including monoterpene hydrocarbons and oxygenated ones, against seed germination and subsequent primary radicle growth of
L. Among the 27 components tested, geraniol, borneol, β-citronellol and α-terpineol are the most active components. Further, the authors reported that the radicle elongation of two test species was inhibited mainly by alcohols and ketones. Similar to our data, various authors have reported that the essential oil components (1,8-cineole, camphor citronellal, citronellol, linalool, α-pinene and limonene) effectively inhibited seed germination and seedling growth
(Abrahim et al., 2000
Kordali et al., 2007
Singh et al., 2002
. In the present study, the results showed that the oxygenated monoterpenes (carvone, citronellol, citral, eugenol, and geraniol) had higher inhibitory activity on seedling growth than monoterpene hydrocarbons.
Vokou et al. (2003)
studied the effects of 47 individual monoterpenoids from different chemical group, acting alone or in pairs, on seed germination and subsequent seedling growth of
, and they concluded that the most active components were terpinen-4-ol, dihydrocarvone, and two carvone stereoisomers.
Structure of the compounds citral and geraniol.
- Phytotoxic effect of individual components under greenhouse experiment
Seed bioassay was an important preliminary screening method to determine the phytotoxic potential of plant extracts or compounds. However, greenhouse and field experiments are important criteria in order to understand the efficacy of herbicidal compounds under field conditions for further utilization of products commercially. Based on the results from seed bioassay, a greenhouse experiment was conducted using eight individual components such as benzyl acetate, carvone, citral, citronellol, eugenol, geraniol, D-limonene and terpinene against 5 monocot plants (
) and 5 dicot plants (
). The phytotoxic activity of 8 components showed considerable variation among the plant species tested. Except D-limonene and terpinene, all other components showed appreciable phytotoxic activity against the tested plants at the highest concentration (100 kg ha
). The most phytotoxic components among them were geraniol and citral. After 14 days of spray treatment, citral and geraniol showed potent phytotoxic activity by totally killed all the tested 10 plants at the concentration of 100 kg ha
. Moreover, citral and geraniol also killed all the tested plants at the concentration of 50 kg ha
with the exception of
). The compound citral completely suppressed the growth of
even at the lowest concentration (25 kg ha
). Whereas geraniol suppressed the growth of
at the lowest concentration tested. However, the concentrations of citral and geraniol used in this study were higher than that of commercial herbicides (4 kg ha
). Therefore, further large scale field studies are required to understand the phytotoxic effect of these compounds.
Herbicidal effect of individual essential oil components with early post-emergence treatment on ten plants in a greenhouse.
|Component Name ||Dose (kg ha−1) ||Abutilon theophrasti ||Aeschynomene indica ||Gossypium hirsutum ||Glycine max ||Ipomoea angulata ||Echinochloa crus-galli ||Digitaria ciliaris ||Setaria virdis ||Poa annua ||Zea mays |
|Benzyl benzoate ||25Z ||4y ||2 ||0 ||3 ||2 ||2 ||2 ||0 ||0 ||5 |
|50 ||7 ||10 ||0 ||4 ||3 ||3 ||7 ||2 ||2 ||10 |
|100 ||10 ||10 ||10 ||10 ||9 ||7 ||10 ||10 ||6 ||10 |
|Carvone ||25 ||1 ||4 ||0 ||2 ||1 ||1 ||0 ||1 ||1 ||6 |
|50 ||10 ||9 ||10 ||5 ||4 ||3 ||4 ||7 ||2 ||9 |
|100 ||10 ||10 ||10 ||10 ||10 ||6 ||10 ||10 ||10 ||10 |
|Citral ||25 ||10 ||10 ||10 ||6 ||10 ||3 ||2 ||8 ||2 ||10 |
|50 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||4 ||10 |
|100 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 |
|Citronellol ||25 ||10 ||2 ||10 ||4 ||4 ||3 ||7 ||7 ||3 ||9 |
|50 ||10 ||10 ||10 ||10 ||6 ||4 ||8 ||10 ||4 ||10 |
|100 ||10 ||10 ||10 ||10 ||10 ||7 ||10 ||10 ||10 ||10 |
|Eugenol ||25 ||6 ||9 ||4 ||4 ||1 ||1 ||1 ||2 ||1 ||2 |
|50 ||10 ||10 ||10 ||9 ||10 ||2 ||3 ||3 ||5 ||8 |
|100 ||10 ||10 ||10 ||9 ||10 ||10 ||10 ||10 ||10 ||9 |
|Geraniol ||25 ||10 ||10 ||0 ||7 ||3 ||4 ||4 ||6 ||2 ||9 |
|50 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||6 ||10 |
|100 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 ||10 |
|D-Limonene ||25 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||9 |
|50 ||0 ||0 ||0 ||1 ||0 ||0 ||2 ||1 ||2 ||10 |
|100 ||1 ||10 ||0 ||2 ||0 ||3 ||3 ||10 ||4 ||10 |
|Terpinene ||25 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||0 ||1 |
|50 ||0 ||8 ||2 ||1 ||1 ||1 ||0 ||0 ||0 ||7 |
|100 ||2 ||8 ||2 ||3 ||2 ||2 ||7 ||1 ||2 ||10 |
zEach treatment has 10 plants with four replicates. Herbicidal activity was determined 14 days after treatment by visual injury. yResults were expressed as 0-no effect; 10-totally killed.
The most effective components, citral and geraniol are coming under the group of oxygenated monoterpene. The primary oxidation products of geraniol/nerol are geranial (citral A) and neral (citral B) known together as citral
(Dapurkar et al., 2011)
. Citral and geraniol exhibit various biological properties and found abundantly in large number of aromatic plants. These are the most important avoring compounds used widely in beverages, foods, and fragrances for their characteristic avor prole. Previous studies have stated that the phytotoxic effects of these compounds might be due to anatomical and physiological changes in seedlings by reducing some organelles like mitochondria, accumulation of lipid globules in the cytoplasm, inhibiting the synthesis of DNA or disruption of membranes and suppression of metabolic enzymes activity that involved in glycolysis and in oxidative pentose phosphate pathway
(Podesta and Plaxton, 1994
Muscolo et al., 2001
Nishida et al., 2005)
. The essential oil of
inhibited germination and plant root growth by generating ROS-induced oxidative stress
(Singh et al., 2009)
. The mechanism behind its phytotoxic effect might be affecting chlorophyll content, cellular respiration and electrolyte leakage of weed plants
(Kaur et al., 2010)
Sanchez-Moreiras et al. (2008)
suggested that the inhibitory effects of essential oils have been associated with their inuence on the regulation of shoot elongation and cell division of the target plants. In addition, plant essential oils have been shown some other mechanisms including delay crystallization, reduce the volatilization and photo-degradation of the herbicides on the leaf surface
(Bunting et al., 2004
Si et al., 2004
Ramsey et al., 2006)
. Phytotoxic compounds released from plants that aid them in both interspecific and intraspecific competitions
(Meyer et al., 2007)
. Overall results showed that the citral and geraniol have strong herbicidal potential than other compounds. The findings of present investigation indicated that the individual components provided a good platform to develop novel and effective herbicides.
The present study reveals that the different essential oil samples showed a considerable variation in the phytotoxic effect on rapeseed seedling growth. The effective essential oil samples mainly composed of oxygenated monoterpenes. The results confirmed that citral and geraniol provided excellent phytotoxic activity under
seed bioassay as well as in greenhouse experiment than other essential oil components. It could be concluded that citral and geraniol may be favorably used for incorporating in agricultural practices as natural herbicides for the management of weeds. Further studies in relation to mechanism of action and field experiment are under progress.
This work was supported by the R&D Program of MOTIE/KEIT [10035240, Development of New Herbicides for Resistant Weeds with Mutated Genes].
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