Allelopathic potential of essential oils isolated from local plants on common weeds found in Malaysian croplands
Continuous use of the synthetic herbicides to control weeds in agricultural production can have an adverse impact on the environment and the ecosystems creating safety and health concerns to the operators, consumers and the community. However, it is the resistance to the synthetic herbicides that de...
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| Format: | Thesis |
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| Language: | English |
| Subjects: | |
| Online Access: | http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/78022/1/Page%201-24.pdf http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/78022/2/Full%20text.pdf http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/78022/3/Ahmad%20Abdulwahid.pdf |
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| Summary: | Continuous use of the synthetic herbicides to control weeds in agricultural production can have an adverse impact on the environment and the ecosystems creating safety and health concerns to the operators, consumers and the community. However, it is the resistance to the synthetic herbicides that developed in the targeted weeds and its consequent that provide strong justification for the need to develop an eco-friendly, natural and low risk but effective alternative bioherbicides. The study thus explores the benefits of using plant’s allelopathic potential that manifested in its essential oil, as an alternative herbicide. The research involved the isolation of the essential oils from eight selected plant species of Cupressus macrocarpa Hartweg. (Goldcrest), Melaleuca bracteata F. Muell. (Tea tree), Plectranthus amboinicus (Lour.) Spreng (Spanish
thyme), Cymbopogon nardus L. (Lemongrass), Pelargonium radula Cav. (Radula
geranium), Baeckea frutescens L. (Cucur atap), Murraya koenigii L. (Curry tree) and
Persicaria odorata (Lour.) Sojak (Kesum plant) by steam distillation. Isolated essential
oils were screened for their herbicidal activity as preemergence applied at three
concentrations on two major weed types (2 grassy and 2 broad leaves weed species)
grown under bioassay laboratory and pot culture conditions. The compounds were
characterized using GC-MS. The phytotoxic effects of the eight essential oils were also
evaluated on the four weeds as postemergence by analyzing the total chlorophyll
content, relative electrolyte leakage, cellular respiration and stomata mechanism in the
leaf membrane. The most effective essential oils were then evaluated as postemergence
by applying singly and in a combination of two essential oils on widely known weed
grown in the open field and compared with the known synthetic herbicide, Halexone
(H130) as a control. The best essential oils were selected based on their efficacy of more
than 70 % inhibition. The results showed that the oils isolated from C. macrocarpa, C.
nardus and P. radula were the most effective in inhibiting seed germination and
seedling growth completely in laboratory bioassay and caused the most severe effects
on weeds grown under the pot culture. GC-MS analysis showed monoterpene was the
most dominant and effective component of all essential oils followed by sesquiterpene
and phenylpropanoids. The phytotoxic experiment showed total chlorophyll content,
relative electrolyte leakage and cellular respiration were significantly affected by the
application of the bioherbicides. The effects increased by increasing the oil concentration. There was a significant influence of the essential oils on plant
membranes affecting the stomata mechanism, rupturing cell membrane, dissolution of
its contents which eventually kill the weeds. The application of essential oils as
postemergence herbicides to weed grown in the open field showed desirable efficiency
against the weeds as non-selected contact bioherbicides comparable with the
performance of the conventional synthetic herbicides H130. Application of the essential
oils formulated in combinations improved the phytotoxic effects as compared to using
oils singly. The combination of C. macrocarpa and P. radula at 5% each proved to
produce the best phytotoxic effects in suppressing weed population. |
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