Bioherbicidal Potential of Some Plant Extracts in Weed Control in West-Cameroon
Abstract
The use of herbicides poses problems of multifaceted environmental pollution, toxicity and depletion of microflora and microfauna in the soil. Farmers and environmentalists are powerless in the face of this problem. However, certain plant extracts are known for their allelopathic properties through their allelochemicals, which is primarily demonstrated by their effectiveness on weeds. It is in this context that the present study was conducted, with the aim of evaluating the bioherbicidal efficacy of extracts of Cupressus lusitanica, Bambusa vulgaris and Ricinus communis on Bidens pilosa, a weed frequently found in cultivated plants and which causes enormous crop losses. To achieve this objective, 75 seeds of these weeds were sterilised using 0.5% sodium hypochlorite for 2 minutes. Subsequently, 15 Petri dishes were prepared with plant extract, then filter paper was moistened with 2 ml of distilled water and placed at the bottom of each Petri dish. Seventy-five (75) previously sterilised weed seeds were placed in each of these Petri dishes at a rate of 5 per dish. Each seed was sprayed with 1 ml of each extract at concentrations of 7.5, 15 and 30 mg/ml. The Petri dishes containing distilled water and those sprayed with the herbicide at the manufacturer'srecommended dose were used as negative and positive controls, respectively. All of the dishes were placed in a growth chamber at 23 ± 1°C in the dark. From the second day of incubation, the seeds were carefully observed for any signs of germination, and when this was visible, it was counted and noted, and the lengths of the stems, the number of leaves and their surface areas were measured. The highest concentrations of the extracts that had shown some efficacy in vitro were brought back to the field for bioherbicide testing under pre-emergence conditions.
The results showed that all three plant extracts significantly inhibited the germination of Bidens pilosa seeds compared to the negative control. However, the percentage of inhibition of weed seed germination was significant at the highest concentrations. Thus, concentrations of 30 mg/ml of the three plant extracts were the most effective, with no germination of Bidens spilosa seeds, i.e. a rate of 0%. On the other hand, the highest germination rates were observed with concentrations of 7.5 and 15 mg/ml. These rates varied between 26.67 and 80% and were similar to those of the negative controls according to Duncan's 5% test. Of all three concentrations of the different plant extracts tested in the field, only those of Cupressus lusitanica were the most effective insignificantly destroying the leaves of Bidens pilosa.
These results suggest the possibility of using extracts from this plant at a concentration of 30 mg/ml to control this weed, however further studies are needed to complete the information associated with this.
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Introduction
Weeds are one of the main causes of crop losses. These adventitious plants can compete with cultivated plants for nutrients or serve as shelters for pathogens that can attack these plants and cause considerable economic damage. In response to this damage, several weed control methods are available, including mechanical and thermal methods. However, these methods have proven ineffective, and farmers are still forced to resort to chemical herbicides. Furthermore, the application of these chemical herbicides on weeds poses risks to consumers and the environment, in addition to the development of resistant weeds (Uddin et al., 2014; Sofiene, 2020). Furthermore, some herbicides are limited on the market and others, such as glyphosate, are gradually being withdrawn from the market. However, public demand for alternative herbicides that are biological in origin (bioherbicides) and more environmentally friendly is growing. Medicinal plants are known for their bioherbicidal properties and low or no toxicity. Researchers have been exploring this avenue for sometime with a view to formulating bioherbicides that are safe for consumers and environmentally friendly. In fact, the work of Sofiene Ben Kaab (2020) has shown that Rosmarinus officinalis essential oil and Cynara cardunculus extract have high bioherbicidal activity compared to extracts of Trifolium incarnatum (T. incarnatum), Sylibum marianum (S. marianum) and Phalaris minor, which showed low activity on weeds.
Similarly, Claudia et al. (2022) on the bioherbicidal activity of Campomanesia lineatifolia seed extract on the weed Sonchus oleraceus L. showed a 100% incidence of chlorosis and necrosis symptoms with foliar application of this plant extract, but these applications did not result incomplete plant death. However, all of these previous studies are limited in terms of both the plant extracts tested and the number and diversity of weeds on which they were tested. It is in this context that the present work was carried outwith the aim of evaluating the bioherbicidal of plant extracts on Bidens pilosa under pre-and post-germination conditions.
Conclusion
Having completed this work, the objective of which was to evaluate the bioherbicidal efficacy of extracts of Cupressus lusitanica, Bambusa vulgaris and Ricinus communis on Bidens pilosa, a weed frequently found in cultivated plants and causing enormous crop losses, it appears that all three plant extracts significantly inhibited the germination of Bidens pilosa seeds compared to the negative control. However, the percentages of inhibition of weed seed germination were significant at the highest concentrations. Thus, concentrations of 30 mg/ml of the three plant extracts were the most effective, with no germination of Bidens pilosa seeds, i.e. a rate of 0%. On the other hand, the highest germination rates were observed with concentrations of 7.5 and 15 mg/ml. These rates varied between 26.67 and 80% and were similar to those of the negative controls according to Duncan's 5% test. Of all three concentrations of the different plant extracts tested in the field, only those from Cupressus lusitanica were the most effective insignificantly destroying Bidens pilosa leaves compared to those from Bambusa vulgaris, Ricinus communis and the negative controls. These results suggest the possibility of using extracts from this plant at the recommended concentration to control this weed, but further studies are needed to supplement the data obtained in this research.
CONFLICT OF INTEREST STATEMENT Authors declare that they have no conflict of interest.
