Chemical analysis and evaluation of a homemade pest control mixture used by a local farmer from Maloti-A-Phofung municipality of the Afromontane region in the Free State
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Date
2022
Authors
Sebotsa, Maria Mojabeng
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University of the Free State
Abstract
The indigenous community of the Afromontane region has developed and adopted strategies for survival to reduce diseases and eliminate ticks and pests on crops at a lower cost. Biopesticides are efficient in eradicating various plant pests, affordable, quickly biodegradable, with multiple mechanisms of action, freely available supplies, and low toxicity to non-target organisms. The phytochemical composition of different plants is thought to be responsible for their various modes of action. Synthetic pesticides are expensive for small-scale farmers in undeveloped regions like the Afromontane region. Investigating agrochemical alternatives will benefit small-scale farmers who cannot access these due to their high cost. This study aims to analyse and evaluate the effectiveness of homemade pest control used by a small-scale farmer in the Afromontane region. The homemade pest control mixture used by local farmers was collected, then sequentially extracted and sonicated using hexane, chloroform, ethyl acetate, methanol and water. The extracts were screened for active compounds by phytochemical analysis and characterized using ultraviolet-visible (UV-Vis) spectroscopy, Fourier-Transform Infrared Spectroscopy (FTIR), and liquid chromatography-tandem mass spectrometry (LC-MS/MS. Biological testing was used to examine for antibacterial and antifungal activities. Saponins, phenolic compounds, and terpenes were found in all of the extracts after phytochemical analysis of the samples. Through using FTIR spectroscopy, the functional groups of the extracts were detected while
UV/Vis spectroscopy identified the presence of chromophore at a region of 220-300 nm. LCMS/MS was performed to dereplicate the analyte components with a focus on their collision induced dissociation (CID) spectra. LC-MS/MS and molecular networking enabled annotation of metabolites active in the different extracts of the homemade pesticide. Based on the connectivity of the molecular network, the homemade pest control molecular networking nodes were grouped into five clusters (1–5). Cluster 1 consists of features annotated as flavonoids, cluster 2 corresponds to compounds of the alkaloids and flavonoids, cluster 3 corresponds to amino acids and alkaloids, cluster 4 consists of fatty acids and alkaloids and cluster 5 consists of features annotated as isoflavonoids. The annotated compounds exhibited various characteristics; some were insecticidal, while others showed antimicrobial activities. The antibacterial and antifungal properties of the sequential and ultrasonic extracts were examined using microdilution. Among the tested extracts, chloroform sequentially and sonicated extracts, methanol sequentially and sonicated extracts showed the best antibacterial activity with the MIC values of 0.09-0.195 mg/ml. The antibacterial activity for sequential chloroform extract showed the best activity against all the bacterial strains, with MIC values ranging between 0.098-0.39 mg/ml. Most of the extracts tested were ineffective against the fungal strains for antimitotic activity. Only a sonicated methanol extract showed the best antifungal activity. The sonicated methanol extract showed good activity (0.39-0.78 mg/ml) against Candida albicans, C. vulgaris and Trichophyton mucoides. In the case of water extracts, no activity was observed in the gram-negative bacteria and antifungal activity. The growth of Fusarium culmorum was suppressed by the sequence water extract and sonicated hexane extract. The current study's phytochemical and annotated compounds revealed that homemade pest-control bioactive compounds such as saponins, terpenoids, alkaloids, isoflavonoids and amino acids have antimicrobial properties against a variety of pathogens. Overall, the findings indicate that the mixture contains phytoconstituents that are effective against plant pathogens and capable of killing insect pests.
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Keywords
Dissertation (M.Sc. (Chemistry))--University of the Free State, 2022, Biopesticides, homemade pest control, extraction, bioactive compounds, molecular networking