Coleus amboinicus (Lour.) as potential source for pesticidal compounds
1999
Vasquez, E.A. | Kraus, W. | Zebitz, K. | Rejesus, B.M. | Solsoloy, A. (Visayas State Coll. of Agriculture, Baybay, Leyte 6521-A (Philippines). Philippine Rootcrops Research and Training Center)
Secondary products from higher plants represent an enormous diversity of biologically active compounds that can be exploited as pesticides or source for new pesticide chemistry. In this study, the methanolic extract and the essential oil obtained from the whole plant of Coleous amboinicus were bioassayed on: phytophagous beetle, Epilachna varivestis, for antifeedant and contact toxicity; Bacillus subtilis (gram +) and Pseudomonas flourescens (gram-) for antibacterial; pathogenic fungus attacking cucumber, Cladosponium cucumerinum, for antifungal; golden snail, Pomacea caniculata, and one of the carriers of schistosomiasis, Biomphalaria glabrata, for molluscicidal; and root-knot nematode, Meloidogyne incognita, for nematicidal activities. The methanolic extract had moderate antifeedant effect (5000 ppm) while the essential oil was active against the fungus, bacteria and 2 species of snails (100 ppm); and moderately active on insect and nematode (500 ppm). The narrow range and moderate activity of methanolic extract preclude further investigation. Bioassay-guided fractionation of the essential oil led to the isolation of the highly active compounds carvacrol and thymol (1-25 ppm on bacteria, 25-50 ppm on fungus, 25 ppm on snails, 250 ppm on insect and nematode) and moderately active alpha-terpinene and alpha-pinene (100 ppm on snails only). Alpha-Humelene and p-cymene which were present in significant amounts were inactive in all test made. Identification of the isolated compounds was done through GC-MS and NMR spectroscopic analysis and by comparing the spectra with published data
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