Abstract
The essential oil of Haplophyllum tuberculatum was prepared by hydrodistillation of the fresh flowering aerial parts of the plant collected from Saudi Arabia. The oil was subsequently analyzed by GC and GC-MS. Thirty seven compounds, accounting for 96.4 % of the oil composition were identified. The major components were trans-p-menth-2-en-1-ol (19.2 %), cis-p-menth-2-en-1-ol (13.2 %), myrcene (10.1 %), delta-3-carene (8.8 %), beta-phellandrene (6.9 %), limonene (6.6 %) and cis-piperitol (6.4 %). The antimicrobial activity of the essential oil was determined using the broth microdilution method against various human pathogens, where a relatively low inhibitory range was observed (MIC 1 mg/mL). Furthermore, the oil was evaluated for its antifungal activity against the strawberry anthracnose-causing fungal plant pathogens Colletotrichum acutatum, C. fragariae and C. gloeosporioides using the direct overlay bioautography assay. The essential oil showed no antifungal activity at 80 and 160 g/spot concentrations compared to commercial antifungal standards. The oil was also investigated for its insecticidal and repellent activity against Aedes aegypti. The oil was repellent to the yellow fever mosquito Ae. aegypti using the "cloth patch assay" down to a concentration of 0.074 mg/cm(2); however, the oil had low toxicity against first instar larvae and adults of Ae. aegypti in a high throughput larval bioassay and adult topical assay. Additionally, enzyme activity was measured using the spectrophotometric Ellman method. The oil showed weakly acetylcholinesterase (AChE) inhibitory activity at the tested concentration, compared to standard substances, whereas no inhibition on butyrylcholinesterase (BuChE) activity was observed.