Chemical Composition and Allelopathic Activity of Parthenium hysterophorus and Ambrosia polystachya Weeds Essential Oils

The volatile constituents of the essential oils from leaves from the weed plants Parthenium hysterophorus and Ambrosia polystachya were identified and quantified by GLC-MS and GLC. Allelopathic activities were determined by methods that evaluated the volatile effects and the direct application of these essential oils on the seed germination and seedling vigor of lettuce. We identified 27 compounds in the essential oil from P. hysterophorus, and the main constituents were germacrene-D (35.9%), trans-β-ocimene (8.5%) and β-myrcene (7.6%). In the essential oil from A. polystachya, 40 constituents were identified and the principal compounds were germacrene-D (29.3%), trans-β-ocimene (13.6%) and β-caryophyllene (9.8%). In both methods, the essential oil from A. polystachya presented a greater potential for reducing seed germination and seedling vigor in lettuce than the essential oil from P. hysterophorus, and this activity might be attributed to its higher content of monoterpenes.