Isolation and Bioassay of Herbicidal Active Ingredient fromPaulownia tomentosa

Herbicidal active ingredient extracted,isolated and identified from Paulownia tomentosa (Thund)Steud against Amaranthus retroflexus L.,Lactuca sative var. capitata L. and Cucumis sativus L. were tested by bioassay-guided separation. The extracts from P.tomentosa flower with ethanol were extracted with petroleum ether,ethyl acetate and n-butanol.The inhibition rate of the ethyl acetate extract to growth of the 3 kinds of plant radicel were 99.89%,63.53% and 32.74% respectively at 0.5 mg/mL concentration,and that of petroleum ether were 76.30%,56.17% and 23.36%.One compound had been obtained with silica gel column chromatography from ethyl acetate extraction,and it was authenticated as p-ethoxybenzaldehyde.The inhibitory EC50 of this compound against A.retroflexus radical growth was 55.20 μg/mL.p-Ethoxybenzaldehyde was the first reported from Paulownia tomentosa with herbicidal activity.