The essential oils of air-dried Geranium carolinianum L. and G. koreanum Kom. were obtained by hydrodistillation and analyzed by GC/MS. Twenty and 22-compounds were identified in the essential oils from G. carolinianum and G. koreanum, respectively. The effects of these essential oils were investigated against two weed species Amaranthus viridis L. and Portulaca oleracea L. Based on bioactivity-guided fractionation, the main active constituent maltol (36.13%) was isolated from G. carolinianum oil and 1,2-Benzenedicarboxylic acid, mono(2-ethylhexyl) ester (38.25%) and (E)-2-Hexen-1-ol (11.98%) were isolated from G. koreanum oil and their structures were determined by EI-MS and 1D NMR. As a result, the inhibitory effects of G. koreanum oil on seed germination and seeding growth of A. viridis L. and P. oleracea L. were much stronger than G. carolinianum L. At 200 µg/mL concentration, three isolated active allelochemicals had different inhibitory effects on seed germination and seeding growth of A. viridis L. and P. Oleracea L. Among them, the inhibitory effects of 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl) ester on shoot length of A. viridis L. (RI =-0.92±0.03) was strongest. These results suggested that the essential oils play major role in allelopathic activity of these two aromatic plants.
1† et al. (Sun,) studied this question.