Fatty acids from itchgrass (Rottboellia cochinchinensis) and their herbicidal activity

There is increasing attention towards phytotoxic substances from plants as they offer an alternative biological approach to control weeds. Itchgrass (Rottboellia cochinchinensis (Lour.) W.D. Clayton) is used as mulching material for weed control in vegetable fields and is suspected to release allelochemicals. Thus, we conducted this research to find the phytotoxic compounds from itchgrass shoot. Their phytotoxic activities were assayed in-vitro on the shoot and root growth of lettuce (Lactuca sativa L.). Two active substances were isolated from n-hexane crude extracts of itchgrass shoots and identified as linoleic acid (9,12-octadecadienoic acid) and linolenic acid (9,12,15-octadecatrienoic acid) by H-1 and C-13 nuclear magnetic resonance spectral analyses. In addition, the average individual inhibition from each concentrations of two active compounds inhibited shoot growth of lettuce seedlings by 16.7 % and 38.8 % and root growth by 34.1 % and 58.8 %, respectively. These results indicated that the two phytotoxic compounds: linoleic acid and linolenic acid may contribute to the phytotoxic activity of itchgrass.