Chemical constitution and allelopathic effects of Curcuma zedoaria essential oil on lettuce achenes and tomato seeds

Abstract

The contamination of food, water, and soils by herbicides, as well as the growing resistance of weeds to these products, has increased demands for alternative methods of weed control that have less impact on the environment and human health. Curcuma zedoaria (zedoary), a species of the Zingiberaceae family, is a promising plant for alternative weed control as it produces an essential oil with herbicidal action. We evaluated the chemical composition of C. zedoaria essential oil and its allelopathic effects on the vigor and germination of lettuce achenes and tomato seeds. The essential oil was extracted from the plant rhizome by hydrodistillation and subjected to gas chromatography-mass spectrometry to identify its component chemical compounds. Bioassays to evaluate allelopathic potential were performed in gerbox-type containers maintained in a refrigerated biochemical oxygen demand incubator at 25°C. The treatments consisted of five essential oil concentrations (0.00, 0.25, 0.50, 0.75, and 1.00%) and two bioindicators (lettuce and tomato). C. zedoaria essential oil comprises monoterpene hydrocarbons (4.63%), oxygenated monoterpenes (25.88%), sesquiterpene hydrocarbons (21.95%), and oxygenated sesquiterpenes (47.54%). The major compounds encountered were 1.8-cineole (15.75%) and epi-curzerenone (18.20%). We believe that the isolated effect of these compounds or the synergism between them may have influenced the observed results. Germination was inhibited in both bioindicator species, but the percentage inhibition was greater in lettuce achenes. Germination rates decreased in lettuce and tomato with increasing concentrations of essential oil, and bioindicator growth was slowed. The root system was more heavily damaged than the hypocotyl, especially in tomato compared to lettuce. These preliminary results indicate that C. zedoaria essential oil has allelopathic effects on seed germination and seedling growth and thus shows potential for weed control.