Identification and bioactivity of volatile allelochemicals from amaranth residues

Volatile organic compounds emitted from the residues of the aerial portions of Amaranthus retroflexus, Amaranthus hybridus, Amaranthus cruentus, Amaranthus spinosus, Amaranthus hypochondriacus , and Amaranthus palmeri have been identified by capillary gas chromatography/mass spectrometry after thermal desorption from Tenax and Carbotrap. Seed germination bioassays using carrot, tomato, and onion were conducted at a vapor concentration of 34.4 mu mol/L with 31 of the identified compounds. While all the compounds were inhibitory, the most bioactive toward one or more of the test species were 3-methyl-1-butanol, 3-hexen-1-ol, 2-heptanol, pentanal, 2-methylbutanal, 3-methylbutanal, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl 2-methylbutyrate, 2-pentanone, 3-pentanone, 3-methyl-2-butanone, 2-heptanone, and 2-nonanone. The results suggest that these volatiles, usually categorized as components of flavor, fragrance, and/or insect attractant mixtures, are also important factors in allelopathy and soil chemical ecology.