Allelopathic Properties of α-terthienyl and Phenylheptatriyne, Naturally Occurring Compounds from Species of Asteraceae

Alpha-terthienyl (α-T), a naturally occurring polyacetylene derivative from roots ofTagetes erecta L., and phenylheptatriyne (PHT), from leaves ofBidens pilosa L., were tested as possible allelopathic agents against four seedling species (Asclepias syriaca L.,Chenopodium album L.,Phleum pratense L.,Trifolium pratense L.).Asclepias was the most sensitive of the species. Allelopathic activity was enhanced in the presence of sunlight or sources of near-UV, with LC50s forA. syriaca of 0.15 ppm and 0.66 ppm with α-T and PHT, respectively; 0.27 and 0.85 forC. album; 0.79 and 1.43 forP. pratense, and 1.93 and 1.82 forT. pratense. Near-UV exposure was saturating but never more than found in summer sunlight at Ottawa, Canada. Growth inhibition was observed with seedlings treated with α-T and PHT but without near-UV irradiation. Germination of seedlings was also sensitive to α-T and PHT with or without near-UV treatment. α-T was extracted from soil surrounding the roots ofTagetes. Concentrations calculated for the soil (0.4 ppm) indicate that seedling growth could be significantly hindered. The activity and specificity of α-T was sufficiently high to warrant future field trials to assess its potential as a natural weed-control agent.