Allelopathic polyacetylenes fromCentaurea repens (Russian knapweed)

The allelopathic weed Russian knapweed (Centaurea repens) was found to contain polyacetylenes VIII–XIV in the roots. Dose vs. response of the root length elongation against lettuce, alfalfa, barnyard grass, and red millet showed IX to be active. Closely related isomers were not active. Examination of the soil surrounding the Russian knapweed roots revealed the presence of IX in sufficient concentration to have an appreciable effect on the surrounding plant community.