A GROWTH INHIBITOR FOUND IN CENTAUREA SPP.

Abstract

The growth of tomato and barley plants was inhibited in soils naturally infested with knapweed or in soils artificially infested with powdered knapweed residues. The leaves contained a higher proportion of the toxic material than did other plant parts, and the leaves of Centaurea repens L. were more inhibitory than those of Centaurea diffusa Lam. and Centaurea maculosa Lam. Chromatographic techniques were developed to isolate an inhibitor common to the three species which was soluble in both water and ether, and inhibitory to the seedling development of barley and lettuce. The material was relatively more inhibitive to root development than to the top growth of the species tested. Chromogenic sprays and ultraviolet absorption spectra indicated that the inhibitor was an indole derivative. The presence of a plant growth inhibitor in these Centaureas may partially explain their rapid establishment in almost pure stands.