Plant Growth Inhibitors in Catchweed Seeds and Their Allelopathy

Abstract

Two Asp-related iridoidglucosides, compounds A and B were isolated from the dormant seeds of catchweed. By chemical analysis, compound A was identified as asperulosidic acid which was derived from Asp through the cleavage of a lactone ring, and compound B as deacetyl asperulosidic acid produced through the deacetylation of asperulosidic acid. Asperulosidic acid inhibited the seed germination and growth of seedlings of large crabgrass and alfalfa to the same degree as Asp, but did not inhibit white clover, while deacetyl asperulosidic acid showed lower inhibitory effect on the tested plants than Asp and asperulosidic acid. Furthermore, asperulosidic acid showed similar inhibitory activity to Asp on the germination of catchweed seeds themselves. Since these compounds were only detected in the exudate obtained from the seed coat of catchweed seeds, inhibition of the germination and growth of lettuce placed together with catchweed seeds may be due to iridoidglucosides liberated from the latter seeds which have been soaked in water.