GERMINATION AND GROWTH-INHIBITORY SESQUITERPENE LACTONES AND A FLAVONE FROM TITHONIA-DIVERSIFOLIA

Inhibitory effects of two sesquiterpene lactones tagitinin A, tagitini n C and a flavonoid hispidulin isolated from Tithonia diversifolia wer e determined on germination of radish, cucumber and onion seeds. The f lavonoid hispidulin was more toxic to the crop seeds tested and the ac tivity of tagitinin C was weaker than that of tagitinin A and hispidul in. Seventeen derivatives have been prepared from tagitinin A and C by chemical transformation and their phytotoxicity has been compared wit h the parent compounds (all at 250 mu M) using radish seeds. The struc tural requirements related to their biological activity have also been delineated.