Allelopathic Effect of Quercetin, a Flavonoid from Roots in the Radicle Growth of : Quercetin Natural and Semisynthetic Analogues Were Used for a Structure-Activity Relationship Investigation.

Allelopathic potential of buckwheat roots on the radicle growth of the broomrape weed species and was studied. Buckwheat root exudates induced a significant growth inhibition in radicles but radicles of were not affected. Among the metabolites present in the root organic extract we identified the flavonol quercetin and the stilbene -coumaric acid methyl ester with only quercetin showing inhibitory effect on . The activity of quercetin was compared with other two similar flavanoids, the flavone apigenin and the dihydroflavanol 3--acetylpadmatin extracted respectively from and plants. In this comparative assay only 3--acetylpadmatin besides quercetin, showed inhibition activity of radicle growth while apigenin was inactive. These results indicated that the presence of two -free hydroxy groups of C ring, like catechol, could be an important feature to impart activity while the carbon skeleton of B ring and substituents of both A and B rings are not essential. Besides reduction of radicle growth, haustorium induction was observed at the tip of radicles treated with quercetin which swelled and a layer of papillae was formed. Activity of quercetin on haustorium induction in was assayed in comparison with the known haustorium-inducing factor 2,6-dimethoxy--benzoquinone (DMBQ) and a three partial methyl ether derivatives semisynthetized from quercetin. Results indicated that haustorium was induced by DMBQ at concentrations of 1-0.5 mM and quercetin and its derivatives at concentration range 0.1-0.05 mM.