Allelopathic inhibition of seed germination by Cinchona alkaloids?

Abstract

The inhibition of seed germination by quinoline alkaloids synthesized by plants of the tropical genus Cinchona was studied. The germination of Ocimum (a tropical herb), of Spermacoce and Catharanthus (two tropical, alkaloid-producing plants), and of Cinchona itself was strongly inhibited by the alkaloids when applied at concentrations higher than about 0.3 mM. To test for the possible allelopathic significance of this finding, the soil in which two-year-old Cinchona plants were grown was examined for its quinoline alkaloid content. Although the roots of the plants contain high concentrations of these alkaloids ( ca 10 mM), in the soil only very low concentrations were found ( ca 0.02 mM). Upon germination of seeds sown close by the plants, no toxic effects were observed. So, although several studies have reported inhibition of seed germination by Cinchona alkaloids under laboratory conditions, our results indicate that this property does not play a role under natural circumstances at realistic concentrations.