Identification of biologically active substances from Ginkgo biloba L.
The presence of allelopathic substances in the leaves of Ginkgo biloba was investigated. Water extracts from G. biloba leaves, collected during different seasons, markedly inhibited the germination and growth of O. sativa [rice], Echinochloa crus-galli, Digitaria sanguinalis and Lactuca sativa [lettuces], indicating the presence of biological substances. Linolenic and palmitic acid were the major fatty acids of G. biloba leaves. Substances such as salicylic acid, p-coumaric acid, catechol, hydroquinone, orchinol, ferulic acid, phloroglucinol and umbelliferone, phenolic compounds, were detected in large amounts, and may have been responsible for the inhibitory effects. The phenolic compounds most commonly detected in early- and late-harvested G. biloba leaves were salicylic and p-coumaric acid.