Allelopathic potential of essential oils isolated from peels of three citrus species

In this study the essential oils were extracted from the peels of Citrus sinensis (sweet orange), Citrus aurantium (bitter orange) and Citrus reticulata (mandarins) by hydrodistillation using a Clevenger-type apparatus for 4 h. The essential oils of all samples were subjected to Gas chromatography-mass spectrometry. The results indicated that the major compounds were D-limonene, terpinene and myrcene. Essential oils from these species were tested against seed germination and seedling growth of Heliantus annus (sunflower), Portulaca oleracea (purslane), Lupinus albus (field lupine) and Malva parviflora (Egyptian mallow) in laboratory experiments at different concentrations. The assay results showed that the essential oil extracted from C. reticulata peels was the most inhibitory followed by the essential oil extracted from C. aurantium and C. sinensis peels. Essential oils of C. reticulata and C. aurantium peels inhibited completely seed germination and seedling growth of H. annus at all concentrations. Portulaca oleracea seed germination and seedling growth were inhibited completely by essential oil of C. aurantium (2%). The essential oil of C. sinensis (3%) inhibited 100% of germination and growth of Lupinus albus. And. M. parviflora germination was 100% inhibited by C. aurantium (3%) and C. reticulata (1%) peel oils. The results obtained suggested that citrus peel essential oils present significant growth inhibitory property of the listed species and has potential to be used in allelopathic processes.