Chemical composition of essential oils in the leaves of Delairea odorata during flowering and post-flowering periods

Abstract

on their mass spectra. The percentage of essential oil isolated was 1.6%, and the major compounds identified were germacrene D (17.9%), caryophyllene (11.9), trans-isocroweacin (9.6), acoradiene (7.6), and -curcumene (6.5%) during the flowering season. During the post -flowering period trans--bergamotene (36.8%), trans--ocimene (16.5), bicyclo[7.2.0]undec-4-ene (11.5) and carene (9.3) were the major compounds identified, and the extract percentage was 1.9%. The chemical composition of D. odorata was completely different from Senecio scandens [4]. Though there is confusion in differentiating D. odorata from S. scandens with this chemical variation in the volatile oil composition, we suggest that D. odorata is a different species. The differences in the yield and composition can partly be attributed to the different types of secretory structures [5]. Both in the flowering and post-flowering periods, the essential oils were dominated by sesquiterpenes, which constitute about 89.1 and 42.1%, respectively. There was a considerable amount of alkenes (11.9%) and alkanes (6.6%) recorded during the post-flowering period. The terpene turnover depends on photosynthesis and the utilization of photosynthates [6]. Bergamotene was the major compound during the vegetative phase and plays an important role as an insect repellent [7]. The higher concentration of bergamotenes in the essential oil during the vegetative phase may be the reason why D. odorata has no natural insects feeding on them in the study area. The decrease in the concentration of bergamotenes during the flowering period may be an evolutionary strategy adapted by the plant to attract pollinating agents. These variations obtained in the essential oil constitution may be due to the fact that flowering and fruiting events were influenced by biotic and abiotic factors.