The effect of diurnal variability on the ratio , composition and allelopathic potential of oregano (Origanum onites L. ) essential oil

İzmir thyme (Origanum onites L.), plants which were propagated from seed in Samsun ecological conditions in 2016 were used in the research carried out to evaluate the effect of diurnal variability on essential oil content and composition in İzmir thyme and the allelopathic potential of its essential oil on mustard (Sinapis arvensis L., population) seeds. The plants were harvested at 3 different hours at the beginning of flowering (05:00-MORNING, 12:00-NOON, and 19:00-EVENING). Essential oils were obtained by hydro distillation method and the chemical components of the essential oil were determined by GC-MS. Mustard seeds were kept in essential oil and distilled water (control) for four different periods: 30 minutes, 60 minutes, 90 minutes, and 120 minutes, and at the end of 21 days, the germinating seeds in petri dishes were counted and recorded. The highest percentage of essential oil (3.650%) was obtained from the harvest at 05:00, followed by the harvests at 19:00 (3.583%) and 12:00 (3.227%) respectively. Carvacrol, the main component of the essential oil, ranged from 68.16% (evening) to 79.10% (noon). The lowest germination rate (70%) was recorded in the seeds kept in the essential oil (carvacrol: 79.10%) of the plants harvested at 12:00 for 120 minutes. A negative correlation was recorded between the germination value of the seeds and the application time (r=-0.596) and the carvacrol ratio (r=-0.649). The inhibitory effect of O. onites essential oil on the germination of wild mustard seeds varied according to the time the seeds were kept in the essential oil and the carvacrol ratio.