Essential oil composition and yield of a Rosmarinus officinalis L. natural population with an extended flowering season in a coastal Mediterranean environment and perspectives for exploitation

There are numerous and different uses of rosemary essential oil (e.o.) and experimental results indicating which of the e.o. components is responsible for a specific biological activity. Consequently, it is worth to consider not only the seasonal variation of the the e.o. content but also the proportion of e.o. components that might vary according to season as well. Our aim was to determine the monthly variation in the e.o. composition, plant growth and e.o. yield of an almost continuously flowering rosemary natural population in a coastal Mediterranean environment, in order to understand the best utilization of e.o. according to the oil components detected by means of GC/MS along the different seasons. Alpha pinene ranging from 75.4% to 18.2% and eucalyptol from 15.6 to 3.5%, were the most represented components in all periods of samplings. Camphor and borneol increased in the samplings done after summer. Flowering occurred almost continuously except in the period from mid May to mid August. Production of e.o. was slightly affected by sampling period. The high concentration in alpha pinene, up to a level not recorded before according to the available literature, could be exploited for new pharmaceutical uses. The observation of leaves, stems and flowers by means of scanning electron microscopy, showed in all the examined plant parts the presence of glandular trichomes particularly numerous on leaves in the basal part of the adaxial lamina indicating the importance of leaves for e.o. production.