Essential Oils in Holy Basil (Ocimum tenuiflorum L.) as Influenced by Planting Dates and Harvest Times in North Alabama

Commonly known as Holy basil, Ocimum tenuiflorum (Lamiaceae), is a popular medicinal herb used for treating ailments ranging from colds to chronic diseases, such as cancers and diabetes. While Holy basil is well known in India and Southeast Asia, the plant is less known in western countries where a lack of information on cultural practices exists. In the current study, a field trial was established to determine the optimum planting date, the changes in essential oil content, and composition of O. tenuiflorum in Alabama. A total of three Holy basil accessions, PI 652056, PI 652057, and PI 288779, were planted three times at monthly intervals, beginning in April 2007. At 30, 60, and 90 days after transplanting (DATP), the aerial parts of two plants from each plot were harvested and used to determine essential oil content and composition of stems and leaves using gas chromatography-mass spectrometry. Sensory properties, yield, and composition of essential oils were affected by planting dates and harvest times. Harvesting during summer months yielded the highest amounts of oil for all three accessions. The chemotypes were identified as one high in eugenol (PI 652056), one high in β-caryophyllene (PI 652057), and a third dominated by eugenol (PI 288779) at the end of the growing period. In accession PI 652056, the level of eugenol increased with a delay in harvest time. For accession PI 652057, the level of β-caryophyllene was high at the 30-day harvest, but decreased significantly by the time of the 60-day harvest when eugenol became the dominant essential oil constituent. For the third accession (PI 288779), the essential oil was dominated by eugenol, reaching over 50% eugenol at 60 days DATP in the June planting, but the percentage of eugenol decreased towards the end of the growing season with a significant increase in (trans)-β-guaiene by 90-DATP. Of the 26 essential oil components identified in the accessions, eugenol, β-caryophyllene, E-methyl cinnamate and (trans)-β-guaiene were the most abundant constituents. The level of these essential oil constituents varied significantly in all accessions at all harvest stages. For O. tenuiflorum seedlings, the date of seeding, transplanting, and harvest DATP (plant maturity) significantly impacted total essential oil content and composition, although the level of changes within the various constituents were dependent upon the accession