The 2012 ASHS Annual Conference

Basil (Ocimum basilicum L.), a popular herb enjoyed by many home gardeners, can be used for cooking, as a source of essential oils, and as a fragrant ornamental.  The objective of this study was to quantify the relationship between limited irradiance and the growth and essential oil production of ‘Italian Large Leaf’ basil.  Basil plants were grown in a greenhouse under shade cloth that provided 0%, 30%, 50%, or 70% shade.  Six pooled sub-sample plants with three replicate shade treatments were grown in a randomized complete block design for three months and then harvested for dry weight and aromatic sampling. Peak areas for common basil aromatic compounds, including linalool, 1,8-cineole, eugenol, and methyl-cinnamate, were quantified from headspace samples derived from fresh shredded basil leaves and analyzed via gas chromatography.  Plant growth increased with irradiance, resulting in highest dry weight under 0% shade.  Basil plants flowered under 0% or 30% shade, while plants under 50% or 70% shade did not. Differences in essential oil aromatic compounds were not significant among shade treatments; however, there was considerable variability between samples suggesting a need for greater replication in future experiments.  Our results suggest that higher irradiance allows for more photosynthetic activity to occur, resulting in greater dry mass accumulation. This is likely responsible for the differences in flowering between treatments as well.