Growth and Essential Oil Yield of African Basil, Ocimum gratissimum, under Light and Water Stress

Abstract

The growth and essential oil yield of African basil, Ocimum gratissimum L., grown under watered and water-stressed field conditions in full sunlight and natural shade (26.7-44.2% full sunlight) conditions were investigated. Seedlings, 42 days old and growing in a prepared mix contained in plastic bags, were randomly placed in one of four adjoining field plots, one in full sunlight with daily watering, one in full sunlight watered at five day intervals, one in natural shade with daily watering, and one in natural shade watered at five day intervals. Plant height and total leaf area of the African basil were decreased more by water stress than by the light or shade condition. Shade enhanced essential oil content and water stress boosted essential oil content under shade, but reduced oil content under full sunlight. The effects of water stress were only observed in plants in full sunlight. The results demonstrated that African basil will produce relatively high essential oil yields per plant when grown under natural shade, irrespective of water stress and despite poor vegetative growth. Introduction African basil, Ocimum gratissimum L., is a perennial herbaceous, drought tolerant plant with lime-green pubescent leaves, a characteristically strong fragrance, and a slight pungency. In Nigeria and several other countries, the plant plays an important role in traditional medicine preparations (Gill, 1992), including use as a stomachic and for treatment sunstroke, headache and influenza. In the coastal areas of Nigeria, the plant is used in the treatment of epilepsy, high fever, and diarrhea (Effraim, et al., 2003), while in the Savannah areas leaf decoctions are used to treat mental illness (Akinmoladun, et al., 2007). Other uses include the treatment of fungal infections, fevers, colds, and catarrh (Ijeh et al., 2005). A number of other traditional uses of African basil have also been reported (Freire,, et al., 2006; Ilori et al., 1996; Nadkarni, 1999; Ngassoum et al., 2003; Okigbo and Igwe, 2007). The plant is known to contain phenolic compounds with therapeutic potential (Vierra and Simon, 2000). Light and water stresses are environmental factors that can affect crop growth and yield. Reduced light can limit photosynthesis and alter plant development (Whitelam and Halliday, 2007). Water deficits result in lowered water potential, reducing the water flow and cell turgor pressure needed to maintain plant structure and promote growth (Hopkins, 1995). In the case of aromatic crops, reduced light levels and water deficits have been demonstrated to alter essential oil levels and constituency (Radusiene et al., 2011; Sabih et al., 1999). Studies with sweet basil (Ocimum bacilicum) have corroborated these effects for both light (Loughrin and Kasperbauer, 2003; Shiga et al, 2009) and water (Mirsa and Strivastov, 2000; Simon et al., 1992). The deficit of a single environmental resource on plant growth and productivity are frequently Omobolanle Ade-Ademilua et al.: Growth and Essential Oil Yield of African Basil, Ocimum gratissim