Mechanisms by which plants acclimatize to water deficit conditions can affect development and, especially in aromatic plants, the essential oil synthesis. To evaluate the effects of water deficit on Ocimum africanum, seedlings were exposed to water levels corresponding to 100, 80, 70 and 60% of the substrate field capacity. The different watering regimes corresponded to predawn water potentials of –0.5, –0.9, –1.6 and –1.9 MPa, respectively. Decreased stomatal conductance and increased glandular and tector trichome density were observed under water deficit. In addition, reductions in leaf gas exchange and water consumption under water deficit led to decreased plant height, numbers of leaves and inflorescences, and total biomass production. As a result, lower essential oil yield and water use efficiency for biomass production occurred in the -1.9 MPa treatment. The content and production efficiency of essential oil (quantity of oil produced per unit water consumed) were higher in the –0.9 and –1.6 MPa treatments. There were no significant differences among treatments in the chemical composition of essential oil, and the major component of essential oil in leaves and inflorescences was isoeugenol in all treatments. The 80% field capacity watering regime (branch water potential of –0.9 MPa) was best for the growth and production of essential oil in O. africanum, for the cultivation of aromatic plant under drought economically viable in the semi-arid climatic regions.
Key words: Drought adaptation, essential oil, irrigation, water use efficiency.
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