Effects of HPS supplemental lighting and soil water levels on growth, essential oil content and composition of two thyme (Thymus vulgaris L.) clonal selections

Abstract

The growth, esssential oil content and composition of two clonally selected Thymus vulgaris plants were each significantly affected by two light regimes (LR) and three different soil water levels (SWL). The highest dry matter accumulation was achieved from plants grown under supplemental light (SL) at 90% SWL. The leaf area increased linearly from 959 cm2 to 1635 cm2 for Selection 1 and from 543 cm2 to 1322 cm2 for Selection 2 under natural light and from 1180 cm2 to 3512 cm2 for Selection 1 and from 958 to 2821 cm2 for Selection 2 under supplemental light, respectively, for plants grown under 50 to 90% SWL. The coefficient of correlation between shoot yield and leaf area was highly significant (r2 = 0.96). However, maximum essential oil content and yield per plant were recorded at 70% SWL for Selection 1 grown under SL. There were significant shifts in the content of phenols, particularly in monoterpene hydrocarbons in the essential oil, due to the differences in LR and SWL. The major constituent of the essential oil, thymol, accounted for the shift from about 48.6% to 85.5% for Selection 1 and the shift from 47.2% to 68.9% for Selection 2, depending on the treatment levels. Our data showed a maximum level of 85.5% thymol accumulation in the essential oil of Selection 1 grown at 70% SWL under SL. We established that both selections under investigation belonged to the thymol chemotype. Key words:Thymus vulgaris L., Lamiaceae, essential oil, thymol