Changes in Essential Oil Yield and Composition at Different Parts of Dill (Anethum graveolens L.)Under Limited Irrigation Conditions

The influence of water stress during vegetative and reproductive growth stages on essential oil yield and composition of Iranian dill was evaluated in 2006 and 2007 at the Research Farm of Faculty of Agriculture of the University of Zanjan. Experiments were carried out as split plat design based on randomized complete block in four replications. Irrigation treatments were allocated to main plots and harvest times were assigned to sub plots. Irrigation treatments were full irrigation (control) to achieve 100% of field capacity (FC) during the growth season, two moderate (66% of FC) and two severe (33% of FC) water stresses during vegetative and reproductive stages. Three harvests were carried out at vegetative, full flowering and seed maturity stages. The essential oil contents of the leaves (H1), flowering shoots (H2) and mature seeds (H3) were isolated by hydro distillation and analyzed by GC and GC/MS. 24, 29 and 25 compounds were identified from leaves, flowering shoots and seeds respectively. Both moisture availability and harvesting times had significant effects on essential oil content. The percentage and yield of essential oil contents of seeds (H3) and flowering shoots (H2) were much higher than those of leaves (H1) under all irrigation treatments. Essential oil percentage of leaves was increased with decreasing water availability. However, essential oil percentages of seeds and flowering shoots were considerably high, when plants were subjected to moderate and severe water deficit at different developmental stages. In contrast, the highest essential oil yield (6.146g/m2) was obtained from flowering shoots under moderate water stress during flowering and seed filling phases (S3H2), while the lowest essential oil yield (0.216 g/m2) was produced from leaves under severe water deficit during early growth stage (S2H1) in both years. The main oil constituents of the leaves and flowering shoot were α – phellandrene, β – phellandrene and β – pinene, while that of seeds oil was carvone 70.78%). The amount apiol increased under severe stress, while carvone content increased under moderate stress. The quality of β – phellandrene was unaffected by irrigation treatments, but the amountof α – phellandrene decreased under moderate and severe water stress.