The interaction between shade and drought affects essential oil quantity and quality of Vitex agnus-castus L. leaves and seeds

Chaste tree (Vitex agnus-castus L.) is an industrial plant whose quality and yield may be affected by shade and drought. Therefore, leaf and seed dry weights, and the essential oil (EO) content and composition of leaves and seeds were determined under three shading levels (full light, 50% shading, and 80% shading) and three irrigation regimes (50, 70, and 90% available water depletion). Gas chromatography–mass spectrometry analysis showed the presence of 26 compounds (α-pinene (16.4–60.7%), β-terpinyl acetate (15.5–40.2%), caryophyllene (2.7–9.0%), and camphene (0.09–6.2%)) in the leaves, as well as 28 compounds (α-pinene (29.2–46.3%), isozonarol (33.9%), caryophyllene (1.6–26.8), β-iraldeine (0.55–22.1%), isopulegyl acetate (10.7–15.6%), and terpinolen (0.51–6.3%)) in the seeds. The highest leaf and seed dry weights, leaf essential oil content and yield, and seed essential oil yield were achieved under full light and non-stressed conditions. The highest α-pinene and caryophyllene contents were recorded in the full light condition under 70% water depletion and the highest β-terpinyl acetate was observed under 50% shading with 70% water depletion in the leaves. However, seeds had the highest β-terpinyl acetate and caryophyllene contents under 80% shading with the 50% water depletion condition. Isopulegyl acetate and bioformen were found in the seeds, but they were not obtained in the leaves. Based on the leaf and seed yield, as well as leaf essential oil content and yield, full light and 50% water depletion could be the best treatment in both leaves and seeds. However, based on the essential oil composition, 50% shading could be applied under 70% water depletion for the leaves, and 50% shading under 90% water depletion could be appropriate for the seeds.