Effect of Foliar-Applied Silicon on Flower Yield and Essential Oil Composition of Damask Rose (Rosa damascena Miller) under Water Deficit Stress

A field experiment was conducted to investigate the effect of silicon on the flower yield and essential oil composition of damask rose under water deficit stress. Silicon was applied as foliar spray at 0.2 and 0.4% concentrations in spring, summer, or both in spring and summer. Half of the plants irrigated to receive 100% plant water requirement while the other half received only 25% plant water requirement. Water deficit stress resulted in reduction of flower yield of rose (by 20%), while foliar spray of Si, regardless of time and dose of application, resulted in higher flower yield. Both Si nutrition and water deficit stress modified the flower essential oil composition of damask rose by increasing concentration of the acyclic monoterpenoid alcohol compounds including citronellol, citronellol acetate, geraniol, and eugenol. An increase in the concentration of methyl eugenol and n-heptadecan in the essential oil by Si application was also observed. In contrast, concentration of alkane compounds in the oil was decreased by Si application. Water deficit stress resulted in 52.4, 46.4, and 43.2% increase in the concentrations of geraniol, citranolol, and eugenol. Foliar application of Si at 0.2% concentration on spring and summer particularly under water stress conditions is useful to increase the essential oil content and concentration of geraniol, citronellol, eugenol and methyl eugenol which are main compounds useful for medicinal, cosmetic, and health applications of rose oil.