Effect of Foliar Application of Methyl Jasmonate and Extracts of Juniper and Sagebrush on Essential Oil Yield and Composition of ‘Native’ Spearmint

Abstract

Spearmint (Mentha spicata L.) is a major essential oil crop in the United States. Developing means for increased biomass and oil yields and increased concentrations of carvone would be beneficial for the essential oil industry. A field experiment was conducted to study the effect of foliar application treatments [water (control), water + Tween20, sagebrush essential oil + Tween20, sagebrush water extract, juniper essential oil + Tween20, juniper water extract, and methyl jasmonate] on ‘Native’ spearmint essential oil content, shoot fresh weight, oil yield, and oil composition. The essential oil content was low in the water + Tween20 and in juniper essential oil (EO) + Tween20 treatments and high in the juniper water extract and in methyl jasmonate (MJ) treatments; however, neither of these were different from the water control or from the sagebrush EO + Tween20. Biomass fresh weight was lower in the sagebrush water extract (SWE) and in the juniper water extract (JWE) relative to the water control. The application of juniper EO + Tween20 reduced the concentration of carvone in the oil relative to the water control or to the water + Tween20 treatment. The sagebrush water extract, juniper EO + Tween20, juniper water extract, and MJ increased the concentrations of beta-caryophyllene relative to the water treatment. The concentration of trans-beta-farnesene was lower in the control water treatment and higher in all other treatments. Also, with the exception of sagebrush EO + Tween20, all treatments increased the concentration of germacrene D relative to the water control but not relative to water + Tween20. This study demonstrated that foliar application of sagebrush EO, sagebrush water extract, juniper EO, or juniper water extract to ‘Native’ spearmint may affect the essential oil profile of spearmint essential oil. Some of the treatments increased the concentrations of beta-caryophyllene, trans-beta-farnesene, and germacrene D in the essential oil; however, neither of the treatments increased the concentration of carvone, the main essential oil constituent of ‘Native’ spearmint oil.