Brassinosteroid Modifies Growth and Essential Oil Production in Peppermint (Mentha piperita L.)

This study was carried out to determine the effect of brassinosteroid (BR) (24-epibrassinolide (24-eBL) at concentration 0.5, 1.5 and 2.5 ppm) on the growth and essential oil accumulation in peppermint ( Mentha piperita L.). Plants were planted in pots with vermiculite and perlite in a growth chamber at 25 ± 1 °C. Hormone was applied by spraying of vegetatively propagated plants twice. The first application was done to 3-week-old plants, and the second application was performed 7 days after the first application. The following parameters were studied: biomass accumulation and essential oil content and composition. It was demonstrated that fresh and dry weights of plants increased in line with rising concentrations of 24-eBL. Essential oil content in the plants sprayed with 0.5 ppm of 24-eBL was significantly higher than that in control plants. BR also modified essential oil composition. Especially important is that, 24-eBL had positive effects on menthol content; the highest menthol content was found in plants treated with 0.5 ppm 24-eBL. Simultaneously, 24-eBL decreased the content of less desirable essential oils. To conclude, 2.5 ppm of 24-eBL was the most suitable concentration providing the highest plant growth. On the other hand, 0.5 ppm of 24-eBL was optimum for essential oil production because it resulted in the maximum essential oil and menthol content. 24-eBL may be promising compound for use in peppermint cultivation.