Chemical Composition of Essential Oils of Peppermint and Spearmint Dry Leaves and Their Allelopathic Effects on Wheat Species

This study was carried out to determine the chemical composition of essential oils of the spearmint and the peppermint dry leaves and their allelopathic effects on seed germination and seedling growth of different wheat species. The ratios of essential oil isolated by hydrodistillation were found to be 2.5 % and 2.0 % (w/w), respectively. The GC/MS analysis revealed that the peppermint essential oil contained 20 compounds, while spearmint essential oil incorporated 17 compounds. The main components in the spearmint essential oil were identified to be carvone (62.9 %) and limonene (8.2 %), while those of the peppermint essential oil was to be menthone (34.5 %) and menthol (41.4 %). The seed germination started to be negatively affected by 0.2 mu L of essential oil and the negative effect increased in parallel with the increase in essential oil dose. The reducing effect of the mint essential oils on seed germination was the lowest for Triticum spelta and the highest for T. aestivum. In the pot trial, the negative effect began to appear with 0.8 mu L of essential oil and increased with the higher doses. The effect of mint essential oils on root lengths and dry weights of single seedlings was the lowest for T. spelta and the highest for T. dicoccum. The estimated field application dose of the peppermint essential oil for the investigated wheat species was determined to be approximately 208 mL da(-1).