Variation in the Amount of Yield and in the Extract Composition Between Conventionally Produced and Micropropagated Peppermint and Spearmint

The quality and quantity of oil obtained from three different peppermint Mentha x piperita L. origins and the spearmint Mentha spicata L. were compared in micropropagated and conventionally propagated plants in northern Finland (64°40′N) in 1997-1998. Each block comprised M. piperita peppermint plants from three different origins; namely, the United States, Bulgaria and Egypt (Black Mitcham), and a spearmint, M. spicata of Egyptian origin. The micropropagated plantlets and conventionally propagated plants were transferred to the experimental field in June. In the first year, there were no differences in the dry leaf yield between the micropropagated plants and their conventionally produced counterparts, although the former had a higher leaf/stem ratio. In the second year, the dry leaf yield of micropropagated plants, which were left in 1997 in field and developed from the underground stolons, was higher than that of conventionally propagated plants. The percentage of oil was higher with conventionally propagated plants, but only in the first year. Significant differences were observed between mint origins in the different propagation methods. Moreover, conventionally propagated plants showed a higher menthol percentage. There was no significant difference in the isomenthone content of the plants. In spearmint, the dry yield was higher in the second year with micropropagated plants, but there were no significant differences in the percentage of carvone between the two propagation methods.