Oil composition of Mentha aquatica x M. spicata F1 hybrids in relation to the origin of M. x piperita

Fertile M. aquatica L. (2n = 96) having the genotype cc AA PP RR ff and 40–80% menthofuran hybridized with fertile M. spicata L. (2n = 48) or M. spicata L. var. crispata Schrader (2n = 48) having the genotype Cc Aa PP rr FF, a strong spearmint odor, and the ketones carvone and dihydrocarvone produced sterile F1 hybrids (2n = 72) that had a ratio of 1 hybrid having the 2-oxygenated ketones carvone and dihydrocarvone to 1 hybrid having the 3-oxygenated ketones pulegone and menthone. M. aquatica hybrids with an S1 strain of M. spicata having the genotype CC (AA, Aa, or aa) PP rr FF and carvone are all carvone/carveol/carveyl acetate odored, whereas hybrids with S1 strains of M. spicata having the genotype cc AA PP rr FF and the ketones pulegone and menthone are all somewhat peppermint odored but highly variable in oil composition. Gas chromatographic analyses of the peppermint-type hybrids having the genotype cc (AA or Aa) PP Rr Ff show that all hybrids have the same 14 major oil constituents as the Mitcham cultivar (source of all U.S. produced peppermint oil) and one non-Mitcham strain of X M. piperita L. but in very different quantitative amounts. Individual hybrids differed greatly in the quantitative amounts of 13 of the 14 oil constituents and organoleptic tests indicate that there are probably equally great differences in the minor oil constituents. The great variability of the F1 hybrids in morphological appearance is largely due to the heterozygosity of the M. spicata parent, since the self-pollinated progeny of M. aquatica are indistinguishably alike. Certain hybrids resemble the natural strains of X M. piperita, whereas others do not. We were unable to make the 66-chromosomed cytotype, but have studied three secondary cytotypes having 84, 96, and 120 chromosomes.