Influence of salt stress on growth and essential oil production in peppermint, pennyroyal, and apple mint.

摘要

Effects of salt stress on the growth and chemical composition of the essential oils of peppermint (Mentha x piperita), pennyroyal (M. pulegium) and apple mint (M. suaveolens) were investigated. Plantings in a greenhouse were irrigated with full-strength Hoaglund's solution containing 0, 1.5, 3.0, or 4.5 g/l of NaCl for 74 days. Under salt stress, reduced growth was observed in all 3 species, although differences in sensitivity to the stress were noted. The fresh wt. of apple mint was reduced more, as compared with respective untreated controls, than the other tested species at all the tested salinity levels. Essential oil yields per plant under salt stress were reduced in all 3 species, as compared with untreated controls not under salt stress. The lower oil yields were a function of smaller plant size and, for peppermint and apple mint, the lower concn. of oil within the tissue as compared with untreated controls. In pennyroyal, the oil concn. in the plant tissue under salt stress increased as compared with untreated controls, suggesting that oil synthesis and/or oil degradation processes were less sensitive to salt stress than similar processes in peppermint and apple mint. Within the essential oil, the relative level for various constituents increased, decreased, or did not change in all 3 tested plant species under salt stress as compared with nonstressed control plants. For example, menthone contents of peppermint increased with increasing levels of salt stress, whereas contents of several other constituents decreased at the highest salt concn. tested. Pennyroyal essential oil composition was not as greatly affected by salt stress as peppermint and apple mint essential oils.