Influence of Salt Stress on Growth and Essential Oil Production in Peppermint, Pennyroyal, and Apple Mint

Abstract

ABSTRACT The effect of salt stress on the growth and chemical composition of the essential oils of peppermint (Mentha x piperita L.), pennyroyal (Mentha pulegium L.) and apple mint (Mentha suaveolens Ehrh.) was investigated. Plantings in a greenhouse were irrigated with full-strength Hoaglund's solution containing 0, 1.5, 3.0, or 4.5 g/L− 1 of NaCl for 74 days. Under salt stress, reduced growth was observed in all three species, although differences in sensitivity to the stress were noted. The fresh weight 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 three 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 concentration of oil within the tissue as compared with untreated controls. In pennyroyal, the oil concentration 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 three tested plant species under salt stress as compared with nonstressed control plants.