Fennel outperforms ajwain and anise in saline environment: physiological response mechanisms in germinating seeds and mature plants

The potential of different medicinal species as alternative crops for saline conditions needs to be explored. Comparative physiological responses of germinating seeds and mature plants of three genotypes of anise (Pimpinella anisum L.), fennel (Foeniculum vulgare Mill.), and ajwain (Trachyspermum ammi L.) to salt were studied in a 2-year field experiment using 0 and 100 mcM, and a laboratory experiment using 0, 25, 50, 75, 100, and 125 mM NaCl. Catalase and ascorbate peroxidase activities increased in the salt-stricken plants of all genotypes, but only peroxidase activity of the salt-treated plants of anise genotypes and two of the fennel genotypes increased under field conditions. Chlorophyll and K+ concentrations of all genotypes decreased, but proline and Na+ concentrations and Na+/K+ increased under saline conditions. Dry mass, grain yield, and essential oil yield decreased in the salt-exposed plants across all genotypes and species. Germination, root, and shoot length were suppressed upon exposure to saline water. Despite the increasing trend of the proline and polyphenol concentrations and catalase and peroxidases activities, ascorbate peroxidase activity of germinating seeds decreased with an increase in NaCl concentration. Smaller adverse effects of salt on fennel germination attributes, grain and essential oil yields were evident. Moreover, greater activities of antioxidative enzymes and maintained Na+ and Na+/K+ of salt-stricken fennel plants were observed. These findings indicate that germinating seeds and mature plants of fennel have a greater ability to withstand salinity than the other examined species.