Physiological and biochemical mechanisms of salinity tolerance in several fennel genotypes: Existence of clearly-expressed genotypic variations

Medicinal plants such as fennel (Foeniculum vulgare Mill.) are potent to be utilized as alternatives to conventional crop plants in the face of ever-increasing drought and salinity stresses in arid regions. However, scientific data on the physiological responses of F. vulgare to salt stress is scarce. Six F. vulgare genotypes were subjected to five concentrations of irrigation water NaCl (i.e. 0, 30, 60, 90, and 120 mM) in a pot experiment. Photosynthetic pigments of chlorophyll a (Chl-a) and b (Chl-b) and carotenoids (Cars) concentrations, leaf water potential (P-w), and plant height were decreased but Chl-a/b, proline concentration and ascorbate peroxidase (APX) activity were increased with increase in NaCI concentration. Averaged over NaCI concentrations, genotypes Urmia, Kashan and Isfahan out-numbered the other genotypes in terms of these traits. Relative water content (RWC), shoot K(+ )and Na+ concentrations, Na+/K+, superoxide dismutase (SOD) and catalase (CAT) activities, total soluble carbohydrates (TSC), H2O2 and malondialdehyde (MDA) concentrations, plant leaf area (LA), seed weight/plant and above-ground dry mass (DM) responded to salt in a genotype-specific manner, with genotypes Urmia, Kashan, and Isfahan tending to out-number the remaining genotypes in terms of the latter traits with the exception of MDA and Na+ concentrations. Results revealed that tolerance to modest salinity of genotypes Urmia, Kashan and Isfahan, manifested in smaller decreases in seed weight/plant and DM, was associated with their smaller Na+ but greater photosynthetic pigments, K+, proline and TSC concentrations, RWC, P-w , and antioxidant activities of the salt-stricken plants, compared to the remaining genotypes.