Drought stress mitigation by foliar application of salicylic acid and their interactive effects on physiological characteristics of fennel (Foeniculum vulgare Mill.) genotypes

This study was aimed at characterization of physiological responses of fennel to water deficit and exogenous application of salicylic acid (SA). Six fennel genotypes namely ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’, and ‘Yazd’ were subjected to two levels of irrigation (irrigation after 35 and 75 % depletion of available soil water) and three levels of SA (0.0, 0.5, and 1.0 mM). Leaf water potential, relative water content (RWC), proline, total soluble carbohydrates, chlorophyll a (Chl a), b (Chl b), total (Chl a + b), a/b (Chl a/b) and carotenoids contents, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) specific activities along with seed yield per plant and seed essential oil content were measured. Water deprivation left significant effects on all characteristics, i.e., in contrast to the antioxidative enzymes activities and seed essential oil content, the rest of the attributes were decreased significantly with water deficit. Drought-tolerant genotypes (‘Yazd’ and ‘Shiraz’) exhibited higher accumulation of osmotic solutes and carotenoids along with higher leaf water potential, RWC, and antioxidant enzymes activities (CAT, APX, and SOD) than drought sensitive genotypes (‘Hamadan’ and ‘Birjand’). SA affected the activities of antioxidant enzymes and increased water potential, RWC, leaf osmolytes, chlorophyll and carotenoids, and seed essential oil content; the extent of the increases appeared greater when fennel was grown under drought. All the above effects helped the seed yield of fennel genotypes to increase with increase in SA level and led to the conclusion that droughtinduced harmful effects on fennel could be alleviated by exogenously applied SA.