Salicylic acid and calcium pretreatments alleviate the toxic effect of salinity in the Oueslati olive variety

Pretreatment in arboriculture is a new physiological approach allowing the improvement of plant tolerance to salt stress. This research aims to screen various pretreatments of salicylic acid (SA) and/or calcium chloride (CaCl2) to mitigate the effect of salinity on 'Oueslati' olive plants (Olea europeae L.) on physiological attributes under 200 mmol L−1 of NaCl application. One - year- old plants were transplanted to sand culture in a greenhouse, and were pretreated with two levels of foliar application of SA (0.5 and 1 mmol L−1) and by adding CaCl2 (10 and 20 mmol L−1) to the culture solution twice a week for 45 days. At the end of the pretreatment, the plants were subjected to 200 mmol L−1 NaCl exposure for 75 days. The result showed that shoots and roots growth were decreased significantly due to salinity, sodium (Na+) ions increased and K+/Na+ ratio decreased in leaves. Rate of assimilation (A), transpiration (E) and stomatal conductance (gs) decreased in leaves. Salinity caused significant increase in both malondialdehyde (MDA) and H2O2 concentration, a decrease in total polyphenol and flavonoid levels and an increase in scavenging activity (IC50) (21%). Moreover, salinity caused a decrease in xylem and an increase in phloem thickness in leaves. However, pretreatments could partly improve the adverse effects of salinity on the most studied parameters. SA (1 mmol L−1) is able to restrict Na+ ions transport from the roots to the leaves limiting its toxicity in the sensitive organs. SA (1 mmol L−1) and CaCl2 (10 mmol L−1) pretreatment alleviate the effects of salinity on dry weight of shoots and roots as well as, photosynthetic activity in pretreated plants. Moreover, at the same pretreatment, results showed a decrease of the Na+ translocation to the leaves. Furthermore, it has been shown that pretreatment of 'Oueslati' olive plants enhance the non-enzymatic antioxidant activity (total polyphenol and flavonoid content).These results suggest that pretreatments may be useful methods to increase salt tolerance in olive, for use in arid and semi-arid environments.