Changes caused by NaCl salinity on growth, gas exchange, chemical composition, and oxidative stress symptoms have been measured in six olive (Olea europaea L.) cultivars (Casta Cabra, Cornicabra, Frantoio, Ocal, Picual, and Picudo) grown in nutrient solution in a growth chamber pot experiment. Six-month-old plants were transplanted to a sand–perlite culture and irrigated with half-strength Hoagland nutrient solution containing 0 and 200 mm NaCl for 12 weeks. Salinity significantly depressed growth and leaf gas exchange, but to a different degree in each cultivar, Picudo was the cultivar that showed less growth inhibition. The effectiveness of Na+ exclusion mechanism in the roots differed significantly among studied cultivars, working effectively in ‘Ocal’ and ‘Picudo’ and being less efficient in ‘Picual’. Furthermore, ‘Picudo’ showed the ability to maintain the concentration of leaf K+ under the stress condition. ‘Ocal’ accumulated phenolic compounds and did not reduce carotenoid or total thiol concentration under saline stress. Between the cultivars studied, ‘Picudo’ and ‘Ocal’ were the most tolerant.

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Salinity is one the most recurrent abiotic stresses worldwide and severely affects crop productivity in arid and semiarid environments. This research analyzed several plant growth regulators that could mitigate the effects of salinity on olive plants (Olea europaea L. cultivar Picual). Mist-rooted cuttings were grown in a growth chamber and pretreated with gibberellic acid (GA3), indole-3-acetic acid (IAA), salicylic acid (SA), and Kinetin by foliar spraying twice a week for three weeks. At the end of the pretreatment, the plants were exposed to 100 mM and 200 mM sodium chloride (NaCl) for six weeks. The results showed that plants pretreated with the plant growth regulators significantly increased their biomass under saline conditions. In addition, IAA and SA restricted the transport of sodium (Na+) ions from roots to leaves and improved the leaf potassium (K+)/Na+ ratio. IAA and SA favored proline, fructose, and mannitol accumulation in leaves at 100 mM and 200 mM NaCl, as did glucose at 200 mM NaCl. Salicylic acid and IAA increased pigments (chlorophylls and carotenoids) and polyamines accumulation under saline conditions. The findings of this study suggest that pretreatments with IAA and SA may be a highly effective way of increasing salt tolerance in olive plantlets.

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