Ecophysiological and biochemical aspects of olive tree (Olea europaea L.) in response to salt stress and gibberellic acid-induced alleviation

Soil salinization is considered as one of the most important risks for agricultural soils. The objective of this experiment was to study the ecophysiological and the biochemical behaviour of two cultivars of Olea europaea L., 'Chemlali' and 'Koroneiki' under two salinity levels (100 and 200mM NaCl) and the potential alleviation induced by gibberellic acid (GA3) foliar sprays. Salinity treatments significantly decreased photosynthetic assimilation rate and stomatal conductance compared to the control for both cultivars, but 'Chemlali' showed a higher resistance to increasing NaCl salinity compared to 'Koroneiki'. Leaf chlorophyll index also reduced gradually with increasing salinity concentration compared to the control. At the end of the experiment, a decrease in growth and dry matter accumulation was observed. Under high salinity stress, a significant decrease in root DW was recorded by 37% and 59% for 'Chemlali' and 'Koroneiki', respectively. High salinity stress decreased also shoot DW up to 51% for 'Chemlali'. However, mannitol concentration increased under increasing salinity levels compared to control for 'Chemlali' cultivars. Interestingly, foliar application of GA3 alleviated the negative effects of salinity on ecophysiological parameters especially for 'Koroneiki'. Indeed, GA3 improved photosynthetic assimilation up to 14% for 'Chemlali' and 36% for 'Koroneiki' compared to high salinity treatment. Both cultivars showed an increase in leaf chlorophyll index after applying GA3. Under high salinity combined with GA3, growth and dry weight were increased compared to salt stressed plants without GA3. The obtained results report that 'Chemlali' cultivar is more tolerant to salinity than 'Koroneiki' and suggest that GA3 plays an important role to reduce negative effects of NaCl salinity.