Root morphological and anatomical responses of olive tree cultivars 'Oliana' and 'Lecciana' under salinity stress

Olive trees (Olea europaea) exhibit a moderate to high salinity tolerance, varying by cultivar. Interest in cultivating olive trees is growing in coastal areas, which are characterized by poorly drained soil and low-quality brackish groundwater, leading to salt accumulation in the root zone. The rising salinity levels in these areas present a significant challenge for crop cultivation; therefore, evaluating new salt-tolerant cultivars is necessary. Various studies demonstrated the salinity tolerance of olive cultivars, but there is little information available for the novel cultivars 'Oliana' and 'Lecciana'. For this study, eight-month-old plants (n = 9) were assigned to a completely randomized experimental design and grown in pots using a sand medium under greenhouse conditions, treated with varying salt concentrations (0 mM - control, 50 mM, and 100 mM NaCl), and half-strength Hoagland solution was applied to meet their nutrient requirements. Height and trunk diameter were measured at three different time points (15, 30, and 45 days). At the same three time points, cohorts of plants were destructively sampled to study the root morphological traits, sodium (Na) and potassium contents, and root anatomical measurements. Both cultivars demonstrated a decrease in plant height, trunk diameter, and negative effects on root morphological traits under salinity treatments; moreover, translocation factors confirmed that the translocation of Na from roots to leaves was lower in both the cultivars. Microscopy analysis revealed that root apoplastic barriers developed near to the root tip in both the cultivars under salinity stress. Results indicate that both 'Oliana' and 'Lecciana' cultivars can be considered cultivars tolerant to salinity under the tested conditions.