A Comparative Analysis of Novel and Established Olive Cultivars for Super-High-Density Olive Orchards

Introduction: The intensification of olive cultivation in Mediterranean regions faces significant challenges from increasing soil salinity, necessitating a comprehensive understanding of salt tolerance mechanisms across both emerging and established cultivars. Rising global temperatures and reduced water quality are exacerbating soil salinization, particularly affecting intensive olive orchards.

Goals: This study aimed to evaluate and compare salt tolerance mechanisms among three novel olive cultivars (Lecciana, Coriana, Siquitita) and two commercial standards (Arbequina, Arbosana). The investigation focused on characterizing their physiological responses, growth performance, and ion management strategies under saline conditions, with particular emphasis on identifying cultivar-specific adaptation mechanisms and their potential implications for breeding programs.

Methodology: Five olive cultivars were evaluated under controlled greenhouse conditions over a five-month period, using a salt stress treatment (0, 25, 50, and 75 mM NaCl). The comprehensive investigation encompassed multiple parameters: growth measurements (shoot length, trunk diameter, fresh and dry weights), physiological responses (stomatal conductance, transpiration rate), ion relationships (Na⁺, K⁺, Ca²⁺, Cl⁻ concentrations in different tissues), and photosynthetic efficiency through chlorophyll fluorescence measurements.

Results: Genotype-specific variations in stress tolerance mechanisms were identified across cultivars, revealing distinct adaptation strategies. Siquitita emerged as promising for moderate-salinity conditions, demonstrating effective biomass maintenance and enhanced stomatal conductance regulation under stress, though showing sensitivity in photosynthetic parameters (reduced PI(abs) and φ(Po)) at higher salinity levels. Chlorophyll fluorescence measurements revealed cultivar-specific responses: Lecciana maintained stable fluorimetry parameters and SPAD values under moderate salinity, while demonstrating superior potassium retention with the highest K⁺/Na⁺ ratios across treatments. Arbosana exhibited moderate tolerance across multiple parameters, maintaining consistent biomass production (with only 5.4% reduction at 75 mM NaCl) and showing intermediate photosynthetic responses. Coriana displayed variable responses, with stable fluorimetry values (F_v/F_m and ETo/RC) at moderate salinity but significant limitations in growth and ion discrimination under higher salinity levels. Ion compartmentalization analysis revealed shared patterns across cultivars, with roots accumulating the highest Na⁺ concentrations (1.51% at 75 mM NaCl) and wood tissue maintaining the lowest levels (0.54%).

Conclusions: Cultivar performance under saline conditions depends on the complex interaction between growth maintenance, photosynthetic efficiency, and ionic regulation capacity. Siquitita shows promise for areas with moderate salinity where biomass maintenance is crucial, while Lecciana may be more suitable where ion regulation capacity is the primary concern. These findings emphasize the complexity of salt tolerance mechanisms in olive trees and the need for site-specific cultivar selection based on both environmental conditions and desired performance characteristics.