Evaluating salinity tolerance in Xylella fastidiosa-resistant olive cultivars: implications for future orchards

Soil salinization and Xylella fastidiosa outbreak constitute the main problems related to olive cultivation in Mediterranean area. In the last years, many efforts have been made to identify cultivars resistant to X. fastidiosa. However, the response of resistant cultivars to salt stress should be thoroughly investigated to avoid replanting cultivars susceptible to the expected level of soil salinization. In Salento peninsula, one of the more important Italians regions for olive cultivation, soil salinization in orchards is expected to increase at values even higher than 60 mM NaCl, concurrently with increased drought periods. Therefore, the aim of this work was to test the two X. fastidiosa resistant cultivars currently replanted in Salento peninsula, ‘Leccino’ and ‘FS-17’, under a predicted salinity average level and duration (i.e., 60 mM NaCl for 90 days). This treatment was sufficient to lead to a Na+ translocation in both cultivars even if important differences in Na+ accumulation and cation balances were found, suggesting a different sensitivity of the two tested cultivars. ‘Leccino’ plants showed lower leaf biomass and higher Na+ concentration in roots. However, these negative effects caused by salt stress matched with Ca2+, Mg2+, and Mg2+ increases in leaves and an increase in Water Use Efficiency, suggesting a lower cation imbalance and photosynthesis damages in this cultivar that might lead to an improved osmotic stress response at leaf level. This behaviour suggests a higher sensitivity of ‘Leccino’ to salt stress but also the ability of this cultivar to activate the cation mobilization strategy to balance nutrient uptake and sustain photosynthesis.