Response to salinity stress in four Olea europaea L. genotypes: A multidisciplinary approach

Despite a drought- and erosion-tolerant root system, olive trees are vulnerable to abiotic stress due to limitedgenetic variability. Though some olive cultivars are moderately tolerant to salinity stress, soil salinity isincreasing in the semi-arid and arid regions where olive cultivation is common, significantly reducing overallproduction. In response, breeding programs may rely on proper selection markers for abiotic stresses, includingsalinity, but these are generally lacking for olive. Here, physiological and biochemical parameters were measuredin four Olea europaea genotypes (Frantoio, Leccino, Lecciana, and Oliana) subjected to different intensities ofsalinity stress (0 mM, 100 mM and 200 mM NaCl). At moderate and high salt concentrations, Na+ exclusion,higher photosynthetic productivity and tissue water content in the tolerant cultivar Frantoio were linked withincreased production of polyphenols, with more favorable K+/Na+ values (quercetin and rutin), mitigation ofoxidative stress (oleuropein) and increased water absorption (luteolin). In Frantoio and Leccino, a significantchange of the proteome repertoire occurred, with overrepresentation of components regulating cellular metabolism,ion transport, redox insult and dissipation of excess photochemical energy. Conversely, Lecciana andOliana showed increased sensitivity to salinity stress in terms of photosynthetic parameters and elevated internalNa+ concentrations, together with the lowest number of differentially represented proteins. These resultshighlighted olive germplasm strategies to cope with osmotic stress, suggested a physiological and molecular basisfor the augmented responsiveness of tolerant cultivars and identified specific biomarkers as useful targets forfuture breeding programs.