Salinity Tolerance of Diplotaxis tenuifolia Varieties Growing in Spring–Summer Season Under Mediterranean Greenhouse and Optimal Growing Conditions

Salinity is one of the principal abiotic stresses that occurs in the Mediterranean area, causing loss of productivity and decrease of vegetable crop quality. The effect of salinity (0, 25, 75, 150 mM NaCl) was evaluated in three Diplotaxis tenuifolia varieties (Dragon Tongue, Capriccio, Piccante), previously selected for salinity tolerance and high glucosinolates production in leaves. The aim of this research was to explore the salinity tolerance of three wild rocket varieties cultivated under optimal temperature conditions and under high temperature that typically characterized the Mediterranean greenhouse. Biometric, biomass, pigment production and physiological parameters were evaluated. Biometric, physiological, and biochemical parameters significantly varied because of variety, salt level used and environmental conditions. PCA analysis highlighted that the two cultivation systems deeply affected the wild rockets response to salt stress. In general, under optimal growing conditions, wild rocket varieties showed higher growth parameters compared to greenhouse conditions. Overall Capriccio was the most susceptible variety to salinity, while Dragon Tongue (V1) and Piccante (V3) were more tolerant to salt stress. Furthermore, in both growing conditions V1 was the less productive variety while V3 showed an opposite trend. Interestingly, gene (DtOxo and DtGst) expression analysis revealed a significant increase of the target gene expression as response of salinity levels, with a clear increase of DtOxo level in V1 and V3. The results obtained in this study can be useful to plan future breeding programs aimed to increase rocket quality grown under Mediterranean conditions.