The impact of salinity on the physiological and biochemical parameters of tolerant (‘Bonica’) and susceptible (‘Black Beauty’) eggplant varieties (Solanum melongena L.) was determined. The results revealed that the increase in salinity contributes to a significant decline in net photosynthesis (A_n) in both varieties; however, at the highest salt concentration (160 mM NaCl), the decrease in photorespiration (R_l) was less pronounced in the tolerant cultivar ‘Bonica’. Stomatal conductance (g_s) was significantly reduced in ‘Black Beauty’ following exposure to 40 mM NaCl. However, g_s of ‘Bonica’ was only substantially reduced at the highest level of NaCl (160 mM). In addition, a significant decrease in Chla, Chlb, total Chl, Chla/b and carotenoids (p > 0.05) was found in ‘Black Beauty’, and soluble carbohydrates accumulation and electrolyte leakage (EL) were more pronounced in ‘Black Beauty’ than in ‘Bonica’. The total phenols increase in ‘Bonica’ was 65% higher than in ‘Black Beauty’. In ‘Bonica’, the roots displayed the highest enzyme scavenging activity compared to the leaves. Salt stress contributes to a significant augmentation of root catalase and guaiacol peroxidase activities. In ‘Bonica’, the Na concentration was higher in roots than in leaves, whereas in ‘Black Beauty‘, the leaves accumulated more Na. Salt stress significantly boosted the Na/K ratio in ‘Black Beauty’, while no significant change occurred in ‘Bonica’. ACC deaminase activity was significantly higher in ‘Bonica’ than in ‘Black Beauty’.

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208–305–370 µmol min⁻¹ mg⁻¹ FW) and catalase (CAT) (136–211–238 µmol min⁻¹ mg⁻¹ FW) activities compared to control plants (231 and 126 µmol min⁻¹ mg⁻¹ FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants.