Salt stress affects germination, seedling growth and physiological responses differentially in eggplant cultivars (Solanum melongena L.)

Salinity tolerance levels and physiological changes were evaluated in four eggplant cultivars (Solanum melongena L.). Seeds and seedlings were exposed to increasing salinity levels. In vitro germination kinetics and young seedling growth divided the cultivars in a sensitive and a tolerant group. 'Adriatica' and 'Black Beauty' supported only moderate salt stress up to 40 mM NaCl while the tolerance level of 'Bonita' and 'Galine' was up to 80 mM NaCl. Effects of salinity levels (0, 20, 40, 80 and 160 mM of NaCl) were also tested in a greenhouse experiment. Increasing NaCl concentration increased strongly the levels of proline, malondialdehyde and soluble carbohydrates in the. leaves of 'Adriatica' and 'Black Beauty'. In contrast, 'Bonita' and 'Galine' showed a decrease in soluble carbohydrates and a significant increase in starch under saline stress. The midday leaf water potential (psi(1)) and leaf osmotic potential (psi(pi)) were significantly affected in sensitive cultivars and remained quite stable in tolerant cultivars under salt stress. Leaf Na+ and Cl- content was higher in sensitive than in tolerant cultivars. The leaf K+ Ca2+ and Mg2+ contents were reduced under salt stress in sensitive cultivars. Under increasing salinity 'Bonica' and 'Galine' combine low leaf Na+ accumulation with a high plant tolerance index (PTI) thus maintaining a normal level of growth, while 'Adriatica' and 'Black Beauty' accumulate significantly higher concentrations of leaf Na+ and fail to maintain a normal level of growth from 80 mM NaCl on.