Tolerance of eggplant (Solanum melongena L.) seedlings to stress factors

The aim of the present study was to describe eggplant (Solanum melongena L.) tolerance to stress factors in the seedling stage as a basis for future studies on cross-tolerance to other stressors in subsequent stages of growth. After germination (3 days / 26oC), ‘Epic F1’ seedlings were exposed to chilling stress (3, 6 and 9oC × 48 h-1), heat stress (35, 40 and 45oC × 2 h-1), osmotic stress (mannitol 0.2; 0.6 and 1.0 M x 2 h-1), and oxidative stress (H2O2 0.2; 0.4 and 0.6 M × 2 h-1). A linear measurement of seedling radicle growth, electrolyte leakage and external symptoms of radicle damage under the stress conditions, compared to the non-stressed control, were analyzed. It was found that stressors in all experimental combinations caused a morphological and physiological response from eggplant seedlings. A significant reduction in linear growth of radicles, showed as an absolute length and as a percentage of the control, was found in the treatments exposed to chilling stress (3 and 6oC), heat stress (35, 40 and 45oC), osmotic stress (0.2, 0.6 and 1.0 M mannitol) as well as oxidative stress (0.2, 0.4 and 0.6 M H2O2). The changes in seedling length as a result of stress factors did not always correspond with the changes in seedling mass. Electrolyte leakage in the treatments exposed to the following stressors: 3 and 6oC as well as 0.6 M H2O2, was significantly greater than that observed in control plants. Based on the obtained results and microscopic observations of radicle damage, the following stressors can be identified as those which cause a physiological response without severe damage: 9oC × 48 h-1 (chilling stress), 35oC × 2 h-1 (heat stress), 0.2 M mannitol × 2 h-1 (osmoticum), and H2O2 0.2 M × 2 h-1 (oxidation factor). We propose these stressors as a basis for future studies on plant acclimation and hardening to other stresses.