Effect of salt stress on physiological response of tomato fruit grown in hydroponic culture system

The effect of salt stress on physiological response of hydroponically grown tomato fruit was investigated. Fruit growth rate, water status, cuticle permeability and induction of blossom-end rot (BER) of tomato fruit were considered for this study. Salt stress was applied by using Ca salt treatment and it plays an important role on all parameters studied in this experiment. Fruit growth rate, predawn water potential, osmotic potential and cuticle permeability were significantly lower in treated plants than in control plants. On the other hand, tissue turgor of control and treated fruit showed almost similar values 12 days after flowering (DAF). This result indicated that turgor was osmotically regulated in fruit under stress condition. Fruit growth rate was found to decline from 12 DAF and eventually ceased when BER externally appeared on fruit surface at the age of 19 DAF in this experiment. The reduction of growth rate coincided with the reduction of water potential in fruit tissue due to salt stress. Although BER externally appeared at 19 DAF anatomical investigation showed that intercellular air space becomes discoloured at least one week before external symptoms appeared on fruit tip. Different levels of cuticular permeability indicated that the deposition of cuticular wax on fruit surface was enhanced by the salt stress condition in tomato fruit. Since, BER was found to appear on fruit tip under high calcium concentration in solution it can be concluded that calcium deficiency was not the only the cause of BER in tomato, rather salt stress might alter metabolic activity in developing tomato fruit.