Responses of trifoliate orange (Poncirus trifoliata (L.) Raf.) to continuously and gradually increasing NaCl concentration

The effect of continuous or gradual stress due to NaCl on in vitro growth, proline and sugar accumulation and nutrient acquisition of trifoliate orange (Poncirus trifoliata (L.) Raf.) explants was studied. Apical shoot tips obtained from previous subculture were transferred to a Murashige and Skoog nutrient medium for proliferation and were exposed to continuous or gradual salinity stress for 42 days. The salt used to induce salinity was NaCl added in six concentrations: 0, 50, 100, 150, 200 and 300 mM. Gradual salinization was achieved by transferring the explants sequentially every week to the above mentioned NaCl concentrations. Most salt treatments had a negative effect on the growth parameters of explants. Sodium concentration of explants increased in all NaCl treatments compared to control and it was higher in the treatmentswith gradual exposure to salinity. Potassium concentration was reduced, mostly in the treatments with continuous exposure. Calcium andMg concentrations increased in all saline treatments. In general, the high salinity level in the substrate enhanced the proline and sugar concentrations of the studied explants. In conclusion, salinity had significant impacts on the growth and chemical status of P. trifoliata.