In vitro studies on salt and water stress tolerance in Eucalyptus tereticornis Sm

Abstract

The present work focuses on the screening and characterization of selected elite clones ( CE2 , KE8 , KE2 , Y8 , T and T1 ) of Eucalyptus tereticornis for salt stress. These commercially important elite clones were selected from the plantation of Ballarpur Industries Ltd. and screened for salt tolerance on Murashige and Skoog s (MS) medium fortified with different concentrations of NaCl. The seeds and shoot cultures were used as explants for screening. This resulted in the identification of salt-tolerant, moderately salt-tolerant, and salt sensitive clones. The results of the in vitro experiments were further verified under greenhouse and field conditions. Further, the salt tolerance of sensitive clone Y8 was improved in two different ways: exposure to iron-oxide nanoparticles (IONPs) and overexpressing the osmotin gene of potato. The three different in vitro screening approaches (direct, indirect, and gradual exposure to salt stress) were employed for the identification of salt-tolerant (ST) seedlings. The screening via gradual step-wise exposure to salt stress (0 to 400 mM NaCl) was highly efficient and promoted tolerance level up to 400 mM NaCl. Shoot growth of seedlings demonstrated a 91.93% increase due to physiological acclimatization to salt stress. The indirect screening approach was also effective but only a 12.8% rise in shoot length was recorded when cultured on a medium fortified with 400 mM NaCl. On the other hand, the direct screening approach could only identify seedlings with a tolerance level of 200 mM NaCl. Further, when salt sensitive (SS) and salt-tolerant (ST) seedlings were exposed to salt stress (0, 200, and 400 mM NaCl) for 14 days, a significant increase in chlorophyll, osmolyte accumulation, and antioxidant enzyme activity was only observed in ST seedlings. The tolerance of ST seedlings was also associated with significantly higher transcript levels of genes encoding superoxide dismutase, peroxidase, and catalase. The response of individual shoot cultures of six elite clones of E