In Vitro Screening and Characterization of Selected Elite Clones of Eucalyptus tereticornis Sm. for Salt Stress

The present investigation aimed to determine the salt tolerance level of six already selected elite clones of Eucalyptus tereticornis. The response of individual shoot cultures was evaluated on basal MS medium supplemented with different concentrations of NaCl (0, 100, 200, 300, 400, and 500 mM) for 28 days. The increase in NaCl concentration affected the survival of microshoots along with inhibition in shoot and root growth in all the clones. A better performance of clone 'KE8' was evident with higher survival of microshoots (65.18%) in comparison to clones 'CE2' (36.29%), and 'Y8' (10.37%) on medium containing 500 mM NaCl. The highest salt tolerance index (0.30) was recorded for clone 'KE8', followed by 0.24 for clone 'CE2' and 0.10 for clone 'Y8' on medium containing 500 mM NaCl. The 50% growth inhibition dose of NaCl was also found to be 479 mM for clone 'KE8', as compared to 385 mM and 206 mM for clones 'CE2' and 'Y8', respectively. Various physiological and biochemical parameters were investigated in microshoots of putatively higher salt-tolerant clone 'KE8', moderately salt-tolerant clone 'CE2' and less salt-tolerant clone 'Y8' at different intervals of culture period (7, 14, 21, 28 days). The relative water content and pigment levels (chlorophyll and carotenoid) declined significantly during culture on medium containing 500 mM NaCl with increasing culture period. Furthermore, the decline was higher in the case of clone 'Y8' than 'CE2' followed by 'KE8'. A significant increase in the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), accumulation of proline and lower levels of malondialdehyde content were recorded in clone 'KE8' as compared to the other clones 'CE2' and 'Y8'. The present study suggested that clone 'KE8' is more tolerant to salt stress, which can be commercially grown in saline soils.