Effect of NaCl salinity and different root zone temperatures on growth and mineral composition of two mango rootstocks (Mangifera indica L.)

The influence of NaCl salinity (0 and 30 mM NaCl added) in combination with different root zone temperatures (18, 24, and 30°C) on two mango rootstock cultivars (Mangifera indica L., '13-1' and 'Turpentine') was investigated. Expressed on a dry matter basis, NaCl salinity had the lowest effects on leaf growth of the more tolerant rootstock '13-1' (reduction 40.8% from control), roots of '13-1' and roots and leaves of 'Turpentine' were more affected (56.9, 69.0, and 63.9%, respectively). '13-1' stored significantly more Na⁺ and Cl^- in the roots than 'Turpentine'. In 'Turpentine' leaves a significantly higher Na⁺ content was found, while the Cl^- content was slightly lower. It was concluded that the difference in saline tolerance probably based on the ability of '13-1' to protect leaves from excessive Na⁺ and to accept higher Cl^- contents in the leaves without severe growth damage. Significantly higher Ca²⁺ and Mg²⁺ contents were found in leaves and roots of '13-1' compared to 'Turpentine'. They might be responsive for tolerating higher Cl^- contents in leaf tissues of '13-1' as well as for a higher Na⁺ retention potential in roots and stems of '13-1'. Optimum vegetative growth was found between 24 and 30°C root zone temperature. Increasing root temperature had no increasing effect on salinity. Highest Na⁺ and Cl^- contents in leaves were found at 18°C. This indicates that at low (30 mM NaCl) saline levels, increasing root zone temperature promoted tolerance mechanisms like higher growth, active exclusion under optimum root temperatures and higher Ca²⁺ uptake.