Biochemical and salt ion uptake responses of seven mango (Mangifera indica L.) rootstocks to NaCl stress

Uniform-sized, 6-month-old seedlings of seven mango (Mangifera indica L.) rootstocks (`Moovandan', 'Bappakai', 'Nekkare', 'Kurukkan', 'Olour', 'Terpentine', and 'Chandrakaran') were irrigated with tap water containing 0, 50, 100, or 150 mM NaCl at 4 d intervals for 40 d. NaCl stress increased the activities of peroxidase (PDX), catalase (CAT), and superoxide dismutase (SOD), and the concentrations of malondialdehyde (MDA), proline, and trehalose. The highest anti-oxidant enzyme activities were observed in the rootstocks 'Olour', 'Bappakai' and 'Terpentine' at the highest level of salinity (150 mM NaCl). Leaf proline concentrations increased most in 'Olour', 'Kurukkan', and `Terpentine' with increasing levels of salinity. The concentration of Na+ ions in leaf tissues increased to a maximum (123.5%) of the respective (0 mM NaCl) control in 'Chandrakaran', while `Bappakai' had the highest Na+ ion concentration in root tissues at the highest level of salinity (77.3%) compared to the respective control. Compared to the respective controls, the maximum increase (109.1%) in leaf Cl- ion concentration was recorded in `Moovandan', while 'Chandrakaran' had the highest concentration of Cl- ions (139.3%) in its root tissues when irrigated with water containing 150 mM NaCl. Our results suggest that the salt-tolerant behaviour of the mango rootstocks `Olour' and `Terpentine' may be due to their ability to inhibit the uptake of Cl- and Na+ ions, combined with higher accumulations of proline. These two rootstocks may therefore be used to improve the yield and quality of commercial mango cultivars grown in salt-affected areas.