Morphological indicators of salinity stress and their relation with osmolyte associated redox regulation in mango cultivars

Soil salinization is a global issue impeding horticulture production and is approaching an alarming status due to climate change and urbanization. Breeding salt-tolerant rootstock varieties is an ideal strategy to mitigate stress due to salinity in mango and other perennial fruit species. Stress combating strategies employed by seedlings of 7 mango were studied under saline conditions (200 mM NaCl, EC: > 4.0 dSm⁻¹, pH 8.5) in pot experiments. Significantly high accumulation of proline (19.07 µg g⁻¹ FW in Bappakai), glycine betaine (55.11 µg g⁻¹ FW in 13–1), and total sugars (17.33 mg g⁻¹ FW in Kurukkan) were found to be the common mechanism employed by the tolerant cultivars to counter the osmotic stress, under suboptimal conditions. Non-enzymatic antioxidants viz., tannins (17.18 mg g⁻¹), phenols (18.68 mg g⁻¹), and anthocyanins (1.59 mg g⁻¹) were increased in seedling of "13–1", the salt-resistant cultivar from Israel. Reactive oxygen species (ROS) regulation by increased activity of superoxide dismutase and catalase in the two polyembryonic cultivars of Indian origin (Kurukkan and Nekkare) suggests their potential use as rootstocks to combat oxidative stress. The tolerance index of various cultivars was calculated by averaging the scores of morphological stress indicators, and its correlation with studied parameters suggests that salinity resilience is more tightly linked to enhanced catalase accumulation (r² = 0.8361) that is reduced ionic stress. This evidence assign the role of osmotic stress alleviation and redox regulation in salt tolerance mechanism operational in native Indian cultivars, Nekkare and Kurukkan at par with known salt tolerant rootstocks.