Comparative Response of Two Rice (Oryza sativa L.) Cultivars to Applied Zinc and Manganese for Mitigation of Salt Stress

Soil salinity, together with zinc (Zn) and manganese (Mn) deficiencies, adversely affects rice growth and yield. The comparative salinity stress mitigation response of rice to Zn or Mn remains largely unknown. Rice cultivars, viz. Basmati-515 and KSK-282, were grown in saline soil having electrical conductivity (EC) of 7.5 dS m−1 (as control) parallel to EC 7.5 dS m−1 + Zn 3.5 mg kg−1 and EC 7.5 dS m−1 + Mn 3.5 mg kg−1 treatments in a pot experiment. Application of Zn in saline soil decreased (p < 0.05) sodium (Na+) and chloride (Cl−) concentrations (6% and 26%, respectively) and increased potassium (K+) concentration (25.9%) in leaves compared with the control. The increments in superoxide dismutase (SOD), glutathione reductase (GR), and catalase activities (CAT) reduced salinity-induced oxidative damage which translated into 50.5% and 74% increased membrane stability index (MSI) and relative water content (RWC), respectively. A 5-fold increment of Zn in soil solution ensured its adequate availability for rice which increased SPAD value for an effective photosynthesis to reinforce above ground biomass and grain production. The enhancements in indole-3-acetic acid (46% and 39%) whereas reductions in abscisic acid (18% and 11%) in shoot and root highlighted the Zn-dependent mitigation of salinity stress in both rice cultivars. Ameliorative effect of Mn remained second to Zn despite the increased shoot Mn concentration in KSK-282. Conclusively, both rice cultivars preferred Zn to mitigate salinity; however, KSK-282 responded better through increased antioxidant activities, indole-3-acetic acid biosynthesis, and decreased abscisic acid accumulation.