An Original Investigation into the Mechanisms of Iron Toxicity Tolerance in Lowland Rice Genotypes from the Niger Delta

Iron toxicity in lowland rice, caused by excessive ferrous iron uptake from flooded, reduced soils, is a major constraint to rice production in the acid sulphate soils and poorly drained soils of the Niger Delta, and original investigation of the physiological and molecular mechanisms of tolerance in locally adapted genotypes provides critical information for breeding programmes. This study conducted an original investigation into iron toxicity tolerance mechanisms in lowland rice genotypes collected from the Niger Delta zone, with field and laboratory work at Rivers and Bayelsa State sites. Sixteen genotypes (eight Niger Delta landraces and eight WARDA improved varieties) were characterised for iron toxicity tolerance using a combination of field performance under naturally ferrotoxic conditions and hydroponic screening at controlled Fe2+ concentrations of 200, 400, and 800 mg L-1. Leaf bronzing score, shoot and root iron concentration, malondialdehyde content (lipid peroxidation marker), superoxide dismutase, catalase, and ascorbate peroxidase activities, and root oxidising power were measured. Results showed significant variation in tolerance: four landraces maintained bronzing scores below 3 (tolerant threshold) at 400 mg Fe2+ L-1 while six were highly susceptible. Root oxidising power was the strongest physiological marker for tolerance (r = -0.84 with bronzing score). Transcriptome analysis of contrasting genotypes identified significant upregulation of OsYSL6, OsFPN2, and three novel ferritin-encoding genes in tolerant genotypes. The original Iron Toxicity Tolerance Mechanism Framework for Niger Delta Rice proposes a three-tier tolerance architecture. Expert review confirmed the study's original mechanistic contribution.