Physiological and biochemical responses of three lowland rice (oryza sativa l.) varieties to iron toxicity under semi-controlled conditions

Iron toxicity is one of the major abiotic constraints limiting rice production in tropical hydromorphic lowland soils. Excessive accumulation of ferrous iron (Fe²⁺) induces oxidative stress, leading to physiological and biochemical disturbances that ultimately reduce plant growth and productivity. This study aimed to evaluate the physiological and biochemical responses of three lowland rice varieties (DANANE, NERICA L19, and WITA 9) in order to identify genotypes with superior tolerance to iron toxicity. The experiment was conducted under semi-controlled conditions using a randomized complete block design with three replications in a 3 × 5 factorial arrangement. The rice varieties were exposed to five Fe²⁺ concentrations (Control, 150, 300, 600, and 900 ppm). Chlorophyll contents, antioxidant enzyme activities (catalase, peroxidase, and ascorbate peroxidase), stress tolerance indices (STIs), and the chlorophyll stability index (CSI) were determined. Data were analyzed using two-way analysis of variance (ANOVA), Pearson's correlation analysis, and principal component analysis (PCA). Increasing Fe²⁺ concentrations resulted in a progressive decline in chlorophyll contents and CSI, whereas antioxidant enzyme responses varied according to genotype and stress intensity. NERICA L19 exhibited the highest total chlorophyll content (1.50 mg g⁻¹ FW), the highest CSI value (58.53), and the highest STIPOD and STIAPX values under 900 ppm Fe²⁺. DANANE showed an intermediate response, whereas WITA 9 was the most susceptible variety. Multivariate analyses confirmed the varietal differences and clearly discriminated treatments according to Fe²⁺ concentrations. Overall, the results indicate that NERICA L19 possesses superior adaptive capacity to iron toxicity and represents a promising genotype for breeding programs aimed at improving iron toxicity tolerance in rice.