Foliar riboflavin application confers morphophysiological adaptation, oxidative stress mitigation, and enhanced nutrient use efficiency in maize under chromium toxicity

Chromium contamination severely impairs crop growth and yield, yet effective mitigation strategies remain limited. This study tested whether foliar riboflavin application could alleviate chromium toxicity in maize cultivars with contrasting tolerance. Two cultivars, Sadaf (sensitive) and Pearl (tolerant), were exposed to chromium stress with or without riboflavin sprays (50 and 60 mg L–1). Chromium stress reduced plant height (56% in Sadaf, 34% in Pearl), shoot dry weight (62% in Sadaf), chlorophyll (52% in Sadaf, 34% in Pearl), and photosynthetic rate (48% in Sadaf, 32% in Pearl), while oxidative stress markers rose (MDA +61%, H2O2 + 58%). Riboflavin restored chlorophyll b (39% in Sadaf, 25% in Pearl), improved stomatal conductance (41% in Pearl, 27% in Sadaf) and transpiration (38% in Pearl, 24% in Sadaf), enhanced osmotic adjustment via proline and sugars, and reinforced antioxidant defenses (CAT +47%; phenolics +39%; flavonoids +33%). Nutrient uptake increased by 22–45%, membrane stability 31%, oxidative injury declined (MDA −35%, H2O2 − 32%), and yield recovered (grain number +28%, 1000-grain weight +23%, harvest index +21%). Foliar riboflavin supplementation should be adopted as a practical strategy to mitigate chromium phytotoxicity, enhance antioxidant defenses, and improve nutrient efficiency in maize, thereby supporting sustainable production under Cr stress.